A mathematical model for border irrigation II. Vertical and horizontal recession phases

Summary This paper, second in a series of three, develops a mathematical model, using the volume balance approach, to simulate vertical and horizontal recession of border irrigation. An equation is proposed for computing Manning's roughness factor N in both laminar and transitional flow regimes in recession phases. The model has four parameters which can be determined experimentally. Experimental data from ten vegetated as well as nonvegetated borders were used to verify the model. Average difference (AD) between calculated and observed vertical recession times was less than 4.4 min, and between calculated and observed horizontal recession times less than 4.6 min for the ten experimental data sets. Average relative error (ARE) in computed horizontal recession was less than 13% for these data sets. The model was found to be especially accurate for Reynold's number between 1,800 and 2,500.     

Evaluation of the sap flow determined with a heat balance method to measure the transpiration of a sugarcane canopy

Sap flow measurements based on the heat balance method offers the opportunity to evaluate directly and quite easily the mass flow rate of water in plants. However, extrapolation of measurements of water use by individual stems to that for a canopy is tricky. In the present study, 14 sugarcane stems, out of a canopy of nearly 200 000, were equipped with Dynamax sap flow gauge. We extrapolated these individual measurements to determine the transpiration of the canopy and compare this transpiration to the crop evapotranspiration calculated on the basis of the Penman–Monteith method. The method used for the extrapolation assumes that the transpiration of a sugarcane plant is proportional to its leaf area. Transpiration of the canopy determined by this method was overestimated by more 35% as compared to the reference evapotranspiration results. Different sources of possible errors were examined and lead to suppose that it is very difficult to determine the transpiration of a heterogeneous canopy in growth by using the sap flow measurement technique.     

Irrigated land retirement

Land retirement is ceasing irrigation withthe goal of reducing load, in general, ofdissolved constituents and, in particular,of trace elements, present in subsurfacedrainage generated from irrigated lands. Retirement is achieved through a process ofgoal setting, strategy development anddetermining effects, developing landselection criteria, implementation, andmonitoring. In this study, effects of landretirement are evaluated using hydrologic,soil and economic models as well as resultsfrom a field demonstration study. From themodeling and field monitoring, a process isdeveloped to meet the goals of a landretirement program in the San JoaquinValley of California.Potential negative effects listed for landretirement included loss of agriculturalproductivity, perhaps permanently, and lossof revenue to surrounding communities. Uncertainties included those associatedwith reuse of retired lands as wildlifehabitat, with retired-land maintenanceincluding dust control, with potentialpreservation of retired lands in reservefor future re-introduction to irrigated ordry-land agriculture, and withinstitutional changes concerning repaymentof federal and state water contracts. Benefits would accrue from economic returnto the landowner from the sale of property,the sale or lease of irrigation watersupply, the reduced cost of handlingdrainage, and allocation of freed-up waterto beneficial uses, and the reduced risk ofselenium exposure to fish and wildlife.A recommended sequential approach to selectand manage retired land is to identifyprimary objectives; formulate and implementarea-specific land retirement scenarios;measure biologic, hydrologic, soils andeconomic consequences in the short term andthe long term and manage and monitorretired lands based on dynamic biologic,hydrologic and soil conditions.     

Trickle and sprinkler irrigation of potato (Solanum tuberosum L.) in the Middle Anatolian Region in Turkey

The potato (Solanum tuberosum L.) is widely planted in the Middle Anatolian Region, especially in the Nigde-Nevsehir district where 25% of the total potato growing area is located and produces 44% of the total yield. In recent years, the farmers in the Nigde-Nevsehir district have been applying high amounts of nitrogen (N) fertilizers (sometimes more than 900 kg N ha⁻¹) and frequent irrigation at high rates in order to get a much higher yield. This situation results in increased irrigation and fertilization costs as well as polluted ground water resources and soil. Thus, it is critical to know the water and nitrogen requirements of the crop, as well as how to improve irrigation efficiency. Field experiments were conducted in the Nigde-Nevsehir (arid) region on a Fluvents (Entisols) soil to determine water and nitrogen requirements of potato crops under sprinkler and trickle irrigation methods. Irrigation treatments were based on Class A pan evaporation and nitrogen levels were formed with different nitrogen concentrations.The highest yield, averaging 47,505 kg ha⁻¹, was measured in sprinkler-irrigated plots at the 60 g m⁻³ nitrogen concentration level in the irrigation treatment with limited irrigation (480 mm). Statistically higher tuber yields were obtained at the 45 and 60 g m⁻³ nitrogen concentration levels in irrigation treatments with full and limited irrigation. Maximum yields were obtained with about 17% less water in the sprinkler method as compared to the trickle method (not statistically significant). On the loam and sandy loam soils, tuber yields were reduced by deficit irrigation corresponding to 70% and 74% of evapotranspiration in sprinkler and trickle irrigations, respectively. Water use of the potato crop ranged from 490 to 760 mm for sprinkler-irrigated plots and 565–830 mm for trickle-irrigated treatments. The highest water use efficiency (WUE) levels of 7.37 and 4.79 kg m⁻³ were obtained in sprinkle and trickle irrigated plots, respectively. There were inverse effects of irrigation and nitrogen levels on the WUE of the potato crops. Significant linear relationships were found between tuber yield and water use for both irrigation methods. Yield response factors were calculated at 1.05 for sprinkler methods and 0.68 for trickle methods. There were statistically significant linear and polynomial relationships between tuber yield and nitrogen amounts used in trickle and sprinkler-irrigated treatments, respectively. In sprinkler-irrigated treatments, the maximum tuber yield was obtained with 199 kg N ha⁻¹. The tuber cumulative nitrogen use efficiency (NUE_cu) and incremental nitrogen use efficiency (NUE_in) were affected quite differently by water, nitrogen levels and years. NUE_cu varied from 16 to 472 g kg⁻¹ and NUE_in varied from 75 to 1035 g kg⁻¹ depending on the irrigation method. In both years, the NH₄-N concentrations were lower than NO₃-N, and thus the removed nitrogen and nitrogen losses were found to be 19–87 kg ha⁻¹ for sprinkler methods and 25–89 kg ha⁻¹ for trickle methods. Nitrogen losses in sprinkler methods reached 76%, which were higher than losses in trickle methods.     

Estimation irrigation water requirements with derived crop coefficients for upland and paddy crops in ChiaNan Irrigation Association,Taiwan

Field experiments were performed at the HsuehChia Experimental Station from 1993 to 2001 to calculate the reference and actual crop evapotranspiration, derived the crop coefficient, and collected requirements input data for the CROPWAT irrigation management model to estimate the irrigation water requirements of paddy and upland crops at the ChiaNan Irrigation Association, Taiwan. For corn, the estimated crop coefficients were 0.40, 0.78, 0.89 and 0.71 in the initial, crop development, mid-season and late-season stages, respectively. Meanwhile, the estimated crop coefficients for sorghum were 0.44, 0.71, 0.87 and 0.62 in the four stages, respectively. Finally, for soybean, the estimated crop coefficients were 0.45, 0.89, 0.92 and 0.58 in the four stages, respectively. With implementation of REF-ET model and FAO 56 Penman–Monteith method, the annual reference evapotranspiration was 1268 mm for ChiaNan Irrigation Association.In the paddy fields, the irrigation water requirements and deep percolation are 962 and 295 mm, respectively, for the first rice crop, and 1114 and 296 mm for the second rice crop. Regarding the upland crops, the irrigation water requirements for spring and autumn corn are 358 and 273 mm, respectively, compared to 332 and 366 mm for sorghum, and 350 and 264 mm for soybean. For the irrigated scheme with single and double rice cropping patterns in the ChiaNan Irrigation Association, the CROPWAT model simulated results indicate that the annual crop water demands are 507 and 1019 mm, respectively, and the monthly water requirements peaked in October at 126 mm and in January at 192 mm, respectively.     

Yield performance of spring wheat improved by regulated deficit irrigation in an arid area

A field experiment was conducted in 2003 and 2004 growing seasons to evaluate the effects of regulated deficit irrigation on yield performance in spring wheat (Triticum aestivum) in an arid area. Three regulated deficit irrigation treatments designed to subject the crops to various degrees of soil water deficit at different stages of crop development and a no-soil-water-deficit control was established. Soil moisture was measured gravimetrically in the increment of 0–20 cm every five to seven days in the given growth periods, while that in 20 increments to 40, 40–60, 60–80, and 80–100 cm depth measured by neutron probe. Compared to the no-soil-water-deficit treatment, grain yield, biomass, harvest index, water use efficiency (WUE), and water supply use efficiency (WsUE) in spring wheat were all greatly improved by 16.6–25.0, 12.4–19.2, 23.5–27.3, 32.7–39.9, and 44.6–58.8% under regulated deficit irrigation, and better yield components such as thousand-grain weight, grain weight per spike, number of grain, length of spike, and fertile spikelet number were also obtained, but irrigation water was substantially decreased by 14.0–22.9%. The patterns of soil moisture were similar in the regulated deficit treatments, and the soil moisture contents were greatly decreased by regulated deficit irrigation during wheat growing seasons. Significant differences were found between the no-soil-water-deficit treatment and the regulated soil water deficit treatments in grain yield, yield components, biomass, harvest index, WUE, and WsUE, but no significant differences occurred within the regulated soil water deficit treatments. Yield performance proved that regulated deficit irrigation treatment subjected to medium soil water deficit both during the middle vegetative stage (jointing) and the late reproductive stages (filling and maturity or filling) while subjected to no-soil-water-deficit both during the late vegetative stage (booting) and the early reproductive stage (heading) (MNNM) had the highest yield increase of 25.0 and 14.0% of significant water-saving, therefore, the optimum controlled soil water deficit levels in this study should range 50–60% of field water capacity (FWC) at the middle vegetative growth period (jointing), and 65–70% of FWC at both of the late vegetative period (booting) and early reproductive period (heading) followed by 50–60% of FWC at the late reproductive periods (the end of filling or filling and maturity) in treatment MNNM, with the corresponding optimum total irrigation water of 338 mm. In addition, the relationships among grain yield, biomass, and harvest index, the relationship between grain yield and WUE, WsUE, and the relationship between harvest index and WUE, WsUE under regulated deficit irrigation were also estimated through linear or non-linear regression models, which indicate that the highest grain yield was associated with the maximum biomass, harvest index, and water supply use efficiency, but not with the highest water use efficiency, which was reached by appropriate controlling soil moisture content and water consumption. The relations also indicate that the harvest index was associated with the maximum biomass and water supply use efficiency, but not with the highest water use efficiency.     

Combining remote sensing-simulation modeling and genetic algorithm optimization to explore water management options in irrigated agriculture

We present an innovative approach to explore water management options in irrigated agriculture considering the constraints of water availability and the heterogeneity of irrigation system properties. The method is two-folds: (i) system characterization using a stochastic data assimilation procedure where the irrigation system properties and operational management practices are estimated using remote sensing (RS) data; and (ii) water management optimization where we explored water management options under various levels of water availability. We set up a soil–water–atmosphere–plant model (SWAP) in a deterministic–stochastic mode for regional modeling. The distributed data, e.g. sowing dates, irrigation practices, soil properties, depth to groundwater and water quality, required as inputs for the regional modeling were estimated by minimizing the residuals between the distributions of field-scale evapotranspiration (ET) simulated by the regional application of SWAP, and by surface energy balance algorithm for land (SEBAL) using two Landsat7 ETM+ images. The derived distributed data were used as inputs in exploring water management options. Genetic algorithm was used in data assimilation and water management optimizations. The case study was conducted in Bata minor (lateral canal), Kaithal, Haryana, India during 2000–2001 rabi (dry) season. Our results showed that under limited water condition, regional wheat yield could improve further if water and crop management practices are considered simultaneously and not independently. Adjusting sowing dates and their distribution in the irrigated area could improve the regional yield, which also complements the practice of deficit irrigation when water availability is largely a constraint. This result was also found in agreement with the scenario that water is non-limited with the exception that the farmers have more degrees of freedom in their agricultural activities. An improvement of the regional yield to 8.5% is expected under the current scenario.     

Salt tolerance analysis of chickpea,faba bean and durum wheat varieties: II. Durum wheat

Seven varieties of durum wheat (Triticum turgidum), provided by ICARDA, were tested in a greenhouse experiment for their salt tolerance. Afterwards two varieties, differing in salt tolerance, were irrigated with waters of three different salinity levels in a lysimeter experiment to analyse their salt tolerance.The characteristics of the salt tolerant variety compared to the salt sensitive variety are:

• -a shorter growing season and earlier senescence;
• -a higher pre-dawn leaf water potential;
• -a stronger osmotic adjustment;
• -a better maintenance of the number of productive stems per plant.

Salt tolerance of durum wheat corresponds with drought tolerance because the tolerance is caused by earlier senescence and stronger osmotic adjustment, both reducing the transpiration of the plant.     

Farm salinity appraisal with water reuse

The need for a better understanding of the interaction between irrigation practices and the elevation and quality of the water table is of paramount importance for developing irrigation management strategies to ameliorate the regional problems of elevated saline water tables in the San Joaquin Valley, California. An area of approximately 3000 ha which includes portions of the Diener Ranch and the adjacent University of California, Westside Research and Extension Center, located south of Five Points in the Westlands Water District on the west side of the San Joaquin Valley was chosen for extensive field measurements. Field work consisted of four main activities namely, field instrumentation, collection of records of field activities, periodic data collection, and analyses of field data. Field measurements of water table carried out during 1994 indicated that the water table elevation was sensitive to the irrigation practices. There was a general increase in the area with a water table close to the surface during the irrigation season, and a return to water table elevations similar to the starting conditions at the end of the season. During the study period, the surface water quality deteriorated more in areas irrigated with reuse water and persisted through the end of the season. Depth averaged electrical conductivity for the study area over 6.5 m decreased between December 1993 and December 1994. Vertical hydraulic gradients in the saturated zone, were found to be an order of magnitude larger than horizontal gradients. The direction of vertical gradients changed, with downward gradients following pre-irrigations and upward gradients later in the season, when crop water requirements increased. Based on the results of the field study, it can be concluded that the irrigation management practices have a direct effect on local water table response as well as on water quality. Therefore, irrigation practices that promote less deep percolation losses may be helpful in controlling the water table rise.     

Soil N and salinity leaching after the autumn irrigation and its impact on groundwater in Hetao Irrigation District,China

Soil water and salinity are crucial factors influencing crop production in arid regions. An autumn irrigation system employing the application of a large volume of water (2200–2600 m³ ha⁻¹) is being developed in the Hetao Irrigation District of China, since the 1980s with the goal to reduce salinity levels in the root zone and increase the water availability for the following spring crops. However, the autumn irrigation can cause significant quantities of NO₃⁻ to leach from the plant root zone into the groundwater. In this study, we investigated the changes in soil water content, NO₃–N and salinity within a 150 cm deep soil profile in four different types of farmlands: spring wheat (F_W), maize (F_M), spring wheat–maize inter-planting (F_W–M) and sunflower (F_S). Our results showed that (1) salt losses mainly occurred in the upper 60 cm of the soil and in the upper 40 cm for NO₃–N; (2) the highest losses of salt and NO₃–N could be observed in F_W, whereas the lowest losses were found in F_W–M.NO₃–N concentration, pH and electrical conductivity (EC) in the groundwater were also monitored before and after the autumn irrigation. We found that the autumn irrigation caused the groundwater concentration of NO₃–N to increase from 1.73 to 21.6 mg L⁻¹, thereby, exceeding the standards of the World Health Organization (WHO). Our results suggest that extensive development of inter-planting tillage might be a viable measure to reduce groundwater pollution, and that the application of optimized minimum amounts of water and nitrogen to meet realistic yield goals, as well as the timely application of N fertilizers and the use of slow release fertilizers can be viable measures to minimize nitrate leaching.