SOIL-SOILN simulations of water drainage and nitrate nitrogen transport from soil core lysimeters

Water resources protection from nitrate nitrogen (NO3-N) contamination is an important public concern and a major national environmental issue. The abilities of the SOIL-SOILN model to simulate water drainage and nitrate N fluxes from orchardgrass (Dactylis glomerata L.) were evaluated using data from a 3-yr field experiment. The soil is classified as a Hagerstown silt loam soil (fine, mixed, semiactive, mesic Typic Hapludalf). Nitrate losses below the 1-m depth from N-fertilized grazed orchardgrass were measured with intact soil core lysimeters. Five N-fertilizer treatments consisted of a control, urine application in the spring, urine application in the summer, urine application in the fall, and feces application in the summer. The SOIL-SOILN models were evaluated using water drainage and nitrate flux data for 1993-1994, 1994-1995, and 1995-1996. The N rate constants from a similar experiment with inorganic fertilizer and manure treatments under corn (Zea mays L.) were used to evaluate the SOILN model under orchardgrass sod. Results indicated that the SOIL model accurately simulated water drainage for all three years. The SOILN model adequately predicted nitrate losses for three urine treatments in each year and a control treatment in 1994-1995. However, it failed to produce accurate simulations for two control treatments in 1993-1994 and 1995-1996, and feces treatments in all three years. The inaccuracy in the simulation results for the control and feces treatments seems to be related to an inadequate modeling of N transformation processes. In general, the results demonstrate the potential of the SOILN model to predict NO3-N fluxes under pasture conditions using N transformation rate constants determined through the calibration process from corn fields on similar soils.     

Low-disturbance manure incorporation effects on ammonia and nitrate loss

Low-disturbance manure application methods can provide the benefits of manure incorporation, including reducing ammonia (NH3) emissions, in production systems where tillage is not possible. However, incorporation can exacerbate nitrate (NO3?) leaching. We sought to assess the trade-offs in NH3 and NO3? losses caused by alternative manure application methods. Dairy slurry (2006-2007) and liquid swine manure (2008-2009) were applied to no-till corn by (i) shallow (<10 cm) disk injection, (ii) surface banding with soil aeration, (iii) broadcasting, and (iv) broadcasting with tillage incorporation. Ammonia emissions were monitored for 72 h after application using ventilated chambers and passive diffusion samplers, and NO3? leaching to 80 cm was monitored with buried column lysimeters. The greatest NH3 emissions occurred with broadcasting (35-63 kg NH3-N ha?), and the lowest emissions were from unamended soil (<1 kg NH-N ha?1). Injection decreased NH-N emissions by 91 to 99% compared with broadcasting and resulted in lower emissions than tillage incorporation 1 h after broadcasting. Ammonia-nitrogen emissions from banding manure with aeration were inconsistent between years, averaging 0 to 71% that of broadcasting. Annual NO3? leaching losses were small (<25 kg NO3-N ha?1) and similar between treatments, except for the first winter when NO3? leaching was fivefold greater with injection. Because NO3? leaching with injection was substantially lower over subsequent seasons, we hypothesize that the elevated losses during the first winter were through preferential flow paths inadvertently created during lysimeter installation. Overall, shallow disk injection yielded the lowest NH3 emissions without consistently increasing NO3? leaching, whereas manure banding with soil aeration conserved inconsistent amounts of N.     

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.     

Fate of nitrate and bromide in an unsaturated zone of a sandy soil under citrus production

Understanding water and nutrient transport through the soil profile is important for efficient irrigation and nutrient management to minimize excess nutrient leaching below the rootzone. We applied four rates of N (28, 56, 84, and 112 kg N ha(-1); equivalent to one-fourth of annual N rates being evaluated in this study for bearing citrus trees), and 80 kg Br- ha(-1) to a sandy Entisol with >25-yr-old citrus trees to (i) determine the temporal changes in NO3-N and Br- distribution down the soil profile (2.4 m), and (ii) evaluate the measured concentrations of NO3-N and Br- at various depths with those predicted by the Leaching Estimation and Chemistry Model (LEACHM). Nitrate N and Br concentrations approached the background levels by 42 and 214 d, respectively. Model-predicted volumetric water content and concentrations of NO3-N and Br- at various depths within the entire soil profile were very close to measured values. The LEACHM data showed that 21 to 36% of applied fertilizer N leached below the root zone, while tree uptake accounted for 40 to 53%. Results of this study enhance our understanding of N dynamics in these sandy soils, and provide better evaluation of N and irrigation management to improve uptake efficiency, reduce N losses, and minimize the risk of ground water nitrate contamination from soils highly vulnerable to nutrient leaching.     

Bromide and nitrate movement through undisturbed soil columns

Field experiments often assume that Br-, 14NO3(-)-N, and 15NO3(-)-N have similar leaching kinetics. This study tested this assumption. Twenty-four undisturbed soil columns (15-cm diameter) were collected from summit-shoulder, backslope, and footslope positions of a no-tillage field with a corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] rotation. Each of the landscape positions had a different soil series. After conditioning the columns with 4 L of 0.01 M CaCl2 (2 pore volumes), 15N-labeled Ca(NO3)2 and KBr were applied to the soil surface and leached with 4 L of 0.01 M CaCl2. Leachate was collected, weighed, and analyzed for NO3(-)-N, NH4(+)-N, 15N, 14N, and Br-. The total amount of 15NO3(-)-N and 14NO3(-)-N collected in 1000, 2000, and 3000 mL of leachate was similar. These data suggest that 15N discrimination during leaching did not occur. Bromide leached faster through the columns than NO3(-)-N. The more rapid transport of Br- than NO3(-)-N was attributed to lower Br- (0.002 +/- 0.036 mg kg(-1)) than NO3(-)-N (0.17 +/- 0.03 mg kg(-1)) sorption. Results from this study suggest that (i) if Br- is used to estimate NO3(-)-N leaching loss, then NO3(-)-N leaching losses may be overestimated by 25%; (ii) the potential exists for landscape position to influence anion retention and movement in soil; and (iii) 15N discrimination was not detected during the leaching process.     

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.     

Nitrogen fertilizer form and associated nitrate leaching from cool-season lawn turf

Various N fertilizer sources are available for lawn turf. Few field studies, however, have determined the losses of nitrate (NO(3)-N) from lawns receiving different formulations of N fertilizers. The objectives of this study were to determine the differences in NO(3)-N leaching losses among various N fertilizer sources and to ascertain when losses were most likely to occur. The field experiment was set out in a completely random design on a turf typical of the lawns in southern New England. Treatments consisted of four fertilizer sources with fast- and slow-release N formulations: (i) ammonium nitrate (AN), (ii) polymer-coated sulfur-coated urea (PCSCU), (iii) organic product, and (iv) a nonfertilized control. The experiment was conducted across three years and fertilized to supply a total of 147 kg N ha(-1) yr(-1). Percolate was collected with zero-tension lysimeters. Flow-weighted NO(3)-N concentrations were 4.6, 0.57, 0.31, and 0.18 mg L(-1) for AN, PCSCU, organic, and the control, respectively. After correcting for control losses, average annual NO(3)-N leaching losses as a percentage of N applied were 16.8% for AN, 1.7% for PCSCU, and 0.6% for organic. Results indicate that NO(3)-N leaching losses from lawn turf in southern New England occur primarily during the late fall through the early spring. To reduce the threat of NO(3)-N leaching losses, lawn turf fertilizers should be formulated with a larger percentage of slow-release N than soluble N.     

MEASURED AND CREAMS-PREDICTED NITROGEN LOSSES FROM TOMATO AND CORN MANAGEMENT SYSTEMS1

Nitrogen runoff and leaching losses from two tomato and four corn field plots were compared to model predictions by CREAMS, a field-scale model for Chemicals, Runoff, and Erosion from Agricultural Management Systems. The tomato treatments were (1) trickle irrigation with one-half of applied N at preplant and one-half of applied N through the trickle irrigation system and (2) overhead sprinkler irrigation with one-half of applied N at preplant and one-half of applied N in two equal sidedressings. The corn treatments consisted of multiple N applications, minimum tillage, and “conventional” management. Soil type appeared to influence the ability of CREAMS to predict seasonal trends and treatment influences. Model predictions for N losses from tomato and corn treatments that were located on sandy soils often disagreed with measured values. Treatment influences and seasonal trends for N losses from corn treatments that were located on a higher clay content soil were more satisfactorily predicted by CREAMS. Even though model input parameter estimation and measurement techniques may be imperfect, the simulation ability of CREAMS for predicting N leaching losses from systems on deep sands probably needs to be improved. Sensitivity analyses indicated that annual NC₃^?-N leaching loss predictions were either minimally or not affected by changes in saturated hydraulic conductivity. Input estimations of the fraction of soil pore space filled at field capacity and soil organic matter were inversely related to annual NO₃^?-N leaching losses, while potential mineralizable N was directly related to yearly N leaching losses.     

Fertilizer, tillage, and dairy manure contributions to nitrate and herbicide leaching

Few studies have examined the water quality impact of manure use in no-tillage systems. A lysimeter study in continuous corn (Zea mays L.) was performed on Maury silt loam (fine, mixed, semiactive, mesic Typic Paleudalf) to evaluate the effect(s) of tillage (no-till [NT] and chisel-disk [CD]), nitrogen fertilizer rate (0 and 168 kg N ha(-1)), and dairy manure application timing (none, spring, fall, or fall plus spring) on NO3-N, atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine), and alachlor [2-chloro-2'-6'-diethyl-N-(methoxymethyl)acetanilide] concentrations in leachate collected at a 90-cm depth. Herbicides were highest immediately after application, declining to less than 4 mug L(-1) in about two months. Manure and manure timing by tillage interactions had little effect on leachate herbicides; rather, the data suggest that macropores rapidly transmitted atrazine and alachlor through the soil. Tillage usually did not significantly affect leachate NO3-N, but no-tillage tended to cause higher NO(3)-N. Manuring caused higher NO3-N concentrations; spring manuring had more impact than fall, but fall manure contained about 78% of the N found in spring manure. Nitrate under spring "only fertilizer" treatment exceeded 10 mg L(-1) 38% of the time, compared with 15% for spring only manure treatment. After three years, manured soil leachate NO3-N exceeded that for soil receiving only N fertilizer. Soil profile (90 cm) NO3-N after corn harvest exceeding 22 kg N ha(-1) was associated with winter leachate NO3-N greater than 10 mg N L(-1). Manure can be used effectively in conservation tillage systems on this and similar soils. Accounting for all N inputs, including previous manure applications, will be important.     

Ryegrass cover crop effects on nitrate leaching in spring barley fertilized with 15NH415NO3

Cover crops are a management option to reduce NO3 leaching under cereal grain production. A 2-yr field lysimeter study was established in Uppsala, Sweden, to evaluate the effect of a perennial ryegrass (Lolium perenne L.) cover crop interseeded in barley (Hordeum vulgare L.) on NO3-N leaching and availability of N to the main crop. Barley and ryegrass or barley alone were seeded in mid-May 1992, in lysimeters (03-m diam. x 1.2-m depth) of an undisturbed, well-drained, sandy loam soil. Fertilizer N was applied at the same time as labeled l5NH415NO3 (10 atom % 15N) at a rate of 100 kg N ha(-1). In 1993, barley was reseeded in May in the lysimeters but with nonlabeled NH4NO3 and no cover crop (previous year's cover crop incorporated just prior to seeding). Barley yields and total and fertilizer N uptake in Year 1 (1992) were unaffected by cover crop. Total aboveground N uptake by the ryegrass was 28 kg ha(-1) at the time of incorporation the following spring. Recovery of fertilizer-derived N in May 1993 was about 100%; 53% in soil, 46% in barley, <2% in ryegrass, and negligible amounts in leachate. In May 1994, the corresponding figures were: 32% in soil, <3% in barley, and, again, negligible amounts in leachate. The cover crop reduced concentrations of NO3-N in the leachate considerably (<5 mg L(-1), compared with 10 to 18 mg L(-1) without cover crop) at most sampling times from November 1992 to April 1994, and reduced the total amount of NO3-N leached (22 compared with 8 kg ha(-1)).     

Residual soil nitrate after potato harvest

Nitrogen loss by leaching is a major problem, particularly with crops requiring large amounts of N fertilizer. We evaluated the effect of N fertilization and irrigation on residual soil nitrate following potato (Solanum tuberosum L.) harvests in the upper St-John River valley of New Brunswick, Canada. Soil nitrate contents were measured to a 0.90-m depth in three treatments of N fertilization (0, 100, and 250 kg N ha(-1)) at two on-farm sites in 1995, and in four treatments of N fertilization (0, 50, 100, and 250 kg N ha(-1)) at four sites for each of two years (1996 and 1997) with and without supplemental irrigation. Residual soil NO3-N content increased from 33 kg NO3-N ha(-1) in the unfertilized check plots to 160 kg NO3-N ha(-1) when 250 kg N ha(-1) was applied. Across N treatments, residual soil NO3-N contents ranged from 30 to 105 kg NO3-N ha(-1) with irrigation and from 30 to 202 kg NO3-N ha(-1) without irrigation. Residual soil NO3-N content within the surface 0.30 m was related (R2 = 0.94) to the NO3-N content to a 0.90-m depth. Estimates of residual soil NO3-N content at the economically optimum nitrogen fertilizer application (Nop) ranged from 46 to 99 kg NO3-N ha(-1) under irrigated conditions and from 62 to 260 kg NO3-N ha(-1) under nonirrigated conditions, and were lower than the soil NO3-N content measured with 250 kg N ha(-1). We conclude that residual soil NO3-N after harvest can be maintained at a reasonable level (<70 kg NO3-N ha(-1)) when N fertilization is based on the economically optimum N application.     

Long-term effects of sustained beef feedlot manure application on soil nutrients, corn silage yield, and nutrient uptake

A field study was initiated in 1992 to investigate the long-term impacts of beef feedlot manure application (composted and uncomposted) on nutrient accumulation and movement in soil, corn silage yield, and nutrient uptake. Two application strategies were compared: providing the annual crop nitrogen (N) requirement (N-based rate) or crop phosphorus (P) removal (P-based rate), as well as a comparison to inorganic fertilizer. Additionally, effects of a winter cover crop were evaluated. Irrigated corn (Zea mays L.) was produced annually from 1993 through 2002. Average silage yield and crop nutrient removal were highest with N-based manure treatments, intermediate with P-based manure treatments, and least with inorganic N fertilizer. Use of a winter cover crop resulted in silage yield reductions in four of ten years, most likely due to soil moisture depletion in the spring by the cover crop. However, the cover crop did significantly reduce NO3-N accumulation in the shallow vadose zone, particularly in latter years of the study. The composted manure N-based treatment resulted in significantly greater soil profile NO3-N concentration and higher soil P concentration near the soil surface. The accounting procedure used to calculate N-based treatment application rates resulted in acceptable soil profile NO3-N concentrations over the short term. While repeated annual manure application to supply the total crop N requirement may be acceptable for this soil for several years, sustained application over many years carries the risk of unacceptable soil P concentrations.     

Nitrogen- vs. phosphorus-based dairy manure applications to field crops: nitrate and phosphorus leaching and soil phosphorus accumulation

Management of animal manures to provide nutrients for crop growth has generally been based on crop N needs. However, because manures have a lower N/P ratio than most harvested crops, N-based manure management often oversupplies the crop-soil system with P, which can be lost into the environment and contribute to eutrophication of water bodies. We examined the effects of N- vs. P-based manure applications on N and P uptake by alfalfa (Medicago sativa L.), corn (Zea mays L.) for silage, and orchardgrass (Dactylis glomerata L.), leaching below the root zone, and accumulation of P in soil. Treatments included N- and P-based manure rates, with no nutrient input controls and inorganically fertilized plots for comparison. Nitrate concentrations in leachate from inorganic fertilizer or manure treatments averaged 14 mg NO(3)-N L(-1), and did not differ by nutrient treatment. Average annual total P losses in leachate did not exceed 1 kg ha(-1). In the top 5 cm of soil in plots receiving the N-based manure treatment, soil test P increased by 47%, from 85 to 125 mg kg(-1). Nitrogen- and P-based manure applications did not differ in ability to supply nutrients for crop growth, or in losses of nitrate and total P in leachate. However, the N-based manure led to significantly greater accumulation of soil test P in the surface 5 cm of soil. Surface soil P accumulation has implications for increased risk of off-field P movement.     

Evaluation of simulated strategies for reducing nitrate-nitrogen losses through subsurface drainage systems

The nitrates (NO(3)-N) lost through subsurface drainage in the Midwest often exceed concentrations that cause deleterious effects on the receiving streams and lead to hypoxic conditions in the northern Gulf of Mexico. The use of drainage and water quality models along with observed data analysis may provide new insight into the water and nutrient balance in drained agricultural lands and enable evaluation of appropriate measures for reducing NO(3)-N losses. DRAINMOD-NII, a carbon (C) and nitrogen (N) simulation model, was field tested for the high organic matter Drummer soil in Indiana and used to predict the effects of fertilizer application rate and drainage water management (DWM) on NO-N losses through subsurface drainage. The model was calibrated and validated for continuous corn (Zea mays L.) (CC) and corn-soybean [Glycine max (L.) Merr.] (CS) rotation treatments separately using 7 yr of drain flow and NO(3)-N concentration data. Among the treatments, the Nash-Sutcliffe efficiency of the monthly NO(3)-N loss predictions ranged from 0.30 to 0.86, and the percent error varied from -19 to 9%. The medians of the observed and predicted monthly NO(3)-N losses were not significantly different. When the fertilizer application rate was reduced ~20%, the predicted NO(3)-N losses in drain flow from the CC treatments was reduced 17% (95% confidence interval [CI], 11-25), while losses from the CS treatment were reduced by 10% (95% CI, 1-15). With DWM, the predicted average annual drain flow was reduced by about 56% (95% CI, 49-67), while the average annual NO(3)-N losses through drain flow were reduced by about 46% (95% CI, 32-57) for both tested crop rotations. However, the simulated NO(3)-N losses in surface runoff increased by about 3 to 4 kg ha(-1) with DWM. For the simulated conditions at the study site, implementing DWM along with reduced fertilizer application rates would be the best strategy to achieve the highest NO(3)-N loss reductions to surface water. The suggested best strategies would reduce the NO(3)-N losses to surface water by 38% (95% CI, 29-46) for the CC treatments and by 32% (95% CI, 23-40) for the CS treatments.     

EPIC tile flow and nitrate loss predictions for three Minnesota cropping systems

Subsurface tile drains are a key source of nitrate N (NO3-N) losses to streams in parts of the north central USA. In this study, the Erosion Productivity Impact Calculator (EPIC) model was evaluated by comparing measured vs. predicted tile flow, tile NO3-N loss, soil profile residual NO3-N, crop N uptake, and yield, using 4 yr of data collected at a site near Lamberton, MN, for three crop rotations: continuous corn (Zea mays L.) or CC, corn-soybean [Glycine max (L.) Merr.] or CS, and continuous alfalfa (Medicago sativa L.) or CA. Initially, EPIC was run using standard Soil Conservation Service (SCS) runoff curve numbers (CN2) for CC and CS; monthly variations were accurately tracked for tile flow (r2 = 0.86 and 0.90) and NO3-N loss (r2 = 0.69 and 0.52). However, average annual CC and CS tile flows were underpredicted by -32 and -34%, and corresponding annual NO3-N losses were underpredicted by -11 and -52%. Predicted average annual tile flows and NO3-N losses generally improved following calibration of the CN2; tile flow underpredictions were -9 and - 12%, whereas NO3-N losses were 0.6 and -54%. Adjusting a N parameter further improved predicted CS NO3-N losses. Predicted monthly tile flows and NO3-N losses for the CA simulation compared poorly with observed values (r2 values of 0.27 and 0.19); the annual drainage volumes and N losses were of similar magnitude to those measured. Overall, EPIC replicated the relative impacts of the three cropping systems on N fate.     

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.     

Nitrate losses in subsurface drainage from a corn-soybean rotation as affected by fall and spring application of nitrogen and nitrapyrin

Substantial amounts of NO3 from agricultural crop production systems on poorly drained soils can be transported to surface water via subsurface drainage. A field study was conducted from the fall of 1993 through 2000 on a tile-drained Canisteo clay loam soil (fine-loamy, mixed, superactive, calcareous, mesic Typic Endoaquoll) to determine the influence of fall vs. spring application of N and nitrapyrin [NP; 2-chloro-6-(trichloromethyl) pyridine] on NO3 losses from a corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] rotation. Four anhydrous ammonia treatments (fall N, fall N + NP, spring preplant N, and spring N + NP) were replicated four times and applied at 135 kg N ha(-1) for corn on individual drainage plots. Drainage occurred in all seven years. Seventy-one percent of the annual drainage and 75% of the annual NO3 loss occurred in April, May, and June. Fifty-four percent of the NO3 lost in the drainage occurred during the corn phase and 46% during the soybean phase. Annual flow-weighted NO3-N concentrations for the fall, fall + NP, spring, and spring + NP treatments averaged 14.3, 11.5, 10.7, and 11.3 mg L(-1) during the corn phase but annual NO3-N concentrations were still > or =10 mg L(-1) in three of six years for the spring preplant treatment. Averaged across the six rotation cycles, flow-normalized NO3-N losses ranked in the order: fall N > spring N + NP > fall N + NP > spring N. Under these conditions, NO3 losses in subsurface drainage from a corn-soybean rotation can be reduced 14% by spring N and 10% by late fall N + NP compared with fall-applied N. Nitrate losses were not appreciably reduced by adding NP to spring preplant N.     

Testing soils and cornstalks to evaluate nitrogen management on the watershed scale

High nitrate (NO3-N) concentrations in Iowa rivers have been linked to areas of intensive row crop production, but they have not been experimentally linked to specific management practices used during row crop production. This study demonstrates how the late-spring test for soil NO3-N and the end-of-season test for cornstalk NO3-N can be used to measure N sufficiency levels across many fields and how the results can be used to evaluate management practices within a watershed. More than 3200 soil and cornstalk samples were collected over a 12-yr period from fields planted to corn (Zea mays L.) and already fertilized by farmers using their normal practices. Results showed that early-season rainfall and associated N losses were major factors affecting N concentrations in soils and cornstalks. Evidence for NO3-N movement from fields to rivers was provided by an inverse relationship between annual means for NO3-N concentrations in soils and rivers. Because these losses can be avoided by delaying N applications, the practice of applying N several weeks or months before plants grow was linked to inefficient use of fertilizer and manure N by crops. Results of the study demonstrate how aggregate analyses of soil and cornstalk samples collected across many farms and years make it possible to identify the major factors affecting N management outcomes and, therefore, N management practices that are likely to produce the best outcomes within a watershed or region. This approach seems to have unique potential to interrelate the management practices of farmers, the efficiency of N fertilization, and NO3-N concentrations in rivers.     

Nitrate and chloride loading to groundwater from an irrigated north-central U.S. sand-plain vegatable field

Groundwater pollution and associated effects on drinking water have increased with the expansion of irrigated agriculture in north-central U.S. sand plains. Controlling this pollution requires an ability to measure and predict pollutant loading by specific agricultural systems. We measured NO3 and Cl loading to groundwater beneath a Wisconsin central sand plain irrigated vegetable field using both a budget method and a new monitoring-based method. By relying on frequent monitoring of shallow groundwater, the new method overcomes some limitations of other methods. Monitoring-based and budget methods agreed well, and indicated that loading to groundwater was 165 kg ha(-1) NO3-N and 111 kg ha(-1) Cl for sweet corn (Zea mays L.) in 1992, and 228 kg ha(-1) NO3-N and 366 kg ha(-1) Cl for potato (Solanum tuberosum L.) in 1993. Nitrate N loading was 56 to 60% of available N, or 66 to 70% of fertilizer N. Sweet corn NO3 loading was about typical for this region, but potato NO3 loading was probably 50% greater than typical because heavy rains provoked extra fertilizer application. Our results imply that typical NO3-N loading would be 119 kg ha(-1) for sweet corn and 203 kg ha(-1) for potato, even with strict adherence to University Extension fertilizer recommendations. To keep average groundwater NO3-N within the 10 mg L(-1) U.S. drinking water standard, each irrigated vegetable field would need to be offset by five to eight times as much land supplying NO3-free groundwater recharge.