Analysis of the effects of organic matter using plant growth and microbial activity as soil health indicators

Soil organic matter (SOM) contributes to the stabilisation of soil structure by aggregating mineral particles together. SOM also provides nutrients for plant growth and carbon for microorganisms. To identify what the effects of SOM on soil function such as plant growth and microbial diversity and function are, three different waste materials, compost, water treatment residual (WTR) and anaerobic digestate (AD), were mixed in various combinations with agricultural soil to make several ‘soil types’. Maize was grown for 7 weeks in these soil types. The first hypothesis was that organic matter/inorganic mineral co-amendments can improve soil health and thereby its capacity to remove pollutants such as hydrocarbons. The second hypothesis was that organic matter has important biological and physical roles in improving soil structure as well as the already well understood chemical role of providing nutrients. Analysis of biomass shoot measurements showed that without NPK AD only and AD/WTR soil types provided the best medium for plant growth giving 52.32% increased shoot biomass with AD only soil type compared to soil alone, and 47.59% with AD/WTR soil type compared to soil alone. NPK addition to AD/WTR soil type provided the best medium for plant growth with statistically significantly increased biomass shoot compared to all soil types with NPK. In oil contaminated soils, the effect of residual NPK in soil was to reduce CO2 concentration rates used as a proxy for oil biodegradation, and this was statistically significant for AD as a single amendment