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PNW CONSERVATION TILLAGE HANDBOOK SERIES
Chapter 9 — Irrigated Systems, No. 4, Spring 1988


Economical Erosion Control Under Furrow Irrigation

Roger Veseth

Conservation tillage is an effective and economical option for controlling soil loss from water erosion under furrow irrigation. That is the conclusion of a USDAAgricultural Research Service (ARS) scientist following 3 years of an ongoing field research effort in the Twin Falls area of southern Idaho.

This project, part of the STEEP conservation farming research program in the Northwest, is coordinated by Dave Carter, an ARS soil scientist at the Snake River Conservation Research Center near Kimberly. Soil erosion has had a major impact on productivity of furrow-irrigated cropland in that region. Through research on topsoil depthproductivity relationships and extensive field surveys, Carter has determined that soil erosion has reduced crop yield potential by approximately 25 percent over the past 80 years.

Carter stresses that once the lime/silica cemented or lime enriched subsoils are exposed by erosion, the productivity loss is essentially irreversible with current technology. On the severely eroded areas, the only way to improve productivity near that on non-eroded areas is to haul in topsoil.

Sediment Retention Practices

Historically, many of the conservation practices used under furrow irrigation have been directed at preventing sediment from leaving the field and entering the drainage ditch. This was the focus of part of Carter's research on furrow irrigation erosion from 1970 to 1984. He was involved in developing "Best Management Practices".

(BMP's) such as sediment basins, furrow mini-basins, buried pipe systems and vegetative filter strips, which provide a varying range of effectiveness in preventing sediment loss into drainage ditches, Carter points out, however, that these practices do little to control in-field erosion and maintain soil productivity.

Although, the quality of drainage water leaving the field is improved, topsoil is still being eroded from the upper portions of the fields and deposited on the downslope areas. This is why his research emphasis has now shifted to the development of conservation tillage systems for fhrrowirrigated land; to prevent the initial movement of soil in the firrow, instead of trapping the sediment later.

Obstacles to Conservation Tillage

Since the fall of 1984, Carter has conducted an extensive research effort on the use of conservation tillage practices under firrow irrigation. This was contrary to the traditional attitude that fields with a significant amount of residue on the soil surface could not be successfully furrow-irrigated. In addition, clean-tilled, residue-free fields have long been the socially-accepted practice and the "sign of a good farmer. "

Carter has found these traditional attitudes to be some of the major obstacles to the acceptance and adoption of conservation tillage systems, Other obstacles are present as well. Some crop contracting organizations will not contract with growers if conservation tillage methods are used. Consequently, growers who depend upon such contracts are reluctant to adopt conservation tillage practices. Carter believes that persistence in education and demonstration programs will overcome these deterrents, but acceptance by organizations and growers will take time. New products and technologies are also needed to enhance the effectiveness and adoption of some conservation farming practices. For example, in some row crops such as dry beans and sugarbeets, the lack of herbicides, which do not require soil incorporation to be fully effective for weed control, has restricted intmst in conservation tillage for those crops.

Conservation Tillage Research

Rotational Change Needed

An important part of developing a successful conservation tillage system can often be a change in crop rotation. A common crop rotation under furrow irrigation in the central part of southern Idaho includes alfalfa production for 3 or more years, followed by dry beans and other row crops for two to three seasons, and then cereals or other crops for one or more seasons before replanting to alfalfa.

Carter points out that conventionally-planted dry beans after alfalfa typically results in one of the highest furrow erosion potentials. A total of 8 to 12 tillage operations are ofien used to remove the alfalfa stand and prepare the field for seeding beans. After all these tillage operations, the soil is highly susceptible to erosion, and soil losses are generally high on slopes greater than 1 percent.

Carter suggests that beans be delayed in the crop rotation until the second crop year after the alfalfa has been taken out. His research demonstrates that corn and cereals can be planted after alfalfa with no-till and reduced tillage systems. Beans can then be grown following corn or cereals under reduced tillage, providing a substantial reduction in soil erosion and production costs in the rotation. He also points out that, unlike beans, corn and cereals require significant quantities of nitrogen and would make more efficient use of the nitrogen fixed by the alfalfa crop and released as the alfalfa roots decompose. Crop uptake of part of this nitrogen, which would not be effectively utilized by another legume crop such as beans, would also reduce the amount of nitrogen leached into the groundwater.

Research by Carter indicates that fall application of a herbicide to kill the alfalfa generally allows a greater amount of nitrogen release and results in higher yields of cereals and corn than with a spring application. This is cereals and corn than with a spring application. This is particularly important with cereals, which need a greater portion of their nitrogen uptake earlier in development than does corn. Spring application of herbicides can tilso be effective to kill alfalfa, but additional nitrogen fertilizer is needed because of the delayed release of nitrogen from the decomposing alfalfa roots.

From 1984 through 1987, Carter has conducted no-till or minimum tillage experiments under more than 13 different crop rotation sequences in tillage comparisons on growers fields and ARS-operated land. These have included: corn and five different cereal crops after alfalfa; dry beans and two cereal crops afier corn, and dry beans and corn after three cereal crops. Crop yields with these conservation tillage systems were generally not significantly different from yields under conventional tillage.

Conservation Tillage Equipment

Conventional double-disk drills were used for no-till seeding of cereals in the experiments, although commercial no-till drills were included on a few plots. A variety of reduced tillage combinations were evaluated in the experiments. They range from a light disking before seeding with conventional drills to the substitution of a disking operation for moldboard plowing. A few experiments included a chisel plow, but most did not. In general, no major changes in equipment were required for the conservation tillage systems.

For no-till seeding of row crops, bull tongue chisels were mounted on a separate tool bar directly ahead of the conventional planting units. These chisels assured penetration of the planters for proper seed placement.

Irrigation Efficiency

In the no-till and minimum tillage plantings, conventional corrugating equipment was used to clean or form the furrows. Carter concluded that the common fear that crop residue on the soil surface would prevent successful irrigation is unfounded, provided early season furrow cleaning is done. Furthermore, he showed that it is advantageous to irrigate in the old furrows without significant tillage.

Irrigation efficiency comparisons were an important aspect of some of the field experiments, particularly those following alfalfa. Few problems were encountered irrigating the no-till and minimum tillage plots, and infiltration was reasonably uniform along the entire length of the furrows. This was not the case with conventional tillage. Sometimes, two separate irrigations were required for water to reach the end of the furrows. Carter estimated that the conventionally-tilled plots required 20 to 40 percent more water than did the no-till plots, Most of this extra water was lost to deep percolation below the root zone in the upper one/third of the plots.

Erosion Control

Carter found that the use of some type of conservation tillage system reduced erosion and sediment loss 50 to 100 percent compared to conventional tillage practices. Notill planting after alfalfa almost eliminated erosion and sediment loss, averaging a 95 percent reduction compared to conventional tillage. The wide variety of minimum tillage systems evaluated resulted in an average erosion reduction of 80 percent. He points out that the application of conservation tillage practices could eliminate the need for sediment retention BMP's. However, until conservation tillage is widely adopted, the need for these previouslyimplemented BMP's will continue.

Economics

Perhaps the most important finding of Carter's conservation tillage research, from the perspective of extensive adoption in the future, is that conservation tillage under furrow irrigation can have a positive economic impact. Based on comparisons of actual costs or standard custom rates, no-till costs averaged 26 percent below the costs of conventional tillage. Operating costs for the variety of reduced tillage systems averaged about 18 percent below those for conventional tillage systems, These reduced operating costs translate into additional profits because crop yields with conservation tillage were generally the same as with conventional tillage.

Conclusions

Carter concludes that conservation tillage systems can control soil erosion and reduce production costs while maintaining yields comparable to conventional tillage. Fields under conservation tillage can be furrow-irrigated with less labor, less water and at a higher efilciency rate than conventionally-tilled fields. No special equipment or major equipment modifications were needed for the conservation tillage systems used in these experiments. Carter is convinced that conservation tillage can be a viable, economical farming system for fiwrow-irrigated land. Conservation tillage research and demonstrations will continue to be a high priority in his program.

     
 

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