Effect of Tillage and Crop Residue on Soil Chemical Properties and Rice Yields on an Acid Ultisol at Abakaliki Southeastern Nigeria

A study was conducted in 2008 and 2009 raining seasons, to evaluate the possibility of alleviating the degraded soil conditions at Abakaliki. The measures employed were combination(s) of different tillage methods [No-Tillage (NT), Hoe Tillage (HT), Ploughing (PL) and Ploughing and Harrowing (PH)] and crop residues [No Residue (NR), Rice Straw (RS), Burnt Rice Straw (BRS) and Legume Residue (LR)] treatments. Improved rice cultivars (ITA 257, Ex-China and ITA 315) were the test crops. The design of the experiment was a 4 x 4 x 3 factorial in a Randomized Complete Block Design replicated three times.. The results obtained showed that soil organic matter, pH, available P, exchangeable K, Ca, Mg and CEC significantly (p<0.05) improved in the plots that received crop residue across the four tillage methods compared to where crop residues were not applied. The soil chemical properties were also significantly (p<0.05) superior with the application of BRS across the four tillage methods compared to the application of the other residue treatments. Rice growth and grain yield were significantly (p<0.05) higher on the plots that received the combination of the different tillage methods and crop residues respectively than the combination of the different tillage methods without crop residues. There were grain yield increases of 1.47, 1.21 and 1.20 t/ha in the first year and 2.05, 1.64 and 1.53 t/ha in the second year with the application of NT+BRS, NT+RS and NT+LR respectively compared to the application of NT+NR. The application of HT+BRS, HT+RS and HT+LR brought about significant (p<0.05) grain yield increases of 1.65, 1.20 and 1.16 t/ha and 2.67, 2.45 and 2.42 t/ha in the first year and second year respectively. Grain yield significantly (p<0.05) increase by 1.91, 1.68 and 1.62 t/ha in the first year and 2.44, 1.95 and 1.91 t/ha in the second year respectively as a result of PL+BRS, PL+RS and PL+LR treatments compared to PL+NR. PH+BRS, PH+RS and PH+LR treatments led to significant (p<0.05) grain yield increases of 2.55, 1.54 and 1.52 t/ha respectively in the first year and 2.74, 1.72 and 1.71 t/ha respectively in the second year compared to the application of PH+NR treatment. The ITA 315 and Ex-China produced 0.55 and 0.47 t/ha, and 0.62 and 0.50 t/ha significantly (p<0.05) higher grains than ITA 257 in the first and second years respectively. The highest grain yield of 4.87 t/ha in the study was obtained from ITA 315 grown on soil that received PH+BRS treatment.