Nutrient quality and phytotoxicity assessment of phospho-compost prepared under two bone meal fortification methods

The advent of the green revolution, characterised by intensive use of chemical fertilisers, has contributed significantly to degradation processes in the low activity clay mineral tropical soils. This has led to recent campaigns to use organic fertilisers. The use of phospho-compost, which is a phosphorus (P) fortified compost as an amendment on P-deficient tropical soils is relatively new in Nigeria and information on its production, especially on the P fortification method that assures nutrient quality and environmental safety, is scanty. This study evaluated the effects of P fortification and methods on phospho-compost nutrient quality and phytotoxicity effects on maize seedling performance. Two carbon sources (sawdust (SD) and rice bran (RB)), poultry manure (PM), Gliricidia sepium (GL) leaves and bone meal (BM) (phosphorus fortifier) were mixed in 1:3:0.125:0.125 (60:180:7.5:7.5 kg feedstock mix) ratio under two bone meal (phosphorus) fortification methods: Co-composting (BMC) and post-stability fortification (BMP) methods were used to prepare four phospho-composts, SD+PM+GL+BMC, SD+PM+GL+BMP, RB+PM+GL+BMC, and RB+PM+BMP, following a standard procedure. Two bone meal unfortified sawdust (SD+PM+GL) and rice bran (RB+PM+GL) based composts were included for comparison. Data were taken on pH, electrical conductivity, P, calcium (Ca), magnesium (Mg), manganese (Mn) and iron (Fe) contents of the cured compost. Data on maize seed germination and root elongation percentages were used for estimation of germination index of maize in each compost extract. Data were analysed by descriptive statistics and multidimensional analysis (MDA) was computed to rank the properties of the composts for use on tropical acid soils. Phosphorus fortification improved pH, electrical conductivity and P content of composts. The post-stability phosphorus fortification method, however, was superior in increasing pH (8%), P (223%), Ca (139%), Mg (15%) and germination index of maize (64%) and reducing Mn (23%) and Fe contents (68%) compared to the co-composting phosphorus fortification method. The MDA results showed a decreasing ranking order of the composts for use on tropical acid soils as SD+PM+GL+BMP > SD+PM+GL+BMP > RB+PM+GL > SD+PM+GL > SD+PM+GL+BMC > RB+PM+GL+BMC. Poststability bone meal fortification method is thereby recommended for use in the production of high quality and environmentally safe phospho-compost..