Role of organic matter in microbial transport during irrigation with sewage effluent

Reduction of migration of fecal coliforms (FC) and streptococci (FS) by limiting the leaching in effluent-irrigated soil was tested in lysimeters packed with quartz sand without or with added biosolids compost or with one of two clayey soils. The 200-L, 70-cm-deep lysimeters were either planted with a Eucalyptus camaldulensis or an Oroblanco citrus tree (in the sand only), or not planted. The Eucalyptus was irrigated with oxidation pond effluent (OPE) and the Oroblanco with mechanical-biological treatment plant effluent (MBTPE). The leaching fraction (LF) ranged from 0.2 to about 1.0, and the residence time (RT) from under 1 to 40 d. The Eucalyptus was also tested under intermittent leaching (RT 11-20 d) and deficit irrigation (without leaching for about 6 mo) regimes. Under MBTPE irrigation there was little or no leaching of FC and FS. Under OPE irrigation at LF 1 without a Eucalyptus there was little or no bacterial leaching at irrigation rates below 40 L d(-1) per lysimeter (RT > or = 0.8 d). Bacterial counts in the leachate were substantial in the presence of a Eucalyptus tree under LF 0.2 and intermittent leaching regimes, and when sand-packed unplanted lysimeters received OPE effluent at >45 L d(-1). Bacterial recovery peaked at LF 0.2, at up to 45% of the input level. At LF 1 (RT 0.6-2.8 d) and with intermittent leaching the recoveries were minute. Bacterial counts in the washout from the deficit-irrigated lysimeters were typical of nonpolluted soils. The bacterial concentration and recovery patterns in the leachate mostly matched the organic carbon (OC) load in the irrigation water, and its concentration and bioavailablity in the leachate. We related the leaching patterns of the fecal bacteria to their relative reproduction and die-off rates, and to the dependence of their regrowth on available carbon sources.     

Monitoring of nitrate leaching in sandy soils: comparison of three methods

Proper N fertilizer and irrigation management can reduce nitrate leaching while maintaining crop yield, which is critical to enhance the sustainability of vegetable production on soils with poor water and nutrient-holding capacities. This study evaluated different methods to measure nitrate leaching in mulched drip-irrigated zucchini, pepper, and tomato production systems. Fertigation rates were 145 and 217 kg N ha(-1) for zucchini; 192 and 288 kg N ha(-1) for pepper; and 208 and 312 kg N ha(-1) for tomato. Irrigation was either applied at a fixed daily rate or based on threshold values of soil moisture sensors placed in production beds. Ceramic suction cup lysimeters, subsurface drainage lysimeters and soil cores were used to access the interactive effects of N rate and irrigation management on N leaching. Irrigation treatments and N rate interaction effects on N leaching were significant for all crops. Applying N rates in excess of standard recommendations increased N leaching by 64, 59, and 32%, respectively, for pepper, tomato, and zucchini crops. Independent of the irrigation treatment or nitrogen rate, N leaching values measured from the ceramic cup lysimeter-based N leaching values were lower than the values from the drainage lysimeter and soil coring methods. However, overall nitrate concentration patterns were similar for all methods when the nitrate concentration and leached volume were relatively low.     

Land application of domestic effluent onto four soil types: plant uptake and nutrient leaching

Land application has become a widely applied method for treating wastewater. However, it is not always clear which soil-plant systems should be used, or why. The objectives of our study were to determine if four contrasting soils, from which the pasture is regularly cut and removed, varied in their ability to assimilate nutrients from secondary-treated domestic effluent under high hydraulic loadings, in comparison with unirrigated, fertilized pasture. Grassed intact soil cores (500 mm in diameter by 700 mm in depth) were irrigated (50 mm wk(-1)) with secondary-treated domestic effluent for two years. Soils included a well-drained Allophanic Soil (Typic Hapludand), a poorly drained Gley Soil (Typic Endoaquept), a well-drained Pumice Soil formed from rhyolitic tephra (Typic Udivitrand), and a well-drained Recent Soil formed in a sand dune (Typic Udipsamment). Effluent-irrigated soils received between 746 and 815 kg N ha(-1) and 283 and 331 kg P ha(-1) over two years of irrigation, and unirrigated treatments received 200 kg N ha(-1) and 100 kg P ha(-1) of dissolved inorganic fertilizer over the same period. Applying effluent significantly increased plant uptake of N and P from all soil types. For the effluent-irrigated soils plant N uptake ranged from 186 to 437 kg N ha(-1) yr(-1), while plant P uptake ranged from 40 to 88 kg P ha(-1) yr(-1) for the effluent-irrigated soils. Applying effluent significantly increased N leaching losses from Gley and Recent Soils, and after two years ranged from 17 to 184 kg N ha(-1) depending on soil type. Effluent irrigation only increased P leaching from the Gley Soil. All P leaching losses were less than 49 kg P ha(-1) after two years. The N and P leached from effluent treatments were mainly in organic form (69-87% organic N and 35-65% unreactive P). Greater N and P leaching losses from the irrigated Gley Soil were attributed to preferential flow that reduced contact between the effluent and the soil matrix. Increased N leaching from the Recent Soil was the result of increased leaching of native soil organic N due to the higher hydraulic loading from the effluent irrigation.     

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.     

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.     

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.     

In situ measurements of nitrate leaching implicate poor nitrogen and irrigation management on sandy soils

Minimizing the risk of nitrate contamination along the waterways of the U.S. Great Plains is essential to continued irrigated corn production and quality water supplies. The objectives of this study were to quantify nitrate (NO(3)) leaching for irrigated sandy soils (Pratt loamy fine sand [sandy, mixed, mesic Lamellic Haplustalfs]) and to evaluate the effects of N fertilizer and irrigation management strategies on NO(3) leaching in irrigated corn. Two irrigation schedules (1.0x and 1.25x optimum) were combined with six N fertilizer treatments broadcast as NH(4)NO(3) (kg N ha(-1)): 300 and 250 applied pre-plant; 250 applied pre-plant and sidedress; 185 applied pre-plant and sidedress; 125 applied pre-plant and sidedress; and 0. Porous-cup tensiometers and solution samplers were installed in each of the four highest N treatments. Soil solution samples were collected during the 2001 and 2002 growing seasons. Maximum corn grain yield was achieved with 125 or 185 kg N ha(-1), regardless of the irrigation schedule (IS). The 1.25x IS exacerbated the amount of NO(3) leached below the 152-cm depth in the preplant N treatments, with a mean of 146 kg N ha(-1) for the 250 and 300 kg N preplant applications compared with 12 kg N ha(-1) for the same N treatments and 1.0x IS. With 185 kg N ha(-1), the 1.25x IS treatment resulted in 74 kg N ha(-1) leached compared with 10 kg N ha(-1) for the 1.0x IS. Appropriate irrigation scheduling and N fertilizer rates are essential to improving N management practices on these sandy soils.     

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.     

Soil water nitrate and ammonium dynamics under a sewage effluent irrigated eucalypt plantation

Managed forests and plantations are appropriate ecosystems for land-based treatment of effluent, but concerns remain regarding nutrient contamination of ground- and surface waters. Monthly NO3-N and NH4-N concentrations in soil water, accumulated soil N, and gross ammonification and nitrification rates were measured in the second year of a second rotation of an effluent irrigated Eucalyptus globulus plantation in southern Western Australia to investigate the separate and interactive effects of drip and sprinkler irrigation, effluent and water irrigation, irrigation rate, and harvest residues retention. Nitrate concentrations of soil water were greater under effluent irrigation than water irrigation but remained <15 mg L(-1) when irrigated at the normal rate (1.5-2.0 mm d(-1)), and there was little evidence of downward movement. In contrast, NH4-N concentrations of soil water at 30 and 100 cm were generally greater under effluent irrigation than water irrigation when irrigated at the normal rate because of direct effluent NH4-N input and indirect ammonification of soil organic N. Drip irrigation of effluent approximately doubled peak NO3-N and NH4-N concentrations in soil water. Harvest residue retention reduced concentrations of soil water NO3-N at 30 cm during active sprinkler irrigation, but after 1 yr of irrigation there was no significant difference in the amount of N stored in the soil system, although harvest residue retention did enhance the "nitrate flush" in the following spring. Gross mineralization rates without irrigation increased with harvest residue retention and further increased with water irrigation. Irrigation with effluent further increased gross nitrification to 3.1 mg N kg(-1) d(-1) when harvest residues were retained but had no effect on gross ammonification, which suggested the importance of heterotrophic nitrification. The downward movement of N under effluent irrigation was dominated by NH4-N rather than NO3-N. Improving the capacity of forest soils to store and transform N inputs through organic matter management must consider the dynamic equilibrium between N input, uptake, and immobilization according to soil C status, and the effect changing microbial processes and environmental conditions can have on this equilibrium.     

Nitrate leaching beneath a containerized nursery crop receiving trickle or overhead irrigation

Container production of nursery crops is intensive and a potential source of nitrogen release to the environment. This study was conducted to determine if trickle irrigation could be used by container nursery producers as an alternative to standard overhead irrigation to reduce nitrogen release into the environment. The effect of overhead irrigation and trickle irrigation on leachate nitrate N concentration, flow-weighted nitrate N concentration, leachate volume, and plant growth was investigated using containerized rhododendron (Rhododendron catawbiense Michx. 'Album') supplied with a controlled-release fertilizer and grown outdoors on top of soil-monolith lysimeters. Leachate was collected over two growing seasons and overwinter periods, and natural precipitation was allowed as a component of the system. Precipitation accounted for 69% of the water entering the overhead-irrigated system and 80% of the water entering the trickle-irrigated system. Leachate from fertilized plants exceeded the USEPA limit of 10 mg L(-1) at several times and reached a maximum of 26 mg L(-1) with trickle irrigation. Average annual loss of nitrate N in leachate for fertilized treatments was 51.8 and 60.5 kg ha(-1) for the overhead and trickle treatments, respectively. Average annual flow-weighted concentration of nitrate N in leachate of fertilized plants was 7.2 mg L(-1) for overhead irrigation and 12.7 mg L(-1) for trickle irrigation. Trickle irrigation did not reduce the amount of nitrate N leached from nursery containers when compared with overhead irrigation because precipitation nullified the potential benefits of reduced leaching fractions and irrigation inputs provided under trickle irrigation.     

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.     

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)).     

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.     

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.     

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.     

Nitrate leaching and turf quality in established 'Floratam' St. Augustinegrass and 'Empire' zoysiagrass

The objectives of this research were to evaluate nitrate N (NO3-N) leaching and turf response to nitrogen rate (NR) and irrigation regime (IR) in 'Floratam' St. Augustinegrass ( [Walt.] Kuntze.) and 'Empire' zoysiagrass ( Steud). The research was conducted in Citra, FL, from 2005 through 2007. Nitrogen (N) was applied at annual rates of 32, 64, 128, and 196 kg ha?1 in 2005, and at 49, 196, 343, or 490 kg ha?1 in 2006 and 2007. Irrigation treatments consisted of 1.3 cm applied twice weekly or 2.6 cm applied once weekly. In general, NO?-N leaching was greater from zoysiagrass. In 2007, annual NO?-N leached varied due to the interaction of NR, IR, and grass. There was little association between NR and increased NO?-N leaching in St. Augustinegrass in any year. While St. Augustinegrass had no differences in NO?-N leached within NR due to IR, there were some differences in NO?-N leached from zoysiagrass at some N levels, with greater NO?-N leached from the more frequent irrigation regime. Turf quality (TQ) was generally above an acceptable level in St. Augustinegrass at all but the lowest NRs and at all NRs in zoysiagrass with the exception of the spring fertilizer cycle (SFC) in 2007, when high NR treatments resulted in disease. Maintenance of a healthy turfgrass cover is an important strategy for reducing potential nutrient movement from fertilizer application. The current recommended rates for St. Augustinegrass provide good turf cover and health, and result in minimal NO?-N leaching. Zoysiagrass N rates may need to be revised downward to reduce disease, improve turf cover, and reduce NO?-N leaching.     

Nitrogen and carbon leaching in agroecosystems and their role in denitrification potential

The drainage of water and leaching of dissolved constituents represent major components of agroecosystem mass budgets that have been exceedingly difficult to measure. Equilibrium-tension lysimeters (ETLs) were used to monitor drainage, nitrogen (N), and carbon (C) leaching through Plano silt loam (fine-silty, mixed, superactive, mesic Typic Argiudoll) for a 4-yr period in a restored prairie and N-fertilized no-tillage and chisel-plowed maize (Zea mays L.) agroecosystems. Mean drainage recorded during 4 yr for the prairie, no-tillage, and chisel-plowed ecosystems totaled 461, 1,116, and 1,575 mm and represented 16, 33, and 47% of precipitation plus melting of drifted snow received, respectively. Total inorganic N leaching losses during the 4-yr period for the prairie, no-tillage, and chisel-plowed ecosystems were 0.6, 201, and 179 kg N ha(-1), respectively. Inorganic N leaching represented 26 and 24% of applied fertilizer N additions to the no-tillage and chisel-plowed agroecosystems. Total dissolved C leaching losses were 119, 435, and 502 kg C ha(-1) for the prairie, no-tillage, and chisel-plowed ecosystems, respectively. Sufficient dissolved organic carbon (DOC) and nitrate N (NO3- -N) existed in the prairie and agroecosystems to support subsoil denitrification. Potential denitrification, however, was limited by insufficient lengths of saturated soil conditions in all three ecosystems, the supply of DOC in the agroecosystems, and the supply of nitrate N in the prairie. Based on available DOC and nitrate N, the maximum contribution of denitrification below the root zone in the agroecosystems was less than 25% of the total amount of leached nitrate N and the probable contribution of denitrification was much less.     

Fertilizer residence time affects nitrogen uptake efficiency and growth of sweet corn

Understanding plant N uptake dynamics is critical for increasing fertilizer N uptake efficiency (FUE) and minimize the risk of N leaching. The objective of this research was to determine the effect of residence time of N fertilizer on N uptake and FUE of sweet corn. Plants were grown in 25 L columns during the fall and spring to mimic short-term N uptake dynamics. Nitrogen was applied either 1, 3, or 7 d before a weekly leaching event, using KNO3 solution (total of 393 kg N ha(-1)). Residence times (tR) were tR-1, tR-3, and tR-7 d before weekly removal of residual soil N. Plant N uptake was calculated by comparing weekly N recovery from planted with non-planted columns. During the fall, N uptake values at 70 d after emergence were 59, 73, and 126 kg N ha(-1). During the spring, corresponding values were 54, 108, and 159 kg N ha(-1). A linear response of plant growth and yield to the tR was observed under cooler conditions, whereas a quadratic response occurred under warmer conditions. There was correlation between root length density and yield. It is concluded that increasing N fertilizer residence time, which is indicative of better irrigation practices, enhanced overall sweet corn growth, yield, N uptake, and FUE, consequently reduced the risk of N being leached below the root zone before complete N uptake.     

Nitrogen removal and nitrate leaching for forage systems receiving dairy effluent

Florida dairies need year-round forage systems that prevent loss of N to ground water from waste effluent sprayfields. Our purpose was to quantify forage N removal and monitor nitrate N (NO3(-)-N) concentrations in soil water below the rooting zone for two forage systems during four 12-mo cycles (1996-2000). Soil in the sprayfield is an excessively drained Kershaw sand (thermic, uncoated Typic Quartzipsamment). Over four cycles, average loading rates of effluent N were 500, 690, and 910 kg ha(-1) per cycle. Nitrogen removed by the bermudagrass (Cynodon spp.)-rye (Secale cereale L.) system (BR) during the first three cycles was 465 kg ha(-1) per cycle for the low loading rate, 528 kg ha(-1) for the medium rate, and 585 kg ha(-1) for the high. For the corn (Zea mays L.)-forage sorghum [Sorghum bicolor (L.) Moench]-rye system (CSR), N removals were 320 kg ha(-1) per cycle for the low rate, 327 kg ha(-1) for the medium, and 378 kg ha(-1) for the high. The higher N removals for BR were attributed to higher N concentration in bermudagrass (18.1-24.2 g kg(-1)) than in corn and forage sorghum (10.3-14.7 g kg(-1)). Dry matter yield declined in the fourth cycle for bermudagrass but N removal continued to be higher for BR than CSR. The BR system was much more effective at preventing NO3(-)-N leaching. For CSR, NO3(-)-N levels in soil water (1.5 m below surface) increased steeply during the period between the harvest of one forage and canopy dosure of the next. Overall, the BR system was better than CSR at removing N from the soil and maintaining low NO3(-)-N concentrations below the rooting zone.     

The relationship between milk production and farm-gate nitrogen surplus for the Waikato region, New Zealand

As the scope and scale of New Zealand (NZ) dairy farming increases, farmers and the industry are being challenged by Government and the New Zealand public to address growing environmental concerns. Dairying has come under increasing scrutiny from local authorities tasked with sustainable resource management. Despite recent efforts of farmers and industry to improve resource use efficiency, there is increasing likelihood of further regulatory constraints on water use and nutrient management. This study uses available data on farm-gate nitrogen (N) surpluses and milk production from the Waikato, New Zealand's largest dairying region, together with a farm scale modeling exercise, to provide a perspective on the current situation compared to dairy farms in Europe. It also aims to provide relevant guidelines for N surpluses and efficiencies under NZ conditions. Waikato dairy farms compare favorably with farms in Europe in terms of N use efficiency expressed as L milk/kg farm-gate N surplus. Achievable and realistic good practice objectives for Waikato dairy farmers could be 15,000 L milk/ha (1200 kg milk fat plus protein/ha) with a farm-gate N surplus of 100 kg/ha giving an eco-efficiency (L milk/kg N surplus) of 150, and long-term average nitrate leaching losses of approximately 25-30 kg/ha/yr. This can be achieved by increasing the N conversion efficiency through lower replacement rates (16 versus 22%), lower stocked (< 3 cows/ha) high genetic merit cows (30 L milk/day at peak) milked for longer (277 versus 240 days), feeding effluent-irrigated, home-grown, low-protein supplements to cows on high-protein, grass-clover pastures to dilute N concentration in the diet, removing some of the urinary N from the paddocks during critical times by standing cows on a loafing pad for part of the day, and through lower N fertilizer rates (50-70 kg/ha/yr compared to the norm of 170-200 kg/ha/yr) and using a nitrification inhibitor and gibberellins to boost pasture growth and the former to reduce N leaching.