A review of the use of organic supplements to cropland indicated that application of long-lasting organic amendments increased organic carbon by up to 90% versus unfertilized soil, and up to 100% versus chemical fertilizer treatments. Furthermore, regular addition of organic residues, particularly composted ones, increased soil physical fertility, mainly by improving aggregate stability and decreasing soil bulk density. The best agronomic performance was obtained with the highest rates and frequency of applications. Crop yields increased by up to 250% after long-term applications of high rates of municipal solid waste compost (1).
Compost is the end of product of a controlled aerobic decomposition of organic wastes (such as yard waste, food waste, animal manures, and other materials that come from recently living organisms). Compost has readily available and other slow-releasing plant nutrients, as well as a high organic matter content, which helps to feed the microbes in charge of creating a well-rounded environment for life to flourish.
The reason that compost is so effective in increasing crop yields is that compost is more slowly decomposed compared to fresh plant residues, with composts typically having mean residence times several times greater than un-composted organic matter (2).
A single application of composted green waste to California rangeland significantly increased forage production from 40 to 70% over three years (3).
Compost has also been shown to increase yields for field crops. In a six year field experiment studying the effect of farm compost amendment on a crop rotation of potato, fodder beet, forage maize, and Brussels sprouts demonstrated that farm compost increased soil quality and crop yields establishing a causal relationship between soil quality and crop production (4).
Finally, it has been estimated that an increase in the SOC pool within the root zone by 1 t C/ha/year could enhance food production in developing countries by 30 to 50 Mt/year including 24 to 40 Mt/year of cereal and legumes, and 6 to 10 Mt/ year of roots and tubers (4).

1) Diacono M, and Montemurro, F, Long-term effects of organic amendments on soil fertility. A review, Agron. Sustain. Dev. 30, 401–422 (2010).
2) Paustian, et al. Climate Smart Soils, Nature, 532, 49-57 (2016).
3) Ryals, R., and W. L. Silver. 2013. Effects of organic matter amendments on net primary productivity and greenhouse gas emissions in annual grassland ecosystems. Ecological Applications 23:46-59.
4) D’Hose, et al. The positive relationship between soil quality and crop production, Applied Soil Ecology 75, 189– 198 (2014).