Eficiência de fontes alternativas de fósforo e nitrogênio para a agricultura familiar do Maranhão

Abstract

In the humid tropics, alternative sources of nitrogen and phosphorus are more recommended for smallholder farmers than synthetic fertilizers due to the high costs of the latter. In this paper we evaluated the effect of different doses of a calcined phosphate from Northwest Maranhão in the growth of maize, and the effect of natural and synthetic sources of nitrogen and phosphorus on growth and yield of maize, efficiency of use and remobilization of nutrients in the plant. In the first experiment we used different doses of natural phosphate from Trauíra (NPT) (0 mg kg-1, 10 mg kg-1, 20 mg kg-1, 40 mg kg-1, 80 mg kg-1, 120 mg kg-1) compared with 80 mg kg-1 of superphosphate on dry matter accumulation and root development of maize, and in the second experiment we tested the effect of the combination of two sources of nitrogen and phosphorus (phosphate from Trauíra + urea; superphosphate + urea; phosphate from Trauíra + leucena and superphosphate + leucena) on tasseling and maturity of maize. The concentration of P-total from NPT ranged from 30.4 to 37.9% after calcination and about 7% P2O5 in acid citric 2% extractor. There was an increase of 39% and 63% of dry mass in the Argissolo and Plintossolo, in the highest dose (120 mg kg-1). The highest yield was observed in SS + L treatment compared with the treatments with urea and without fertilizer. The highest values of agronomic efficiency occurred with leucena, independent of the source of phosphorus applied. The recovery efficiency of nitrogen and phosphorus and dry matter accumulation increased the supply of nutrients provided by leucena, increasing the grain yield. We recommend the combined use of SS + L, since the plants benefited by the increasing absorption of nitrogen from leucena, seen by the high recovery efficiency of nitrogen together with the rapid dissolution of superphosphate.