Deficit Irrigation as a Strategy to Save Water： Physiology and Potential Application to Horticulture

Water is an increasingly scarce resource worldwide and irrigated agriculture remains one of the largest and most inefficient users of this resource. Low water use efficiency （WUE） together with an increased competition for water resources with other sectors （e.g. tourism or industry） are forcing growers to adopt new irrigation and cultivation practices that use water more judiciously. In areas with dry and hot climates, drip irrigation and protected cultivation have improved WUE mainly by reducing runoff and evapotranspiration losses. However, complementary approaches are still needed to increase WUE in irrigated agriculture. Deficit irrigation strategies like regulated deficit irrigation or partial root drying have emerged as potential ways to increase water savings in agriculture by allowing crops to withstand mild water stress with no or only marginal decreases of yield and quality. Grapevine and several fruit tree crops seem to be well adapted to deficit irrigation, but other crops like vegetables tend not to cope so well due to losses in yield and quality. This paper aims at providing an overview of the physiological basis of deficit irrigation strategies and their potential for horticulture by describing the major consequences of their use to vegetative growth, yield and quality of different crops （fruits, vegetables and ornamentals）.     

Root growth and water uptake in winter wheat under deficit irrigation

Root growth is critical for crops to use soil water under water-limited conditions. A field study was conducted to investigate the effect of available soil water on root and shoot growth, and root water uptake in winter wheat (Triticum aestivum L.) under deficit irrigation in a semi-arid environment. Treatments consisted of rainfed, deficit irrigation at different developmental stages, and adequate irrigation. The rainfed plots had the lowest shoot dry weight because available soil water decreased rapidly from booting to late grain filling. For the deficit-irrigation treatments, crops that received irrigation at jointing and booting had higher shoot dry weight than those that received irrigation at anthesis and middle grain filling. Rapid root growth occurred in both rainfed and irrigated crops from floral initiation to anthesis, and maximum rooting depth occurred by booting. Root length density and dry weight decreased after anthesis. From floral initiation to booting, root length density and growth rate were higher in rainfed than in irrigated crops. However, root length density and growth rate were lower in rainfed than in irrigated crops from booting to anthesis. As a result, the difference in root length density between rainfed and irrigated treatments was small during grain filling. The root growth and water use below 1.4 m were limited by a caliche (45% CaCO₃) layer at about 1.4 m profile. The mean water uptake rate decreased as available soil water decreased. During grain filling, root water uptake was higher from the irrigated crops than from the rainfed. Irrigation from jointing to anthesis increased seasonal evapotranspiration, grain yield, harvest index and water-use efficiency based on yield (WUE), but did not affect water-use efficiency based on aboveground biomass. There was no significant difference in WUE among irrigation treatments except one-irrigation at middle grain filling. Due to a relatively deep root system in rainfed crops, the higher grain yield and WUE in irrigated crops compared to rainfed crops was not a result of rooting depth or root length density, but increased harvest index, and higher water uptake rate during grain filling.     

不同荫蔽栽培下亏缺灌溉对干热区小粒咖啡水光利用和产量的影响

干热区小粒咖啡水光管理粗放,产量和品质得不到保证.为探明干热区小粒咖啡最佳灌水和荫蔽栽培耦合模式,通过大田试验,设3个灌水水平(充分灌水、轻度亏缺灌水和重度亏缺灌水)和4个荫蔽栽培模式(无荫蔽:单作咖啡;轻度荫蔽:4行咖啡间作1行香蕉;中度荫蔽:3行咖啡间作1行香蕉;重度荫蔽:2行咖啡间作1行香蕉),研究香蕉荫蔽栽培下亏缺灌溉对小粒咖啡生长、叶片光合特性、水光利用和产量的影响.结果表明: 小粒咖啡叶片的净光合速率(P_n)、蒸腾速率(T_r)、气孔导度(g_s)、叶片水分利用效率(LWUE)、叶片表观光能利用效率(LRUE)随灌水量的增大而增大,胞间CO₂浓度(C_i)随灌水量的增大而减小;与充分灌水相比,轻度亏缺灌水的干豆产量减小9.4%,重度亏缺灌水的干豆产量减小36.7%,水分利用效率(WUE)减小16.9%.P_n、T_r、g_s、LWUE随荫蔽度的增大呈先增大后减小的趋势,中度荫蔽栽培的增量最大;与无荫蔽模式相比,轻度荫蔽模式干豆产量增加13.0%,WUE增加12.9%,中度荫蔽栽培模式干豆产量增加23.1%,WUE增加23.4%.干豆产量、WUE、百粒咖啡豆的体积和百粒鲜质量随灌水量和荫蔽度的增大呈不同程度增大,其中,中度荫蔽栽培下充分灌水的干豆产量和WUE增量最大.相同土层深度的土壤含水率随荫蔽度的增加而减小;在0~50 cm土层,土壤含水率随土层深度的增加先增大后减小.LRUE与光合有效辐射呈显著的负指数关系或符合Logistic曲线变化.因此,从优质高产、水光高效利用的综合效益考虑,中度荫蔽栽培下充分灌水是小粒咖啡灌水处理和香蕉荫蔽栽培模式的最佳组合.     

Deficit irrigation for reducing agricultural water use

At present and more so in the future, irrigated agriculture will take place under water scarcity. Insufficient water supply for irrigation will be the norm rather than the exception, and irrigation management will shift from emphasizing production per unit area towards maximizing the production per unit of water consumed, the water productivity. To cope with scarce supplies, deficit irrigation, defined as the application of water below full crop-water requirements (evapotranspiration), is an important tool to achieve the goal of reducing irrigation water use. While deficit irrigation is widely practised over millions of hectares for a number of reasons - from inadequate network design to excessive irrigation expansion relative to catchment supplies - it has not received sufficient attention in research. Its use in reducing water consumption for biomass production, and for irrigation of annual and perennial crops is reviewed here. There is potential for improving water productivity in many field crops and there is sufficient information for defining the best deficit irrigation strategy for many situations. One conclusion is that the level of irrigation supply under deficit irrigation should be relatively high in most cases, one that permits achieving 60-100% of full evapotranspiration. Several cases on the successful use of regulated deficit irrigation (RDI) in fruit trees and vines are reviewed, showing that RDI not only increases water productivity, but also farmers' profits. Research linking the physiological basis of these responses to the design of RDI strategies is likely to have a significant impact in increasing its adoption in water-limited areas.     

Prospects of partial root zone irrigation for increasing irrigation water use efficiency of major crops in the Mediterranean region

Field experiments were conducted for 3 years from 2000 to 2002 to assess proportional crop yield differences obtained under conventional deficit irrigation (CDI) and partial root zone irrigation (PRI) practices, compared with full irrigation (FULL) where plant water requirements were fully met. The experimental crops included vegetables (tomato and pepper), field crops (maize and cotton) and citrus. The fruit yield of greenhouse‐grown tomato with FULL irrigation was higher than with PRI (7–22% lower) but was not significantly different. The PRI treatments had 7–10% additional tomato yield over CDI receiving the same amount of water. The yield of pepper, however, decreased in proportion to the level of irrigation deficit with no increase of irrigation water use efficiency (IWUE). No seed yield decrease was evident for cotton with the deficit treatments (PRI and CDI) compared with FULL irrigation. Similarly, the PRI treatment did not give any yield benefit for maize compared with CDI. The ranking of fruit yields of mandarin, FULL > PRI > CDI, was the same as that of other crops; however, the differences were not significant. Although the deficit treatments (PRI and CDI) had as high as 39% increase in IWUE, compared with FULL treatment, some adverse effects on fruit quality were evident such as smaller size of fruits under the deficit treatments.     

Water-use efficiency and transpiration efficiency of wheat under rain-fed conditions and supplemental irrigation in a Mediterranean-type environment

Growth and water use were measured in wheat (Triticum aestivum L.) grown in northern Syria in a typical Mediterranean climate over five seasons 1991/92–1995/96. Water use was partitioned into transpiration (T) and soil evaporation (E_s) using Ritchie's model, and water-use efficiency (WUE) and transpiration efficiency (TE) were calculated. The aim of the study was to examine the influence of irrigation and nitrogen on water use, WUE and TE. By addition of 100 kg N ha^-1, E_s was reduced from 120 mm to 101 mm under rain-fed conditions and from 143 mm to 110 mm under irrigated conditions, and T was increased from 153 mm to 193 mm under rain-fed conditions and from 215 mm to 310 mm under irrigated conditions. Under rain-fed conditions, about 35% of evapotranspiration (ET) may be lost from the soil surface for the fertilized crops and 44% of ET for the unfertilized crops. Transpiration accounted for 65% of ET for the fertilized crops and 56% for the unfertilized crops under rain-fed. As a result of this, WUE was increased by 44% for dry matter and 29% for grain yield under rain-fed conditions, and by 60% for dry matter and 57% for grain yield under irrigated conditions. Transpiration efficiency for the fertilized crops was 43.8 kg ha^-1 mm^-1 for dry matter and 15 kg ha^-1 mm^-1 for grain yield, while TE for the unfertilized crops was 33.6 kg ha^-1 mm^-1 and 12.2 kg ha^-1 mm^-1 for dry matter and grain yield, respectively. Supplemental irrigation significantly increased post-anthesis water use, transpiration, dry matter and grain yield. Water-use efficiency for grain yield was increased from 9.7 to 11.0 kg ha^-1 mm^-1 by supplemental irrigation, although WUE for dry matter was not affected by it. Irrigation did not affect transpiration efficiency for grain yield, but decreased transpiration efficiency for dry matter by 16%. This was associated with higher harvest index as a result of good water supply in the post-anthesis period and increased transpiration under irrigated conditions.     

Oxygation Enhances Growth, Gas Exchange and Salt Tolerance of Vegetable Soybean and Cotton in a Saline Vertisol

Impacts of salinity become severe when the soil is deficient in oxygen. Oxygation (using aerated water for subsurface drip irrigation of crop) could minimize the impact of salinity on plants under oxygen-limiting soil environments. Pot experiments were conducted to evaluate the effects of oxygation (12% air volume/volume of water) on vegetable soybean (moderately salt tolerant) and cotton (salt tolerant) in a salinized vertisol at 2, 8, 14, 20 dS/m ECe. In vegetable soybean, oxygation increased above ground biomass yield and water use efficiency (WUE) by 13% and 22%, respectively, compared with the control. Higher yield with oxygation was accompanied by greater plant height and stem diameter and reduced specific leaf area and leaf Na+ and Cl-concentrations. In cotton, oxygation increased lint yield and WUE by 18% and 16%, respectively, compared with the control, and was accompanied by greater canopy light interception, plant height and stem diameter. Oxygation also led to a greater rate of photosynthesis, higher relative water content in the leaf, reduced crop water stress index and lower leaf water potential. It did not, however, affect leaf Na+ or Cl- concentration. Oxygation invariably increased, whereas salinity reduced the K+ : Na+ ratio in the leaves of both species. Oxygation improved yield and WUE performance of salt tolerant and moderately tolerant crops under saline soil environments, and this may have a significant impact for irrigated agriculture where saline soils pose constraints to crop production.     

The growth characteristics and yield potential of rice (Oryza sativa) under non‐flooded irrigation in arid region

The objectives of this field experiment were to study the growth characteristics and yield potential of rice plants under non‐flooded irrigation in arid area. Non‐flooded treatments included drip irrigation with plastic mulching treatments (DIs), furrow irrigation with plastic mulching treatment (FIM) and furrow irrigation with non‐mulching treatment (FIN). Conventional flooded cultivation (F) was check treatment (CK). The four drip irrigation treatments differed in the amount of water applied before and after panicle initiation. Root length density, leaf dry weight, shoot dry weight and root activity were generally higher in the non‐flood‐irrigated treatments (especially the drip‐irrigated treatments) than in the flood‐irrigated treatment at mid‐tillering. However, the growth and development of rice plants were limited after jointing in the non‐flooded irrigation treatments. Increasing the root/shoot ratio and root length density in the 20–40 cm depth and decreasing specific root length at 0–20 cm soil layer were important mechanisms for helping the rice plants to adapt to the non‐flooded environmental stresses. Finally, the grain yield in the non‐flooded irrigation treatments was lower than that in the F treatment. These low yields were mainly attributed to the low root length density at 0–20 cm depth and root activity. Generally speaking, the restricted degrees in the DIs were smaller than that in the FIM and FIN treatments. Among the DIs, both the highest grain yield (8223–8900 kg ha^?1) and the highest water use efficiency (WUE) (0.63) were observed when the soil water content was kept at ?30 kPa before panicle initiation and at ?15 kPa after panicle initiation (referred to as the DI2 treatment). The yield in the DI2 treatment was not significantly different than that in the flood‐irrigated treatment. However, WUE was 2.5 times higher in the DI2 treatment than in the F treatment. These results suggest that drip irrigation technology can be considered as a better water‐saving cultivation of rice plants in arid region.     

节水农业及其生理生态基础

提高自然降水和灌溉水利用效率是节水农业要解决的中心问题。近年实践证明,通过提高水分利用率的途径增加农田生产力存在很大潜力,节水和增产的目标可能同时实现。为实现这一目标,需要研究确定植物水分亏缺的允许程度。植物各个生理过程对水分亏缺的敏感性不同,综合文献报道和作者研究结果,水分亏缺对与作物产量密切相关生理过程影响的先后顺序为:生长—蒸腾—光合—运输。在一定条件下,有限水分亏缺不会对作物最终经济产量造成影响,但却能显著提高水分利用效率。     

High levels of microbial contamination of vegetables irrigated with wastewater by the drip method.

The public health aspects of the use of wastewater in agriculture and the effects of the drip irrigation method on the contamination of vegetables were studied. The method used was to simulate enteric microorganisms' dissemination by contaminated irrigation water in the field. The vegetables were irrigated with an effluent inoculated with a high titer of traceable microorganisms: poliovirus vaccine and a drug-resistant Escherichia coli. The dissemination of the marker organisms in the field was followed, and the effects of certain manipulations of the drip irrigation method on the contamination of the crops by the effluent were examined. It was shown that drip irrigation under plastic sheet cover with the drip lines placed either on the soil surface or buried at a depth of 10 cm significantly reduced crop contamination from inoculated irrigation water even when massive doses of bacteria and viruses were used. The microbial contamination was found to persist in the irrigation pipes and in the soil for at least 8 and 18 days, respectively. The data indicate that the recovery of the marker organisms was affected by soil texture and environmental conditions.     

High levels of microbial contamination of vegetables irrigated with wastewater by the drip method.

The public health aspects of the use of wastewater in agriculture and the effects of the drip irrigation method on the contamination of vegetables were studied. The method used was to simulate enteric microorganisms' dissemination by contaminated irrigation water in the field. The vegetables were irrigated with an effluent inoculated with a high titer of traceable microorganisms: poliovirus vaccine and a drug-resistant Escherichia coli. The dissemination of the marker organisms in the field was followed, and the effects of certain manipulations of the drip irrigation method on the contamination of the crops by the effluent were examined. It was shown that drip irrigation under plastic sheet cover with the drip lines placed either on the soil surface or buried at a depth of 10 cm significantly reduced crop contamination from inoculated irrigation water even when massive doses of bacteria and viruses were used. The microbial contamination was found to persist in the irrigation pipes and in the soil for at least 8 and 18 days, respectively. The data indicate that the recovery of the marker organisms was affected by soil texture and environmental conditions.     

Physiological mechanisms contributing to the increased water-use efficiency in winter wheat under deficit irrigation

Deficit irrigation in winter wheat has been practiced in the areas with limited irrigation water resources. The objectives of this study were to (i) understand the physiological basis for determinations of grain yield and water-use efficiency in grain yield (WUE) under deficit irrigation; and (ii) investigate the effect of deficit irrigation on dry matter accumulation and remobilization of pre-anthesis carbon reserves during grain filling. A field experiment was conducted in the Southern High Plains of the USA and winter wheat (cv. TAM 202) was grown on Pullman clay loam soil (fine mixed thermic Torretic Paleustoll). Treatments consisted of rain-fed, deficit irrigation from jointing to the middle of grain filling, and full irrigation. The physiological measurements included leaf water potential, net photosynthetic rate (Pn), stomatal conductance (Gs), and leaf area index. The rain-fed treatment had the lowest seasonal evapotranspiration (ET), biomass, grain yield, harvest index (HI) and WUE as a result of moderate to severe water stress from jointing to grain filling. Irrigation application increased seasonal ET, and ET increased as irrigation frequency increased. The seasonal ET increased 20% in one-irrigation treatments between jointing and anthesis, 32-46% in two-irrigation treatments, and 67% in three- and full irrigation treatments. Plant biomass, grain yield, HI and WUE increased as the result of increased ET. The increased yield under irrigation was mainly contributed by the increased number of spikes, and seeds per square meter and per spike. Among the irrigation treatments, grain yield increased significantly but the WUE increased slightly as irrigation frequency increased. The increased WUE under deficit irrigation was contributed by increased HI. Water stress during grain filling reduced Pn and Gs, and accelerated leaf senescence. However, the water stress during grain filling induced remobilization of pre-anthesis carbon reserves to grains, and the remobilization of pre-anthesis carbon reserves significantly contributed to the increased grain yield and HI. The results of this study showed that deficit irrigation between jointing and anthesis significantly increased wheat yield and WUE through increasing both current photosynthesis and the remobilization of pre-anthesis carbon reserves.     

亏缺灌溉对棉花生长和水分利用效率的影响研究进展

棉花是世界上最主要的农作物之一。随着全球水资源的日益紧张,灌溉用水将成为限制棉花生产的主要因素。亏缺灌溉是一种低于作物正常腾发量的灌溉方式,可以在保证棉花产量和品质的前提下提高水分利用效率,是一种有效的节水灌溉方式。本文综述了亏缺灌溉对棉花生长和水分利用效率的影响。亏缺灌溉可以通过促进棉花由营养生长向生殖生长转化,降低棉花株高、叶面积、总生物量,从而提高收获指数、茎粗和水分利用效率。最后,综合现有的研究,结合棉花生产实际,提出亏缺灌溉应用推广建议,以期为旱区棉花可持续发展提供理论指导。     

Translational research impacting on crop productivity in drought-prone environments

Conventional breeding for drought-prone environments (DPE) has been complemented by using exotic germplasm to extend crop gene pools and physiological approaches that consider water uptake (WU), water-use efficiency (WUE), and harvest index (HI) as drivers of yield. Drivers are associated with proxy genetic markers, such as carbon-isotope discrimination for WUE, canopy temperature for WU, and anthesis-silking interval for HI in maize. Molecular markers associated with relevant quantitative trait loci are being developed. WUE has also been increased through combining understanding of root-to-shoot signaling with deficit irrigation. Impacts in DPE will be accelerated by combining proven technologies with promising new strategies such as marker-assisted selection, and genetic transformation, as well as conservation agriculture that can increase WU while averting soil degradation.     

Comparison on physiological adaptation and phosphorus use efficiency of upland rice and lowland rice under alternate wetting and drying irrigation

As one of the most widely promoted water-saving irrigation strategies for rice, alternate wetting and drying irrigation (AWD) can not only save water but also increase mineral nutrient use efficiency. In this study, we compared the growth conditions of four rice varieties (two lowland and two upland varieties) under three irrigation regimes: continuously flooded (CF), alternate wetting and moderate soil drying (AWD15) and alternate wetting and severe soil drying (AWD30). AWD15 and AWD30 enabled the plants to receive fewer irrigation events and less irrigation water than CF, thereby saving both water resources and labor. AWD15 reduced redundant vegetative growth, promoted root growth, and increased the root-shoot ratio and harvest index. AWD15 increased the grain yield, water use efficiency (WUE) and phosphorus use efficiency (PUE) of upland rice and maintained the grain yield while increasing the WUE and PUE of lowland rice. More developed root systems under AWD helped upland rice to maintain a higher water status than lowland rice when plants were subjected to soil drying, which resulted in superior performance in grain yield in upland rice. AWD30 could not reconcile the demands of higher yield and the desire to reduce irrigation water use because it decreased grain yield. The results indicate that AWD15 irrigation of rice can not only increase rice yield and WUE but also enhance PUE, which can potentially reduce the use of phosphorus fertilizers. The results provide theoretical and technical support for improving rice cultivation.     

不同基因型冬小麦旗叶的稳定碳同位素比值及其与产量和水分利用效率的关系

以我国北方12个冬小麦(Triticum aestivum)品种(系)和美国德克萨斯州3个冬小麦品种(系)为供试材料, 在甘肃陇东黄土高原旱作和拔节期有限补灌条件下, 比较研究了不同基因型冬小麦之间产量、水分利用效率(WUE)和灌浆期旗叶稳定碳同位素比值(δ¹³C)的差异, 以及δ¹³C值与产量和WUE的关系。旨在通过分析δ¹³C值与产量和WUE的关系, 明确δ¹³C值在评价植物WUE方面的可靠性, 为抗旱节水品种的筛选提供理论依据。结果表明: 不论旱作还是有限补灌, 不同基因型冬小麦之间产量、WUE、旗叶δ¹³C值存在显著差异, 随着灌浆过程的进行, 旗叶δ¹³C值呈缓慢增大的趋势, 而且旗叶δ¹³C值旱作高于有限补灌。不论旱作还是补灌条件, 旗叶δ¹³C值在4个测定时期的平均值与籽粒产量、WUE呈显著正相关关系(R²= 0.527 3-0.691 3)。小麦拔节期补灌100 mm水分后, 不同基因型小麦表现出明显的水分超补偿效应。说明冬小麦灌浆期旗叶δ¹³C值在旱作条件下和在补灌条件下均可较好地评价WUE, 可将冬小麦灌浆期旗叶δ¹³C值作为筛选高效用水品种的参考指标之一。     

Salmonella contamination of vegetables irrigated with untreated wastewater

The irrigation of vegetables with raw wastewater has been practised in El Azzouzia, the wastewater-spreading field of Marrakesh city (Morocco), for many years. This water was found to be contaminated with different serogroups of Salmonella. B and C were the most frequently isolated groups. These same serogroups were detected on vegetables irrigated with these wastewater effluents. The crops whose edible product develops on the ground surface, such as lettuce and parsley, were more contaminated than those which grow, above the soil surface, like tomatoes and pimento. Except on lettuce, Salmonella on crops did not persist beyond 3 days after irrigation.     

Growing floricultural crops with brackish water

In the current review we focus on the opportunity to use brackish water in the cultivation of floricultural plants, plants for which, due to their high economic value, growers have traditionally used good quality water for irrigation. Now, even for these crops the use of alternative water sources for irrigating nursery plants is needed because of the limited supplies of fresh water in many countries; understanding how saline water can be used will also enhance sustainable development in floriculture. While salt stress usually reduces plant growth, any such reduction might not be negative for ornamentals, where shoot vigour is sometime undesirable, although on flower crops salt stress can delay flowering or decrease flower quality characteristics. However, a decrease in growth rate is not enough to characterize the salt tolerance of ornamental plants, but traits like tip and marginal leaf burn, as consequence of sodium and chlorine accumulation, have to be considered for their effects on aesthetical value. With this in mind, some halophytes should be considered for floriculture because of their ability to cope with saline environments; their potential to tolerate salt is an important factor in reducing production costs. Consequently, the identification of ornamental halophytes is important for producing a commercially acceptable crop when irrigated with brackish waters. Many aspects of a plant's reaction to salt are genetically determined, so selection of suitable genotypes or breeding for salt tolerance in ornamentals are interesting options. Developing salt-tolerant floricultural crops, together with typical management practices that avoid excessive salinity stress in the root media, will provide the grower with economically and environmentally sound wastewater reuse options.     

高产条件下不同小麦品种耗水特性和水分利用效率的差异

设置不灌水(W0)、底墒水+拔节水(W1)、底墒水+拔节水+开花水(W2)3个灌水处理,采用6个冬小麦(Triticum aestivum.L.)品种,研究了不同品种耗水特性和水分利用效率的差异.结果表明:(1)依据籽粒产量和水分利用效率2个因子,采用聚类分析的方法,将供试品种分为高水分利用效率组(Ⅰ组)、中水分利用效率组(Ⅱ组)和低水分利用效率组(Ⅲ组).同一灌水条件下的籽粒产量,Ⅰ组显著高于Ⅱ组和Ⅲ组;Ⅱ组和Ⅲ组在W0条件下无显著差异,在W1和W2条件下Ⅱ组显著高于Ⅲ组.(2)从Ⅰ组、Ⅱ组、Ⅲ组中分别取1个品种,泰山23、潍麦8号、山农12进一步分析表明,在W0 和W1条件下,泰山23和潍麦8号的阶段耗水量和耗水模系数为开花至成熟>播种至拔节>拔节至开花,山农12为播种至拔节>开花至成熟>拔节至开花.W2条件下,3个品种的阶段耗水量和耗水模系数为开花至成熟>播种至拔节>拔节至开花;播种至拔节和拔节至开花的耗水模系数为泰山23>山农12>潍麦8号,此阶段的耗水量和耗水强度为泰山23品种最高;开花至成熟的耗水模系数为潍麦8号>山农12 >泰山23,此阶段的耗水量和耗水强度为泰山23品种最低.(3) 在W0 和W1条件下,总耗水量和灌水量、降水量及土壤耗水量占总耗水量的百分率为泰山23品种居中;W2条件下,灌水量和降水量占总耗水量的百分率为泰山23>潍麦8号>山农12,土壤耗水量及其占总耗水量的百分率反之,但泰山23的总耗水量最低.(4) 同一灌水条件下,泰山23品种100～200cm土层的土壤耗水量高于潍麦8号,表明该品种能充分利用深层土壤水;山农12品种在W0和W2条件下,100～200 cm土层的土壤耗水量高于泰山23和潍麦8号,但其籽粒产量和水分利用效率显著低于上述两品种.     

交替地下滴灌对春玉米产量和水分利用效率的影响

采用自动式遮雨棚水分精量控制试验研究了交替地下滴灌条件下不同灌溉定额对春玉米产量和水分利用效率的影响.结果表明:交替地下滴灌春玉米需水关键时期为拔节-抽雄期、抽雄-灌浆期,具体表现为耗水模系数与耗水强度大,且对水分敏感性高,在灌溉条件有限的情况下要优先满足春玉米这两个时期的水分需求.随着灌溉定额的增加,产量呈现增加趋势;灌溉定额小于2764.5 m³·hm^-2时产量随灌溉定额增加快速增加,大于2764.5 m³·hm^-2时产量随灌溉定额增加缓慢增加;当灌溉定额为3357.1 m³·hm^-2时产量最高,达12109.0 kg·hm^-2.与固定地下滴灌相比,在灌溉定额相同条件下,交替地下滴灌产量提高5.4%,水分利用效率提高1.4%,灌溉水利用效率提高5.6%.与固定地下滴灌相比,灌溉定额减少20%时,交替地下滴灌虽然产量下降1.8%,但水分利用效率提高11.0%,灌溉水利用效率提高22.7%.综合考虑产量、水分利用效率两个指标,确定试验区春玉米交替地下滴灌的适宜灌溉定额为1600.4～3357.1 m³·hm^-2.