Nitrate leaching in a silage maize field under different irrigation and nitrogen fertilizer rates

Quantification of the interactive effects of nitrogen (N) and water on nitrate (NO₃) loss provides an important insight for more effective N and water management. The goal of this study was to evaluate the effect of different irrigation and nitrogen fertilizer levels on nitrate-nitrogen (NO₃-N) leaching in a silage maize field. The experiment included four irrigation levels (0.7, 0.85, 1.0, and 1.13 of soil moisture depletion, SMD) and three N fertilization levels (0, 142, and 189 kg N ha⁻¹), with three replications. Ceramic suction cups were used to extract soil solution at 30 and 60 cm soil depths for all 36 experimental plots. Soil NO₃-N content of 0-30 and 30-60-cm layers were evaluated at planting and harvest maturity. Total N uptake (NU) by the crop was also determined. Maximum NO₃-N leaching out of the 60-cm soil layer was 8.43 kg N ha⁻¹, for the 142 kg N ha⁻¹ and over irrigation (1.13 SMD) treatment. The minimum and maximum seasonal average NO₃ concentration at the 60 cm depth was 46 and 138 mg l⁻¹, respectively. Based on our findings, it is possible to control NO₃ leaching out of the root zone during the growing season with a proper combination of irrigation and fertilizer management.     

Efficiency of controlled drainage and subirrigation in reducing nitrogen losses from agricultural fields

In northeast Italy, a regimen of controlled drainage in winter and subirrigation in summer was tested as a strategy for continuous water table management with the benefits of optimizing water use and reducing unnecessary drainage and nitrogen losses from agricultural fields.To study the feasibility and performance of water table management, an experimental facility was set up in 1996 to reproduce a hypothetical 6-ha agricultural basin with different land drainage systems existing in the region. Four treatments were compared: open ditches with free drainage and no irrigation (O), open ditches with controlled drainage and subirrigation (O-CI), subsurface corrugated drains with free drainage and no irrigation (S), subsurface corrugated drains with controlled drainage and subirrigation (S-CI). As typically in the region free drainage ditches were spaced 30 m apart, and subsurface corrugated drains were spaced 8 m apart.Data were collected from 1997 to 2003 on water table depth, drained volume, nitrate-nitrogen concentration in the drainage water, and nitrate-nitrogen concentration in the groundwater at various depths up to 3 m.Subsurface corrugated drains with free drainage (S) gave the highest measured drainage volume of the four regimes, discharging, on average, more than 50% of annual rainfall, the second-highest concentration of nitrate-nitrogen in the drainage water, and the highest nitrate-nitrogen losses at 236 k ha⁻¹.Open ditches with free drainage (O) showed 18% drainage return of rainfall, relatively low concentration of nitrate-nitrogen in the drainage water, the highest nitrate-nitrogen concentration in the shallow groundwater, and 51 kg ha⁻¹ nitrate-nitrogen losses.Both treatments with controlled drainage and subirrigation (O-CI and S-CI) showed annual rainfall drainage of approximately 10%. O-CI showed the lowest nitrate-nitrogen concentration in the drainage water, and the lowest nitrogen losses (15 kg ha⁻¹). S-CI showed the highest nitrate-nitrogen concentration in the drainage water, and 70 kg ha⁻¹ nitrate-nitrogen losses. Reduced drained volumes resulted from the combined effects of reduced peak flow and reduced number of days with drainage.A linear relationship between daily cumulative nitrate-nitrogen losses and daily cumulative drainage volumes was found, with slopes of 0.16, 0.12, 0.07, and 0.04 kg ha⁻¹ of nitrate-nitrogen lost per mm of drained water in S-CI, S, O, and O-CI respectively.These data suggest that controlled drainage and subirrigation can be applied at farm scale in northeast Italy, with advantages for water conservation.     

Nitrate leaching assessment in a long-term experiment under supplementary irrigation in humid Argentina

Applying high rates of nitrogen (N) fertilizer to crops has two major disadvantages: (1) the low N fertilizer use efficiency and (2) the loss of N by leaching, which may cause groundwater nitrate (NO₃⁻) pollution, especially in humid areas.The objectives of this study were to adjust and validate the LEACH-W model simulations with data observed in the field; to quantify nitrate concentrations in the soil solution; to estimate N loss by leaching; and to determine the moments during the year when greatest nitrate transport events occur beyond the rooting profile.A randomized complete block design with four replications was established on a typic Argiudoll. Crop fertilization treatments consisted of three N rates (0, 100, and 200 kg N ha⁻¹) using urea and ammonium nitrate solution (UAN) as the N source. Corn (Zea mays L.) was planted and ceramic soil-water suction samplers were installed to depths of 1, 1.5 and 2 m. Drainage was estimated by the LEACH-W model, which adjusted very well the actual volume of water in the soil profile. Nitrogen losses were statistically analyzed as repeated measure data, using the PROC MIXED procedure.Losses of nitrate-nitrogen (NO₃⁻-N) during the study increased as the rate of N applied increased. At all depths studied, statistically significant higher values were found for 200 N compared to 100 N and 0 N, and for 100 N compared to 0 N (p < 0.001).The greatest NO₃⁻-N losses through leaching occurred during crop growth. Significant differences (p < 0.05) were found between cropping and fallow in the three treatments and depths studied for seasons 4 and 5; these two seasons produced the highest drainage volumes at all depths.     

Simulation of drainage water quality with DRAINMOD

The design and management of drainage systems should consider impacts on drainage water quality and receiving streams, as well as on agricultural productivity. Two simulation models that are being developed to predict these impacts are briefly described. DRAINMOD-N uses hydrologic predictions by DRAINMOD, including daily soil water fluxes, in numerical solutions to the advective-dispersive-reactive (ADR) equation to describe movement and fate of NO₃-N in shallow water table soils. DRAINMOD- CREAMS links DRAINMOD hydrology with submodels in CREAMS to predict effects of drainage treatment and controlled drainage losses of sediment and agricultural chemicals via surface runoff. The models were applied to analyze effects of drainage intensity on a Portsmouth sandy loam in eastern North Carolina. Depending on surface depressional storage, agricultural production objectives could be satisfied with drain spacings of 40 m or less. Predicted effects of drainage design and management on NO₃-N losses were substantial. Increasing drain spacing from 20 m to 40 m reduced predicted NO₃-N losses by over 45% for both good and poor surface drainage. Controlled drainage further decreases NO₃-N losses. For example, predicted average annual NO₃-N losses for a 30 m spacing were reduced 50% by controlled drainage. Splitting the application of nitrogen fertilizer, so that 100 kg/ha is applied at planting and 50 kg/ha is applied 37 days later, reduced average predicted NO₃-N losses but by only 5 to 6%. This practice was more effective in years when heavy rainfall occurred directly after planting. In contrast to effects on NO₃-N losses, reducing drainage intensity by increasing drain spacing or use of controlled drainage increased predicted losses of sediment and phosphorus (P). These losses were small for relatively flat conditions (0.2% slope), but may be large for even moderate slopes. For example, predicted sediment losses for a 2% slope exceeded 8000 kg/ha for a poorly drained condition (drain spacing of 100 m), but were reduced to 2100 kg/ha for a 20 m spacing. Agricultural production and water quality goals are sometimes in conflict. Our results indicate that simulation modeling can be used to examine the benefits of alternative designs and management strategies, from both production and environmental points-of-view. The utility of this methodology places additional emphasis on the need for field experiments to test the validity of the models over a range of soil, site and climatological conditions.     

Simulation of transpiration, drainage, N uptake, nitrate leaching, and N uptake concentration in tomato grown in open substrate

Free-drainage or “open” substrate system used for vegetable production in greenhouses is associated with appreciable NO₃⁻ leaching losses and drainage volumes. Simulation models of crop N uptake, N leaching, water use and drainage of crops in these systems will be useful for crop and water resource management, and environmental assessment. This work (i) modified the TOMGRO model to simulate N uptake for tomato grown in greenhouses in SE Spain, (ii) modified the PrHo model to simulate transpiration of tomato grown in substrate and (iii) developed an aggregated model combining TOMGRO and PrHo to calculate N uptake concentrations and drainage NO₃⁻ concentration. The component models simulate NO₃⁻-N leached by subtracting simulated N uptake from measured applied N, and drainage by subtracting simulated transpiration from measured irrigation. Three tomato crops grown sequentially in free-draining rock wool in a plastic greenhouse were used for calibration and validation. Measured daily transpiration was determined by the water balance method from daily measurements of irrigation and drainage. Measured N uptake was determined by N balance, using data of volumes and of concentrations of NO₃⁻ and NH₄⁺ in applied nutrient solution and drainage. Accuracy of the two modified component models and aggregated model was assessed by comparing simulated to measured values using linear regression analysis, comparison of slope and intercept values of regression equations, and root mean squared error (RMSE) values. For the three crops, the modified TOMGRO provided accurate simulations of cumulative crop N uptake, (RMSE = 6.4, 1.9 and 2.6% of total N uptake) and NO₃⁻-N leached (RMSE = 11.0, 10.3, and 6.1% of total NO₃⁻-N leached). The modified PrHo provided accurate simulation of cumulative transpiration (RMSE = 4.3, 1.7 and 2.4% of total transpiration) and cumulative drainage (RMSE = 13.8, 6.9, 7.4% of total drainage). For the four cumulative parameters, slopes and intercepts of the linear regressions were mostly not statistically significant (P < 0.05) from one and zero, respectively, and coefficient of determination (r²) values were 0.96-0.98. Simulated values of total drainage volumes for the three crops were +21, +1 and −13% of measured total drainage volumes. The aggregated TOMGRO-PrHo model generally provided accurate simulation of crop N uptake concentration after 30-40 days of transplanting, with an average RMSE of approximately 2 mmol L⁻¹. Simulated values of average NO₃⁻ concentration in drainage, obtained with the aggregated model, were −7, +18 and +31% of measured values.     

Carbon and nitrogen cycling in a tropical Brazilian soil cropped with sugarcane and irrigated with wastewater

Carbon (C) and nitrogen (N) dynamics in agro-systems can be altered as a consequence of treated sewage effluent (TSE) irrigation. The present study evaluated the effects of TSE irrigation over 16 months on N concentrations in sugarcane (leaves, stalks and juice), total soil carbon (TC), total soil nitrogen (TN), NO₃⁻-N in soil and nitrate (NO₃⁻) and dissolved organic carbon (DOC) in soil solution. The soil was classified as an Oxisol and samplings were carried out during the first productive crop cycle, from February 2005 (before planting) to September 2006 (after sugarcane harvest and 16 months of TSE irrigation). The experiment was arranged in a complete block design with five treatments and four replicates. Irrigated plots received 50% of the recommended mineral N fertilization and 100% (T100), 125% (T125), 150% (T150) and 200% (T200) of crop water demand. No mineral N and irrigation were applied to the control plots. TSE irrigation enhanced sugarcane yield but resulted in total-N inputs (804-1622 kg N ha⁻¹) greater than exported N (463-597 kg N ha⁻¹). Hence, throughout the irrigation period, high NO₃⁻ concentrations (up to 388 mg L⁻¹ at T200) and DOC (up to 142 mg L⁻¹ at T100) were measured in soil solution below the root zone, indicating the potential of groundwater contamination. TSE irrigation did not change soil TC and TN.     

Nitrate-N loadings through subsurface environment to agricultural drainage ditches in two flat Midwestern (USA) watersheds

A study was conducted to understand the contributions of tile flow and baseflow to total nitrate-N (NO₃-N) loadings in two subsurface (tile)-drained watersheds, namely the Big Ditch (BD) and the Upper Embarras River (UER) watersheds in Illinois. Two stream sections were selected in the watersheds and rectangular cutthroat flumes were installed at the upstream and downstream ends of the stream sections to calculate the flow mass balance for separating baseflow. The stream section at BD site had two tile outlets draining into it. The stream section at UER watershed did not have any tile drain. Tile flow was also measured along with stream flow. Water samples were collected not only from the stream sections using auto-samplers but also manually from the tile drains. Average baseflow rates per unit lengths of the stream sections at BD and UER sites were 3.5 × 10⁻⁰⁴ and 9.4 × 10⁻⁰⁵ m² s⁻¹, respectively. At BD site, for six study periods, the percentages of baseflow and tile flow contributions of NO₃-N loads within the stream section were 90 and 10%, respectively. Annual NO₃-N contributions by the upstream subwatersheds for BD and UER stream sections were 61,819 and 16,155 kg, respectively. Annual NO₃-N loss from these two subwatersheds within BD and UER watersheds was 42.9 and 7.0 kg ha⁻¹, respectively. For the stream section at BD site, baseflow seemed to play a more important role than tile flow in raising the NO₃-N concentration level in the stream water. Land use seemed to play a major role in the significant difference in NO₃-N concentrations at the two subwatersheds upstream from the project sites. Nitrate-N loadings primarily depended on precipitation, antecedent moisture condition (AMC), fertilizer application time, and evapotranspiration (ET).     

Cover crop effects on nitrogen load in tile drainage from Walnut Creek Iowa using root zone water quality (RZWQ) model

Studies quantifying winter annual cover crop effects on water quality are mostly limited to short-term studies at the plot scale. Long-term studies scaling-up water quality effects of cover crops to the watershed scale provide more integrated spatial responses from the landscape. The objective of this research was to quantify N loads from artificial subsurface drainage (tile drains) in a subbasin of the Walnut Creek, Iowa (Story county) watershed using the hybrid RZWQ-DSSAT model for a maize (Zea mays L.)-soybean [Glycine max (L.) Merr.] and maize-maize-soybean rotations in all phases with and without a winter wheat (Triticum aestivum L.) cover crop during a 25-year period from 1981 to 2005. Simulated cover crop dry matter (DM) and N uptake averaged 1854 and 36 kg ha⁻¹ in the spring in the maize-soybean phase of the 2-year rotation and 1895 and 36 kg ha⁻¹ in the soybean-maize phase during 1981-2005. In the 3-year rotation, cover crop DM and N uptake averaged 2047 and 44 kg ha⁻¹ in the maize-maize-soybean phase, 2039 and 43 kg ha⁻¹ in the soybean-maize-maize phase, and 1963 and 43 kg ha⁻¹ in the maize-soybean-maize phase during the same period. Annual N loads to tile drains averaged 29 kg ha⁻¹ in the maize-soybean phase and 25 kg ha⁻¹ in the soybean-maize phase compared to 21 and 20 kg ha⁻¹ in the same phases with a cover crop. In the 3-year rotation, annual N loads averaged 46, 43, and 45 kg ha⁻¹ in each phase of the rotation without a cover crop and 37, 35, and 35 kg ha⁻¹ with a cover crop. These results indicate using a winter annual cover crop can reduce annual N loads to tile drains 20-28% in the 2-year rotation and 19-22% in the 3-year rotation at the watershed subbasin scale over a 25-year period.     

Tomato nitrogen accumulation and fertilizer use efficiency on a sandy soil, as affected by nitrogen rate and irrigation scheduling

Tomato production systems in Florida are typically intensively managed with high inputs of fertilizer and irrigation and on sandy soils with low inherent water and nutrient retention capacities; potential nutrient leaching losses undermine the sustainability of such systems. The objectives of this 3-year field study were to evaluate the interaction between N-fertilizer rates and irrigation scheduling on crop N and P accumulation, N-fertilizer use efficiency (NUE) and NO₃-N leaching of tomato cultivated in a plastic mulched/drip irrigated production system in sandy soils. Experimental treatments were a factorial combination of three irrigation scheduling regimes and three N-rates (176, 220, and 330 kg ha⁻¹). Irrigation treatments included were: (1) surface drip irrigation (SUR) both the irrigation and fertigation line placed underneath the plastic mulch; (2) subsurface drip irrigation (SDI) where the irrigation drip was placed 0.15 m below the fertigation line which was located on top of the bed; and (3) TIME (conventional control) with the irrigation and fertigation lines placed as in SUR and irrigation applied once a day. Except for the TIME treatment all irrigation treatments were soil moisture sensor (SMS)-based with irrigation occurring at 10% volumetric water content. Five irrigation windows were scheduled daily and events were bypassed if the soil water content exceeded the established threshold. The use of SMS-based irrigation systems significantly reduced irrigation water use, volume percolated, and nitrate leaching. Based on soil electrical conductivity (EC) readings, there was no interaction between irrigation and N-rate treatments on the movement of fertilizer solutes. Total plant N accumulation for SUR and SDI was 12-37% higher than TIME. Plant P accumulation was not affected by either irrigation or N-rate treatments. The nitrogen use efficiency for SUR and SDI was on the order of 37-45%, 56-61%, and 61-68% for 2005, 2006 and 2007, respectively and significantly higher than for the conventional control system (TIME). Moreover, at the intermediate N-rate SUR and SDI systems reduced NO₃-N leaching to 5 and 35 kg ha⁻¹, while at the highest N-rate corresponding values were 7 and 56 kg N ha⁻¹. Use of N application rates above 220 kg ha⁻¹ did not result in fruit and/or shoot biomass nor N accumulation benefits, but substantially increased NO₃-N leaching for the control treatment, as detected by EC monitoring and by the lysimeters. It is concluded that appropriate use of SDI and/or sensor-based irrigation systems can sustain high yields while reducing irrigation application as well as reducing NO₃-N leaching in low water holding capacity soils.     

Effects of changes in N-fertilizer management on water quality trends at the watershed scale

In this study, the ADAPT (Agricultural Drainage and Pesticide Transport) model was calibrated and validated for monthly flow and nitrate-N losses, for the 2000-2004 period, from two minor agricultural watersheds in Seven Mile Creek (SMC-1 and SMC-2) in south-central Minnesota. First, the model was calibrated and validated using the water quality data from the SMC-1 and again independently validated with the SMC-2 dataset. The predicted monthly flow and associated nitrate-N losses agreed reasonably with the measured trends for both calibration (r² = 0.81 and 0.70 for flow and nitrate-N losses, respectively) and validation (r² = 0.85 and 0.78 for flow and nitrate-N losses from SMC-1, and 0.89 and 0.78 for flow and nitrate-N losses from SMC-2, respectively) periods. The model performed less satisfactorily for the snowmelt periods than it did for the entire simulation period. Using the calibrated model, long-term simulations were performed using climatic data from 1955 to 2004 to evaluate the effects of climatic variability and N application rates and timing on nitrate-N losses. The predicted nitrate-N losses were sensitive to N application rates and timing. A decrease in the fall N application rate from 179.3 to 112 kg/ha decreased nitrate-N losses by 23%. By changing application timing from fall to spring at a rate of 112 N kg/ha, nitrate-N losses decreased by 12%. The predicted nitrate-N losses showed a linear response to precipitation with larger losses generally associated with wet years. A 25% increase in mean annual precipitation would offset reductions in nitrate-N loss achieved using better N fertilizer management strategies described above.     

Simulation of bromide and nitrate leaching under heavy rainfall and high-intensity irrigation rates in North China Plain

Heavy rainfall and irrigations during the summer months in the North China Plain may cause losses of nitrogen because of nitrate leaching. The objectives of this study were to characterize the leaching of accumulated N in soil profiles, and to determine the usefulness of Br⁻ as a tracer of surface-applied N fertilizer under heavy rainfall and high irrigation rates. A field experiment with bare plots was conducted near Beijing from 5 July to 6 September 2006. The experiment included three treatments: no irrigation (rainfall only, I0), farmers’ practice irrigation (rainfall plus 100 mm irrigation, I100) and high-intensity irrigation (rainfall plus 500 mm irrigation, I500), with three replicates. Transport of surface-applied Br⁻ and NO₃⁻ (assuming no initial NO₃⁻ in the soil profile) and accumulated NO₃⁻ in soil profiles were all simulated with the HYDRUS-1D model. The model simulation results showed that Br⁻ leached through the soil profile faster than NO₃⁻. When Br⁻ was used as a tracer for surface-applied N fertilizer to estimate nitrate leaching losses, the amount of N leaching may be overestimated by about 10%. Water drainage and nitrate leaching were dramatically increased as the irrigation rate was increased. The amounts of N leaching out of the 2.1-m soil profile under I0, I100 and I500 treatments were 195 ± 84, 392 ± 136 and 612 ± 211 kg N ha⁻¹, equivalent to about 20 ± 5%, 40 ± 6% and 62 ± 7% of the accumulative N in the soil profile, respectively. N was leached more deeply as the irrigation rate increased. The larger amount of initial accumulated N was in soil profile, the higher percentage of N leaching was. N leaching was also simulated in summer under different weather conditions from 1986 to 2006. The results indicated that nitrate leaching in rainy years were significantly higher than those in dry and normal years. Increasing the irrigation times and decreasing the single irrigation rate after fertilizer application should be recommended.     

Simulating soil water flow and nitrogen dynamics in a sunflower field irrigated with reclaimed wastewater

Soil water flow and nitrogen dynamics were simulated in sunflower field during and after the growing period, in Northern Greece. Soil water and nitrogen dynamics were evaluated using a one-dimensional simulation model based on the Galerkin finite element method. We examined the effects of irrigation with reclaimed wastewater and nitrogen fertilizer applications on plant growth, water and nitrogen distribution in the soil profile, water and nitrogen balance components and nitrogen leaching to groundwater. The model simulated the temporal variation of soil water content with reasonable accuracy. However, an over estimation of the measured data was observed during the simulation period. Relatively good agreement was found between the simulated and measured NH₄-N and NO₃-N concentrations over time and depth, whereas fluctuations at greater depths were relatively small. Most of the cumulative nitrate-N leaching (44.7 kg N ha⁻¹) occurred during the winter.     

Forage quality, water use and nitrogen utilization efficiencies of pearl millet (Pennisetum americanum L.) grown under different soil moisture and nitrogen levels

The increasing scarcity of water for irrigation is becoming the most important problem for producing forage in all arid and semi-arid regions. Pearl millet is a key crop in these regions which needs relatively less water than other crops. In this research, a field study was conducted to identify the best combination of irrigation and nitrogen (N) management to achieve acceptable pearl millet forage both in quantity and quality aspects. Pearl millet was subjected to four irrigation treatments with interaction of N fertilizer (0, 75, 150 and 225 kg ha⁻¹). The irrigation treatments were 40%, 60%, 80% and 100% of total available soil water (I₄₀, I₆₀, I₈₀ and I₁₀₀, respectively). The results showed that increasing moisture stress (from I₄₀ to I₁₀₀) resulted in progressively less total dry matter (TDM), leaf area index (LAI), and nitrogen utilization efficiency (NUzE), while water use efficiency (WUE) and the percentage of crude protein (CP%) increased. The highest TDM and LAI were found to be 21.45 t ha⁻¹ and 8.65, in I₄₀ treatment, respectively. TDM, WUE, CP% and profit responses to N rates were positive. The maximum WUE of 4.19 kg DM/m³ was achieved at I₁₀₀ with 150 kg N ha⁻¹. The results of this research indicate that the maximum profit of forage production was obtained in plots which were fully irrigated (I₄₀) and received 225 kg N ha⁻¹. However, in the situation which water is often limited and not available, application of 150 kg N ha⁻¹ can produce high forage quality and guaranty acceptable benefits for farmers.     

Evaluation of DRAINMOD using saturated hydraulic conductivity estimated by a pedotransfer function model

Direct measurement of soil saturated hydraulic conductivity (K_s) is time-consuming and therefore costly. The ROSETTA pedotransfer function model is able to estimate K_s from soil textural data, bulk density and one or two water retention points. This study evaluated the feasibility of running the DRAINMOD field-scale hydrological model with K_s input produced using ROSETTA. A hierarchical approach was adopted to estimate K_s using ROSETTA, with four limited-more extended sets of soil information used as inputs: USDA textural class (H1); texture (H2); texture and bulk density (H3); texture, bulk density, water retention at −33 kPa (θ_33 kPa) and −1500 kPa (θ_1500 kPa) (H4). ROSETTA-estimated K_s values from these four groups (H1-H4) were used in DRAINMOD to simulate drain outflows during a 4-year period from a conventional drainage plot (CD) and two controlled drainage plots (CWT1 and CWT2) located in south-east Sweden. The DRAINMOD results using ROSETTA-estimated K_s values were compared with observed values and with model results using laboratory-measured K_s values (H0). Deviations in simulated drainage outflow (D), infiltration (F) and evapotranspiration (ET) resulting from the use of ROSETTA-estimated rather than laboratory-measured K_s values were evaluated. During the study period, statistical comparisons showed good agreement on a monthly basis between observed and DRAINMOD-simulated drainage rates using five soil datasets (H0, H1, H2, H3 and H4). The monthly mean absolute error (MAE) ranged from 0.57 to 0.82 cm for CD, 0.38 to 0.41 cm for CWT1, and 0.15 to 0.22 cm for CWT2. On a monthly basis, the modified coefficient efficiency (E′) values were in the range of 0.62 to 0.74 for CD, 0.72 to 0.74 for CWT1, and 0.79 to 0.86 for CWT2. The modified index of agreement (d′) for monthly predictions ranged from 0.80 to 0.86 cm for CD, 0.87 to 0.88 cm for CWT1, and 0.89 to 0.93 cm for CWT2. The absolute values of the percent-normalised error (NE) on an overall basis when using ROSETTA-estimated rather than laboratory-measured K_s values were less than 3% in E, less than 1% in F, and less than 15% in D. The results suggest that ROSETTA-estimated K_s values can be used in DRAINMOD to simulate drainage outflows as accurately as laboratory-measured K_s values (H0) in coarse-textured soils.     

Effect of tile effluent on nutrient concentration and retention efficiency in agricultural drainage ditches

Tile drainage is a common water management practice in many agricultural landscapes in the Midwestern United States. Drainage ditches regularly receive water from agricultural fields through these tile drains. This field-scale study was conducted to determine the impact of tile discharge on ambient nutrient concentration, nutrient retention and transport in drainage ditches. Grab water samples were collected during three flow regimes for the determination of soluble phosphorus (SP), ammonium nitrogen (NH₄⁺-N), nitrate nitrogen (NO₃-N) concentrations and their retention in three drainage ditches. Measured nutrient concentration indicated lower SP and NH₄⁺-N, and greater NO₃-N concentrations in tile effluents compared to the ditch water. Net uptake lengths were relatively long, especially for NO₃-N, indicating that nutrients were generally not assimilated efficiently in these drainage systems. Results also indicated that the study reaches were very dynamic showing alternating increases or decreases in nutrient concentration across the flow regimes. The drainage ditches appeared to be nutrient-rich streams that could potentially influence the quality of downstream waters.     

Effects of N fertilization on root development and activity of water-stressed cotton (Gossypium hirsutum L.) plants

The objective of this investigation was to study effects of nitrogen on drought resistance in terms of changes in cotton (Gossypium hirsutum L.) root dry matter accumulation, N concentration, antioxidant enzyme activities and root vigor during short-duration water stress (withholding water for 8 days and then permitting to 10 days recover by re-watering). Cotton plants were grown in pots with three N levels (0, 240, and 480 kg N ha⁻¹). Soil-relative water content decreased with increasing N supply during the soil water stress period, while leaf area, dry matter production and N accumulation were enhanced. The root/shoot ratio and root-N/shoot-N ratio increased with water stress, and were smallest at 240 kg N ha⁻¹. Application of N increased the activities of peroxidase (POD) and catalase (CAT) of cotton root, but decreased superoxide dismutase (SOD) activity during water stress as well as during recovery. Malondialdehyde (MDA) content was significantly (p < 0.05) increased, and was lowest in the 240 kg N ha⁻¹ N treatment during water stress. At the 10th day after soil re-watering, MDA content of 240 kg N ha⁻¹ was similar to that of 480 kg N ha⁻¹, but less than that of 0 kg N ha⁻¹. The root vigor, which was debased by water stress, was the highest at 240 kg N ha⁻¹. After soil re-watering, N application promoted root vigor. The trends of net photosynthetic rate were the same as that of root vigor during water stress. These results suggest that appropriate N supply (240 kg N ha⁻¹ in this investigation) may contribute to drought resistance of cotton plants by adjusting the antioxidant enzyme activities of root, debasing lipid peroxidation and boosting root vigor during short-duration water stress (withholding water for 8 days in this investigation), however, excessive N supply (480 kg N ha⁻¹) had a deleterious effect on plant drought resistance.     

Simulation of nitrate-N movement in southern Ontario,Canada with DRAINMOD-N

DRAINMOD-N, a mathematical model to predict nitrate-N concentrations in surface runoff and drain outflows from subsurface-drained farmlands, has been tested against field data collected in southern Ontario. The data was collected in a corn field from 16 conventional drainage and subirrigation plots in Woodslee, Ontario, from 1992 to 1994. The model performance was evaluated by comparing the observed and simulated nitrate-N concentrations in surface runoff and drain outflows. A precise calculation of water-table depth is an essential prerequisite for a model to obtain a proper prediction of nitrate-N movement. For the simulation of water-table depth, the lowest root mean square error and the highest correlation coefficient of linear regression were 173 mm and 0.51 for the subirrigation plots; and 178 mm and 0.84 for the subsurface drainage plots. Therefore, the performance of DRAINMOD-N for soil hydrologic simulations was satisfactory and it could be used for assessing nitrogen fate and transport. For the simulation of nitrate-N losses in the subirrigation plots, the lowest root mean square error and the highest correlation coefficient of linear regression were 0.74 kg/ha and 0.98 for surface runoff; and 6.53 kg/ha and 0.91 for drain outflow. For the simulation in the subsurface drainage plots, the lowest root mean square error and the highest correlation coefficient of linear regression were 0.70 kg/ha and 0.96 for surface runoff; and 6.91 kg/ha and 0.92 for drain outflow. The results show that DRAINMOD-N can perform satisfactory simulation of soil hydrology and nitrate-N losses in surface runoff under various water-table management practices. The model can, therefore, be used to evaluate different water pollution scenarios and help in the development and testing of various pollution control strategies for fields in cold weather such as that in southern Canada.     

Modelling of water and nitrogen balances in the ponded water and soil profile of rice fields in Northern Greece

This paper presents a water and nitrogen balance model for the surface ponded water and soil profile system of rice (Oryza sativa L.) fields. The model estimates the daily water balance components, as well as, the daily losses and transformations of nitrogen. Data from two neighbouring rice fields during the growing season of 2005 in the Thessaloniki plain of Northern Greece were used for the application of the model. The data set of field A was used for the calibration of the model, while the data set from the field B for validation of model. Simulation results of total inorganic nitrogen in the soil and runoff water exhibited reasonable agreement with the measured data during calibration and verification of the model. Significant amounts of applied irrigation water were lost through surface runoff and deep percolation into the groundwater. The sum of nitrogen inputs from fertilization, mineralization and irrigation water were 292.7 and 280.4 kg ha⁻¹ for field A and B, respectively. Nitrogen uptake by algae in ponding water and plants was one of the main processes of nitrogen reduction in the rice field systems with an amount of 125.7 and 131.8 kg ha⁻¹ for field A and B, respectively. Leaching through percolated water was the other significant process with 118.3 and 120.8 kg ha⁻¹, respectively. Gaseous losses of nitrogen (via volatilization and denitrification) were also substantial processes of nitrogen reduction in the flooded compartment. The study showed that the simple model presents important results for the water and nitrogen management in rice fields. This information can be used for irrigation water saving and prevention of water resources contamination in rice-based agroecosystems.     

Chickpea water use efficiency in relation to cropping system, cultivar, soil nitrogen and Rhizobial inoculation in semiarid environments

Crops grown in semiarid rainfed conditions are prone to water stress which could be alleviated by improving cultural practices. This study determined the effect of cropping system, cultivar, soil nitrogen status and Rhizobium inoculation (Rz) on water use and water use efficiency (WUE) of chickpea (Cicer arietinum L.) in semiarid environments. The cultivars Amit, CDC Anna, CDC Frontier, and CDC Xena were grown in no-till barley, no-till wheat, and tilled-fallow systems and under various rates of N fertilizer (0, 28, 56, 84, and 112 kg N ha⁻¹) coupled with or without Rz. The study was conducted at Swift Current and Shaunavon, Saskatchewan, from 2004 to 2006. On average, chickpea used about 10 mm of water from the top 0-15 cm soil depth. In the tilled-fallow system, chickpea extracted 20% more water in the 15-30 cm depth, 70% more in the 30-60 cm depth, and 156% more in the 60-120 cm depth than when it was grown in the no-till systems. CDC Xena had WUE of 5.3 kg ha⁻¹ mm⁻¹ or 20% less than the average WUE (6.6 kg ha⁻¹ mm⁻¹) of the three other cultivars, even though these cultivars used the same amounts of water. Water use efficiency increased from 4.7 to 6.8 kg ha⁻¹ mm⁻¹ as N fertilizer rate was increased from 0 to 112 kg N ha⁻¹ when chickpea was grown in the no-till barley or wheat systems, but chickpea grown in the tilled-fallow system did not respond to changes in the fertilizer N rates averaging WUE of 6.5 kg ha⁻¹ mm⁻¹. In the absence of N fertilizer, the application of Rz increased WUE by 33% for chickpea grown in the no-till barley system, 30% in the no-till wheat system, and 9% in the tilled-fallow system. Chickpea inoculated with Rhizobium achieved a WUE value similar to the crop fertilized at 84 kg N ha⁻¹. Without the use of Rz, chickpea increased WUE in a linear fashion with increasing fertilizer N rates from 0 to 84 kg N ha⁻¹. Cropping system, cultivar, and inoculation all had greater impact on WUE than on the amount of water extracted by the crop from the soil. The improvement of cultural practices to promote general plant health along with the development of cultivars with improved crop yields will be keys for improving water use efficiency of chickpea in semiarid environments.     

Soil water dynamics under various agricultural land covers on a subsurface drained field in north-central Iowa, USA

Modification of land cover systems is being studied in subsurface drained Iowa croplands due to their potential benefits in increasing soil water and nitrogen depletion thus reducing drainage and NO₃-N loss in the spring period. The objective of this study was to evaluate the impacts of modified land covers on soil water dynamics. In each individual year, modified land covers including winter rye-corn (rC), winter rye-soybean (rS), kura clover as a living mulch for corn (kC), and perennial forage (PF), as well as conventional corn (C) and soybean (S), were grown in subsurface drained plots in north-central Iowa. Results showed that subsurface drainage was not reduced under modified land covers in comparison to conventional corn and soybean. Soil water storage (SWS) was significantly reduced by PF treatments during the whole growing seasons and by kC during May through July when compared to the cropping system with corn or soybean only (p < 0.05). Treatments of rC and rS typically maintained higher SWS than C and S, respectively, during the 3 years of this study. In the spring during a 10-15-day period when the rainfall was minimal, SWS in plots with rye, kura clover, and forage decreased at a significantly higher rate than the C and S plots which were bare. Estimated evapotranspiration (ET) during this period was significantly higher in rS, kC, and PF treatments than C and S. The results of this study suggested that significantly higher ET and similar drainage for modified land covers may increase water infiltration, which would be expected to reduce surface runoff thus to decrease stream flow. Because subsurface drainage reduction was not seen in this study, impact of modified land covers on NO₃-N loss needs further investigation.