Nutrient Management Research Database

ABSTRACT
Controlled- and slow-release nitrogen (N) fertilizers have been commonly used in
high-value applications, such as horticultural production. Traditional controlled release products have not been economical for use in major grain crops because of high cost and low crop prices. New economical, controlled-release fertilizers are available for use in field crops such as corn (Zea mays L.), wheat (Triticum aestivum L.), and other commodity grains. Technology improvements have reduced manufacturing costs, while high N prices and interest in improved N-use
efficiency have increased demand for new products. Polymer-coated fertilizers
seem to offer the most promise. Nitrogen release from polymer-coated fertilizers
is by temperature-controlled diffusion. Coupling N release with soil temperature,
a primary factor in crop growth rate and N demand, allows N release to be
programmed to better match crop needs. Research shows that controlled N
release improves crop output per unit of applied N and reduces N losses.

SUMMARY AND CONCLUSIONS
Controlled-release nitrogen fertilizers have the potential to significantly improve N-use efficiency while maintaining crop productivity. Controlled-release nitrogen is demonstrated in these studies to be a more efficient nitrogen source for grain crops without sacrificing yields. When applied at the same rate as conventional N sources, CRN increased corn yields sufficiently to offset additional cost of the product – in most cases increasing grower profit – while reducing risk of N loss to the environment. It was also demonstrated that CRN can be applied to corn at significantly lower rates, conservatively 25 to 35% less, than conventional N sources without sacrificing crop yield.

A variety of controlled release fertilizers are available to help growers improve nitrogen fertilization efficiency.

This paper outlines results of a number of controlled release fertilizer technology studies.

Products covered include nitrification and urease inhibitors as well as slow release fertilizers.

Controlled-release N (CRN) produces higher yields in the large majority of studies examined.

On average, CRN products increased grain yields by 6.3 bu/ac. Increases as high as 12 bu/ac were quite common, with the highest increases of more than 24 bu/ac observed when N was at the highest risk for loss due to environmental conditions. When soil is wet and temperatures are high N is at higher risk of being lost to the environment.

Conventional N sources produced yield plateaus of 94% at 165 lbs N/ac, while CRN sources showed 94% of yield potential at 118 lbs N/ac, a savings of 47 lbs N/ac.

These studies were performed in grain systems with climates different from California's.