Wheat Response to Nitrogen under Low Phosphorus and Potassium Fertility in a Wheat–Soybean Production System

Abstract

Producers control crop fertilization practices. If the amount of grain yield per unit of aboveground biomass produced can be optimized with proper fertilization, nongrain aboveground biomass will be minimized. Achieving this goal would be especially beneficial in a wheat (Triticum aestivum L.) and soybean (Glycine max L.) double‐crop production system where proper fertilization could promote a residue‐management shift from burning and conventional tillage to a conservation or no‐tillage system. The objectives of this study were to i) determine the effect of nitrogen (N) rate on wheat yield, aboveground biomass, and partial harvest index (PHI), and ii) identify an appropriate predictive response model for wheat yield and PHI as a function of total N applied under low phosphorus (P) and potassium (K) fertility. This study was conducted over two cropping seasons at two locations on similar silt‐loam Fragiudalfs in eastern Arkansas where wheat was fertilized at 10 N rates ranging from 0 to 101 kg N ha⁻¹ applied once at the early‐jointing stage and from 151 to 269 kg N ha⁻¹ applied in a split application at the early‐jointing stage and at the late‐jointing stage as depicted in the Feekes staging method. The effects of N fertilization on wheat growth and production varied somewhat between locations and from one year to the next. However, the current N recommendation for wheat in Arkansas (i.e., a single application of 101 kg N ha⁻¹) appears to be too low to produce maximum yields under low P and K fertility. Differing yield responses between locations were likely due to the combination of inherent P and K fertility differences and carryover N from the previous crop during the first year of the study. Capitalizing on the relationship among N rate, grain yield, and PHI will allow wheat producers to minimize N applications and production of excessive aboveground biomass, while still being able to produce an economically viable yield.

Keywords:

• Arkansas
• wheat
• soil
• fertility
• nitrogen
• phosphorus
• potassium
• silt loam

Acknowledgments

Funding for this project was provided by the Arkansas Soil Testing and Research Board. William Johnson, Trey Reaper, Claude Kennedy, Roger Eason, Shawn Clarke, and other research station personnel are gratefully acknowledged for their support in conducting this project.