University of Nebraska-Lincoln Extension, Institute of Agriculture and Natural Resources

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April 21, 2006

Save 5-12+ inches

Use no-till and residue to conserve soil moisture

Figure 1. After a 6-inch rain, on a tilled, crusted soil, most of the rain was lost as runoff.
Figure 2. Nearby after the same 6-inch rain, much of the rain soaked into a field of continuous no-till.

Using no till can save you far more than fuel, labor, and equipment costs. The savings in soil moisture can be just as important, especially in a year when soil moisture and precipitation are short or when irrigation is costly and water supplies are limited. With continuous no-till, the improved soil structure and residue cover will enhance productivity and profitability even more.

Irrigate to reduce moisture loss from evaporation. Learn more.

Too often soils dry to the depth of tillage. An average silt loam soil holds about 2 inches of plant available soil moisture per foot of soil. Tilling the soil can result in a loss of 1/2 to 3/4 inch of soil moisture with each trip. With multiple tillage trips, there may not be adequate soil moisture in the seed zone for uniform germination and emergence, resulting in lower yields, even though there may be sufficient moisture the rest of the year.

Greater yet are the soil moisture losses from evaporation once tillage destroys residue cover. The residue mulch reduces evaporation in several ways: by reducing solar heating of the soil, by keeping drying winds off the soil surface, by insulating the soil to keep it cooler, and by intercepting some of the water as it evaporates. Research has shown that the residue mulch can reduce water losses from evaporation by 50%, saving as much as 3 to 5 inches, increasing yields in dryland production or decreasing irrigation costs in irrigated production (see Research review: Residue reduces soil moisture evaporation).

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Some say “the soil needs to be tilled to open it up to let water in.” Unfortunately, tillage breaks up soil structure, pulverizes the soil surface, and destroys residue cover, making the soil prone to crusting from raindrop impact. Tillage actually creates a condition that seals the soil, resulting in more runoff and less effective rainfall or irrigation. With residue, the raindrop impact is absorbed - erosion and crusting are reduced. The residue also slows the runoff allowing more time for infiltration. UNL research with a rainfall simulator at Sidney demonstrated that effect in a wheat-fallow rotation. More than 3.75 inches of water was applied, in 90 minutes, on continuous no-till before runoff started compared to only 1.0 inch of water applied, in 20 minutes, on plowed ground.

With the improved soil structure of continuous no-till, infiltration also improves, reducing runoff even more. Research at the UNL Rogers Memorial Farm near Lincoln showed a much greater infiltration rate for no-till, over 4 inches per hour, than for tilled conditions, only 0.4 inches per hour, after 25 years of continuous tillage system evaluation. Similar results were measured at the UNL South Central Ag Lab near Clay Center after 30 years of continuous tillage system evaluation (Table 1).

Table 1. Effects of tillage on infiltration and runoff potential. Tillage System Soil Permeability, in/hr Rainfall Rate to Create Runoff, in/hr Disk & Plant 0.4 1.5 Ridge-plant 1.5 3.2 Slot-plant 4.0 6.4

Others may say that “they have to till the soil or a wet spot to dry it out.” Driving on or tilling a wet soil is the major source of compaction. The wet soil particles are lubricated such that they slide below the weight of tillage implement, causing compaction. While the surface may dry out, the tillage itself compacts the soil below the tillage layer, slowing the infiltration rate, making the soil surface stay wetter next time. With less water infiltrating into the soil and some compaction restricting root growth, those wet spots that were tilled to dry them out are often the first areas in the field to show moisture stress during hot or dry weather. With the improved soil structure of continuous no-till, excess water near the soil surface soaks into the soil profile and is stored for use later in the season.

By adopting continuous no-till and using residue management, more water is available for crop production. If producers don't change their cropping practices to make use of that water, they will complain that no-till soils are too cold and wet. Examples of changes include: increasing seeding and fertilizer rates for higher yields; implementing more intense and diverse crop rotations; using cover crops, relay cropping, or double cropping; and, for irrigators, applying less irrigation water. It all starts with residue and continuous no-till.

Paul Jasa
Extension Engineer

Copyright 2006 by the University of Nebraska Board of Regents. All rights reserved.

Published by University of Nebraska-Lincoln Extension in the Institute of Agriculture and Natural Resources Cooperating with the counties and the U.S. Department of Agriculture.

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