Straw-Filled Trenches Help Reduce Erosion

Straw-Filled Trenches Help Reduce Erosion CROPS Straw 4-6-33 Stuffing trenches full of straw may reduce erosion and save runoff water for crop production, according to studies in the Palouse area of Eastern Washington and Oregon and Northern Idaho. USDA researchers in the area are resurrecting "vertical mulching" - even using one of the machines built for the same idea some 20-25 years ago. According to Keith Saxton, USDA ag engineer at Washington State University, Pullman, they are seeking ways to reduce heavy water runoff from winter rains when the land may be frozen from 4 to 6 in. deep. By opening trenches about 8-10 in. deep and filling them with straw, water is able to penetrate into the soil and be absorbed below the frost line because straw in the trenches seldom if ever freezes solid. Significant reduction in erosion and increased infiltration have been obtained in winters when soil was frozen for extended periods of time. However, in winters with less freezing, there was less apparent benefit. In addition, in years of short precipitation, the extra moisture caught and held in the soil should appreciably increase crop yields. The machines built about 20 years ago included a flail chopper to shred corn stalks, straw or other residue and blow it into a trench opened by a chisel or subsoiler-type opener on the rear. Interest in these machines and their performance was short-lived at that time. Saxton blames the lack of results on subsequent tillage operations: "After trenches were filled with crop residue, conventional tillage immediately worked the entire soil surface and effectively closed off the trenches preventing surface water from entering the soil. Now, with more reduced, minimum or notillage, it is possible to keep the slots open longer to catch and hold more moisture," Saxton explains. In many areas, he notes, excessive straw interferes with later tillage and planting. Thus, stuffing some of the excess residue into trenches could help alleviate that problem, too. Researchers are still investigating trench spacing, but in most cases, 12 to 24 ft. between trenches appears reasonable. It may prove feasible to simply remove the combine straw spreader and follow it with a vertical mulcher. Trenches should follow the contour as near as practical, suggests Saxton, and the trench should be completely filled with straw or other residue to avoid water flow along the trench. Saxton also believes the straw should extend above the surface to help catch moisture and keep the slot open longer. Recent tests indicate that longer straw may be more effective in keeping trenches open and improve water flow into the soil. Fine chopping by the original vertical mulching machines may have caused residue to quickly pack together and reduce vertical moisture movement through the trench, says Saxton. He notes, however, that corn stalks and similar material would probably have to be chopped or broken up some as they are placed in the slot. The success of vertical mulching in various soils, says Saxton, will depend on whether there is a water restricting layer in the soil and at what depth, and whether soil below that level can absorb additional surface water. Although one of the old vertical mulching machines has been used in some Oregon tests, and other machines designed or modified for use in field studies, vertical mulching machines are not now commercially available. (The one shown is strictly a research model.) But studies are continuing, and the USDA researchers involved hope to soon draw up performance requirements and make them available to equipment designers who could then build machines to meet those needs. For more information, contact: FARM SHOW Followup, Keith Saxton, Hydraulic Engineer, USDASEA-AR, Washington State U., Pullman, Wash., 99164 (ph 509 3352724).

To read the rest of this story, download this issue below or click here to register with your account number.