SOIL AMELIORANTS TO IMPROVE SOIL CHEMICAL AND MICROBIAL BIOMASS PROPERTIES IN SOME SOUTH AFRICAN SOILS

Abstract

Rainfed field trials on effects of seed, foliar and soil amendments herein referred as industrially manufactured biological amendments (IMBAs) on selected soil chemical and microbial biomass properties were conducted from 2006/07through 2008/09 at four sites in South Africa under light and heavy-textured soils. The IMBAs were classified as growth boosters and partial or total replacements of conventional NPK fertiliser. The IMBAs were applied according to product recommendations in a randomised complete block design with four replications. An optimum conventional NPK rate at each site and untreated control were also included as check. Application of IMBAs with optimum recommended NPK fertiliser rate promoted acidity in soils compared to the IMBAs used as either partial or total replacements of conventional NPK fertiliser. The use of the different IMBA types significantly increased contents of organic C, available N and P only in light-textured soils than in the NPK check. The different IMBAs promoted higher microbial biomass-C immobilisation at 4-weeks after planting, while biomass-C mineralisation was predominant at flowering and crop harvest regardless of soil type. Farmers could apply any category of IMBAs to complement revitalisation of degraded South African soils and also minimise nutrient leaching due to synergetic effects.