Agronomic and Ecological Impacts on Cotton with Changing Crop Rotation

Abstract

Agronomic and ecological impacts of changing from fallow - cotton monoculture to  double-crop cotton in rotation with sesame and soybean was studied by the UNA Managua at CEA Posoltega, Nicaragua, from 1987 to 1992. A bifactorial pennanent field  experiment combined five rotations and three weed management systems. The highest cotton raw yield (1368 kg/ha) was obtained after preceding sesame. Inoculated soybean  (1583 kg/ha) yielded higher than soybean without inoculation (1241 kg/ha), showing a  better adoption to Primera growing season with irregular precipitation, but requiring a  major mineral fertilization the succeeding crop. The composition of the adventive flora changed drastically due to shortening of the fallow period and introduction of double-cropping. In 1988, the total initial abundance was 139 ind./m², Cyperus rotundus with  94 ind./m², Poaceae with 9 ind./m² and Dicotyledoneae with 36 ind./m². In 1992, the  total initial abundance augmented to 241 ind./m², nearly disappearing Cyperus rotundus with 8 ind./m², which was replaced by Poaceae (154 ind./m²). The Dicotyledoneae  duplicated their abundance to 79 ind./m². Five years after starting the experiment, the  soybean monoculture (inoculated) resulted in the minor abundance with 182 ind./m².  The lowest weed biomass (141 g/m²) was reached in the rotation soybean (without inoculation) - cotton.