Submitted to: Proceedings of the US Dairy Forage Research Center Information Conference
Publication Type: Proceedings
Publication Acceptance Date: September 1, 1996
Publication Date: N/A
Technical Abstract: Pastureland comprises about 72 million acres in the humid eastern one-half of the USA, and there is evidence that many pastures are being used more intensively. Although nitrogen generally is well conserved in mechanically harvested perennial crops, grazing by large herbivores alters the N balance and cycling rate in grassland. Livestock utilize only 5 to 30% of the N ingested to produce meat, milk, and wool, and lactating dairy cows are mos efficient. The remainder of the N is excreted in urine and dung on a small proportion of the pasture. Urine N output responds to dietary changes more than dung N. Urine N is applied at rates that far exceed plant uptake capacity, and a large proportion of this N is lost to the atmosphere and is susceptible to leaching. There are few sources of data on N cycling and loss in pasture systems in the USA. Results from the literature suggest that N recycling in pastures can be improved by: applying moderate, split rates of fertilizer N applied during times of rapid plant growth; encouraging balanced mixtures of legumes and grasses to optimize both herbage quality and nitrate uptake capacity; providing supplemental feed in appropriate amounts and quality to improve pasture N utilization by livestock, without exceeding animal N needs; adjusting stocking rate to match feed availability in herbage and supplements; avoiding grazing from late autumn to early spring to reduce overwinter leaching and runoff losses; and installing drainage tile only where substantial plant yield increases will result. These and other approaches will help retain N in the pasture ecosystem and help ensure economically viable, environmentally sound livestock production systems.