Relações da produção de massa seca e as quantidades de nutrientes exportados por Brachiaria brizantha em solos sob o manejo pelo sistema "barreirão"

Abstract

The relation between dry matter yield and the nutrients exported by Brachiaria brizantha on a dystrophic Oxisol (Goiás, Brazil) was assessed in a pasture established after clearing an original Cerrado area. This pasture was established by applying 1.5 t/ha of calcitic lime and direct sowing of Brachiaria decumbens. After ten years, this pasture was renewed using the “Barreirão System”. In a single operation, rice was sowed at a depth of 3 cm to 5 cm together with B. brizantha, mixed with fertilizers, placed at a depth of 8 cm to10 cm. Areas where the system has been used from one to six years were compared with a native forest and a seventeen years-old traditional pasture as reference areas. Considering the amounts of exported nutrients from the system, the data allow us to conclude that to sustain productivity of the Barreirão System: a) nitrogen from soil organic matter, levels of exchangeable calcium, magnesium and potassium, and available phosphorus and zinc (extracted by Mehlich-1 method) are insufficient after four years of use; b) available iron, copper and manganese are sufficient to keep the system going longer than six years; c) no consistent relationship between potassium exported and dry matter yield was found.