Fertilizer Application Influence on Soil Tests and Soybean Yield

Introduction

Soil testing research has shown that knowledge of soil test levels can improve fertilizer profitability. Profits increase if more fertilizer is used when soil test levels are low, and less or no fertilizer is used when test levels are high. It is still a common practice, however, to apply fertilizer without a current soil test. Frequently, all the major nutrients (N, P, and K) and sometimes zinc are used. This experiment was initiated to demonstrate the effects of applying P, K and Zn regardless of soil test. The objective was to demonstrate soil testing’s ability to predict crop response to fertilizer and fertilizer influence on soil tests.

Materials and Methods

Treatments listed in Table 1 are applied as listed below. These treatments have been applied since 1996, however no P, K or Zn were applied in 2015 and 2016.

Results and Discussion

The influence of annual fertilizer nutrient application on soil test is clearly shown in Table 1. The P check (No-P) had 4 ppm Olsen P compared to a range of 13 to 19 ppm P when fertilizer P was applied. The K check (No-K) had 117 ppm extractable K compared with 148 to 169 ppm K when fertilizer K was applied. The Zn check (No-Zn) had 0.73 ppm Zn compared with 9.6 to 13.4 when Zn was applied. The large soil test differences between treatment 1 and the nutrient check treatments can be used to determine if these lower soil nutrient tests are limiting grain yields.

During 2016, the P, K and Zn check plots limited soybean yields (Table 1). When no P was applied, soybean grain yield was approximately 14.1 bu/a less than with treatment #1. When © 2017, South Dakota Board of Regents 2 no K was applied, soybean grain yields were 4.4 bu/a lower and the treatment without zinc was 1.5 bu/a less

Modified from:

http://igrow.org/up/resources/03-7008-2017.pdf

By: Anthony Bly, SDSU Extension Soils Field Specialist and Sara Berg, SDSU Extension Agronomy Field Specialist