Organic soil amendments have been used in Oman since prehistoric agriculture began and are still being used today. Recently, interest in certified organic farming, and the use of organic soil amendments to enhance soil quality has motivated more research on traditional and new diverse soil amendment products. In addition, the arid climate of Oman combined with sandy soils benefit from non-traditional soil amendments and nutrient sources, such as treated human waste and wastewater. These two are not allowed in certified organic farming but offer sustainable solutions to building soil health for non-certified crops. This review will cover studies of soil quality in Oman related to the comparison of these various amendments, including manures, composts, organic mulch materials, biochar, ash, and others. In general, most of these amendments improve the soil by adding organic carbon, increasing the water holding capacity, improving infiltration rate, and stimulating or providing habitat and food sources for diverse soil microbiological communities. Some amendments can also help crops overcome some of the stresses of agriculture in Oman, such as soil salinity, heat and drought. Most also provide macro and micronutrients for crop growth. Some anti-quality factors may be present however, such as a high carbon to nitrogen ratio in some mulches, or high heavy metal content, human pathogens, and pharmaceutical residues in treated waste or wastewater. Biochar may have a positive or negative effect on soil microbes, depending on the source material and temperature of combustion can result in byproducts that inhibit microbes. The value of soil microorganisms has been shown in organic cropping systems, and several new species have been discovered in Oman. Some of these provide possibilities for biocontrol of pathogens, and increased salt tolerance in crops like tomato. Though much valuable research has been done in Oman and the rest of the world, there is much left to be done to determine the effects of these organic amendments over the long term, and also the interactions among various amendments, soil conditions, soil microbes, and on crops grown with different irrigation methods and cropping systems.

Organic soil amendments have been used in Oman since prehistoric agriculture began and are still being used today. Recently, interest in certified organic farming, and the use of organic soil amendments to enhance soil quality has motivated more research on traditional and new diverse soil amendment...