How you manage your soil today could have impacts on the productivity of your soil in the near and distant future. Water infiltration and plant available water are two key soil hydraulic properties to manage in the Great Plains, and both water infiltration and plant available water are affected by residue management, cover crops and tillage.

Plant available water is the volume of water that is held in the soil but can be removed from the soil by plants. Water infiltration is the rate or amount of water that enters the soil. Any water that does not infiltrate into the soil is lost as runoff or evaporation.

Plant available water is a kind of water tank where plants can remove water. The larger the volume of plant available water stored by your soil, the more water available through the growing season.

Water infiltration and plant available water can be increased by improving or maintaining soil structure and soil organic carbon. Soil organic carbon functions as a binding agent for soil particles to hold together as aggregates. Research suggests soil structure can be improved by managing surface plant residues or planting cover crops.

Residue and cover crops' role
Research from Ohio State University and the University of Nebraska-Lincoln shows plant available water can decrease in as little as one year when all residue is removed, and within four years when about 60% is removed.

Additionally, research on an irrigated continuous corn rotation in south-central Nebraska showed that after removing about 60% of the corn residue for six years, plant available water decreased from 1.61 to 1.21 inches per 4 inches of soil.

However, residue removal also reduced water infiltration. After six years of removing 60% of corn residue, the water infiltration rate decreased from 2.13 inches per hour to 1.43 inches per hour.

In short, residue removal caused less water to enter the soil and less water to be available for plant use in between rain and irrigation events.

Long term, 12-year experiments in Kansas and Maryland have found that cover crops increase water infiltration. Meanwhile, cover crops were found to increase plant available water after 12 years in an experiment in Iowa using cereal rye and in Kansas using legume cover crops.

Six years of research in south-central Nebraska showed cover crops had no effect on plant available water or on water infiltration, although an effect is expected over the long term. However, cover crops did partially offset soil carbon losses caused by aggressive corn residue removal.

Why soil organic carbon matter?
Plant available water is positively correlated with soil organic carbon. The positive relationship between plant available water and soil organic carbon is due to the greater water absorption capacity of organic particles compared with inorganic particles.

Also, as soil organic carbon increases, soil aggregates become more stable and can support more pore spaces that can store more plant available water. As soil carbon is lost from the soil, the aggregates become weaker and the larger pore spaces collapse into smaller pores, decreasing water storage capacity of the soil for plant use. So, if soil organic carbon is lost from the soil, plant available water is lost from the soil. Unfortunately, it's easier to lose carbon than build carbon in soils.

TABLE 1. The effects either cover crop or corn residue removal had on select soil properties after three or six years. The table is based on data from an ongoing experiment in south-central Nebraska.

It is easy to rapidly lose plant available water and soil organic carbon when removing plant residues. However, it takes time (more than 10 years) to increase soil organic carbon in the soil and improve the soil structure to increase plant available water. The same is true for water infiltration. Table 1 shows soil aggregate stability and organic carbon can decrease in just three years due to high rates of corn residue removal, but their restoration with cover crops may take much longer. This means management decisions made now will affect the future productivity of your field and the sustainability of your farming operation.

This report comes from UNL CropWatch.