Flood-irrigated Fields Research Articles

A Water Balancing Act: Water Balances Highlight the Benefits of Community-Based Adaptive Management in Northern New Mexico, USA

Quantifying groundwater recharge from irrigation in water-scarce regions is critical for sustainable water management in an era of decreasing surface water deliveries and increasing reliance on groundwater pumping. Through a water balance approach, our study estimated deep percolation (DP) and characterized surface water and groundwater interactions of two flood-irrigated fields in northern New Mexico to evaluate the regional importance of irrigation-related recharge in the context of climate change. DP was estimated for each irrigation event from precipitation, irrigation input, runoff, change in soil water storage, and evapotranspiration data for both fields. Both fields exhibited positive, statistically significant relationships between DP and total water applied (TWA), where one field exhibited positive, statistically significant relationships between DP and groundwater level fluctuation (GWLF) and between GWLF and total water applied. In 2021, total DP on Field 1 was 739 mm, where 68% of irrigation water applied contributed to DP. Field 2′s total DP was 1249 mm, where 81% of irrigation water applied contributed to DP. Results from this study combined with long-term research indicate that the groundwater recharge and flexible management associated with traditional, community-based irrigation systems are the exact benefits needed for appropriate climate change adaptation.

Evaluation of water use efficiency and optimal irrigation quantity of spring maize in Hetao Irrigation District using the Noah-MP Land Surface Model

Hetao Irrigation District (HID), one of the main grain-producing areas in China, is facing the severe challenge of agricultural water shortages. Improving water use efficiency (WUE) is the most appropriate way to achieve sustainable agricultural development and obtain high returns. However, farmers knew little about efficient irrigation strategies for flood-irrigated fields in the HID. In this study, the Noah-MP Land Surface Model (LSM) with dynamic crop and irrigation schemes is used to jointly simulate the maize yield and irrigation amount in the HID from 2003 to 2012. A sensitivity test for ten sets of irrigation setup with different soil moisture (SM) triggering thresholds (CRI=0–1) is conducted, and the corresponding WUE and irrigation water use efficiency (IWUE) are evaluated and analyzed. In addition, irrigation at different crop growth stages affects total irrigation amounts and crop yield. The results show that under rain-fed conditions, the severe SM deficit during the growing season significantly decreases the maize yield in the HID, with almost no harvest in dry years. With traditional flood irrigation, the irrigation amount per unit area exceeds 1000 mm, leading to low WUE and IWUE, while more than 18–25% of irrigation water is wasted as runoff. With the increase of irrigation intensity, both WUE and IWUE show a significant diminishing marginal effect, usually occurring when SM is greater than 0.24–0.27 m3/m3. The optimal WUE is obtained near CRI= 0.6, while the worst WUE is obtained at CRI= 1. In a normal year, efficient irrigation amount is about 390–480 mm, 53–63% less than that in flood irrigation. In this scenario, most irrigation water becomes SM and transpiration, and less than 5% becomes runoff. With effective irrigation in the reproductive stage, only a small amount of irrigation is needed to promote yield formation. Fully considering the maize yield, WUE, ecosystems, and the available water resources in the HID, the recommended irrigation amount is about 600–650 mm to achieve the optimal maize yield and WUE.

Irrigation Water Productivity of Basmati Rice; An On-Farm Comparison Between Rice Grown With Drip and Conventional Flood Methods of Irrigation.

In this on farm study, drip irrigation systems were installed in 21 farmers’ fields in 1 acre area each, where rice is  grown conventionally by flood irrigation. Pan E based irrigation schedule is followed in the drip treatments. A fertigation schedule is also implemented for fertilizer application in the drip irrigated fields. A comparison between conventional flood and drip method of irrigations were done on  data of Irrigation water consumption, rice grain yield and irrigation water productivity (IWP). Overall hike in yield because of drip method of irrigation was 10-18 % of that in flood and mean IWP were 0.8 kg/m3 in drip and 0.3 kg/m3 in flood irrigated field.

Hydrologic modeling of reach scale fluxes from flood irrigated fields

Agricultural water is of considerable interest to water managers and policymakers as irrigation—particularly flood irrigation—accounts for the largest portion of freshwater use. However, characterization of how and when flood applied water contributes to storage and adjacent surface water bodies via return flow remains limited, particularly relative to the volume of studies addressing surface processes. This study focuses on improving our understanding of return flow paths and explicitly quantifying subsurface return flow contributions using hydro-geophysical observations coupled with a vadose zone transport flow model. Our approach, which simulates return flow in agricultural fields in a small, heavily instrumented field site in northern Wyoming, leverages daily measured values of evapotranspiration obtained from a large aperture scintillometer and atmospheric conditions, and uses seismic data to characterize heterogeneous structure of the soil profiles at field scale. We use these high-resolution, site specific datasets to parameterize a process-based vadose zone flow model that quantifies hydrologic response to flood irrigation along the stream reach, allowing us to identify return flow fluxes out of the fields. Using our approach, we found that the majority of applied irrigation water (60%) left the fields through subsurface flow paths, while only 13% was consumed by vegetation. Subsurface runoff over less-permeable soil layers, governed by the subsurface structural characteristics, was identified as the dominant subsurface flow process contributing to fluxes out of the fields. Importantly, our findings about the importance of subsurface return flow paths nuance previous research which has emphasized surface flow paths. By improving our understanding of return flow processes through a high- resolution vadose zone model that leverages climatological, geophysical, and hydrological observations, this study advances our understanding of return flow processes. Understanding how subsurface characteristics influence return flow generation in semi-arid agriculturally productive regions will help managers and policy makers balance desires for improved irrigation efficiency against concerns about irrigation-dependent ecosystem services.

Long-term monitoring of soil bulk density and erosion rates in two Prunus Persica (L) plantations under flood irrigation and glyphosate herbicide treatment in La Ribera district, Spain

Early season fruit production for the northern European market is highly intensive in fertilization, machinery, irrigation and the use of herbicides. Those conditions increase the soil losses and soil compaction and threaten the Sustainable Goals for Development of the United Nations by 2030. Long-term soil erosion measurements are necessary to determine the sustainability of agriculture managements. Moreover, soil erosion on flood irrigation land is a topic that request more surveys and research as rainfed sloping terrains attracted all the attention of scientists and research investment. Improved Stock Unearthing Method (ISUM) was applied to two 15 years-old herbicide treated fields of Saturn peaches (Prunus persica var. platycarpa) to determine long-term soil erosion rates (2004–2019). Using ISUM, a 1 mm thick nylon rope (700 mm length) was used to connect trees perpendicular to the direction of rows at the height of the graft. To detection soil lowering, the vertical distance of the rope to the soil surface was measured at 10 cm intervals along the rope. The ring method (264 samples at 0–6 cm) was used to determine the soil bulk density, which was in average 1.15 gr cm−3 for both plots. There was found a compaction in the centre of both plots due to the pass of machinery with mean bulk density values of 1.23 gr cm−3, meanwhile underneath of the trees, the soil bulk density was 1.05 gr cm−3. The topography survey carried out with ISUM (2508 sampling points) informed that flood irrigation redistributed the soil from the upper to the lower field position, where a sedimentation layer was measured. We found that the two studied fields showed a contrasted response, with low soil erosion values in Benimodo and high in L'Alcúdia study sites. Soil erosion rates were in average 1.46 Mg ha−1 yr−1 and 8.02 Mg ha−1 yr−1 for Benimodo and L'Alcúdia, respectively. However, the maps development using ISUM allow to inform that the pattern of soil redistribution is similar for both fields as the highest soil lowering was found in the upper field part, where the flood discharge detach soil particles. In the lower field position sedimentation takes place. The dataset allows us to conclude that soil erosion in Saturn peaches fields is non-sustainable and more soil conservation management should be applied to reduce the soil erosion rates due to the bare soils as a consequence of the use of herbicides. This research informs that soil erosion in flood irrigated fields is a relevant process that needs more investigations around the world, where 94% of the irrigated land is under flood or furrow irrigation, and where irrigation is growing year after year.

Improving groundwater recharge estimates in alfalfa fields of New Mexico with actual evapotranspiration measurements

Quantifying groundwater recharge from irrigation practices of arid regions is necessary for efficient and sustainable groundwater resources management. Recharge is difficult to measure directly, many studies have quantified recharge from agricultural fields as a residual of the soil water balance method (WBM) or by other mathematical models estimating evapotranspiration (ET) and measuring soil moisture, rainfall, and irrigation. ET is often estimated using weather parameters from climate stations that are distant from crops. Flooding of fields is the most common form of irrigation used by farmers in the Mesilla Valley, New Mexico to grow alfalfa, one of the state’s major crops. The objectives of this study were to quantify recharge in flood irrigated alfalfa fields in the Mesilla Valley, New Mexico using the WBM and actual ET measurements during the 2017 growing season. The study fields were different sizes, crop ages, and soil textures. Actual ET of alfalfa was measured on the largest field using the eddy covariance − energy budget method and applied to the two other nearby fields as estimated ET. All other WBM parameters were measured at each study site (i.e. soil moisture, rainfall, and applied irrigation). Recharge using ET referenced to grass (ETsz) was then calculated using weather parameters and compared with measured ET. Recharge ranged from 618 to 716 mm with no significant statistical differences between the three alfalfa fields (f-ratio of 0.8876 and a p-value of 0.42 using ANOVA). Recharge to irrigation ratio ranged from 37% to 45%. On-farm irrigation efficiency ranged from 54.86% to 59.94%. When compared to measured ET, ETsz underestimated recharge of alfalfa by 11% in the WBM and overestimated recharge by 6% when a reduction in ETsz during harvest periods are considered. The results show that the measurement of actual ET improved recharge estimates in the alfalfa fields.

Modeling soil water balance and irrigation strategies in a flood-irrigated wheat-maize rotation system. A case in dry climate, China

Demand for irrigation water has been steadily increasing in arid regions where intensification of crop production is supported by flood-irrigation. An assessment of irrigation performance, water productivity, and irrigation schedules is critical to water conservation in dry climates. In this study, we conducted a field experiment to compare soil water balance in a flood-irrigated wheat-maize rotation system during the growing season of 2015–2016. We then modeled the soil water balance and improved irrigation strategies by coupling Hydrus-1D with the CROPWAT model, and using evapotranspiration calculated from climatic data. The calibrated Hydrus-1D model was used to simulate the temporal and spatial variation of evapotranspiration and deep percolation based on measured soil water distribution of soil profiles in the unsaturated zone. Results showed that using soil hydraulic parameters from inversion modeling can simulate soil water flow in multi-layer soil during a crop growing season. Simulation results indicated that about 36.6 and 40.6% (478.6 and 680.1 mm) of total water input in 2015 and 2016, respectively, was consumed by evapotranspiration. Furthermore, simulated deep percolation amounted for approximately 32.3 and 42.9% (403.9 and 696.6 mm) of the total amount of irrigation water in 2015 and 2016, respectively. These results indicated that only a small proportion of irrigation water was used by crops for transpiration. In addition, irrigation performance indicators such as relative water supply, relative irrigation supply, depleted fraction, and overall consumed ratio values indicated poor performance of irrigation practices in the study area. Particularly, crop yields did not increase with increases in irrigation water in flood-irrigated fields during the last ten years. Results of the CROPWAT model indicated that combinations of a fixed irrigation depth and timing, of 40 mm every 10 days, and 50 mm every 10 days were reasonable for wheat and maize, respectively, given the sandy soil in the study area. The improved irrigation strategies will limit water irrigation loss to 20% without significant effects on crop yields. This study provides an alternative approach for estimating deep percolation and crop water requirements supporting management efforts in water conservation in dry climates.

Sensor-Based Assessment of Soil Salinity during the First Years of Transition from Flood to Sprinkler Irrigation.

A key issue for agriculture in irrigated arid lands is the control of soil salinity, and this is one of the goals for irrigated districts when changing from flood to sprinkling irrigation. We combined soil sampling, proximal electromagnetic induction, and satellite data to appraise how soil salinity and its distribution along a previously flood-irrigated field evolved after its transformation to sprinkling. We also show that the relationship between NDVI (normalized difference vegetation index) and ECe (electrical conductivity of the soil saturation extracts) mimics the production function between yield and soil salinity. Under sprinkling, the field had a double crop of barley and then sunflower in 2009 and 2011. In both years, about 50% of the soil of the entire studied field—45 ha—had ECe < 8 dS m−1, i.e., allowing barley cultivation, while the percent of surface having ECe ≥ 16 dS m−1 increased from 8.4% in 2009 to 13.7% in 2011. Our methodology may help monitor the soil salinity oscillations associated with irrigation management. After quantifying and mapping the soil salinity in 2009 and 2011, we show that barley was stunted in places of the field where salinity was higher. Additionally, the areas of salinity persisted after the subsequent alfalfa cropping in 2013. Application of differential doses of water to the saline patches is a viable method to optimize irrigation water distribution and lessen soil salinity in sprinkler-irrigated agriculture.

Using Remote Sensing to Characterize and Compare Evapotranspiration from Different Irrigation Regimes in the Smith River Watershed of Central Montana

According to the 2005 U.S. Geological Survey national water use compilation, irrigation is the second largest use of fresh water in the United States, accounting for 37%, or 484.48 million cubic meters per day, of total freshwater withdrawal. Accurately estimating the amount of water withdrawals and actual consumptive water use (the difference between water withdrawals and return flow) for irrigation at a regional scale is difficult. Remote sensing methods make it possible to compare actual ET (ETa) rates which can serve as a proxy for consumptive water use from different irrigation regimes at a regional scale in a systematic manner. This study investigates crucial components of water use from irrigation such as the difference of ETa rates from flood- and sprinkler-irrigated fields, spatial variability of ETa within a watershed, and the effect of sprinkler irrigation on the water budget of the study area. The mean accumulated ETa depth for the 1,051 square kilometer study area within the upper Smith River watershed was about 467 mm 30-meter per pixel for the 2007 growing season (April through mid-October). The total accumulated volume of ETa for the study area was about 474.705 million cubic meters. The mean accumulated ETa depth from sprinkler-irrigated land was about 687 mm and from flood-irrigated land was about 621 mm from flood-irrigated land. On average, the ETa rate from sprinkler-irrigated fields was 0.25 mm per day higher than flood-irrigated fields over the growing season. Spatial analysis showed that ETa rates within individual fields of a single crop type that are irrigated with a single method (sprinkler or flood) can vary up to about 8 mm per day. It was estimated that the amount of sprinkler irrigation in 2007 accounted for approximately 3% of the total volume of ETa in the study area. When compared to non-irrigated dryland, sprinkler irrigation increases ETa by about 59 to 82% per unit area.

Environmental factors and agronomic practices associated with Savi’s pine vole abundance in Italian apple orchards

The development of an integrated rodent pest management strategy requires the adoption of protocols that should be based on a good knowledge of species–habitat relationships. Vole damage to orchards has increased in Italy in recent decades, as new cultivation practices have been introduced, despite the use of rodenticides. To improve our understanding of factors influencing Savi’s pine vole abundance in Italian apple orchards, we monitored the relationship between environmental and agronomic variables and population densities. Vole population sizes were influenced by the abundance of voles in the neighbouring fields and the presence of kiwifruit orchards, usually not treated with rodenticides, bordering on apple orchards. The type of irrigation system had the strongest influence on vole abundance and flood-irrigated fields had fewer voles than drip-irrigated fields. Apple-tree age and tilling practices also had an influence on vole abundance. Our research provides evidence that vole populations are influenced mostly by agronomic practices and type and extension of fruit orchards. An integrated management strategy in the apple orchard district should include coordination in chemical treatments between farmers and the experimentation of flood irrigation and regular soil tillage management as a possible cost-effective way to reduce vole populations.

Lower-Than-Expected Floret Sterility of Rice under Extremely Hot Conditions in a Flood-Irrigated Field in New South Wales, Australia

Rice florets are susceptible to high-temperature damage at anthesis, but rice production remains stable in the Riverina region of Australia even when the air temperature during flowering exceeds 40°C. To identify the mechanism that supports rice production under these conditions, we examined sterility and pollination in relation to microclimate and panicle temperature in an extremely hot paddy field in the Riverina region of New South Wales. In windy > 40°C weather, the panicle temperature was > 38°C at the windward edge of the crop but around 35°C inside the crop, probably because of strong transpirational cooling due to the extremely dry wind (15% RH). Pollen from the windward edge of the crop showed extremely poor germination, yet that from inside the crop showed sufficient germination for fertilization. Moreover, sterility inside the crop was significantly lower than that at windward edge. We concluded that the wind with large vapor pressure deficit enabled stable rice production under the extreme heat during flowering.

Seed losses at harvest and seed persistence of oilseed rape (Brassica napus) in different cultural conditions in Chinese farming systems

Zhu YM, Li YD, Colbach N, Ma KP, Wei W &amp; Mi XC (2012). Seed losses at harvest and seed persistence of oilseed rape (Brassica napus) in different cultural conditions in Chinese farming systems. Weed Research52, 317–326.SummaryThis article reports experiments that explore the critical factors for gene flow in oilseed rape (Brassica napus) via the soil seedbank under Chinese farming systems. Research was carried out on 16 farmer’s fields to estimate harvest seed losses after different planting methods and harvest timings, during the four components of the harvest operations. An additional field experiment was set up to estimate the potential germination proportion of seeds in flood‐irrigated and un‐irrigated fields, as a function of seed burial depth over time. Seed losses were largest during the sun‐drying of harvested plants in the field, accounting for about three quarters of the total seed losses. The number of intact seeds declined quickly after they entered the soil, particularly in un‐irrigated fields, and no volunteers germinated in the irrigated field after 3 months. Burial depth did not affect the potential for germination and emergence of volunteers in the flood‐irrigated field. However, the potential germination declined with increasing burial depth in the un‐irrigated field. No viable seeds remained in the soil after 16 months. Seed losses during harvest could be limited to 0.7–1.1% by weight of total seed production by placing a plastic membrane under the cut plants during drying and no rape seeds could germinate after 3 months in water‐logged condition. Thus, the risk of gene flow via the soil seedbank is probably small in Chinese oilseed rape farming systems.

Transport of two sulfonylurea herbicides in runoff from border dyke irrigation

Sulfonylurea herbicides have been detected in reservoirs and wetlands in the North American Great Plains. However, since little is known about the transport characteristics of these herbicides, the mechanism of contamination has not been established. In order to assess the potential contribution of surface runoff, transport of two sulfonylurea herbicides (thifensulfuron-methyl and tribenuron-methyl) was measured in surface runoff from a flood-irrigated field in the Outlook Irrigation District of Saskatchewan, Canada. Following herbicide application, the field was flood irrigated, and surface runoff was monitored. Surface drain flow rates and herbicide concentrations were measured from three 0.85 ha (2.1 ac) plots in the field. Although the rate of application of tribenuron-methyl (4.9 g ha -1 [0.07 oz ac -1 ]) was half that of thifensulfuron-methyl (9.8 g ha -1 [0.14 oz ac -1 ]), concentrations of the herbicides in surface runoff water were similar. The highest concentrations (0.98 μg L -1 for thifensulfuron-methyl and 0.81 μg L -1 for tribenuron-methyl) were measured during periods of low flow at the beginning of the runoff events. For both herbicides, concentrations decreased as flow in the drain increased but then recovered somewhat as flow receded. Total loss of tribenuron-methyl in runoff water five days after herbicide application averaged 1.9% of the amount applied, which was significantly greater than thifensulfuron-methyl losses that were approximately 0.8% of the application. These results confirm postapplication transport in surface runoff as a significant pathway for contamination of surface waters by thifensulfuron-methyl and tribenuron-methyl.

Transport of thifensulfuron-methyl and tribenuron-methyl in runoff

S ulfonylurea herbicides are highly phytotoxic herbicides that are widely used around the world for the pre- and postemergence control of a wide range of annual and perennial grasses and broadleaf weeds. They have been detected in reservoirs and wetlands in the North American Great Plains with reported detection frequencies of 35% to 52%. Although the source of contamination is not known, high concentrations of a number of herbicides followed rain-fall-generated runoff, suggesting that surface runoff likely contributed to the herbicide loadings. In order to assess the potential contribution of surface runoff, transport of two sulfonylurea herbicides (thifensulfuron-methyl and tribenuron-methyl) was measured in surface runoff from a flood-irrigated wheat field in the Outlook Irrigation District of Saskatchewan, Canada. Five days after application of thifensulfuron-methyl and tribenuron-methyl for in-crop control of broadleaf weeds in late June (4-leaf stage), the field was irrigated using the border dyke method and surface runoff was monitored. Surface drain flow rates and herbicide concentrations were measured from three 0.85 ha (2.1 ac) plots in the field. Flow rates were calculated by applying the Manning equation to water depths measured in a culvert downstream from the plots using a sonic water level sensor. Automated water samplers were programmed…

Near-source particulate emissions and plume dynamics from agricultural field operations

Particulate matter emissions generated by agricultural field preparation and harvesting operations were measured remotely via aerosol lidar and sampled simultaneously with a variety of aerosol point samplers in order to quantify dust plume space and time dynamics and particulate mass and number concentrations. Data for two cotton operations (disking, harvesting) in a flood-irrigated field in New Mexico are presented. Dust plume dynamics varied with boundary layer meteorological conditions, especially atmospheric stability, with plume maximum height significantly lower under stable conditions. Plume tracking indicated little change in plume area with height under unstable conditions and plume movement depended on wind speed and direction. Particle mass distributions indicate approximately 50% of the measured PM10 mass was PM2.5, significantly higher than previously reported values, possibly due to the near-source nature of the samples collected here. Variability in plume movement matched the variability in short-term wind fluctuations and this variability helps explain why models that utilize long-term averages perform poorly when trying to capture plume dynamics for nonsteady sources such as tractor operations.

Using electro-magnetic induction technology to identify sampling sites for soil acidity assessment and to determine spatial variability of soil acidity in rice fields

Irrigated agriculture has contributed to increasing topsoil acidity, which in turn can increase acidification of the subsoil. Lime is typically applied at a uniform rate to raise the pH of the soil, with no accounting for the variation in soil acidity that may exist within a field. Current commercial sampling protocols use surface soil composites taken across the whole field or in parts of fields where visual soil differences are apparent. Current liming recommendations may not account for in-field soil pH spatial variability, especially if the variability is not related to visual differences. Three studies were undertaken over 10 fields, to investigate the potential of using electro-magnetic induction instruments (Geonics EM38 and EM31) to target soil sampling in order to identify differences in soil acidity within flood-irrigated fields in southern New South Wales (NSW), Australia. Within individual fields, large differences in surface soil acidity were identified and a strong relationship (r2 = 0.49 to 0.91) between the soil’s apparent electrical conductivity and soil pH was found. It is proposed that fields from southern NSW that have grown rice, be divided into zones to soil sample for acidity assessment, based on EM instrument readings. Proposed ECa levels for the delineation of zones are &lt;80, 80–140 and &gt;140 mS/m for EM31v and &lt;80, 80–110 and &gt;110 mS/m for EM38v. Many rice growers in southern NSW currently have EM maps of their fields. Using these maps to target soil sampling for soil acidity would be a more cost-effective method of determining the spatial variability of soil acidity in a field than grid sampling. Knowledge of the variability of soil acidity within the field would potentially allow the application of appropriate lime rates, relative to soil pH and cation exchange capacity to all parts of the field. This knowledge could make the variable application of lime a cost effective approach, compared with whole field management approaches.

Drainage, salt leaching and physico-chemical properties of irrigated man-made terrace soils in a mountain oasis of northern Oman

Little is known about the sustainability of irrigated oasis agriculture in northern Oman. The objective of this study therefore was to examine which factors allowed agricultural productivity to be apparently maintained during the two millenia of a mountain oasis' existence. Soil moisture and physico-chemical properties were measured in a typical flood-irrigated field sown to alfalfa ( Medicago sativa L.). Particle size, organic ( C org) and inorganic carbon content, pH and electrical conductivity (EC) of the soil profile were analyzed at 0.15, 0.45 and 1.00 m. Saturated hydraulic conductivity and the soil's apparent bulk density and water potential were determined from undisturbed samples at 0.05, 0.25 and 0.60 m. During irrigation cycles of 6–9 days, volumetric water contents ranged from 30% to 13%. A tracer experiment with potassium bromide revealed that 52–56% of the irrigation water was stored in the upper 0.4 m of the soil. The rest of the water moved further down the profile, thus providing the necessary drainage to avoid the build-up of toxic salt concentrations. Due to differences in pore size, plant-available water in the topsoil amounted to 18.7% compared to 13% and 13.5% at 0.25- and 0.60-m depth, respectively. The aggregate structure in the upper 1.0 m of the profile is likely preserved by concentrations of calcium carbonate (CaCO 3) from 379 to 434 mg kg −1 and C org from 157 to 368 mg kg −1 soil. The data indicate that the sustainability of this irrigated landuse system is due to high water quality with low sodium but high CaCO 3 concentration, the elaborate terrace structure and water management which allows adequate drainage.

Herbicide and nutrient transport from an irrigation district into the South Saskatchewan River.

Pesticides and nutrients can be transported from treated agricultural land in irrigation runoff and thus can affect the quality of receiving waters. A 3-yr study was carried out to assess possible detrimental effects on the downstream water quality of the South Saskatchewan River due to herbicide and plant nutrient inputs via drainage water from an irrigation district. Automated water samplers and flow monitors were used to intensively sample the drainage water and to monitor daily flows in two major drainage ditches, which drained approximately 40% of the flood-irrigated land within the irrigation district. Over three years, there were no detectable inputs of ethalfluralin into the river and those of trifluralin were less than 0.002% of the amount applied to flood-irrigated fields. Inputs of MCPA, bromoxynil, dicamba and mecoprop were 0.06% or less of the amounts applied, whereas that for clopyralid was 0.31%. The relatively higher input (1.4%) of 2,4-D to the river was probably due its presence in the irrigation water. Corresponding inputs of P (as total P) and N (as nitrate plus ammonia) were 2.2 and 1.9% of applied fertilizer, respectively. Due to dilution of the drainage water in the river, maximum daily herbicide (with the exception of 2,4-D) and nutrient loadings to the river would not have resulted in significant concentration increases in the river water. There was no consistent remedial effect on herbicides entering the river due to passage of the drainage water through a natural wetland. In contrast, a considerable portion of the nutrients entering the river originated from the wetland.

Competition between maize and Datura stramonium in an irrigated field under semi‐arid conditions

Crop growth of maize (Zea mays L.) and Datura stramonium L. in monoculture and competition was studied over 4 years in a flood irrigated field in Zaragoza (Spain). Plant density was 8.33 m–2 for maize and 16.66 m–2 (1994 and 1995) and 8.33 m–2 (1996 and 1997) for D. stramonium. Maize yield was decreased by 14–63% when competing with the weed. Yield reduction increased as the time between crop and weed emergence decreased. The development of leaf area per plant during the exponential growth phase was faster in maize primarily because the leaf area of maize seedlings at emergence time was greater than that of the weed. The faster growth of maize in leaf area and height reduced the photosynthetically active radiation received by the weed. Datura stramonium had a lower radiation use efficiency (RUE) than maize. Competition from the weed slightly decreased the maximum leaf area index (LAI) of the crop, and leaf senescence of maize was accelerated. The weed competed with the crop late in the season reducing crop growth rate, grain number per ear and grain weight. Competitive ability of D. stramonium for light was mainly due to its growth habit, with the leaves concentrated in the upper part of the canopy (more than 75% of LAI in the upper 25% of its height), its higher light extinction coefficient (0.89) and its indeterminate growth habit. The N plant content of maize was not influenced by the presence of the weed. The weed had a higher N plant content than the crop throughout the season and took up more N in monoculture.

POTENTIAL FOR CONTAMINATION OF THE SOUTH SASKATCHEWAN RIVER WITH HERBICIDES APPLIED IN AN IRRIGATION DISTRICT

Herbicide inputs to the South Saskatchewan River in irrigation return flow water from a major drainage ditch within the South Saskatchewan River Irrigation District #1 were monitored over a growing season in relation to herbicide use on flood-irrigated fields drained by this ditch. Approximately 70% of the flood-irrigated area (2,038 ha) drained by this drainage ditch was treated with herbicides. The herbicides monitored included three base/neutral herbicides (atrazine, triallate and trifluralin) and four acidic herbicides (2,4-D, diclofop, bromoxynil and dicamba). Atrazine was not detected in the drainage water. Triallate and trifluralin were detected infrequently and concentrations of both herbicides were consistently less than 0.1 μg L−1. Of the acidic herbicides monitored, diclofop and bromoxynil were applied in the greatest amounts. Seasonal inputs to the river of these herbicides were approximately 1,600 and 390 g, respectively, which corresponded to 0.22 and 0.15% of the amounts applied within the study site.