Effect of long-term application of biosolids for land reclamation on surface water chemistry

Biosolids are known to have a potential to restore degraded land, but the long-term impacts of this practice on the environment, including water quality, still need to be evaluated. The surface water chemistry (NO3-, NH4+, and total P, Cd, Cu, and Hg) was monitored for 31 yr from 1972 to 2002 in a 6000-ha watershed at Fulton County, Illinois, where the Metropolitan Water Reclamation District of Greater Chicago was restoring the productivity of strip-mined land using biosolids. The mean cumulative loading rates during the past 31 yr were 875 dry Mg ha(-1) for 1120-ha fields in the biosolids-amended watershed and 4.3 dry Mg ha(-1) for the 670-ha fields in the control watershed. Biosolids were injected into mine spoil fields as liquid fertilizer from 1972 to 1985, and incorporated as dewatered cake from 1980 to 1996 and air-dried solids from 1987 to 2002. The mean annual loadings of nutrients and trace elements from biosolids in 1 ha were 735 kg N, 530 kg P, 4.5 kg Cd, 30.7 kg Cu, and 0.11 kg Hg in the fields of the biosolids-amended watershed, and negligible in the fields of the control watershed. Sampling of surface water was conducted monthly in the 1970s, and three times per year in the 1980s and 1990s. The water samples were collected from 12 reservoirs and 2 creeks receiving drainage from the fields in the control watershed, and 8 reservoirs and 4 creeks associated with the fields in the biosolids-amended watershed for the analysis of NO3- -N (including NO2- N), NH4+-N, and total P, Cd, Cu, and Hg. Compared to the control (0.18 mg L(-1)), surface water NO3- -N in the biosolids-amended watershed (2.23 mg L(-1)) was consistently higher; however, it was still below the Illinois limit of 10 mg L(-1) for public and food-processing water supplies. Biosolids applications had a significant effect on mean concentrations of ammonium N (0.11 mg L(-1) for control and 0.24 mg L(-1) for biosolids) and total P (0.10 mg L(-1) for control and 0.16 mg L(-1) for biosolids) in surface water. Application of biosolids did not increase the concentrations of Cd and Hg in surface water. The elevation of Cu in surface water with biosolids application only occurred in some years of the first decade, when land-applied sludges contained high concentrations of trace metals, including Cu. In fact, following the promulgation of 40 CFR Part 503, the concentrations of all three metals fell below the method detection level (MDL) in surface water for nearly all samplings. Nitrate in the surface water tends to be higher in spring, and ammonium, total P, and total Hg in summer and fall. Mean nitrate, ammonium, and total phosphorus concentrations were found to be greater in creeks than reservoirs. The results indicate that application of biosolids for land reclamation at high loading rates from 1972 to 2002, with adequate runoff and soil erosion control, had only a minor impact on surface water quality.     

Phosphorus and nitrogen runoff from a forested watershed fertilized with biosolids

Municipal biosolids are typically not used on the steepest of forested slopes in the U.S. Pacific Northwest. The primary concern in using biosolids on steep slopes is movement of biosolids particles and soluble nutrients to surface waters during runoff events. We examined the pattern and extent of P and N runoff from a perennial stream draining a small, forested 21.4-ha watershed in western Washington before and after biosolids application. In this study, we applied biosolids at a rate of 13.5 Mg ha(-1) (700 kg N ha(-1) and 500 kg P ha(-1)) to 40% of the watershed following nearly 1.5 years of pre-application water sampling and 1.5 years thereafter. There was no evidence of direct runoff of P or N from biosolids into surface water. Elevated surface water discharge did not change the concentration of PO4-P, biologically available phosphorus (BAP), bioavailable particulate phosphorus (BPP), or total P nor did it affect the concentration-discharge relationship. Some instances of total P concentrations exceeding the USEPA surface water standard of 0.1 mg L(-1) were observed following biosolids application. However, total P in 27 Creek was predominately in particulate form and not labile, suggesting that detritus moving into the main creek channel and ephemeral drainage courses may be the principal P source. Ammonium N concentrations in runoff water were consistent before and after biosolids application, ranging from below detection limits (0.01 mg L(-1)) to 0.1 mg L(-1); no concentration-discharge relationship existed. Biosolids application changed the 27 Creek concentration-discharge relationship for NO3(-)-N. Before application, no relationship existed. Beginning nine months after biosolids application, increases in discharge were positively related to increases in NO3(-)-N concentrations. Nitrate concentrations in runoff following biosolids application were approximately 10 times less than the USEPA drinking water standard of 10 mg L(-1).     

Transformations of nitrogen and carbon in entrenched biosolids at a reclaimed mineral sands mining site

Biosolids deep-row incorporation (DRI) provides high levels of nutrients to the reclamation sites; however, additions of N in excess of the vegetation requirements can potentially impair water quality. The effects of anaerobically digested (AD) and lime stabilized (LS) DRI biosolids and inorganic N fertilizer were compared on C and N transformations and transport at a reclaimed mineral sands mining site. Biosolids were applied at 213 and 426 Mg AD biosolids ha(-1) and 328 and 656 Mg LS biosolids ha)(-1) (dry mass), and inorganic N fertilizer was applied at 0 (control) and 504 kg N ha-(-1) yr(-1). Zero tension lysimeters were installed to collect leachate for determination of vertical N transport, and the biosolids seams were analyzed for N and C transformations after 28 mo aging. The leachijng masses from the DRI biosolids treatments were 139 to 291 kg ha(-1) NO3-N, 61 to 243 kg ha(-1) NH4-N, and 61 to 269 kg ha(-1) organic N, while the fertilizer treatment did not differ from the control. Aged biosolids analysis showed that total N lost over the course of 2 yr was 15.2 Mg ha(-1) and 10.9 Mg ha(-1) for LS and AD biosolids, respectively, which was roughly 50% of the N applied. Organic C losses were 81 Mg ha(-1) and 33 Mg ha(-1) for LS and AD biosolids, respectively. Our results indicated that entrenchment of biosolids in coarse-textured media should not be used as a mined land reclamation technique because the anaerobic conditions required to limit mineralization and nitrification cannot be maintained in such permeable soils.     

Accelerated weathering of biosolid-amended copper mine tailings

Application of municipal biosolids to mine tailings can enhance revegetation success, but may cause adverse environmental impacts, such as increased leaching of NO3- and metals to ground water. Kinetic weathering cells were used to simulate geochemical weathering to determine the effects of biosolid amendment on (i) pH of leachate and tailings, (ii) leaching of NO3- and SO4(2-), (iii) leaching and bioavailability (DTPA-extractable) of selected metals, and (iv) changes in tailing mineralogy. Four Cu mine tailings from southern Arizona differing in initial pH (3.3-7.3) and degree of weathering were packed into triplicate weathering cells and were unamended and amended with two rates (equivalent to 134 and 200 Mg dry matter ha(-1)) of biosolids. Biosolid application to acid (pH 3.3) tailings resulted in pH values as high as 6.3 and leachate pH as high as 5.7, and biosolids applied to circumneutral tailings resulted in no change in tailing or leachate pH. Concentrations of NO3--N of up to 23 mg L(-1) occurred in leachates from circumneutral tailings. The low pH of the acidic tailing apparently inhibited nitrification, resulting in leachate NO3--N of <5 mg L(-1). Less SO4(2-)-S was leached in biosolid-amended versus unamended acid tailings (final rate of 0.04 compared with 0.11 g SO4(2-)-S wk(-1)). Copper concentrations in leachates from acidic tailings were reduced from 53 to 27 mg L(-1) with biosolid amendment. Copper and As concentrations increased slightly in leachates from biosolid-amended circumneutral tailings. Small increases in DTPA-extractable Cu, Ni, and Zn occurred in all tailings with increased biosolid rate. Overall, there was little evidence of potential for adverse environmental impacts resulting from biosolid application to these Cu mine tailings.     

Nitrate leaching and nitrogen recovery following application of polyolefin-coated urea to potato

High N fertilizer and irrigation amounts applied to potato (Solanum tuberosum L.) on coarse-textured soils often result in nitrate (NO3) leaching and low recovery of applied fertilizer N. This 3-yr study compared the effects of two rates (140 and 280 kg N ha(-1)) of a single polyolefin-coated urea (PCU) application versus split applications of urea on 'Russet Burbank' potato yield and on NO3 leaching and N recovery efficiency (RE) on a loamy sand. Standard irrigation was applied in all years and excessive irrigation was used in another experiment in the third year. At the recommended rate of 280 kg N ha(-1), NO3 leaching during the growing season was 34 to 49% lower with PCU than three applications of urea. Under standard irrigation in the third year, leaching from five applications of urea (280 kg N ha(-1)) was 38% higher than PCU. Under leaching conditions in the first year (> or = 25 mm drainage water in at least one 24-h period) and excessive irrigation in the third year, PCU at 280 kg N ha(-1) improved total and marketable tuber yields by 12 to 19% compared with three applications of urea. Fertilizer N RE estimated by the difference and 15N isotope methods at the 280 kg N ha(-1) rate was, on average, higher with PCU (mean 50%) than urea (mean 43%). Fertilizer N RE values estimated by the isotope method (mean 51%) were greater than those estimated by the difference method (mean 47%). Results from this study indicate that PCU can reduce leaching and improve N recovery and tuber yield during seasons with high leaching.     

Dairy slurry application method impacts ammonia emission and nitrate in no-till corn silage

Reducing ammonia (NH3) emissions through slurry incorporation or other soil management techniques may increase nitrate (NO3) leaching, so quantifying potential losses from these alternative pathways is essential to improving slurry N management. Slurry N losses, as NH3 or NO3 were evaluated over 4 yr in south-central Wisconsin. Slurry (i.e., dairy cow [Bos taurus] manure from a storage pit) was applied each spring at a single rate (-75 m3 ha(-1)) in one of three ways: surface broadcast (SURF), surface broadcast followed by partial incorporation using an aerator implement (AER-INC), and injection (INJ). Ammonia emissions were measured during the 120 h following slurry application using chambers, and NO3 leaching was monitored in drainage lysimeters. Yield and N3 uptake of oat (Avena sativa L.), corn (Zea mays L.), and winter rye (Secale cereale L.) were measured each year, and at trial's end soils were sampled in 15- to 30-cm increments to 90-cm depth. There were significant tradeoffs in slurry N loss among pathways: annual mean NH3-N emission across all treatments was 5.3, 38.3, 12.4, and 21.8 kg ha(-1) and annual mean NO3-N leaching across all treatments was 24.1, 0.9, 16.9, and 7.3 kg ha' during Years 1, 2, 3, and 4, respectively. Slurry N loss amounted to 27.1% of applied N from the SURF treatment (20.5% as NH3-N and 6.6% as NO,-N), 23.3% from AER-INC (12.0% as NH3-N and 11.3% as NO3-N), and 9.19% from INJ (4.4% as NH3-N and 4.7% as NO3-N). Although slurry incorporation decreased slurry N loss, the conserved slurry N did not significantly impact crop yield, crop N uptake or soil properties at trial's end.     

Soil nitrate nitrogen dynamics after biosolids application in a tobosagrass desert grassland

Dormant-season application of biosolids increases desert grass production more than growing season application in the first growing season after application. Differential patterns of NO3-N (plant available N) release following seasonal biosolids application may explain this response. Experiments were conducted to determine soil nitrate nitrogen dynamics following application of biosolids during two seasons in a tobosagrass [Hilaria mutica (Buckl.) Benth.] Chihuahuan Desert grassland. Biosolids were applied either in the dormant (early April) or growing (early July) season at 0, 18, or 34 dry Mg ha(-1). A polyester-nylon mulch was also applied to serve as a control that approximated the same physical effects on the soil surface as the biosolids but without any chemical effects. Supplemental irrigation was applied to half of the plots. Soil NO3-N was measured at two depths (0-5 and 5-15 cm) underneath biosolids (or mulch) and in interspace positions relative to surface location of biosolids (or mulch). Dormant-season biosolids application significantly increased soil NO3-N during the first growing season, and also increased soil NO3-N throughout the first growing season compared to growing-season biosolids application in a year of higher-than-average spring precipitation. In a year of lower-than-average spring precipitation, season of application did not affect soil NO3-N. Soil NO3-N was higher at both biosolids rates for both seasons of application than in the control treatment. Biosolids increased soil NO3-N compared to the inert mulch. Irrigation did not significantly affect soil NO3-N. Soil NO3-N was not significantly different underneath biosolids and in interspace positions. Surface soil NO3-N was higher during the first year of biosolids application, and subsurface soil NO3-N increased during the second year. Results showed that biosolids rate and season of application affected soil NO3-N measured during the growing season. Under dry spring-normal summer precipitation conditions, season of application did not affect soil NO3-N; in contrast, dormant season application increased soil NO3-N more than growing season application under wet spring-dry summer conditions.     

Nitrogen leaching from Douglas-fir forests after urea fertilization

Leaching of nitrogen (N) after forest fertilization has the potential to pollute ground and surface water. The purpose of this study was to quantify N leaching through the primary rooting zone of N-limited Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] forests the year after fertilization (224 kg N ha(-1) as urea) and to calculate changes in the N pools of the overstory trees, understory vegetation, and soil. At six sites on production forests in the Hood Canal watershed, Washington, tension lysimeters and estimates of the soil water flux were used to quantify the mobilization and leaching of NO(3)-N, NH(4)-N, and dissolved organic nitrogen below the observed rooting depth. Soil and vegetation samples were collected before fertilization and 1 and 6 mo after fertilization. In the year after fertilization, the total leaching beyond the primary rooting zone in excess of control plots was 4.2 kg N ha(-1) (p = 0.03), which was equal to 2% of the total N applied. The peak NO(3)-N concentration that leached beyond the rooting zone of fertilized plots was 0.2 mg NO(3)-N L(-1). Six months after fertilization, 26% of the applied N was accounted for in the overstory, and 27% was accounted for in the O+A horizon of the soil. The results of this study indicate that forest fertilization can lead to small N leaching fluxes out of the primary rooting zone during the first year after urea application.     

Fertilizer use efficiency and nitrate leaching in a tropical sandy soil

Maize (Zea mays L.) production in the smallholder farming areas of Zimbabwe is based on both organic and mineral nutrient sources. A study was conducted to determine the effect of composted cattle manure, mineral N fertilizer, and their combinations on NO3 concentrations in leachate leaving the root zone and to establish N fertilization rates that minimize leaching. Maize was grown for three seasons (1996-1997, 1997-1998, and 1998-1999) in field lysimeters repacked with a coarse-grained sandy soil (Typic Kandiustalf). Leachate volumes ranged from 480 to 509 mm yr(-1) (1395 mm rainfall) in 1996-1997, 296 to 335 mm yr(-1) (840 mm rainfall) in 1997-1998, and 606 to 635 mm yr(-1) (1387 mm rainfall) in 1998-1999. Mineral N fertilizer, especially the high rate (120 kg N ha(-1)), and manure plus mineral N fertilizer combinations resulted in high NO3 leachate concentrations (up to 34 mg N L(-1)) and NO3 losses (up to 56 kg N ha(-1) yr(-1)) in 1996-1997, which represent both environmental and economic concerns. Although the leaching losses were relatively small in the other seasons, they are still of great significance in African smallholder farming where fertilizer is unaffordable for most farmers. Nitrate leaching from sole manure treatments was relatively low (average of less than 20 kg N ha(-1) yr(-1)), whereas the crop uptake efficiency of mineral N fertilizer was enhanced by up to 26% when manure and mineral N fertilizer were applied in combination. The low manure (12.5 Mg ha(-1)) plus 60 kg N ha(-1) fertilizer treatment was best in terms of maintaining dry matter yield and minimizing N leaching losses.     

Leaching and crop uptake of nitrogen from nitrogen-15-labeled green manures and ammonium nitrate

Green manures can be used as an N source for agricultural crops as a substitute for inorganic N fertilizers. The effects of using green manures on leaching and uptake of N by spring barley (Hordeum vulgare L.) were evaluated in a 2-yr lysimeter study. Ryegrass (Lolium perenne L.) and red clover (Trifolium pratense L.) labeled with (15)N were applied in May of the first year at 160 kg total N ha(-1). Simultaneously, (15)NH(4)(15)NO(3) was applied at 80 kg N ha(-1) to additional lysimeters and others were left without N additions (control). During the second year, all lysimeters, except the control, received 80 kg N ha(-1) as unlabeled NH(4)NO(3). The cumulative, average loads of total N leached during the two years were: 37 (control), 62 (NH(4)NO(3)), 50 (ryegrass manure), and 73 (red clover manure) kg ha(-1). The differences among the treatments were not significant (P > 0.05), but the control had significantly smaller (P < 0.05) leaching loads than the treatments. About 24% of ryegrass- and red clover-derived N and 43% of NH(4)NO(3) were removed through spring barley grain and stover during the two growing seasons. Thus, the N use efficiency in barley was substantially larger when grown with inorganic N fertilizer than when grown with green manure. Viewed in combination with the tendency for larger N leaching loads under red clover manure, claims about water quality benefits of legume-based green manures should be evaluated with regard to the timing of N release and demand for N by the plant.     

Effect of manure application timing, crop, and soil type on nitrate leaching

Timing of manure application affects N leaching. This 3-yr study quantified N losses from liquid manure application on two soils, a Muskellunge clay loam and a Stafford loamy sand, as affected by cropping system and timing of application. Dairy manure was applied at an annual rate of 93 800 L ha(-1) on replicated drained plots under continuous maize (Zea mays L.) in early fall, late fall, early spring, and as a split application in early and late spring. Variable rates of supplemental sidedress N fertilizer were applied as needed. Manure was applied on orchardgrass (Dactylis glomerata L.) in split applications in early fall and late spring, and early and late spring, with supplemental N fertilizer topdressed as NH4NO3 in early spring at 75 kg N ha(-1). Drain water was sampled at least weekly when lines were flowing. Three-year FWM (flow-weighted mean) NO3-N concentrations on loamy sand soil averaged 2.5 times higher (12.7 mg L(-1)) than those on clay loam plots (5.2 mg L(-1)), and those for fall applications on maize-cropped land averaged >10 mg L(-1) on the clay loam and >20 mg L(-1) on the loamy sand. Nitrate-N concentrations among application seasons followed the pattern early fall > late fall > early spring = early + late spring. For grass, average NO3-N concentrations from manure application remained well below 10 mg L(-1). Fall manure applications on maize show high NO3-N leaching risks, especially on sandy soils, and manure applications on grass pose minimal leaching concern.     

Integrated BIosphere Simulator (IBIS) yield and nitrate loss predictions for Wisconsin maize receiving varied amounts of nitrogen fertilizer

Agriculture in the U.S. Midwest faces the formidable challenge of improving crop productivity while simultaneously mitigating the environmental consequences of intense management. This study examined the simultaneous response of nitrate nitrogen (NO3-N) leaching losses and maize (Zea mays L.) yield to varied fertilizer N management using field observations and the Integrated BIosphere Simulator (IBIS) model. The model was validated against six years of field observations in chisel-plowed maize plots receiving an optimal (180 kg N ha(-1)) fertilizer N application and in N-unfertilized plots on a silt loam soil near Arlington, Wisconsin. Predicted values of grain yield, harvest index, plant N uptake, residue C to N ratio, leaf area index (LAI), grain N, and drainage were within 20% of observations. However, simulated NO3-N leaching losses, NO3-N concentrations, and net N mineralization exhibited less interannual variability than observations, and had higher levels of error (20-65%). Potential effects of 30% higher (234 kg N ha(-1)) and 30% lower (126 kg N ha(-1)) fertilizer N use (from optimal) on NO3-N leaching loss and maize yield were simulated. A 30% increase in fertilizer N use increased annual NO3-N leaching by 56%, while yield increased by only 1%. The NO3-N concentration in the leachate solution at 1.4 m below the soil surface was 30.7 mg L(-1). When fertilizer N use was reduced by 30% (from optimal), annual NO3-N leaching losses declined by 42% after seven years, and annual average yield only decreased by 8%. However, NO3-N concentration in the leachate solution remained above 10 mg L(-1) (11.3 mg L(-1)). Clearly, nonlinear relationships existed between changes in fertilizer use and NO3-N leaching losses over time. Simulated changes in NO3-N leaching were greater in magnitude than fertilizer N use changes.     

Biosolids application in the Chihuahuan desert: effects on runoff water quality

Surface-applied biosolids, the option most often used on range-lands, can increase the concentration of macronutrients and trace elements in the runoff water and can potentially produce eutrophication or contamination of surface waters. In this study, the effects of postapplication age of biosolids (18, 12, 6, and 0.5 mo) and rate of application (0, 7, 18, 34, and 90 Mg ha(-1)) on the quality of runoff water from shrubland and grassland soils were assessed. Between July and October 1996 simulated rainfall was applied to 0.50-m2 plots for 30 min at a rate of 160 mm h(-1). All of the runoff water was collected. The concentration of NH4+ -N, NO3- -N, PO4(3-)-P, total dissolved phosphorus (TDP), Cu, and Mn in the runoff water increased with rate of biosolids application and decreased with time of postapplication on the two soils. The highest PO4(3-)-P and NH4+ -N concentrations, 4.96 and 97 mg L(-1), respectively, were recorded in the grassland soil treated with 90 Mg ha(-1) of biosolids 0.5 mo postapplication. For the same soil, rate, and postapplication age of biosolids, Cu exceeded the upper limit (0.50 mg L(-1) in drinking water for livestock. Ammonium N and PO4(3-)-P should be the main compounds considered when surface-applying biosolids. Ammonium N at concentrations found in all biosolids-treated plots may affect the quality of livestock drinking water by causing taste and smell problems. Orthophosphate can contribute to eutrophication if the runoff from biosolids-treated areas enter surface waters.     

Pig slurry application and irrigation effects on nitrate leaching in Mediterranean soil lysimeters

Land application of animal manures, such as pig slurry (PS), is a common practice in intensive-farming agriculture. However, this practice has a pitfall consisting of the loss of nutrients, in particular nitrate, toward water courses. The objective of this study was to evaluate nitrate leaching for three application rates of pig slurry (50, 100, and 200 Mg ha(-1)) and a control treatment of mineral fertilizer (275 kg N ha(-1)) applied to corn grown in 10 drainage lysimeters. The effects of two irrigation regimes (low vs. high irrigation efficiency) were also analyzed. In the first two irrigation events, drainage NO(3)-N concentrations as high as 145 and 69 mg L(-1) were measured in the high and moderate PS rate treatments, respectively, in the low irrigation efficiency treatments. This indicates the fast transformation of the PS ammonium into nitrate and the subsequent leaching of the transformed nitrate. Drainage NO(3)-N concentration and load increased linearly by 0.69 mg NO(3)-N L(-1) and 4.6 kg NO(3)-N ha(-1), respectively, for each 10 kg N ha(-1) applied over the minimum of 275 kg N ha(-1). An increase in irrigation efficiency did not induce a significant increase of leachate concentration and the amount of nitrate leached decreased about 65%. Application of low PS doses before sowing complemented with sidedressing N application and a good irrigation management are the key factors to reduce nitrate contamination of water courses.     

Nitrogen and phosphorus leaching from growing season versus year-round application of wastewater on seasonally frozen lands

Land application of wastewater has become an important disposal option for food-processing plants operating year-round. However, there are concerns about nutrient leaching from winter wastewater application on frozen soils. In this study, P and N leaching were compared between nongrowing season application of tertiary-treated wastewater plus growing season application of partially treated wastewater (NGS) vs. growing season application of partially treated wastewater (GS) containing high levels of soil P. As required by the Minnesota Pollution Control Agency (MPCA), the wastewater applied to the NGS fields during October through March was treated such that it contained < or =6 mg L(-1) total phosphorus (TP), < or =10 mg L(-1) NO3-N, and < or =20 mg L(-1) total Kjeldahl nitrogen (TKN). The only regulation for wastewater application during the growing season (April through September) was that cumulatively it did not exceed the agronomic N requirements of the crop in any sprayfield. Application of tertiary-treated wastewater during the nongrowing season plus partially treated wastewater during the growing season did not significantly increase NO3-N leaching compared with growing season application of nonregulated wastewater. However, median TP concentration in leachate was significantly higher from the NGS (3.56 mg L(-1)) than from the GS sprayfields (0.52 mg L(-1)) or nonirrigated sites (0.52 mg L(-1)). Median TP leaching loss was also significantly higher from the NGS sprayfields (57 kg ha(-1)) than from the GS (7.4 kg ha(-1)) or control sites (6.9 kg ha(-1)). This was mainly due to higher hydraulic loading from winter wastewater application and limited or no crop P uptake during winter. Results from this study indicate that winter application of even low P potato-processing wastewater to high P soils can accelerate P leaching. We conclude that the regulation of winter wastewater application on frozen soils should be based on wastewater P concentration and permissible loading. We also recommend that winter irrigation should take soil P saturation into consideration.     

Nitrate exported in drainage waters of two sprinkler-irrigated watersheds

Nitrate contamination of surface waters has been linked to irrigated agriculture across the world. We determined the NO3-N loads in the drainage waters of two sprinkler-irrigated watersheds located in the Ebro River basin (Spain) and their relationship to irrigation and N management. Crop water requirements, irrigation, N fertilization, and the volume and NO3-N concentration of drainage waters were measured or estimated during two-year (Watershed A; 494 irrigated ha) and one-year (Watershed B; 470 irrigated ha) study periods. Maize (Zea mays L.) and alfalfa (Medicago sativa L.) were grown in 40 to 60% and 15 to 33% of the irrigated areas, respectively. The seasonal irrigation performance index (IPI) ranged from 92 to 100%, indicating high-quality management of irrigation. However, the IPI varied among fields and overirrigation occurred in 17 to 44% of the area. Soil and maize stalk nitrate contents measured at harvest indicated that N fertilizer rates could be decreased. Drainage flows were 68 mm yr(-1) in Watershed A and 194 mm yr(-1) in Watershed B. Drainage NO3-N concentrations were independent of drainage flows and similar in the irrigated and nonirrigated periods (average: 23-29 mg L(-1)). Drainage flows determined the exported mass of NO3-N, which varied from 18 (Watershed A) to 49 (Watershed B) kg ha(-1) yr(-1), representing 8 (Watershed A) and 22% (Watershed B) of the applied fertilizer plus manure N. High-quality irrigation management coupled to the split application of N through the sprinkler systems allowed a reasonable compromise between profitability and reduced N pollution in irrigation return flows.     

Monitoring nitrate leaching from submerged drains

Monitoring nitrate N (NO3-N) leaching is important in order to judge the effect that agricultural practices have on the quality of ground water and surface water. Measuring drain discharge rates and NO3-N concentrations circumvents the problem of spatial variability encountered by other methods used to quantify NO3-N leaching in the field. A new flow-proportional drainage water sampling method for submerged drains has been developed to monitor NO3-N leaching. Both low and high discharge rates can be measured accurately, and are automatically compensated for fluctuations in ditch-water levels. The total amount of NO3-N leached was 10.6 kg N ha(-1) for a tile-drained silt-loam soil during the 114-d monitoring period. The NO3-N concentrations fluctuated between 5 mg L(-1) at deep ground water levels and 15 mg L(-1) at shallow levels, due to variations in water flow. A flow-proportional drainage water sampling method is required to measure NO3-N leaching accurately under these conditions. Errors of up to 43% may occur when NO3-N concentrations in the drainage water are only measured at intervals of 30 d and when the precipitation excess is used to estimate cumulative NO3-N leaching. Measurements of NO3-N concentrations in ground water cannot be used to accurately estimate NO3-N leaching in drained soils.     

Tree species for recovering nitrogen from dairy-farm effluent in New Zealand

Land treatment of dairy-farm effluent is being widely adopted as an alternative to disposal into surface waters in New Zealand. This study investigated water balances and associated N leaching from short-rotation forest (SRF) species irrigated with dairy-farm effluent. Single trees were grown in lysimeters filled with Manawatu fine sandy loam (mixed mesic Dystric Eutrochrept). Dairy-farm effluent was applied during two irrigation periods at 21.5 mm wk(-1) with a total loading equivalent to 870 kg N ha(-1) occurring over 17 mo. Following tree harvest in April 1997, measurements continued until August 1997 to monitor tree reestablishment. Cumulative N leached did not differ between lysimeters in which evergreen Sydney blue gum (Eucalyptus saligna Sm.) and shining gum [Eucalyptus nitens (H. Deane & Maiden) Maiden] and deciduous kinu-yanagi (Salix kinuyanagi Kimura) were grown. Leachate N concentrations of all treatments were on average higher than the New Zealand drinking water standard of 11.3 mg N L(-1). The E. nitens and S. kinuyanagi treatments leached 33 and 35 kg N ha(-1) yr(-1) in 1996 following application of 236 kg N ha(-1) during the first irrigation season. Leaf area was strongly correlated to evapotranspiration, drainage volume, and nitrogen leached. The majority of leaching in the tree treatments occurred after harvest. Reducing the leaching in the regrowth phase may be achieved through timing harvest in the spring when growth rates are higher and leaching potential is lower. Based on N uptake rates observed in this study and average pond discharge, a plantation of 5.4 ha would be required for N recovery on a typical dairy farm in New Zealand.     

Leaching and crop uptake of nitrogen and phosphorus from pig slurry as affected by different application rates

The influence of increasing pig slurry applications on leaching and crop uptake of N and P by cereals was evaluated in a 3-yr study of lysimeters filled with a sandy soil. The slurry was applied at N rates of 50 (S50), 100 (S100), 150 (S150), and 200 (S200) kg ha(-1) during 2 of the 3 yr. The P rates applied with slurry were: 40 (S50), 80 (S100), 120 (S150), and 160 (S200) kg ha(-1) yr(-1). Simultaneously, NH4NO3 and Ca(H2PO4)2 were applied at rates of 100 kg N ha(-1) and 50 kg P ha(-1), respectively, to additional lysimeters (F100), while others were left unfertilized (F0). During the 3-yr period, the leaching load of total N tended to increase with increasing slurry application to, on average, 139 kg ha(-1) at the highest application rate (S200). The corresponding N leaching loads (kg ha(-1)) in the other treatments were: 75 (F0), 103 (F100), 93 (S50), 120 (S100), and 128 (S150). The loads of slurry-derived N in the S100, S150, and S200 treatments were significantly larger (P < 0.05) than those of fertilizer-derived N. In contrast, P leaching tended to decrease with increasing input of slurry, and it was lower in all treatments that received P at or above 50 kg P ha(-1) yr(-1) with slurry or fertilizer than in the unfertilized treatment. The crop use efficiency of added N and P was clearly higher when NH4NO3 and Ca(H2PO4)2 were used rather than slurry (60 vs. 35% for N, 38 vs. 6-9% for P), irrespective of slurry application rate. Therefore, from both a production and water quality point of view, inorganic fertilizers seem to have environmental benefits over pig slurry when used on sandy soils.     

Inputs and losses by surface runoff and subsurface leaching for pastures managed by continuous or rotational stocking

Pasture management practices can affect forage quality and production, animal health and production, and surface and groundwater quality. In a 5-yr study conducted at the North Appalachian Experimental Watershed near Coshocton, Ohio, we compared the effects of two contrasting grazing methods on surface and subsurface water quantity and quality. Four pastures, each including a small, instrumented watershed (0.51-1.09 ha) for surface runoff measurements and a developed spring for subsurface flow collection, received 112 kg N ha(-1) yr(-1) and were grazed at similar stocking rates (1.8-1.9 cows ha(-1)). Two pastures were continuously stocked; two were subdivided so that they were grazed with frequent rotational stocking (5-6 times weekly). In the preceding 5 yr, these pastures received 112 kg N ha(-1) yr(-1) after several years of 0 N fertilizer and were grazed with weekly rotational stocking. Surface runoff losses of N were minimal. During these two periods, some years had precipitation up to 50% greater than the long-term average, which increased subsurface flow and NO(3)-N transport. Average annual NO(3)-N transported in subsurface flow from the four watersheds during the two 5-yr periods ranged from 11.3 to 22.7 kg N ha(-1), which was similar to or less than the mineral-N received in precipitation. Flow and transport variations were greater among seasons than among watersheds. Flow-weighted seasonal NO(3)-N concentrations in subsurface flow did not exceed 7 mg L(-1). Variations in NO(3)-N leached from pastures were primarily due to variable precipitation rather than the effects of continuous, weekly rotational, or frequent rotational stocking practices. This suggests that there was no difference among these grazing practices in terms of NO(3)-N leaching.