Litter Decomposition and Root Production in Response to Grazing on Sandhills Subirrigated Meadow

Stocking density can be manipulated by management factors including herd size, pasture size, and grazing period length. Ultrahigh stocking density (mob grazing) is commonly characterized at 200,000 kg animal live weight ha-1 or higher with multiple movements of livestock per day. Practitioners claim increased plant production, soil development, and nutrient cycling rates because of high trampling percentages resulting from ultrahigh socking densities. This study was conducted on subirrigated meadow in the Nebraska Sandhills in 2012 and 2013 to determine grazing method effect on annual root production and litter decomposition. Stocking rates were held constant while stocking densities varied by treatment. Treatments included two replications of mob grazing (202,000 kg ha-1), 4-pasture rotation grazing (4-PR-1) (6700 kg ha-1), continuous grazing (5000 kg ha-1), and an ungrazed control. Cattle grazed for 60 days from early June to early August. Each May, 12 soil cores (5 cm diameter x 15 cm depth) per treatment replication were taken and roots removed. Root-free soil was placed in mesh cylinders of the same dimensions as the cores and inserted into the cores in the field. The mesh cylinders were excavated in November and roots separated from soil, dried, and weighed. Mob grazing did not increase root production. The control contained 60% more annual root biomass (P \u3c 0.05) than grazing. In June and July, wire mesh bags containing 1.5 g of stem and leaf material of quackgrass (Elymus repens L.) were placed at eight locations in the mob, 4-PR-1, and control. Bags were placed on the soil surface either in grazing exclosures measuring effects one year after grazing or in a mob-grazed paddock immediately following grazing. Four samples were retrieved per replication after 1, 5, 9, 21, and 46 weeks. Samples were dried and weighed to determine biomass disappearance and decomposition rate. The dried samples were analyzed for nitrogen (N), carbon (C), and Neutral Detergent Fiber (NDF) contents. Mob grazing did not affect decomposition rate, N or C levels, or fiber. Month of placement differed in all variables with June placements decomposing faster, had lower C, higher N, and lower fiber. Advisors: Walter H. Schacht and Jerry D. Volesk