Losses In Drainage Water Research Articles

Reuse of biogas sludge for the slow-release fertilizer production to improve fertilizer use efficiency and soil fertility

Fertilizer overuse causes negative impacts on the environment and crop yields. Therefore, the production of slow-release fertilizers from biogas sludge is a potential solution for waste reuse and sustainable use of fertilizers. Granular fertilizers containing primary macronutrients (N, P and K) were formulated using biogas sludge and supplementary chemical compounds before coating with a thin film of glutaraldehyde cross-linked gelatin. The coating films reduced the release rates of N and P effectively. The application of formulated biogas fertilizers resulted in the competitive yield and growth rate of mustard greens over the 45-days cultivation compared to the application of commercial fertilizers. Particularly, the application of coated biogas fertilizers led to less nutrient losses in drainage water while maintained a balanced supply of available nutrients and beneficial bacteria in soils. This study emphasizes the feasibility to reuse biogas sludge for slow-release fertilizers production in improving fertilizer use efficiency and soil fertility.

Effect of varying sand percentage in sheath of nature-based capillary barriers composite on water storage capacity and okra growth in arid climate

Agricultural development in many arid countries including Oman is limited due to water scarcity which is currently exacerbated with increasing demand due to rapid population growth, economic development, and mismanagement of water resources. Impact of climate change is expected to adversely impact the water resources. Therefore, finding new efficient, environmentally friendly, and affordable water-saving techniques in agronomy is a necessity for achieving agricultural sustainability. Irrigation water can be saved by creating capillary barriers (CB) to unsaturated moisture flow. In this study, a “nature-inspired capillary barrier design” called hereafter as Smart Capillary Barrier (SCB) (mosaic of fine textured blocks, made of silt loam, and sandy sheath surrounding the blocks) was tested in series of field experiments with soil columns and pots. We investigated the effect of the percentage of sand of the sheath on water storage capacity of the SCB blocks and growth of okra (Abelmoschus esculentus L.) under deficit irrigation. Three proportions of sand to silt loam (sand%:silt loam%) in the sheaths were used in this study, SCB-25 (25:75%), SCB-50 (50:50%) and SCB-75 (75:25%). Our results show that increasing the percentage of sand in the designed and constructed SCB composite reduces evaporative and drainage water losses and therefore increases the water storage capacity of the blocks. Our SCB-75 attains 1.7–1.3 smaller drying rate than that for SCB-25 and SCB-50, respectively. Therefore, this composite had higher water saving capacity than a homogeneous soil (no capillary barrier) and a soil with a standard sand mulch (coarse soil overlies fine soil). The study found that using SCB composite did not consistently have a clear effect on the growth of okra plants at all stages of their development. However, during the development stage, using SCB-75 resulted in significantly higher dry biomass of the plants compared to using a homogeneous soil (the control). Additionally, during the initial stage of fruit yield, using SCB-75 also resulted in significantly higher fruit yield compared to using a homogeneous soil. Application of our SCB composite is a promising approach for saving water in desertic farming.

Nitrification inhibitor 3,4-Dimethylpyrazole phosphate improves nitrogen recovery and accumulation in cotton plants by reducing NO3− leaching under 15N-urea fertilization

PurposeThe use of nitrification inhibitors could be an interesting alternative when applied to enhance nitrogen (N) fertilizer use efficiency in annual crops such as cotton under tropical soil conditions. Thus, our aim was to evaluate the efficiency of the nitrification inhibitor 3,4-Dimethylpyrazole phosphate (DMPP) in a typical tropical soil by evaluating the fate of nitrogen (N-NO3−, N-NH4+ and total N in soil and leached water), N accumulation and N recovery by cotton plants and soil.MethodsLeaching columns with cotton plants were used to assess N-NO3− and N-NH4+ losses in drainage water. The treatments consisted of three N levels applied in side-dressing (corresponding to 50, 100 and 150 kg N ha−1) as 15N-urea with and without DMPP application. An additional treatment (absence of N application in side-dressing) was used as a control.Results3,4-Dimethylpyrazole phosphate efficiently improved N recovery after urea fertilizer was applied to plants and in the soil by reducing NO3− leaching, leading to enhanced N acquisition from fertilizer and soil and augmenting N accumulation in plants, mainly when high N levels above 100 kg N ha−1 were applied. We found that total N recovery increased 31% when 150 kg N ha−1 was applied as a urea + DMPP source compared to the application of conventional urea. In addition, DMPP application reduced NO3− leaching losses (by approximately 11 to 20%), although it had no significant effect on the shoot or root dry matter yields.ConclusionThe reduction in NO3− leaching losses obtained herein highlights the potential of DMPP to mitigate the impact of increased urea inputs on leaching losses, thereby improving N use efficiency and N uptake in cotton crops.

Leaching and surface runoff after fall application of fungicides on putting greens

AbstractMany greenkeepers and authorities are concerned about the environmental risks resulting from pesticide use on golf courses. We studied leaching and surface runoff of fungicides and metabolites for two winter seasons after fall application of boscalid, pyraclostrobin, prothioconazole, trifloxystrobin, and fludioxonil in field lysimeters at NIBIO Landvik, Norway. The applications were made on creeping bentgrass greens (5% slope) that had been established from seed or sod (26‐mm mat) on USGA‐specification. root zones amended with Sphagnum peat or garden compost, both with 0.3–0.4% organic carbon in the root zone. The proportions of the winter precipitation recovered as surface and drainage water varied from 3 and 91% in 2016–2017 to 33 and 55% in 2017–2018 due to differences in soil freezing, rainfall intensity, and snow and ice cover. Detections of fungicides and their metabolites in drainage water were mostly within the environmental risk limits (ERLs) for aquatic organisms. In contrast, concentrations in surface runoff exceeded ERLs by up to 1,000 times. Greens established from sod usually had higher fungicide losses in surface runoff but lower losses in drainage water than greens established from seed. Presumably because of higher microbial activity and a higher pH that made prothioconazole‐desthio more polar, fungicide and metabolite losses in drainage water were usually higher from greens containing compost that from greens containing peat. Leaching of fungicides and metabolites occurred even from frozen greens. The results are discussed in a practical context aiming for reduced environmental risks from spraying fungicides against turfgrass winter diseases.

Effect of Drainage Water Management on Nitrate Nitrogen Loss to Tile Drains in North Carolina

Abstract. Short-term studies have demonstrated that drainage water management (DWM), or controlled drainage (CD), can be used to substantially reduce the loss of nitrogen (N) from drained lands for a wide range of soils, crops, locations, and climates. Long-term studies on the effects of the practice are limited. This article presents results on the effects of CD on nitrate-N (NO3-N) losses for three crops, corn ( L.), wheat ( L.), and soybean ( [L.] Merr.), in a two-year rotation in North Carolina. Nitrate losses were measured on replicated plots under CD and conventional, or free drainage (FD), treatments for nine years between 1992 and 2012 on a tile-drained site near Plymouth, North Carolina. The site is on a Portsmouth sandy loam soil with parallel drains 22.9 m apart and 1.15 m deep. The subsurface drainage characteristics under FD were drainage intensity (DI) = 8 mm d-1, drainage coefficient (DC) = 14 mm d-1, and Kirkham coefficient (KC) = 18 mm d-1. Compared to FD, CD reduced annual drainage outflow by 33% and NO3-N export by 30%, with an average annual reduction of 6.3 kg ha-1 year-1. CD increased average NO3-N concentrations by 0.9 mg L-1, but the difference was not significant. The reduction in NO3-N export observed in the CD treatment was equal to the increase in N removed by the harvested grain. The results document the effects of CD on NO3-N export over a wide range of weather conditions during the nine-year study. While the average 30% reduction in NO3-N losses in drainage water is in the midrange of that reported by previous studies for different soils and climates, this is believed to be the first time such a reduction has been attributed to the effect of CD on increasing yields and N removed in the harvested grain. Keywords: Controlled drainage (CD), Corn, Drainage water, Drainage water management (DWM), Nitrate, Nitrogen, Soybean, Water quality, Wheat.

Assessment and Synthesis of 50 Years of Published Drainage Phosphorus Losses.

The prevalence of anthropogenic drainage systems in intensively cropped areas across North America combined with the degradation of important freshwater resources in these regions has created a critical intersection where understanding phosphorus (P) transport in drainage waters is vital. In this study, drainage-associated nutrient load data were retrieved and quantitatively analyzed to develop a more comprehensive understanding of the P loading and crop yield impacts of agronomic management practices within drained landscapes. Using the Drain Load table in the MANAGE (Measured Annual Nutrient loads from AGricultural Environments) database, the effect of factors such as soil characteristics, tillage, and nutrient management on P loading were analyzed. Across site-years, generally less than 2% of applied P was lost in drainage water, which corroborates the order of magnitude difference between agronomic P application rates and P loadings that can cause deleterious water quality impacts. The practice of no-till significantly increased drainage dissolved P loads compared with conventional tillage (0.12 vs. 0.04 kg P ha). The timing and method of P application are both known to be important for P losses, but these conclusions could not be verified due to low site-year counts. Findings indicate there is a substantial need for additional field-scale studies documenting not only P losses in drainage water but also important cropping management, nutrient application, soil property, and drainage design impacts on such losses.

Soil moisture dynamics in a hedgerow olive orchard under well-watered and deficit irrigation regimes: Assessment, prediction and scenario analysis

A study was conducted in a hedgerow olive orchard (SW Spain) to assess the capability of the HYDRUS 2D/3D model in predicting seasonal soil water dynamics in a well-watered (full irrigation, FI) and two regulated deficit irrigated plots (60RDI and 30RDI) differing in the timing and level of water stress imposed. The simulated soil water balance components were used to assess the suitability of the irrigation management accomplished in the experimental orchard and that of the irrigation treatments for different soil types and management scenarios. Soil water content (θ) was measured in all four plots per irrigation treatment with two access tubes per plot installed at 0.1m and 0.4m away from the dripper. Comparison of simulated against observed θ showed mean absolute errors ranging from 0.03 to 0.045cm3cm−3, root mean square errors from 0.035cm3cm−3 to 0.056cm3cm−3 and Nash–Sutcliffe efficiency coefficients from 0.438 to 0.834 across all treatments and probe locations. The modelled soil water balance components showed that drainage water losses represented 9–12% only of the applied irrigation water across all irrigation treatments. Scenario analysis revealed that daytime irrigation led to higher drainage water losses in FI than nighttime irrigation. For the same irrigation volumes, rootzone soil pressure head decreased (i.e. became more negative) when the irrigation frequency of the RDI treatments increased, thus supporting the lower irrigation frequencies scheduled in RDI as compared to FI in the experimental orchard. Scenario analysis also revealed the importance of adjusting irrigation schedules to soil type, irrespective of whether FI or RDI treatments were to be implemented.

Applicability of models to predict phosphorus losses in drained fields: a review.

Most phosphorus (P) modeling studies of water quality have focused on surface runoff loses. However, a growing number of experimental studies have shown that P losses can occur in drainage water from artificially drained fields. In this review, we assess the applicability of nine models to predict this type of P loss. A model of P movement in artificially drained systems will likely need to account for the partitioning of water and P into runoff, macropore flow, and matrix flow. Within the soil profile, sorption and desorption of dissolved P and filtering of particulate P will be important. Eight models are reviewed (ADAPT, APEX, DRAINMOD, HSPF, HYDRUS, ICECREAMDB, PLEASE, and SWAT) along with P Indexes. Few of the models are designed to address P loss in drainage waters. Although the SWAT model has been used extensively for modeling P loss in runoff and includes tile drain flow, P losses are not simulated in tile drain flow. ADAPT, HSPF, and most P Indexes do not simulate flow to tiles or drains. DRAINMOD simulates drains but does not simulate P. The ICECREAMDB model from Sweden is an exception in that it is designed specifically for P losses in drainage water. This model seems to be a promising, parsimonious approach in simulating critical processes, but it needs to be tested. Field experiments using a nested, paired research design are needed to improve P models for artificially drained fields. Regardless of the model used, it is imperative that uncertainty in model predictions be assessed.

Phosphorus fate, management, and modeling in artificially drained systems.

Phosphorus (P) losses in agricultural drainage waters, both surface and subsurface, are among the most difficult form of nonpoint source pollution to mitigate. This special collection of papers on P in drainage waters documents the range of field conditions leading to P loss in drainage water, the potential for drainage and nutrient management practices to control drainage losses of P, and the ability of models to represent P loss to drainage systems. A review of P in tile drainage and case studies from North America, Europe, and New Zealand highlight the potential for artificial drainage to exacerbate watershed loads of dissolved and particulate P via rapid, bypass flow and shorter flow path distances. Trade-offs are identified in association with drainage intensification, tillage, cover crops, and manure management. While P in drainage waters tends to be tied to surface sources of P (soil, amendments or vegetation) that are in highest concentration, legacy sources of P may occur at deeper depths or other points along drainage flow paths. Most startling, none of the major fate-and-transport models used to predict management impacts on watershed P losses simulate the dominant processes of P loss to drainage waters. Because P losses to drainage waters can be so difficult to manage and to model, major investment are needed (i) in systems that can provide necessary drainage for agronomic production while detaining peak flows and promoting P retention and (ii) in models that can adequately describe P loss to drainage waters.

Balancing agricultural and hydrologic risk in farming systems of the Chaco plains

Like in other semiarid areas of the world, farming systems in semiarid Chaco tend to use water-conservative crop systems to minimize production risks associated to water stress. While this strategy aims to stabilize crop yields and farmers income, the underutilization of water resources in wet years may result in heavy deep drainage water losses which could potentially lead to the development of dryland salinity. Conversely, more intensive crop systems that consume water exhaustively present lower drainage rates but are more prone to crop failure. We employed a monthly soil water balance approach to analyze the productive and ecohydrologic effects of five different farming systems across the region (winter, spring, summer, late-summer and a winter–summer double crop system) and to assess the possibility of minimizing emerging trade-offs between them through flexible water-informed cropping sequences. Our results indicate that water stress diminishes as crop systems are delayed towards the rainy season (winter > spring > summer > late-summer), but the productively safer late-summer strategy is the one with highest drainage rates. In most of the region, the relatively high production risk and insignificant drainage probability generally determine the convenience of conservative late-summer systems. However, in areas (or years) with higher amount and/or seasonality of rainfall, more intensive double-crop systems are necessary to minimize the likely high drainage fluxes. As rainfall is highly variable from one year to the other, the knowledge of soil water content at the onset of the season is useful to predict part of the available water offer and to asses expected production and ecohydrologic risks. In the most drainage-prone areas the implementation of flexible sequences that alternate conservative and intensive crop systems depending on soil water status, significantly reduced mean annual drainage with an acceptable increase in mean water stress index.

Temporal Variations and Controlling Factors of Nitrogen Export from an Artificially Drained Coastal Forest

Nitrogen losses in drainage water from coastal forest plantations can constrain the long term sustainability of the system and could negatively affect adjacent nutrient sensitive coastal waters. Based on long-term (21 years) field measurements of hydrology and water quality, we investigated the temporal variations and controlling factors of nitrate and dissolved organic nitrogen (DON) export from an artificially drained coastal forest over various time scales (interannual, seasonal, and storm events). According to results of stepwise multiple linear regression analyses, the observed large interannual variations of nitrate flux and concentration from the drained forest were significantly (p < 0.004) controlled by annual mean water table depth, and annual drainage or precipitation. Annual precipitation and drainage were found to be dominant factors controlling variations of annual DON fluxes. Temporal trends of annual mean DON concentration could not be explained explicitly by climate or hydrologic factors. No significant difference was observed between nitrogen (both nitrate and DON) export during growing and nongrowing seasons. Nitrate exhibited distinguished export patterns during six selected storm events. Peak nitrate concentrations during storm events were significantly (p < 0.003) related to 30-day antecedent precipitation index and the minimum water table depth during individual events. The temporal variations of DON export within storm events did not follow a clear trend and its peak concentration during the storm events was found to be significantly (p < 0.006) controlled by the short-term drying and rewetting cycles.

Effectiveness of oat and rye cover crops in reducing nitrate losses in drainage water

Much of the NO3 in the riverine waters of the upper Mississippi River basin in the United States originates from agricultural land used for corn (Zea mays L.) and soybean (Glycine max [L.] Merr.) production. Cover crops grown between maturity and planting of these crops are one approach for reducing losses of NO3. In this experiment, we evaluated the effectiveness of oat (Avena sativa L.) and rye (Secale cereale L.) cover crops in reducing NO3 concentrations and loads in subsurface drainage water. The oat fall cover crop was broadcast seeded into living corn and soybean crops before harvest in late August or early September and was killed by cold temperatures in late November or early December The rye winter cover crop, which had already been used annually for four years, was planted with a grain drill after corn and soybean harvest, overwintered, grew again in the spring, and was killed with herbicides before main crop planting. These treatments were evaluated in subsurface-drained field plots with an automated system for measuring drainage flow and collecting proportional samples for analysis of NO3 concentrations from each plot. The rye winter cover crop significantly reduced drainage water NO3 concentrations by 48% over five years, but this was less than the 58% reduction observed in its first four years of use. The oat fall cover crop reduced NO3 concentrations by 26% or about half of the reduction of the rye cover crop. Neither cover crop significantly reduced cumulative drainage or nitrate loads because of variability in cumulative annual drainage among plots. Both oat and rye cover crops are viable management options for significantly reducing NO3 losses to surface waters from agricultural drainage systems used for corn and soybean production.

Nitrate dynamics of forested watersheds: spatial and temporal patterns in North America, Europe and Japan

The relationships of nitrogen biogeochemistry are reviewed, focusing on forested watersheds in North America, Europe and Japan. Changes in both local and global nitrogen cycles that affect the structure and function of ecosystems are described. Within northeastern United States and Europe, atmospheric deposition thresholds of ~8 and ~10 kg N ha−1 year−1, respectively, result in enhanced mobilization of nitrate. High nitrate concentrations and drainage water loss rates up to 22 kg N ha−1 year−1 have also been found near Tokyo. Although atmospheric deposition may explain a substantial portion of the spatial pattern of nitrate in surface waters, other factors also play major roles in affecting the spatial patterns of nitrogen biogeochemistry. Calcium availability influences the composition of the vegetation and the biogeochemistry of nitrogen. The abundance of sugar maple is directly linked to soil organic matter characteristics and high rates of nitrogen mineralization and nitrification. Seasonal patterns of nitrate concentration and drainage water losses are closely coupled with differences in seasonal temperature and hydrological regimes. Snow-dominated forested catchments have highest nitrate losses during snowmelt. Watersheds in the main island of Japan (Honshu) with high summer temperatures and precipitation inputs have greatest losses of nitrate occur during the late summer. Understanding future changes in nitrate concentrations in surface waters will require an integrated approach that will evaluate concomitantly the influence of both biotic and biotic factors on nitrogen biogeochemistry.

Soil water storage and drainage under cotton-based cropping systems in a furrow-irrigated Vertisol

Comparative studies of drainage and leaching under tillage systems in irrigated tropical and sub-tropical Vertisols are sparse. The objective of this study was to quantify drainage under cotton-based cropping systems sown on permanent beds in an irrigated Vertisol. Drainage and soil water storage were measured with the chloride mass balance method and neutron moisture meter, respectively, during the 2002�03, 2004�05, 2006�07 and 2008�09 cotton seasons in an on-going experiment in a Vertisol in NW NSW. The experimental treatments were: cotton monoculture sown either after conventional tillage or on permanent beds, and a cotton�wheat rotation on permanent beds where the wheat stubble was retained as in situ mulch into which the following cotton crop was sown. Subject to in-crop rainfall, irrigation frequency varied between 7 and 14 days for cotton and 2�3 months for wheat. In 2005, a split-plot design was superimposed on the existing experiment such that the main-plot treatments were irrigation frequency (�frequent�, 7�14-day irrigation interval; �infrequent�, 14�21-day irrigation interval), and sub-plot treatments were the historical tillage system/crop rotation combinations. In comparison with cotton monoculture sown either after conventional tillage or on permanent beds, soil water storage, particularly during the early part of growing season when rainfall provided the major proportion of crop water requirements, and drainage were greatest when a cotton�wheat rotation was sown on permanent beds. Seasonal drainage out of the 1.2 m depth, averaged among all seasons, was of the order of 25 mm, 33 mm and 70 mm with cotton monoculture sown either after conventional tillage or on permanent beds, and a cotton�wheat rotation on permanent beds, respectively. Soil water storage and drainage were also greater when irrigation frequency was greater. Seasonal drainage out of the 1.2 m depth, averaged between the 2006�07 and 2008�09 seasons, was 54 mm with �frequent irrigation�, and 28 mm with �infrequent� irrigation. Infiltration was less in management systems which resulted in wetter soil; viz. frequent irrigation or a cotton�wheat rotation on permanent beds with in situ stubble retention. Drainage water losses in a furrow-irrigated Vertisol may be reduced and soil water storage increased (i.e. water conservation improved) by sowing a cotton�wheat rotation with in situ stubble retention under less frequent irrigation

Denitrification activity, wood loss, and N 2O emissions over 9 years from a wood chip bioreactor

Loss of nitrate in subsurface drainage water from agricultural fields is an important problem in the Midwestern United States and elsewhere. One possible strategy for reducing nitrate export is the use of denitrification bioreactors. A variety of experimental bioreactor designs have been shown to reduce nitrate losses in drainage water for periods up to several years. This research reports on the denitrification activity of a wood chip-based bioreactor operating in the field for over 9 years. Potential denitrification activity was sustained over the 9-year period, which was consistent with nitrate removal from drainage water in the field. Denitrification potentials ranged from 8.2 to 34 mg N kg −1 wood during the last 5 years of bioreactor operation. Populations of denitrifying bacteria were greater in the wood chips than in adjacent subsoil. Loss of wood through decomposition reached 75% at the 90–100 cm depth with a wood half-life of 4.6 years. However, wood loss was less than 20% at 155–170 cm depth and the half-life of this wood was 36.6 years. The differential wood loss at these two depths appears to result from sustained anaerobic conditions below the tile drainage line at 120 cm depth. Pore space concentrations of oxygen and methane support this conjecture. Nitrous oxide exported in tile water from the wood chip bioreactor plots was not significantly higher than N 2O exports in tile water from the untreated control plots, and loss of N 2O from tile water exiting the bioreactor accounted for 0.0062 kg N 2O-N kg −1 NO 3-N.

Effect of Controlled Drainage on Water and Nitrogen Balances in Drained Lands

Field studies have shown that subsurface drainage systems can be managed to conserve water and reduce losses of nitrogen (N) to surface waters. The practice, called controlled drainage (CD) or drainage water management (DWM), is a viable alternative for reducing N loads from drained cropland, including millions of acres in the Midwest. This article reviews past studies on the effect of CD on drainage volumes and N losses for a wide range of soils and climatological conditions and uses simulations to examine mechanisms affecting the practice. Results published in the literature show that CD has reduced drainage volumes and N losses in drainage waters by 17% to over 80%, depending on soil properties, crops, drainage intensities, control strategies, and location. This study resulted in the following conclusions. CD reduces subsurface drainage and raises water tables, while increasing ET, seepage, and surface runoff. Seepage, which depends on soil properties and site conditions, is an important factor that often governs the effectiveness of CD. Experiments to determine the effect of CD on drainage volumes and N losses should be conducted on the field or watershed scale so that impacts of seepage are properly represented. Increases in ET in response to CD are important but are rarely greater than 10%. The effect of this increase in water use on drainage water loss is also less than 10% for most locations. CD reduces N losses in drainage water by about the same percentage as its effect on subsurface drainage volume in most cases. The effect of CD on N loss to surface waters depends on denitrification, both in the profile and in reduced zones along seepage paths. For soils that do not develop reduced zones, the effect of CD on N loss may be substantially less than its effect on drainage volume.

The effect of DCD on nitrate leaching losses from a winter forage crop receiving applications of sheep or cattle urine

Dicyandiamide (DCD) is an effective mitigation option for decreasing nitrate-nitrogen (NO3-N) losses in drainage water from New Zealand pastures. This study determined the relative effect of DCD on decreasing NO3-N losses from simulated sheep or cattle urine patches applied to a winter forage crop. Lysimeters were collected from a site in North Otago (Mottled Fragic Pallic Timaru silt loam). Keywords: drainage, lysimeters, urine, nitrate, dicyandiamide, winter forage cropping

DRAINMOD-N II: Evaluated for an Agricultural System in Iowa and Compared to RZWQM-DSSAT

A new simulation model for N dynamics, DRAINMOD-N II, has been previously evaluated for only a few sites. We evaluated the model using ten years (1996-2005) of measured data from a subsurface-drained, corn-soybean agricultural system near Story City, Iowa. Nitrogen fertilizer was applied to plots at low, medium, and high rates (57 to 67 kg N ha-1, 114 to 135 kg N ha-1, and 172 to 202 kg N ha-1, respectively) during corn years, and nitrate (NO3) losses from subsurface drains under each plot were monitored biweekly for ten years. Average annual simulated and measured NO3 losses in drainage water were 21.9 and 20.1 kg N ha-1 for the low N rate, 26.6 and 26.5 kg N ha-1 for the medium N rate, and 36.6 and 37.0 kg N ha-1 for the high N rate, respectively. The model efficiency statistics for DRAINMOD-N II simulations of annual subsurface drain NO3 losses were 0.89, 0.95, and 0.94 for the low, medium, and high N rates, respectively. For the same experimental dataset, a comparison of DRAINMOD-N II simulations to that of another model that simulates hydrologic and N dynamics of agricultural systems, the RZWQM-DSSAT hybrid model, demonstrated that the two models were most different in their simulations of soybean N fixation, plant N uptake, and net N mineralization. Future field investigations should focus on generating better understandings of these processes. The results suggest that DRAINMOD-N II can reasonably simulate the effects of different corn-year N rates on losses of NO3 through subsurface drainage lines and that simulations of subsurface drainage NO3 losses by DRAINMOD-N II are comparable to that of RZWQM-DSSAT.

Key Performance Indicators for Simulated Variable-Rate Irrigation of Variable Soils in Humid Regions

Decision support tools for precise irrigation scheduling are required to improve the efficiency of irrigation water use globally. This article presents a method for mapping soil variability and relating it to soil hydraulic properties so that soil management zones for variable-rate irrigation can be defined. A soil-water balance is used to schedule hypothetical irrigation events based on one blanket application of water to eliminate plant stress (uniform rate irrigation, or URI) and compares this to variable-rate irrigation (VRI), where irrigation is tailored to specific soil zone available water-holding capacity (TAWC) values. The key performance indicators, i.e., irrigation water use, drainage water loss, nitrogen leaching, energy use, irrigation water use efficiency (IWUE), and virtual water content, are used to compare URI and VRI at three contrasting sites using four years of climate data for a dairy pasture and maize crop and two years of climate data for a potato crop. Our research found that VRI saved 9% to 19% irrigation water, with accompanying energy saving. Loss of water by drainage, during the period of irrigation, was also reduced by 25% to 45% using VRI, which reduced the risk of nitrogen leaching. Virtual water content of these three primary products further illustrates potential benefits of VRI and shows that virtual water content of potato production used the least water per unit of dry matter production.

Field Evaluation of a Model for Predicting Nitrogen Losses from Drained Lands

The N simulation model, DRAINMOD-N II, was field-tested using a 6-yr data set from an artificially drained agricultural site located in eastern North Carolina. The test site is on a nearly flat sandy loam soil which is very poorly drained under natural conditions. Four experimental plots, planted to a corn (Zea mays)-wheat (Triticum aestivum L.)-soybean (Glycine max.) rotation and managed using conventional and controlled drainage, were used in model testing. Water table depth, subsurface drainage, and N concentration in drain flow were measured and meteorological data were recorded continuously. DRAINMOD-N II was calibrated using the data from one plot; data sets from the other three plots were used for model validation. Simulation results showed an excellent agreement between observed and predicted nitrate-nitrogen (NO(3)-N) losses in drainage water over the 6-yr period and a reasonable agreement on an annual basis. The agreement on a monthly basis was not as good. The Nash-Sutcliffe modeling efficiency (EF) for monthly predictions was 0.48 for the calibration plot and 0.19, 0.01, and -0.02 for the validation plots. The value of the EF for yearly predictions was 0.92 for the calibration plot and 0.73, 0.62, and -0.10 for the validation plots. Errors in predicting cumulative NO(3)-N losses over the 6-yr period were remarkably small; -1.3% for the calibration plot, -8.1%, -2.8%, and 4.0% for the validation plots. Results of this study showed the potential of DRAINMOD-N II for predicting N losses from drained agricultural lands. Further research is needed to test the model for different management practices and soil and climatological conditions.