Soil water regimes of rotationally grazed perennial and annual forages

To maintain a sustainable agricultural system, management practices such as grazing must ensure adequate soil water for plant growth, yet minimize the risk of soil erosion. The objective of this study was to characterize the soil water regime of perennial and annual forages under three grazing inten sities (heavy, medium and light). The study was conducted at the Lacombe Re search Station, Alberta, on an Orthic Black Chemozem of loam to silt loam t exture. The forages used were smooth bromegrass (Bromus inermis L. 'Carlton '), meadow bromegrass (Bromus ripanius L. 'Paddock'), a mixture of tritical e (X Triticosecale Wittmack 'Pika') and barley (Hordeum vulgare L. 'AC Laco mbe') and triticale. Soil water measurements were conducted between April a nd October of 1994 and 1995 using a neutron scattering hydroprobe to a dept h of 90 cm. Surface (0-7.5 cm) soil water was more responsive to grazing in tensity than soil water accumulated to various depths. For all grazing trea tments and forages, both surface soil water and accumulated soil water gene rally fluctuated between field capacity and wilting point during the growin g season. Although plant water status was not determined, no visual permane nt wilting of forages was observed during the study. Differences in evapotr anspiration (ET), as determined by differences in soil water were evident a mong forage species but not grazing intensities, with perennials having hig h ET in spring and annuals having high ET in summer. Estimated values of wa ter-use efficiency (WUE) were greater for perennials than for annuals and g razing effects on WUE were minimal. From a management perspective, grazing of annuals and perennials altered soil water dynamics but still maintained adequate soil water for plant growth.