FIELD WATER MANAGEMENT AND N-RATES TO SAVE WATER AND CONTROL IRON TOXICITY IN LOWLAND RICE

Poor level of development of lowlands in West Africa, epitomized with bad water management generates favorable conditions for occurrence of iron toxicity which is responsible for limiting yields of lowland rice. Field trial was conducted in 2009, 2010 and 2011 to evaluate the effect of water and nitrogen management on iron toxicity and yield of lowland rice in the Bida, Niger State, Nigeria. Treatments imposed were: (1) Continuous flooding with 5 cm water head from transplanting to hard dough stage. (2) Alternate 30 days flooding with 5 cm water head - 7 days drainage - 30 days flooding - 7 days drainage - 30 days flooding -7 days drainage and flood up to hard dough stage. (3) Alternate 60 days flood with 5 cm water head - 7 days drainage - 30 days flooding - 7 days drainage and flood up to hard dough stage. (4) Alternate 90 days flooding with 5 cm water head - 7 days drainage - flood up to hard dough stage. The N-rates applied were: 40 (control), 60, 80 and 100 kg N ha -1 . Treatments were replicated four times and data obtained were statistically analyzed using SAS statistical package. Results obtained showed that irrigation and N-rates had significant influence (P<0.05) on plant height, panicles number, straw and grain yield when compared with the control (farmers practice). There were no significant differences in grain yield between application of 80 kg N ha -1 and 100 kg N ha -1 . Yields generally increased with increasing levels of nitrogen up to 80 kg N ha -1 and declined with further increase in N-level. Nitrogen use efficiency decreased with increasing levels of nitrogen rates and was 25 kg kg -1 for application of 40 kg N ha -1 . There were also significant differences in plant tissue iron content. Iron concentration was higher in the control than treatments with higher levels of nitrogen. Continuous flooding with 5 cm water head from transplanting to hard dough and the application of 80 kg N ha -1 gave the highest yield in the 3 seasons. The average irrigation water applied for the 3 seasons was 1441 mm including rainfall and crop water use. Treatment 2 of water management saved 143 mm and average water use efficiency was 3.80 kg mm -1 . This treatment also had a marginal decline in grain yield but there was a tradeoff between yield and drainage. Appropriate water and nitrogen management can reduce the intensity of iron in rice to enhance sustainable yield increases of paddy rice in the lowland soils of Bida area.