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The comparative influence of past management and rainfall on range herbaceous standing crop in east-central Argentina: 14 years of observations

Abstract:

Impacts of six initial treatments and rainfall on maximum above-ground herbaceous standing crop were assessed in 1978 and annually from 1984 to 1992 in rangelands of east-central semi-arid Argentina. Treatments applied in 1977-1978 were: (1) untreated control; (2) burning; (3) herbicide application (shrub control); (4) Old Field 1 or (5) Old Field 2 (areas previously exposed to different degrees of mechanical soil disturbance for 25 years); and (6) overgrazing. Domestic herbivores were excluded thereafter from all treatments until 1993. During 1984-1992, total above-ground herbaceous standing crop often remained greater in both Old Fields than in the other treatments; highest mean values were 2336 and 1640 kg ha-1 for Old Field 1 and Old Field 2 treatments, respectively. Lowest total above-ground standing crops in all treatments (M = 296-475 kg ha-1) occurred in 1989, the year with the lowest annual rainfall (257.5 mm). Desirable perennial grasses contributed most (44-100%) to total herbaceous standing crop in all treatments during the study period. Most of this standing crop was made up of the cool-season grasses Piptochaetium napostaense, Poa ligularis, Stipa clarazii, and papposa and S. tenuis. Annual rainfall was closely related (p < 0.05) to total herbaceous and desirable perennial grass standing crops in most treatments, and accounted for most of the variation in herbage production between years.