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The main objective of this paper is to review the main effects of organic amendments on soil fertility and environmental quality. The review showed that both organic amendment types could improve the physical, chemical and biological characteristics of soil and environmental quality in a dose dependent manner and frequency of application. Application of organic amendments lower soil bulk density values by more than 5% versus sole urea fertilized soil and for each 1% increase inorganic matter, soil water holding capacity increased by up to 3.7%. Organic amendments play a positive role in chemical characteristics of the soil including increase in organic carbon (up to 58% with 120 t ha-1 versus unfertilized soil) and organic nitrogen up to 90% depending on the type and the level applied. Repeated application of organic amendments to cropland led to an improvement of microbial biomass by up to 100% and increased enzymatic activity by 30%. Organic amendments also play a positive role in climate change mitigation by soil carbon sequestration although the size of which is dependent on their type, rates and frequency of application. However, organic amendments have more of long-term return rather than short-term positive effect and there is competition of organic materials for the purpose of fodder or fuel. As a result, additional measures such as physical and biological soil conservation measures should get due attention and it is better to use the combination of organic and inorganic fertilizers in order to sustain soil fertility and environmental quality.
Aytenew et al. (Wed,) studied this question.