Nitrogen In Runoff Research Articles

Nitrogen Runoff Losses during Warm-Season Turfgrass Sod Establishment.

Concern exists over the potential loss of nitrogen (N) and phosphorus (P) in runoff from newly established and fertilized lawns. Nutrient losses can be higher from turf when shoot density and surface cover are low and root systems are not fully developed. This study was conducted to evaluate fertilizer source and timing effects on nutrient losses from newly sodded lawns of St. Augustinegrass [ (Walt.) Kuntze]. For each study, 12 33.6-m plots were established on an undisturbed Alfisol having a 3.7% slope. Each plot was equipped with a runoff collection system, instrumentation for runoff flow rate measurement, and automated samplers. A 28-d establishment study was initiated on 8 Aug. 2012 and repeated on 9 Sept. 2012. Treatments included unfertilized plots, fertilized plots receiving 4.88 g N m as urea 6 d after planting, fertilized plots receiving 4.88 g N m as sulfur-coated urea 6 d after planting, and fertilized plots receiving 4.88 g N m as urea 19 d after planting. Runoff events were created by irrigating with 17 mm of water over 27 min. Runoff water samples were collected after every 37.8 L and analyzed for NO-N, NH-N, dissolved organic N (DON), and PO-P. Increases of approximately 2 to 4 mg L NO-N and 8 to 12 mg L PO-P occurred in runoff 1 d after fertilization, which returned to background levels within 7 d. Total fertilizer N lost to runoff was 0.6 to 4.2% of that applied. Delaying fertilizer application until 19 d after planting provided no reduction in nutrient loss compared with a similar application 6 d after planting. Approximately 33% of the N lost in runoff was as DON. This large amount of DON suggests significant N loss from decomposing organic matter may occur during sod establishment.

Application of a Bayesian Watershed Model Linking Multivariate Statistical Analysis to Support Watershed-Scale Nitrogen Management in China

Excessive nitrogen loads and subsequent eutrophication risk have led to a series of critical water quality problems in Chinese watersheds. To address this issue, a modeling approach is useful for quantifying nitrogen sources, assessing source apportionment, and guiding management responses. In this study, we modeled the main hydrochemical processes of the Lian River watershed located in the south of China using the Regional Nutrient Management (ReNuMa) model, a model derived from the Generalized Watershed Loading Function (GWLF) model and incorporating Net Anthropogenic Nitrogen Inputs (NANI) to estimate runoff nitrogen concentrations. An informal Bayesian method, the Generalized Likelihood Uncertainty Estimation (GLUE) procedure, was applied for model calibration and uncertainty analysis. The resulting modeled monthly total nitrogen fluxes have high Nash-Sutcliff coefficients (>0.85) for the calibration (2005–2009) and verification (2003, 2004 and 2010) periods, representing an acceptable goodness-of-fit. The model outputs were further processed using multivariate statistical analysis to determine latent rules of nitrogen source apportionment under different circumstances, including different water regimes, seasonal patterns, and loading levels. The main nitrogen contributions in different natural and management-driven conditions have been identified, and appear to be significant for supporting decision-making priorities. We find that the ReNuMa model, with its Bayesian procedure and the linkage of subsequent multivariate statistical analysis, represents a useful approach with applicability within China and a great potential to be extended elsewhere.

Nitrogen Runoff from Tunnel Blasted Rocks— a Large-Scale Test

Eight tunnel blasted rock samples were washed five times in 10 m3 containers to calculate the runoff potential of nitrogen from unexploded remains of the ammonium nitrate slurry explosive in rock piles. During the first wash, 65% of total nitrogen was washed off. The average concentrations of NH4+ and NO3- in the first wash water were 46 mg N/L and 58 mg N/L, respectively, being reduced to 2.5 and 1.2 mg N/L after the last wash. The average runoff of total nitrogen from the blasted rocks was 24.2 g N/ton, being 14.7% of nitrogen in the loaded explosives. pH was high (range 8.1 to 11.8) resulting from shotcrete spill, pushing the NH4+/NH3 equilibrium toward the toxic NH3. The consequences of runoff from blasted rock piles may be damaging for water quality and biology in small recipients, and abatement measures should be assessed.

Urban Stormwater Runoff Nitrogen Composition and Fate in Bioretention Systems

Multiple chemical forms of nitrogen in urban stormwater make its management challenging. Sixteen storm events were monitored and analyzed for total nitrogen (TN), particulate organic nitrogen (PON), nitrate (NO3-N), nitrite (NO2-N), ammonium (NH3-N), and dissolved organic nitrogen (DON) in stormwater runoff and in treated discharge through a conventional bioretention cell. Influent PON can be effectively removed via bioretention sedimentation/filtration, NH3-N by ion exchange/sorption, and NO2-N by oxidation. However, significant DON and NO3-N leached from the bioretention cell, resulting in only 9% net overall TN concentration reduction. Captured PON and vegetation detritus in the bioretention cell can be leached as DON or mineralized into NO3-N. The effluent N is dominated by NO3-N (46%) and DON (42%). Therefore, in addition to creating denitrification conditions for NO3-N, preventing DON leaching is also critical for effective nitrogen removal though bioretention systems. The bioretention cell exhibited a moderate mass load reduction for TN (41%), which mainly results from runoff volume reduction.

Water, soil and nutrient losses caused by Wenchuan Earthquake: a case study in Pengzhou

Wenchuan Earthquake triggered a large number of geological hazards, dramatically stimulating soil erosion. This study was carried out in Pengzhou County, Sichuan Province. By comparison of sediment, runoff and nutrient losses in earthquake-damaged forests (EF) and unaffected forests (UF), the actual status of soil erosion after the Wenchuan Earthquake was investigated by runoff plots. Results showed that water and soil losses were dramatically increased after earthquake. During the study period (from August to November 2010), UF runoffs were 19.26, 36.76, 10.68 and 7.51 L m(-2), while total runoffs in EF sites were 30.41, 25.79, 5.03 and 2.67 L m(-2) respectively, which were 15, 15, 18 and 19 times more than those in UF. Total sediment losses in EF sites were 28.94, 25.16, 4.11 and 1.98 t km(-2) respectively while in UF they were 707.69, 610.05, 113.43 and 58.95 t km(-2) respectively during the same study period, i.e. 23, 23, 32 and 29 times more than those in UF. Path analysis showed that both vegetation and rainfall exerted an indirect influence on sediment loss by significantly influencing runoff, which correlated with sediment loss very significantly. Although no obvious differences of the nutrients' concentration in runoff water (soluble organic carbon (SOC), total nitrogen (TN), total phosphorus (TP) and total potassium (TK)) between EF and UF sites were observed, total losses of the four nutrients were significantly higher in EF than in UF sites (for example, in EF sites, SOC, TN, TP and TK losses were 970.52, 114.46, 2.26 and 307.00 g m(-2) respectively, while in UF they were 38.13, 4.22, 0.10 and 13.28 g m(-2)) due to significantly higher runoff in EF sites. In conclusion, soil erosion was significantly more serious due to the loss of forested lands resulting from the Wenchuan Earthquake, delaying the restoring process of forest cover and weakening the ecological linkage between upstream and downstream.

Responses of runoff, sedimentation, and induced nutrient loss to vegetation change in the Tengger Desert, northern China

Runoff and nutrient loss in drylands are closely related to vegetation cover. Simulated rainfall experiments with an intensity of 80 mm/h were conducted in sandy grassland and shrubland in the Tengger Desert, China, to investigate the responses of runoff and associated carbon (C) and nitrogen (N) losses to the replacement of grassland by shrubland. Times to ponding and to generate runoff, and the amount of rainfall for runoff commencement in bare, inter-shrub plots were significantly smaller than in shrub (ST) and grassland (GT) plots; no statistical differences were found for these parameters between ST and GT. Overall, this indicated a higher soil water infiltration rate in grassland than in shrubland. The volume-weighted concentrations of organic C (OC) and total N (TN) in runoff from shrubland (0.083 and 0.011 g/L, respectively) were lower than those from grassland (0.103 and 0.012 g/L, respectively). The cover-weighted runoff coefficients, and sediment, OC, and TN losses from shrubland (34.46%, and 44.95 1.72, and 0.23 g/m2, respectively) were greater than from grassland (15.22%, and 15.91, 0.94, and 0.11 g/m2). Vegetation degradation was accompanied by reduced nutrient retention capacity; both soil OC and TN of grassland (8.97 and 0.62 g/kg, respectively) were greater than those weighted values for shrubland (4.18 and 0.26 g/kg). Understanding of these processes suggests that decline or loss of vegetation cover, with the appearance of biological soil crust patches, inevitably leads to increases in runoff and induced soil loss, further accelerating desertification.

The Nitrogen Runoff Characteristics in Agricultural Watersheds after Enforcement of Animal Waste Regulation

The Nitrogen Runoff Characteristics in Agricultural Watersheds after Enforcement of Animal Waste Regulation

A Study on the Characteristics of Nitrogen and Phosphorus Runoff from Farmland under Wheat-Rice Rotation in Nansi Lake Basin

Field runoff pools were used to collect the surface runoff samples of wheat-rice rotation in Nansi Lake region, and different forms of nitrogen (N) and phosphorus (P) data were analyzed. The average runoff concentrations, losses, and characteristic ratios of N and P were studied. The average runoff concentrations of TN and TP in wheat–rice rotation were 0.87–7.94 and 0.08–0.81, respectively. The characteristic ratios of N and P were also observed. And the characteristic ratios of NO3--N, NH4+-N, DP, and PO43--P were 45.03%, 17.55%, 71.43%, and 54.01% in wheat–rice rotation, respectively.

Comparison of nitrogen and phosphorus removal efficiencies by storm runoffs for the ponds in the upper and lower reaches of a typical sub-catchment in Lake Chaohu drainage basin

从流域上下游环境条件及氮磷输出强度差异出发,探讨上下游水塘对径流氮磷去除的特征及效率,选取巢湖小柘皋河源头流域上下游水塘开展水塘去除暴雨径流氮磷的对比试验,研究暴雨及暴雨间期上下游水塘氮磷去除效率差异及原因,为流域上下游设计不同类型净化塘去除氮磷提供科学依据.结果表明:暴雨期,上游径流氮磷浓度高于下游,且颗粒态所占比例上游大于下游,流域上游应作为防治暴雨径流氮磷流失的重点区域;暴雨期,上游塘对暴雨径流中的氮磷去除效果明显,氮、磷去除率分别为74%和52%,且对颗粒态去除效果好于溶解态,下游塘没有表现出明显的去除效果;暴雨间期,上游塘塘内氮磷浓度平均下降50%和20%,下游塘则分别为72%和16%,且均以溶解态去除为主;水塘去除暴雨径流氮磷有一定的浓度适用范围,浓度过低,去除效果不明显;流域部位不同引起入塘径流氮磷浓度和形态的差异是上下游水塘对暴雨径流去除效果差异的主要外部原因.流域上游出山口,可以在渗透性好的山前洪积扇上构建深水宽塘,通过增加暴雨径流拦截量和降低流速增强物理沉降作用,实现暴雨径流氮磷的高效去除;流域下游农田区,宜构建水面较大的浅滩湿地,通过延长滞留时间和促进生物活动增强去除暴雨径流氮磷的效果.;In this paper, we analyze the removal efficiencies and characteristics of nitrogen and phosphorus in storm runoff in two ponds located in the upper and lower reaches of Xiaozhegao Stream, Lake Chaohu drainage basin. Results indicate that in the storm period, the runoff nitrogen and phosphorus levels in the upper reaches of stream are higher than those in the lower reaches. There is a good removal performance for the upper pond on both nitrogen and phosphorus (mainly in particulate), with a removal efficiency of 74% and 52%, respectively, while no evident removal performance has been found in the lower pond. During non-storm period, both ponds have good removal performances for dissolved nutrients. In the upper pond, the removal rates are 50% and 20% for nitrogen and phosphorus, respectively; in the lower pond, the rates are 72% and 16% for nitrogen and phosphorus, respectively. There is a range of nutrient concentration that ponds could play a good removal performance:if the nutrient concentration is too low, there will be no evident nutrient removal. The two ponds have different removal efficiencies on runoff nutrients due to their different locations in the catchment. The study concludes that in the upper reaches of a catchment, which is the most important area to prevent and control the loss of nutrients from storm runoff, ponds should be constructed deep and wide in the front of alluvial fan. It will enhance the physical settlement of nutrients by intercepting the runoff and lowering the flow velocity. While in the lower reaches of a catchment, it is appropriate to construct big and shallow wetlands which will remove much nitrogen and phosphorus in storm runoff by delaying nutrient retention time and promoting biological activity. The research could benefit better design of the ponds which aims to control water eutrophication.

Socioeconomic Response to Water Quality: a First Experience in Science and Policy Integration for the Izmit Bay Coastal System

Deterioration of the Izmit Bay ecosystem, mainly caused by heavy industrialization and urbanization, has significantly impaired its beneficial use and resulted in the surrounding coastal zone losing its attractiveness for the inhabitants. An integrated coastal zone management approach has become an important requirement of future development plans to protect this fragile bay ecosystem. One of the main indicators of deterioration of the Izmit Bay coastal system is the decreasing water quality resulting from increased nutrient loads from the surrounding land.The consensus during the initial stakeholder meeting confirmed the widespread awareness of this phenomenon and “improvement of water quality in Izmit Bay” was determined as the main policy issue at stake. Public perception of and satisfaction with water quality were measured by a willingness to pay (WTP) survey. The WTP for improved water quality was analyzed using the contingent valuation method. According to the questionnaire survey, 55% of the participants are willing to pay to increase the water quality. Impact of water quality on realestate values was evaluated by hedonic pricing method, which is suitable for estimating direct and indirect use values of water resources. These results were used in a simulation model to assess coupled ecosystem, social, and economic system functioning of the Izmit Bay in response to various scenarios, and thus, to permit the necessary actions to be taken proactively. Two scenario simulations, for which domestic and runoff nitrogen loads are reduced independently, showed that hypothetical domestic wastewater treatment resulted in an improvement in simulated water transparency. The results suggest that domestic wastewater treatment should be a first priority for local administrations.

Phosphorus and Nitrogen in Runoff after Phosphorus- or Nitrogen-based Manure Applications

Application of beef cattle () manure based on nitrogen (N) requirements of crops has resulted in elevated concentrations of soil test phosphorus (P) in surface soils, and runoff from this cropland can contribute to eutrophication of surface waters. We conducted a 3-yr field study (2005-2007) on a Lethbridge loam soil cropped to dryland barley () in southern Alberta, Canada to evaluate the effect of annual and triennial P-based and annual N-based feedlot manure on P and N in runoff. The manure was spring applied and incorporated. There was one unamended control plot. A portable rainfall simulator was used to generate runoff in the spring of each year after recent manure incorporation, and the runoff was analyzed for total P, total dissolved P, total particulate P, dissolved reactive P, total N, total dissolved N, total particulate N, NO-N, and NH-N. Annual or triennial P-based application resulted in significantly ( ≤ 0.05) lower (by 50 to 94%) concentrations or loads of mainly dissolved P fractions in runoff for some years compared with annual N-based application, and this was related to lower rates of annual manure P applied. For example, mean dissolved reactive P concentrations in 2006 and 2007 were significantly lower for the annual P-based (0.12-0.20 mg L) than for the annual N-based application (0.24-0.48 mg L), and mean values were significantly lower for the triennial P-based (0.06-0.13 mg L) than for the annual N-based application. In contrast, other P fractions in runoff were unaffected by annual P-based application. Our findings suggested no environmental benefit of annual P-based application over triennial P-based application with respect to P and N in runoff. Similar concentrations and loads of N fractions in runoff for the P- and N-based applications indicated that shifting to a P-based application would not significantly influence N in runoff.

Evapotranspiration-based Irrigation Scheduling for Container-grown Viburnum odoratissimum (L.) Ker Gawl.

The capacity for evapotranspiration (ET)-based irrigation scheduling to reduce runoff volume and nutrient leaching was tested in Fall 2004 and Spring 2005. Runoff (container leachate plus unintercepted irrigation and precipitation) was collected continuously for 17 weeks during production of sweet viburnum [Viburnum odoratissimum (L.) Ker Gawl.] in 2.4-L (16-cm top diameter) containers fertilized with an 18N–2.6P–10K polymer-coated, controlled-release fertilizer. Treatments were a factorial arrangement of two irrigation rates (fixed rate of 1 cm·d−1 or a variable, ET-based rate) and two fertilizer rates (15 or 30 g/container in 2004 and 10 or 15 g/container in 2005). Averaged over the two experiments and compared with the 1-cm·d−1 rate, ET-based irrigation reduced the amount of irrigation water applied (L/container) by 39% and runoff volume (L/container) by 42% with greatest reductions observed during the second half of the 2004 experiment and the first half of the 2005 experiment. Compared with 1-cm·d−1 rate, ET-based irrigation reduced runoff nitrogen (N), phosphorus (P), and potassium (K) (mg/container) by 16%, 25%, and 22%, respectively, in 2004 and runoff K 15% in 2005 with irrigation effects varying on a weekly basis. Irrigation treatments did not affect the response of plants to fertilizer rate. Because shoot dry weight was unaffected by irrigation treatments, results indicate that compared with a fixed irrigation rate, ET-based irrigation can reduce irrigation and runoff volumes and to a lesser extent nutrient loss while providing adequate water for plant growth.

Self-purification process and retention of nitrogen in floodplains of River Nemunas

Due to its catchment size and its significant level of agricultural pollution, the Nemunas river basin has been identified as an agricultural hot spot in the Baltic Sea basin. On average, the total annual inorganic nitrogen runoff into the river is 26.9 × 106 kg, which corresponds to a load of 275 kg km−2 yr−1. A submerged floodplain, covering 605 km2 of the River Nemunas lowland, maintains the natural retention threshold for pollutants in the water of the main canal and the outfall at Curonian Lagoon, as well as improving farming conditions in the inundated meadows of the valley. It also increases the sedimentation and nitrogen retention capacities of the Nemunas catchment. It has been estimated that about 40% of the fine suspended sediments can be retained and deposited in the flooded meadows of the delta. Controlled inundation of the floodplains in the Nemunas delta may reduce its runoff nitrogen load by 21 kg km−2 per flood event. As a result, nitrogen concentration decreases by approximately 8–10%, causing a self-purification process in the flooded area. Nitrogen retention is dependent upon the velocities of the flood current and has mostly been observed in zones of stagnating water.

Runoff Nitrogen Loss with Simulated Rainfall Immediately Following Poultry Manure Application for Corn Production

Nitrogen loss from a soybean [Glycine max (L.) Merr.]–corn (Zea mays L.) rotation by runoff to surface water can be significant. This study was conducted to determine short‐term N loss in runoff immediately after poultry manure application and assess the effects of manure rate and incorporation on losses. The study was conducted for 3 yr at nine Iowa fields previously cropped to soybean. Poultry manure sources were applied in the fall or spring to untilled soybean stubble at intended rates of 0, 84, and 168 kg total N ha−1with three replications. Within 2 d of application, simulated rainfall was applied to 3‐m2 areas to provide a single 30‐min runoff event. The total Kjeldahl N (TKN) and NH4+–N concentration and load in runoff increased with higher manure rates, with the associated manure TKN and NH4+–N correlated with runoff losses. With the high manure rate, runoff TKN and NH4+–N concentration averaged 33 and 15 mg L−1 and the TKN and NH4+–N load 2.6 and 1.1 kg ha−1, respectively. Runoff concentration and load of TKN and NH4+–N was significantly decreased with incorporation, approximately 50% and 90%, respectively. Tillage increased TKN in runoff when no manure was applied, but loses were lower than the treatment with manure and incorporation. The NO3−–N load in runoff was low and not affected by manure application. The results show that rainfall shortly after surface application of poultry manure can result in increased runoff TKN and NH4+–N, with loss related to manure rate, specific N fraction, and incorporation, which significantly reduced manure N in surface runoff.

Nitrogen in Runoff from Residential Roads in a Coastal Area

Non-point sources of nitrogen (N) contribute to pollution of many coastal waters. Road runoff of N has been estimated for busy highways, but residential roads could also be important non-point sources. Here we estimate N in runoff from two small residential roads (average annual daily traffic [AADT] <1,000) and a state highway (AADT = 8,800) in a coastal watershed of Massachusetts, USA. The antecedent dry-day traffic was correlated with total dissolved nitrogen (TDN) concentrations at the beginning of each rain event for the highway, but not for the residential roads. The TDN concentrations declined exponentially with cumulative precipitation during storms. Estimated annual road runoff is about 10 kg TDN-N ha−1 of road surface for all three roads, which is about twice the bulk precipitation input. Because much of this road runoff enters sensitive coast water bodies directly, these inputs could be important for local water quality concerns.

Side-by-Side Comparison of Nitrogen Species Removal for Four Types of Permeable Pavement and Standard Asphalt in Eastern North Carolina

A 1 year-old parking lot in eastern North Carolina consisting of four types of side-by-side permeable pavement and standard asphalt was monitored from January 2007 to July 2007 for water quality differences among pavement types. The four permeable sections were pervious concrete (PC), two different types of permeable interlocking concrete pavement (PICP) with small-sized aggregate in the joints and having 12.9% (PICP1) and 8.5% (PICP2) open surface area, and concrete grid pavers (CGP) filled with sand. The site was located in poorly drained soils, and all permeable sections were underlain by a crushed stone base with a perforated pipe underdrain. Composite, flow-weighted samples of atmospheric deposition and asphalt runoff were compared to those of permeable pavement subsurface drainage for pH, TN, NO2,3–N, TKN, NH4–N, and ON concentrations and loads. All pavements buffered acidic rainfall pH (p<0.01). The pH of permeable pavement subsurface drainage was higher than that of asphalt runoff (p<0.01) with the PC cell having the highest pH values (p<0.01). Permeable pavement subsurface drainage had lower NH4–N(p<0.01) and TKN concentrations than asphalt runoff and atmospheric deposition. With the exception of the CGP cell, permeable pavements had higher NO2,3–N concentrations than asphalt (p<0.01), a probable result of nitrification occurring within the permeable pavement profile. The CGP cell had the lowest mean TN concentrations; however, results were not significantly different from those of asphalt runoff. The possible nitrogen removal exhibited by the CGP cell is similar to that observed in sand filter research, not surprising considering CGP contained a 10 cm (4 in.) sand bedding layer. Overall, different permeable pavement sections performed similarly to one another with respect to water quality, with the CGP cell appearing to best improve storm-water runoff nitrogen concentrations.

Runoff and inorganic nitrogen export from Boreal Plain watersheds six years after wildfire and one year after harvest

This investigation in the Swan Hills, Alberta, located on the Canadian Boreal Plain, examined May through October runoff before, during and six years after wildfire in a 4th order watershed, compared to a 3rd order reference watershed. It also examined runoff and inorganic nitrogen flow-weighted mean concentration and areal export for 1 year after winter harvest in four 1st order watersheds compared to five reference 1st and 2nd order watersheds. Runoff and areal exports were normalized to precipitation at each site. Runoff impact ratios (year 1 post-disturbance value divided by the pre-disturbance value) for burned and harvested watersheds were 60 and 70% higher, respectively, than reference watersheds (P = 0.06). Runoff from the burned watershed remained elevated 6 years after fire. A trend for higher nitrate and ammonium concentrations, combined with higher runoff yielded impact ratios for areal ammonium and nitrate exports that were 130 and 170% higher, respectively, in harvested than reference watersheds (P = 0.08 for both). The proportion of the watershed harvested was positively related to runoff (r2 = 0.94, P = 0.03) and ammonium impact ratios (r2 = 0.96, P = 0.02), but not nitrate impact ratios (P = 0.30). Areal nitrate export in snowmelt was low in harvested watersheds compared to their pre-harvest condition and to reference watersheds.

Nitrogen Runoff and Leaching Losses During Rice-Wheat Rotations in Taihu Lake Region, China

Although nitrogen (N) loss through runoff and leaching from croplands is suspected to contribute to the deterioration of surrounding water systems, there is no conclusive evidence for paddy soils to prove this hypothesis. In this study, field plot experiments were conducted to investigate N losses through runoff and leaching for two consecutive years with 3 N fertilization rates in rice ( Oryza sativa L.)-wheat ( Triticum aestivum L.) rotations in the Taihu Lake region, China. A water collection system was designed to collect runoff and leachates for both the rice and wheat seasons. Results showed that dissolved N (DN), rather than particulate N (PN), was the main form of N loss by runoff. The NO 3 −-N concentration in runoff was between 0.1 and 43.7 mg L −, whereas the NH 4 +-N concentration ranged from below detection limit to 8.5 mg L −. Total N (TN) loads by runoff were 1.0–17.9 and 5.2–38.6 kg ha − during rice and wheat seasons, respectively, and the main loss occurred at the early growing stage of the crops. Nitrogen concentrations in leachates during the rice seasons were below 1.0 mg L − and independent of the N application rate, whereas those during the wheat season increased to 8.2 mg L − and were affected by the fertilizer rate. Annual losses of TN through runoff and leaching were 13.7–48.1 kg ha-1 from the rice-wheat cropping system, accounting for 5.6%–8.3% of the total applied N. It was concluded that reduction in the N fertilization rate, especially when the crop was small in biomass, could lower the N pollution potential for water systems.

Runoff nitrogen from a large sized paddy field during a crop period

Nutrient load management is an important environmental issue because nutrient loads from farmlands degrade surface waters as a result of anthropogenic eutrophication. Nitrogen load from a large sized paddy field during the crop period was examined from the results of field measurements carried out in 2004. The 1.5 ha paddy field was located east of Biwa Lake. Irrigation water volume and ponded water depth were continuously observed. Field measurements were carried out at least once a week to analyze total nitrogen (TN) concentration in the irrigation water and ponded water. Daily inflow and outflow of nitrogen was obtained by multiplication of the nitrogen concentration and transported water volume, consisting of irrigation, precipitation, evapotranspiration, percolation and surface discharge. Water outflow volume was calculated by a tank model that consisted of three small tanks connected to represent ponded water depth differences in the large paddy field. The calculated nitrogen load was 18.8 kg ha −1, with 7.2 kg ha −1 from surface drainage and 11.6 kg ha −1 from percolation loss. The runoff nitrogen value of 18.8 kg ha −1 was within the range of the reported values investigated in a medium-sized paddy field. The observed value was close to the value for a low percolation flux paddy field where less irrigation water has been applied. These results suggest that less irrigation water keep runoff nitrogen low. This also indicates that irrigation water management can reduce nitrogen load from large sized paddy fields.

Gypsum Amendment and Exchangeable Calcium and Magnesium Affecting Phosphorus and Nitrogen in Runoff

Loss of N and P from soil to water is not only an agronomic but also an environmental and human health problem. The main objective of this study was to evaluate the effect of gypsum amendment and soil‐exchangeable Ca and Mg on the concentration and loss of nutrients in runoff, sediment, and soil. The experiment was performed in the laboratory using a programmable rainfall simulator and erosion pans. The soil was a Miami silt loam, and treatments were (i) gypsum amendment, (ii) five target exchangeable Ca/Mg ratios, and (iii) a control. Nitrogen, P, and K were applied in all treatments based on soil test results and standard recommendations for corn (Zea mays L.). The fertilizers were mixed to a 2.5‐cm depth before pre‐wetting the soil. Gypsum was applied to the surface just before the rain. Two rainfall intensities (30 and 60 mm h−1) were simulated, and infiltrated water and runoff samples were taken every 5 min over 2 h. Nitrate N, NH4–N, and P in runoff, sediment, and soil were determined. The results showed that gypsum, as compared with the control, significantly decreased the mass loss in runoff of dissolved reactive P (DRP), total P (TP), soluble NH4–N, and total N by 85, 60, 80, and 59%, respectively. The concentration of these constituents was also significantly decreased by 83, 52, 79, and 50%, respectively. Nitrate N concentration in runoff was not decreased by gypsum. Gypsum also affected sediment and soil water–extractable P. The only significant effect of exchangeable Ca/Mg ratios was observed in the sediment water–extractable P, where Ca‐treated soil decreased by 50% the concentration of P compared with Mg‐treated soil. The results of this study demonstrated the potential of gypsum to decrease transport of total N and total P in runoff and the importance of Ca in the soil solution to decrease P solubility.