Chapter 7b Soil Testing and Composting PDF

PRINCIPLES OF SOIL SCIENCE AGRICULTURE 51 Chapter 7b Soil Testing and Composting  Determining Nutrient Needs 1. Tissue testing -involves a complete and detailed laboratory analysis of nutrient elements in the plant leaves. This is a very accurate way of assess...

PRINCIPLES OF SOIL SCIENCE AGRICULTURE 51 Chapter 7b Soil Testing and Composting  Determining Nutrient Needs 1. Tissue testing -involves a complete and detailed laboratory analysis of nutrient elements in the plant leaves. This is a very accurate way of assessing how much nutrient the plant has actually taken up from the soil. Recommendations are made on the basis of these test results: – Backed by research – Dependent on plant growth stage and plant part.  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.  Determining Nutrient Needs 2. Visual Deficiency Symptoms Useful to aid in identifying when plant is deficient in a nutrient. They are often difficult to interpret because many symptoms look similar or may look like disease or insect damage. When we see deficiency symptoms it is often too late to add additional fertilizer to aid the plants future growth.  Determining Nutrient Needs 3. Soil testing is based on the concept that a crop’s response to fertilizer will be related to the amounts of available nutrients in the soil.  Determining Nutrient Needs 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.  Soil Testing Collecting a soil sample to determine the current nutrient status of the soil. Sufficiency Method of Nutrient Needs Uses soil testing to predict fertilizer needs. Based on green house and field research. Two phased process – Correlation – Calibration Soil test is truly a predictive tool. Gives soil credit for it’s nutrient providing ability.  Correlation Process used to determine if a soil nutrient, as extracted by a soil test, and crop response to added nutrient, are so related that one directly implies the other. Process of selecting the best soil test for the soils of the area.  Correlation - process Exploratory fertilization trial – Greenhouse – a controlled environment with soil homogeneity. Trials in field with selected soils.  Correlation - process Cate-Nelson method – Determine 120 percentage yield 110 values for each Relative corn yield (% ) 100 fertilizer rate 90 trial. 80 – Determine soil test values for 70 nutrient being 60 studied. 50 – Plot percentage 40 yield vs soil test 0 20 40 60 80 value. Bray-P (ppm)  Soil Test Categories Category Chance of response 1.00 Profitable Response 0.85 Very low 90 % Probability of 0.60 Low 75 % 0.40 0.15 Medium 50 % 0.00 V. Low Low Med. High V. High High 30 % Level of soil fertility Very high 10 %  Fertilizers To the extent possible, growers do use, and should continue to use, organic waste materials such as manure to replace nutrients lost from the soil. Generally, these organic amendments are found to be inadequate for optimal yield, so commercial fertilizers are widely used.  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 to the elemental analysis for P and K fertilizers, use this formula:  P2O5 à P and 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 = 44% K2 O ® K (39 x 2) ÷ (39 x 2) + 16 = 0.83 78 ÷ 94 x 100 = 83%  Fertilizer Computations Wt of Fertilizer Needed = Wt. Nutrient Needed ÷ Percentage of Nutrient In Fertilizer Kg of Fertilizer Needed = KgNN ÷ PNIF KgNN – Kilograms of Nutrient Needed PNIF – Percentage of Nutrient In Fertilizer  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 Banding fertilizer is especially important for P fertilizers. In this way, the roots after germination will have to grow through the fertilizer. The negative effect of the immobility of P are reduced by the close association of roots with the banded fertilizer.  Fertilizer Application Broadcasting fertilizer is 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 turf grass 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 spray can also be used to apply nutrients where it is absorbed by the leaves. 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 or zinc are applied in a foliar spray.  Composting A biological process that breaks down organic material (such as grass clippings and leaves) into more stable molecules  Stages of Composing Process Mesophilic stage – Brief – Temperature rises to 40 oC – Sugars and readily available microbial food sources are rapidly metabolized  Stages of Composing Process Mesophilic stage – Brief – Temperature rises to 40 oC – Sugars and readily available microbial food sources are rapidly metabolized  Stages of Composing Process Thermophilic stage – 50 to 70 oC – Easily decomposed compounds are used up and humus-like compounds are formed – Frequent mixing essential to maintain oxygen levels and assure even heating of all material  Stages of Composing Process Mesophilic (2nd) – Curing stage – Temperatures fall back to ambient – Material recolonized by mesophilic organisms  Benefits from Composting Safe storage Easier handling – Volume reduced 30 to 50% – Material more uniform Nitrogen competition avoidance – No nitrate depression Nitrogen stabilization – N in organic form  Benefits from Composting 4) Partial sterilization – Thermophilic stage kills most weed seeds and pathogenic organisms 5) Detoxification – Most organic compounds are destroyed 6) Disease suppression – Compost suppresses soil borne diseases by encouraging microbial