Browse on keywords: organic matter dryland agriculture
Search results on 05/21/13
6929. Unger, P.W., C.W. Lindwall, D.W. Anderson, and C.A. Campbell. 1989. Mechanized farming systems for sustaining crop production and maintaining soil quality in semiarid regions.. unpublished manuscript, USDA-ARS, Conservation and Production Research Lab, Bushland, TX 79012.
This review paper presents research results primarily from the Northern Plains, Southern Plains, Pacific Northwest, and Australia, addressing issues of soil quality and organic matter, erosion, water storage and utilization, and how these are affected by tillage choices, crop rotations, and other management aspects. Cultivation of semiarid soils generally leads to soil organic matter (SOM) losses of 40-60%, with most loss in the first 20 years. The active fraction of SOM will change faster than the total SOM. The fraction of N that is readily mineralizable decreased more quickly than total N, indicating a reduction in the nutrient-supplying power of the soil over time. Cultivation decreases the proportion of soil aggregates >1 mm. Dry-stable aggregates >0.84 mm are needed to prevent wind erosion. In the Northern Plains, about 60% of the precipitation falls in the May to August growing season. The crop-fallow system here is relatively inefficient at water storage, storing only 20-25% of the precipitation during the fallow period. Crop stubble is crucial to snow trapping and moisture retention. Alternating strips about 5 m. wide of tall and short stubble increased snow depth and density and resulted in 30% more water storage compared to a uniform medium-height stubble. No-till improved yields in many cases by increasing stored moisture, but suitable herbicides are necessary for weed control. Flex cropping in Montana was the most efficient system for using moisture. In the Central Plains, increased evapotranspiration makes ample surface residue very effective. Yields for wheat in a fallow system were more than double those for continuous wheat, making the fallow system more economic. In the Pacific Northwest, major losses result from runoff and from evaporation, due to capillary action in undisturbed surface soils. Water storage efficiencies were 50-75% during the first winter, and 10-50% during the second winter at Pendleton, OR. Surface residues resulted in greater evaporative losses during the summer. To control erosion, innovations such as the slot mulch system, the paraplow, and basin pitters (dammer-diker) have been used. The paper has an excellent list of references on dryland cropping.
8714. Power, J.F. and R.J.K. Myers. 1989. Soil quality in semiarid agriculture: North America and Australia.. unpublished manuscript, International Conference on Soil Quality in Semiarid Agriculture.
Exploitation of semiarid soils in North America and Australia over the past 100 years has reduced soil quality primarily as a result of loss of organic matter. Cultivation has accelerated organic matter loss through soil erosion and greater oxidization, as well as leading to problems of soil fertility, compaction, water conservation, and salinization. Recent improvements in reduced and no-tillage systems and improved cropping practices have the capacity to arrest or reverse organic matter declines. No-till usually conserves soil water, permitting more frequent cropping and often greater crop growth. Ley farming in Australia also enhances soil organic matter, but may reduce soil pH. Generally, practices that increase quantity of organic matter returned to the soil improve soil quality. Government policies also have a major effect on soil quality -- both positive and negative. Incentives are needed to encourage resource conservation and to counteract temptations for short-term profit at the expense of long-term soil quality maintenance.