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Long-term management effects on soil productivity and crop yield in semi-arid regions of Eastern Oregon

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  • Long-term experiments were started at Pendleton and Moro, Oregon in the 1930's to evaluate the effects of tillage, fertilizer, and residue management on crop productivity in non-irrigated semi-arid regions. Coupled with multi-year varietal improvement, rotation, and green manure studies, they define those practices which sustain soil productivity and improve crop quality without degrading the environment. Because summer moisture is too low to support warm-season crops, this region of the Pacific Northwest is uniquely adapted to winter annuals and cool-season grasses. Winter cereal grains presently yield from 25 to 45% more than spring cereals. Winter wheat yield has risen steadily from 45 bushels/acre in the 1930's to 83 bushels/acre in 1980's. The increase results from both varietal improvement and the application of adequate nitrogen (N) to meet crop need. The yield advantage of fallowing over annual cropping is significantly less today than it was 50 years ago because drought stress has less impact on semidwarf winter wheats than on older, taller varieties. Soil organic matter continues to decline with time in a wheat/fallow rotation, even though soil erosion is minimal. Soil N availability has correspondingly declined, accentuating the need for greater amounts of N to achieve optimum yield. Residue management practices have a significant impact on organic matter level in soil. Generous manure application is capable of preventing organic matter decline. Burning of wheat stubble accentuates organic matter loss while N fertilization or pea vine addition reduces the decline. Soil organic matter deterioration appears to be substantially less in annual cropping than in a cereal/fallow rotation. Biological activity is about 50% lower with fallow than with annual cropping. Stubble mulching, which leaves residue on the soil surface to deter erosion, favors organic matter retention. Soil under 50 years of stubble-mulch now has about one-third more organic matter in the top 3 inches than soil that was plowed. Legume green manures are an effective source of N, supplying from 40 to 80 lbs N/acre to the following crop. But green manures remove soil moisture, and cereals following green manure have lower yield and net return than cereals following fallow where annual precipitation is less than 17 inches. The requirement for increasing amounts of N fertilizer to attain optimum yield in the 1980's is accompanied by increasing difficulty in determining the correct amount to apply. Variation in growing-season precipitation has a strong impact on yield and utilization of applied N. This leads to the potential for over application of N and possible N loss to surface or ground water. Nitrogen fertilizers, but not tillage, have affected the physical condition of soil, probably because greater root densities are associated with higher N application rates. The development of alternate crops to cereals has not been very productive because of low yield performance. The oilseed crops, winter rape and safflower have marginally lower return than cereals. Legumes, grasses, grass seed, coarse feed grains, and vegetables all produce substantially lower returns than cereals, primarily because they are warm-season crops with a high summertime water requirement.
  • Published June 1994. Facts and recommendations in this publication may no longer be valid. Please look for up-to-date information in the OSU Extension Catalog: http://extension.oregonstate.edu/catalog
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