Effects of amending compost and green manure with phosphate rock on soil organic carbon in tomato and amaranth plots.

摘要

Declining soil fertility is a major problem hindering agricultural production in Tanzania. This is mainly caused by inadequate use of fertilizers or organic amendments and burning or removal of crop residues. Vegetable crops demand high levels of nutrients for good yields and quality which require sustainable management of soil fertility. A field experiment was conducted in Iringa Tanzania to evaluate the effect of amending compost and green manure with Minjingu Phosphate Rock (MPR) on soil organic carbon in vegetable plots. The experiment was laid in a split plot design with three replications. Crop species were main plots while fertilizer treatments constituted the sub plots. Two amaranth species (Amaranthus cruentus and Amaranthus hypochondriacus) and two tomato cultivars ('Tengeru 97' (indeterminate) and 'Tanya' (determinate)) were used. The treatments included compost, compost+MPR, crotalaria (Crotalaria ochroleuca), crotalaria+MPR, NPK and control (no fertilizer application). Compost was more effective in increasing soil organic carbon and moisture content compared with green manure in both amaranth and tomato plots. Amaranth plots treated with compost+MPR had highest soil organic carbon (1.00%) followed by compost alone (0.89%) then crotalaria+MPR (0.62%) and crotalaria alone (0.56%). The lowest organic carbon was recorded in the NPK (0.50%) and control (0.45%) plots. In tomato plots, compost+MPR treatment increased soil organic carbon by 126.6% while crotalaria+MPR increased organic carbon by only 9.57%. There was no significant interaction between varieties and fertilizer type on soil organic carbon. The results suggest that, compost is more effective in humus synthesis than crotalaria green manure. Addition of MPR provides nutrient source to the micro-organisms thus leading to accelerated rates of decomposition and synthesis of humus.