Presentation on theme: "Long-Term Soil P and K Trends in Relation to Nutrient Removal in Corn-Soybean Rotations Antonio Mallarino Iowa State University Joint Meeting NEC-17, NCERA-13,"— Presentation transcript:
Long-Term Soil P and K Trends in Relation to Nutrient Removal in Corn-Soybean Rotations Antonio Mallarino Iowa State University Joint Meeting NEC-17, NCERA-13, SERA-6 June 22-25 2008
Basis of Soil P and K Testing Use Soil test correlation and calibration Interpretation: interpretation categories Fertilizer recommendations Response-based and often some buildup for the low-testing categories, those with high probability of response. Maintenance of desirable soil-test levels, those with low probability of response. Based on nutrient removal and/or empirical data.
Removal-Based P and K Maintenance CropUnit of Yield P 2 O 5 K 2 O Cornbu0.3750.30 Corn silagebu grain equiv.0.551.25 Corn silage ton, 65% H 2 O 3.508.0 Soybeanbu0.801.5 Oat and strawbu0.401.0 Oat strawton5.033.0 Wheatbu0.600.30 Alfalfaton12.540.0 Red cloverton12.035.0 Pounds per unit of yield Pm-1688 pub, ISU Example from Iowa
Some Relevant Questions Are assumed buildup and maintenance rate appropriate? Does maintenance make sense? What level should be maintained? Does removal-based fertilization really maintain STP and STK levels? How do yield, removal, and soil-test values in the short term and long term? What are the impacts of wrong yield and nutrient concentration estimates?
Long Term Studies in Iowa 5 trials for P, 12 years each, no-till 5 trials for K, 10 years each, no-till Corn/Soybean rotations, both crops each year on adjacent identical trials 3 P rates: 0, 14, and 28 kg P/ha 3 K rates: 0, 33, and 66 kg P/ha Broadcast and band placement methods Measured yield from all plots and soil tests for the control and the high rate
Cumulative P Removal & Soil P 47 lb P 2 O 5 /acre/year for 1 ppm/year decrease Averages of Non-Fertilized Plots Across Locations
P Removal & Soil P Increase Averages of Fertilized Plots Across Locations
Grain Yield and Concentrations Crop yields vary greatly across field and years. We overestimated yield, as most farmers do with yield goals. Grain P and K concentration also vary across field and years Estimates of P and K concentration in grain were much higher than observed averages. Increased up to a certain plateau with the fertilizer rate and soil-test values Grain P and K concentrations were not correlated with yield level across sites.
Removal and Soil Test Values Our overestimation of yield levels and nutrient concentrations resulted in a significant overestimation of removal. Removal was well reflected on soil-test values in the long term, but very poorly or not at all in the short term slow P recycling of residue P and K? slow equilibria between soil P and K pools?
Implications for Management Major errors at estimating P and K removal is caused by error in grain yield estimates. Removal-based P and K maintenance based on good yield and concentration estimates maintain or only slightly increase soil-test P and K it over time. Removal-based maintenance rates must be based on yield averages over time, not from year to year changes.