Effects of green manure and compost amended with phosphate rock on soil properties, yield and quality of amaranth and tomato.

Abstract

A study was conducted in Iringa, Tanzania to evaluate the potential of crotalaria (Crotalaria ochroleuca) green manure and compost applied alone or amended with Minjingu phosphate rock (MPR) as sources of N and P and their effects on selected soil physical and chemical properties, plant nutrient concentration and uptake, yield and some quality attributes. Two field experiments, one for amaranth and the other for tomato were conducted using a split plot design with three replications. Crop cultivars were main plots while fertilizer treatments constituted the sub plots. Two amaranth species (Amaranthus cruenlus and Amaranthus hypochondriacus) and two tomato cultivars, Tanya (determinate) and Tengeru-97 (indeterminate) were used. Fertilizer treatments included crotalaria as green manure, crotalaria + MPR, compost, compost + MPR and NPK which was used as the standard. The results indicated that compost was more effective than crotalaria in increasing organic matter and soil moisture content. Crotalaria contributed more N to the test crops than compost. Amendment of compost or crotalaria with MPR enhanced P supply, plant N and P uptake and relative agronomic effectiveness (RAE). All fertilizer materials were able to supply adequate levels of N and P as required by the two crops at their critical growth stages. The tested materials significantly increased yields, vitamins C and A, and crude protein of the two crops. The yields and nutrient content levels obtained for the two vegetables were within the range reported in literature. There were significant and positive correlations between soft available N, P and yield, protein, calcium, iron, vitamin C and A contents of the vegetables. Keeping quality of the vegetable crops was mostly influenced by their Ca contents probably due to the role of Ca in cell wall synthesis and integrity. Due to its high Ca content, MPR-amended treatments increased the evaluated keeping quality attributes of the test vegetables. It is therefore recommended that the tested organic materials could be attractive sources of N and P in organic production of tomato and amaranth. Application of crotalaria and compost should be supplemented with P sources such as MPR in order to increase their P contents. Soil fertility improvement programmes in this area and others with similar soil properties should include farmers training on proper management of organic materials such as application methods, storage and time of application.