Herd Management Opportunities for Decreasing the Nitrogen Load on the Dairy Farm
Charles G. Schwab, University of New Hampshire, Durham, and Rick A. Kohn,University of Maryland, College Park

INTRODUCTION

Dairy farming in the United States faces two major challenges, an economic challenge and an environmental challenge. The solution to the economic challenge continues to be one of becoming more efficient. Two ways of becoming more efficient has been to increase milk production per cow (i.e., rolling herd average) and to increase cow numbers.

Unfortunately, increasing cow numbers on the farm has contributed to the environmental challenge. From an environmental point of view, in regard to nitrogen, there are two major areas of increasing concern. The first is the pollution of surface water (e.g., streams, lakes, wetlands and estuaries) and ground water from excessive land application of nitrogen. Some nitrogen may be lost with runoff water after a rainfall (Baker and Senft, 1993). Nitrogen incorporated into the soil in excess of crop needs is eventually lost to ground water (Joshi et al., 1994).

The second environmental concern is the volatilization of manure nitrogen into ammonia and its emission into the air. Ammonia contributes to acid rain that endangers forests and lakes (Luebs et al., 1973). Also, some nitrogen may be lost from the farm by conversion to atmospheric N2 in a process known as denitrification (Thompson et al., 1987). Studies indicate that up to 50% of manure nitrogen can be lost to the atmosphere during handling, storage, and land application (Borton et al., 1995; Hutson et al., 1998). The problem is that 60 to 80% of the nitrogen imported onto most dairy farms in the form of feed and commercial fertilizers stays on the farm. The reason for this is that only about 30% of the nitrogen consumed by lactating cows in high producing herds is transferred to the milk, the remainder is excreted in feces and urine (Wilkerson et al., 1997).

It is becoming increasingly clear that how we handle nitrogen and other nutrients (particularly phosphorus) on the dairy farm will affect both farm profitability and the number of animals per unit of cropland that will be allowed. The challenge is to find the appropriate balance between environmental stewardship and an efficient,economically viable dairy production system.Thus, the goal is to increase dairy farm efficiency and profitability while maintaining or reducing nutrient losses to the environment.

The purpose of this presentation is to compare the potential impact of some of the newer technologies in dairy cattle feeding and management on reducing nitrogen losses per unit of milk produced from typical dairy farms.

These technologies are grouped into those aimed at improving biological efficiency through increased production and those aimed at providing a better match of protein sources with the animal’s needs. The reader is referred to other publications that focus on manure, soil, and crop management practices as strategies for reducing nitrogen losses to the environment (e.g., Borton et al., 1997; Joshi et al., 1994; Van Horn et al., 1994).

Source: Monsanto Dairy Group
Author: Schwab,  Durham, Cohn