EFFECTS OF AMENDING COMPOST AND GREEN MANURE WITH PHOSPHATE ROCK ON QUALITY OF AMARANTH

Abstract

A study was conducted in Iringa, Tanzania to evaluate the effects of crotalaria green manure and compost applied alone or amended with Minjingu Phosphate Rock (MPR) as sources of N and P and their effects on vegetable quality attributes. The field experiment was conducted using a split plot design with three replications. Crop species formed main plots, while fertilizer treatments constituted the subplots. Two amaranth species (Amaranthus cruentus and Amaranthus hypochondriacus) were used. The treatments included crotalaria (Crotalaria ochroleuca), crotalaria + MPR, compost, compost + MPR and NPK, which was used as a standard. Results indicated that amendment of compost or crotalaria with MPR enhanced P supply by 22% and 100%, respectively. The tested materials significantly increased vitamin C, vitamin A and crude protein content of amaranth. Plants from plots treated with crotalaria had significantly higher levels of protein, calcium, vitamins C and A contents, compared to those fertilized with compost. There were significant and positive correlations between soil available N, P, and uptake with protein, calcium, iron, vitamin C and A content of amaranth. Due to the role of Ca in cell wall synthesis, it probably influenced the keeping quality of amaranth. The high Ca content in MPR amended treatments increased the evaluated keeping quality attributes of amaranth. It is therefore recommended that the tested organic materials be adopted as sources of N and P in the organic production of amaranth. Application of crotalaria and compost should be supplemented with P sources such as MPR in order to increase their P contents.