Abstract
Nitrogen (N) is necessary for food production, but when N in excess of crop-plant requirements enters the environment, it creates a number of detrimental impacts. Alternative agricultural practices, such as pasture-based livestock production, are often suggested as possible strategies for minimizing negative environmental impacts of modern agriculture. To evaluate the potential for these practices to decrease N losses to the environment, this thesis quantifies the influxes and effluxes of N from an alternative livestock farm (beef, pork, poultry, eggs) in central Virginia and evaluates the role of a farm pond in influencing the effluxes.
The majority of the N brought into Timbercreek Farm (5,300 – 8,100 kg N year-1) is not exported as product (750 – 2,300 kg N year-1). On an annual scale, farm N use efficiency (output as product/total input) is 14 – 28%, which lead to N surpluses (inputs minus outputs) of 28 – 35 kg N ha-1 year-1. Total dissolved N (TDN) flux via stream water into the farm is similar to TDN flux out of the farm (1140 120 kg N year-1 and 1370 150 kg N year-1, respectively). Therefore, the farm has a surplus of N, over what is needed for livestock production, but the majority of the excess N is not exported in the farm’s streams. The farm pond is a small sink of N (100 60 kg N year-1) and denitrification and/or burial in sediment are the likely fates of the N. During high flows and over short time scales, the pond is also a sink for N (3 – 40 kg N per storm). However, relative to other fluxes, the magnitude of the N sink represented by the pond is small (1 – 3% of surplus N on the farm).
Timbercreek Farm N use efficiencies are similar to conventional farm efficiencies, but, in contrast to conventional farms, spread surplus N over a larger area. On-site biogeochemical processes store and/or transform surplus N and prevent it from being exported in the streams. Relative to conventional agriculture, alternative livestock practices, such as those at Timbercreek Farm, have the potential to reduce negative environmental impacts on the farm scale, but are not likely to address the larger issue of inefficient resource use.
