Start Date

1-12-2011 12:00 AM

Description

The prevailing phosphorus (P) and potassium (K) management system in Iowa and the Midwest is based on soil testing, response-based fertilizer application for low-testing soils, and removal-based fertilizer application to maintain desirable soil-test P (STP) and soil-test K (STK) values. Several issues are important for an effective implementation of this management concept. These include use of appropriate soil-test methods and field calibrations to determine optimum soil-test levels and fertilization rates, knowledge of fertilization and cropping impacts on soil-test values over time, and reliable estimates of P and K removal with harvest. In Iowa, continued research during the last two decades has provided calibrations for various soil-test methods for P and K, which have been used for existing soil-test interpretations in Iowa State University (ISU) Extension publication PM 1688. This publication also suggests to use estimates of P and K removal to maintain optimum STP and STK values, assuming there is a good relationship between P and K removal and STP or STK trends over time. Research during the last two decades has shown large temporal variability of yield and both STK and STP but very large for STK. Therefore, better study of the relationship between P or K removal and STP or STK in the short term and long term should be useful to improve the effectiveness of P and K management for crop production and to maintain acceptable water quality in Iowa.

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Dec 1st, 12:00 AM

Nutrient uptake by corn and soybean, removal, and recycling with crop residue

The prevailing phosphorus (P) and potassium (K) management system in Iowa and the Midwest is based on soil testing, response-based fertilizer application for low-testing soils, and removal-based fertilizer application to maintain desirable soil-test P (STP) and soil-test K (STK) values. Several issues are important for an effective implementation of this management concept. These include use of appropriate soil-test methods and field calibrations to determine optimum soil-test levels and fertilization rates, knowledge of fertilization and cropping impacts on soil-test values over time, and reliable estimates of P and K removal with harvest. In Iowa, continued research during the last two decades has provided calibrations for various soil-test methods for P and K, which have been used for existing soil-test interpretations in Iowa State University (ISU) Extension publication PM 1688. This publication also suggests to use estimates of P and K removal to maintain optimum STP and STK values, assuming there is a good relationship between P and K removal and STP or STK trends over time. Research during the last two decades has shown large temporal variability of yield and both STK and STP but very large for STK. Therefore, better study of the relationship between P or K removal and STP or STK in the short term and long term should be useful to improve the effectiveness of P and K management for crop production and to maintain acceptable water quality in Iowa.