Drought Resistance
Published studies show that organic farming systems are more resilient to weather extremes and can produce higher yields than conventional farming systems in such conditions (Drinkwater et al., 1998; Pimentel, 2005). For instance, the Wisconsin Integrated Cropping Systems Trials found that organic yields were higher in drought years and the same as conventional in normal weather years (Posner et al., 2008).
The Importance of Organic Matter for Water Retention
There is a strong relationship between the levels of soil organic matter and the amount of water that can be stored in the root zone of the soil. The table below should be taken as a rule of thumb, rather than as a precise set of measurements. Different soil types will hold different volumes of water when they have the same levels of organic matter due to pore spaces, specific soil density, and a range of other variables. Sandy soils as a rule hold less water than clay soils.
The table below gives an understanding of the potential amount of water that can be captured from rain and stored at the root zone in relation to the percentage of soil organic matter.
This table is designed to be a rule of thumb. The precise amount of water stored is dependent on soil type, specific soil density, and a range of other variables, and consequently, the amount could be higher or lower. This table is sufficient to allow an understanding of the concept, though. (Adapted from Morris, 2004.)