Effect of Crop Residue on Soil Chemical Properties and Rice Yield on an Ultisol at Abakaliki, Southeastern Nigeria

The influence of crop residue amendments on the chemical properties of an acid soil and rice yields was investigated at Abakaliki for two cropping growing seasons (2006 and 2007). The residue treatments were rice straw, burnt rice husk and legume residue, while the rice cultivars were ITA 315, Ex-China and ITA 257. The design of the experiment was a 3 x 4 factorial in a Randomize Complete Block Design (RCBD) and replicated three times. Data were collected on soil pH, organic matter, soil total nitrogen, available P, exchangeable Ca, Mg, P and CEC and crop growth and yield. Significantly (p<0.05) higher levels of the entire soil chemical properties measured were detected on the soil treated with the different crop residue than the soil that was not treated with crop residue. There were significant differences (p<0.05) on the effect of residue sources on soil N, P, K, Ca, Mg and CEC. The soil organic matter was significantly higher on the soils treated with rice straw and legume residue than the soils treated with burnt rice husk, where as burnt rice husk significantly reduced soil acidity than the rice straw and legume residue. Rice growth was superior in were the soil was treated with crop residue than the soil without crop residue treatment. Grain yield was also significantly (p<0.05) higher when the soil was treated with crop residue than when the soil was not treated with crop residue. There were average grain yield increases of 1.15, 1.60 and 1.50 t/ha for ITA 315, 1.30, 1.55 and 1.35 t/ha for Ex-China and 0.85, 1.05 and 0.90 t/ha for ITA 257 were the soil was treated with rice straw, burnt rice husk and legume residue compared to the soil with no residue treatments. The highest grain yield of 3.40 t/ha in the study was recorded with ITA 315 planted on soil treated with burnt rice husk. Generally, ITA 315 and Ex-China produced significantly (p<0.05) higher grain yield than ITA 217. The superior yield of rice on residue treated soil was attributed to the improved soil chemical properties where as the superior performance and yield of ITA 315 and Ex-China were ascribed to genetic variability.