Nutrient Assessment of Rain-Fed Lowland and Upland Rice Production Systems in Okigwe, South-Eastern Nigeria

The study was carried out to assess the nutrient status of the two major rice production systems (rain-fed lowland and upland) and the relationship among the nutrient contents of the soil in Okigwe area of Imo State, Nigeria. Soil samples from 15 cm depth were collected from 10 farms in the area: 5 farms from rain-fed lowland and 5 from upland rice production system. The soil samples were prepared and analyzed for macro and micro nutrients together with the particle size distribution. The results from the nutrient concentration in both rain-fed lowland and upland soils showed that pH favoured conditions for more availability of nutrients as seen in upland soils. The t-test results indicates a significant variation in % Clay (0.01*), % TS (0.008**), pH (0.0005**), TN (0.038*), available P (0.01*), Exchangeable Ca (0.03*) and Extractable B (0.02*). Correlation results showed TN as the major determinant of the other soil nutrients in both rain-fed lowland and upland rice production systems. In rain-fed lowland production system, TN correlated negatively and strongly with % TS (-0.81) and Cu (-0.70) with a weak negative association with Na (-0.57), K (-0.55), Mg (-0.50), available P (-0.57) and Fe (-0.64). In the upland rice production system, TN also had a negative association with many soil nutrients though some were weakly correlated while some were of strong association. They include Ca (-0.93), Mg (-0.65), Cu (-0.86), Mn (-0.69) and Zn (-0.76) with a positive association with Na (0.83) and pH (0.69). Despite TN being perceived as the major determinant of nutrients, OM in upland soils had a more positive association with other nutrients compared to that in the lowland soils. Hence, any management practices which will enhance nutrient status should be encouraged to help boost and sustain rice yield in both rain-fed lowland and upland rice production systems.