Restoring Soil Organic Matter through Biochar and Other Organic Amendments to Increase Agro-Ecosystem Resilience to Water Scarcity.

Soil organic matter (SOM) can promote soil water-holding capacity, particularly in sandy soils. SOM is recognized as one of the most important factors controlling water retention, through altering soil structure (e.g., promoting aggregation) and bulk density as well as because of its own water adsorbing capacity. Intensive cropping has deprived agricultural soils of much of their original SOM, driving large attention to SOM restoration management. Surprisingly, this has traditionally been designed to promote soil fertility and C sequestration, with little focus on soil water benefits. More recently, in the era of biochar, addition of organic amendments such as biochar, but also manure or other organic substrates, are also been considered as a strategy to increase soil moisture retention, and make agroecosystem more resilient to water scarcity. We will present results from three corn field trials, where SOM was manipulated by the addition of different types and amendment rates of woody chars, bio-engineered carbon and manure, in interaction with levels of irrigation, over one to three growing seasons. While we saw a tendency for increasing soil moisture in amended plots, this had not resulted in significant changes in corn production, over the first two growing seasons. We will discuss organic amendment effects also in a broader soil health perspective and speculate on the way forward.