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1.
The southeastern United States typically receives more than 130 cm of precipitation per year. In this region, as in others around the world, irrigation is used as a supplement to rainfall. Over the past thirty years the number of hectares under irrigation in the region has grown considerably, as has population. Policy makers are currently searching for effective tools to address water demand. This study tests the effect of water costs, crop prices and technology on the multiple crop production decision using supplemental irrigation. Results for Georgia row crop producers indicate water demand is modestly affected by water price (with elasticities between −0.01 and −0.17), but more so by crop price (with elasticities between 0.5 and 0.82). Results also suggest adoption of lower pressure irrigation systems does not necessarily lead to lower water application rates on corn, cotton, peanuts, and soybeans.  相似文献   

2.
Deficit irrigation (DI) has been widely investigated as a valuable and sustainable production strategy in dry regions. By limiting water applications to drought-sensitive growth stages, this practice aims to maximize water productivity and to stabilize - rather than maximize - yields. We review selected research from around the world and we summarize the advantages and disadvantages of deficit irrigation. Research results confirm that DI is successful in increasing water productivity for various crops without causing severe yield reductions. Nevertheless, a certain minimum amount of seasonal moisture must be guaranteed. DI requires precise knowledge of crop response to drought stress, as drought tolerance varies considerably by genotype and phenological stage. In developing and optimizing DI strategies, field research should therefore be combined with crop water productivity modeling.  相似文献   

3.
Drip irrigation systems and irrigation strategies like deficit irrigation (DI) and partial root drying (PRD) are potential water saving irrigation systems and strategies. This paper analyses the Serbian farmer's economic incentive to use these water saving systems and strategies instead of the present sprinkler irrigation. The analysis is a partial budgeting analysis, based on irrigation application efficiency from the literature, standard figures for power requirements, pumping efficiency and friction losses for various sources of water and pressure requirements, yields and water use from recent Serbian field experiments, as well as prices and cost structures for potatoes collected in the Belgrade region. The analysis shows that changing the present system and strategy can save a significant amount of water (almost 50%). At the same time, however, irrigation costs are also significantly increased (more than doubled), and the total production costs are increased by 10% (deficit drip irrigation) and 23% (PRD). Increased taxes on water, investment subsidies, increased energy prices, and an increased yield or yield quality may provide incentives for farmers to change to new systems and strategies. The analysis indicates that a 0.80 to 1.97 € m−3 water tax is needed to make deficit drip irrigation and PRD profitable. The socioeconomic cost of providing water for irrigation and the alternative value of saved water are probably not that high. Thus, water taxation may not be a socioeconomic efficient means to improve the irrigation water productivity of Serbian potato production. Drip irrigation and PRD may, however, also increase the yield quality, and a 10-23% quality premium (price increase) is needed to make deficit drip irrigation and PRD profitable.  相似文献   

4.
The West Asia and North Africa (WANA) region, with a Mediterranean climate type, has an increasing deficit in cereal production, especially bread wheat. Rainfed cropping in the highlands of this region coincides with the severely cold winter with mostly, snow from November to April. Cereal yields, are low and variable mainly as a result of inadequate and erratic seasonal rainfall and associated management factors, such as late sowing (or late crop emergence). In an area where water is limited, small amounts of supplemental irrigation (SI) water can make up for the deficits in seasonal rain and produce satisfactory and sustainable yields. This field study (1999–2002) on a deep clay silty soil in north west of Iran was conducted with four SI levels (rainfed, 1/3, 2/3 and full irrigation requirements) combined with different N rates (0, 30, 60, 90 and 120 kg ha−1) with one wheat variety (Sabalan). Yields of rainfed wheat varied with seasonal rainfall and its distribution. A delay in the crop emergence from October (SI treatment) to November (rainfed) consistently reduced yields. With irrigation, crop responses to nitrogen were generally significant up to 60 kg N ha−1. An addition of only limited irrigation (1/3 of full irrigation) significantly increased yields and maximized water use efficiency (WUE). Use efficiency for water and N was greatly increased by SI. Under deficit irrigation, maximum WUE would be achieved when 60 kg N ha−1 is combined with 1/3 of full SI. Early crop germination is essential to ensure adequate crop stand before the winter frost and to achieve high yield. Early emergence can be achieved by applying a small amount (40–50 mm) of SI after sowing. Thus, when limited SI is combined with appropriate management, wheat production can be substantially and consistently increased in this highland semi-arid zone.  相似文献   

5.
Crop yield is primarily water-limited in areas of West Asia and North Africa with a Mediterranean climate. Ten years of supplemental irrigation (SI) experiments in northern Syria were conducted to evaluate water–yield relations for bread wheat (Triticum aestivum L.) and durum wheat (Triticum turgidum L.), and optimal irrigation scheduling was proposed for various rainfall conditions. The sensitive growth stages of wheat to water stress were from stem elongation to booting, followed by anthesis, and grain-filling. Water stress to which crop subjected depends on rainfall and its distribution during the growing season; the stress started from early March (stem-elongation stage) or even in seedling stage in a dry year, and from mid-April (anthesis) in an average or wet year. Crop yield linearly increased with increase in evapotranspiration (ET), with an increase of 160 kg for bread wheat and of 116 kg for durum wheat per 10 mm increase of ET above the threshold of 200 mm. Water-use efficiency (WUE) with a yield ≥3 t ha−1 was ca. 60% higher than that with yield <3 t ha−1; this emphasises the importance of that to achieve effective use of water, optimal water supply and relatively high yields need to be ensured. Quadratic crop production functions with the total applied water were developed and used to estimate the levels of irrigation water for maximizing yield, net profit and levels to which the crops could be under-irrigated without reducing income below that which would be earned for full SI under limited water resources. The analysis suggested that irrigation scenarios for maximizing crop yield and/or the net profit under limited land resource conditions should not be recommended. The SI scenarios for maximizing the profit under limited water resource conditions or for a targeted yield of 4–5 t ha−1 were recommended for sustainable utilization of water resources and higher WUE. The time of irrigation was also suggested on the basis of crop sensitivity index to water stress taking rainfall probability and available soil water into account.  相似文献   

6.
Supplemental irrigation (SI) is a common practice in the dry environments and aims at improving and stabilizing rainfed crops by adding small amounts of water to rainfed crops during times when rainfall fails to provide sufficient moisture for normal plant growth. Results from long-term research in experimental stations and farmer fields showed substantial increases in rainfed crop yields and water use efficiency in response to SI. Nevertheless, SI comes at a cost.The date of sowing winter wheat in a rainfed Mediterranean-type environment depends upon the onset of rainfall. The optimal date for achieving highest yield under rainfed conditions is around mid-November. However, farmers tend to sow wheat later than this date because of the delay and/or unreliability of initial rains. With SI, early sowing and crop establishment can be ensured. However, early sowing of all the fields’ results in higher water demand during a very short period in spring because all the fields will be at the peak use rate. Spreading out dates of sowing allows peak water demand to occur over a longer period, thus reducing the discharge and the size of irrigation system needed, and hence improves the economics of this practice. In this paper, the impact of adopting a multi-sowing date strategy on farm water demand and crop production is considered. A simplified optimization model solved by linear programming is presented. Four-years’ data (1992–1996) from field experimental research conducted on bread wheat in northern Syria have been used in the analysis.We showed that a multi-sowing date strategy has reduced the peak farm water demand rate by more than 20%, thus potentially reducing irrigation system capacity and/or size. Alternatively, the water demand rate of a larger area can be met with the same water supply. However, optimal sowing dates that minimize farm water demand rate do not always maximize total farm production. The outcome depends on crop water requirements and yield for each sowing date. Furthermore, this selection is greatly influenced by the level of water scarcity. The approach used can help in reducing the cost of irrigation and improving the efficiency of water use in SI.  相似文献   

7.
The Central Anatolian Plateau of Turkey is a typical cool highland rainfed wheat area with an annual rainfall of 300–500 mm. Due to suboptimal seasonal rainfall amounts and distribution, wheat yields in the region are low and fluctuate substantially over seasons. Delayed sowing due to late rainfall affects early crop establishment before winter frost and causes substantial reduction in yield. A 4-year field study (1998/1999 to 2001/2002) was carried out at Ankara Research Institute of Rural Services to assess the impact of early sowing with supplemental irrigation (SI) and management options during other dry spells on the productivity of a bread wheat cultivar, “Bezostia”. Treatments included early sowing with 50 mm irrigation and normal sowing with no irrigation as main plots. Four spring (SI) levels occupied the sub-plots. These are rainfed (no-irrigation), full irrigation to sature crop water requirements and two deficit irrigation levels of 1/3 and 2/3 at the full irrigation treatments.Results showed that early establishment of the crop, using 50 mm of irrigation water at sowing, increased grain yield by over 65% and adding about 2.0 t/ha to the average rainfed yield of 3.2 t/ha. Early sowing with SI allowed early crop emergence and development of good stand before being subjected to the winter frost. As a result, the crop used rainwater more efficiently. Additional supplemental irrigation in the spring also increased yield significantly. Grain yields of 5120, 5170 and 5350 kg/ha were obtained by applying 1/3, 2/3 and full SI, respectively. The mean productivity of irrigation water given at sowing was 3.70 kg/m3 with maximum value of 4.5 kg/m3. Water productivity of 1/3, 2/3 and full SI were 2.39, 1.46 and 1.27 kg/m3, respectively, compared to rainwater productivity of 0.96 kg/m3.  相似文献   

8.
The tomato industry reformed its system of payment by weight of tomato, introducing a corrective system based on percent level of fruit dry matter produced. Such a decision implies significant changes in the management of irrigation systems, with a need to emphasize the technological quality of the marketable product. Three levels of distribution uniformity of the irrigation system are analysed, and related production functions of crop yield and percent of dry matter are presented as well as their use on the optimisation of dry matter, expected revenues and seasonal applied water. Results are critically influenced by the distribution uniformity. They demonstrate the inter-relationship between crop production, percent fruit dry matter and irrigation management, and the importance of considering non-uniformity in the economic analysis of industrial tomato production. Decreases in uniformity lead to a reduction in dry matter production per unit land. Decreases in dry matter are also observed with increasing levels of seasonally applied water, with the optimal level always lower than the required for maximum yield. Such interaction suggests a continuous and inverse relationship between profit and water applied. However, due to the corrective system of payment, by levels of percent of dry matter produced, for some uniformity, the expected revenue follows the yield-water production function instead of the dry matter function. This fact introduces disturbances in the optimal water applied inducing higher than expected levels of water applied for profit maximisation. The simulated data also show that incentives to switch to new systems or management practices able to raise the distribution uniformity result more from profit losses than increases in water price.  相似文献   

9.
Chickpea is one of the major legume crops grown in the West Asia and North Africa (WANA) region. It has considerable importance as a food, feed and fodder. Traditionally, it is sown in spring as a rainfed crop in the region, which has highly variable and often insufficient rainfall. It is, therefore, largely raised on residual moisture, which results in low and variable yields and discourages farmers from investing inputs in its production. In the early 1990s, a winter-sown chickpea technology was developed that outweighs spring-sown chickpea in terms of productivity, water use efficiency and other traits. Limited supplemental irrigation can, however, play a major role in boosting and stabilizing the productivity of both spring-sown and winter-sown chickpea. Therefore, we investigated the effect of supplemental irrigation and sowing date on yield and water use efficiency in winter-sown chickpea.An experiment was carried out over four cropping seasons (1997–2001) at ICARDA’s main station at Tel Hadya, Aleppo, northern Syria (mean annual rainfall 330 mm). A cold-tolerant chickpea cultivar with improved resistance to ascochyta blight (ILC 3279, released as Ghab 2 in Syria) was grown in rotation with wheat. The experiment included three sowing dates (late November, mid-January, and late February) and four levels of supplemental irrigation (SI): full SI, 2/3 SI, 1/3 SI, and no SI, i.e. rainfed. The plots were replicated three times in a split-plot design, with date of sowing being the main plot treatment. Soil water content was monitored at approximately at 7–14-day intervals using a neutron probe. Crop evapotranspiration was determined for each subplot during each time interval, from sowing to harvest, using the soil-water balance equation. Water use efficiency was determined as the ratio of crop yield per unit area to seasonal evapotranspiration.The results showed that chickpea yield per unit area increases with both earlier sowing and increased SI. However, water use efficiency under supplemental irrigation decreases with earlier sowing, due to the relatively large increase that occurs in the amount of evapotranspiration at early sowing dates. The study’s results indicated that a 2/3 SI level gives the optimum water use efficiency for chickpea under supplemental irrigation. Under rainfed conditions, however, it was found that sowing chickpea around mid-January resulted in the highest WUE. The analysis also proposed a function, based on regression, which relates winter-sown chickpea yield to water use and which is applicable under both supplemental and rainfed conditions.  相似文献   

10.
玉米灌溉模型及遗传算法的优化求解   总被引：2，自引：0，他引：2  
张兵  袁寿其  李红  成立  蒋惠凤 《农业机械学报》2006,37(9):104-106,115
在综合考虑了灌溉水量、作物水分需求、水分生产函数、降雨量、土壤水分平衡、不同生育阶段缺水对产量的敏感指数、粮食市场价格、农田灌溉用水价格、最低产量需求和灌溉成本等因素的基础上，建立了基于灌水收益最大的多约束非线性灌溉模型，同时应用遗传算法对模型的实数编码解空间进行搜索。求解结果显示该模型很好地解决了玉米的优化灌溉问题，遗传算法能在很短时间内搜寻到模型的最优解。  相似文献   

11.
The Southeast U.S. receives an average of 1300 mm annual rainfall, however poor seasonal distribution of rainfall often limits production. Irrigation is used during the growing season to supplement rainfall to sustain profitable crop production. Increased water capture would improve water use efficiency and reduce irrigation requirements. Furrow diking has been proposed as a cost effective management practice that is designed to create a series of storage basins in the furrow between crop rows to catch and retain rainfall and irrigation water. Furrow diking has received much attention in arid and semi-arid regions with mixed results, yet has not been adapted for cotton production in the Southeast U.S. Our objectives were to evaluate the agronomic response and economic feasibility of producing cotton with and without furrow diking in conventional tillage over a range of irrigation rates including no irrigation. Studies were conducted at two research sites each year from 2005 to 2007. Irrigation scheduling was based on Irrigator Pro for Cotton software. The use of furrow diking in these studies periodically reduced water consumption and improved yield and net returns. In 2006 and 2007, when irrigation scheduling was based on soil water status, an average of 76 mm ha−1 of irrigation water was saved by furrow diking, producing similar cotton yield and net returns. Furrow diking improved cotton yield an average of 171 kg ha−1 and net return by $245 ha−1 over multiple irrigation rates, in 1 of 3 years. We conclude that furrow diking has the capability to reduce irrigation requirements and the costs associated with irrigation when rainfall is periodic and drought is not severe.  相似文献   

12.
In a vegetative crop like sugar cane, soil water stress will invariably result in reduced growth and yield. Under inadequate rainfall conditions such a crop needs supplemental irrigation to maximize the yield.The present article discusses the relationship between sugar cane yield and rainfall/irrigation requirements. Special attention is given to the potential sugar cane yields and benefit/cost ratios in the Malaiman area in Thailand, under four water conveyance systems (from low- to high-density irrigation and drainage network) and under optimized rainfed cultivation.A linear relationship between cane yield and water use is applied for the prediction of potential crop yields for the various water conveyance systems. These yields are compared with the actual cane production in pilot areas with different irrigation infrastructure, which has been monitored over a period of years. Actual yields fall short of predicted in all cases. This is mainly be attributed to the low cane prices, resulting in sub-optimal cultivation practices by the farmers.Prediction of potential sugar cane yields for local circumstances is quite possible. At present sugar cane price levels, development of a low-density irrigation infrastructure seems to be the most economical solution.  相似文献   

13.
Worldwide growing water scarcity has increased the call for economic instruments to stimulate rational water use in agriculture. Furthermore, cost-recovery is now widely accepted as a cornerstone of sustainable water management. In many developing countries, where agricultural water use is often still subsidised, water pricing policies are developed for allocating water efficiently and achieving sustainability of water systems. However, the impacts of water pricing policies on irrigation water use and on farm production systems is mostly unknown. We introduce an innovative two-stage methodology that allows estimating these effects at farm level. Applying the method to small-scale irrigators in South Africa, we show that water demand is quite responsive even to small changes in water price. In addition, the introduction of a water price significantly decreases farm profit. This appears to be a problem primarily for the poorer farmers.  相似文献   

14.
In the semi-arid region of Tigray, Northen Ethiopia a two season experiment was conducted to measure evapotranspiration, estimate yield response to water stress and derive the crop coefficient of teff using the single crop coefficient approach with simple, locally made lysimeters and field plots. During the experiment we also estimated the water productivity of teff taking into account long-term rainfall probability scenarios and different levels of farmers’ skills. During the experimental seasons (2008 and 2009), the average potential evapotranspiration of teff ranged from 260 to 317 mm. The total seasonal water requirement of teff was found to lower in contrast to the assumptions of regional agronomists that teff water requirement is comparable to that of wheat and barley (375 mm). The average single crop coefficient values (kc) for the initial, mid and late season stages of teff were 0.8-1, 0.95-1.1 and 0.4-0.5, respectively. The seasonal yield response to water stress was 1.04, which indicates that teff exhibits a moderately sensitive and linear response to water stress. The results suggest that teff is likely to give significantly higher grain yield when a nearly optimal water supply is provided. The study showed that, in locations where standard equipment is not affordably available, indicative (rough) crop evapotranspiration values can be obtained by using field plots and employing locally made lysimeters. The difference in economic water productivity (EWP) and the crop water productivity (CWP) for teff were assessed under very wet, wet, normal, dry and very dry scenarios. In addition two groups of farmers were evaluated, a moderately (I) and a highly skilled (II) group. The results showed that higher EWP and CWP were obtained under very wet scenario than very dry scenario. There was also a 22% increase in EWP and CWP under group II compared to group I farmers. The increase was due to a 22% reduction in unwanted water losses achieved through use of improved technology and better irrigation skills. Both EWP and CWP can be used to evaluate the pond irrigation water productivity (IWP) for a given climate, crop and soil type, and skill and technology level of the farmer. For special crops like teff extra criteria may be needed in order to properly evaluate the pond irrigation water productivity. During the experimental seasons, a high IWP for teff was attained when about 90% of the optimal water need of the crop was met. IWP can be used as an indicator as how much supplementary irrigation has to be applied in relation to the rainfall and other sources of water supply in order to assure greatest yield from a total area. However, the supplemental irrigation requirement of the crops may vary with season due to seasonal rainfall variability.  相似文献   

15.
As water resources are limited and the demand for agricultural products increases, it becomes increasingly important to use irrigation water optimally. At a farm scale, farmer's have a particularly strong incentive to optimize their irrigation water use when the volume of water available over a season is production limiting. In this situation, a farmer's goal is to maximize farm profit, by adjusting when and where irrigation water is used. However, making the very best decisions about when and where to irrigate is not easy, since these daily decisions require consideration of the entire remaining irrigation season. Future rainfall uncertainty further complicates decisions on when and which crops should be subjected to water stress. This paper presents an innovative on-farm irrigation scheduling decision support method called the Canterbury irrigation scheduler (CIS) that is suitable when seasonal water availability is limited. Previous optimal scheduling methods generally use stochastic dynamic programming, which requires over-simplistic plant models, limiting their practical usefulness. The CIS method improves on previous methods because it accommodates realistic plant models. Future farm profit (the objective function) is calculated using a time-series simulation model of the farm. Different irrigation management strategies are tested using the farm simulation model. The irrigation strategies are defined by a set of decision variables, and the decision variables are optimized using simulated annealing. The result of this optimization is an irrigation strategy that maximizes the expected future farm profit. This process is repeated several times during the irrigation season using the CIS method, and the optimal irrigation strategy is modified and improved using updated climate and soil moisture information. The ability of the CIS method to produce near optimal decisions was demonstrated by a comparison to previous stochastic dynamic programming schedulers. A second case study shows the CIS method can incorporate more realistic farm models than is possible when using stochastic dynamic programming. This case study used the FarmWi$e/APSIM model developed by CSIRO, Australia. Results show that when seasonal water limit is the primary constraint on water availability, the CIS could increase pasture yield revenue in Canterbury (New Zealand) in the order of 10%, compared with scheduling irrigation using current state of the art scheduling practice.  相似文献   

16.
In the dry areas, water, not land, is the most limiting resource for improved agricultural production. Maximizing water productivity, and not yield per unit of land, is therefore a better strategy for dry farming systems. Under such conditions, more efficient water management techniques must be adopted. Supplemental irrigation (SI) is a highly efficient practice with great potential for increasing agricultural production and improving livelihoods in the dry rainfed areas. In the drier environments, most of the rainwater is lost by evaporation; therefore the rainwater productivity is extremely low. Water harvesting can improve agriculture by directing and concentrating rainwater through runoff to the plants and other beneficial uses. It was found that over 50% of lost water can be recovered at a very little cost. However, socioeconomic and environmental benefits of this practice are far more important than increasing agricultural water productivity. This paper highlights the major research findings regarding improving water productivity in the dry rainfed region of West Asia and North Africa. It shows that substantial and sustainable improvements in water productivity can only be achieved through integrated farm resources management. On-farm water-productive techniques if coupled with improved irrigation management options, better crop selection and appropriate cultural practices, improved genetic make-up, and timely socioeconomic interventions will help to achieve this objective. Conventional water management guidelines should be revised to ensure maximum water productivity instead of land productivity.  相似文献   

17.
This study analyzes the effects of irrigation modernization on water conservation, using the Riegos del Alto Aragón (RAA) irrigation project (NE Spain, 123354 ha) as a case study. A conceptual approach, based on water accounting and water productivity, has been used. Traditional surface irrigation systems and modern sprinkler systems currently occupy 73% and 27% of the irrigated area, respectively. Virtually all the irrigated area is devoted to field crops. Nowadays, farmers are investing on irrigation modernization by switching from surface to sprinkler irrigation because of the lack of labour and the reduction of net incomes as a consequence of reduction in European subsidies, among other factors. At the RAA project, modern sprinkler systems present higher crop yields and more intense cropping patterns than traditional surface irrigation systems. Crop evapotranspiration and non-beneficial evapotranspiration (mainly wind drift and evaporation loses, WDEL) per unit area are higher in sprinkler irrigated than in surface irrigated areas. Our results indicate that irrigation modernization will increase water depletion and water use. Farmers will achieve higher productivity and better working conditions. Likewise, the expected decreases in RAA irrigation return flows will lead to improvements in the quality of the receiving water bodies. However, water productivity computed over water depletion will not vary with irrigation modernization due to the typical linear relationship between yield and evapotranspiration and to the effect of WDEL on the regional water balance. Future variations in crop and energy prices might change the conclusions on economic productivity.  相似文献   

18.
皂河灌区农民用水者协会水价探讨   总被引：2，自引：1，他引：2  
如何实现灌区的经济自立，水价改革首当其冲，皂灌灌区用自己的探索，走出了一条切实可行的水价核定、征收、使用和管理的新路子。皂河灌用用水者协会参与灌溉管理后用水协会会员水价由水利工程水价、供水公司供水水价和用水者协会供水价构成，并建立健全了收费组织，完善收费计量方式，合理分配使用消费，减少水价管理中的危害性、随意性和不合理现象，以促进灌区的经济自立和可持续发展。  相似文献   

19.
Cotton (Gossypium hirsutum L.) is the most important industrial and summer cash crop in Syria and many other countries in the arid areas but there are concerns about future production levels, given the high water requirements and the decline in water availability. Most farmers in Syria aim to maximize yield per unit of land regardless of the quantity of water applied. Water losses can be reduced and water productivity (yield per unit of water consumed) improved by applying deficit irrigation, but this requires a better understanding of crop response to various levels of water stress. This paper presents results from a 3-year study (2004-2006) conducted in northern Syria to quantify cotton yield response to different levels of water and fertilizer. The experiment included four irrigation levels and three levels of nitrogen (N) fertilizer under drip irrigation. The overall mean cotton (lint plus seed, or lintseed) yield was 2502 kg ha−1, ranging from 1520 kg ha−1 under 40% irrigation to 3460 kg ha−1 under 100% irrigation. Mean water productivity (WPET) was 0.36 kg lintseed per m3 of crop actual evapotranspiration (ETc), ranging from 0.32 kg m−3 under 40% irrigation to 0.39 kg m−3 under the 100% treatment. Results suggest that deficit irrigation does not improve biological water productivity of drip-irrigated cotton. Water and fertilizer levels (especially the former) have significant effects on yield, crop growth and WPET. Water, but not N level, has a highly significant effect on crop ETc. The study provides production functions relating cotton yield to ETc as well as soil water content at planting. These functions are useful for irrigation optimization and for forecasting the impact of water rationing and drought on regional water budgets and agricultural economies. The WPET values obtained in this study compare well with those reported from the southwestern USA, Argentina and other developed cotton producing regions. Most importantly, these WPET values are double the current values in Syria, suggesting that improved irrigation water and system management can improve WPET, and thus enhance conservation and sustainability in this water-scarce region.  相似文献   

20.
Crop production in Mediterranean-type environments is invariably limited by low and erratic rainfall (200-600 mm year−1), and thus soil moisture, and by high evapotranspiration resulting from high temperature. Consequently, a major research challenge is to devise cropping systems that maximize water-use efficiency (WUE). In a long-term trial in northern Syria (1986-1998) we compared the effects of seven wheat-based rotations on soil water dynamics and WUE in both the wheat and non-wheat phase. The cropping systems were durum wheat (Triticum turgidum L.) in rotation with fallow, watermelon (Citrullus vulgaris), lentil (Lens culinaris), chickpea (Cicer arietinum), vetch (Vicia sativa), medic pasture (Medicago spp.), and wheat. Seasonal recharge/discharge were identified using the neutron probe. Depth of wetting varied with seasonal rainfall (233-503 mm). Based on crop yields, WUE was calculated for each cropping option in relation to the durum wheat crop.The greatest limitation to growth was the supply of water and not the soil moisture storage potential. Wheat grain yield was dictated by the extent to which the alternative crops in the rotation dried out the soil profile, in addition to seasonal rainfall and its distribution. Chickpea and medic extracted as much water as continuous wheat. Wheat after these crops was solely dependent on current seasonal rainfall, but fallow, lentil, watermelon, and vetch did not deplete soil moisture to the same extent, leaving some residual soil moisture for the succeeding wheat crop. This difference in soil water resulted in a significant difference in wheat yield and hence WUE, which decreased in the following crop rotation sequence: fallow, medic, lentil, chickpea, and continuous wheat. However, on the system basis, the wheat/lentil or wheat/vetch systems were most efficient at using rainfall, producing 27% more grain than the wheat/fallow, while the wheat/chickpea system was as efficient as wheat/fallow system, with continuous wheat being least efficient. With N added to the cereal phase, system WUE of the system increased, being least for continuous wheat and greatest for wheat/lentil. Wheat-legume rotation systems with additional N input in the wheat phase not only can maintain sustainable production system, but also are more efficient in utilizing limited rainfall.  相似文献   

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