The Use of Organic and Mineral Amendments to Improve Zimbabwean Soil Health Utilising Plant Growth and Hydrocarbon Breakdown as Indicators

Abstract

Southern Africa faces a great problem threatening the sustainability of maize crops because of the inability of African soils to grow said plants and their deficiency in many different factors such as water holding capacity, nutrients availability, and aggregate stability, amongst others. The hypothesis behind this study is that mineral and organic matter amendments can improve soil health and thereby increase potential hydrocarbon bioremediation, since this is only possible in a well structured, healthy soil. Soil health is measured in this study using plant health itself as an indicator, as well as the soil’s ability to bioremediate hydrocarbons. It is also expected that with the addition of mineral and organic amendments not only the physical characteristics of the soil change, but the chemical and biological ones as well. To date, the use of both mineral and organic amendments for soil improvement has not been deeply explored by many researchers. The study is composed of two growth trials in which Zimbabwean soil is mixed with either compost, quartzite, water treatment residual (WTR), or a combination of them, two identical sets of amendments were done with the difference that one of the sets contained an addition of nutrients (plant food). The main findings are firstly that for plant health a single compost amendment (10% of compost combined with soil) and a coamendment of compost and WTR (10% of each material in combination with soil) are both statistically significantly (P<0.05) better for plant height and for above ground and below ground biomass. Nutrients addition (plant food), improves the co-amendment’s biomass but does not have the same effect in the single compost amendment’s biomass. Secondly, it was found that of all soil types the single amendment of compost had the highest CO2 emissions, after 30 days of oil contamination. This implies that the addition of nutrients (NPK) negatively affected CO2 emissions rates when soil was contaminated with oil, potentially suggesting that NPK addition has a negative effect in the soil microbiome of this Zimbabwean sandy soil.