Nitrogen is essential for plant growth, being one of the main building blocks of proteins. In grain corn, the highest yields generally come from N-rates of 178 - 223 lb/ac. Rates need to be high enough to maximize plant growth. Lack of nitrogen results in short cobs with a low number of grains.
Applications up to 134 lb/ac of P2O5 provide positive yield responses in trials on low P index soils However, even at very high P index soils a starter application of about 18 lb P2O5/ac is required to achieve high yields.
Trials commonly show large responses to high rates of potassium. Annual rates in most countries will range from 150 to 250kg K2O/ha. Corn requires potassium and nitrogen in similar quantities for high yields and low N application will reduce K uptake, restricting growth. A lack of potassium and phosphorus can lead to incomplete grain set at the point end of the corn cob.
Boron is involved in cell extension and pollen tube growth; hence, it has a direct effect on grain set. A lack of boron can lead to a restricted grain set, with the cob having many missing kernels and a few large grains. Foliar or soil applied boron during stem elongation (V5 to V7) can contribute to higher grain corn yield.