INCREASING BEAN YIELD THROUGH SITE-SPECIFIC CULTURAL PRACTICES AND ADAPTED LINES UNDER CENTRAL PIVOT IRRIGATION SYSTEM IN THE TROPICS

摘要

Intensive pasture production for raising beef cattle under central pivot irrigation system has become a common activity in tropical region of Brazil. However, after 4 to 5 years the pasture production starts to decline because of soil fatigue and self-induced incompatibility of the pasture. So, is crop rotation of grass followed by maize/soybean, sorghum and bean in no-till planting has been introduced with moderate success. Bean yield is still too low due to nitrogen deficiency. Traditional side dressing with N several days after planting did not solved the problem in the area with high organic matter accumulation on the surface. In this region with low latitude and altitude and maximum air temperature around 35° C, bean growth cycle is reduced toless than 70 days. Bean can grow, however, in this region because night temperatures drop to below 28° C and soil maximum temperatures never exceed 30° C at 5 to 20 cm depth. Bean is planted during the dry winter period between May and September underirrigation, but average bean yield has never reached 2 t ha~(-1). No commercial bred cultivar is available for this region. The objectives of these experiments were to increase bean yield through better nitrogen application methods and evaluate the performance of new lines in the tropical environment.