Increasing grain corn number and size

Nitrogen, phosphorus, potassium and boron have a particular impact on grain set and size, thereby influencing corn yield.

Crop Nutrition and Grain Corn Number and Size


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.