Search

Supplementing beef cattle with 3‐nitrooxypropanol (3‐NOP) decreases enteric methane production, but it is unknown if fertilizing soil with 3‐NOP manure influences soil health. We measured soil health indicators 2 yr after manure application to a bromegrass (BromusL.) and alfalfa (Medicago sativaL.) mixed crop. Treatments were: composted conventional manure (without supplements); stockpiled conventional manure; composted manure from cattle supplemented with 3‐NOP; stockpiled 3‐NOP manure; composted manure from cattle supplemented with 3‐NOP and monensin (3‐NOP+Mon), a supplement that improves digestion; stockpiled 3‐NOP+Mon manure; inorganic fertilizer (150 kg N ha–1and 50 kg P ha–1); and an unamended control. Select chemical (K+, Mg2+, Mn+, Zn+, pH, and Olsen‐P), biological (soil organic matter, active C, respiration, and extractable protein), physical (wet aggregate stability, bulk density, total porosity, and macro‐, meso‐, and micro‐porosity), and hydraulic (saturation, field capacity, wilting point, water holding capacity, and hydraulic conductivity) variables were measured. The inclusion of monensin decreased soil Zn+concentrations by 70% in stockpiled 3‐NOP+Mon compared with stockpiled conventional manure. Active C and protein in composted conventional manure were 37 and 92% higher compared with stockpiled manure, respectively, but did not vary between 3‐NOP treatments. 3‐Nitrooxypropanol did not significantly alter other soil health indicators. Our results suggest that composted and stockpiled 3‐NOP manure can be used as a nutrient source for forage crops without requiring changes to current manure management because it has minimal influence on soil health. Chemical soil health indicators were not affected by 3‐nitrooxypropanol manure.3‐Nitrooxypropanol influenced biological indicators linked to organic matter quality.3‐Nitrooxypropanol manure affected active carbon and protein.Physical and hydraulic properties were unaffected by 3‐nitrooxypropanol manure.

Crop canopy reflectance sensors make it possible to estimate crop N demand and apply appropriate N fertilizer rates at different locations in a field, reducing fertilizer input and associated environmental impacts while maintaining crop yield. Environmental benefits, however, have not been quantified previously. The objective of this study was to estimate the environmental impact of sensor‐based N fertilization of corn using model‐based environmental Life Cycle Assessment. Nitrogen rate and corn grain yield were measured during a sensor‐based, variable N‐rate experiment in Lincoln County, MO. Spatially explicit soil properties were derived using a predictive modeling technique based on in‐field soil sampling. Soil N2O emissions, volatilized NH3loss, and soil NO3−leaching were predicted at 60 discrete field locations using the DeNitrification‐DeComposition (DNDC) model. Life cycle cumulative energy consumption, global warming potential (GWP), acidification potential, and eutrophication potential were estimated using model predictions, experimental data, and life cycle data. In this experiment, variable‐rate N management reduced total N fertilizer use by 11% without decreasing grain yield. Precision application of N is predicted to have reduced soil N2O emissions by 10%, volatilized NH3loss by 23%, and NO3−leaching by 16%, which in turn reduced life cycle nonrenewable energy consumption, GWP, acidification potential, and eutrophication potential by 7, 10, 22, and 16%, respectively. Although mean N losses were reduced, the variations in N losses were increased compared with conventional, uniform N application. Crop canopy sensor‐based, variable‐rate N fertilization was predicted to increase corn grain N use efficiency while simultaneously reducing total life‐cycle energy use, GWP, acidification, and eutrophication. Efficient use and application of N fertilizer likely reduces environmentally harmful N losses.Sensor‐based N fertilization has the promise of maximizing yield while minimizing N loss.Sensor‐based fertilization maintained corn yield and reduced losses of NO3−and N2O.Sensor‐based fertilization yielded life cycle GWP, acidification, and eutrophication benefits.

To reduce atmospheric CO2concentrations and provide food for a growing world population, sustainable management practices must be adopted. An important consideration in the development of sustainable practices is the maintenance of soil organic carbon (SOC). Critical assumptions, with unknown errors, are used to calculate SOC maintenance requirements. This study investigated the impact of three approaches for estimating belowground nonharvested carbon (NHC) on SOC maintenance requirements, SOC and nonharvested C mineralization rate constants, and the capacity of the soil to sequester carbon. Common protocols were used to develop databases from eight historical carbon studies. The SOC to CO2(kSOC) and NHC to SOC (kNHC) rate constants were calculated using the model NHCa/SOCi= kSOC/kNHC+ dSOC/dt(1/kNHCSOCi), where NHCais the amount of applied NHC, SOCeis SOC at the equilibrium point, t= time, and SOCiis the initial SOC value. Analysis showed that (i) despite the difficulty in measuring belowground biomass, it is needed to calculate the SOC and NHC mineralization rate constants when using nonisotopic approaches; (ii) decreasing NHC by reducing the relative contribution of roots to NHC reduced the calculated SOC maintenance requirements and the amount of corn stover that could be sustainably harvested; iii) changes in the belowground NHC calculation approach do not result in a consistent impact on calculated rate constants; iv) changes in the belowground NHC calculation approach had a minimal impact on the calculated carbon sequestration potential (kNHCNHC)/kSOC; (v) SOC at the beginning of the experiments was negatively correlated with temperature, while kSOCwas positively correlated with tillage intensity; and (vi) the kSOCand kNHCrate constants can be used to directly assess the impact of different management scenarios on carbon turnover.

Many models of phosphorus (P) transfer at the catchment scale rely on input from generic databases including, amongst others, soil and land use maps. Spatially detailed geochemical data sets have the potential to improve the accuracy of the input parameters of catchment‐scale nutrient transfer models. Furthermore, they enable the assessment of the utility of available, generic spatial data sets for the modeling and prediction of soil nutrient status and nutrient transfer at the catchment scale. This study aims to quantify the unique and joint contribution of soil and sediment properties, land cover, and point‐source emissions to the spatial variation of P concentrations in soil, streambed sediments, and stream water at the scale of a medium‐sized catchment. Soil parent material and soil chemical properties were identified as major factors controlling the catchment‐scale spatial variation in soil total P and Olsen P concentrations. Soil type and land cover as derived from the generic spatial database explain 33.7% of the variation in soil total P concentrations and 17.4% of the variation in Olsen P concentrations. Streambed P concentrations are principally related to the major element concentrations in streambed sediment and P delivery from the hillslopes due to sediment erosion. During base flow conditions, the total phosphorus (<0.45 μm) concentrations in stream water are mainly controlled by the concentrations of P and the major elements in the streambed sediment.

Nitrate leaching is a potential in humid regions when crops and forages are fertilized. This study was conducted to compare NO3leaching with two different N fertilizer formulations applied to forages. For 11 yr, ammonium nitrate (AN) was applied to a large (8.1 m2surface area), undisturbed, monolithic lysimeter Y101B at an annual rate of 168 kg N ha−1, and methylene urea (MU), a slow‐release fertilizer, was applied to a similar lysimeter (Y101D) at the same rate. Nitrate‐N concentrations in the percolate from these 2.4 m‐deep lysimeters were measured weekly. Even though NO3‐N levels increased steadily with the AN applications, the greatest increases occurred during the eighth year of treatment and reached levels above 20 mg L−1. With the MU, NO3‐N concentrations remained relatively constant until after 8 yr of treatment, reaching concentrations of 6 mg L−1. The highest rates of annual NO3‐N transport in percolate were 42.3 and 12.1 kg ha−1from lysimeters treated with AN and MU, respectively. (Losses from NH3volatilization were measured at 12.0 and 44.8 kg N ha−1for AN and MU, respectively.) Nitrate‐N transport in percolate varied seasonally with the greatest amounts being moved during the late winter‐early spring. Following 11 yr, the NO3‐N concentrations in each lysimeter declined to approximately 1 mg L−1. Based on this study with a 168 kg N ha−1annual application rate, less NO3‐N leaching will occur when a slow‐release N fertilizer, such as MU, is applied to forages than when AN is applied.

Many studies that address the impact of tropospheric O3on agricultural and forested ecosystems utilize the open‐top chamber. During the production of O3using electrical discharge generators fed with dry air, there is an inadvertent addition of HNO3vapor, a highly reactive trace gas. While several studies have proposed that HNO3vapor introduces artifacts, none has measured concentrations of the odd‐N2trace gas in the chamber or investigated the fate of the N in the context of whole‐plant physiology and growth. These questions were investigated using open‐top chambers containing seedlings of loblolly pine (Pinus taedaL.) during the 1988 growing season in Oak Ridge, TN. The O3treatments consisted of charcoal‐filtered or subambient (0.96 µmol m−3, 24‐h mean), ambient (1.62 µmol m−3, 24‐h mean), and elevated (2.36 µmol m−3, 24‐h mean) concentrations, the last being accomplished by proportional O3addition over the diurnal period. Measurements of the HNO3vapor concentration during dry periods only (no rainfall or ground‐level fog) averaged 28.6 nmol m−3(subambient), 55.4 nmol m−3(ambient air), and 240.0 nmol m−3(elevated O3), an 8.4‐fold range. For every 100 mol of O3added to the chamber, 28 mol of HNO3vapor were inadvertently added; this ratio is several times higher than that previously reported. This result, taken with published estimates of leaf conductance to HNO3vapor, indicates a maximum N deposition in the form of HNO3vapor ranging from 19.5 pmol N cm−2leaf area h−1(subambient O3) to 171.9 pmol N cm−2h−1(elevated O3). Given the nutrient content of the seedlings and knowledge of the fate of HNO3vapor on the leaf surface and leaf interior, the degree to which N deposition via HNO3vapor met the N requirements of the loblolly pine seedlings was estimated. Seedlings in the elevated O3treatment had an upper‐limit estimate of 3.5% for the needles and 1.8% for the whole plant of N derived from HNO3vapor. The concentration of HNO3vapor in the chambers, site of HNO3vapor deposition, N requirements of the loblolly pine seedlings, and estimated threshold for phytotoxic effects of HNO3vapor indicate that the inadvertent production of this odd‐N2trace gas is important in understanding the atmospheric chemistry within the chambers, but that the level of N loading in this study is unlikely to affect physiology or growth. However, we recommend that studies that employ higher O3‐exposure scenarios recognize the potential for inadvertent N deposition, particularly in trees grown in N‐deficient substrate.

Potassium bromide was applied at a rate of 168 kg Br−/ha to two 1.1‐ha pasture watersheds in east‐central Ohio to study the impacts on groundwater quality of a one‐time application of a soluble constituent. The watersheds had well‐drained residual silt loam soils and average slopes of about 20%. A nearly impermeable clay layer under the watersheds created a perched aquifer from which groundwater samples could be taken at developed springs. Three monolith, grassed lysimeters having soil profiles similar to the watersheds also received the Br−1treatment. The lysimeters, which were 8 m2in surface area and had a depth of 2.4 m, had shorter leaching pathways than the watersheds and showed peak Br−1concentrations in percolation (24.0 mg/L maximum peak) occurring 52–78 weeks following the Br−1application. The Br−1concentration in the groundwater from the watersheds had lower peaks (9.2 mg/L maximum peak) but occurred 84 to 104 weeks after the Br−1application. Because of variable leaching pathway lengths, including pathways much longer than those in the lysimeters, the watershed groundwater Br−1applications had shown no meaningful decrease by 2 yrs after the Br−1application. A one‐time application of a soluble, nondegradable chemical constituent can have a multi‐year influence on groundwater quality.

Four small, medium fertility (56 kg/ha per year N) watersheds were used in a rotational summer‐grazing and winter‐feeding program to determine its effects on N levels in water. During a 5‐year study on sloping uplands in Ohio, the concentrations of NO3‐N and NH4‐N were determined in precipitation, surface runoff, subsurface flow, and sediment. Although the NO3‐N concentration was generally higher in the surface runoff from the summer‐grazing/winter‐feeding area than from the summer‐grazing‐only areas, it usually resulted in no significant impairment of water quality, except on a few occasions when the NO3‐N concentration exceeded 10 mg/liter. The N transported in the subsurface flow from the summer‐grazing only areas was approximately equal to that transported from the winter‐feeding area and to the amount of N received in the precipitation. Both surface runoff transport and sediment transport of N were much greater in the winter‐feeding area than in the summer‐grazing‐only areas because these latter areas yielded very little surface runoff and only a trace of soil loss. Reduction of vegetative cover and increased soil disturbance on the winter‐feeding area resulted in increased surface runoff and soil erosion and thus more N was transported. Surface and subsurface losses of N from the winter‐feeding area were nearly equal. A large percentage of N was transported by the large storms, which represented a small percentage of the total number of storms.

Four small, sloping upland watersheds in Ohio (0.5–1.1 ha) were studied for 5 years to investigate hydrologic and soil erosion changes resulting from a beef cattle pasturing program. The cattle grazed all four pastures rotationally during the summer (May–October) and were wintered on hay (November–April) on the same pasture each year. The long‐term record for these pastures, which had been in meadow and light pasturing during the previous years, showed average annual surface runoff to be approximately 15 mm. During the 5 years of the grazing project, the three summer‐grazing‐only pastures showed a slight increase in surface runoff and a trace of soil loss. However, the winter‐feeding/summer‐grazing area showed a large increase in surface runoff (131 mm/year) and soil loss (1,355 kg/ha per year). Eighty‐one percent of the soil loss occurred during the dormant season. Large runoff events, although a small percentage of the total number of events, produced most of the runoff volume and most of the soil loss. Water balance studies indicated that subsurface flow was relatively unchanged by the grazing program. The increase in surface runoff was offset by a decrease in the evapotranspiration.

Each year for 3 y, 56 steer calves were fed to market weight on a corn‐silage and shelled‐corn ration in a 243‐m2paved lot. Storm runoff was measured and sampled as it left the feedlot, and again after it passed through a shallow, concrete settling basin and two consecutive 30 m long by 4.5 m wide sod filter strips. Storm runoff amounts and transport of TS (total solids), COD (chemical oxygen demand), BOD5(5‐d biological oxygen demand), N (total nitrogen), and P (total phosphorus) were smaller during the fall and winter months, when the steers were small and being fed silage than during May through July, when the animals were larger and eating shelled corn. The settling basin reduced transport of TS and COD by about 55%, while retaining only 35–40% of the BOD5, N, and P. Total reduction of all parameters was increased to 80–90% in the filter strips. The basin was more effective in large storm events, and the filter strips were more effective when the basin was slowly drained after settling of the settleable solids. Rainfall on the filter strips reduced the concentration of all parameters during large storms, and infiltration during other events reduced transport to downstream areas.

A beef cattle‐pasturing system involving four rotationally grazed summer pastures (SG) and four pastures used rotationally for winter grazing/feeding (WGF) was studied on sloping upland watersheds in Ohio to determine effects of livestock management on N levels in water. Both summer and winter areas annually received 224 kg N/ha as NH4NO3fertilizer. Surface runoff was collected automatically during runoff events, and subsurface flow was sampled from spring developments on a weekly basis. Although seasonal N concentration and transport in surface runoff tended to be greater in the area occupied by the cattle, N concentration and transport in runoff from the two areas were quite similar and did not significantly impair water quality, based on U.S. Public Health Standards. The NO3‐N concentration in the subsurface flow from the WGF area was higher than in the subsurface flow from the SG area. The NO3‐N concentration in the subsurface flow from both areas increased progressively throughout the study period, and reached levels as high as 18 mg/L. The subsurface flow provided the main pathway for N transport, with the surface transport being approximately 20 and 14% of the total N transport from the SG and WGF areas, respectively. The amount of sediment‐N transported was very small because of low soil loss.

Five small watersheds (0.25–3.1 ha) on sloping uplands in eastern Ohio were used to evaluate environmental effects of a beef management program of rotational summer grazing on one area, and rotational winter grazing/feeding with stored hay on another area. During the 5‐y study, annual precipitation was 1080 mm, which was 8–15% greater than the long‐term average. The surface runoff was measured by precalibrated H‐flumes, and automatically sampled using Coshocton wheels. Surface runoff from watersheds with beef cattle management increased, compared with the long‐term averages when hay was grown on the watersheds. Greater precipitation was the primary factor causing more runoff during the growing season (May–October), and the cattle management was a major contributing influence on the runoff increase during the dormant season (November–April). Maintenance of good vegetative cover on the study areas was a major factor in limiting annual average surface runoff to < 110 mm, which was a relatively small amount. The large runoff events, although a small percentage of the total number of events, produced most of the runoff volume. Soil loss from these pastures was minimal.

The influence of pasturing on surface runoff water quality was studied on a 26‐ha, unimproved pasture watershed in eastcentral Ohio. Data were collected for 2 y with no cattle in the pasture and for 3 y with summer grazing by a 17‐cow beef cattle herd. Because of springs and seep areas in the pasture, a small stream (accessible to the cattle) in the watershed flowed permanently. Samples of storm runoff were collected with a rotating vane sampler. The concentrations of most of the measured chemical parameters (NO3‐N, mineral N, organic N, total P, K, Ca, Mg, Na, S, Cl, HCO3, total organic C, salts) in the storm discharge water were low and changed very little as a result of grazing. The weighted annual NO3‐N concentrations for the ungrazed period and grazed period were 0.5 and 0.7 mg/L, respectively, and the highest event concentrations were 1.2 and 3.8 mg/L, respectively. A 17.7‐ha, wooded watershed that contained no pastured areas and received no agricultural chemical inputs, had concentrations of chemical parameters in surface discharge that were greater than or equal to those from the unimproved pasture during the grazing period. Nutrient transport during storm runoff from the unimproved pasture was greater during the 3‐y period with summer grazing than during the 2‐y, ungrazed period. This largely resulted from increased precipitation and subsequent increased surface runoff during the 3‐y period. The transport levels from the pasture during the 3‐y period were similar to or less than the transport levels from the wooded watershed during the same period. The increase in sediment transport from the pastured area was more than could be attributed solely to the increased surface runoff.

Wastewater treatment in southern West Virginia is limited by steep terrain and shallow soil. Surface mine reclamation replaces soil materials that may be suitable for wastewater treatment. Two minesoil series, Kaymine (a loamy‐skeletal, mixed, nonacid, mesic Typic Udorthent) and Sewell (a loamy‐skeletal, mixed, acid, mesic Typic Udorthent), were selected and soil samples were collected on six reclaimed surface mines to determine texture, bulk density, water retention, and saturated hydraulic conductivity (Ksat). Kaymine had more clay and silt and higher moisture retention than Sewell. In A horizons, Kaymine Ksat was about two orders of magnitude faster than Sewell, but Ksat values were highly variable within and among sites. On two reclaimed mine sites (one Sewell and one Kaymine), tapwater or wastewater was surface applied to 9 m2field plots over 32 wk. Leachate was collected in 50 and 100 cm wells and analyzed for chemical and microbiological properties. On the Sewell minesoil, little water was collected in wells after application, therefore water failed to move adequately in this minesoil. On Kaymine, Fe, Mn, sulfate, and suspended solids were present in all wells, indicating flushing of these materials from minesoils into wells. Nitrate (NO3)‐N was about two times greater in wastewater than tapwater and this same ratio was found in corresponding wells. Biological oxygen demand was decreased by 87% from wastewater to water in wells. Fecal coliform bacteria were not removed by wastewater passing through Kaymine soils. In general, these minesoils are not suitable for wastewater renovation based on the application methods and rates employed in this study.

A common practice for grazing land in the humid, eastern USA is continuous grazing with little or no fertilizer use. Concentrations and transport of nutrients from a 28‐ha unimproved grassed watershed were assessed in east‐central Ohio for 2 yr without the presence of livestock, for 3 yr with a 17‐cow beef (Bos taurus) herd grazing during the summer months only, and for an additional 6‐yr period with all‐year grazing with hay being brought in for winter feed. Nutrient concentrations remained low during all three grazing levels. An exception was K concentration, which increased with all‐year grazing. Concentrations of NO3‐N, mineral‐N, P, Ca, Mg, Na, and Cl were similar to or less than the concentrations from a nearby 17.7‐ha wooded watershed that contained no pastured areas and received no agricultural inputs. Nutrient concentrations showed no consistent seasonal variation. Concentrations of organic‐N, total organic C and sediment increased with increased grazing pressure. Greatest sediment concentrations and transport rates generally occurred during July and August regardless of grazing system. Largest monthly average sediment concentrations were 0.8, 1.3, and 3.2 g/L for the three systems, respectively; annual sediment losses were 0.2, 1.2, and 2.1 Mg/ha, respectively. All‐year cattle grazing/feeding on an unimproved pasture in this area would not be expected to produce degradation of stream water quality from nutrient concentrations or transport.

Three monolith lysimeters, each with a surface area of 8.1 m2and a depth of 2.4 m, were planted to no‐till corn (Zea maysL.) for 6 consecutive years. The lysimeters contained a Rayne silt loam (Typic Hapludult), a well‐drained residual soil. Urea was placed in a slot approximately 10‐cm deep and 10 to 15 cm from the corn row at a rate of 336 kg N/ha. The urea applied to two of the lysimeters was treated with nitrapyrin [2‐chloro‐6‐(trichloromethyl)pyridine], a nitrification inhibitor, and applied untreated on the third lysimeter. Two years of unfertilized meadow immediately preceded the corn. Concentrations of NO−3; in the leachate from the lysimeters were higher during the corn years than during the meadow period. Concentrations showed seasonal variations during the last 3 yr of the study, but showed no increasing trend. The leachate from the lysimeters receiving the nitrapyrin treated urea had seasonally flow‐weighted NO−3; concentrations ranging from 6 to 40 mg/L, while the leachate from the lysimeter receiving untreated urea had seasonally flow‐weighted NO−3;‐N concentrations ranging from 20 to 54 mg/L. Nitrate‐N losses showed a similar treatment difference. The 6‐yr annual average NO−3; loss was 117 and 160 kg/ha from the lysimeters with the treated urea and untreated urea, respectively. This study demonstrates that nitrification inhibitors such as nitrapyrin, have a potential to reduce NO−3; leaching when applied with ammoniacal fertilizers.

This study examined the impact on groundwater quality of conventional and slow‐release N fertilizer to small, grazed watersheds in eastern Ohio. Three small watersheds (each less than 1 ha) received 56 kg N/ha annually as NH4NO3for 5 yr. For the next 10 yr, one watershed received 168 kg N/ha annually as NH4NO3and two others received the same amount of N as methylene urea, a slow‐release fertilizer. Shallow groundwater samples were collected from springs and analyzed. After the 5‐yr prestudy period, NO3‐N levels in the groundwater from the three watersheds were in a 3 to 5 mg/L range. Groundwater NO3‐N concentrations increased slightly during the first 3 yr at the higher N fertilizer rate, though they remained in the 3 to 5 mg/L range. Nitrate‐N levels increased more sharply during the rest of the study. Although these NO3‐N levels varied more between the growing and dormant seasons than when lower rates of fertilizer were applied, they eventually reached a slower rate of increase. During the 9th and 10th yr of the high application, seasonal NO3‐N levels in groundwater ranged from 10 to 16 and 7 to 14 mg/L from the watersheds receiving NH4NO3and methylene urea, respectively. This study showed that 168 kg N/ha was too much for this system, regardless of whether conventional or slow‐release N was used.

Many of the reported nutrient losses from agricultural areas, especially where artificial subsurface drainage is not present, have been from surface runoff. In unglaciated, well drained silt loams in eastcentral Ohio, a portion of the infiltrated rainfall moves through the soil returning to the surface at springs or seep areas. Such return flow often creates a constant baseflow in multi‐hectare watersheds. The purposes of this study were to compare relative water and nutrient transports via storm runoff with amounts removed in continuous baseflow and to evaluate the influence of different management practices on such transport. Baseflow and storm runoff from four watersheds with different land use practices were measured, sampled, and analyzed for these comparisons. In two watersheds, 123 and 32.1 ha in size, containing woodland, pasture, and row crops, the majority of N moved from the watersheds in the storm runoff; however, 25 to 50% of the N transport was via baseflow. Using 10‐yr averages, 5.0 and 2.8 kg/ha of mineral N were annually transported from the 123‐ha watershed via 242 and 196 mMof storm runoff and baseflow, respectively; from the 32‐ha watershed, 3.6 and 3.2 kg/ha of mineral N were annually transported via 144 and 198 mm of storm runoff and baseflow, respectively. Mineral N transport from a 28.8‐ha poor practice pasture watershed and from a 17.7‐ha wooded watershed was less than above, but the proportions in storm runoff and baseflow were similar. Although stormflow was the larger transport pathway for nutrients leaving a watershed, a sizable portion of the nutrients can be carried with the baseflow. This comparison of watersheds in an unglaciated area indicates that there is a negligible difference in the quality of water leaving an unfertilized wooded area or unfertilized pasture or a watershed that receives fertilization on 55% of its area.

High levels of N fertilizer applied to pastures can result in NO3‐N concentrations in groundwater exceeding the USEPA potable water standard of 10 mg N/L. This study was conducted to determine groundwater NO3‐N levels following a change in N source from fertilizer to a legume in a grass‐pasture grazed by beef cattle. For 5 yr, 224 kg N/ha was applied annually to small watersheds with orchardgrass (Dactylis glomerataL.) pastures used for summer‐grazing and tall fescue (Festuca arundinaceaSchreb.) areas used for winter‐grazing‐feeding. At the beginning of the sixth year, alfalfa (Medicago sativaL.) was interseeded into the grass pastures and N fertilizer was no longer applied. Groundwater sampies from developed springs and surface runoff samples were collected and analyzed for NH4‐N, NO3‐N, and total N for the 5‐yr fertilization period and for the following 10‐yr period without applied N fertilizer. Nitrogen in groundwater was present mainly in the NO3form, and concentrations increased throughout the 5‐yr period of fertilizer application and reached levels that were usually in excess of 10 mg N/L. With the change from N fertilizer to legume N, the NO3‐N concentrations in groundwater dropped rapidly during a 2‐yr period. In a tall fescue‐alfalfa area, NO3‐N levels decreased from 17.7 to 9.3 mg N/L. In two orchard‐grass‐alfalfa areas, NO3‐N levels decreased from 11.2 to 2.7 and from 8.3 to 3.6 mg N/L. During the remainder of the 10‐yr period, NO3‐N concentrations declined to levels similar to those before N fertilization. Although the amount of N lost via subsurface flow decreased with decreasing concentrations, subsurface flow remained the main pathway for N loss compared with surface runoff or sediment‐attached N.

The purpose of this experiment was to use a conservative tracer to study the impacts on groundwater quality of a one‐time application of a water soluble chemical. Potassium bromide was applied at a rate of 168 kg Br−/ha to two 1.1‐ha pasture watersheds in east‐central Ohio. The watersheds had well‐drained residual silt loam soils and with slopes of 12 to 25%. A nearly impermeable clay layer under the watersheds created a perched aquifer from which groundwater samples could be taken at developed springs. There were seasonal variations in Br−concentrations in the groundwater and the highest concentrations (9.2 mg/L maximum peak) occurred within 3 yr following the Br−application. Ten years following the Br−application, Br−concentration in the groundwater was still slightly above initial baseline levels. Even with a one‐time application of a soluble chemical constituent on the surface of a small aquifer system, a multiyear impact was produced on the quality of groundwater.

Watershed studies have documented that summer storms produce less runoff from fields farmed with continuous no‐tillage corn (Zea maysL.) than from the same soils when corn is produced with conventional tillage practices. The lack of tillage favors a continuous surface cover of crop residue and the persistence of earthworm burrows, which have been shown to be preferential flow paths for water and chemicals, especially during intense summer storms. We investigated factors affecting preferential water and chemical transport in burrows formed by the earthworm Lumbricus terrestris(L.) in the field using individual burrow samplers and in the laboratory using blocks of undisturbed soil subjected to simulated rainfall. Rainfall amount and intensity and antecedent soil moisture content affected the amount of water transmitted in earthworm burrows, with high intensity storms on relatively dry no‐till soils producing the greatest amounts of preferential flow. Atrazine (2‐chloro‐4‐ethylamino‐6‐isopropylamino‐s‐triazine) transport was affected by the factors influencing the amount of preferential flow and by the time of storms relative to the time of herbicide application. Atrazine movement in earthworm burrows was greatest when high‐intensity rainfall occurred shortly after application. Atrazine transport was reduced by a delay in rainfall and by low‐intensity events prior to high intensity, percolate‐producing events.

Growing concern that N from agricultural sources is a major pollutant of groundwater has stimulated research on NO3‐N concentrations in groundwater under crops receiving N fertilizer. Knowledge of the effects of legumes on groundwater quality and their potential for reducing NO3‐N concentrations is limited. Three Coshocton monolith lysimeters (Y‐102A, B, and C) containing a well‐drained silt loam soil on a 13% slope, and four lysimeters (Y103A, B, C, and D) containing a moderately well‐drained silt loam soil on a 6% slope were used to study the effects of a legume‐grass mixture on groundwater quality. Between experiments with corn (Zea maysL.), an alfalfa‐orchard grass mix (70% Medicago sativaL. + 30% Dactylis glomerataL.), was grown for 2 yr and 3 yr on the Y102 and Y103 lysimeters respectively. The corn, some of which received high rates of N fertilizer, produced NO3‐N concentrations in percolate ranging from 15 to 40 mg/L. Under alfalfa, NO3‐N concentrations in leachate often were less than 5 mg/L, especially on the moderately well‐drained lysimeters. The highest NO3‐N percolate concentrations under all treatments occurred during the winter/early spring months.