By Hans Klopp
Introduction
Two key principles of soil health are minimizing soil disturbance and keeping the soil surface covered. Both can be achieved by adopting no-till practices and leaving crop residue on the soil surface.
Conventional tillage buries crop residue and exposes darker soil. Dark soil absorbs more sunlight, causing it to warm more quickly and remain warmer throughout much of the growing season, particularly before crop canopy closure. Warmer soils, combined with the increase in oxygen that occurs when soil is disturbed, accelerate the breakdown of organic matter. Over time, this can reduce soil organic matter levels and decrease the soil's ability to retain water.
Tillage also disrupts soil structure and destroys pores formed by soil organisms as well as by natural wetting-drying and freezing-thawing cycles. These larger pores are important pathways for water infiltration. Following a dry summer, such as many areas of South Dakota experienced this year, large soil cracks often develop. Snowmelt and rainfall can rapidly infiltrate through these cracks and be stored in the soil for future plant use. Disturbing these natural pore networks can reduce infiltration rates and limit the amount of water entering the soil profile. In addition, warmer soils lose more moisture through evaporation.
Leaving crop residue on the soil surface provides several benefits. Residue returns organic matter and nutrients to the soil while protecting the surface from direct sunlight. Because residue is generally lighter in color than bare soil, it reflects more sunlight and reduces heat absorption. This helps conserve soil moisture by reducing evaporation.
Surface residue also contributes to higher soil organic matter levels over time, increasing the soil's water-holding capacity. In addition, residue protects the soil from raindrop impact, which can break down soil structure and lead to surface crusting. Figure 1 shows a conventionally tilled soil surface that has experienced raindrop impact. The crusted surface contains few large pores connected to the soil surface, limiting water infiltration. Soil cover can also support greater populations of beneficial soil organisms such as earthworms, bacteria and fungi. These organisms create channels and pores that improve water infiltration, drainage, and water storage. Figure 2 shows a no-till soil with adequate residue cover.
Source : sdstate.edu