The Effect of Moderate Salinity on Nitrate Leaching from Bermudagrass Turf: A Lysimeter Study

A column lysimeter study was conducted under greenhouse conditions to determine the impact of moderately saline irrigation water on NO₃ leaching from turfgrass. Bermudagrass (Cynodon dactylon L. ‘NuMex Sahara’) was fertilized at three N levels (25, 50 and 75 kg NH₄NO₃-N ha^?1 month^?1) and irrigated with saline water (0, 3.0 and 6.0 dS m^?1) in a factorial arrangement. Leachate was analyzed for salinity and NO₃, and clippings were collected and analyzed for total N. Nitrate leaching was not affected by either N level or salinity. Nitrate concentrations in the leachate were low, averaging approximately 0.3 mg N L^?1; less than 1% of the applied N leached. Longer-term N allocation to leaf growth accounted for up to 98% of applied N, whereas short-term allocation, determined using ¹⁵N, ranged from 46–67%. Salinity had no affect on clipping yield, the biomass of root and verdure, or root distribution. These data indicate the potential for moderately saline irrigation water to be used on bermudagrass turf without increasing NO₃ contamination of groundwater, as long as leaching is adequate to prevent rootzone salinity reaching damaging levels.     

Nitrogen fertilization and nitrate leaching into groundwater on arable sandy soils

Nitrate leaching depending on N fertilization and different crop rotations was studied at two sites with sandy soils in N Germany between 1995 and 2000. The leaching of NO was calculated by using a numerical soil‐water and N model and regularly measured N_min values as input data. Also the variability of N_min values on the sandy soils was determined along transects. They reveal the high variability of the N_min values and show that it is not possible to confirm a significant N_min difference between fertilizer treatments using the normal N_min‐sampling intensity. Nitrate‐leaching calculations of five leaching periods showed that even strongly reduced N‐fertilizer applications did not result in a substantially lower NO leaching into the groundwater. Strong yield reductions of even more than 50%, however, were immediately measured. Mean NO concentrations in the groundwater recharge are >50 mg L^–1 and are mainly due to mineralization from soil organic matter. Obviously, the adjustment of the N cycle in the soil to a new equilibrium and a reduced NO ‐leaching rate as a consequence of lower N inputs need a much longer time span. Catch crops are the most efficient way to reduce the NO concentrations in the groundwater recharge of sandy soils. Their success, however, strongly depends on the site‐specific development possibilities of the catch crop. Even with all possible measures implemented, it will be almost impossible to reach NO concentrations <50 mg L^–1 in sandy soils. The only way to realize this goal on a regional scale could be by increasing areas with lower nitrate concentrations in the groundwater recharge like grassland and forests.     

The use of a nitrification inhibitor, dicyandiamide (DCD), to decrease nitrate leaching and nitrous oxide emissions in a simulated grazed and irrigated grassland

Abstract. In grazed dairy pasture systems, a major source of NO₃^– leached and N₂O emitted is the N returned in the urine from the grazing animal. The objective of this study was to use lysimeters to measure directly the effectiveness of a nitrification inhibitor, dicyandiamide (DCD), in decreasing NO₃^– leaching and N₂O emissions from urine patches in a grazed dairy pasture under irrigation. The soil was a free‐draining Lismore stony silt loam (Udic Haplustept loamy skeletal) and the pasture was a mixture of perennial ryegrass (Lolium perenne) and white clover (Trifolium repens). The use of DCD decreased NO₃^–‐N leaching by 76% for the urine N applied in the autumn, and by 42% for urine N applied in the spring, giving an annual average reduction of 59%. This would reduce the NO₃^–‐N leaching loss in a grazed paddock from 118 to 46 kg N ha^–1 yr^–1. The NO₃^–‐N concentration in the drainage water would be reduced accordingly from 19.7 to 7.7 mg N L^–1, with the latter being below the drinking water guideline of 11.3 mg N L^–1. Total N₂O emissions following two urine applications were reduced from 46 kg N₂O‐N ha^–1 without DCD to 8.5 kg N₂O‐N with DCD, representing an 82% reduction. In addition to the environmental benefits, the use of DCD also increased herbage production by more than 30%, from 11 to 15 t ha^–1 yr^–1. The use of DCD therefore has the potential to make dairy farming more environmentally sustainable by reducing NO₃^– leaching and N₂O emissions.     

Effects of tile drainage repair on nutrient leaching from a field under ordinary cultivation in Sweden

Leaching losses of nitrogen (N), phosphorus (P) and potassium (K) from arable land can be high, with N and P contributing significantly to the eutrophication of lakes and coastal waters. This study examined whether agriculture management and drain repair changed the chemical properties of shallow groundwater and affected nutrient leaching in the field. The hydrology of a subsurface-drained agricultural observation field included in the Swedish water quality monitoring programme was simulated for the period 1976–2006 using the process-based, field-scale model DRAINMOD. On the assumption that the drainage system operated similarly before and after repair, 54% more water was assigned to low-moderate flow events. Measured concentrations of sulphate-sulphur (SO₄-S), sodium (Na), chloride (Cl) and potassium (K) were significantly lower in shallow groundwater in the period before drainage system repair (1980–1998) than afterwards (1998–2010). The concentrations were also significantly correlated with the corresponding concentrations in near-simultaneously sampled drain water. A similar connection was not observed for Na and Cl in the period before drain repair. Elevated concentrations of nitrate-nitrogen (NO₃-N) were recorded both in shallow groundwater and in drainage water from 1998 to 2010, especially after incorporation of chicken manure into the soil in 1998. Based on simulated discharge (assuming a functioning measuring station throughout), estimated flow-weighted mean NO₃-N concentration in drainage water increased from 5.6 mg L^?1 (1977–1998) to 15.7 mg L^?1 in the period 1998–2000. Simultaneously, mean NO₃-N concentration in shallow groundwater increased from 0.2 to 4.0 mg L^?1, and then to 4.8 mg L^?1 in the period 2000–2012. It was estimated that after drain repair, a greater proportion of infiltrated NO₃-N entered the receiving stream directly via the outlet of the tile drainage system close to the field's monitoring station than was the case before repair.     

Uptake,transport and assimilation of 15N-nitrate and 15N-ammonium in tea (Camellia sinensis L.) plants

¹⁵N studies were conducted using hydroponically grown tea (Camellia sinensis L.) plants to clarify the characteristics of uptake, transport and assimilation of nitrate and ammonium. From the culture solution containing 50 mg L^-1 N0₃-N and 50 mg L^-1 NH.-N, the uptake of NH₃-N after 24 h was twice as high as that of NO₃-N, while the uptake of N0₃-N from the culture solution containing 90 mg N0₃-N and 10 mg NH₃-N was twice that of NH₄-N. The presence of 0.4 mM Al had no significant effect on the N0₃-N and NH₄-N uptake from the culture solutions containing 50 mg L^-1 N0₃-N and 50 mg L^-1 NH₄-N, 90 mg L^-1 N0₃-N and 10 mg L^-1 NH₄-N or 99 mg L^-1 N0₃-N and 1 mg L^-1 NH₄-N. Transport of N0₃-derived N to young leaves was much more rapid than that of NH₄-derived NO₃ and NH₄-derived N was largely retained in the roots and lower stem. Young and mature shoots separated from the roots absorbed more N0₃-N than intact plants. Nitrate assimilation occurred in both, roots and young as well as mature leaves. Internal cycling of N0₃-derived Nand NH₄-derived N from one root part to another part was not appreciable after 28 h, suggesting that a longer of time is required for cycling in woody plants.     

Optimizing livestock manure applications to reduce nitrate and ammonia pollution:scenario analysis using the MANNER model

Abstract. Measures to reduce ammonia (NH₃) emissions by incorporating livestock manures into the soil may increase the potential for nitrate (NO₃^‐) leaching. The Manure Evaluation Routine (MANNER) model estimates the amount of N available to crops following livestock manure applications after calculating losses due to NH₃ volatilization and NO₃^‐ leaching. The main objective of this study was to use the MANNER model to quantify the impact on NO₃^‐ leaching of introducing measures to reduce NH₃ emissions, following application of livestock manures. The data produced were also used to make preliminary estimates of the likely effect of selected NH₃ abatement techniques on the potential for nitrous oxide (N₂O) emissions. At typical UK rates of application, the potential for increased NO₃^‐ leaching following either injection of slurry or rapid incorporation of solid manures was greatest for broiler/turkey manure (22–58 kg N ha^–1) and least for straw‐based cattle manure (6–10 kg N ha^–1). The results suggest that in order to avoid substantially increasing the potential for NO₃^‐ leaching as a consequence of NH₃ abatement, livestock manures should not be applied by low NH₃ emission techniques prior to autumn‐sown crops in the UK. Instead, low‐emission applications should be made from October onwards to grassland and where possible, late autumn‐sown combinable crops or to arable land which will be planted in the spring. However, in several areas of England and Wales there is currently insufficient land planted to spring crops on which to incorporate the livestock manures produced in those areas.     

A field trial to evaluate the pollution potential to ground and surface waters from woodchip corrals for overwintering livestock outdoors

Outwintering beef cattle on woodchip corrals offers stock management, economic and welfare benefits when compared with overwintering in open fields or indoors. A trial was set up on a loamy sand over sand soil to evaluate the pollution risks from corrals and the effect of design features (size and depth of woodchips, stocking density, and feeding on or off the corral). Plastic‐lined drainage trenches at 9–10 m spacing under the woodchips allowed sampling of the leachate. Sampling of the soil to 3.6 m below the corral allowed evaluation of pollutant mitigation during vadose zone transport. Mean corral leachate pollutant concentrations were 443–1056 mg NH₄‐N L^?1, 372–1078 mg dissolved organic carbon (DOC) L^?1, 3–13 mg NO₃‐N L^?1, 8 × 10⁴–1.0 × 10⁶Escherichia coli 100 mL^?1 and 2.8 × 10²–1.4 × 10³ faecal enterococci 100 mL^?1. Little influence of design features could be observed. DOC, NH₄ and (in most cases) E. coli and faecal enterococci concentrations decreased 10²–10³ fold when compared with corral leachate during transport to 3.6 m but there were some cores where faecal enterococci concentrations remained high throughout the profile. Travel times of pollutants (39–113 days) were estimated assuming vertical percolation, piston displacement at field moisture content and no adsorption. This allowed decay/die‐off kinetics in the soil to be estimated (0.009–0.044 day^?1 for DOC, 0.014–0.045 day^?1 for E. coli and 0–0.022 day^?1 for faecal enterococci). The mean [NO₃‐N] in pore water from the soil cores (n = 3 per corral) ranged from 114 ± 52 to 404 ± 54 mg NO₃‐N L^?1, when compared with 59 ± 15 mg NO₃‐N L^?1 from a field overwintering area and 47 ± 40 mg NO₃‐N L^?1 under a permanent feeding area. However, modelling suggested that denitrification losses in the soil profile increased with stocking density so nitrate leaching losses per animal may be smaller under corrals than for other overwintering methods. Nitrous oxide, carbon dioxide and methane fluxes (measured on one occasion from one corral) were 5–110 g N ha^?1 day^?1, 3–23 kg C ha^?1 day^?1, and 5–340 g C ha^?1 day^?1 respectively. Ammonia content of air extracted from above the woodchips was 0.7–3.5 mg NH₄‐N m^?3.     

成都平原农区地下水中NO3--N含量变化规律研究

采用硝酸根电极法对成都平原温江县天府乡农区田间和水井的地下水NO-3 N含量进行了一年多的连续测定 ,探讨了该农区地下水中NO-3 N的变化规律和氮肥用量的影响。结果表明 :(1)田间地下水NO-3 N含量周年变化规律是冬春枯水季较高 ,且变幅较大 (0 3 6～ 2 62mgL- 1) ,平均值为 2 59mgL- 1;夏秋丰水季较低 ,且变幅较小 (0 84～ 5 48mgL- 1) ,平均值为 1 10mgL- 1。 (2 )前作麦季氮肥施用量 ,对稻季地下水中NO-3 N含量有明显影响 ,当前作施纯氮达 3 75kghm- 2 时 ,稻季地下水NO-3 N含量最高达 3 4 6mgL- 1,其平均值为 17 97mgL- 1,是施纯氮 150kghm- 2 平均值 1 3 0mgL- 1的 13 7倍。 (3 )井水中NO-3 N含量变化幅度为 0 14～ 16 53mgL- 1,3口井水平均值分别为 2 54、3 60、6 52mgL- 1,未超出我国生活饮用水卫生标准 ,但明显高于灌溉水NO-3 N含量的平均值 1 81mgL- 1。 (4)地下水位的高低与井水中NO-3 N含量没有线性关系     

Impact of Organic Amendments on Groundwater Nitrogen Concentrations for Sandy and Calcareous Soils

Experiments were conducted on calcareous and sandy soils to investigate the effects of organic amendments for vegetable production on groundwater nitrogen (N) concentration in south Florida. The treatments consisted of applying yard and food residuals compost, biosolids compost, a cocompost of the municipal solid waste and biosolids, and inorganic fertilizer. Nitrate nitrogen (NO₃-N), ammonium nitrogen (NH₄-N), and total N concentrations were collected for a period of two years for both soils. Statistical analysis results revealed that for the three species tested, there were no significant differences among treatments. NO₃-N concentrations for all treatments remained less than the maximum contamination level (10 mg/L). NO₃-N transport to groundwater was higher in calcareous soil (mean=5.3 mg/L) than in sandy soil (mean=0.6 mg/L). NH₄-N concentrations ranged from 0 to 13.6 mg/L throughout the experiment. Calcareous soil had lower NH₄-N concentrations (mean=0.1 mg/L) than sandy soils (mean=0.7 mg/L). Total N ranged from 0.4 to 21.7 mg/L for all treatments for both soils reflecting high adsorption of dissolved organic N in both soils. Overall, results indicated that all the compost treatments were comparable to inorganic fertilizer with regard to N leaching and N concentrations in the groundwater while producing similar or higher yields.     

稻田土壤中氮素淋失的研究

本文应用稻田大型原状土柱渗漏计，研究了双季稻田土壤中氮素随渗漏水流淋失的形态、数量、季节性变化以及若干农化因子的影响。明确了稻田中氮素淋失的基本形态是硝态氮（ＮＯ３＾－－Ｎ），估算出双季稻田中氮素淋失总量可接近３０ｋｇＮ／ｈａ，同时肯定了农田施用氮肥对地下水体环境可能的ＮＯ３＾－－Ｎ污染，建议双季稻田中每季水稻的氮肥用量宜控制在１５０ｋｇＮ／ｈａ；本文还证实氮肥用量对氮素淋失有明显影响，不同氮肥品     

Soil carbon and nitrogen response to 25 annual cattle manure applications

Improving manure management to benefit both agricultural production and the environment requires a thorough understanding of the long‐term effects of applied manure on soil properties. This paper examines the effect of 25 annual solid cattle manure applications on soil organic carbon (OC), total N (TN), and KCl‐extractable NO₃‐N and NH₄‐N under both non‐irrigated and irrigated conditions. After 25 annual manure applications, OC and TN contents increased significantly with the rate of manure application at the top two sampling depths (0–15 cm and 15–30 cm), and the increases were not affected by the irrigation treatment. The NO₃ content increased at all sampling depths with greater increases observed under non‐irrigated conditions, while NH₄ content was not affected by manure application rates or the irrigation treatment. The changes in OC and TN at the surface (0–15 cm) and 15–30 cm depth were dependent on the cumulative weight of manure added over the years. The relationships between cumulative manure OC added and soil OC content and between cumulative manure TN added and soil TN content were linear and not affected by the irrigation treatment. For every ton of manure OC added, soil OC increased by 0.181 g kg^–1 in the topsoil (0–15 cm). Similarly, for every ton of manure TN added, surface soil TN increased by 0.192 g kg^–1. The linear relationship between manure C added and soil C content suggests that the soil had a high capacity for short‐term C sequestration. However, the total amount of NO₃‐N in the soil profile (0–150 cm) was affected by both the manure application rates and the irrigation treatment. A large amount of NO₃ accumulated in the soil, especially under non‐irrigated conditions. The extremely high level of NO₃ in the soil increases the potential risk of surface and groundwater pollution and losses to atmosphere as N₂O.     

Effect of Water Bicarbonate Concentration,pH and the Presence,or Not,of a Nitrification Inhibitor in the Nitrification Process

Ammonium (NH₄⁺) is an important nitrogen (N) source for plant growth. Nevertheless, NH₄⁺–N can be oxidized to nitrate (NO₃^?) by nitrification and then nitrate and nitrite can be leached into groundwater. The aims of this study were to investigate the effect of the water bicarbonate concentration, pH, and the presence, or not, of a nitrification inhibitor, on the nitrification process. Six treatments were established, changing the pH and the bicarbonate concentration, with or without the nitrification inhibitor. The results showed that an active nitrification process occurred in treatments with high pHs (8 and 7) and with no nitrification inhibitors. This causes an increase in the nitrate and nitrite concentration in the substrate. The use of N–NH₄⁺ fertilizers joint to a nitrification inhibitor, especially in nutritive solutions with a high concentration of bicarbonate and a pH of 8 and 7, decreases nitrate and nitrite accumulation in substrate which can prevent nitrate and nitrite leaching.     

Nitrate leaching in forest soils: an analysis of long‐term monitoring sites in Germany

Elevated atmospheric inputs of NH₄⁺ and NO₃^– have caused N saturation of many forest ecosystems in Central Europe, but the fate of deposited N that is not bounded by trees remains largely unknown. It is expected that an increase of NO₃^– leaching from forest soils may harm the quality of groundwater in many regions. The objective of this study was to analyze the input and output of NH₄⁺ and NO₃^– at 57 sites with mature forest stands in Germany. These long‐term study sites are part of the European Level II program and comprise 17 beech, 14 spruce, 17 pine, and 9 oak stands. The chloride balance method was used to calculate seepage fluxes and inorganic N leaching below the rooting zone for the period from 1996 to 2001. Nitrogen input by throughfall was significantly different among most forest types, and was in the order: spruce > beech/oak > pine. These differences can be largely explained by the amount of precipitation and, thus, it mirrors the regional and climatic distribution of these forest types in Germany. Mean long‐term N output with seepage was log‐normal distributed, and ranged between 0 and 26.5 kg N ha^–1 yr^–1, whereby 29 % of the sites released more than 5 kg N ha^–1 yr ^–1. Leaching of inorganic N was only significantly lower in the pine stands (P < 0.05) compared with leaching rates of the spruce stands. Median N output : input ratio ranged between 0.04 and 0.11 for the beech, oak, and pine stands, while the input : output ratio of the spruce stands was 0.24, suggesting a higher risk of NO₃^– leaching in spruce forests. Following log‐transformation of the data, N input explained 38 % of the variance in N output. The stratification of the data by the C : N ratio of the O horizon or the top mineral soil revealed that forests soils with a C : N ratio < 25 released significantly more NO₃^– (median of 4.6 kg N ha^–1 yr^–1) than forests with a C : N ratio > 25 (median of 0.8 kg N ha^–1 yr^–1). The stratification improved the correlation between N input and N output for sites with C : N ratios < 25 (r² = 0.47) while the correlation for sites with C : N ratios > 25 was weaker (r = 0.21) compared with the complete data set. Our results suggest that NO₃^– leaching may increase in soils with wide C : N ratios when N deposition remains on a high level and that the potential to store inorganic N decreases with C : N ratios in the O horizons becoming more narrow.     

灌溉施肥对壤质潮土硝态氮淋溶的影响

在衡水市邓庄乡壤质潮上上进行了以灌水为主处理、氮用量为副处理,各五水平的定位试验。结果表明,氮肥用量是硝态氮淋溶损失的决定因素,冬小麦施氮150kghm-2不发生淋溶,施氮225～300kghm-2则硝态氮的淋溶增强。小麦播前基施氮肥量过高会使冬季发生硝态氮的淋溶。小麦拔节期和灌浆期灌溉一般不会引起硝态氮的淋溶损失;尽管一次灌水1350m3hm-2硝态氮的淋失量不高,但土壤剖面中的硝态氮含量显著比低灌水量的低。为降低硝态氮的损失,应控制一次灌水量不超过1050m3hm-2。雨季降水导致大量硝态氮淋溶损失,防治雨季土壤硝态氮的淋溶损失至关重要。     

Leaching of nitrogen from a forest catchment at söder»sen in southern Sweden

Water balance and leaching of plant nutrients, with special reference to N, were described for a 46-ha catchment consisting mainly of coniferous forest (one third of it clear-cut) during the period January 1982-August 1988. The atmospheric N load in this region is high compared with most other parts of Scandinavia. On average, annual N leaching amounted to 9.5 kg ha^?1 in the form of NO₃-N (83%), org-N (15%) and NH₄-N (2%). The highest monthly rate of N transport observed was 3.9 kg ha^?1. The NO₃-N levels in groundwater in the 60-yr-old coniferous stand ranged from 0.5 to 3.1 mg L^?1. The effect of clear-cutting on groundwater-NO₃-N levels lasted 4 yr. The highest annual NO₃-N transport from the clear-cut area observed was 18 kg ha^?1. The groundwater in the spruce forest was very acidic (pH=4.3) in contrast to the stream water (pH=6.3). The relatively higher pH-value of the stream water was probably a result of chemical and biological processes occurring in the highly humified, periodically waterlogged peat soil (alder swamp) in the vicinity of the small stream.     

Best Nitrogen and Irrigation Management Practices for Citrus Production in Sandy Soils

Drinking water monitoring data have indicated anincrease in nitrate-nitrogen (NO₃-N) concentration ingroundwater in some parts of the citrus production region ofFlorida. A proactive, incentive-based program of developingcrop-specific best management practices (BMP) began with theFlorida N-BMP legislation passed in 1994. A combination ofcareful irrigation and nitrogen (N) management is needed toimprove N uptake efficiency and to minimize potential leaching ofnitrate (NO₃-N) to the groundwater. An improved Nmanagement practice is considered as a BMP, only if that practiceis proved to decrease NO₃-N leaching into groundwater incommercial groves without adversely impacting the economics ofproduction. Therefore, long-term evaluation of horticulturalresponses as well as monitoring of groundwater NO₃-N wereconducted in five commercial groves representing different soiltypes, citrus variety and rootstock, tree age, and culturalpractices to determine the impact of changes in N managementand/or irrigation scheduling. Groundwater NO₃-N, leafnutrient concentrations, fruit yield and fruit quality weremonitored for 15 months under the growers' routine managementand, subsequently for 48 months, with improved N and irrigationmanagement practices. The N management practices evaluated inthis study included broadcast application of a combination ofwater soluble and slow release granular products, fertigation,and a combination of foliar application and fertigation. Irrigation management was improved by using tensiometer set pointof 10 and 15 cbar. This article presents the fruit yield, andconcentrations of N, P, K in six-month spring flush during thestudy period. The study showed that 5 to 8 yr old Valenciatrees on Volkamar lemon rootstock produced high quality fruit inthe range of 59 to 81 Mg ha^-1 with 168 kg N ha^-1 asfertigation combined with improved irrigation scheduling. Fruityield of 36 yr old Valencia orange trees on Rough lemonrootstock was greater with application of 180 kg N ha^-1 yr^-1 as fertigation compared to that of the trees whichreceived a similar rate of N as three broadcast applications ofgranular product. Fertilizer program comprising three foliarapplications of N using low biuret urea to deliver 66 kg N ha^-1 yr^-1 and an additional 76 kg N ha^-1yr^-1as fertigation was the most effective for decreasing the surficialgroundwater NO₃-N while maintaining optimal fruit productionand nutritional status of the leaves. This study demonstratedthat economically and technically feasible N-BMPs can bedeveloped for citrus grown on sandy soils with a combination ofimproved N management and irrigation scheduling.     

Nitrogen Source and Concentration Affect Growth and Performance of Bedding-Plant Impatiens

ABSTRACT

Impatiens (Impatiens wallerana Hook. f.) is the most important annual bedding plant in the United States, based on wholesale dollar volume. Production of high-quality plants requires optimization of the nutrition regimen during growth, especially the total nitrogen (N) concentration and the ratio of N sources. The objective was to determine the N concentration and the nitrate (NO₃ ^??N):ammonium (NH₄ ⁺?N) ratio of N source that optimized bedding-plant impatiens growth and flower development. Four N concentrations (3.5, 7, 10.5, and 14 mmol N · L^?1) were used in factorial combination with four ratios of NO₃ ^??N:NH₄ ⁺?N (4:0, 3:1, 1:1, and 1:3). Application of treatments was made for 30 d. Then for 10 d only deionized water was applied to reduce salt buildup. Substrate pH was lowest (4.9) with the NH₄ ⁺?N source and electrical conductivity (EC) highest, but never > 2.4 dS m^?1. Nitrogen concentration and N source displayed an interaction for most growth parameters. Shoot fresh and dry weights and flower bud number were maximized at the 1:3 NO₃ ^??N:NH₄ ⁺?N ratio with a N concentration of 10.5 mmol L^?1. However, plant diameter, leaf number, and leaf chlorophyll content responded quadratically to N form ratio, with the 1:1 ratio optimum at a concentration of 10.5 mmol N· L^?1.     

Nitrogen and Phosphorus Leaching from Fertilizer Applied on Golf Course: Lysimeter Study

Fertilizers applied to turfgrass may pose a threat to surface and groundwater quality, and hence, a study was carried out to evaluate the fate of fertilizer applied to turfgrass of the Clearwater Bay Golf and Country Club in Hong Kong. Lysimeters with reconstituted soils collected from fairways and greens with Bermudagrass (Cynodon dactylon) growing in the surface were used to evaluate the leaching loss of nitrate (NO₃ ^-), ammonium (NH₄ ⁺), and phosphate (PO₄ ^3-) for 22 weeks under greenhouse condition. Both soils received a slow release fertilizer at an application rate of 25 (low) or 50 (high) kg N ha^-1, and an application frequency of monthly and fortnightly for fairways and greens, respectively, simulating the fertilizer application strategy of the golf course. Both low and high fertilizer application rate supported the same amount of biomass production for each soil type. Breakthrough of NO₃ ^- occurred only in greens after 11 weeks of leaching, but the total amount of NO₃ ^- leached did not differ significantly for the two different fertilizer application rates. The continued addition of fertilizer to greens resulted in a final leachate NO₃ ^- concentration exceeding 45 mg L^-1, while fairways maintained a concentration below 5 mg L^-1. Also PO₄ ^3- concentration in leachate of greens exceeded the surface water standard of 0.3 mg L^-1. The results of the lysimeter study showed that the current application rate on greens would create adverse environmental impacts on the surface water and groundwater due to leaching loss of PO₄ ^{3 -} and NO₃ ^-.     

Ammonium-nitrate dynamics in the critical zone during single irrigation events with untreated sewage effluents

Purpose

Previous studies in the Mezquital Valley evidenced that irrigation with untreated sewage effluent supplies two- to tenfold larger nitrogen doses to crops than common fertilizer recommendations. However, nitrate concentrations in the groundwater are only slightly above threshold concentrations for drinking water. To understand the N dynamics in this agroecosystem, we quantified nitrogen inputs, outputs, and transformations within the rooting zone and in the vadose zone down to the aquifer (i.e., in the critical zone).

Materials and methods

Single irrigation events were monitored in three different fields cropped with either annual rye grass (Lolium rigidum) or oats (Avena sativa L.) harvested for fodder. For each irrigation event, the total amount of water entering and leaving the field was quantified with a flowmeter. Soil pore water was collected with either microsuction cups or observation wells and groundwater was sampled at two wells. All water samples were analyzed for total nitrogen (Nt), ammonium nitrogen (NH₄ ⁺–N), nitrate nitrogen (NO₃ ^?–N), chloride (Cl^?1), and pH. Organic N was calculated as the difference between total N and inorganic N. The water tension and the soil water content were monitored before, during, and after the irrigation with tensiometers and TDR probes, respectively, installed at different depths and at three sites within each field. Batch experiments were conducted to assess the NH₄ ⁺ adsorption capacity of the soils.

Results and discussion

The irrigations added 537 to 727 kg ha^?1 N in form of organic N (40 %) and NH₄ ⁺–N (60 %) to the fields. Crops absorbed 65 % of the N and 31 to 66 kg NO₃ ^?–N ha^?1 leached out beyond the rooting zone (>40 to 130 cm). Batch experiments evidenced an ammonium adsorption capacity of 43 and 53 % of the input ammonium mass. Nitrification dominated over denitrification as the water infiltrated through the soil, evidenced by changes in nitrate concentrations and pH values in the soil pore water. The behavior of the total N/Cl ratio with depth indicated possible N losses due to NH₃ volatilization at the field surface, a temporal withdrawal of N from the soil solution due to NH₄ ⁺–N adsorption in the rooting zone, as well as probable denitrification losses in the vadose zone.

Conclusions

Although the studied agroecosystem muses the large N inputs relative efficiently, between 7 and 10 % of the added N with each irrigation leaches beyond the crop root zone as nitrate. This is triggered by overflow irrigation, since up to 8,699,000 L of water with N concentrations of up to 50 mg total N L^?1 infiltrate rapidly through macropores beyond the rooting zone. Additionally, ammonia volatilization and denitrification seem to be occurring. The latter could provide a self-cleaning potential to the system, if it reaches N₂ and needs further verification. Nevertheless, N inputs to the system should match crop uptake to avoid groundwater and atmospheric pollution.

     

太行山前平原农田生态系统氮素循环与平衡研究

在中国科学院栾城生态农业试验站1公顷小麦玉米轮作农田,运用乙炔抑制原状土柱培育法、微气象学法和陶土头多孔杯水量平衡法分别定量测定了氮素硝化反硝化损失、氨挥发、NO3--N淋溶损失等氮素循环转化途径。研究结果表明,每年因氨挥发而造成的肥料氮损失量为N.60.kg/hm2,占施入肥料氮的15%;NO3--N淋溶损失量为N.68～4.kg/hm2,占肥料施用量的1.4%2～0.3%;每年因硝化反硝化过程造成的肥料损失量为N.2.021～0.49.kg/hm2,占肥料施入量的0.51%1～.37%。氨挥发、NO3--N淋溶和硝化反硝化损失主要发生在施肥灌溉/降雨之后,玉米季肥料损失明显高于小麦生长季节。氨挥发和NO3--N淋溶损失是本区域农田氮素损失的主要途径,是氮肥利用率低的重要原因。在当地农民所采用的常规农业管理措施下,小麦玉米轮作农田氮素平衡处于盈余状态,小麦季盈余N+115.5～+124.5.kg/hm2,明显高于玉米季;由于玉米季氮素损失严重,氮素盈余较少,甚至出现亏缺,玉米季氮素平衡状况为-54.6～+14.3.kg/hm2。