Polymer Coated Urea In a Corn Field: Soil N-Nitrate Availability.

The use of controlled release urea can achieve better synchronization between the corn needs and the availability of nitrogen (N) in the soil. To evaluate the effect of two sources of N, polymer coated urea (PCU) and conventional urea (U), on the availability of soil N-nitrate (N-NO₃^-) throghout the corn cycle, an experiment was carried out in the 2012-2013 growing season, in Piracicaba-Brazil, in a clayey Oxisol. The experimental design was randomized blocks with four replications, and the treatments consisted of 180 kg N ha^-1 applied at seeding (incorporated into the soil) and were: (i) an untreated control (without N), (ii) 100% PCU, (iii) blend of 50% PCU + 50% U, (iv) 100% U applied at seeding, and (v) 100% U in conventional management (UMC), split-applied (40 kg N ha^-1 at seeding and the remaining sidedressed in V6 stage). The fertilizers applied at seeding were placed in bands 5 cm depth and 10 cm aside the corn row. To determine the N-Nitrate content of the soil, samples were collected at the seeding, at V6, V14 and R4 stages of corn plants, in soil different layers (0-10, 10-20, 20-40, and 40-60 cm). All data were analyzed using analysis of variance (ANOVA). Means were separated using test t (LSD) at probability level of P ≤ 0.05. The utilization of PCU and the blend of PCU + U, led to a greater availability of soil N-nitrate in the top layers (0-10 and 10-20 cm) in later stages of the corn plants (R4), comparing with the utilization of U. It could promote greater N uptake until later stages of the corn plants.