Variable Alternate Furrow Irrigation Research Articles

Winter wheat root distribution with irrigation, planting methods, and nitrogen application

Soil water uptake is a function of root growth and distribution. Therefore, restrictions on root system growth may reduce water and nutrient uptake, which results in slower plant growth. The objective of this study was to determine the effects of different irrigation strategies, nitrogen application rates, and planting methods on the winter wheat root growth. The experimental factors included two irrigation strategies (variable alternate furrow irrigation defined as partial root-zone irrigation and ordinary furrow irrigation), two planting methods (in-furrow planting and on-ridge planting), and three nitrogen (N) application rates (0, 150, and 300 kg N ha−1) in 2015–2016 and 2016–2017 growing seasons. Results indicated that the in-furrow planting decreased mean root length density and root mass density (8% and 10%, respectively, in the fertilized treatments) compared to that obtained in the on-ridge planting. The partial root-zone irrigation reduced root length density by about 5% and 7% in the fertilized treatments compared to that obtained in full irrigation in the first and second year, respectively; however, these reductions were not statistically significant. Furthermore, the results implied that nitrogen fertilizer application increased root length density by 48% and 24% in the first and second year, respectively. Likely, root mass density increased by 32% and 5% in the first and second year, respectively. The exponential decaying relationship between root length density and soil depth indicated that the in-furrow planting with 300 kg N ha −1 produced the highest root density at the soil surface layer and reduced deep root penetration compared to the on-ridge planting and the other N treatments. Further analysis revealed that grain yield linearly correlated with root length density and root mass density in the first year. However, a polynomial (quadratic) relationship was obtained in the second year. Consequently, increasing the main root traits, including root length and root mass, enhanced winter wheat grain yield until it reached a threshold value. Higher values negatively affected grain yield, which might be due to allocating carbon to roots instead of grains.

Soil drainage water and nutrient leaching in winter wheat field lysimeters under different management practices

The objective of this study was to investigate the effects of different irrigation strategies, planting methods and various nitrogen application rates on water and solutes transport under the root zone. Furthermore, Hydrus-1D model was used to simulate the drainage water and soil nutrient (N, K) leaching by the drainage water in the experimental treatments. Results indicated that variable alternate furrow irrigation (VAFI) decreased drainage water by a mean value of 30% compared with that obtained in full irrigation (OFI); whereas, precipitation played a significant role in increasing drainage water. About 60% and 80% of drainage water occurred due to rainfall in the full irrigation strategy in the first and second year, respectively, and most of the drainage water in VAFI strategy occurred due to precipitation as 90% for both years. Additionally, precipitation during the low growth stages of winter wheat (fall and winter) had noticeable influence on solute transport. On average, 75%, and 65% of leached nitrate, and potassium, respectively, occurred due to rainfall in OFI method; however, about 85% of leached nitrate, and potassium in VAFI strategy occurred due to rainfall events. Application of 150 kg N ha−1 decreased about 40% nitrate leaching below the root zone in comparison with that obtained in 300 kg N ha−1 without significant difference in crop yield. Hydrus-1D model reasonably simulated solute transport especially nitrate and potassium. Therefore, Hydrus-1D could be a successful tool for predicting N, and K transport and making proper management decisions to improving environmental problems.

Winter Wheat Yield and DSSAT Model Evaluation in a Diverse Semi-Arid Climate and Agronomic Practices

Because of human dependence on sustainable food production, it is needed to adopt agricultural production to climate change, and their consequences on associated socioeconomic issues. Crop modelling potentially can contribute to global food and nutrition security. Therefore, in this context DSSAT (decision support system for agro-technology transfer) was validated for predicting growth and yield of wheat under a diverse semi-arid climate (2 years with diverse climates) and different irrigation strategies, planting methods, and nitrogen rates. The irrigation strategies were ordinary furrow irrigation (OFI) and variable alternate furrow irrigation (VAFI), and the planting methods were on-ridge planting (ORP) and in-furrow planting (IFP) methods. The fertilizer levels were 0 (N0), 150 (N1) and 300 (N2) kg N ha−1. Results indicated that water stress and inappropriate weather especially during the stem elongation influences the grain yield remarkably without noticeable effect on straw yield. Furthermore, VAFI strategy did not impose any limitation on top dry matter N concentration in both years. Calibration of DSSAT showed that the model underestimated the actual evapotranspiration at the end of growing season (during spring with high temperature) and resulted in overestimating the soil water content at depths under 10 cm during this period of time. Since the potential transpiration has an important role in calculating the effect of water stress factor, the model overestimated slightly the maximum leaf area index (LAI) and consequently biomass and yield in water stress condition; however, overall, model could statistically simulate LAI (NRMSE = 0.3, d = 0.96, R2 = 0.95), total dry matter (NRMSE = 0.07, d = 0.99, and R2 = 96) and grain yield (NRMSE = 0.13, d = 0.96, and R2 = 90). Model also could reasonably simulate the nitrogen components including the grain N concentration (NRMSE = 0.05, d = 0.95), above-ground nitrogen uptake (NRMSE = 0.11, d = 0.99), and soil nitrate content (NRMSE = 0.23, d = 0.86). However, evaluating the model with data set from 2015 to 2016 indicated that the model could not simulate wheat yield and nitrogen components in validation year due to strong effects of diverse weather condition and water stress on grain yield and crop development.

Partial root zone drying irrigation, planting methods and nitrogen fertilization influence on physiologic and agronomic parameters of winter wheat

The effectiveness of water-saving irrigation strategies such as partial root zone drying (PRD) should be explored to ensure food security as the availability of water for irrigation declines and population increases. PRD is easily performed by localized irrigation method; however very small percentage of irrigated area is under this irrigation method and main irrigation method is furrow irrigation that should be adapted to PRD. In this respect, present study was conducted to explore the effects of PRD in furrow irrigation strategies on physiological and agronomic behavior of winter wheat. The field experiment included two irrigation strategies (variable alternate furrow irrigation (VAFI) as PRD and ordinary furrow irrigation (OFI), two different planting method (in-furrow planting and on-ridge planting) and three nitrogen rates (0, 150, and 300 kg N ha−1) over 2015–2016 and 2016–2017. Results showed that decreasing leaf water potential (LWP) during the stem elongation stage resulted in increasing the sensitivity of winter wheat to water stress and yield reduction. The leaf photosynthesis rate (An) was not significantly lowered in VAFI (PRD) in comparison with that obtained in OFI. The VAFI strategy reduced the stomatal conductance (gs) about 12% and 7% in comparison with that obtained in OFI in the first and second year, respectively that were statistically significant. The lower slope of linear relationship between leaf transpiration efficiency (An/Tr) and vapor pressure deficit (VPD) in VAFI strategy indicated that with increasing VPD, leaf transpiration efficiency was higher than that obtained in OFI. As a consequence, VAFI strategy as PRD was effective in increasing An/Tr and can be an alternative irrigation management in winter wheat farms with limited water supplies. Although, in-furrow planting showed higher efficiency in increasing yield in comparison with that obtained in on-ridge planting, on-ridge planting showed higher effects on leaf transpiration efficiency. Furthermore, there was no significant difference between two application rates of nitrogen (150 kg N ha−1 and 300 kg N ha−1) for different parameters; therefore, application of 150 kg N ha−1 can be suggested as an effective rate to increase winter wheat yield. Consequently, in areas with scarce water and furrow irrigation, combination of VAFI, in-furrow planting and 150 kg N ha−1 is recommended to achieve optimum yield with possibility of saving water during the winter wheat growing season.

Interaction Effects of Planting Method, Irrigation Regimes, and Nitrogen Application Rates on Yield, Water and Nitrogen Use Efficiencies of Winter Wheat (Triticum aestivum)

Arid and semi-arid regions in the world that produce wheat (Triticum aestivum) are faced with frequent droughts in recent years. Moreover, wheat production is highly dependent on irrigation and it is essential to increase irrigation water productivity in these regions. Therefore, the aim of this study was to investigate the effects of irrigation methods, planting methods, and nitrogen application rates on yield, water and nitrogen use efficiencies of winter wheat. The experiment arranged in split–split plot with randomized blocks with two surface irrigation methods [ordinary furrow irrigation (OFI) and variable alternate furrow irrigation (VAFI)] as the main plots, two planting methods [on-ridge planting (ORP) and in-furrow planting] as the sub plots, and three nitrogen application rates (N0 = 0, N1 = 150 and N2 = 300 kg N ha−1) as the sub–sub plot. Results indicated that VAFI reduced the winter wheat grain yield, dry matter, grain number per spike, and harvest index as 12, 9, 3, and 4%, respectively; however, these reductions were not significant in comparison with OFI method with a reduction of 33% in irrigation water; as a consequence, the straw nitrogen concentration, grain protein concentration, and also water use efficiencies (WUE), irrigation water productivity (IWP), economic irrigation water productivity (EIWP) and nitrogen use efficiency (NUE) were improved in VAFI as 14, 5, 6, 26, 25, and 8%, respectively. In spite of a slight reduction in grain yield, VAFI method increased EIWP. Economic nitrogen productivity decreased about 50% by increase in N rate, and 150 kg N ha−1 was the optimum rate to apply. Furthermore, VAFI decreased the seasonal ET, thereby improved WUE and IWP. In-furrow planting increased significantly the WUES while it did not enhance significantly WUE for grain. Generally, increasing the nitrogen rate increased the grain yield; whereas, there was no significant difference between the treatments of 150 and 300 kg N ha−1. Results suggest that application of 150 kg N ha−1 combined with in-furrow planting method and variable alternate furrow irrigation is an effective way to improve WUE, yield, yield components and NUE for winter wheat in the study area.

Water and nitrate dynamics in safflower field lysimeters under different irrigation strategies, planting methods, and nitrogen fertilization and application of HYDRUS-1D model.

World recent concerns about the shortage of water resources and contamination of groundwater supplies have motivated scientists seeking for more efficient techniques in irrigation and fertilization of farms while taking the advantage of models. The objective of this study is to address how water and nitrogen (N) dynamics are affected by efficient management strategies and to evaluate the application of HYDRUS-1D model in these conditions. In terms of using management policies, different irrigation strategies, planting methods, and different N fertilization rates applied on safflower (Carthamus tinctorius L.) in volumetric field lysimeters. The irrigation regimes were ordinary furrow irrigation (OFI) and variable alternate furrow irrigation (VAFI) as a partial root drying (PRD) technique. The planting methods were on-ridge planting (P1) and in-furrow planting (P2) methods. The fertilizer levels were 0 (N0), 100 (N1), and 200 (N2) kgha-1 of urea as 0, 46, and 92kg Nha-1. Results showed that VAFI regime and in-furrow planting method favorably reduced the amount of drainage water below safflower root zone in comparison with the ordinary methods. Furthermore, VAFI regime satisfactorily decreased the seasonal nitrate (NO3-N) leaching below the root zone, whereas differences between the leached NO3-N in in-furrow and on-ridge planting methods were not significant. Moreover, VAFI regime did not show any negative effects on total N uptake in safflower seed and straw, whereas in-furrow planting accumulated higher N in comparison with the on-ridge planting method. In addition, safflower nitrogen (N) uptake was responsive to application of nitrogen, although the rate of increase in N accumulation was not significant between the application rates of 46 and 92kg Nha-1. The soil nitrate concentration decreased during the growing season indicating that safflower root system has a great ability in absorption of NO3-N from soil N supplies. HYDRUS-1D model favorably predicted the drainage water, nitrate concentration of drainage water, crop N uptake, and residual soil NO3-N concentration for safflower field. Therefore, it can be an applicable model for prediction of water and nitrogen dynamics, despite of two-dimensional flow conditions in furrow irrigation. It was concluded that VAFI strategy and in-furrow planting method are suitable alternatives helping farmers produce food while conserving water and preserving the environment.

Barley (Hordeum vulgare L.) Response to Partial Root Drying Irrigation, Planting Method and Nitrogen Application Rates

Barley (Hordeum vulgare L.) is an important crop in many areas of the world. Drought and scarce resource of irrigation water are serious concerns in agricultural production in Iran and other arid and semi-arid regions. The objective of this study is to investigate the interaction effects of partial root drying (PRD) irrigation, planting method and different nitrogen application rates on yield, water and nitrogen use efficiencies and economical nitrogen and water use for barley in 2011–2012 cropping season. The experiment was designed as split–split plot that arranged in randomized complete blocks with irrigation strategy as the main plot, planting method as the subplot and nitrogen levels as the sub-subplot in three replications. The irrigation strategies consisted of ordinary furrow irrigation (OFI) and variable alternate furrow irrigation (VAFI) as a PRD technique. The planting methods included of on-ridge planting (ORP) and in-furrow planting (IFP) methods. The nitrogen levels were 0 (N0), 90 (N1) and 180 (N2) kg N ha−1 as urea. The results indicated that using VAFI method, 25% reduction in irrigation water depth was occurred compared with OFI, with no significant yield reduction. Furthermore, in IFP method, yield increased 13% compared with ORP. The maximum profits, water economic productivity, water use efficiency and water productivity were obtained in VAFI with IFP and nitrogen application rate of 180 kg/ha. Nitrogen use efficiency in VAFI compared with OFI was increased due to higher nitrogen absorption by plant. Thus, it is indicated that in areas with water limiting, it is preferable to recommend VAFI, IFP and 180 kg N ha−1 as best management practice for barley farm in the study region.

Irrigation and nitrogen managements affect nitrogen leaching and root yield of sugar beet

Irrigation water and nitrogen (N) are the limiting factors for crop production in arid and semi-arid areas. However, excess irrigation and N application rate is a source of groundwater contamination. Partial root drying irrigation (PRD) is the water-saving technique and would perform as a controlling measure of groundwater N contamination as it reduces irrigation amount. Sugar beet is an industrial crop that is widely grown in arid and semi-arid area where N and water are highly required for high sugar beet yield production. The objectives of this study were to evaluate the interaction effect of ordinary furrow irrigation (OFI), and PRD irrigation as variable alternate furrow irrigation (VAFI) and fixed alternate furrow irrigation (FAFI) with different N application rates (0, 80, 160, and 240 kg ha−1) on sugar beet root and sugar yield, yield quality, drainage water, N leaching, N uptake, and N efficiency indices. Results indicated that the alternate furrow irrigation (AFI) used 24% less irrigation water compared with the OFI in the study region, whereas its sugar yield was reduced just by 9%. However, it resulted in higher water productivity by 12 and 17% for root and sugar yields, respectively. In different N application rates nitrate leaching reduced by 46 and 52% in the VAFI and FAFI irrigation treatments compared with the OFI, respectively. Physiologic nitrogen efficiency enhanced in VAFI with 160 kg N ha−1 that implied higher production of uptake N in plants. Therefore, considering the nitrogen use economics and environmental impacts, the VAFI and 160 kg N ha−1 were preferred to the other irrigation treatments and N application rates in the study region. Higher nitrogen saving occurred because of less leaching and higher soil residual in the AFI treatment compared with the OFI. Furthermore, leaf level stress sensitivity index indicated that VAFI increased the sugar beet resistance to water stress. Overall, in order to avoid N losses in sugar beet production, the amount of N fertilizer should be reduced in proportion to the amount of soil water available under VAFI water-saving irrigation.

Safflower model for simulation of growth and yield under various irrigation strategies, planting methods and nitrogen fertilization

Development and use of crop growth models is an effective tool for agricultural planningand decision making in agricultural industry. Besides, the drought and limited supplies of waterin many areas of the world has increased attention to favourable strategies in farm managementsuch as efficient irrigation and planting methods. The objective of this study was to develop acrop model for safflower known as a multi-purpose crop under various irrigation regimes,planting methods and nitrogen fertilization. The experiment was designed as split-split plot thatarranged in randomized complete blocks with irrigation strategy as the main plot, plantingmethod as the subplot and nitrogen levels as the sub-subplot in three replications. The irrigationstrategies consisted of ordinary furrow irrigation (OFI) and variable alternate furrow irrigation(VAFI) as a partial root drying (PRD) technique. The planting methods were on-ridge planting(P1) and in-furrow planting (P2) methods. The fertilizer levels were 0 (N0), 100 (N1) and200 (N2) kg ha-1 of urea as 0, 46 and 92 kg N ha-1. Two years of the experiment carried out in asemi-arid area from 2012 to 2014. The field data of the second year of experiment were used todevelop the model and it was validated by the data of first year. The results indicated that theproposed safflower model is able to estimate evapotranspiration, soil water content, leaf areaindex, soil surface evaporation, crop transpiration, biomass, straw and seed yield of safflower inan appropriate manner. The safflower model is useful for having better field management andreducing administrative costs with respect to the model simplicity and its briefness in data input.

Physiologic and agronomic traits in safflower under various irrigation strategies, planting methods and nitrogen fertilization

Drought and limited supplies of water in many areas of the world have created serious concerns about agricultural production and global food security. Hence, application of more efficient management strategies in fields has been favourably developed in arid and semi-arid regions. In this respect, physiological and agronomic behaviour of a crop can be an advantageous index for identification of its response to different management policies. The objective of this study is to investigate the effects of partial root drying (PRD) irrigation, planting methods and nitrogen fertilization on some agronomic and physiologic behaviour of safflower (Carthamus tinctorius L.). The experiment was designed as split–split plot that arranged in randomized complete blocks with irrigation strategy as the main plot, planting method as the subplot and nitrogen levels as the sub-subplot in three replications. The irrigation strategies consisted of ordinary furrow irrigation (OFI) and variable alternate furrow irrigation (VAFI) as a PRD technique. The planting methods included of on-ridge planting (P1) and in-furrow planting (P2) methods The fertilizer levels were 0 (N0), 100 (N1) and 200 (N2)kgha−1 of urea as 0, 46 and 92kgha−1 of nitrogen. Results of this study indicated that VAFI strategy can be an alternative irrigation policy for safflower farms in which certain irrigation water saving, low yield reduction and more drought adaptation in crop is provided. Furthermore, it was shown that safflower is relatively drought-tolerant to water stress in which the stem elongation stage was more sensitive to drought than the heading and flowering stages. Since, photosynthesis rate (An) was strongly correlated with heads formation (number of heads per plant, NHP) and seeds accumulation (number of seeds per plant, NSH) in safflower, the photosynthesis deficiency by water stress resulted in decrease of safflower seed yield mainly thorough the reduction in NHP and NSH than other components such as number of branch per plant (NBP) and thousand seeds weight (TSW). Based on findings, in-furrow planting method can be another favourable strategy due to its influence on enhancement of yields, photosynthesis, stomatal conductance (gs), transpiration rate (Tr), leaf area index (LAI) and vegetative growth of safflower. Besides, nitrogen fertilization at rate of 46kgha−1 is recommended for improving the agronomic and physiologic traits of safflower.

Effects of irrigation strategies, planting methods and nitrogen fertilization on yield, water and nitrogen efficiencies of safflower

Safflower (Carthamus tinctorius L.) is a multipurpose crop that is used as food dyeing spice, edible oil, livestock feed, biofuels and medicinal applications in many areas of the world. Drought and scarce resource of irrigation water are serious concerns in agricultural production and global food security that have occurred in Iran and other arid and semi-arid regions. The objective of this study is to investigate the effects of partial root drying (PRD) irrigation, planting method and different nitrogen application rates on yield, water and nitrogen use efficiencies of safflower. The experiment was designed as split-split plot that arranged in randomized complete blocks with irrigation strategy as the main plot, planting method as the subplot and nitrogen levels as the sub-subplot in three replications. The irrigation strategies consisted of ordinary furrow irrigation (OFI) and variable alternate furrow irrigation (VAFI) as a PRD technique. The planting methods included of on-ridge planting (ORP) and in-furrow planting (IFP) methods. The fertilizer levels were 0 (N0), 100 (N1) and 200 (N2) kgha−1 of urea as 0, 46 and 92kgNha−1. In present study, VAFI technique dominantly saved applied irrigation water by 30.2% against only a 13% reduction in safflower seed yield that was not statistically significant among treatments. The coefficient of crop response to water (Ky) obtained as 0.83 which shows that safflower is a tolerant crop to VAFI strategy which is recommended in areas with limited water resources. Furthermore, in-furrow planting method resulted in 13.5% enhancement in safflower seed yield due to the better soil conditions (temperature and moisture) that is provided by this technique. Therefore, this method is considered as an appropriate alternative for safflower planting due to its favourable influence on water use efficiency (WUE) and other safflower traits, especially in semi-arid and arid regions. Most of safflower traits were definitely enhanced by application of 46kgNha−1 such as yield production, WUE and nitrogen use efficiencies; whereas higher rate of nitrogen showed negligible effect on safflower traits compared with 46kgNha−1.

Optimum Design of Alternate and Conventional Furrow Fertigation to Minimize Nitrate Loss

AbstractAlternate-furrow fertigation has shown potential to improve water and fertilizer application efficiency in irrigated areas. A combination of simulation and optimization approaches permits researchers to identify optimum design and management practices in furrow fertigation, resulting in optimum cost, irrigation performance, or environmental impact. The objective of this paper is to apply one-dimensional (1D) surface and two-dimensional (2D) subsurface simulation-optimization models to the minimization of nitrate losses in two types of alternate-furrow fertigation, as follows: (1) variable alternate-furrow irrigation, and (2) fixed alternate-furrow irrigation. For comparison purposes, optimizations are also reported for conventional furrow irrigation. The model uses numerical surface fertigation and soil-water models to simulate water flow and nitrate transport in the soil surface and subsurface, respectively. A genetic algorithm is used to solve the optimization problem. Four decision variables (i...

Comparison of One- and Two-Dimensional Models to Simulate Alternate and Conventional Furrow Fertigation

AbstractSimulation models have recently been used in many studies for simulation of water flow and solute transport in soil under different irrigation systems. The objective of this study was to compare the HYDRUS-1D and HYDRUS-2D simulation models to simulate water and nitrate transfer for three furrow irrigation technologies [conventional furrow irrigation (CFI), fixed alternate furrow irrigation (FFI), and variable alternate furrow irrigation (AFI)] under fertigation practice. Filed measured data were used to calibrate and validate the one-dimensional (1D) and two-dimensional (2D) HYDRUS models. An inverse solution technique was applied to optimize soil-hydraulic and solute transport parameters to calibrate the models. The results indicated that the HYDRUS-2D model provided better performance to predict soil water contents, nitrate concentrations, and deep percolation caused by the geometry of the infiltration domain in furrow irrigation. Standard errors for HYDRUS-1D ranged from 0.107 to 0.170 for soi...

Yield and nitrogen leaching in maize field under different nitrogen rates and partial root drying irrigation

Irrigation water is limiting for crop production in arid and semi-arid areas. Furthermore, excess nitrogen (N) application is a source of groundwater contamination. Partial root drying irrigation (PRD) can be used as water saving technique and a controlling measure of groundwater N contamination. The objectives of this investigation were to evaluate the effect of ordinary furrow irrigation (OFI), variable alternate furrow irrigation (VAFI) and fixed alternate furrow irrigation (FAFI) and different N application rates (0, 100, 200, and 300 kg ha -1 ) on maize yield and yield quality, drainage water, N leaching, uptake and N use efficiency (NUE). Results indicated that the interaction between irrigation treatments and N application rates was statistically significant for all treatments applied in this investigation. Maize grain yield was reduced by alternate furrow irrigation due to high sensitivity of maize to water stress, however, in case of water shortage, VAFI is superior to FAFI. In the study region, N application of 200 kg ha -1 is optimum for maize grain yield to obtain optimum grain yield, NUE and N-yield efficiency. Drainage water and total leached nitrate decreased for VAFI and FAFI as compared to OFI and their amount were lowest for FAFI (drainage water) and in VAFI (total leached nitrate), respectively. Total leached nitrate bellow the root zone increased in response to the increase in total available nitrogen for water applications higher than crop ET. N loss was reduced for FAFI and VAFI for N application rates of 200 and 300 kg ha -1 . Only for FAFI and VAFI, the N uptake decreased and the soil residual N increased as compared with OFI. Thus, in order to avoid N loss, the amount of N fertilizer should be reduced in proportion to the amount of soil water available for plant uptake under deficit irrigation. Furthermore, it was indicated that leaf level stress sensitivity index (LLSSI) was higher for VAFI and it was about 2.5 times of OFI.

Yield and nitrogen leaching in rapeseed field under different nitrogen rates and water saving irrigation

Irrigation water is limiting for crop production in arid and semi-arid areas and excess nitrogen (N) application is a source of groundwater contamination. Therefore, alternate furrow irrigation can be used as water saving irrigation (WSI) and a controlling measure of groundwater N contamination. The objectives of this investigation were to evaluate the effect of ordinary furrow irrigation (OFI), variable alternate furrow irrigation (VAFI) and fixed alternate furrow irrigation (FAFI) and different N application rates (0, 100, 200, and 300kgha−1) on rapeseed yield and yield quality, drainage water, N leaching, uptake and N use efficiency. Results indicated that in terms of seed yield the VAFI is superior to FAFI and it is equivalent to the full irrigation (OFI). Therefore, VAFI is a water saving irrigation in the study region (25% reduction in water use) even under drought conditions with 175mm of rainfall occurred mostly in winter. Furthermore, based on the seed yield, nitrogen use efficiency (NUE) and water use efficiency (WUE), it was concluded that VAFI with 200kgNha−1 is appropriate irrigation and N fertilizer management for rapeseed in the study region. However, based on the seed oil, protein yields, oil yield based WUE and apparent N recovery, VAFI with 300kgNha−1 is best treatment. Leaching during the growing season could be reduced by using VAFI especially under conditions with low rainfall in winter. Only in FAFI, N uptake decreased and soil residual N was increased as compared with OFI and VAFI. Thus, in order to avoid N losses, the amount of N fertilizer should be reduced in proportion to the amount of soil water available for plant water uptake under water saving irrigation (VAFI).

Distribución y pérdidas de agua y nitrato bajo fertirriego por surcos alterno y convencional

El riego por surcos alternos y el fertirriego por superficie se han venido utilizando por separado como técnicas con capacidad demostrada para controlar las pérdidas de agua y fertilizantes. El principal objetivo del ensayo descrito en este trabajo fue caracterizar el efecto del uso conjunto de estas técnicas en las pérdidas de agua y nitratos, en el agua en el suelo y en la concentración de nitrato en el suelo. En el ensayo se consideraron dos tipos de fertirriego por surcos alternos, variable (AFI) y fijo (FFI), así como el riego por surcos convencional (CFI). Los resultados evidenciaron una mayor infiltración en los surcos AFI y FFI que en los surcos CFI. El aumento del movimiento lateral del agua en el riego alterno resultó en menores pérdidas de agua y nitrato por escorrentía y percolación profunda. La eficiencia de aplicación del agua para las estrategias CFI, FFI y AFI fue de 61,3%, 71,8% y 77,0% en el primer fertirriego, y de 36,4%, 58,8% y 60,7% en el segundo fertirriego, respectivamente. Las escorrentías de nitrato en las estrategias CFI, FFI y AFI fueron de 32,4%, 31,2% y 25,7% en el primer fertirriego y de 44,3%, 35,1% y 32,7% en el segundo fertirriego, respectivamente. El contenido de agua en el suelo y la concentración de nitrato en el extremo aguas arriba del campo experimental resultó mayor que en la parte media o en el extremo aguas abajo en las tres estrategias ensayadas. El fertirriego por surcos alternos (AFI en particular) resulta una técnica de manejo simple y práctica para conservar agua y fertilizantes en la agricultura de regadío.

Effects of Alternate Furrow Irrigation and Nitrogen Application Rates on Yield and Water-and Nitrogen-Use Efficiency of Winter Wheat (Triticum aestivum L.)

A study was conducted in Bajgah (deep water table condition) and Kooshkak (shallow water condition) areas in Fars province in I.R. of Iran to investigate the effects of different nitrogen application rates, deficient irrigation by alternate furrow irrigation (AFI) method and their interaction on the yield and water- and nitrogen use efficiency of winter wheat. The experimental design was split plot with three main plots as irrigation treatments [ordinary furrow irrigation (OFI), fixed alternate furrow irrigation (FAFI) and variable alternate furrow irrigation (VAFI)] and four subplots as nitrogen application rates (0, 90, 180 and 270 kg ha-1) repeated three times. The amount of irrigation water for each irrigation event was considered equal to readily available water of soil in the root zone, and the time of irrigation was determined by the cumulative evapotranspiration (according to Penman-FAO method). The total amounts of irrigation water were 439.0 and 256 mm for OFI and AFI, respectively in the Bajgah area, and 367 and 226 mm, respectively, in the Kooshkak area. Total seasonal rainfalls were 409.0 and 470.5 mm in the Bajgah and Kooshkak, respectively. The results indicated that the interaction between irrigation method and nitrogen application rate was statistically significant for total biomass but not for grain yield and other traits. In terms of grain production, VAFI was superior to FAFI in the Bajgah and Kooshkak areas. VFAI in Bajgah and Kooshkak resulted in 42 and 39% reduction in irrigation water use and 22 and 13% reduction in grain yield, respectively, compared with OFI. Based on the grain yield, nitrogen use efficiency, apparent nitrogen recovery and water use efficiency, it was concluded that VAFI with application of 180 kg N ha-1 is appropriate in the experimental areas. Based on the grain yield and protein content, VAFI with application of 270 kg N ha-1 was also appropriate due to 21-35% greater production of total protein, although nitrogen use efficiency, and apparent nitrogen recovery decreased by 20 and 16%, respectively, compared with 180 N ha-1. Further, water-use efficiency in VAFI with 180 kg N ha-1 was 0.89 and 0.85 kg m-3 in the Bajgah and Kooshkak areas, respectively, which were values not significantly different from those obtained in VAFI with a nitrogen application rate of 270 kg ha-1. Therefore, VAFI with a nitrogen application rate of 180 kg ha-1 is a recommendable practice in the study areas.

Alternate Furrow Irrigation with Different Irrigation Intervals for Maize (Zea mays L.)

This research was conducted to determine the yield and water-use efficiency of maize under fixed and variable alternate furrow irrigation (fixed AFI, variable AFI) and every furrow irrigation (EFI) at different irrigation intervals in areas with shallow and deep groundwater. In variable AFI, water was applied to the furrow, which was dry in the previous irrigation cycle. The results indicated that even at 4-day irrigation intervals the water needs of maize on a fine textured soil in both areas (with deep and shallow water table) are not met by AFI. The decrease in grain yield due to water stress was mainly due to the decrease in the number of grains per cob and to a lesser extent to the decrease in 1000-grain weight. At the Kooshkak site with shallow groundwater (between 1.31 and 1.67 m), grain yields in AFI at 4- and 7-day intervals were comparable to those obtained in EFI at 7- and 10-day intervals, respectively. This might be due to the contribution of groundwater to the water use of the plant (about 5-10%). In the Badjgah area, with deep water depth, grain yield in AFI at 7-day intervals was statistically lower than that obtained in EFI at 10-day interval. In AFI, a shorter irrigation interval (4-day) may alleviate the water stress and result in no yield reduction compared with that in EFI at 7-day intervals even though water application was reduced. Furthermore, in the area with a shallow water table, AFI at 7-day intervals may be superior to EFI at 10-day irrigation intervals. When seasonal irrigation water is less than 700 mm, it may be preferable to use AFI at 10-day intervals to increase water-use efficiency, especially in areas with shallow groundwater. In general, when water was insufficient for full irrigation, the relative grain yield (yield per unit water applied) of maize under AFI was higher than those under EFI.