Deere Precision Farming Guide - Brief Excerpts PDF

Yield Monitoring and Mapping Introduction Each year, farmers in the United States produce over ten billion bushels of corn, about three billion bushels DXP00769 —UN—10...

Yield Monitoring and Mapping Introduction Each year, farmers in the United States produce over ten billion bushels of corn, about three billion bushels DXP00769 —UN—10NOV08 of wheat, and another almost three billion bushels of soybeans on over 180 million acres of cropland. Obviously, a farmer’s economic gains and losses have a lot to do with the volume of crops harvested each season. The size of a harvest, or crop yield, is the measure of crop production in terms of volume per unit area (bu/ac) or mass per unit area (lb/ac or ton/ac). Competitive farmers strive to increase crop yields while minimizing costs. In other words, they work to “maximize” economic returns. agriculture and the trend toward larger equipment meant Of course, anything that causes crop yields or economic farmers could cultivate larger areas. Unfortunately, many returns to decline is of great concern to the farmer. In an continued to treat their larger fields as single management effort to learn as much as they can about what affects crop units. Variations in large fields were ignored as farmers production and profits, many farmers monitor crop yields sought to farm more land more efficiently. This meant in their fields. Traditionally, farmers measured crop yields large-scale, high-speed uniform applications of inputs for whole fields or for large sections of fields. Recently such as seed, fertilizers, and pesticides. Yet, for years available technologies permit farmers to measure yields farmers and researchers have documented variability in more precisely, on areas much smaller than whole fields. soil properties, environmental conditions, and crop yields. Early farmers, relying on human and animal labor, Soil and environmental variability inevitably affect crop cultivated relatively small fields. Early farmers no doubt production. Recent technological advances and data knew their small fields well. And, because smaller fields processing improvements allow farmers to address this tend to have less soil and yield variability, farmers could issue. treat them as individual units. The mechanization of OUO1023,000412B -19-31MAR17-1/2 A growing number of crop producers today practice site-specific crop management (SSCM). Crop yield monitoring is often the first step in developing their SSCM or precision farming programs. Precise crop yield data can be combined with soil and environmental data of many kinds to begin the process of developing a precision crop management system. In this section, we introduce the process of grain yield monitoring and mapping. For our purposes, we will include soybeans in the grain category since they are harvested and handled in much the same way as corn, wheat, and other grains. First, we mention a few of the ways to measure crop yield. Then, we present the basic components of the yield monitor, discussing each in turn. DXP00807 —19—29SEP10 We also address calibration, yield data collection, and yield mapping. We go on to explain what yield maps can and cannot reveal and mention some factors to consider with yield monitors. Yield monitors for crops other than grains are discussed briefly. Fig. 1 — The cycle of processes included in a precision crop management system OUO1023,000412B -19-31MAR17-2/2 03-1 040317 PN=47  Yield Monitoring and Mapping Methods for Measuring Crop Yield There are a number of ways to measure crop yields. Most DXP01526 —UN—03MAY10 of the methods developed over the years have involved weighing the crop after it has been threshed, separated, and cleaned. Grain yields are most often expressed in terms of bushels per acre. This means there must be some way to associate measured quantities of grain with measured harvested areas in the field. Of course, grain moisture content has a large impact on measured yields. Different moisture contents will cause grain samples of Fig. 2 — Grain yield measurement using the collect-and-weigh method equal volumes to weigh different amounts. Grain yields are, therefore, stated in terms of volume per unit area at and for harvested strips within fields. Scales at a grain a specific moisture content. It should be noted that even receiving facility or scale-equipped wagons in the field though a bushel is a measure of volume, crop yields in the weigh the crop harvested from large areas. Many farmers United States are measured by weight. A bushel weight weigh and record the weight of each wagon or truckload is either assumed (56 lb/bu for shelled corn, for example) of grain harvested from a field. Crop moisture content is or measured. typically measured by sampling each weighed load. Three major yield measuring approaches are listed in the It is possible to make yield maps based on upcoming paragraphs. The first method is the oldest, collect-and-weigh data, but there must be some way to and is still in use. The second method is considered the measure the area from which each load was harvested. forerunner of modern, site-specific yield monitoring. The Most yield records based on the collect-and-weigh method last method, instantaneous crop yield monitoring, is the are field-scale records. This means that a single average subject of this chapter. yield value is assigned to an entire field. The average yield value is determined from the total amount of weighed Collect-and-Weigh grain harvested from the total planted area of a field. Used for many years, the collect-and-weigh method determines yields for whole farms, for individual fields, OUO1023,000412C -19-31MAR17-1/3 Batch-Type Yield Monitors A batch-type yield monitor weighs grain in a wagon in which the grain is loaded or as the grain tank of the combine is unloaded. The weight measurement may be displayed to the combine operator on a monitor in the combine cab. A typical combine grain tank holds a relatively large volume, or batch, of grain harvested from a relatively large area. For instance, the corn filling a 200-bushel grain tank will generally have been harvested from an area of between one and two acres. As with the collect-and-weigh method, the area harvested must be measured or estimated in order to calculate yield. Though DXP00809 —UN—10NOV08 yield values determined from a batch-type monitor are not truly site-specific, grain weight estimates are available to the farmer quickly, and without the need for a separate weighing operation. As yield monitoring technologies have advanced, batch-type systems have given way almost entirely to instantaneous yield monitors. Fig. 3 — An early in-cab batch-type yield monitor display Continued on next page OUO1023,000412C -19-31MAR17-2/3 03-2 040317 PN=48  Yield Monitoring and Mapping Instantaneous Yield Monitors Instantaneous yield monitors measure and record yields on-the-go. A number of different methods are used to measure crop yields on-the-go. On-the-go measurement simply means that the process is continuous as the grain is being harvested. Data points are continuously collected as the combine operates. Some systems record each data point separately. Others collect a number of points that are then processed to provide load summary DXP01675 —UN—22JUN10 data. Some systems measure crop volume directly while others weigh the crop. All systems have the capability to measure the area harvested for each recorded weight or volume. When combined with positioning systems such as DGPS, instantaneous yield monitors provide the central data for generating site-specific yield maps. Yields are associated with specific locations within a Fig. 4 — Instantaneous yield monitor displaying crop field automatically. Most site-specific yield monitors yield and moisture content also measure grain moisture content on-the-go. The collect-and-weigh method is typically used in conjunction with instantaneous yield monitoring for the purpose of calibrating the on-the-go monitors to ensure accuracy. OUO1023,000412C -19-31MAR17-3/3 Basic Yield Monitor Components To determine instantaneous crop yield, a farmer must know four things: the grain flow rate through the combine’s clean grain system, moisture content of the grain, the combine’s travel speed, and the cutting width of the header. The DXP00811 —UN—10NOV08 grain flow rate is measured within the combine near the grain tank. The flow rate is measured in units of volume or mass per unit time (bu/sec or lb/sec). Travel speed can be measured in a number of different ways, which we will discuss, and has units of distance per unit time (mi/hr or ft/sec). Cutting width is measured (in feet, inches, or number of rows) by the combine operator. If travel speed and cutting width are known, the area harvested per unit Fig. 5 — Instantaneous grain yield monitoring system of time can be calculated. If the volume or mass of crop harvested per unit time and the area harvested per unit A—Moisture Sensor D—Grain Flow Sensor time are known, then the yield can be determined. B—GPS Antenna E—Ground Speed Sensor C—Yield Monitor Console The following components are found in most common instantaneous grain yield monitoring systems. These components work together to measure the necessary flow ground speed sensor and working rates and to calculate, display, and record header position switch crop yields: The arrangement of components in a typical instantaneous grain moisture sensor grain yield monitoring system is shown in Fig. 5. display/processor console grain flow sensor Continued on next page OUO1023,000412D -19-31MAR17-1/17 03-3 040317 PN=49  Yield Monitoring and Mapping Grain Flow Sensors Methods of measuring grain flow vary, but a number of popular yield monitoring systems use flow sensors mounted in the path of clean grain flow. The grain flow sensor is typically mounted at the top of the clean grain elevator or conveyor, but in instances may be located in other areas along the clean grain elevator. Impact-Type Mass Flow Sensors DXP00812 —UN—10NOV08 Grain flow can be sensed by placing an impact plate in the path of grain flow and measuring either the force applied by the grain impacting the plate or the amount of plate displacement that occurs when grain strikes the spring loaded plate. The force and displacement measurement methods are quite similar. Force is measured by a load cell, a device that converts the Fig. 6 — Impact-type mass flow sensor effect of a load acting on it into an electrical signal. The conversion from a load into an electrical signal is A—Clean Grain Elevator C—Loading Auger accomplished by using a strain gage that is bonded to B—Mass Flow Sensor the load cell. A very slight deformation of the load cell causes a measurable change in the resistance offered by the strain gage to electrical current flow. A potentiometer current flow as the relative positions of its component can be used to measure the displacement of an impact parts are changed. The distance that the impact plate is plate that is struck by flowing grain. A potentiometer is a displaced is proportional to the grain flow for both force- device that produces a changing resistance to electrical and displacement-type sensors. OUO1023,000412D -19-31MAR17-2/17 Optical-Type Volume Flow Sensors A final category of grain yield monitoring systems measures grain volume within the clean grain system. Fig. 7 shows the use of a light source and a photosensor to detect the degree to which a combine’s clean grain elevator is loaded. A photosensor is a device used to detect light. The radiant energy is converted into an electrical signal. Measurements of light and dark periods by the photosensor are used to estimate grain volume flow rates through the clean grain system. Measurements of this type are affected by the type of crop being harvested and by grain moisture content. It is also necessary to DXP00815 —UN—10NOV08 measure the bulk density (weight per unit volume) of the harvested grain in order to calculate crop yields with the system. A—Clean Grain Elevator C—Light Source B—Photo Sensor Fig. 7 — Optical-type volume flow sensor Continued on next page OUO1023,000412D -19-31MAR17-3/17 03-4 040317 PN=50  Yield Monitoring and Mapping Other Flow Sensors Other types of flow sensors have been used occasionally: System for Weighing Grain Stream This system weighs a short section of the clean grain cross auger floor using a load cell, to calculate the grain stream weight. Mass flow rate is then calculated from the stream weight and the auger speed. DXP00814 —UN—10NOV08 A—Electronics D—Weigh Pad B—Auger Flighting E—Transfer Arm C—Combine Clean Grain F— Load Cell Auger Tube Fig. 8 — System for weighing grain stream OUO1023,000412D -19-31MAR17-4/17 Radiometric System Another approach to measuring grain flow is to use a radiometric method. A radiometric system measures the intensity of radiant energy. The isotopic, or radioactive, source directs radiation toward a sensor. The intensity of radiation detected by the sensor is at a maximum when there is nothing to obstruct its path. Any obstruction between the source and sensor will reduce the intensity of DXP00813 —UN—10NOV08 radiation detected by the sensor. In a grain yield monitor, the reduction in intensity is dependent upon the amount of grain between the source and the sensor. The less radiation the sensor detects, the greater the mass of grain flowing between the isotopic source and the sensor. The system measures grain mass and the measurement is not affected by the type of grain being sensed. When the mass data is combined with data for the speed the grain Fig. 9 — Radiometric measurement system for monitoring grain yields flows past the sensor, the mass data can be converted into a mass flow rate. A—Clean Grain Elevator C—Source B—Detector Continued on next page OUO1023,000412D -19-31MAR17-5/17 03-5 040317 PN=51  Yield Monitoring and Mapping Grain Moisture Sensors Grains are complex mixtures of compounds that include proteins, starches, water, and oils. Grain quality, as it relates to these compounds, is of increasing importance in the marketplace. However, at harvest time, the farmer is usually most concerned with only two grain components: dry matter and water. Grain moisture content will affect the timing of harvest. Moisture content affects the amount of grain damage that will occur during harvest and how DXP00816 —UN—06MAY10 grain must be handled and stored following harvest. Of great importance is the effect of moisture content on grain weight and volume. When the farmer sells grain to an elevator, the grain buyer purchases dry matter and water. The buyer demands moisture contents within a range that will permit storage and handling with minimal losses. The farmer’s interests are served by selling as much water as Fig. 10 — A capacitance-type grain moisture sensor the buyer will accept. Too little water and the farmer loses. Too much water and the farmer loses again because the grain will need to be dried. Grain moisture content is of A—Capacitance Sensor great practical importance to the farmer. Grain moisture content also affects the farmer’s ability A capacitance-type sensor is most often used to to compare crop performance within and among fields. measure grain moisture content. Capacitors accumulate Moisture contents can vary widely within a field and will and hold an electrical charge on metal plates separated certainly vary over time. It is necessary to record moisture by a dielectric. (A dielectric is a material that does not content at the time of harvest so that all yield data can be conduct electricity and can contain an electrical field.) The converted to a standard value. For corn, the standard sensor measures the dielectric properties of the grain that moisture content is 15.5% wet basis (weight of water flows between the metal plates. The higher the moisture divided by the weight of water plus dry matter). Most yield content of the grain, the higher the dielectric constant. monitoring systems include some means of measuring Therefore, this measurement indicates the moisture grain moisture content automatically, on-the-go. This content of the grain. allows each yield data point to have an associated moisture content value. Capacitance-Type Sensor The moisture sensor is generally located in the combine’s clean grain conveying system near the grain flow sensor. Continued on next page OUO1023,000412D -19-31MAR17-6/17 03-6 040317 PN=52  Yield Monitoring and Mapping Ground Speed Sensors If the ground speed and grain flow rate are measured and the cutting width is known, instantaneous crop yield can be determined. The calculation for crop yield performed by a yield monitor would look something like the following: Grain flow rate x Unit conversion DXP00817 —UN—10NOV08 Instantaneous yield = factor Cutting width x Ground speed An appropriate unit conversion factor must be included in the equation for instantaneous yield. The reason is to permit grain flow rate, cutting width, and ground speed to be entered in convenient units such as pounds per second, feet, and miles per hour and give the result, instantaneous Fig. 11 — Instantaneous yield measurement by a combine in the field yield, in standard units such as bushels per acre. Shaft Speed Sensor A—Grain Flow into Tank C—Travel Speed B—Cutting Width Ground speed can be supplied to the yield monitor by a magnetic sensor that measures the rotational speed of a driveshaft from the combine’s transmission. Transmission fills, regardless of soil surface conditions. The increased output shaft speed is directly related to wheel speed. loading causes the tires to deflect and reduces the rolling However, shaft speed sensors are subject to errors radius of the drive wheels. This affects the accuracy of resulting from slippage of combine drive wheels. Slippage ground speed readings that are being estimated from causes travel speed to be overestimated and is especially transmission output shaft speed. So, many farmers have troublesome when the soil surface is slippery. In addition, searched for other, more accurate ways of measuring the load on a combine’s tires increases as the grain bin speed. Continued on next page OUO1023,000412D -19-31MAR17-7/17 03-7 040317 PN=53  Yield Monitoring and Mapping Radar and Ultrasonic Sensors Alternatives for sensing ground speed include radar and ultrasonic sensors, as shown in Figs. 12 and 13, or global positioning system output. Radar and ultrasonic speed-sensing devices are more accurate than shaft DXP00818 —UN—10NOV08 speed sensors. Both radar and ultrasonic systems use “guns” that direct a signal toward the ground. Radar systems emit a microwave signal and ultrasonic systems emit high-frequency sound waves. The signals are reflected back to the sensor after they strike the ground. In each case, the relative motion between the combine and the ground will produce a frequency shift in the signal that returns to the speed sensor. Radar sensor accuracy Fig. 12 — A radar ground speed sensor can be affected by surface roughness produced by debris such as crop residue. Therefore, it is important to aim the radar sensor at an area of the ground that will remain relatively smooth. In most cases, radar and ultrasonic speed sensors are mounted on the combine frame close to the ground. DXP00819 —UN—10NOV08 Fig. 13 — An ultrasonic ground speed sensor OUO1023,000412D -19-31MAR17-8/17 GPS-Based Speed Measurement DXP00820 —19—29SEP10 Fig. 14 — A data sentence including position and ground speed data produced by a GPS receiver GPS-based systems calculate ground speed based on and vehicle heading. It is necessary to have a yield the effect of vehicle motion on the frequency of the radio monitor that can receive and properly interpret the data signals that are received from satellites. Ground speed sentence in order to use a GPS system to supply ground is calculated by the GPS receiver and can be output as speed data. Speed estimation accuracy is related to the part of a data sentence that includes latitude, longitude, positional accuracy of a receiver. Continued on next page OUO1023,000412D -19-31MAR17-9/17 03-8 040317 PN=54  Yield Monitoring and Mapping Header Position Sensor Some yield monitoring systems rely on a header position sensor to control the calculation of harvested acreage. When the sensor detects the header in the raised position, area counting is suspended, even when the combine is in motion and all systems are operating. When the sensor detects that the header has been lowered to a reasonable cutting height, area counting is resumed. The sensitivity of the sensor can be adjusted to permit header height DXP00821 —UN—12MAY10 changes that are necessary during harvest without shutting off the area counting process. This feature permits the combine to turn at field endrows and cross waterways and other non-crop areas without including the area covered in the yield monitor’s harvested acreage calculations Some yield monitoring systems include software that allows the operator to specify an operation delay to Fig. 15 — Header position sensor account for the time required for grain to move from the header to the grain flow sensor. Some systems include a start of pass delay to permit the initial flow of grain into the combine to be ignored in yield monitoring computations. The initial flow of grain past the flow sensor is often not indicative of actual yield; a characteristic “ramping” occurs before steady state grain flow conditions DXP00822 —UN—12MAY10 are achieved. On the other hand, an end of pass delay permits the grain flow that occurs after the header is lifted and the acre counting process is suspended to be included in yield monitoring computations. A—Header Position Sensor C—Time (sec) B—Yield (bu/ac) Fig. 16 — Grain flow measured by a yield monitor at the start of a pass through a field Continued on next page OUO1023,000412D -19-31MAR17-10/17 03-9 040317 PN=55  Yield Monitoring and Mapping Display Console The monitor console or display unit is mounted in the combine cab within easy view of the operator. The console connects to all of the sensors that supply information needed to calculate grain yield. In addition to sensor inputs, the display console receives inputs from the combine operator. This permits the operator to provide data for which no sensor is installed (width of cut, for example) or field or load information to permit tagging or referencing of the yield and moisture data that is being collected. For instance, the data collected from a field could all be tagged with, or referenced by, a user-supplied name such as “Field A” or “North Forty.” Each load could be tagged or referenced in a similar manner. Display consoles include a keypad for information input and a visual display. Information that can be entered or displayed can include the following: Operator-Supplied Information field name load name or number DXP01676 —UN—22JUN10 cutting width Sensed/Calculated Information crop moisture content instantaneous yield average yield area harvested Fig. 17 — Yield monitor display console travel speed quality of DGPS signal reception DXP01675 —UN—22JUN10 Fig. 18 — Close-up view of a yield monitor display console Continued on next page OUO1023,000412D -19-31MAR17-11/17 03-10 040317 PN=56  Yield Monitoring and Mapping Calibration The types of calibration that are required by yield monitoring systems vary by monitor type. However, regardless of the type of monitor, yields are not measured directly. Instead, measurements of force, displacement, or volume, speed of material flow, crop moisture content, DXP00825 —UN—10NOV08 harvester travel speed, and working width are combined to produce an estimate of crop yield. Crop yield is a derived, or calculated, value. Calibration is performed to ensure that sensor data and operator input are properly used by a monitor to produce a final output in units of bushels per acre. In addition, force- and displacement-sensing grain flow meters must be calibrated to nullify, or cancel, the effects of machine vibration on yield readings. In Fig. 19 — Simulated yield monitor calibration curve some cases, flow measuring devices are so sensitive that vibrations caused by the movement of machine components such as the straw walkers and cleaning shoe A—Grain Flow B—Simulated Yield Monitor Calibration Curve will produce errors in yield data if not accounted for. Most calibration processes involve comparing the weights of several loads estimated by a yield monitor with those accuracies can suffer. It is for this reason that it is wise measured on a separate set of scales. During calibration, to perform the calibration process over a range of grain the farmer harvests a series of full or partial grain tank flow rates. This requires the farmer to harvest at different loads. The loads are transferred to a wagon and each speeds and cutting widths during calibration and to weigh load is weighed on a separate set of scales and the data a number of loads of grain. If changing environmental recorded. The farmer can then enter the actual weights conditions over the course of a harvest season cause into the yield monitor. Software within the yield monitor crop condition to change significantly, recalibration might console then computes a set of calibration curves. become necessary, even if a farmer harvests only a single An example of a calibration curve is provided below. type of crop. The curves are fitted to the yield monitor data in such a It is advisable to compare moisture content estimates way that the difference between the corrected weights from the yield monitor’s moisture sensor with estimates calculated by the yield monitor and the actual measured from samples tested by a reliable moisture tester. Errors weights is minimized. in measuring moisture content will lead to errors in If harvesting conditions remain similar to those that existed measuring yields. Some yield monitoring systems permit at the time of calibration, yield monitors can produce very the operator to adjust the readings from the moisture high accuracies. If actual harvesting conditions (grain sensor to make them agree with the readings from a flow rates or moisture content, for example) vary a great reference moisture tester. deal from the conditions at calibration, yield estimate Continued on next page OUO1023,000412D -19-31MAR17-12/17 03-11 040317 PN=57  Yield Monitoring and Mapping Yield Data Collection The components and procedures we’ve discussed so far are all a farmer needs to collect and record yield data. With these basic components, an operator can instantaneously observe yield, speed, moisture content, and so on as these data “flash” on the monitor console. DXP00826 —UN—10NOV08 The “on-the-go” sensors collect data every 1, 2, 3, or 5 seconds, depending on what rate the operator chooses. The console also summarizes the collected data. This summary provides an average yield and moisture content for larger areas. An operator may also view summary data on the console display. The monitor can store an extensive record of crop production information including yield values for the Fig. 20 — Data transfer within a yield monitoring and mapping system season, farm, field, and load. With a data storage device in the monitor console, the operator can transfer monitor A—Combine Console E—Laptop/Farm Computer data onto the card. Having transferred collected data to B—Yield Monitor F— (Via Color Printer for Color the PC card, the user simply removes the card from the C—Card Slot Maps) D—PC Data Card (Physical G—Yield Maps monitor console. The user then inserts the card into a PC Transfer) H—Yield Tables data card reader on a desktop computer or into a PC card slot on a laptop or notebook computer. With the proper software, the operator can transfer data into a file that can later be accessed for printing summary yield data tables. OUO1023,000412D -19-31MAR17-13/17 Yield Mapping To produce yield maps that are based on sets of instantaneous yield data points, farmers need one more thing during harvest — a means of determining and recording the combine’s in-field location for each yield data point. Each yield data point must correspond to a particular location on the earth’s surface. The process of associating data such as crop yield values with geographic DXP00827 —UN—10NOV08 coordinate data is known as georeferencing. The most common georeferencing method for establishing and recording the locations of sites within a field is through the use of a global positioning system (GPS) receiver. To calculate a relatively accurate combine location estimate, the user needs some form or source of differential correction (DC) for the positioning system. Since yield monitoring is a data logging process and since the data Fig. 21 — A combine equipped to collect yield data for mapping can be processed after it is collected, it is not necessary to have a real-time source of differential corrections (See A—Yield Monitor Console E—Grain Moisture Sensor section 2). However, most farmers have chosen to use (Component of the “Yield (Component of the “Yield real-time differential corrections because GPS hardware is Monitor”) Monitor”) typically used for a number of operations around the farm, B—GPS Receiver Antenna F— True Ground Speed Sensor some of which require high-accuracy position estimates. C—Differential Correction G—Header Position Sensor Receiver Antenna (Component of the “Yield NOTE: In Fig. 21, the GPS and Differential Correction D—Grain Flow Sensor Monitor”) Receivers are shown as two separate items (Component of the “Yield Monitor”) (antennas), but most suppliers of DGPS (differential GPS) equipment and services put both in a single package, with various antenna types and requirements. Continued on next page OUO1023,000412D -19-31MAR17-14/17 03-12 040317 PN=58  Yield Monitoring and Mapping Farmers know that yields vary within a field — they see “paid for itself” in the first year of use based on what they it as material enters the combine header and hear and discovered by studying yield maps. feel it as the crop is threshed. They may even have some idea of how much yields vary. But the new generation of Certainly not all first-time users are that fortunate. But instantaneous yield monitors can put actual numbers to yield monitors can also be extremely useful in other ways. their speculations about yield variability — which might For instance, they can be used to conduct “on-farm be enough reason to use them. Furthermore, with these research” — trials that investigate hybrids, seeding or numbers and the yield maps, farmers can investigate fertilizer application rates, pesticide types and rates, and why the yield variations occur. They can begin to so on. The information gathered through the analysis of establish relationships between yield variability and yield yield data collected over a number of years can forever limiting factors such as soil type differences, or problems change the way a farmer deals with chemical and seed associated with fertility, weed control, drainage, soil suppliers. Accurate, long-term yield information has even compaction, equipment malfunction, and so on. In fact, been credited with increasing the value of such monitored a number of farmers claim their yield monitoring system farmland at the time of sale. OUO1023,000412D -19-31MAR17-17/17 03-15 040317 PN=61  Yield Monitoring and Mapping Issues to Consider DXP01492 —UN—26MAR10 Fig. 25 — Flow of material through a combine Modern instantaneous grain yield monitors are the most combine operates. The following list and Fig. 25 help to accurate tools ever available for measuring crop yield illustrate the basic functions of a combine: on a site-specific basis. However, they are not perfect. Yield calculations can be based on a number of different The Six Functions of a Grain Combine measurements including: Gather and cut standing crop or pick up a windrow the force exerted upon an impact plate Convey the gathered crop to a threshing mechanism crop flow through a combine’s clean grain system Thresh or remove grain from heads, ears, or pods moisture content Separate the grain from material-other-than-grain (MOG) combine travel speed width of cut of the combine header Clean chaff and debris from the grain Handle the clean grain Each of the measurements listed above can produce errors that affect the accuracy of calculated yields. The redistribution of grain begins in the combine header. The grain nearest the center of the header is conveyed Measuring a force (or the displacement of an impact to the threshing process more quickly than grain at either plate) isn’t a problem. The question is, does the force end of the header. The threshing process removes a large that grain exerts on a plate in the clean grain elevator portion of the grain from the material-other-than-grain provide an accurate measure of the crop yield in a field (MOG) almost immediately. Some grain must pass on a second-by-second basis? There is a lag between through the threshing, separating, and cleaning processes the time the crop enters the combine’s header and the before being sent back to the cylinder for rethreshing. time it reaches the top of the clean grain elevator. This lag Separating, cleaning, and handling processes inevitably can be from 8 to 20 seconds — 24 to 150 feet of travel at create time delays and material flow variations. All of this typical speeds. There is also the issue of how elevators, occurs before the grain reaches the clean grain system. augers, cylinders, and sieves change the flow of grain However, it’s not until the crop reaches the clean grain through the combine. Yield data processing software can system that sensors measure grain flow. The flow of grain account for the time lag. The physical effects of grain measured at the sensor in the clean grain system may not processing and handling on flow rates, however, are more be the same as the flow of grain that entered the combine difficult to address. Each combine function changes the just seconds earlier. distribution of grain that existed in the field prior to harvest. In other words, the harvest process mixes up the grain. It will be helpful, at this point, if we briefly review how a grain Continued on next page OUO1023,000412E -19-31MAR17-1/4 03-16 040317 PN=62  Yield Monitoring and Mapping Accurate flow sensing is important for accurate yield speed, the farmer must consider the effects of changing measurement and so is accurate ground speed travel speed on measured yields. Abrupt changes in measurement. We discussed the problems associated travel speed can cause errors in yield measurements. If with ground speed measurement methods earlier in this the operator speeds up suddenly, a series of calculated section. In addition to the problem of accurately measuring yields will be too low. If the operator slows down suddenly, a series of yields will be too high. OUO1023,000412E -19-31MAR17-2/4 Errors in determining cutting width can also lead to yield measurement errors. On essentially all yield monitoring systems marketed in the United States, the operator enters the cutting or working width value at the yield monitor DXP00832 —UN—10NOV08 console. The cutting width ideally equals the header width and remains constant. However, with platform headers, the actual cutting width is virtually always less than the theoretical cutting width. The actual cutting width depends on the ability of the operator to utilize the full theoretical cutting width. Often, however, field conditions force the operator to take less than a full swath into the machine. Fig. 26 — Header cutting width sensor The operator must be prepared to adjust the width-of-cut whenever necessary, such as when working on point rows or when finishing a field that has a single remaining swath A—Sensor D—Ultrasonic Wave of varying width. Obviously, an automatic, instantaneous B—Crop Divider E—Sensor C—Crop Edge F— Echo measurement of cutting width changes would make yield maps more accurate. Cutting width sensors have been used in Europe. They have not performed flawlessly, but condition. Unfortunately, many operators lose three times have shown promise for widespread commercial adoption. that much or more, not counting preharvest losses. In Monitors that measure force or mass must be able to addition, losses from combines vary in relation to the convert that data to a measurement of volume or weight. rate material flows through the machine. Overloading Moisture content data is also necessary to convert yield a combine can produce excessive losses. But so does values to a standard moisture content basis. Moisture operating a combine at less than full capacity. Some content values provided by the combine’s moisture sensor threshing and separating systems produce excessive should be calibrated using an accurate reference moisture losses each time the combine starts into a new pass. tester. Errors in moisture content cause errors in yield Losses do exist and vary across most fields. estimates. The performance of some early moisture The sources of errors mentioned so far affect sensors suffered because the metal sensor plates would measurements of crop flow and/or area. Another category occasionally become coated by sticky crop residues. This of errors that lower the quality of yield maps is positional has been a particular problem when harvesting soybeans. error. The usefulness and accuracy of a yield map Most new moisture sensor designs allow farmers to easily is clearly linked to the accuracy of georeferencing of clean sensor surfaces if moisture content readings become measured yield values. Sources of positional errors are erratic due to surface coating. In addition, the yield monitor listed and discussed in section 2. should provide the option of manually entering a moisture content value if sensor values are known to be in error. Can the current crop of yield monitors provide a relatively Many operators have considered moisture measurement accurate measure of yields in a strip or a swath or a field? the most troublesome aspect of monitoring crop yields. The answer is yes! This fact is ensured through calibration using weighed loads from strips, swaths, and fields. Is Manufacturers of current yield monitors advertise the little colored dot on a yield map an accurate measure accuracies in the ±2% range — some even better! It is of the crop yield at “that point” in the field? Maybe! The not unusual to hear a farmer discuss the overall difference process of calibration forces the sum of weights from a between the crop that crossed the weigh scale and the set of point measurements produced by a yield monitor crop weight measured by a yield monitor in terms of a few to agree with a weight for a strip, swath, or field that is pounds for an entire harvest. However, yield monitors measured by a set of scales. However, that does not measure only the amount of grain that makes it into the ensure the fact that any single point is entirely accurate. combine and ends up in the grain tank. Crop losses, whether they result from preharvest conditions, cutting, Keep in mind that much effort has been spent by software threshing, separating, or cleaning, are not recorded and developers to provide the capability “of smoothing” the do not show up on yield maps or in data files. An expert data so painstakingly collected second-by-second in the operator can keep overall combine losses at or below field. It may be safer to trust the whole picture than each 1% of measured yield depending on the crop and crop colored dot that makes up the picture! Continued on next page OUO1023,000412E -19-31MAR17-3/4 03-17 040317 PN=63  Yield Monitoring and Mapping Keep in mind, also, that the word “point” that is associated with the term “point yield” is misleading. In geometry, a point is an element having definite position, but no size, shape, or extension. Take for instance a combine with a 20-foot header traveling at four miles-per-hour. If the operator has set the yield monitor to collect data at one-second intervals, then each “point yield” is actually based on an area of over 117 square feet. A—Point Yield DXP00833 —UN—10NOV08 Fig. 27 — Illustration of the size of the area represented by a point yield OUO1023,000412E -19-31MAR17-4/4 Is a Yield Monitor for You? and calibration, data storage and handling, working with DGPS sources, and so on. Each topic will have a learning It has been suggested that yield data across several curve associated with it that will need to be dealt with seasons of weather patterns might be required in order sometime. So when should a farmer start? to make decisions concerning the use of variable-rate technologies on a given farm. And yield will be only The application of precision farming concepts may one component of an overall on-farm database that will be destined to bring a whole new way of managing eventually be needed to develop a site-specific crop crop production — one based on data and information management system. management rather than “by guess and by gosh!” Yield monitoring is viewed by many as a good first step toward So when should a farmer start to monitor yields on his that potential reality. Plus, there might be other payoffs or her farm? Should the farmer wait until the profitability along the way. Surveys of precision farmers have shown of yield monitoring is demonstrated on other farms? By that the information gained from site specific crop yield then, he or she could be years behind in terms of data monitoring has changed the way many manage their collection and experience gained in precision farming. It farming operations. should be remembered that monitoring yields involves a whole set of tools and skills including monitor operation OUO1023,000412F -19-31MAR17-1/1 03-18 040317 PN=64  Yield Monitoring and Mapping Yield Measurement for Non-Grain Crops As indicated earlier in the section, yield monitoring Crop Measurement Methods/Tech- has been most widely applied to grain harvesting, but nologies is certainly not limited to grains. Yield monitors are Potatoes load cells being, or have been, developed for several non-grain Tomatoes load cells crops as listed in the table shown. As can be seen, the Sugarbeets load cells predominant means of measuring the yield of non-grain Peanuts load cells crops is weighing the crop at some point during the optical sensors harvesting process. Cotton load cells The list is expected to grow to encompass most optical sensors commercially grown crops. Yield monitoring and mapping Sugar Cane load cells techniques have even been applied to crops that are Coffee load cells harvested by hand. Techniques have been developed to Grapes load cells record picked container weights at or near the harvest Strawberries load cells site within a field or grove, georeference the site, then Horseradish load cells integrate the weight and position data into a yield record. Forage Crops (baled) load cells Forage Crops (chopped) shaft torque sensing radiometric sensors load cells Yield measurement for non-grain crops OUO1023,0004130 -19-31MAR17-1/1 Summary data to a standard moisture content basis. There was also a discussion of how the quality of crop yield data Crop yield monitoring has been performed by various is affected by the quality of material flow and moisture means for a number of years. Today, the ability to content measurements. Yield monitor calibration was measure crop yield on-the-go and associate each yield shown to be an important step in ensuring the quality of value with a specific location on the earth’s surface has yield data. Finally, there was information presented to given farmers a new and powerful management tool — highlight the development of yield monitoring systems for the site-specific crop yield map. This section described a non-grain crops, an area of agricultural technology that number of techniques for measuring grain flow through continues to expand rapidly. combines. In addition, it was shown how grain moisture content is measured to permit the conversion of yield OUO1023,0004131 -19-31MAR17-1/1 03-19 040317 PN=65  Yield Monitoring and Mapping Study Questions ______________________________ 1. _______________________ yield monitors measure ______________________________ and record crop yields on-the-go. ______________________________ 2. A _____________________-type sensor is most often used to measure grain moisture content on-the-go 8. What are three alternative methods for measuring the within combines. travel speed of a combine during the yield monitoring process? 3. What are three types of data that typically appear in each line of a site-specific yield data file? a. ______________________________ a. ______________________________ b. ______________________________ b. ______________________________ c. ______________________________ c. ______________________________ 9. What is the function of a header position sensor in controlling the yield monitoring process on some 4. A _____________________ can be used to measure combines? the displacement of an impact plate that is struck by flowing grain in a yield monitoring system. ______________________________ 5. Most combines built and sold in the United States are ______________________________ equipped with sensors to measure actual cutting width at the header. True/False 10. Describe the situation that might cause a farmer to need to calibrate his or her yield monitor more than 6. Name one of the types of yield monitoring that once during a single harvest season for a single crop. preceded the use of modern, site-specific yield monitoring systems. _______________________________ ______________________________ _______________________________ 7. What are the three methods used to transfer data between an instantaneous yield monitor and a computer? OUO1023,0004132 -19-31MAR17-1/1 03-20 040317 PN=66  Soil Sampling and Analysis Introduction For years agronomists and soil scientists have encouraged farmers to sample and analyze the soil of their fields on DXP00769 —UN—10NOV08 a regular basis. Regular soil sampling is important for developing a successful fertility management program. However, in the past, soil sampling was often overlooked and fertilizer was frequently over-applied to ensure nutrient levels were adequate. One agronomist estimated that in the mid 1990s, despite efforts to convince farmers to adopt soil sampling programs, only 50% of the corn and soybean acreage in Indiana was regularly soil tested. Similar estimates held for the entire Midwest. With the recent saturation have driven farmers to precision farming. Most interest in precision farming, more and more farmers are surveys available estimate ninety percent of Midwest finally beginning to adopt regular soil sampling programs. farms are soil sampling. The technology available today has made it possible to In the first part of this section we will note the soil visually inspect entire fields in minutes with unmanned properties that are important for crop production. Then aerial vehicles (UAV). These UAVs send live data to the we will look at the different sampling methods and farmers and their trusted advisors. This allows early introduce soil property mapping. Finally, we will discuss detection and diagnosis of issues and affords the farmer considerations for selecting a soil sampling program and the opportunity to take tissue samples in problem areas. take a brief look at the present and future uses of sensors This could diagnose plant health issues before they affect for on-the-go analysis of soil properties. their bottom line. This available technology, yield gains, and new regulations on ground and water chemical OUO1023,0004133 -19-31MAR17-1/1 Soil Properties for Crop Production When analyzing soil for crop production, soil fertility usually receives the most attention. Soil fertility refers to the level of all nutrients “available” in the soil for plant DXP00834 —19—29SEP10 use. Plants require many nutrients from the soil in varying levels for optimum growth. Soils contain nutrients in several forms, some of which cannot be consumed by the plant and are considered “unavailable.” For example, some soils containing large amounts of calcium or lime have very little phosphorus available for plants. This is because the phosphorus is quickly tied up, or held, by the calcium and cannot be used by plants. In this case the Fig. 1 — Plants obtain many nutrients from the soil phosphorus is unavailable. Soil testing focuses on the nutrients in the soil to determine if any are at levels that would limit crop growth. Micronutrients The desired level of each nutrient depends on the crop The primary nutrients needed in the soil for crop that is planted and the area of the country where it is being production include: grown. In many cases, soil testing results for primary Nitrogen (N) nutrients are categorized as very low, low, moderate, high, Phosphorus (P) and very high. Very low and low classifications indicate a Potassium (K) high probability for obtaining a yield increase from fertilizer; moderate classifications indicate a crop yield response Other nutrients that are less likely to be added as fertilizer may or may not occur; high and very high classifications are sometimes called: indicate a crop yield response is not likely to occur. Secondary Nutrients Continued on next page OUO1023,0004134 -19-31MAR17-1/5 04-1 040317 PN=67  Soil Sampling and Analysis Nitrogen (N) may be the most important nutrient for crop production for many crops. For example, when nitrogen is applied to the soil, corn yields can easily double those of a field which did not receive nitrogen fertilizer. However, the timing and methods of applying nitrogen are important in achieving these benefits. Ideally, N applications should coincide with N needs of the crop. For corn, this would mean applying N during a period six to ten weeks after planting. Early applications of N during fall or early spring create a risk of N loss from the soil by denitrification, DXP00835 —19—29SEP10 leaching, and/or surface volatilization. Denitrification loss occurs when microorganisms in the soil strip the oxygen from nitrate N (NO3-), producing N gas (N2), which enters the air. Denitrification occurs when soil is wet, compacted, and warm. Leaching losses of N occur when soil receives more water than it can hold. Fig. 2 — Nitrogen in the soil undergoes a complex cycle which includes The water may be from rainfall or irrigation. As water losses from denitrification, leaching, and surface volatilization moves through the soil, the nitrate N is carried away with the water. Surface volatilization of N is the breakdown of some fertilizers into ammonia gas. This volatilization compounds such as sugars, starches, and fats. Sulfur is occurs when the fertilizer is applied to the surface of the found in all living plant cells as part of the protoplasm. soil, especially over a crop residue like cornstalks. All Sulfur aids in the formation of proteins, encourages these pathways of N loss from the soil substantiate the vigorous growth, and helps plants withstand cold need to apply N fertilizer close to the time the plant will temperatures. need it. They also suggest that soil testing for measuring Micronutrients are required by plants in small amounts. N should be performed close to the time of application. Boron (B), chloride (Cl), copper (Cu), iron (Fe), Different chemicals can be added to N to help slow down manganese (Mn), molybdenum (Mo), and zinc (Zn) are the denitrification process. those essential for plant growth. Micronutrients are Phosphorus (P) is an important element in the required in such small amounts that they are rarely development of plant reproductive parts. Typically, large deficient. However, there are some areas of the country amounts of P are found in seeds and fruit and are essential which have soils particularly susceptible to a particular for seed formation. However, since P is strongly held by micronutrient deficiency or which grow a crop particularly soil particles, it is not as easily lost as N. Therefore, the sensitive to a specific micronutrient as shown in the table. timing of P fertilizer application is not as critical as for N For this reason soil testing for micronutrients is becoming application. But, since phosphorus is chemically attached a more widely accepted practice. to the soil particles, it can be lost through soil erosion. Micronutrient Deficiencies Affect Many Crops Also, stratification of P levels may occur under conditions such as no-till. In no-till fields, P levels at the surface may Micronutrient Soil Conditions Crops be higher than at greater depths where the roots have Boron Sand, overlimed acid Cotton, tomatoes, absorbed it. Testing to determine P levels in the soil should soil, organic soil citrus, sweet potatoes, leafy vegetables, fruit be performed at different depths. Soil samples taken from trees, legumes with only one depth may give misleading indications of P levels. heavy lime Potassium (K) has functions that are particularly related Copper Sand, organic soil, Small grains, high pH soil vegetables, fruit trees to the solutions within plant cells. It is the nutrient that keeps things moving through the plant. Enzymes in plants Iron High pH soil, high Blueberries, corn, phosphate sorghum, soybeans, are involved in many important growth processes within ornamentals plants, and K plays an important role in the activity of Manganese Sand, overlimed soil, Soybeans, small these enzymes. Potassium also affects a plant’s ability organic soil grains, tree fruits, to withstand water stress. Of the total amount of K in cotton, sweet the soil, typically only from 1 to 10% is available to potatoes, leafy plants. Therefore soil testing methods attempt to measure vegetables available forms of K in order to recommend the amount Zinc Sand, high pH soil, Soybeans, corn, of K to apply. high phosphate citrus, rice, sorghum, pecans, fruit trees, Secondary nutrients include calcium (Ca), magnesium some vegetables (Mg), and sulfur (S). Calcium stimulates root, stem and Molybdenum Highly weathered acid Legumes, citrus, leaf growth, and improves general vigor and disease soil cauliflower, cabbage, and similar plants resistance. Magnesium is essential for production of chlorophyll. It also aids in formation of many plant Micronutrient deficiencies that may affect crops Continued on next page OUO1023,0004134 -19-31MAR17-2/5 04-2 040317 PN=68  Soil Sampling and Analysis particular crop and conditions. A farmer must evaluate Around the country, the maximum potential for productivity both the fertility of the soil and the potential yield goal of each crop will depend on the region, annual expected before planting. This is best done by having experts test rainfall, tillage system, crop rotation, and soil type where the soil for the available nutrients and the soil pH. it is planted. We call this potential the “yield goal” for a OUO1023,0004134 -19-31MAR17-3/5 Soil pH is a measure of the acidity of the soil. A low pH value means the soil has a lot of free hydrogen particles (high acidity) floating around in the water in the soil. These hydrogen particles (H+) can react with nutrients in the soil and make them less available to plants. In order to neutralize the acid in the soil, limestone is added. The H+ can react with limestone in the soil to form water and carbon dioxide. Hence, the H+ particles are converted to H2O, or water, thereby raising the pH. However, if the limestone is not well mixed with the soil, pH can vary with depth. Therefore, some tillage to mix the limestone into the soil is recommended. Variations in pH with depth should be examined through soil testing. Nutrient level and pH are only two factors that impact crop yield. Farmers must consider many other factors when considering precision farming. Below are several other soil factors that can influence crop yields: Soil Organic Matter (Content SOM) Texture — sand and clay content Structure — density and porosity Cation Exchange Capacity (CEC) Slope and Topography Tillage Drainage Soil Depth Compaction DXP00836 —19—29SEP10 Fig. 3 — Soil pH affects the availability of nutrients Continued on next page OUO1023,0004134 -19-31MAR17-4/5 04-3 040317 PN=69  Soil Sampling and Analysis Farmers must try to control not only the soil’s nutrient content, but its physical condition as well. Keep in mind that the tillage method used for seedbed preparation can affect the soil’s physical condition. As a starting point, farmers look at their soil type, which is usually determined by soil survey maps created by the Natural Resource Conservation Service (NRCS), an example of which is shown in Fig. 4. In most cases, these maps identify approximate values of the soil organic matter content, the DXP00837 —UN—10NOV08 water-holding capacity and drainage properties, and the soil texture through the profile. However, these soil maps were not really intended for precision farming applications. As a result, their accuracy in identifying boundaries between soil types and soil properties may be limited. Soils of the same type or series in different areas of the field may have different properties. Soil testing could be needed to determine variations in soil properties in a field. Fig. 4 — Soil survey map We should note that even successful control of fertility and soil physical properties doesn’t guarantee high crop A—BIA C—MyC3 B—GnB2 D—Pw yields. Farmers must also consider how irrigation and drainage systems can impact the moisture content of the soil. Without a system to control water, crop yields are at the mercy of Mother Nature. OUO1023,0004134 -19-31MAR17-5/5 Methods of Soil Sampling and Analysis In the past, farmers estimated the conditions of an entire field by averaging the results from analysis of soil samples DXP00838 —19—29SEP10 randomly gathered around the acreage. Then the entire field was treated based on the average analysis. This approach of treating a whole field on the average made fertilizer recommendations and applications very simple. Only one rate of fertilizer was applied. With new precision farming technologies that allow changing fertilizer rates on-the-go, fertilizer is applied only as needed within each management until in a field. This change in application Fig. 5 — Dividing the field into small cells by placing a square grid over a field map is the first step in grid sampling methods has shifted the goal of soil sampling from measuring the whole field average to measuring the variability of soil properties throughout the field. The two farmer gathers soil samples from each section and sends most common methods that accomplish this are: them to a laboratory for analysis. The objective of this approach is to better estimate the need for soil nutrients Grid Sampling on a scale smaller than the entire field. Two of the most Soil Type Sampling commonly used methods of grid sampling are: Grid Sampling Grid Center Method Grid sampling involves dividing a field into square or Grid Cell Method rectangular sections of several acres or less in size. The Continued on next page OUO1023,0004135 -19-31MAR17-1/6 04-4 040317 PN=70  Soil Sampling and Analysis DXP00839 —UN—10NOV08 DXP00840 —UN—10NOV08 Fig. 6 — Hand probe used for soil sampling Fig. 7 — Vehicle-mounted soil sampler DXP00841 —19—29SEP10 Fig. 8 — Soil sampling process The goal of the grid center method is to measure the the center of each grid while driving through the field. nutrient levels at the center of the grid cell. This method Upon reaching the center of a grid cell, the farmer stops is sometimes referred to as grid point sampling, or and collects several soil cores using a hand probe or a simply point sampling. When point sampling, many vehicle-mounted sampler as shown in Figs. 6 and 7. farmers use a positioning system like DGPS to pinpoint Continued on next page OUO1023,0004135 -19-31MAR17-2/6 04-5 PN=71 040317  Soil Sampling and Analysis Cell soil cores are taken from within a ten- to thirty-foot diameter circle around the center of the grid as illustrated in Fig. 9. These core samples are then combined into a single soil bag and labeled with the field name and grid cell number. This combining of several samples helps eliminate the chance of sampling only a single spot that is not representative of the grid cell center. The proper method of collecting a sample is outlined in Fig. 8. DXP00842 —19—29SEP10 Fig. 9 — Sampling sites for grid point sampling DXP00843 —UN—10NOV08 Fig. 10 — Soil sample bags OUO1023,0004135 -19-31MAR17-3/6 The grid cell method is very similar to the whole-field method except that the field is broken up into many smaller “fields” or cells. Using the grid cell method, a farmer randomly samples all around each grid cell to obtain an average sample of the entire cell area. Several samples from within each cell are combined into one composite sample representative of the cell area. Thus, the farmer treats the entire grid cell as having the same soil properties. DXP00844 —UN—10NOV08 A—Grid Cell C—Grid B—Sample Sites Fig. 11 — Sample sites for grid cell sampling Continued on next page OUO1023,0004135 -19-31MAR17-4/6 04-6 040317 PN=72  Soil Sampling and Analysis At this time, researchers are still investigating different methods to determine the best way to sample each cell. Several other sampling layouts that are currently being recommended are shown in Fig. 12. Not many commercial soil testing companies use the grid cell method because it requires the person sampling to entirely cover each cell instead of just grid cell centers. DXP00845 —UN—10NOV08 A—Regular D—Systematic Unaligned B—Staggered Start E—Random Cluster C—Random Start F— Simple Random Fig. 12 — Alternative sampling patterns for grid cell sampling OUO1023,0004135 -19-31MAR17-5/6 Soil Type Sampling An alternative to sampling on a square grid is to sample sections of the field that have similar soil types. The farmer employs the same sampling procedures. However, instead of blindly using a uniform grid, he or she uses tools such as soil survey maps to select sampling locations. Several samples are collected from areas having a particular soil type, then combined to represent that soil type. This is done for each soil type of interest within a field. This method results in samples being taken from irregularly spaced sites around a field. DXP00846 —UN—10NOV08 Fig. 13 — Sample locations used for soil type sampling OUO1023,0004135 -19-31MAR17-6/6 Mapping Soil Properties Once soil samples are collected, they are sent to a soil testing lab for analysis. Usually several days, or even weeks, are required to obtain the results. The results of both grid point sampling and grid cell DXP01507 —UN—27MAY10 sampling are used to generate maps of soil fertility. Typically, one soil property is displayed on each map. Fig. 14 — Map of soil properties smoothed between grid points Continued on next page OUO1023,0004136 -19-31MAR17-1/2 04-7 040317 PN=73  Soil Sampling and Analysis After following the grid point sampling technique, one can 8! 7 6 5 4 3 2 1 0 approximate the soil properties between grid centers. 50 55 58 64 54 58 56 6. 62 Mathematical methods, like contouring, inverse distance 0. 50 00 51 01 61 02 66 03 65 04 55 05 64 06 55 07 63 weighting, or kriging (described in section 6), permit 16 15 14 13 12 11 10 1. 08 estimation of soil properties in areas not sampled. This 55 51 55 65 58 56 65 66 65 generates data to “fill in” the areas between samples 17 18 2. 20 21 22 23 24 25 and create continuous maps of soil nutrient levels. This 65 54 55 64 64 66 56 63 56 is similar to creating a contoured elevation map, or 34 33 32 31 30 3. 28 27 26 57 50 60 67 68 68 60 60 6. topographic map, using points of measured elevation. 35 36 37 38 4. 40 41 42 43 45 45 47 58 52 64 61 55 6. After obtaining results from grid cell sampling, maps are 52 51 50 5. 48 47 46 45 44 created to show levels of nutrients for each grid cell. 6. 60 65 6. 54 56 58 60 58 DXP01523 —19—29SEP10 Within each cell, the soil is assumed to have a constant o9 Ldptisp Rmc Heldpsnmd LdanlldmcRsenmp nutrient level. ! Tdhegsdc! =antd 5-6! =tnhc Fhldrsnmd! 06-7 =bodr! Bhdic! 9 6-/ When mapping soil nutrient levels from soil type sampling, 5-2 , 5-6! Ln Fhldrsnmd Lddcdc! 5-6 =bodr! =tdoWed 4-8 , 5-2! 1 Nnmr. =bod!! 1-1 =bodr! the lines on the soil map divide the field into small 4-5 , 4-7! 2 Nnmr. =bod!! 0-3 =bodr! irregularly-shaped areas instead of uniform grid cells. 4-2 , 4-4! 2 Nnmr. =bod 83,84! /-/ =bodr! Usually all soil within each smaller area is considered to Adinv 4-2! 3 Nnmr. =bod 83,84! /-/ =bodr have the same soil nutrient levels. Fig. 15 — Map of soil properties from grid cell sampling OUO1023,0004136 -19-31MAR17-2/2 04-8 040317 PN=74  Soil Sampling and Analysis Selecting a Soil Sampling Program each year. Sampling every year at the same seasonal date minimizes year-to-year variability, helping farmers There are a number of questions farmers ask (or should track th