Late Summer Irrigation and Establishment of Winter Annual Legumes in a Mediterranean‐type Climate¹

Abstract

Winter annual legumes have low fall and early winter forage yields in California's Mediterranean‐type climate. A 2‐year field study was conducted to determine the effects of late summer irrigation on seedling development, forage yield potential, and management problems of subterranean clover (Trifolium subterraneum L.), rose clover (Trifolium hirtum All.), and bur clover (Medicago polymorpha Gaertn). A mixture of three annual grasses, slender wild oats (Avena barbata Pott. ex Link), ‘Blando’ brome (Bromus mollis L.), and annual ryegrass (Lolium multiflorum L.), and a natural stand of indigenous species were included in the study for comparison. By irrigation prior to fall rains, we subjected six successive seedings, 2 weeks apart, to higher temperatures and longer fall‐growth periods than usual. Rates of morphological development of subclover and rose clover were measured until the seven‐leaf stage. In the 1972‐73 season, rose clover showed the largest differences in growth rates between planting dates. Rose clover from the 23 October planting required 90 more days to reach the seven‐leaf stage than when planted 29 September. Early‐flowering subclover from the 23 October planting grew more rapidly than did mid‐flowering subclover and rose clover. In the 1973‐74 season, late‐flowering sub‐clover had the fastest growth rate following 7 August irrigation; there were no differences between clovers following 20 September irrigation. Forage yields for August and September plantings were similar but were greater than those from the October planting. Plants irrigated in August were subjected to daylengths which promoted fall flowering. Summer insect problems, primarily with beet armyworm (Spodoptera exigua Hübner), were associated with August plantings. Subterranean clover produced more dry matter and had fewer problems than did the other legumes tested.

Vegetation Management

“…1) can be produced by supplemental irrigation of annual ryegrass (Lolium multiflorum), winter cereals, or subterranean clover (Trifolium subterraneum). In this uncommon alternative, annual rangeland seeded with ryegrass, winter cereals, or subterranean clover can be irrigated in mid-to late summer to stimulate early germination and early start of the green season (Taggard et al 1976 are often used by sheep operations as a fall forage source.…”