The temperate ‘Flood Pampa’ (Buenos Aires province, east-central Argentina) covers approximately 100,000 km² about 80% of which is covered in natural grasslands. Cattle-grazing is widely practiced even though most natural grasslands have low forage production and forage is of poor quality. The current generally degraded grassland condition is attributed to over-grazing. Plants that grow during the winter are more affected by heavy grazing than spring growing species; summer growing species (preferentially grazed by cattle) have also declined. Seasonal rests from grazing have been suggested as a way of restoring degraded areas.
The study was conducted in a ‘B community’ (i.e. flat areas, hydromorphic soils, usually flooded in winter for 1 -2 months), one of the most prevalent in the region.
In a native pasture, three cattle grazing regimes were tested: spring-summer rest (November-January) aimed at favouring warm-season species; autumn rest (April- June) aimed at favouring cool-season species; and continuous grazing. Variable stocking rates, based on available forage were employed.
From October 1979 to August 1981, changes in above-ground biomass and grass composition were evaluated. Biomass was periodically sampled (vegetation cut to ground level and separated into dead and live components). Live biomass was separated into individual species.
Total above-ground biomass yield averaged 4,600 (± 445) kg/ha and 3,750 (± 120) kg/ha under the spring-summer rest regime during the first and second years, respectively. Warm-season species increased, mainly due to increases of dallisgrass Paspalum dilatatum and bluestem Bothriochloa laguroides.
Total above-ground biomass was 2,000 (± 170) kg/ha during the autumn rest regime; cool-season grasses (e.g. Poa spp. and Stipa spp.) increased.
In general, continuous grazing at a moderate intensity resulted in above-ground biomass of about 2,000 kg/ha. Contributions of warm-season and cool-season species remained unaltered; only the bunch grass, smutgrass Sporobolus indicus increased. Smut grass spreads in areas where soil has been compacted (e.g. by cattle trampling), it is tough, unpalatable and reduces pasture productivity.
Thus over the short duration of the study (2 years), grazing rest periods proved generally beneficial, and appropriately timed rest periods could help to restore degraded areas depauperate in cool- and/or warm-season grasses.
If using or referring to this published study, please read and quote the original paper, this can be viewed at: https://www.uair.arizona.edu/holdings/journal/issue?r=http://jrm.library.arizona.edu/Volume44/Number5/