Simulated carbon and nitrogen dynamics in blue grama swards subject to above- and belowground grazing, irrigation and fertilization part II. The grazing optimization notion

Abstract

The study was designed to explore responses to grazing of primary-production processes, such as patterns of C (carbon) and N (nitrogen) allocation, to better understand the mechanisms by which herbivores affect ecosystem function. A model was created to simulate growth of blue grama in the field. Shoots and roots were divided into structural material (characterized by high C:N ratio) and metabolic/storage material (characterized by lower C:N ratio) to facilitate representation of the quality of the grass subjected to grazing. This plant model was linked to a model of C and N dynamics in grassland soils, and run in conjunction with an abiotic model. The simulation was run for three consecutive years and tested by sensitivity analysis. This paper concentrates on the effects of above- and belowground grazing. Production was maximized at moderate aboveground grazing intensities. However, the difference between maximal primary production and that predicted in the absence of grazing was too small (less than 5%) to be detected in the field.