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CONSERVATION TILLAGE HANDBOOK SERIES
Computer Modeling Evaluation of Best Management Practices
Dryland farming areas in the semiarid region of the Snake River Basin of southeastern Idaho have suffered substantial losses of topsoil since farming began in the area. In the predominant wheat-fallow rotation under conventional tillage, the soil is left unprotected from erosion much of the time with little or no surface residue. Surface runoff from snowmelt and intense rainstorms results in an average soil loss of 8 tons per acre on over 40 percent of the region.
Best Management Practices (BMPs) such as crop residue management (minimum tillage), contour strip cropping, terracing and grassed waterways are among the soil conservation practices which have been used in this region. A computer modeling study was used to evaluate the effectiveness of these four BMPs and their impact on farm net returns in four southeastern Idaho counties: Bannock, Power, Oneida and Cassia. The study was conducted by Marie Powell, former research associate, and Edgar Michalson, STEEP researcher and agricultural economist, both in the University of Idaho Department of Agricultural Economics and Rural Sociology, Moscow. The results were published this year in University of Idaho Agricultural Experiment Station Bulletin 639, An Evaluation of Best Management Practices on Dryland Farms in the Lower Portion of the Upper Snake River Basin of Southeastern Idaho.
Fundamental data for the study were from an interview survey of 95 farmers in the Snake River Basin in 1979. Technical data on the BMPs were provided by the USDA-SCS and ARS. Computer modeling analysis included linear programming, enterprise budgeting and field tillage simulation.
The models evaluated the BMPs in a fallow-winter wheat-spring barley rotation for three farm sizes: 500, 1,300 and 2,700 acres, Soil losses on the three farm sizes without any soil erosion control practices averaged 6.4 tons per acre. To reduce soil loss to 3.5 to 4 tons per acre, the most economical BMP to achieve that level of erosion control was crop residue management, followed by a combination of residue management and strip cropping. For the lowest soil loss restriction of about 2.3 tons per acre, all of the four BMPs were used.
Crop residue management had the lowest average per acre cost followed in increasing order by strip cropping, terracing and grass waterways, With no assumption of increased yields from the BMPs, cutting soil loss to 3.5 to 4 tons per acre on the three farm sizes reduced short-term farm net returns an average of 6 percent. With all BMPs utilized to achieve the 2.3 tons per acre soil loss limit, the average decrease in net return to the three farms was 36 percent when no yield increases were assumed.
To help offset the costs of the BMPs, increased soil water storage with crop residue management, strip cropping and terraces would increase yield potential. Use of the practices would then increase net returns compared to not using any BMPs. In the long run, farm income would also be improved as related to the amount of soil saved. The value of long-term protection and improvement of soil productivity must be considered in these management decisions. A similar study is underway on the higher rainfall (eastern) portion of the Upper Snake River Basin.
us: Hans Kok, (208)885-5971
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