The long-term role of organic amendments in addressing soil constraints to production

Abstract

The use of organic amendments such as composts and manures in agricultural production can be traced back to at least the 3rd millennium BC (Wilkinson 1982), where evidence of urban refuse being used in intensive cultivation was found in Iran, Oman and Syria. Foxhall (1998) also reports on historical scrolls that describe the use of cereal byproducts such as straw and chaff in composts and soil amendments for crop production in ancient Greece and Rome. The role of composts and other organic amendments in modern agriculture has perhaps taken a backseat to practices such as the application of synthetic fertilisers, herbicides and mechanical tillage. Arguably, the development of the Haber–Bosch process and synthetic nitrogen (N) fertilisers is the key driver for improved agricultural productivity worldwide. But numerous reports describe a decline in soil quality from intensive tillage practices and a focus on inorganic fertilizer amendments. These include soil acidification, loss of soil organic carbon (SOC), soil structural decline, heavy metal contamination and off-site nutrient effects including emissions of greenhouse gases from soil. There is no question that recycled organic residues are currently underutilised in modern farming systems. This could be due to any number of factors such as uncertainty around benefits and consequences, economic considerations, and lack of supply or supply chains outside of urban areas or regions with intensive animal production facilities. This special issue focuses on identifying and explaining the long-term mechanisms by which composts, manures and other organic amendments can influence crop productivity, profitability and soil fertility.