The Effect of Different Land Preparation Methods on Erosion and Growth and Yield of Cassava

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A study was undertaken to assess the effects of different land preparation methods on erosion and growth, and yield of cassava. The experiment was carried out on runoff plots at the Department of Crop and Soil Sciences, Kwame Nkrumah University of Science and Technology, Kumasi. The experimental site was 4 km North East of the Faculty of Agriculture on a slope of 6 % within the semi-deciduous forest zone of Ghana. The soil was Akroso, sandy loam to sandy clay loam (Haplic Acrisol). The treatments studied were: T1 (Ridging across slope), T2 (Zero-tillage), T3 (Planting on the flat) and T4 (Bare plot). These treatments were studied in a randomized complete block design (RCBD) with three replications. The results were analysed by ANOVA using SAS. Regression analysis was used to establish relationships among the parameters tested. The test crop was a cassava (Manihot esculenta), variety named Tekbankye. Mean bulk density at the 0-15 cm depth before the experiment ranged from 1.37 to 1.41 g cm-3 in the order of Planting on the flat > Ridging across slope >Bare plot >Zero tillage. The values for 15 -30 cm depth followed the trend of Bare plot > Planting on the flat > Ridging across slope > Zero tillage with a range of 1.36 to 1.52 g cm -3. Three months after imposing the tillage treatments bulk density ranged from 1.18 to 1.36 for the 0 – 15 cm depth in the order of Bare plot > Zero tillage > Planting on the flat >Ridging across slope. At the 15 – 30 cm depth, the values varied between 1.19 and 1.32 in the order of Planting on the flat > Zero tillage > Bare plot > Ridging across slope. Runoff from the Bare plot (248.69 cm) was 3.32, 1.82, and 1.45 times greater than that from Ridging across slope (74.80 cm), Zero tillage (136.48 cm) and Planting on the flat (171.95 cm) respectively. Soil loss ranged from 10.67 to 68.68 t/ha in the order of Ridging across slope < Zero tillage < Planting on the flat < Bare plot. Soil depth loss due to tillage practices was 5 mm for Bare plot, 2.2 mm for Planting on the flat, 1.92 mm for Zero tillage and 0.76 mm for Ridging across slope. Runoff and soil loss correlated positively with total nutrient losses implying an increase in nutrient loss as runoff and soil loss increased. The Enrichment Ratios showed the eroded sediments to be richer in organic matter and all the nutrients studied than those in the parent soil. Financial loss due to nutrient loss, in Ghana Cedis, was GH¢1,304.90, GH¢875.90, GH¢831.70 and GH¢210.15 for Bare plot, Zero tillage, Planting on the flat and Ridging across slope respectively. Cassava fresh tuber yield varied from 25.01 to 28.65 t/ha under Zero tillage and Ridging across slope respectively but did not differ significantly among the treatments. The crop management factor showed Ridging across slope as the most effective tillage method in conserving soil, water, nutrients and enhancing plant growth and yield.
A thesis submitted to the Department of Crop and Soil Sciences, College of Agriculture and Natural Resources, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana, in partial fulfilment of the requirements for the award of MASTER OF SCIENCE DEGREE IN SOIL SCIENCE.