Making Fertilizer Applications Committed to the Environment and High Yields

By Bruce Clevenger and Ed Lentz, OSU Extension Educators

Corn and soybeans continue to be the dominate grain crops for NW Ohio farmers. Growers in the eastern U.S. Corn Belt often fertilize a multi-year rotation with one application rather than fertilizing the individual crops annually. Typically, in the fall prior to corn planting, farmers supply enough phosphorus (P) and potassium (K) to satisfy the nutrient needs of both corn and the following soybean crop. This practice has proven to be a viable option for corn-soybean (CS) rotations on soils with adequate nutrient levels, but questions arise for producers in a 3-year rotation of corn-corn-soybean (CCS).

In 2006, Ohio State University studies assessing P and K fertilization strategies were started in three Ohio locations by Dr. Ed Lentz and Dr. Robert Mullen. Two rotations were compared: corn-soy, and corn-corn-soy. These rotations were fertilized by broadcast application following soybeans and prior to fall tillage, at P and K rates corresponding to zero, once, and twice the crop removal for the rotation. With the 2011 season, this trial has run 6 years: two cycles of the CCS rotation and three cycles of the CS rotation. This provided a total of 36 site-rotation-years of high quality data.

Responses to the fall broadcast applied P and K have been as expected with respect to the critical soil test levels of the Tri-State Soil Fertility Recommendations used in Ohio. Soil test P levels ranged from 16 to 39 ppm by the Bray-P1 test (all above the critical level of 15 ppm), so large responses to P were neither expected nor observed. An economic response frequency of 12 out of 28 site-years provides strong justification for applying P as recommended in the maintenance range. Soil test K levels ranged from 84 to 272 ppm, extending from well below the critical level to well above the maintenance limit. Yield responses to applied K as large as 16% were seen in soils testing below the critical level. These results suggest that the current critical values and maintenance limits for soil test P and K are still appropriate for today’s higher-yielding corn and soybean crops, provided that appropriate adjustments to maintenance rates are made to match the higher removal rates of these nutrients.

Responsible fertilizer/crop nutrient management is the responsibility of farmers and advising agronomists. To balance a profitable yield and environmental responsibility, nutrient applications of commercial fertilizer and/or livestock manure nutrients are best managed by adopting the 4-R approach: the Right source at the Right rate, the Right time and the Right placement. The 4-Rs are without argument a win-win scenario for high yielding agriculture while making an environmental commitment.

This research project conducted by Mullen and Lentz was published by the International Plant Nutrition Institute (IPNI) in September 2012 at:$webcontents/9D377EC9EB2E939E85257A75006E1286/$file/Bruulsema+Insights_2012_final.pdf

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