Overland water and salt flows in a set of rice paddies

Cultivation of paddy rice in semiarid areas of the world faces problems related to water scarcity. This paper aims at characterizing water use in a set of paddies located in the central Ebro basin of Spain using experimentation and computer simulation. A commercial field with six interconnected paddies, with a total area of 5.31 ha, was instrumented to measure discharge and water quality at the inflow and at the runoff outlet. The soil was classified as a Typic Calcixerept, and was characterized by a mild salinity (2.5 dS m⁻¹) and an infiltration rate of 5.8 mm day⁻¹. The evolution of flow depth at all paddies was recorded. Data from the 2002 rice-growing season was elaborated using a mass balance approach to estimate the infiltration rate and the evolution of discharge between paddies. Seasonal crop evapotranspiration, estimated with the surface renewal method, was 731 mm (5.1 mm day⁻¹), very similar to that of other summer cereals grown in the area, like corn. The irrigation input was 1874 mm, deep percolation was 830 mm and surface runoff was 372 mm. Irrigation efficiency was estimated as 41%. The quality of surface runoff water was slightly degraded due to evapoconcentration and to the contact with the soil. During the period 2001–2003, the electrical conductivity of surface runoff water was 54% higher than that of irrigation water. However, the runoff water was suitable for irrigation. A mechanistic mass balance model of inter-paddy water flow permitted to conclude that improvements in irrigation efficiency cannot be easily obtained in the experimental conditions. Since deep percolation losses more than double surface runoff losses, a reduction in irrigation discharge would not have much room for efficiency improvement. Simulations also showed that rice irrigation performance was not negatively affected by the fluctuating inflow hydrograph. These hydrographs are typical of turnouts located at the tail end of tertiary irrigation ditches. In fact, these are the sites where rice has been historically cultivated in the study area, since local soils are often saline-sodic and can only grow paddy rice taking advantage of the low salinity of the irrigation water. The low infiltration rate characteristic of these saline-sodic soils (an experimental value of 3.2 mm day⁻¹ was obtained) combined with a reduced irrigation discharge resulted in a simulated irrigation efficiency of 60%. Paddy rice irrigation efficiency can attain reasonable values in the local saline-sodic soils, where the infiltration rate is clearly smaller than the average daily rice evapotranspiration.     

Effect of temporal variability in soil hydraulic properties on simulated water transfer under high-frequency drip irrigation

The effect of changes in the hydraulic properties of a loamy topsoil on water transfer under daily drip irrigation was studied over a cropping cycle. Soil water contents were measured continuously with neutron probes and capacitance sensors placed in access tubes (EnviroSMART) and were compared to predications made by the Hydrus-2D model. Three different sets of hydraulic parameters measured before and after irrigation started, were used.Our results demonstrated that, based on the assumptions used in this study, the accuracy of the Hydrus predictions is good. Graphical and statistical comparisons of simulated and measured soil water contents and consequently the total water storage revealed a similar trend throughout the monitoring period for the all three different sets of parameters. The soil hydraulic properties determined after irrigation started were found to be much more representative of the majority of the irrigation season, as confirmed by the accuracy of the simulation results with high values of the index of agreement and with values of RMSE similar in magnitude to the error associated with field measurements (0.020 cm³ cm⁻³). The highest RMSE values (about 0.04 cm³ cm⁻³) were found when the model used input soil parameters measured before irrigation started.Generally, changes in topsoil hydraulic properties over time had no significant effect on soil moisture distribution in our agro-pedo-climatic context. One possible explanation is that daily water application was conducted at the same time as maximal root water uptake. This meant the soil did not need to store total daily crop water requirements and consequently that the water redistribution phase represented a very short stage in the irrigation cycle. It is probable that irrigating in the daytime when crop evapotranspiration is highest could prevent the effects of a temporal change and other problems connected with the soil. Moreover, water will be always available for the crop. Further experiments are needed to justify the results and to study the effects of low frequency drip irrigation on soil hydraulic characterization and consequently on soil water transfer in order to improve irrigation scheduling practices.     

Soil water movement under a single surface trickle source

Under a trickle source, the flow of water in unsaturated soil takes place from a disc source having a radius changing with time due to change in the rate of infiltration. To predict the wetting pattern below an emitter placed on the soil surface, an unsteady, non-linearised numerical model has been developed in an oblate spheroidal coordinate system. Using this coordinate system, the problem involving disc source geometry having radius changing with time, is simplified, as the disc is a degenerate case of an oblate spheroid. The results of the proposed model are in close agreement with the experimental results of [Taghavi, S.A., Marino, M.A., Rolston, E., 1984. Infiltration from a trickle irrigation source. J. Irrig. Drain. Eng. ASCE 110 (4), 331–341] and the numerical model of [Bresler, E., 1978. Analysis of trickle irrigation with application to design problems. Irrig. Sci. 1, 3–17] developed in cylindrical coordinates. The applicability of the model has been analysed for special conditions of trickle irrigation e.g. large time water application, redistribution of soil water after discharge is cut off or reduced, and basin irrigation with restriction of surface water flow.     

Irrigation for crops in a sub-humid environment

Summary The water use of two soybean cultivars (Bragg and Ruse) was measured for three seasons for a range of irrigation treatments. The seasonal totals of plant and soil evaporation ranged from 450 to 750 mm or from 36 to 64% of class A pan evaporation for the same period. Both cultivars extracted approximately 60% of the total extractable soil water in the top 1.2 m of soil before actual evaporation (Ea) dropped below potential evaporation (Eo). Up to this point the ratio between Ea and class A pan evaporation averaged 0.8. Ruse used water at a faster rate than Bragg but Ruse was not as effective in extracting the deep (below 1.0 m) soil water as Bragg. Water use efficiency (kg seed ha^–1 mm^–1 water) showed a small but general increase with decreasing irrigation water application. Runoff losses varied from zero for non-irrigated Ruse in 1977/78 to 352 mm for frequently-irrigated Bragg in 1976/77, generally increasing with the number of irrigations.     

Effect of water shortage on yield, and protein and mineral compositions of drip-irrigated sweet corn in sustainable agricultural systems

Water is a natural resource of prime value that is very often limited and costly, particularly in semi-arid regions. While traditional irrigation methods increase the amount of surface runoff, drip irrigation provides efficient use of the limited water resources. This study was conducted to determine the water-yield relationship and the quality of sweet corn grown under deficit drip irrigation in 1998 and 1999 in Sanliurfa, Turkey. Irrigation treatments analysed in this study were full irrigation as well as 10, 20 and 30% deficiency of Class A pan evaporation. In both years, water use efficiency ranged between 1.18 and 1.36 kg m⁻³, and irrigation water use efficiency ranged between 1.36 and 1.62 kg m⁻³. The yield response factor (k_y) or the ratio of the decrease in relative yield to the decrease in relative water consumption varied from 0.82 to 1.43, and the water-saving rate ranged from 10.9 to 31.1%. The relationships between fresh ear yield and the irrigation treatments were statistically significant (P < 0.01), and the yield decreased with increasing deficit irrigation. Root dry matter increased with water shortage. Maximum values of leaf area index were obtained at full irrigation, whereas the lowest values were found at 30% water deficiency. The values of the deficit irrigation stress index increased with decreasing water application. Although the protein content increased, the Fe, Zn and Cu concentration of the kernels decreased with increasing water deficiency. Despite the reduction of fresh ear yield with deficit irrigation, the number of marketable ears at 10% water deficiency was still high and acceptable for sweet corn (var. Reward) in south-eastern Turkey.     

Effect of saline water irrigation and manure application on the available water content, soil salinity, and growth of wheat

Good water management combined with appropriate soil management is necessary for sustainable crop production in drylands. A pot culture experiment was conducted using sand dune soil under greenhouse conditions to evaluate the response of wheat (Triticum aestivum L.) to the application of farmyard manure (FYM) or poultry manure (PM), and irrigation with water at two salinity levels (0.11 and 2.0 dS m⁻¹) and two irrigation intervals (daily and every second day). The manure was applied at a rate of 20 Mg ha⁻¹. The soil water content, measured 1 h before every irrigation, showed that soil treated with PM retained more water than that treated with FYM, while the control (no manure) contained the least water. FYM treatment resulted in 78 and 21% higher dry matter yield compared to the control and PM treatments, respectively, under daily irrigation using good-quality water. The increase was 29 and 55%, respectively, when saline water was used for daily irrigation. A similar trend was observed with the alternate day irrigation treatment; FYM gave the highest dry matter yield. The number of tillers and plant height showed that FYM was better than PM, which in turn was better than the control under irrigation with good-quality water regardless of the irrigation interval. When water of the highest salinity was used for irrigation, FYM was still always the best, but the control was now better than the PM treatment. The electrical conductivity of the soil measured at the end of the experiment was slightly higher with PM, as compared to the FYM and control treatments. A significant interaction between irrigation water quality and manure application was observed, affecting plant growth. PM aggravated the adverse affect of saline water on plant growth by increasing soil salinity.     

Model-based evaluation of low-cost drip-irrigation systems and management strategies using saline water

A drip-irrigation module was developed and included in an ecosystem model and tested on two independent datasets, spring and autumn, on field-grown tomato. Simulated soil evaporation correlated well with measurements for spring (2.62 mm d⁻¹ compared to 2.60 mm d⁻¹). Changes in soil water content were less well portrayed by the model (spring r ² = 0.27; autumn r ² = 0.45). More independent data is needed for further model testing in combination with developments of the spatial representation of below-ground variables. In a fresh-water drip-irrigated system, about 30% of the incoming water was transpired, 40% was lost as non-productive evaporative flows, and the remainder left the system as surface runoff or drainage. Simulations showed that saline water irrigation (6 dS m⁻¹) caused reduced transpiration, which led to higher drainage and soil evaporation, compared with fresh water. Covering the soil with plastic mulch resulted in an increase in yield and transpiration. Finally, two different drip-irrigation discharge rates (0.2 and 2.5 l h⁻¹) were compared; however the simulations indicated that the discharge rate did not have any impact on the partitioning of the incoming water to the system. The model proved to be a useful tool for evaluating the importance of specific management options.

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Measured and simulated soil wetting patterns under porous clay pipe sub-surface irrigation

Sub-surface irrigation with porous clay pipe can be an efficient, water saving method of irrigation for many less developed arid and semi-arid regions. Maximizing the efficiency of clay pipe irrigation requires guidelines and criteria for system design and operation. In this study, experimental and simulated (with HYDRUS (2D/3D)) soil wetting patterns were investigated for sub-surface pipe systems operating at different water pressures. Predictions of the soil water content made with HYDRUS were found to be in good agreement (R² = 0.98) with the observed data. Additional simulations with HYDRUS were used to study the effects of various design parameters on soil wetting. Increasing the system pressure increased the size of the wetted zone. The installation depth affects the recommended lateral spacing as well as the amount of evaporative water loss. For a given water application, the potential rate of surface evaporation affected the shape of the wetted region only minimally. Soil texture, due to its connection to soil hydraulic conductivity and water retention, has a larger impact on the wetting geometry. In general, greater horizontal spreading occurs in fine texture soils, or in the case of layered soils, in the finer textured layers.     

Possible utilization of high-salinity waters and application of low amounts of water for production of the halophyte Kochia scoparia as alternative fodder in saline agroecosystems

Production of halophytes using saline waters and soils and feeding them to livestock is one of the most sustainable methods of conservation in desert ecosystems, in addition to accomplishing food production for the people living in these areas. Therefore, to study the possibility of irrigating Kochia (Kochia scoparia L. Schrad) with minimum quantities of highly saline water for use as a fodder crop in arid environments stretching across saline waters, two experiments were carried out in the Research Farm of the Ferdowsi University of Mashhad, Iran. In the salinity experiments, two populations of Kochia, including the Sabzevar and Indian genotypes, were irrigated with ground water having electrical conductivity (EC) of 5, 15, and 20 dS m⁻¹. In the irrigation-treatment experiments, two local populations of Kochia, including Sabzevar and Borujerd, were subjected to four irrigation regimes as follows: complete irrigation (100%), 80%, 60%, and 40% of the water requirements using a saline ground water with EC = 5 dS m⁻¹. Because, the Indian genotype is preferred as an ornamental plant, it is not suitable for increased dry-matter production under high-salinity irrigation water compared to the local genotype (Sabzevar), which is suitable for forage. The Sabzevar genotype produced a large amount of dry matter (7530 kg ha⁻¹), even when irrigated with 20 dS m⁻¹ saline water. The best time for harvesting Kochia for fresh feeding is at the end of flowering (88 days after sowing or DAS), when the biomass is relatively high (6500 kg ha⁻¹) and the leaf-to-shoot ratio, as a quality index, is approximately 50%. The highest green-area index was observed at 15 dS m⁻¹ and decreased at high levels of salinity. Photosynthesis and transpiration rate did not decline significantly with increasing external salinity four weeks after salinization, but increased in both genotypes at 15 dS m⁻¹, indicating that the salinity-tolerance threshold of Kochia for both photosynthesis and transpiration reduction is above this salinity level. The Indian genotype also showed a very low seed yield (210 kg ha⁻¹) at low levels of salinity, whereas Sabzevar produced 1120 kg ha⁻¹ seed under the same conditions. Different irrigation regimes had a significant effect on the biomass and seed production of Kochia. The highest forage yield was obtained from complete irrigation, with 11.1 Mg ha⁻¹ dry material. Sabzevar local population represented a better performance in terms of all characteristics, except accumulation of inflorescence dry matter, and no significant effects were recorded. In conclusion, Kochia's high foliage production capacity in the presence of salinity and limited irrigation make this plant suitable for use as an alternative forage crop in harsh environmental conditions. There is a wide range of intraspecific variation in K. scoparia, but more investigation is needed to introduce it as a cash crop.     

Integrated management of irrigation water and fertilizers for wheat crop using field experiments and simulation modeling

The reported study aimed at developing an integrated management strategy for irrigation water and fertilizers in case of wheat crop in a sub-tropical sub-humid region. Field experiments were conducted on wheat crop (cultivar Sonalika) during the years 2002–2003, 2003–2004 and 2004–2005. Each experiment included four fertilizer treatments and three irrigation treatments during the wheat growth period. During the experiment, the irrigation treatments considered were I₁ = 10% maximum allowable depletion (MAD) of available soil water (ASW); I₂ = 40% MAD of ASW; I₃ = 60% MAD of ASW. The fertilizer treatments considered in the experiments were F₁ = control treatment with N:P₂O₅:K₂O as 0:0:0 kg ha⁻¹, F₂ = fertilizer application of N:P₂O₅:K₂O as 80:40:40 kg ha⁻¹; F₃ = fertilizer application of N:P₂O₅:K₂O as 120:60:60 kg ha⁻¹ and F₄ = fertilizer application of N:P₂O₅:K₂O as 160:80:80 kg ha⁻¹. In this study CERES-wheat crop growth model of the DSSAT v4.0 was used to simulate the growth, development and yield of wheat crop using soil, daily weather and management inputs, to aid farmers and decision makers in developing strategies for effective management of inputs. The results of the investigation revealed that magnitudes of grain yield, straw yield and maximum LAI of wheat crop were higher in low volume high frequency irrigation (I₁) than the high volume low frequency irrigation (I₃). The grain yield, straw yield and maximum LAI increased with increase in fertilization rate for the wheat crop. The results also revealed that increase in level of fertilization increased water use efficiency (WUE) considerably. However, WUE of the I₂ irrigation schedule was comparatively higher than the I₁ and I₃ irrigation schedules due to higher grain yield per unit use of water. Therefore, irrigation schedule with 40% maximum allowable depletion of available soil water (I₂) could safely be maintained during the non-critical stages to save water without sacrificing the crop yield. Increase in level of fertilization increases the WUE but it will cause environmental problem beyond certain limit. The calibrated CERES-wheat model could predict the grain yield, straw yield and maximum LAI of wheat crop with considerable accuracy and therefore can be recommended for decision-making in similar regions.     

Evaluation on the irrigation and fertilization management practices under the application of treated sewage water in Beijing, China

Irrigation and fertilization management practices play important roles in crop production. In this paper, the Root Zone Water Quality Model (RZWQM) was used to evaluate the irrigation and fertilization management practices for a winter wheat–summer corn double cropping system in Beijing, China under the irrigation with treated sewage water (TSW). A carefully designed experiment was carried out at an experimental station in Beijing area from 2001 to 2003 with four irrigation treatments. The hydrologic, nitrogen and crop growth components of RZWQM were calibrated by using the dataset of one treatment. The datasets of other three treatments were used to validate the model performance. Most predicted soil water contents were within ±1 standard deviation (S.D.) of the measured data. The relative errors (RE) of grain yield predictions were within the range of −26.8% to 18.5%, whereas the REs of biomass predictions were between −38% and 14%. The grain nitrogen (N) uptake and biomass N uptake were predicted with the RE values ranging from −13.9% to 14.7%, and from −11.1% to 29.8%, respectively. These results showed that the model was able to simulate the double cropping system variables under different irrigation and fertilization conditions with reasonable accuracy. Application of RZWQM in the growing season of 2001–2002 indicated that the best irrigation management practice was no irrigation for summer corn, three 83 mm irrigations each for pre-sowing, jointing and heading stages of winter wheat, respectively. And the best nitrogen application management practice was 120 kg N ha⁻¹ for summer corn and 110 kg N ha⁻¹ for winter wheat, respectively, under the irrigation with TSW. We also obtained the alternative irrigation management practices for the hydrologic years of 75%, 50% and 25%, respectively, in Beijing area under the conditions of irrigation with TSW and the optimal nitrogen application.     

Evaluation of options for increasing yield and water productivity of wheat in Punjab, India using the DSSAT-CSM-CERES-Wheat model

The DSSAT-CSM-CERES-Wheat V4.0 model was calibrated for yield and irrigation scheduling of wheat with 2004–2005 data and validated with 13 independent data sets from experiments conducted during 2002–2006 at the Punjab Agricultural University (PAU) farm, Ludhiana, and in a farmer's field near PAU at Phillaur, Punjab, India. Subsequently, the validated model was used to estimate long-term mean and variability of potential yield (Y_p), drainage, runoff, evapo-transpiration (ET), crop water productivity (CWP), and irrigation water productivity (IWP) of wheat cv. PBW343 using 36 years (1970–1971 to 2005–2006) of historical weather data from Ludhiana. Seven sowing dates in fortnightly intervals, ranging from early October to early January, and three irrigation scheduling methods [soil water deficit (SWD)-based, growth stage-based, and ET-based] were evaluated. For the SWD-based scheduling, irrigation management depth was set to 75 cm with irrigation scheduled when SWD reached 50% to replace 100% of the deficit. For growth stage-based scheduling, irrigation was applied either only once at one of the key growth stages [crown root initiation (CRI), booting, flowering, and grain filling], twice (two stages in various combinations), thrice (three stages in various combinations), or four times (all four stages). For ET-driven irrigation, irrigations were scheduled based on cumulative net ETo (ETo-rain) since the previous irrigation, for a range of net ETo (25, 75, 125, 150, and 175 mm). Five main irrigation schedules (SWD-based, ET-driven with irrigation applied after accumulation of either 75 or 125 mm of ETo, i.e., ET75 or ET125, and growth stage-based with irrigation applied at CRI plus booting, or at CRI plus booting plus flowering stage) were chosen for detailed analysis of yield, water balance, and CWP and IWP. Nitrogen was non-limiting in all the simulations.Mean Y_p across 36 years ranged from 5.2 t ha⁻¹ (10 October sowing) to 6.4 t ha⁻¹ (10 November sowing), with yield variations due to seasonal weather greater than variations across sowing dates. Yields under different irrigation scheduling, CWP and IWP were highest for 10 November sowing. Yields and CWP were higher for SWD and ET75-based irrigations on both soils, but IWP was higher for ET75-based irrigation on sandy loam and for ET150-based irrigation on loam. Simulation results suggest that yields, CWP, and IWP of PBW343 would be highest for sowing between late October and mid-November in the Indian Punjab. It is recommended that sowing be done within this planting period and that irrigation be applied based on the atmospheric demand and soil water status and not on the growth stage. Despite the potential limitations recognised with simulation results, we can conclude that DSSAT-CSM-CERES-Wheat V4.0 is a useful decision support system to help farmers to optimally schedule and manage irrigation in wheat grown in coarse-textured soils under declining groundwater table situations of the Indian Punjab. Further, the validated model and the simulation results can also be extrapolated to other areas with similar climatic and soil environments in Asia where crop, soil, weather, and management data are available.     

Skin layer evaporation to account for small precipitation events—An enhancement to the FAO-56 evaporation model

The FAO-56 soil water evaporation model is a simple ‘slab’ model that has been found to produce good estimates of evaporation from bare soil over a range of conditions due to its adherence to conservation of mass and energy. The simplicity of the model makes it straightforward to apply and to parameterize. An enhancement is made to the original formulation to accommodate light wetting events that wet the soil ‘skin’ near the surface and evaporate relatively quickly, even when the underlying soil is dry. In effect, the evaporation process, when the soil skin is wetted, reverts temporarily into stage 1 evaporation. The enhancement utilizes the ‘readily evaporable water’ (REW) term of the original model so that no new parameters are required. The extended model performs similar to the original model in the absence of small precipitation events, but increases the evaporation rate when small events occur. The FAO-56 method with the skin evaporation enhancement is shown to compare well against simulations made using the HYDRUS 1D model that bases evaporation on the Richards equation. The enhanced model also closely followed evaporation recorded by weighing lysimeter for a silt loam soil at Kimberly, Idaho, with root mean square difference of 0.39 and 0.69 mm d⁻¹ for two wetting/drying sequences. Total cumulative evaporation during the longest and wettest sequence was estimated at 92% of the measured value.     

Evaluation of CERES-Wheat and CropSyst models for water–nitrogen interactions in wheat crop

Crop simulation models can provide an alternative, less time-consuming and inexpensive means of determining the optimum crop N and irrigation requirements under varied soil and climatic conditions. In this context, two dynamic mechanistic models (CERES (Crop Environment REsource Synthesis)-Wheat and CropSyst (Cropping Systems Simulation Model)) were validated for predicting growth and yield of wheat (Triticum aestivum L) under different nitrogen and water management conditions. Their potential as N and water management tool was evaluated for New Delhi representing semi-arid irrigated ecosystems in the Indo-Gangetic Plains. The field experiment was carried out on a silty clay loam soil at the Research Farm of the Indian Agricultural Research Institute, New Delhi, India during 2000–2001 to collect the input data for the calibration and validation of both the models on wheat crop (variety HD 2687). The models were evaluated for three water regimes [I4 (4 irrigations within the growing season), I3 (3 irrigations within the growing season) and I2 (2 irrigations within the growing season)] and five N treatments (N₀, N₆₀, N₉₀, N₁₂₀ and N₁₅₀). Both the models were calibrated using data obtained from the treatments receiving maximum nitrogen and irrigations, i.e., N₁₅₀ and I4 treatments. The models were then validated against other water and nitrogen treatments. For performance evaluation, in addition to coefficient of determination (R²), root mean square error (RMSE), mean absolute error (MAE) and Wilmot's index of agreement (IoA) were estimated. Both CERES-Wheat and CropSyst provided very satisfactory estimates for the emergence, flowering and physiological maturity dates. For CERES-Wheat overall prediction (pooled result of the three water regimes) of grain yield was satisfactory with significant R² values (0.88). The model, however, under estimated the biomass under all water regimes and N levels except for N₀ level, under which biomass was overpredicted. CropSyst predicted yield and biomass of wheat more closely than CERES-Wheat. The combined RMSE for the three water regimes between predicted and observed grain yield was 0.36 Mg ha⁻¹ for CropSyst as compared to 0.63 Mg ha⁻¹ for CERES-Wheat. Similarly, RMSE between observed and predicted biomass by CropSyst was 1.27 Mg ha⁻¹ as compared to 1.94 Mg ha⁻¹ between observed and predicted biomass by CERES-Wheat. Wilmot's index of agreement (IoA) also indicated that CropSyst model is more appropriate than CERES-Wheat in predicting growth and yield of wheat under different N and irrigation application situations in this study.     

Numerical investigation of the influence of texture,surface drip emitter discharge rate and initial soil moisture condition on wetting pattern size

Knowledge of the dimensions of the wetted zone formed under point source surface drip irrigation is essential to the design of cost-effective and efficient irrigation systems. Numerical simulations were carried out with Hydrus-2D/3D to investigate the influence of emitter discharge rates and initial soil moisture conditions on the wetting pattern dimensions of a series of soils with varying textures. Numerical simulations of simple 2D soil tank irrigation experiments were also conducted on two soil types. Based on the simulation results, the parameters of the Schwartzman and Zur model were refined. The results showed a small influence of discharge rates >1 L h^?1 on the size of the wetting pattern. The only major difference was observed for the rates lower than 0.5 L h^?1, where the largest wetting patterns were observed. Higher initial soil water content caused larger wetting pattern sizes in all directions. When compared to the 2D tank experimental results, Hydrus-2D/3D predicted the wetting pattern dimensions with a relatively small root mean square error not exceeding 2.6 cm. The numerical data obtained for a wide range of textures provided the opportunity to refine the parameters of the Schwartzman and Zur model, which, when compared to experimental data from the literature, provided good estimates of wetting pattern dimensions. This suggests that this simple model, for which the only soil parameter required is the saturated hydraulic conductivity, could provide a valuable and practical tool for irrigation design.     

Modeling the potential for closing quinoa yield gaps under varying water availability in the Bolivian Altiplano

In the Bolivian Altiplano, the yields of rainfed quinoa are relatively low and highly unstable. We use a validated crop water productivity model to examine the potential of closing quinoa yield gaps in this region. We simulate the expectable yields under rainfed cultivation and under different deficit irrigation (DI) strategies using the AquaCrop model for the Northern, Central and Southern Bolivian Altiplano. Simulated DI scenarios include a reference strategy avoiding stomatal closure during all sensitive growth stages and allowing drought stress during the tolerant growth stages (DI₀) and various restrictive deficit irrigation strategies (DI_i) representing cases when water resources are limited. We obtain a logistic crop water production function for quinoa by plotting the seasonal actual evapotranspiration versus total grain yield. Due to the large scatter, this function only indicatively provides expectable yields. From the scenario analysis, we derive yield probability curves for the 3 agro-climatic regions. DI, without restriction in irrigation water during the drought sensitive growth stages, is able to close the yield gaps in the Northern, Central and Southern Bolivian Altiplano, and would guarantee a high and stable level of water productivity (WP). The yields of quinoa under rainfed cultivation during dry years are only 1.1, 0.5 and 0.2 Mg ha⁻¹ in the Northern, Central and Southern Bolivian Altiplano, whereas under DI₀ they are 2.2, 1.6 and 1.5 Mg ha⁻¹, respectively. Under limited water availability for irrigation, these stable yield levels decrease, most drastically in the Southern Bolivian Altiplano. Below a minimum water availability of 600 m³ per ha and 700 m³ per ha in the Central and Southern Bolivian Altiplano, respectively, the application of DI for quinoa is not significantly effective and should be avoided to save valuable resources. The yield probability curves we derive can serve as input for stochastic economic analysis of DI of quinoa in the Bolivian Altiplano.     

The effect of drip line spacing, irrigation regimes and planting geometries of tomato on yield, irrigation water use efficiency and net return

This study was conducted in order to determine the effect of drip line spacing, irrigation regimes and planting geometries of tomato on yield, irrigation water use efficiency (IWUE) and net return. The experiments were carried out in the conditions of Eskisehir in Central Anatolian part of Turkey, between 2003 and 2005, with cv. Dual Large F1 tomatoes (Lycopercion esculentum L). The maximum yield of 121.1 t ha⁻¹ was obtained from the treatment in which both the lateral and row spacing were 1 m, and irrigated with water amount based on the percentage of canopy cover. The seasonal irrigation water amount of the treatment was 551 mm. Tomatoes yield of 109.9 t ha⁻¹ was obtained under conditions of 491 mm seasonal irrigation water applied for the 2-m lateral spacing in which two plant rows (twin rows) were planted 0.35 m on either side of the lateral with a row spacing of 0.70 m across the drip lateral and 1.30 m in the interrow between each set of twin rows. Although water saving of 60 mm and investments economy of 40% were provided from the twin-row design, the yearly return of the design including one lateral for each row was US$ 1590 ha⁻¹ higher than that the return of the twin-row design. The method of determination of irrigation water amount based on the percentage of canopy cover appeared to be the most reasonable and effective one in terms of the yield and IWUE. On the other hand, the maximum irrigation water use efficiency (22.3 kg m³) was obtained from 2-m lateral spacing and the percentage of canopy cover for calculation of the amount of irrigation water applied. Thus, canopy cover may be used successfully at any lateral design conditions.     

地表滴灌条件下土壤湿润体运移量化表征

基于非饱和土壤水分运动的Richards方程,采用HYDRUS-2D/3D模拟软件对11种典型土质(美国制土壤质地分类系统)中滴灌湿润体的运动过程进行了数值模拟。结果表明,湿润体平均含水率的增量与滴灌流量正相关,与饱和导水率负相关;湿润体垂向迁移距离与滴头流量、饱和导水率和时间呈幂函数关系;湿润体径向迁移距离可用滴头流量、平均含水率的增量、垂向迁移距离和时间来定量表征。据此建立了描述不同土质中湿润体动态变化规律的经验公式,通过与数值模拟结果、文献试验数据等进行对比,表明此经验公式对不同土质中湿润体运移规律的预测效果较好,可为农业生产中地表滴灌设计提供简便实用的计算工具。     

Irrigation and tillage effects on root development,water use and yield of wheat on coarse textured soils

Summary Rapid drying of surface layers of coarse-textured soils early in the growth season increases soil strength and restricts root growth. This constraint on root growth may be countered by deep tillage and/or early irrigation. We investigated tillage and irrigation effects on root growth, water use, dry matter and grain yield of wheat on loamy sand and sandy loam soils for three years. Treatments included all combinations of two tillage systems i) conventional tillage (CT) — stirring the soil to 10 cm depth, ii) deep tillage (DT) — subsoiling with a single-tine chisel down to 35–40 cm, 40 cm apart followed by CT; and four irrigation regimes, i) I₀ — no post-seeding irrigation, ii) I₁ — 50 mm irrigation 30 days after seeding (DAS), iii) I₂ — 50 mm irrigation 30 DAS and subsequent irrigations of 75 mm each when net evaporation from USWB class A open pan (PAN-E) since previous irrigation accumulated to 82 mm, and iv) I₃ — same as in I² but irrigation applied when PAN-E accumulated to 62 mm. The crop of wheat (Triticum aestivum L. HD 2329) was fertilized with 20kg P, 10kg K and 5kg Zn ha^–1 at seeding. The rate of nitrogen fertilization was 60 kg ha^–1 in the unirrigated and 120 kg ha^–1 in the irrigated treatments. Tillage decreased soil strength and so did the early post-seeding irrigation. Both deep tillage and early irrigation shortened the time needed for the root system to reach a specified depth. Subsequent wetting through rain/irrigation reduced the rate of root penetration down the profile and also negated deep tillage effects on rooting depth. However, tillage/irrigation increased root length density in the rooted profile even in a wet year. Better rooting resulted in greater profile water depletion, more favourable plant water status and higher dry matter and grain yields. In a dry year, the wheat in the DT plots used 46 mm more water, remained 3.3 °C cooler at grain-fill and yielded 68% more grain than in CT when unirrigated and grown in the loamy sand. Early irrigation also increased profile water depletion, more so in CT than DT. Averaged over three years, grain yield in DT was 12 and 9% higher than in CT on loamy sand and sandy loam, respectively. Benefits of DT decreased with increase in rainfall and irrigation. Irrigation significantly increased grain yield on both soils, but the response was greatly influenced by soil type, tillage system and year. The study shows that soil related constraints on root growth may be alleviated through deep tillage and/or early irrigation.     

Towards using a thermal infrared index combined with water balance modelling to monitor sugarcane irrigation in a tropical environment

In humid regions, the timing and quantity of a complementary irrigation regime is challenging because of the irregularity of rainfalls events. In this study, we tested the use of a thermal infrared derived empirical crop water stress index (CWSI_e) as an in situ measurement of the water status of sugarcane, to better monitor the irrigation scheduling. To do this, we set up a 2-year experiment in Reunion Island, on a trial with plots under different water conditions (rainfed and irrigated). Crop surface temperature was measured daily with infrared radiometers (Apogee Instruments) installed above the canopy, and soil moisture and drainage measurements were used to derive the ratio between actual and maximum evapotranspiration (AET/MET) values that were then averaged on “hydrically homogeneous” time periods (between 7 and 25 days). Only the thermal data acquired on clear days and 1 h after noon in 2007 were used to define the empirical lower and upper baselines required for the calculation of empirical CWSI. The data set acquired in 2008 was used to test the robustness of the method as we used the upper and lower baselines defined in 2007 to calculate CWSI_e. The linear regression between AET/MET and (1 − CWSI_e) averaged on the same periods (values ranging between 0.4 and 1) showed a significant correlation for both experimental years (global R² = 0.75 and RMSE = 0.12). This result indicates the effectiveness of the CWSI_e to measure the water status of the sugarcane crop, even in humid conditions with a vapor pressure deficit (VPD) between 0.5 and 2.1. We conclude the study by discussing the complementarity of this remote water stress index (CWSI_e) with OSIRI water balance modelling tool currently used in Reunion Island for monitoring sugarcane crop irrigation.