PERFORMANCE OF LOWLAND JUCE-UPLAND RICE-VEGETABLE/COWPEA SEQUENCES AS INFLUENCED BY SOME SOIL PROPERTIES IN THE INLAND VALLEY

摘要

Continual annual inflow of nutrients with the flooding water from adjacent uplands was considered to be the most important factor in maintaining high productivity of inland valleys (I Vs). The potential of IVs to maintain high productivity was examined by growing three crops in sequence within a year without supplemental irrigation. Field experiments were conducted at the University of Agriculture Abeokuta, Nigeria in 2000-2003 to determine the influence of one-cropped, two-cropped and three-croppedsequences on some soil properties in the inland valley. Lowland rice (Oryza sativa L,)-upland rice-fallow, lowland rice-upland rice-cowpea (Vigna unguiculata (L.) Walp), lowland rice-upland rice-okra (Abelmoschus esculentus L.), lowland rice-upland rice-amaranth (Amaranth cruentus), and lowland rice-fallow-fallow sequences, which ran concurrently constituted a cropping cycle. The first, second, and third crops in all the cropping cycles were planted in May, October and January, respectively. The grain yield of lowland rice obtained from lowland rice-fallow-fallow sequence did not decline unlike the yield from two-cropped and three-cropped sequences as the cropping cycle advanced. The yield of upland rice and vegetable dropped significantly in the 2002/2003 cropping cycle as a result of the residual effect of the preceding 2000/2001 and 2001 /2002 cropping cycles. The upland rice had negative residual effects on the succeeding okra but enhance the productivity of amaranth. The best crops combination ofthe three-cropped sequence was BW 311-9-upland rice-amaranth. The two-cropped and three-cropped sequences with or without legume do not seem to make any difference in terms of soil fertility maintenance. The annual inflow of nutrient could not match with the demand two-crop and three-crop sequences. Hence, higher rate of inorganic fertilizer is required for the two-crop and three-crop sequences after two cropping sequences.