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Wednesday, October 17, 2018

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3240. Widtsoe, J.A.. 1908. The storage of winter precipitation in soils.. Utah Agr. Expt. Sta. Bulletin 104, Utah State Univ., Logan, UT.
The storage of winter precipitation was compared between an irrigated farm and six non-irrigated farms in Utah, to determine what proportion of winter precipitation is actually stored in the soil. In the top eight feet, average maximum amounts of winter precipitation stored for five years on an irrigated farm was 82% and for three years on non-irrigated farms the winter precipitation stored was 62%. It was concluded that enough water for dryland farming will be stored in the soils when fallowing is practiced every other summer.

7816. Ford, G.L. and J.L. Krall. 1979. The history of summer fallow in Montana.. Montana Agr. Expt. Sta. Bull. 704.
This excellent publication describes the historical development of summer fallow use in dry farming in Montana and some of its consequences. Data from 1974 indicate that aboaut one-third of the cropland in the state was in summer fallow (5 million acres). In Montana, the fallow period is 14 and 21 months for winter and spring grain respectively. Results from the early 1900's indicated more profitable returns from alternate crop-fallow compared to continuous cropping. This was due to both more moisture and available nitrogen built up under fallow. Summer fallow was not widely adopted until the 1920's, when a series of very unfavorable weather years occurred and showed the risk reduction value of fallow. Serious wind erosion became a problem at that time and led to the introduction and widespread adoption of narrow alternate crop-fallow strips perpendicular to the wind direction. Fallow led to a greater decrease in soil organic matter and total nitrogen (40 and 35 % decrease) than with continuous cropping (35 and 27 % decrease). Further research found that continuous cropping made more efficient use of moisture than fallow. As nitrogen fertilizer and herbicides became available, fallow was no longer as important for these aspects. Summer fallow has also caused the development of saline seep conditions on hundreds of thousands of acres. This condition occurs where summer fallow stores more moisture than a crop uses, and the water then moves deeper in the soil profile until it hits a confining layer, causing it to move laterally with dissolved salts, and to break out as a seep further downslope. In one watershed, the percentage of total land area affected by saline seep increase from 0.1% to 19% over 30 years. Continuous cropping and use of deep-rooted plants such as alfalfa can help solve this problem. The authors propose a new approach to cropping intensity, one called "flex-cropping" in which the decision to plant a crop is based on the presence of at least 3 inches of stored soil water at seeding time. This system would reduce some of the negative effects of summer fallow while also reducing exposure to drought risk. Federal acreage restrictions under the commodity programs pose a major barrier to this approach.

7893. Sims, J.R.. 1978. Predicting nitrate accumulation in fallowed soils.. Agronomy Abstracts p. 162, Amer. Soc. Agron., Madison, WI.

9225. McCall, M.A.. 1922. The soil mulch in its relation to the absorption and retention of soil moisture.. M.S. thesis, Washington State College, Pullman, WA.

9827. Merrill, L.M.. 1910. A report of seven years' investigation of dry farming methods.. Utah Agr. Expt. Sta. Bulletin 112, Utah State Univ., Logan, UT.
Bulletin 112 presents the results of a seven-year dryland farming study that was conducted on six farms, in six counties of Utah. The average annual rainfall over all locations during the study was 14.80 inches. The study looked at time and depth of plowing, time and depth of seeding, fallow vs. continual cropping, and crop varieties. Fall plowing, to a depth of 10 to 18 inches, produced greatest yields. Planting seed in the fall, at a shallow depth of 1 and 1/2 inches, also produced greatest yields. Annual summer fallow was found necessary for assurance of highest yields. It was also concluded that the wheat straw should be plowed under to enhance the water retaining capacity of the soil. For the initiation and set-up of this experiment, see Bulletin 91 by John A. Widtsoe and Lewis A. Merrill.

9837. Widtsoe, J.A. and L.A. Merrill. 1905. Arid farming in Utah.. Utah Agr. Expt. Sta. Bulletin 91, Utah State Univ., Logan, UT.
This bulletin covers the initiation, set-up and first year results of a seven-year dryland farming experiment in Utah. The experiment was conducted on six farms from six low rainfall counties. It was felt that the great depth of the Utah soils would make it possible for a large quantity of water to be stored in them. However, they also realized that the greatest problem would be to get as much of the rainfall to soak into the soil and not run off. After one year, the preliminary conclusions were that subsoiling favored storage and retention of water, fall plowing resulted in greater amounts of stored water and that summer fallowing every second or third year made larger amounts of water available to the next crop. For the results at the conclusion of this seven-year study, see Bulletin 112 by Lewis A. Merrill.

10128. Greb, B.W., D.E. Smika and A.L. Black. 1967. Effect of straw mulch rates on soil water storage during summer fallow in the Great Plains.. Soil Sci. Soc. Amer. Proc. 31:556-559..
A soil water storage experiment was conducted in the Great Plains by tilling in known amounts of wheat straw. Net gains in soil water storage during fallow varied from 1.0 to 4.3 cm at Sydney, MT, from 2.1 to 4.1 cm at Akron, CO, and from 3.1 to 3.3 cm at North Platte, NE. Average amounts of straw at each site were 2,600, 3,800, and 6,000 kg/ha, respectively. The soil water gains were primarily during the spring months of the 14-month fallow season. The water gained by straw mulches tended to improve the soil water content throughout the soil profile.

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