Effects of tillage on soil properties, nutrient uptake and maize growth

A field experiment was conducted at Uyole, Mbeya, to study the effects of tillage on soil physical and chemical properties, nutrient concentration and uptake and maize growth. The treatments consisted of no-tillage, hand hoeing with crop residue returned, hand hoeing with crop residue removed, mould board ploughing, and disc ploughing followed by disc harrowing. The treatments were designated NT, HHT, HHR, MP and DP, respectively. The physical properties assessed are soil moisture content, bulk density, water retention and 0.3 and 15 bar and aggregate size distribution. While for the assessment of the chemical properties, pH, organic carbon, total N, available P, exchangeable Ca, Mg, Na, K, Mn and acidity were determined. Samplings for these were done at six weeks after planting, at the full silking stage and after harvest. Nutrient concentration was determined at four weeks after planting and at at the full silking stage. Nutrient uptake were determined only at the first sampling. To assess plant growth, root and shoot dry weight as well as grain yield were determined. Other observations were plant height, leaf area and weed infestation. Root and shoot development of maize plants were significantly more vigorous on NT plots during the first four weeks of growth. This was attributed to higher moisture content resulting in greater concentration and uptake of plant nutrients. Maize plants on NT plots were in most cases taller than on the other plots. At the full silking stage maize plants grown on NT plots still exhibited more vigorous root and shoot development than the other treatments but grain yield, final top dry weight and harvest index did not show any significant differences among tillage treatments. The results on grain yield suggests that any one of the five tillage methods can be adopted. However, long-term effects of these treatments need to be evaluated because other changes of physical and chemical parameters are likely to occur over time.