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Stocking density effects in short duration grazing systems on botanical composition and soil characteristics of grasslands
To evaluate stocking density effects in short duration grazing systems on grassland forage and soil properties, three replicated pastures containing cool season grass and legume species without (BL1) and with (BL2) warm season grasses were divided into 5 paddocks. In each pasture, one paddock was not grazed (NG) and 4 were strip (moved once daily with a back fence) or mob (moved 4 times daily with a back fence) grazed beginning in May 2011 (BL1) and 2012 (BL2) by 10 cows at a live forage DM allowance of 2% BW/d. Within each pasture, one mob (MR) and strip (SR) paddock were rotationally stocked to remove 50% of the live forage with 35 d rest periods beginning 60 d after mob or strip grazing in yr 1 of each block and in the two (BL1) and one (BL2) subsequent grazing seasons. Water infiltration, soil penetration resistance, soil bulk density, and soil carbon were measured in May and October and botanical composition was determined in May, July, and October of each year. Compared to NG paddocks, water infiltration was lower (P < 0.05) in rotationally stocked paddocks in October 2011 and 2012 in BL1 and greater (P < 0.05) in all grazed paddocks in October 2012 in BL2. Penetration resistance at 5 cm was greater (P<0.05) in rotationally stocked than NG paddocks from May 2012 to October 2013 in BL1 and in October 2013 in BL2. Bulk density to 7.5 cm was less (P < 0.05) in NG than grazed paddocks in BL1 in October 2012 and rotationally stocked paddocks in October 2013 in BL2. Soil carbon content to 7.5 cm was greater (P < 0.05) in BL1 SR and BL2 MR paddocks than NG paddocks in May and October 2013, respectively. The proportions of cool season grasses in BL1 were lower (P < 0.05) in grazed than NG paddocks in July 2011 and in rotationally stocked paddocks after July 2012. Conversely, in grazed paddocks there were greater proportions of annual grasses (P < 0.05) in July, 2011 and legumes (P < 0.10) in May and October 2012 than NG paddocks. In BL2, proportions of warm season grasses were less (P < 0.05) in rotationally stocked than NG paddocks in July 2013. Strategic spring mob or strip grazing will reduce competition from cool season grasses to allow establishment of legumes in perennial grasslands.
Keywords: Beef cattle, Mob stocking, Botanical composition