Objectives Understand the P cycle Learn effects of P in the environment P management exercise Understand K + cycle and management issues
Required and Supplemental Materials Crop nutrient removal charts specific for phosphorus. NRCS 590 Nutrient Management Standard. Land Grant University fertilizer recommendations for phosphorus and potassium for relevant crops. Supplemental Resources –A complete resource on phosphorus is: Understand Phosphorus, University of Wisconsin A-3771 found at http://ipcm.wisc.edu/pubs/nutrient/USP_2002.htm http://ipcm.wisc.edu/pubs/nutrient/USP_2002.htm
Phosphorus P cycle Soil and plant characteristics Environmental resource concerns Phosphorus management
The Phosphorus Cycle Solution P Crop Harvest Crop Harvest Manure P Fertilizer P Crop Residue Crop Residue Labile Stable Organic P Labile Inorganic P Stable From: Livestock and Poultry Environmental Stewardship 34-6 Leaching
Soil Phosphorus Derived from P bearing rocks & minerals Different forms: organic/inorganic, soluble/insoluble Very reactive: Fe, Al, Ca Limiting nutrient in many unfertilized, acid soils
Soil Phosphorus –Maintaining the soil solution concentration for plant uptake is important. –Nutrient strategy Range Maintenance Range Nutrient Rate Buildup Drawdown Level Soil Test Level Critical Maintenance Limit
Soil Test Phosphorus Agronomic soil tests are used to determine plant available P. The tests are a prediction of the amount of desorbed labile (readily available) P into soil solution from the soil mineral surface, over the growing season.
Environmental Concerns Phosphorus is adsorbed to soil particles and moves with soil Pathways that transport soil to surface water are the primary pathways for P movement to surface water
Phosphorus in Water Often limiting nutrient in fresh water systems Addition stimulates algal growth Too much P = less dissolved O 2 Excessive P= EUTROPHICATION
Managing Agricultural P Minimize P sources –Diet manipulation –Manure technologies - No reduction in P, but may increase options for hauling greater distances or marketing Fertilizer Management Conservation Practices No direct application of P to water
Dietary ManipulationManure Treatment Less Available P in Manure Agronomic Application Rates Erosion Control Buffer Strips Improved Water Quality
CNMP Development Create a Farm P Balance –Current soil tests –Current manure tests Determine crop P needs Use manure and wastewater volumes and manure test to determine P 2 O 5 to be applied Use risk assessment tools to determine the lowest risk application areas
P Based Application Rate Soil Test Phosphorus (STP) –Application based upon soil test analysis, and crop P needs, based on university recommendations –Fertility strategy Buildup low P soils Maintenance Drawdown
Nutrient Removal When STP values are optimum, high, or very high, it is recommended to apply on a P removal basis The nutrient removal can be calculated by using a removal factor per unit of yield for the specific crop
Phosphorus Removal Corn removes 0.375 lbs P 2 O 5 per bushel 150 bu x 0.375 = 56 lbs This corn crop would remove approximately 56 lbs of P 2 O 5 per acre Photo: University of Illinois
CNMP Problem Fields Historic P loading (often near production site) –Drawdown mode desirable –Mining results are widely variable Few years to few decades, function of soil mineralogy and chemistry –Utilize risk assessment tool Low risk: load, but poor use of plant nutrient Medium: emergency load High: restrictions
CNMP Problem Fields Low STP –Buildup mode desirable High risk site –PI high (Tennessee 201-300) –Transport factors too high (slope, surface water, coarse textured soil) Siting problems –Floodplain, neighbors, subsurface drainage
Example If the phosphorus index is in the high-risk category, and manure can be applied only on a P removal basis, determine the amount of manure that can be applied to a field for a silage crop that yields 23 tons per acre?
Required Information Corn silage yield23 tons per acre Manure P 2 O 5, based on manure test 3 lbs/1000 gal Total Manure N, based on manure test 10 lbs/1000 gal P removed USDA Plants Database 30 lbs of P per acre
Answer To convert P to P 2 O 5, multiply P x 2.29. 30*2.29= 68.7 lbs P 2 O 5 removed per acre Apply 68.7 or 69 lbs. of P 2 O 5 per acre to meet the P removal rate. Manure analysis: 3 lbs P 2 O 5 /1000 gallons 69 lbs. of P 2 O 5 ÷ 3 lbs. of P 2 O 5 per 1000 gallons = 23 gallons 23 gallons x 1000= 23,000 gallons of manure We can apply 23,000 gallons to meet the P removal rate
Other Considerations The method of application should be considered, in this instance, can the soil accept and hold 23,000 gallons if it is irrigated? If it were applied in one pass via injection, or via multiple applications that add up to 23,000 over time? What rate of other nutrients will be applied (specifically N and K) at this application rate, and are they agronomically acceptable?
Potassium characteristics Soils can have > 40,000 lbs. Total K + ac -1 Almost all fixed in clay bridges and unavailable for plant uptake Exchangeable K + is bound to soil particle surfaces, and is desorbed into soil solution at 1-10 ppm Not easily leached in soils, but can be leached
Excess K + Concerns Grass Tetany –High levels of K + and N in the plant can cause reduced amounts of plant magnesium (Mg) –This can cause a Mg deficiency in grazing animals, and cause a condition called grass tetany or hypocalcaemia –Avoid over-application of K + to pastures Environmental Concerns –Generally, excess K + in surface water has not been a concern Agronomic considerations –Soil Test –Provide adequate K for crop production
Summary Understand the source and transport characteristics of the landscape Develop a crop budget using nutrient strategies and risk assessment tools Evaluate performance using good records Check (often) laws, permit requirements, and regulations governing nutrient management
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