|Increasing soil organic matter makes more water available to crops by improving infiltration. |
Photo by Edwin Remsberg
How you manage your soil can significantly impact water availability. Some soil management practices increase the amount of water available to crops, while others will degrade soil and decrease available soil water.
Good soil structure improves water infiltration and decreases runoff and erosion. Well-structured soils are porous and allow water to enter easily, rather than running off to be lost to streams and rivers. While you are somewhat limited by your soil texture, you can improve soil structure and water-holding capacity, storing water for future use by plant roots. (See Figure 1) On the contrary, when a soil has poor tilth, soil aggregates break down, increasing compaction and decreasing aeration and water infiltration.
Most soil-improving strategies work slowly over several years, although some produce results sooner. In contrast, management practices that degrade soil are often apparent immediately. For example, working your soil when it is too wet will compact the soil and degrade its structure.
Soil organic matter plays a vital role in soil quality and soil water availability. Organic material applied to soil and maintained on the surface protects the soil from the impact of raindrops, a major erosive force. Surface residue and mulches also reduce evaporation and smother weeds, leaving more water for plant use.
Studies show that as organic matter increases, soils develop more macropores. That happens because, as plant residue and other organic amendments decompose, sticky substances bind soil particles and create pore spaces between them. Moreover, organic matter itself can hold water.
“You can change a soil’s pore size distribution, and with that, you can change the available water-holding capacity,” said van Es, a Cornell crop and soil science professor who co-wrote the book, Building Soils for Better Crops. (Resources) “There’s more water available to plants when you have a well-structured soil than if it’s compacted.”
Strategies to increase organic matter content include:
Spreading manure or letting livestock deposit their own manure in well-managed pastures.
Applying composts (from a variety of materials ranging from poultry litter to leaves).
Seeding cover crops, which provide nutrient-rich residue after they die.
Reducing tillage, because plowing breaks down soil aggregation and accelerates organic matter loss.
Van Es is collaborating with other researchers at Cornell in a SARE-funded study examining ways to improve soil health. As part of the project, county extension educators collect data and demonstrate strategies such as reducing tillage, adding cover crops and diversifying from continuous corn to rotations with grass.
Results are promising. On average, and across a range of soil types from clay loam to loamy sand, the researchers found a 10- to 20-percent increase in the soil’s available water content by reducing tillage or adding another crop to the rotation. On a Cornell experiment station site, researchers saw soil improvements after just two seasons of adding a hairy vetch cover crop between cash crops.
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