Blends of Conventional and Slow-Release Urea in Corn: Effects in Early Growth.

The adequate nitrogen (N) supply to corn crops plays important role in high yielding environments. However, N improper usage can result in poor fertilizer N use efficiency, profitability and hazardous environmental effects.   Polymer coated urea (slow-release urea, PCU) has proven to be an effective approach in increasing nitrogen use efficiency in a number of production systems. A study was carried out in Piracicaba, Brazil, 2012/2013 growing season, in a clayey oxisol.  Four different strategies of nitrogen fertilization in corn were used: (i) split-applied urea (U); (ii) urea applied at planting; (iii) PCU applied at planting; (iv) blend of U and PCU (50%U/50% PCU) applied at planting and (v) control (without nitrogen). The nitrogen rate was 180 kg N ha^-1. The fertilizers applied at seeding were placed in bands 5 cm depth and 5 cm aside the corn seeding row. The split-applied urea treatment consisted in 40 kg N ha^-1 at planting and the remaining 140 kg ha^-1 sidedressed at V4.  The experiment design was randomized blocks with four replications. To estimate dry matter yield, four plants per plot were collected at 25, 44 and 81 day after plant emergence (DAE) (V6, V14 and R3 corn stages) oven-dried and weighted. All data were analyzed using analysis of variance (ANOVA). Means were separated using test t (LSD) at probability level of P ≤ 0.05. The treatmens consisting in U applied in soil band-application at seeding and the blend (50%U/50% PCU) resulted in higher V6 leaf stage dry matter yield than split-applied urea and PCU applied at seeding. This difference disappeared in later stages of corn (V14 and R3) and differed only for untreated treatment (control).