Mauro Wagner de Oliveira

Balanço do nitrogênio da uréia (15N) no sistema solo-planta na implantação da semeadura direta na cultura do milho

This work aimed to study possible alterations in the production and partitioning of the phytomass, in the accumulation of total nitrogen and nitrogen in the plant derived from the fertilizer, by using the 15N side-dressing fertilization at the establishment of no-till management. The experiment was carried out in a Nitosol at Agua Sumida Farm located near Barra Bonita, State of Sao Paulo. The experiment was arranged in completely randomized block design, with 4 replicates. The following treatments were studied: conventional tillage system (one ploughing and two harrowings) and no-tilllage, both fertilized with urea (15N) applied at the rate of 100 kg ha-1 nitrogen. All treatments were subjected to sowing fertilization, by applying 25 kg ha-1 N as urea, 80 kg ha-1 P2O5 as simple superphosphate and 60 kg ha-1 K2O as potassium chloride. At the end of the phenological cycle, the following comparisons among the treatments were performed: crop yeld; nitrogen accumulation in the aerial and underground parts; use of nitrogen from urea (15N) and residual nitrogen in the soil. The modifications of the soil caused by implantation of no-till neither restricted the availability of nitrogen to maize plants, nor the production of dry matter. The use efficiency of nitrogen fertilization of maize plants and the recovery of the soil nitrogen fertilizer were around 45% and 30%, respectively, for the urea-N side-dressing fertilization in both conventional and no-till systems. Nitrogen applied as side-dressing fertilization, and not recovered from urea (NNR) averaged 25%, independently of the sowing system.