Soil Fertility Management PDF

AGRICULTURE 51 PRINCIPLES OF SOIL SCIENCE Chapter 7a Soil Fertility Management 1 BUSHEL is equivalent to 35.24 KILOGRAMS  Determining Fertility Status and Fertilizer Needs The available nutrient supply of most soils is seldom adequate to support the requirements of crops....

AGRICULTURE 51 PRINCIPLES OF SOIL SCIENCE Chapter 7a Soil Fertility Management 1 BUSHEL is equivalent to 35.24 KILOGRAMS  Determining Fertility Status and Fertilizer Needs The available nutrient supply of most soils is seldom adequate to support the requirements of crops. Soils become depleted of nutrients by: – crop removal – leaching losses – volatilization (particularly N) – erosion of topsoil – fixation by clays – immobilization Thus, fertilizers must be applied to supplement the soil supply of nutrients.  Determining Fertility Status and Fertilizer Needs The kind and amount of fertilizer to be added may be determined by one/a combination of the following: 1) Soil analysis 2) Field fertilizer experiments 3) Plant tissue analysis 4) Greenhouse tests 5) Evaluation of symptoms of nutrient deficiencies  Determining Fertility Status and Fertilizer Needs A sound fertilizer recommendation is usually arrived by: – a combination of the above approaches – making correlations among plant response and soil and plant nutrient status – consideration of type of crops – physical properties of soils – environmental conditions  Soil Analysis and Fertilizer Recommendation Soil analysis - relatively rapid method of determining the fertilizer needs of crops. The method consists of: – taking soil samples properly – subjecting the soil samples to chemical analysis – interpretation of results of analysis Assumes that the chemical extractants remove the potentially available forms of nutrients from the soil.  Soil Analysis and Fertilizer Recommendation These available forms of nutrients are rapidly absorbed by the plant and are quickly replaced by the reserve forms of nutrients; – so that the same level of the nutrient taken is supplied and maintain at the time of analysis.  Soil Analysis and Fertilizer Recommendation For a simple soil fertility test, the following soil properties are determined: – pH – OM content – available P – exchangeable K – lime requirement (if pH < 5.0)  Soil Analysis and Fertilizer Recommendation Soil pH = important in interpreting results of a soil analysis and helps in predicting other nutritional problems of the soil. When OM content is determined; – N supply can be estimated by assuming that SOM contains 5% N.  Soil Analysis and Fertilizer Recommendation Thus, if the OM = 3%, the total N content (organic) would be about 0.15%. Assuming that one hectare-furrow-slice (HFS) weighs 2,000,000 kg – the potential supply of N in the soil = 3,000 kg. P is determined by any of the following methods: Bray 2, Olsen and Truog. The method to be used depends on the predominant forms of P present in the soil. – these methods differ in the extracting solution used.  Soil Analysis and Fertilizer Recommendation K is likewise determined by different methods. – ammonium acetate – sulfuric acid as extractant the method used must be taken into account because the nutrient sufficiency value for one method is different from that of another. Lime requirement of acidic soils is analyzed by incubating soil samples with increasing amounts of lime (e.g. CaCO3) and then plotting the pH change with lime increments. – the required amount of lime to reach a desired pH value is then found from the curve.  Soil Analysis and Fertilizer Recommendation Soil test results are compared with known values of deficiency/sufficiency. These values are derived from previously calibrated data of correlation between soil tests and field fertilizer experiments.  Soil Analysis and Fertilizer Recommendation Good soil testing requires 3 components: 1) Good representative sample. 2) Adequate laboratory tests that determine the amount of nutrients the plant can remove from the soil. 3) Considerable experimental work to correlate the soil test results with fertilizer recommendations and actual crop yields. How Soil Samples are Collected for Soil Analysis? The farm for soil fertility evaluation by soil analysis is first delineated on a rough map to group similar areas in terms of visible soil properties and management. Homogeneous areas are designated as sampling units. Some of the similarities of each sampling unit are: – soil texture, soil color, topography, previous cropping and management and position in the landscape.  How Soil Samples are Collected for Soil Analysis? Samples are then taken at random all over the sampling area; – by shovel or auger The depth of holes depend on whether shallow-rooted/deep-rooted crops are to be planted. The samples from several holes are mixed in a container and then from the soil sample mixture; – only one composite sample of about one kg is submitted for analysis in the laboratory. How Soil Samples are Collected for Soil Analysis? The composite sample is supposed to represent a big area of thousands of kg of soil, hence the need for careful sampling. – soil analysis has no value, no matter how accurate, if samples are taken improperly.  How field fertilizer experiment is used as basis of fertilizer recommendation? A simple fertilizer experiment to determine the optimum amount of fertilizer for a particular crop; – consists of treatment plots starting from zero and increasing at regular increments. Example: to determine the rate of N for a specific soil and other environmental conditions, the fertilizer treatments could be: 0, 30, 60, 90, and 120 kg N/ha How field fertilizer experiment is used as basis of fertilizer recommendation? The plot size is about 20 m2 and the treatments are replicated at least three times. Agronomic data (e.g. corn as test crop) such as: stand count, plant height, and yield are collected and the results are plotted against the increasing amount of N added. How field fertilizer experiment is used as basis of fertilizer recommendation? The field experiment is repeated for the next season; – may be conducted simultaneously in other locations. One of the most sound bases for formulating fertilizer recommendations; – plants are grown under the natural conditions of their environment.  The following is a sample field experiment on corn to determine the optimum N rate: Treatment Application Rate Number (kg N/ha) 1 0 2 30 3 60 4 90 5 120  Number of replications: 4 Experimental Design: RCBD Test crop: corn  Greenhouse Experiments in Soil Fertility Evaluation Greenhouse studies - primarily preliminary approaches to determine what nutrient is insufficient in specific soils. Cannot be used as a sole basis for fertilizer recommendation because of the highly artificial conditions; – volume of soil explored in a pot by plant roots is limited by the size of the pot. Some advantages of a pot experiment include: – the simultaneous testing of several kinds of soils under similar conditions – cheaper to establish and maintain  Plant Analysis in Soil Fertility Evaluation Plant analysis - usually done to verify what nutrient is deficient in the soil. May also be used to estimate the subsequent nutrient needs of long growth duration crops like: – sugarcane – banana – fruit trees Problems with tissue testing are: 1) Nutrient stress may occur before the fertilizer can be applied. 2) It is difficult to determine how much fertilizer to apply. 3) Can be affected by the weather.  Nutrient Deficiency Symptoms in Soil Fertility Evaluation Visual Deficiency Symptoms Useful to aid in identifying when plant is deficient in a nutrient. – it is usually complemented by plant analysis and/or by soil analysis. They are often difficult to interpret; – many symptoms look similar/may look like disease/insect damage. When we see deficiency symptoms - often too late to apply additional fertilizer to aid the plants’ future growth.  Other Factors Considered in Formulating Fertilizer Recommendations Aside from native fertility of the soil, the other considerations in the formulation of fertilizer recommendations are the following: – seasons of the year – economic value of the crops – nutrient preference of particular types of crops – soil pH – soil moisture conditions – target yield levels  Other Factors Considered in Formulating Fertilizer Recommendations In general, crops require higher rates of fertilizer in the dry season than in the wet season. – greater solar energy available – more vigorous plant metabolism plants have higher demand for nutrients For high value crops: – high fertilizer rates justify their high cost For low value crops: – the value of returns at high fertilizer rates may not offset the cost  Other Factors Considered in Formulating Fertilizer Recommendations High fertilizer rates are applied when high yielding crop varieties and intensive management practices are used. Different crops have different demands for N, P, and K; – grain crops demand for high N – legumes for high P – sugar, fiber, tuber and oil crops for high K  Other Factors Considered in Formulating Fertilizer Recommendations Sufficiency level of a nutrient for a certain crop may not be the sufficiency level for another crop. Soil pH affects the behavior and availability of applied nutrients. – Example: acidic soils = have greater P fixing ability. – Thus, P fertilizer application must take into account the proportion of P that will be immobilized in the soil.  Fertilizers Fertilizer - any organic/inorganic material which contains one/more of the essential nutrients for plant growth. Organic fertilizers - derived from plants and/or animals. Inorganic fertilizers – synthesized/processed from mineral deposits. – usually called chemical fertilizers. Fertilizers, whether organic/inorganic may be: – solid, liquid, or gaseous form  Fertilizers Examples of organic fertilizers are: – animal manures – compost – crop residues – green manures – certain industrial by-products Inorganic fertilizers contain one/combination of the three primary elements: N, P or K  Fertilizers Fertilizers which contain only one of those elements are called = Single element fertilizers. Those which contain two/more are called = Compound fertilizers. Materials containing all three N, P, and K are called = Complete fertilizers.  Fertilizer Grade The numbers on a bag of fertilizer –> “14-14-14” = guaranteed chemical analysis. These numbers indicate the bag of fertilizer contains: – 14% N, 14% P2O5, and 14% K2O. These numbers –> “14-14- 14” = are referred to as the fertilizer grade.  For P and K, the chemical analysis is given in the oxide form. Ø This is the way the nutrients were first thought to be absorbed by the plant and is still used today to express the analysis of fertilizer. For a 14-14-14, elemental analysis: 14 – 6.2 - 11.6 To convert from the chemical analysis à the elemental analysis for P and K fertilizers, use this formula:  P2O5 à P & K2O à K P = 31; O = 16; K = 39 %P in P2O5 = (31 x 2) ÷ (31 x 2) + (16 x 5) x 100 62 ÷ 142 x 100 = 43.66% or 44% %K in K2O = (39 x 2) ÷ (39 x 2) + 16 x 100 78 ÷ 94 x 100 = 82.98% or 83%  General Characteristics of Inorganic Fertilizers Nitrogen Fertilizers Ammonium sulfate = 21-0-0 Urea = 46-0-0 Anhydrous ammonia = 82-0-0 Others – Ammonium nitrate = NH4NO3 (32% N) – Ammonium chloride = NH4Cl (26% N) – Calcium cyanamide = CaCN2 (20% N)  General Characteristics of Inorganic Fertilizers Ammonium Sulfate Contains sulfur Recommended in S-deficient soils Hygroscopic Nearly 100% soluble Crystalline and white In aerobic soils, NH4+ is quickly converted to NO3- Residual acidity can be neutralized by the application of 5 kg lime/kg N.  General Characteristics of Inorganic Fertilizers Urea Hygroscopic and 100% soluble Crystalline and white When applied to soil, it is acted upon by microbial enzyme urease to form ammonium carbonate  General Characteristics of Inorganic Fertilizers Anhydrous Ammonia Basic, pungent, and colorless Less acidifying Residual acidity equivalent to 1.8 kg lime/kg N.  General Characteristics of Inorganic Fertilizers Phosphorus Fertilizers Ordinary Superphosphate = 20% P2O5 Triple Superphosphate = 45-50% P2O5 Ammonium Phosphate = 16-20-0 or 11-48-0  General Characteristics of Inorganic Fertilizers Ordinary Superphosphate Pelleted as grayish granules About 85% of P is water soluble Contains traces of other nutrient elements such as: – Mg, Fe, Cu, Zn, Mn, and Cl  General Characteristics of Inorganic Fertilizers Potassium Fertilizers Muriate of Potash = 60% K20 and 47% Cl – Highly soluble – Contains traces of S, Mg, Ca, Fe, B, and Na.  General Characteristics of Inorganic Fertilizers Complete Fertilizers Examples of the different grades: 14-14-14 15-15-15 12-12-12 12-24-12 8-24-24  Fertilizer Computations Wt of Fertilizer Needed = Wt. Nutrient Needed ÷ Percentage of Nutrient In Fertilizer Wt of Fertilizer = Recommended rate ÷ PNIF PNIF – Percentage of Nutrient In Fertilizer  Example How much ammonium sulfate do you need in order to apply 60 kg of N per hectare? Ammonium sulfate fertilizer: 21-0-0 Wt. of ammonium sulfate = 60 ÷ 0.21 = 285.7 kg  Sample Problems 1) If you apply 50 kg of complete fertilizer (14-14-14) how much N, P, and K did you apply ? 2) How many kilograms of N and P205 were applied if a farmer used a 50 kg bag of 18-46-0 fertilizer?  Answers 1) Complete Fertilizer: 14 - 14 - 14 = 14% N, 14% P205, 14% K20 N ® 0.14 x 50 = 7 kg N P ® 0.14 x 50 = 7 kg P205 7 x 0.44 = 3.1 kg of P K ® 0.14 x 50 = 7 kg K20 7 x 0.83 = 5.8 kg K  Answers 2) N –> 50 x 0.18 = 9 kg N P2O5 –> 50 x 0.46 = 23 kg P2O5  Fertilizer Application Band placement of fertilizer is done in several ways: – applied on the row below the seed level – slightly on the side of the seeds along the row The roots after germination will have to grow through the fertilizer. Especially important for P fertilizers. – the negative effect of the immobility of P are reduced by the close association of roots with the banded fertilizer. Band Application of P Fertilizer Root Fertilizer  Fertilizer Application Broadcast application – the fertilizer is spread evenly on the soil surface. Frequently done after the crop has been harvested, in preparation for the next crop. These materials should then be incorporated by plowing to avoid water pollution by runoff. Generally, more P and K will be needed when broadcasting than if the fertilizer was banded.  Fertilizer Application Top dressing refers to adding fertilizer to the surface of a crop already growing. Fertilizing established turfgrass is also done with top dressing.  Fertilizer Application Side dressing is often done with anhydrous ammonia. It must be accomplished before the crop is too high for the implements. Ammonia is injected into the soil at least 3 inches deep. Ø It is rapidly changed to NH4+ and can be taken up by roots, attached to cation exchange sites, or converted to NO3-. Urea can also be side dressed with cultivators.  Fertilizer Application Foliar application of fertilizers is made when quick action of nutrients is desired or when certain micronutrients are needed to be supplied to the crop. Only small amounts of nutrients can be absorbed by the leaves. Ø if large amount of nutrient is needed, soil application is recommended. Generally, micronutrients such as iron/zinc are applied in a foliar spray.