Protect the Soil Surface to Increase Water Infiltration
If you want your soil to take water faster, protect the surface with crop residues. This was shown in a classic study from 1940.
F.L. Duley took a sandy loam, covered it with straw, and then applied a simulated rainfall to it for five hours at a rate higher than what it could take, resulting in runoff. He measured the rate of water entering the soil (infiltration) which settled to a nearly constant 1.2 inches per hour (click on graph below). After 40 minutes of this, he removed the straw. The infiltration rate of the now bare soil dropped rapidly, then leveled off at just 0.25″ per hour.
Using photomicrographs, Duley investigated the changes in the soil surface. In the bare surfaces affected by the simulated rainfall, he found that there were no large pores (macropores) extending from the surface down into the soil; they had all been sealed as the beating effect of water droplets broke down aggregates. The fines (silt and clay) from the broken aggregates then moved with water and settled around larger sand particles, effectively sealing the surface reducing water intake.
Duley continued his experiment. He removed the top 0.3″ of the soil using “a table fork” and carefully covered the soil with burlap. Then he started the sprinkling again. With a new soil surface, now protected, water intake recovered to 1.6″ per hour. Finally, while continuing the sprinkling, the burlap was removed and again the water intake of the bare soil was reduced drastically to just 0.2″ per hour.
“If the soil is protected by straw or other materials,” Duley concludes, “a high rate of intake may be maintained for a considerable time.”