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Rate and Timing of P and K Fertilization in Corn-Soybean Rotations in Minnesota

Start Date: 2011
Principal Investigator: Daniel Kaiser
Organization: University of Minnesota, Department of Soil, Water, and Climate
Status: Complete

Background Info

In corn-soybean rotations, most farmers apply fertilizer before the corn. However, in cases of high-pH soils, some producers also may apply fertilizer before the soybeans. Corn yield potentials have dramatically increased in the past 10 years, while soybean yields have remained fairly stable. This has caused some soybean growers to wonder if fertilizer should be directly applied to soybeans. More research needs to be conducted focusing on phosphorus (P) and potassium (K) rates, as well as management and timing of applications with regard to crop yields and soil test changes. A research study was initiated in 2009 focusing on a corn and soybean system with multiple rates of P or K applied either before corn, soybeans or as a split application before both crops.

Objectives

Determine optimum phosphorus and potassium fertilizer application rates for corn and soybean

Evaluate the timing of broadcast phosphorus and potassium fertilizer application on corn and soybean yield

Determine if starter fertilizer for corn after broadcast P for soybean can maintain yields of both crops

Evaluate the impacts of P and K fertilizer rates and timing on soybean quality

Study the impacts of P and K fertilizer application rates and crop removal on long term trends in soil test levels

Evaluate critical soil test P and K levels utilizing long-term P and K trials

Compare soil test potassium analysis on air dried versus field moist soils

Key Findings

The addition of P and K significantly increased corn and soybean yields over the two-year test period at selected locations.

Starter fertilizer applied to corn followed by broadcast P for soybean may be a viable option for applying nutrients both years at some locations.

Rate of P or K fertilizer applied within a two-year rotation appears to be the most significant consideration within a fertilizer application program over timing within the rotation.

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