Document: PAT-3-59-97

Nitrogen and phosphorus cycling in relation to grazing and land use in subtropical rangelands.

BOHLEN, P.J.*

Archbold Biological Station, Lake Placid, FL 33852, USA ¹

Abstract:
The effects of livestock grazing on nutrient cycling are not well understood. I examined the influence of cattle stocking density in two different pasture types on nitrogen (N) mineralization, inorganic N pools and phosphorus (P) availability to assess the influence of grazing and grazing land use on the cycling of N and P in subtropical rangelands of central Florida. I measured in situ N mineralization and assessed P availability with ion-exchange resin sheets in sixteen experimental pastures, eight each in improved pastures (24 ha) and semi-native range (38 ha) with replicates of four different stocking densities of beef cattle (0, 15, 20, 35 cow-calf-pairs per pasture). Average inorganic N content was 1.5-fold greater in the improved than in semi-native pastures. Average N mineralization from March through July, 1999, was 28 kg ha^-1 in improved and 22 kg ha^-1 in the semi-native pastures. Average resin extractable P was 3.8-fold greater in improved than in semi-native pastures, probably due to long-term differences in P fertilizer history. Nitrogen mineralization rates were significantly lower in the high stocking density treatment than in the control and middle stocking density treatments in both improved and semi-native pastures. The effects of cattle grazing on N mineralization may have been due to shifts in allocation of belowground production in response to grazing.

Keywords: grazing, nitrogen cycling, phosphorus, rangeland

This abstract is being presented at: 3:30 PM in session:
Oral Session #51: Disturbance Ecology: Harvesting, Grazing and Roads.