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Brigham Young University Science Bulletin, Biological Series

Abstract

A comparative study of micrometeorologic conditions on irrigated and non-irrigated pasture plots was conducted at Provo, Utah, from 1970 to 1972. Daily measurements were taken of the following: precipitation cither as rain or snow, new snowfall and total snow depth during the winter; relative humidity in a standard weather shelter; number of hours at maximum relative humidity; cloud cover each morning; potential evaporation; total wind 1 m above ground level; temperature extremes in a standard weather shelter; and temperatures both on irrigated and non-irrigated plots with sensing devices located 5 cm beneath soil surface under grass cover, at soil surface under grass cover, and at soil surface on bare ground. During the pasture months of May through October, weekly soil moisture measurements from irrigated and non-irrigated plots were gravimetrically determined. All data were entered on columnized work sheets, key punched, and subsequently assimilated and tabulated by a FORTRAN IV program with the IBM 360/65 computer. Graphical representations of all daily measurements for the three years, as well as others depicting the effect of irrigation and snow cover for selected weeks, were completed.

The total precipitation for 1970, 1971, and 1972 was 491.0, 726.4, and 390.1 mm, respectively, and the average monthly mean temperatures in a standard weather shelter for the three years were 9.2, 8.8, and 9.4 °C. Other representative yearly values for 1970, 1971, and 1972, respectively, were total snowfall: 1165.9, 1877.1, and 909.3 mm; average maximum and minimum relative humidity: 97 and 43, 97 and 46, and 97 and 46 percent; average hours at maximum relative humidity each day: 7, 8, and 8 hr; average cloud cover each morning: 3-, 3-, and 3-tenths of covered sky; total potential evaporation and daily average for May through October: 983.8 and 5.3, 1030.7 and 5.6, and 1274.2 and 6.9 mm; average monthly soil moisture content for both irrigated and non-irrigated plots for May through October: 16.1 and 8.4, 16.3 and 5.8, and 8.1 and 3.8 percent; wind totals and daily averages: 19,315 and 52, 22,691 and 61, and 22,255 and 60 km; average annual temperatures 5 cm beneath soil surface on irrigated and non-irrigated plots for 1971 and 1972: 8.4 and 9.0 and 8.2 and 10.4 °C; average annual temperatures at soil surface under grass cover on irrigated and non-irrigated plots for 1971 and 1972: 9.7 and 10.6 and 10.9 and 12.8 °C; and average annual temperatures at soil surface on bare ground on irrigated and non-irrigated plots for 1971 and 1972: 12.9 and 16.5 and 14.9 and 15.0 °C. Temperature extremes on irrigated plots during the pasture season were moderated considerably from those recorded on the non-irrigated plots, and irrigation, when done routinely, provided adequate soil moisture throughout the entire pasture season. These findings are especially obvious when data other than yearly and monthly means are examined. Irrigation is undoubtedly the major factor in providing optimum moisture and temperature conditions for the development and survival of all types of pastureland biological organisms in creating optimum microenvironments in otherwise desolate, arid regions.

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