Assessing the Effect of Managem-ent Intensive Grazing on Water Quality in the Northeast

Stocking rate is the kq, determining effect of management intensive grazing on dairy farm projtability. However, increased stocking rate can increase NOi leaching fiom pastures. Increasing ztocking rate increases NO3loss through leaching because the bulk o f the N conszdmed by the anilnal is excreted in concentrated areas of the pasture mainly in urine. We used experimental uha porn the northeast US. and the literature to assess the relationsh;Ps between stocking rate and NO3leaching losses beneath an intensively grazed pasture. A relatively Low cumulative seasonal stocking rate of about 200 mature Hohtein ha-' could result in a 10 mg L-' NOiN concentration in the leachate beneath a fertilized, intensively pazed pasture. This means that while management intensive grazing can improve firm profitability and help control erosion, it can have a sign$cant negative effect on water quality beneath pastures. The extent to which this @ect occurs within specfic watershed need to be evaluated in context of the other cropping systems and lands uses within the watershed. Keyword: Nitrate, water quality o maintain dairy farm profitability in T the face of rising fuel and machinery costs and decreasing federal subsidies, some dairy farmers in the northeast U.S. are including management intensive grazing (MIG) as a component of the production system on their farms (Fales et al. 1993). Management intensive grazing is a production system in which animals are rotated rapidly through a series of paddocks in order to maximize livestock production on either a per hectare or per animal basis. Economic surveys in Pennsylvania (Parker et al. 1992) and New York (Emmick and Toomer 199 1 ) have shown that inclusion of MIG in a dairy farm can increase net profitability by $121 to $150 per c0w-l per year.'. The key management variable in determining effect of grazing on profitability is stocking rate (Leaver 1985). In a Pennsylvania study, increasing stocking rate from 2.5 to 4.0 cows ha-' (ac) for a WL. Stout is Soil Scientist for the US. Department of Agriculture, Agricultural Research Service (IJSDA-ARS), Pasture Systems and Watershed MLI nugemen t Research La bo rat0 ry (PS WMRL). S.L. F a h i j Profpssor And Head of the Department cf Agrorrorq, The Pennsylvunia State University. L. I). Muller is Professor o f Dairy Science, The Pmnsylzunin Strite University. R. R. Schnabel is Soil Scientist, USDA-ARS-PSWMRL. G. F. Elwinger is Support Scientist at the USDA-ARSPSKJMRL. .S..A. Weawr is a Soil Scientist at the USDA -A RSI?S KTI4R.l. 180 day grazing season increased returns over cost by $1188 ha-' (ac) (Fales et al. 1995). However, the 2.5 cows ha-' (ac) stocking rate was most profitable on a per animal basis, increasing returns over costs by $36 per animal-'. In such temperate maritime regions of the world as the UK, the Netherlands, and New Zealand, increased stocking rate has been shown to be the main factor increasing N leaching losses from pasture (Ball and Ryden 1984; Cut t le and Scholfield 1994; Steenvoorden et al. 1986). Increasing stocking rate affects N03loss through leaching because the bulk of the N consumed by the animal is excreted unevenly over the pasture in urine (Ball and Ryden 1984; Jarvis et al. 1989). The uneven deposition of urine N in pastures has caused N o s leaching from pastures to be higher than that from similarly fertilized cut grasslands; and it has been shown to pose a threat to water quality in many parts of the world (Ball et al. 1979; Ryden et al. 1984; Steenvoorden et al. 1986; Stout et al. 1997). Nitrate leaching from pastures is characterized by high losses from urine patches superimposed over lower losses from the pasture as a whole (Cuttle and Scholfield 1994). Losses from urine patches are affected by animal size, animal type, and forage quality (Whitehead 1995), while N loss from the pasture as a whole can be affected by soil hydrologic properties, fertilization rate, and pasture species composition (Cuttle and Scholfield 1994). In the northeast U.S., about 25% of the N excreted in cattle urine can leach below the root zone (Stout et al. 1997). The purpose of this paper is to assess the potential effect of cattle urine on water quality as affected by intensive pasture management in the northeast U.S.