SIMULATION OF CROP RESPONSE TO POLYOLEFIN-COATED UREA .2. NITROGEN UPTAKE BY CORN

Controlled-release N fertilizers are more desirable if release characteristics are synchronized to plant uptake. This study was conducted to determine the relationship between N dissolution from polyolefin-coated urea (POCU) and N uptake by corn (Zea mays L.) under Andisol field conditions. Cumulative N release (CNR) followed a quadratic curve as a function of either time or cumulative air temperature (CAT). Rate of N dissolution was high at the early growth stages, but gradually decreased with time. The CNR reached about 80% of the total N content of the fertilizer at around 126 d after application or when CAT had reached about 2300-degrees-C. Nitrogen uptake from the fertilizer followed a typical sigmoid curve. Therefore, the fertilizer can supply the N requirements of corn throughout the whole growing period. Since N dissolution can be simulated, it may also be possible to simulate N uptake from POCU by crops. Nitrogen uptake by corn can be predicted in terms of the total amount of N dissolved. Actual recovery of the fertilizer was very high compared with highly soluble fertilizers like (NH4)2SO4 or urea. Since POCU releases N gradually, depending on variations in temperature when soil moisture is sufficient, recovery by crops is less likely to be influenced by variations in climate, such as the occurrence of heavy rains; hence N losses are minimized. Such characteristics of the fertilizer increases nutrient efficiency and contributes to efforts in controlling pollution.