Date of Award:

5-1986

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Wildland Resources

Department name when degree awarded

Range Science

Committee Chair(s)

Douglas A. Johnson

Committee

Douglas A. Johnson

Committee

D. V. Sisson

Committee

F. D. Provenza

Abstract

A short duration grazing system was utilized to determine the effects of intensive periodic defoliation during spring on soil moisture depletion patterns and plant water status in a crested wheatgrass (Agropyron cristatum and A. desertorum) pasture in central Utah. Exclosures were constructed to compare grazed and ungrazed responses. Soil moisture was monitored to a depth of 193 cm at one to two week intervals from mid-April to late-September using a neutron moisture gauge. Predawn and midday leaf water potentials were estimated using a pressure chamber technique. The two paddocks included in the study were grazed three times between mid-April and mid-June in 1985. A difference in time of grazing between the two paddocks was also examined for its effect on soil moisture depletion patterns and plant water status.

Soil moisture was depleted at a higher rate within ungrazed plots than grazed plots during 13 April to 1 July in both paddocks. Soil moisture was depleted at a higher rate after 1 July in grazed compared to ungrazed plots in the early-grazed paddock; however, no difference in soil moisture depletion rate was noted after 1 July within the late-grazed paddock. Total cumulative depletion was greater within ungrazed plots than grazed plots in the early-grazed paddock from 6 June until 13 August, and from 23 May until 30 July in the late-grazed paddock. During the pre-July period, soil moisture was depleted more rapidly in the upper- and mid-portions of the soil profile in ungrazed plots. By 25 September there was no difference in total soil water depletion through 53 cm between grazed and ungrazed treatments, but ungrazed plots extracted relatively more water in the mid- and lower-portions of the soil profile.

Grazing had no effect on predawn leaf water potentials prior to 1 July, but predawn leaf water potentials were lower for ungrazed plants than for grazed plants after 1 July. Midday leaf water potentials were lower for grazed plants than for ungrazed plants before 1 July, but did not differ between grazed and ungrazed plants after 1 July. Time of grazing had no effect on either predawn or midday leaf water potentials.

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