Estimating The Effect Of Application Timing On The Release Rate Of a Controlled Release Fertilizer.

Controlled release fertilizers (CRFs) have the potential to improve nitrogen use efficiency (NUE), and reduce losses to the environment. Release rates can be significantly affected by factors such as application timing, soil temperature and moisture, and coating qualities such as thickness, surface area, and permeability.  Our research goals were to 1) compare the release rates of winter and spring applied CRFs treatments 2) to quantify nitrate leaching using tension lysimeters and 3) to evaluate N availability and NUE between these treatments. A trial was conducted in Decatur, IL in continuous maize (Zea mays), no-till field. CRFs were stratified into small (diameter<2.53mm), medium (2.53mm<3.19mm),  and large (>3.19mm) size classes, enclosed in screen packets and covered to a depth of 7.5cm in late November 2012 and in mid-April 2013. Screen packets were collected prior to planting, at the V6 stage of maize growth, and at tasselling. Initial results indicated that the November applied CRF released ~30% of its nutrient content prior to planting. These results were correlated to field CRF applications in which 200 kg N-ha^-1 were applied in synchrony with the trial. Lysimeter samples were collected 24 hours after any major rain event (>2.5cm) and the nitrate load was estimated based on soil water nitrate concentration and changes in volumetric water content. Initial results correlated well with trial results, showing a significant difference in nitrates leached between winter and spring applications of the CRF. Ongoing investigations will determine how this will affect N availability in the soil, as wells as crop biomass.