RELATIONS BETWEEN DRY MATTER YIELD AND THE AMOUNTS OF NUTRIENTS EXPORTED BY Brachiaria brizantha ON SOILS UNDER THE "BARREIRÃO" CROPPING SYSTEM

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.