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TECHNICAL REPORTS

Ground Water Quality

Reduction of Nitrate Leaching with Haying or Grazing and Omission of Nitrogen Fertilizer

USDA-ARS, P.O. Box 488, Coshocton, OH 43812

^* Corresponding author (owens{at}coshocton.ars.usda.gov).

Received for publication March 3, 2003.

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
In some high-fertility, high-stocking-density grazing systems, nitrate (NO₃) leaching can be great, and ground water NO₃–N concentrations can exceed maximum contaminant levels. To reduce high N leaching losses and concentrations, alternative management practices need to be used. At the North Appalachian Experimental Watershed near Coshocton, OH, two management practices were studied with regard to reducing NO₃–N concentrations in ground water. This was following a fertilized, rotational grazing management practice from which ground water NO₃–N concentrations exceeded maximum contaminant levels. Using four small watersheds (each approximately 1 ha), rotational grazing of a grass forage without N fertilizer being applied and unfertilized grass forage removed as hay were used as alternative management practices to the previous fertilized pastures. Ground water was sampled at spring developments, which drained the watershed areas, over a 7-yr period. Peak ground water NO₃–N concentrations before the 7-yr study period ranged from 13 to 25.5 mg L^–1. Ground water NO₃–N concentrations progressively decreased under each watershed and both management practices. Following five years of the alternative management practices, ground water NO₃–N concentrations ranged from 2.1 to 3.9 mg L^–1. Both grazing and haying, without N fertilizer being applied to the forage, were similarly effective in reducing the NO₃–N levels in ground water. This research shows two management practices that can be effective in reducing high NO₃–N concentrations resulting from high-fertility, high-stocking-density grazing systems, including an option to continue grazing.

Abbreviations: WS, watershed

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
IN AN INCREASINGLY larger number of research papers, there are reports of pasture systems and situations that cause detrimental effects on water quality. Most of these grassland studies have focused on nitrate (NO₃) leaching. Research in New Zealand and England has shown NO₃ subsurface losses from grasslands to be much greater when grazed, especially by cattle (Sharpley and Syers, 1979; Ryden et al., 1984; Steele et al., 1984; Haigh and White, 1986). Ridley et al. (1999) also noted that pastures receiving high N treatments have the potential to contaminate streams and ground water. Research in Ohio has shown NO₃ leaching to be greater from pastures receiving high N fertilization (Owens et al., 1983, 1992) than from moderate N fertilization (Owens et al., 1982) or under a grass–legume mixture (Owens et al., 1994). In England, Tyson et al. (1997) reported that N leaching losses from grass–white clover (Trifolium repens L.) pastures were only 26% of the amount recorded from fertilized grass pastures, although annual liveweight gain of the grazing steers was lower also.

The concern for NO₃ leaching has increased as some grazing practices have shifted to much greater animal density in the grazing systems. Such systems, where forage and animal production are maximized, create more deposition of urine and feces (i.e., spots with high concentrations of N). There have been lysimeter studies comparing N leaching with and without urine applications (Silva et al., 1999; Stout et al., 2000; Di and Cameron, 2002), and the results showed NO₃ leaching in excess of water quality standards with urine applications, especially in connection with high N fertilizer applications.

Some research has been done with management practices to reduce or prevent high N concentrations in water leaching from pastures. Di and Cameron (2002) noted that large amounts of NO₃–N could be lost via leaching but this could be diluted in aquifers that receive recharge from ungrazed areas. In a German study, Anger et al. (2002) compared NO₃ leaching from intensive grazing (4.9 livestock units ha^–1 with 250 kg N ha^–1 applied annually) with extensive grazing (2.9 livestock units ha^–1 with no N fertilizer on a pasture comprised of up to 15% legumes by dry matter). They found that NO₃ leaching could be reduced with the extensive grazing management nearly to levels found under mown grassland. A New Zealand study (de Klein and Ledgard, 2001) compared a "conventional grazing system" with a "restricted grazing system" (grazing is restricted to times when the risk of NO₃ leaching is smallest) and a "nil grazing system" (forage is harvested and fed to the cows; excreta is collected and returned to the field). Nitrate leaching losses were reduced by 35 to 50% and 55 to 65% for the restricted and nil systems, respectively, compared with the conventional grazing system.

Although many of the environmental concerns associated with high N fertilization of pastures and/or intensive grazing relate to leaching pathways, there are other major pathways of N loss. There can be considerable gaseous N losses from grasslands via the processes of N₂O emissions, denitrification, and NH₃ volatilization. Greater amounts of N are lost via each pathway with greater N inputs (Fowler et al., 1997; Oenema et al., 1998; Ryden, 1986; Whitehead, 1995, p. 191–192).

Even with multiple pathways of N loss from grazing systems, there are management situations in which N concentrations and losses moving through the soil into ground water create adverse environmental effects. Changes in management practices can reduce the amount of NO₃ leaching and lower NO₃–N concentrations in subsurface flow to acceptable water quality levels. The purpose of this research was to evaluate reduction of NO₃ leaching and ground water N concentrations with two different, nonfertilized grassland management practices using small watershed systems.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
The study was conducted at the North Appalachian Experimental Watershed near Coshocton, Ohio. A 17.2-ha study area was divided into four paddocks (Fig. 1), each with an instrumented watershed for determining surface runoff. Precipitation and subsurface water-flow measurement sites and a battery of four lysimeters (Harrold and Dreibelbis, 1958) were also located in the study area.

View larger version (21K): [in this window] [in a new window]   Fig. 1. Map of the 17.2-ha study area, showing four pastures (solid lines), gaged watersheds (dashed lines), rain gages, and spring-flow measurement sites. Watersheds (WS) 102 and 135 were grazed rotationally; WS 104 and 129 had forage removed as hay.

During the 11 years before the current study (1979–1990), the vegetation was predominantly orchardgrass (Dactylis glomerata L.) and Kentucky bluegrass (Poa pratensis L.). A spring calving herd of beef cows (Bos taurus) grazed the pastures rotationally during the summer (May–October) and were fed hay, grown elsewhere on the station, in one pasture (Watershed [WS] 129) during the dormant winter period (November–April) until 1986. Then cattle were no longer wintered in this study area. Beginning in April 1979, the annual fertilizer N rate for the summer-grazed-only pastures was 168 kg ha^–1 and split equally among three applications. Methylene urea, a slow-release N fertilizer (39–0–0, containing 37.5% water-insoluble N), was applied to the pastures containing WS 102 and 104; NH₄NO₃ (34–0–0, no water-insoluble N) was applied to WS 135 and its surrounding pasture (Fig. 1). Because of the high rate of N brought into the winter feeding paddock with hay (297 kg ha^–1 annually; Owens et al., 1982), no N fertilizer was applied during this study period. Management details were described by Owens et al. (1992).

From May 1990 through April 1997, the cattle herd was rotated through two paddocks (WS 102 and 135) with the same frequency as with previous management. Hay was harvested and removed from the paddocks containing WS 104 and 129. When the cattle would normally have grazed these paddocks, they were moved to grazing areas outside of the study area. No N fertilizer was applied to any of these paddocks during this study period. Although there was merit in having a positive control (i.e., one watershed continued with the 168 kg N ha^–1 rate), we considered it more important to replicate each of the management practices studied for reduction of N leaching. It was clear that the 168 kg N ha^–1 management was not environmentally sound, and alternatives needed to be studied. Because of the winter-feeding on WS 129, NO₃–N leaching was greater than from the other watersheds. Even though it had the highest peak NO₃–N concentrations in subsurface flow, it offered an excellent opportunity to study reduction in NO₃–N leaching by a nonfertilized forage management practice. Achieving similarly low NO₃–N concentrations from different starting points should confirm the NO₃–N reduction effectiveness of the management practice.

Surface runoff from the watersheds was measured by precalibrated 0.76-m H-flumes. Surface runoff water samples were collected during each runoff event by Coshocton wheels (Brakensiek et al., 1979) modified to continuously deliver a flow-proportional sample of runoff water to a refrigerated container. Precipitation was measured by two recording rain gages located in the study area. Because rain gage measurements have been shown by weighing lysimeters to underestimate true catch at ground level, gage readings were corrected (McGuinness, 1966) to estimate "true" precipitation input.

Subsurface flow was continuously measured with HS and V-notch flumes and sampled monthly by hand. The subsurface basin is larger than the surface watershed, and the quantity of subsurface flow contributed from beneath a watershed is calculated with the aid of lysimeter data (Van Keuren et al., 1979). Using data from 1984 through 1999, the calculated subsurface flow for the individual watersheds correlated strongly with the measured subsurface flow from the subsurface basin (r² ranged from 0.6 to 0.8).

Water samples (surface runoff, subsurface flow, and rainfall) were immediately filtered after collection and refrigerated at 4°C until analyzed. Analyses were performed within a few days of sample collection. Analyses for NH₄–N were conducted using an automated phenate method, and for NO₃–N plus NO₂–N by an automated Cd-reduction method (USEPA, 1979). Total N was determined by an automated phenate method after digestion in a block digestor (Schuman et al., 1973) modified to include NO₃–N and NO₂–N. Organic N was obtained by difference between total N and mineral N (the sum of NH₄–, NO₃–, and NO₂–N). Nitrogen content of hay was determined by the Kjeldahl method (Association of Official Analytical Chemists, 1984).

The chemical data were tabulated on a seasonal basis corresponding to the cattle-management treatments, that is, a 6-mo (May–October) growing–grazing period and a 6-mo (November–April) dormant period. The transport of each chemical for a season is the sum of the transport (i.e., flow times concentration) for all samplings within the season. The seasonal concentration values are flow-weighted averages calculated by dividing the total seasonal chemical transport by the total water flow for that season.

	RESULTS AND DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Precipitation
Before considering the N losses from the watersheds, N inputs should be assessed. Because no N entered the systems in hay or fertilizer during the study period, the main N inputs came with precipitation. Precipitation variation was greater in the 7-yr period than during the seven years before the study period (Table 1). This resulted from an extremely high year (808, 626, and 1434 mm for the 1990–1991 growing, dormant, and annual periods, respectively) followed by an extremely low year (276, 415, and 691 mm for the 1991–1992 growing, dormant, and annual periods, respectively). The 7-yr annual average for mineral N in precipitation was approximately 9 kg ha^–1. This was slightly higher than the input measured during the seven years before the current study period, but the averages were well within a standard deviation unit. Although there was considerable variation in concentrations and inputs, as indicated by the large standard deviations, there did not appear to be any concentration or input trends over the 14 years of study.

View larger version (30K): [in this window] [in a new window]   Fig. 2. Annual subsurface flow throughout the 11-yr pre-study period (1979–1990) and the 7-yr study period (1990–1997).

View larger version (27K): [in this window] [in a new window]   Fig. 3. Average flow-weighted seasonal (growing and dormant) concentration of NO3–N for subsurface flow throughout the 11-yr pre-study period (1979–1990) during which 168 kg N ha–1 was applied annually to rotationally grazed pastures, and the 7-yr study period (1990–1997) during which no N fertilizer was applied and two watersheds were grazed and two were hayed. Each year notation is a grazing year (May–April).

Nitrate N concentrations in the shallow ground water began to decrease while N was still being applied before the current study period (Fig. 3). A closer examination of the data showed that instead of an early concentration decrease occurring, the N concentrations for the 1989 dormant and 1990 growing seasons were unusually high. This resulted from a dry summer in 1988. The subsurface flows during the 1988 growing season were the lowest (except for WS 129) of all the growing seasons from 1974 through 1996. Each of these watersheds were in forage systems all of those years. During that dry summer, less NO₃ leaching occurred and probably less plant uptake of N. Thus, much more than the usual amount of N was available for leaching when normal precipitation and subsurface flow resumed. Tyson et al. (1997) noted that the highest N leaching losses from fertilized grass pastures occurred following dry summers.

Although two different management techniques were used to study the rate of lowering NO₃–N concentration in ground water, haying and grazing, three of the watersheds reached a NO₃–N level below 5 mg L^–1 almost simultaneously. Nitrate N concentrations in the subsurface flow from WS 102 were consistently lower than the other watersheds and reached this level sooner. Even though watershed characteristics and pre-study treatments had WS 102 and 104 and WS 129 and 135 as "matched pairs" in regard to subsurface flow (Table 3) and N transport, NO₃–N concentrations still reached similar levels after five years of no N fertilizer applications. The high levels of N brought into WS 129 with hay produced a higher rate of increase of NO₃–N concentration in subsurface flow than in the other three watersheds, but it also had the highest rate of NO₃–N concentration decease with no N fertilizer inputs (Table 4). Although there were high NO₃–N levels in the ground water from different management practices on these watersheds, this study showed that either haying or grazing without N fertilizer inputs will meet the need of reducing NO₃–N concentrations in ground water, even from heavily N loaded areas.

As NO₃–N concentrations increased with fertilizer applications and decreased with no N fertilizer, NO₃–N transport also increased and decreased, respectively (Fig. 4). Although there were extreme years for subsurface flow, there was no subsurface flow trend during the study and pre-study periods (Fig. 2). But the increasing trend in NO₃–N concentrations produced an increasing trend in annual NO₃–N transport during the pre-study period. The peak year of NO₃–N transport (1990–1991) followed by a very low year of NO₃–N transport (1991–1992) largely resulted from those two years being extreme hydrologic years (Table 3, Fig. 2). The high subsurface flow in the 1990–1991 year had more of a flushing effect than would have occurred in a more nearly average flow year. However, a detailed examination of the effects of extreme hydrologic events is beyond the intended scope of this article.

View larger version (27K): [in this window] [in a new window]   Fig. 4. Annual NO3–N transport in subsurface flow throughout the 11-yr pre-study period (1979–1990) during which 168 kg N ha–1 was applied annually to rotationally grazed pastures, and the 7-yr study period (1990–1997) during which no N fertilizer was applied and two watersheds were grazed and two were hayed. Each year notation is a grazing year (May–April).

Gaseous N losses through N₂O emissions, NH₃ volatilization, and denitrification increase with N inputs (Ryden, 1986; Sommer and Hutchings, 1997; Whitehead, 1995, p. 163–164). Significant N losses can occur from urine and feces deposits with losses from urine being much greater than from feces (Ryden, 1986; Whitehead, 1995, p. 163). In this study, N losses via each of these pathways probably decreased as the N in the systems decreased during the course of the study. Nevertheless, gaseous N losses combined with "calf crop" removal could account for N losses approaching the N losses from the hayed watersheds.

Nitrate N levels in ground water exceeded 10 mg L^–1 in all four watersheds because of high N inputs. Watershed 129 had N inputs both from mineral fertilizer and hay. Thus it was somewhat different from the other three watersheds, but all the watersheds had NO₃–N levels above the maximum contaminant level. Both haying and grazing with no N inputs reduced N leaching and lowered NO₃–N concentrations in the ground water. In a grazing period before this 14-yr period of study (Owens et al., 1982), 56 kg N ha^–1 produced low NO₃–N levels in ground water, 3 to 4 mg L^–1. This level of N input could be used during a period to lower NO₃ leaching, although the rate of reduction would probably not be as fast as with no N inputs. Using the collective research at the North Appalachian Experimental Watershed (Owens et al., 1982, 1983, 1992, 1994), we suggest that N inputs for grazing systems should not exceed 100 kg N ha^–1 annually to maintain ground water NO₃–N concentrations below 10 mg L^–1. All sources of N (e.g., fertilizer, hay, supplemental feed, legumes, and manure) should be included in the total. A higher N rate could probably be used in a haying system without excessive leaching. This is currently being evaluated at the North Appalachian Experimental Watershed. Although an annual rate of N input of 100 kg ha^–1 should be an environmentally friendly rate, this would be too high a rate to be very effective in reducing N leaching or lowering high NO₃–N levels in ground water.

	CONCLUSIONS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Nitrate N concentrations in excess of 10 mg L^–1 can be found in ground water under pastures that receive high N inputs. Two management options, rotational grazing and hay removal, with no N inputs will allow NO₃–N concentrations in ground water to be reduced. Peak ground water NO₃–N concentrations of 13 to 17 mg L^–1 went to less than 5 mg L^–1 within five years of omission of N fertilizer. The ground water NO₃–N concentration from a more heavily N loaded small watershed decreased from 25 to less than 5 mg L^–1 in six years. Nitrate N transport also decreased as NO₃–N concentrations decreased. For these two practices to be effective, there should be little or no N inputs so that the N in the system can be reduced. Thus, N available for leaching will be reduced. When ground water NO₃–N concentrations are above maximum contaminant levels, a livestock producer can achieve lower NO₃ losses and acceptable ground water NO₃–N quality under haying or continued grazing with low or no N inputs, even in an area with previous high N loading.

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 

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This Article Abstract Figures Only Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Related articles in JEQ Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (5) Citing Articles via Google Scholar Google Scholar Articles by Owens, L. B. Articles by Bonta, J. V. Search for Related Content PubMed PubMed Citation Articles by Owens, L. B. Articles by Bonta, J. V. Agricola Articles by Owens, L. B. Articles by Bonta, J. V. Related Collections Best Management Practices Grazing Management Nitrogen Nutrient Cycling Ground Water Quality