La Violada Irrigation District Research Articles

DSSAT modelling for best irrigation management practices assessment under Mediterranean conditions

Water is considered the most critical resource for sustainable development in Spain. Crop models can enhance water efficiency, which provides an economic advantage while also reducing environmental burdens. The aim of this study was to calibrate and evaluate the Decision Support System for Agro-technology Transfer (DSSAT) model for the major crops grown in the fields of the La Violada Irrigation District (VID), Spain; additionally, this research sought to evaluate the current practices and to determine the best irrigation management practices under different soil types in the VID for each crop. Crop and soil type data from 54 plots of farmers’ fields were used for model calibration and evaluation during the 2015 and 2016 irrigation seasons. Two irrigation scenarios were applied in eight soil types in the VID based on the current irrigation applied by farmers and the optimum irrigation adjusted to crop requirement. The DSSAT model demonstrated good performance among maize, wheat, barley and sunflower crops. The evaluation of the current irrigation system showed that farmers were not managing their irrigation systems properly. The adjusted irrigation management application showed a potential reduction in the seasonal irrigation depth for maize-SS (short-season maize) (27%), maize-LS (long season maize) (18%) and sunflower (16%). In a broader context, optimum irrigation practices can reduce the amount of leached N and deep percolation losses by 31% (4.48 T) and 34% (1.2 hm3), respectively, considering the cultivated crop area in each soil type in the entire VID.

Soil variability in La Violada Irrigation District (Spain): I Delineating soil units for irrigation

The knowledge of the soil variability is essential for its hydrologic characterization, for irrigation management and planning and especially for water movement modeling. Nevertheless, the scarcity of soil information in Spain precludes its use in irrigation management and, particularly, in the on-going irrigation modernization process. The Violada Irrigation District (VID) comprises 5234ha and is located in a semi-arid gypsum-rich region in northeast Spain. VID has been under flood irrigation since the mid-20th Century and has been modernized recently to sprinkler irrigation. Since the early 1980s water balances in VID have been based on average soil properties and bulk irrigation data. The current irrigation system provides detailed irrigation data at plot level, thus allowing for performing distributed balances (in hydrologic homogenous zones) that require detailed or semi-detailed soil information in the form of a soil map. The objective of this two-part study is to define homogeneous zones in relation to hydrological properties relevant for irrigation management, first defining the soil variability within the VID and then analyzing the soils hydrologic and salinity features (in a companion paper). The specific objectives of this paper were (i) to draw the VID semi-detailed soil map; (ii) to explain the variability of soil properties; and (iii) to map the main soil characteristics related to irrigation management. Thirty four soil pits, located on all the different geomorphological areas, were opened and described. Samples were taken from all the horizons and analyzed for chemical and physical properties. The limits of soil units were drawn with the aid of 32 additional auger holes, the data from 72 pits opened during the irrigation transformation works, and all the previous soil information available. Finally the soils were classified down to family level. The main soil formation processes in VID were carbonation and gypsification. Thirteen soil units were defined, included in five soil subgroups and six particle size families. “Fine” particle sizes were dominant along the gypsum-rich valley bottoms. Coarser textures were found on the heights and showed higher CaCO3 equivalent content and no presence of gypsum accumulations. A priori, the main limitation for irrigation in the valley soils was the limited drainage (due to fine textures and reduced slope) while in the highland soils it might be constrained by their low retention capacity. The high gypsum and carbonate content of the VID soils may prevent the development of infiltration problems. The soil properties map in this work will be the basis for a companion paper delineating the hydrologic properties of the soils, the basis for improved soil water balances.

Soil variability in La Violada Irrigation District (Spain): II Characterizing hydrologic and salinity features

The recent modernization of 1.1Mha of irrigated land in Spain calls for the evaluation of these transformations in terms of environmental impact and resource use efficiency. The available data for this evaluation has increased with the transformation (better, digital and spatially distributed data) allowing for the use of distributed soil water and solute movement models. But most hydrological models require soil hydrologic properties that are costly and time-consuming to gather and soil information in Spain is generally scarce. This paper focuses in analyzing the soil hydrologic features in La Violada Irrigation District (VID; a 5234ha semi-arid irrigated area recently modernized in northeast Spain) usable in soil water models for the evaluation of the new irrigation system.The recent soil map of the VID (presented in a companion paper) gathered the hydrologic and salinity properties of the horizons in the described soil units. The hydraulic conductivity (Ks) of the horizons was also assessed by the inverse auger-hole method. From these data, the VID was disaggregated in three homogeneous units according to their hydrologic features and Pedotransfer Functions (PTFs) were built for the whole VID (General Model) and separately for the homogeneous soil units (Distributed Model). These PTFs allowed for obtaining field capacity (FC) and wilting point (WP) from texture and organic matter, while Ks depended upon texture and gypsum content.Apparently, there were no salinity issues in VID soils due to irrigation. The high Ca2+ and Mg2+ levels in the saturation extract resulted in generally low SAR, what along with the high gypsum and carbonate contents may help to prevent soil degradation by sodicity.As a result, the homogeneous hydrologic zones defined in VID may be used to recommend specific irrigation practices and as the basis for the application of distributed soil water movement models. These hydrologic properties may be applied directly as inputs to the models while the PTFs may allow for setting adequate parameters in nearby areas with similar soils from more readily available soil information (texture, organic matter and gypsum).

Irrigation management, nitrogen fertilization and nitrogen losses in the return flows of La Violada irrigation district (Spain)

Nitrogen (N) pollution induced by irrigated agriculture is a significant environmental problem. The main N inputs and outputs were measured or estimated in the semi-arid La Violada irrigation district (Spain). Data on two periods (1995–1998 and 2006–2008) were compared and related to observed changes during the decade in cropping patterns and N fertilization and irrigation management. N fertilization exceeded crop N uptake due to over-fertilization of corn (426kgN/ha in 1995–1998 and 332kgN/ha in 2006–2008) and alfalfa (62kgN/ha). Between the two periods, N fertilization decreased by 56%, primarily due to a change from corn to alfalfa and barley. Accordingly, N losses in the irrigation return flows (IRF) diminished from 31% of the applied fertilizer in 1995–1998 to 20% in 2006–2008. NO3− concentrations and NO3-N loads in the IRF decreased from 40mg/L and 106kgN/ha in 1995–1998 to 21mg/L and 22kgN/ha in 2006–2008, due to lower N fertilization, lower corn area and improved irrigation efficiency. N contamination in the IRF will be minimized by increasing the irrigation efficiency and decreasing the corn area and its N fertilization rates, particularly when supplemental organic N is applied at pre-sowing.

Three study decades on irrigation performance and salt concentrations and loads in the irrigation return flows of La Violada irrigation district (Spain)

Irrigation district salt balances identify the main sources and sinks of salts and quantify salt loads in irrigation return flows. Salt balances were performed in La Violada Irrigation District during the 80s (1982–1984), 90s (1995–1998) and 00s (2006–2008) decades. Total Dissolved Solids (TDS) and loads in irrigation return flows were related with changes in irrigation performance and infrastructures during these decades. TDS increased linearly to increases in Irrigation Consumptive Use Coefficient (ICUC) (P<0.01), and decreased with increases in Drainage Fraction (DRF) (P<0.001). The salt balances revealed that 82% of the exported salts originated from soil gypsum dissolution. Annual salt yields in return flows were high and similar in the 80s and 90s (about 19.3Mg/ha year), and halved in the 00s (9.9Mg/ha year) due to comparable reductions in irrigation and drainage volumes derived from a better irrigation performance. Irrigation season salt yields were high and steady around 14.1Mg/ha for ICUC<51% and DRF>66%, and decreased exponentially for values above and below these thresholds, respectively. Therefore, the key management strategy to reduce salt discharge to downstream areas is to decrease drainage volumes by improving irrigation management.

Long-term water balances in La Violada irrigation district (Spain): I. Sequential assessment and minimization of closing errors

Long-term analysis of hydrologic series in irrigated areas allows identifying the main water balance components, minimizing closing errors and assessing changes in the hydrologic regime. The main water inputs [irrigation (I) and precipitation (P)] and outputs [outflow (Q) and potential (ETc) crop evapotranspiration] in the 4000-ha La Violada irrigation district (VID) (Ebro River Basin, Spain) were measured or estimated from 1995 to 2008. A first-step, simplified water balance assuming steady state conditions (with error ɛ = I + P − Q − ETc) showed that inputs were much lower than outputs in all years (average ɛ = −577 mm yr−1 or −33% closing error). A second-step, improved water balance with the inclusion of other inputs (municipal waste waters, canal releases and lateral surface runoff) and the estimation of crop's actual evapotranspiration (ETa) through a daily soil water balance reduced the average closing error to −13%. Since errors were always higher during the irrigated periods, when canals are full of water, a third-step, final water balance considered canal seepage (CS) as an additional input. The change in water storage in the system (ΔW) was also included in this step. CS and ΔW were estimated through a monthly soil–aquifer water balance, showing that CS was a significant component in VID. With the inclusion of CS and ΔW in the water balance equation, the 1998–2008 annual closing errors were within ±10% of total water outputs. This long-term, sequential water balance analysis in VID was an appropriate approach to accurately identify and quantify the most important water balance components while minimizing water balance closing errors.

Long-term water balances in La Violada Irrigation District (Spain): II. Analysis of irrigation performance

Abstract The analysis of long-term irrigation performance series is a valuable tool to improve irrigation management and efficiency. This work focuses in the assessment of irrigation performance indices along years 1995–2008, and the cause–effect relationships with irrigation modernization works taking place in the 4000 ha surface-irrigated La Violada Irrigation District (VID). Irrigation management was poor, as shown by the low mean seasonal irrigation consumptive use coefficient (ICUC = 51%) and the high relative water deficit (RWD = 20%) and drainage fraction (DRF = 54%). April had the poorest irrigation performance because corn (with low water demand in this month) was irrigated to promote its emergence, whereas winter grains (with high water demands in this month) were not fully irrigated in water-scarce years. Corn, highly sensitive to water stress, was the crop with best irrigation performance because it was preferentially irrigated to minimize yield losses. The construction of a new elevated canal that decreased seepage and drainage fractions, the entrance in operation of six internal reservoirs that would increase irrigation scheduling flexibility, and the on-going transformation from surface to sprinkler irrigation systems are critical changes in VID that should lead to improved ICUC, lower RWD and lower DRF. The implications of these modernization works on the conservation of water quantity and quality within and outside VID is further discussed.

Drainage water quality and end-member identification in La Violada irrigation district (Spain)

The identification of the different components in a water course is required to individualize and assess the actual contribution of irrigated agriculture to the pollution of the water course. This paper aimed at identifying and assessing the composition of the end-members in La Violada irrigation district (VID) and establishing a statistical procedure to reduce the sampling effort needed to establish drainage water quality. The quality of irrigation water, groundwater, and irrigated-land drainage water in VID was monitored during three hydrologic years to identify the components of flow in La Violada Gully, the natural exit course of VID. A network of sampling points in the secondary ditches and main drains of VID allowed identifying and separating those collecting irrigated-land drainage waters from those conveying high proportions of irrigation waters. Three end-member flows were identified in La Violada Gully during the irrigation season: (a) irrigation water arising from tail-waters, leakages and spills from the irrigation canals, very low in salts; (b) groundwater originating from the non-irrigated upper reaches of La Violada Gully watershed, high in Cl− and Na+; and (c) VID drainage water, high in SO42- and Ca2+. The overall VID drainage water quality was accurately assessed through a simplified sampling scheme of only four sampling points that produced low errors of 0.1 dS/m for EC and 0.1 mmolc/L for Cl−. The separation of La Violada Gully flow in these three components is essential for estimating the actual contribution of irrigation in VID to the salt and nitrogen loads in La Violada Gully.

Environmental Impact of Irrigation in La Violada District (Spain)

Fertilizer leaching affects farm profitability and contributes to nonpoint-source pollution of receiving waters. This work aimed to establish nitrate nitrogen export from La Violada Gully in relation to nitrogen fertilization practices in its basin (La Violada Gully watershed, VGW, 19,637 ha) and especially in La Violada Irrigation District (VID, 5282 ha). Nitrogen (N) fertilization in VID (and VGW) was determined through interviews with local farmers for the hydrologic years 1995 and 1996 and NO3-N load in the gully was monitored from 1995 to 1998. The N fertilizer applied in VGW was 2175 Mg in 1995 and 2795 Mg in 1996. About 43% was applied in VID (945 Mg in 1995 and 1161 Mg in 1996). The most fertilized crop was corn: 398 kg N ha-1 (665 Mg) in 1995 and 453 kg N ha-1 (911 Mg) in 1996. Nitrogen fertilization was higher than N uptake for irrigated crops, especially for corn and rice. Nitrate N load in La Violada Gully averaged 427.4 Mg yr-1. Seventy-five percent of the exports took place during the irrigation season (321.8 Mg). During the non-irrigation season maximum NO3-N loads (3.1 Mg NO3-N d-1) were found after heavy rains following the N side-dressing of wheat in the rain-fed area of VGW (February). During the irrigation season NO3-N load was determined by outflow from the district (caused by irrigation) and to a lesser extent by changes in NO3 concentration (caused by fertilization), showing peaks in April (pre-sowing corn N fertilization and first irrigations) and June to August (highest irrigation months and corn side-dress N applications, maximum 6.3 Mg NO3-N d-1 in July). Adjusting N fertilization to crops' needs, improving irrigation efficiencies, and better scheduling N fertilization and irrigation in corn could reduce N export from VID.

Environmental Impact of Irrigation in La Violada District (Spain)

Salt loading in irrigation return flows contributes to the salinization of the receiving water bodies, particularly when originated in salt-affected areas as frequently found in the middle Ebro River basin (Spain). We determined the salt loading in La Violada Gully from the total dissolved solids (TDS) and flows (Q) during the 1995 to 1998 hydrological years. Since this gully collects flows from various sources, an end-member mixing analysis (EMMA) was performed to quantify the drainage flow from La Violada Irrigation District (VID). Three flow components were identified in La Violada Gully: drainage waters from VID (Qd); tail-waters from irrigation ditches, spill-over, and seepage from the Monegros Canal (Qo); and ground water inflows (Qg) originating in the dryland watershed. Gypsum in the soils of VID was the main source for salts in La Violada Gully (flow-weighted mean TDS=1720 mg L-1, dominated by sulfate and calcium). The contribution of Qg to the total gully flow during the 1996 irrigation season was low (6.5% of the total flow). The 1995 to 1998 annual salt load average in La Violada Gully was 78 628 Mg, 71% of which was exported during the irrigation season. The 1995 to 1998 irrigation season salt load average in Qd was 43 015 Mg (77% of the total load). Thus, irrigated agriculture in VID was the main source of salt loading in this gully, with a yield of 11.1 Mg of salts per hectare of irrigated land for the irrigation season. Efficient irrigation systems and irrigation management practices that reduce Qd are key factors for controlling off-site salt pollution of these gypsum-rich irrigated areas.

Water balance and irrigation performance analysis: La Violada irrigation district (Spain) as a case study

Diagnosis of water management at the irrigation district level is required for the rational modernisation of the irrigation schemes and the subsequent increase in the efficiency of water allocation and application. Our objectives were to: (i) evaluate the global irrigation performance in the 5282 ha La Violada surface-irrigated district (Ebro River Basin, northeast Spain), and (ii) estimate the water that could potentially be conserved under two scenarios of modernisation and three increased irrigation efficiencies. The main district’s water inputs and outputs were measured (irrigation, precipitation, and outflow surface drainage) or estimated (canal releases, lateral surface runoff, municipal wastewaters, and actual evapotranspiration of crops) during the 1995–1998 hydrological years. The annual average water outputs were 23% higher than the corresponding water inputs, presumably due to canal seepage and lateral groundwater inflows from the 14 355 ha dry-land watershed. The district-level irrigation performance was poor (mean 1995–1998 seasonal irrigation consumptive use coefficient (ICUC)=48%), due to the low distribution (DE) and on-farm (ICUCf) efficiencies (i.e., mean estimates of 83% (DE) and 61% (ICUCf) for the 1995–1996 irrigation seasons). Thus, despite the high volume of applied irrigation water, the actual district ET was 16% lower than the maximum achievable ET, indicating that the water-stressed crops yielded below their maximums. Potential reductions in water allocation were estimated for three ICUC values (65, 75 and 85%) and two scenarios of modernisation (I and II). In scenario I, where the aim was to achieve maximum ET and crop yields, water allocation could be reduced from 8 to 30% of the current allocation. In scenario II, where the aim was to achieve the maximum conservation of water under the actual ET and crop yields, reductions in water allocation would be much higher (from 26 to 43% of current allocation). Thus, significant volumes of water could be conserved in the rehabilitation of this 50-year-old district by increasing the distribution efficiency and, in particular, the on-farm irrigation efficiency.

Sampling strategies for the estimation of salt and nitrate loads in irrigation return flows: La Violada Gully (Spain) as a case study

Appropriate estimates of salt and nitrate loads exported by irrigated agriculture are needed to ascertain the potential negative impacts on the quality of the receiving water bodies. The irrigation return flows of the La Violada irrigation district (NE Spain), collected by La Violada Gully, were monitored for 4 years (1995–1998) in order to estimate salt and nitrate loads. The existence of a daily cycle in the Gully flow during the April to September 1995 irrigation season, associated with a cycle in the electrical conductivity, made it necessary to analyse the influence of the sampling hour on the daily estimates of salt and nitrate loads. Interpolation and regression methods were evaluated using nine 2-days surveys with samples taken at all even hours. The interpolation approach proved to be reliable for daily load estimations, whereas the regression approach was unacceptable due to the poor salinity-flow and nitrate concentration-flow relationships. The sampling time was important for the determination of salt load by the interpolation method, but resulted almost irrelevant for the estimation of nitrate load. Although the biases represent a small percentage of the mean (<7% for both salt and nitrate load estimates), the lack of consideration of the sampling hour will result, depending on the time of sampling, in a systematic over- or under-estimation of the measured loads. The number of samples needed to estimate salt and nitrate loads within a pre-specified margin of error was determined using the 1995 and 1996 irrigation seasons series and confirmed through a Monte Carlo test for the four irrigation seasons. A systematic sampling interval of 9 days (i.e. 21 samples along the irrigation season) allowed estimating salt loading within a 5% error and nitrating loading within a 10% error at the 95% confidence level.