Four Good Reasons to Leave that Stubble

By Jim Bauder and Linzy Carlson
MSU Land Resources and Environmental Sciences

Many Montana farmers choose to till their stubble fields in the fall. Some want to have residue-free fields in preparation for the next planting season, and others just want to get a jump on coming spring work. Although fall tillage is traditionally accepted, recent research, summarized below, shows many benefits of conserving crop residue.

Good Reason #1: Conserve existing soil moisture: Coming out of a dry year, moisture reserves are low in many Montana soils. In many cases, fall tillage makes the deficit even greater by drying out the soil to the depth of tillage. A silt loam soil holds about 2 inches of moisture per foot of soil. Tilling to 6-12 inches could lose 1-2 inches of moisture.

Some argue that fall tillage opens the soil surface, resulting in better infiltration, but any extra water caught because of tillage only goes to replace what was lost. Loss of moisture in the fall can also increase irrigation costs the next year.

Good Reason No. 2: Catch more water and prevent erosion over the winter: Tillage pulverizes the soil, damaging the natural pore structure that allows water to infiltrate. Tillage disrupts pore continuity and makes a lot of small pores from large pores. Because tillage damages soil's infiltration capabilities, it also increases the risk of runoff and erosion. The loose soil surface left by tillage is vulnerable to crusting when raindrops hit it, creating a seal that decreases future infiltration rates by up to 75 percent. Residue on the soil surface reduces crusting by lessening the physical impact of raindrops and reduces erosion by creating small dams that slow runoff water. Standing, attached residue also protects the soil from wind erosion, catches snow, and acts as a protective mulch over winter and spring.

Good Reason No. 3: Make better use of next year's irrigation water: In general, less intensive tillage (including no-till and ridge till systems) leads to increased infiltration rates. However, better infiltration does not automatically correlate to better overall efficiency.

Without management changes, owners of a furrow irrigation system likely would see a great deal of water lost to deep percolation at the head of the field, with considerably less water reaching the end of the field.

Solutions to this problem include applying PAM (polyacrylamide), which allows increased flow rates without increased erosion, or using a surge valve, which alternates between two sets pushing a relatively large volume of water onto each set for a short time. Both of these options will conserve water by reducing deep percolation and runoff. Under pivot irrigation, increased residue helps prevent crusting and reduces runoff and erosion.

Crop residue decreases the amount of water lost to evaporation from the surface of the soil. A study on a Nebraska dryland site determined that fields with wheat stubble left standing at harvest had 2 inches more stored soil moisture the next May when row crops were planted, than fields that had been tilled soon after harvest. Assuming water is a limiting factor for yield, those two inches represented about 20 additional bushels of corn per acre. Crop residue has even greater opportunity to prevent evaporation on irrigated ground, since it is wet more often than dryland sites.

Good Reason No. 4: Time, Labor, and fuel savings: A typical tillage system, including chiseling, disking, knifing in fertilizer, planting and cultivation, requires about 4 gallons of diesel fuel per acre.

In comparison, a no-till system only requires about 1.5 gallons per acre to knife in fertilizer, plant and spray. The time saved by not tilling potentially corresponds to decreased labor costs and increased productivity.

For these reasons, producers should take a look at leaving that stubble stand after harvest.