RESPONSE OF LOWLAND RICE AND COMMON BEAN GROWN IN ROTATION TO SOIL FERTILITY LEVELS ON A VARZEA SOIL

Brazil has approximately 30 million hectares of lowland areas, known l ocally as ''Varzea,'' but very little is known about their fertility a nd crop production potential. A field experiment was conducted for thr ee consecutive years to evaluate response of lowland rice (Oryza sativ a L.) grown in rotation with common bean (Phaseolus vulgaris L.) on a Varzea (low, Humic Gley) soil. Rice was grown at low (no fertilizer), medium (100 kg N ha(-1), 44 kg P ha(-1), 50 kg K ha(-1), 40 kg FTE-BR 12 ha(-1)), and high (200 kg N ha(-1), 88 kg P ha(-1), 100 kg K ha(-1) , 80 kg FTE-BR 12 ha(-1) fritted trace element-Brazil 12 as a source o f micronutrients) soil fertility levels. Green manure with medium fert ility was also included as an additional treatment. Average dry matter and grain yields of rice and common bean were significantly (P < 0.01 ) increased with increasing fertilization. Across the three years, ric e yield was 4327 kg ha(-1) at low fertility, 5523 kg ha(-1) at medium fertility, 5465 kg ha(-1) at high fertility, and 6332 kg ha(-1) at med ium fertility with green manure treatment. Similarly, average common b ean yield was 294 kg ha(-1) at low soil fertility, 663 kg ha(-1) at me dium soil fertility, 851 kg ha(-1) at high fertility, and 823 kg ha(-1 ) at medium fertility with green manure treatment. Significant differe nces in nutrient uptake in bean were observed for fertility, year, and their interactions; however, these factors were invariably nonsignifi cant in rice.