黑河中游春小麦需水量空间分布

合理估计春小麦的需水量(ET_c)是进行干旱区水资源配置的有效方法,利用黑河中游14个气象站1970-2009年的逐日气象资料,应用Penman-Monteith公式估算各站点的参考作物蒸散量,并根据春小麦生长期的作物系数,在地理信息系统(GIS)技术支持下得出黑河中游春小麦需水量的空间分布及变化趋势。结果表明:1970-2009年黑河中游春小麦作物需水量整体分布具有从南向北递增的趋势,全生长期需水量在573-781 mm之间;高台、张掖、临泽、民乐、山丹、酒泉的春小麦需水量分别为731.26、686.88、598.24、728.89、719.77、713.59 mm,其中生长中期需水量最大,分别占全生长期的51.67%、51.11%、50.96%、51.24%、50.83%和50.77%;日平均气温、日照时数、风速、降水量、最小相对湿度和各因子的影响力由大到小分别占总影响力的57.29%、26.92%、15.15%、1.41%和0.78%。     

Combining sap flow and trunk diameter measurements to assess water needs in mature olive orchards

Sap flux (Q) and trunk diameter variation (TDV) are among the most useful plant-based measurements to detect water stress and to evaluate plant water consumption. The usefulness of both methods decreases, however, when applied to species that, like olive, have an outstanding tolerance to drought and a remarkable capacity to take up water from drying soils. Evidence shows that this problem is greater in old, big trees with heavy fruit load. Our hypothesis is that the analysis of simultaneous measurements of Q and TDV made in the same trees is more useful for assessing irrigation needs in old olive orchards than the use of any of these two methods alone. To test our hypothesis, we analysed relations between Q, TDV, midday stem water potential (Ψ_stem), relative extractable water and atmospheric demand in an olive orchard of 38-year-old ‘Manzanilla’ trees with heavy fruit load. Measurements were made during one irrigation season (May-October), in fully irrigated trees (FI, 107% of the crop evapotranspiration, ET_c, supplied by irrigation), and in trees under two levels of deficit irrigation (DI60, 61% ET_c; DI30, 29% ET_c). Time courses of Q and TDV measured on days of contrasting weather and soil water conditions were analysed to evaluate the usefulness of both methods to assess the crop water status. We calculated the daily tree water consumption (E_p) from Q measurements. For both DI treatments we calculated a signal intensity by dividing daily E_p values of each DI tree by those of the FI tree (SI−Ep). We did the same with the maximum daily shrinkage (MDS) values (S_I−MDS). Neither SI−Ep nor S_I−MDS rendered useful information for assessing the crop water needs. On the contrary, the daily difference for maximum trunk diameter (MXTD) between each of the DI trees and the FI tree (D_MXTD) clearly indicated the onset and severity of water stress. A similar analysis with the E_p values, from which DEp values were derived, showed the effect of water stress on the water consumption of the trees. We concluded that the simultaneous use of D_MXTD and DEp values provides more detailed information to assess water needs in mature olive orchards than the use of Q or TDV records alone.     

基于改进的双作物系数法估算辽河三角洲芦苇湿地蒸散量

以辽河三角洲湿地芦苇群落为研究对象,利用涡动相关通量、小气候梯度要素、群落内水面蒸发量以及芦苇群落生长参数等数据,基于FAO-56模型的双作物系数法,分别计算作物系数K_c、基础作物系数K_cb和水面蒸发系数K_w,分析其日变化动态及主导影响因子,建立基于生物因子和环境因子的小时尺度双作物系数模型。结果如下:(1)芦苇生长初期,K_c和K_cb的日变化呈现早晚高、中午略低的多峰波动曲线;在快速生长期和稳定生长期,K_c和K_cb白天波动幅度较小,早晚波动幅度较大;生长末期,K_c和K_cb夜晚波动幅度较大,白天呈现多峰波动曲线;K_w白天较小、夜晚较高,生长初期白天的数值显著高于其他时期。(2)相关分析表明,气温、相对湿度、风速、株高和叶面积指数是K_c、K_cb和K_w的影响因子;基于生物因子和环境因子重新构建双作物系数模型,基...     

Water relations and gas exchange in olive trees under regulated deficit irrigation and partial rootzone drying

It is widely believed that partial root drying (PRD) reduces water losses by transpiration without affecting yield. However, experimental work carried out to date does not always support this hypothesis. In many cases a PRD treatment has been compared to a full irrigated treatment, so doubt remains on whether the observed benefits correspond to the switching of irrigation or just to PRD being a deficit irrigation treatment. In addition, not always a PRD treatment has been found advantageous as compared to a companion regulated deficit irrigation (RDI) treatment. In this work we have compared the response of mature ‘Manzanilla‘ olive trees to a PRD and an RDI treatment in which about 50% of the crop evapotranspiration (ET_c) was supplied daily by localised irrigation. We alternated irrigation in the PRD treatment every 2 weeks in 2003 and every 3 weeks in 2004. Measurements of stem water potential (Ψ_stem), stomatal conductance (g _s) and net CO₂ assimilation rate (A) were made in trees of both treatments, as well as in trees irrigated to 100% of ET_c (Control trees) and in Rain-fed trees. Sap flow was also measured in different conductive organs of trees under both PRD and RDI treatments, to evaluate the influence of alternating irrigation on root water uptake and tree water consumption. We found small and random differences in Ψ_stem, g _s and A, which gave no evidence of PRD causing a positive effect on the olive tree performance, as compared to RDI. Stomatal conductance decreased in PRD trees as compared to Control trees, but a similar decrease in g _s was also recorded in the RDI trees. Sap flow measurements, which reflected water use throughout the irrigation period, also showed no evidence of g _s being more reduced in PRD than in RDI trees. Daily water consumption was also similar in the trees of the deficit irrigation treatments, for most days, throughout the irrigation period. Alternating irrigation in PRD trees did not cause a change in either water taken up by main roots at each side of the trees, or in the sap flow of both trunk locations and main branches of each side. Results from this work, and from previous work conducted in this orchard, suggest that transpiration is restricted in trees under deficit irrigation, in which roots are left in drying soil when water is applied by localised irrigation, and that there is no need to alternate irrigation for achieving this effect. Section Editor: R. E. Munns     

Using trunk diameter sensors for regulated deficit irrigation scheduling in early maturing peach trees

The aim of this paper was to test the possibility of scheduling regulated deficit irrigation (RDI) using exclusively maximum daily trunk shrinkage (MDS) measurements, and that RDI strategies can be applied in early maturing peach trees reducing significantly the seasonal water use. During three growing seasons, 6-year-old peach trees (Prunus persica (L.) Batsch cv. Flordastar) grafted on P. persica × P. amygdalus GF-677 peach rootstock were submitted to different drip irrigation treatments. Control (T0) plants were irrigated above the estimated crop evapotranspiration level (≈130% ET_C) and T1 plants were submitted to RDI, which were irrigated in order to maintain MDS signal intensity (SI) values close to unity (no irrigation-related stress) from the fruit thinning stage to 2 weeks after harvest, at MDS SI values close to 1.3 during the early postharvest period, and at MDS SI values of 1.6 during the late postharvest period. The RDI strategy assayed reduced the seasonal water applied by 35-42% with respect to estimated ET_C without affecting yield efficiency components or the distribution of different peach fruit categories, while improving water productivity. The only vegetative growth component affected by RDI was pruning weight, indicating that vigor regulation as a result of RDI may decrease the competition for assimilates between vegetative apexes and reserve tissues. Also, the absence of any significant effect of RDI on the ratio between yield and the increase in trunk cross sectional area suggested similar carbon partitioning schemes during fruit growth. To improve the precision of MDS SI-driven schedule in RDI strategies changes in the irrigation protocol should be considered so that the scheduled water deficit levels are attained more rapidly. For this, when it is necessary to change from a MDS SI threshold value to a higher one, the daily irrigation rate should be decreased by more than 3%.     

Interactions of plant species mediated plant competition for inorganic nitrogen with soil microorganisms in an alpine meadow

The aim of the present work was to evaluate the effects of regulated deficit irrigation (RDI) applied in the post-harvest stage of peach trees. The 3-year trial was carried out in Italy (N 40°20′, E 16°48′) on mature peach plants (cv “Springcrest”) trained to transverse Y. From bud break to harvest, irrigation was carried out by applying 100% ET_c, while from harvest to early autumn, plants were separated into three groups and subjected to different irrigation treatments (100, 57 and 34% ET_c). The decrease in soil water content caused a reduction in the values of tissue water potential and gas exchange both in 57% ET_c and 34% ET_c treatments. RDI determined the reduction in the growth of waterspouts and lateral shoots but did not influence the growth of fruiting shoots. During the trial, no significant reductions in crop yield and quality were observed in the 57% ET_c treatment, whereas about 1,100, 1,800 and 2,500 m³ ha⁻¹ of water were saved in the first, the second and the third year, respectively. In the second year of the trial, the use of RDI in the post-harvest stage determined carbohydrate and nitrogen accumulation in roots, branches, shoots and floral buds. The results demonstrate that, under scarce water supply conditions, a clear benefit can be obtained through the use of RDI during the post-harvest stage. This confirms the possibility to reduce the irrigation water by applying RDI during phenological stages less sensitive to water deficit without negatively affecting peach growth and yield.     

Interaction between atmospheric CO2 concentration and water deficit on gas exchange and crop growth: testing of ecosys with data from the Free Air CO2 Enrichment (FACE) experiment

Soil water deficits are likely to influence the response of crop growth and yield to changes in atmospheric CO₂ concentrations (C_a), but the extent of this influence is uncertain. To study the interaction of water deficits and C_a on crop growth, the ecosystem simulation model ecosys was tested with data for diurnal gas exchange and seasonal wheat growth measured during 1993 under high and low irrigation at C_a= 370 and 550 μmol mol^?1 in the Free Air CO₂ Enrichment (FACE) experiment near Phoenix, AZ. The model, supported by the data from canopy gas exchange enclosures, indicated that under high irrigation canopy conductance (g_c) at C_a= 550 μmol mol^?1 was reduced to about 0.75 that at C_a= 370 μmol mol^?1, but that under low irrigation, g_c was reduced less. Consequently when C_a was increased from 370 to 550 μmol mol^?1, canopy transpiration was reduced less, and net CO₂ fixation was increased more, under low irrigation than under high irrigation. The simulated effects of C_a and irrigation on diurnal gas exchange were also apparent on seasonal water use and grain yield. Simulated vs. measured seasonal water use by wheat under high irrigation was reduced by 6% vs. 4% at C_a= 550 vs. 370 μmol mol^?1 but that under low irrigation was increased by 3% vs. 5%. Simulated vs. measured grain yield of wheat under high irrigation was increased by 16% vs. 8%, but that under low irrigation was increased by 38% vs. 21%. In ecosys, the interaction between C_a and irrigation on diurnal gas exchange, and hence on seasonal crop growth and water use, was attributed to a convergence of simulated g_c towards common values under both C_a as canopy turgor declined. This convergence caused transpiration to decrease comparatively less, but CO₂ fixation to increase comparatively more, under high vs. low C_a. Convergence of g_c was in turn attributed to improved turgor maintenance under elevated C_a caused by greater storage C concentrations in the leaves, and by greater rooting density in the soil.     

Evapotranspiration,crop coefficient and water use efficiency of giant reed (Arundo donax L.) and miscanthus (Miscanthus × giganteus Greef et Deu.) in a Mediterranean environment.

Giant reed (Arundo donax L.) and miscanthus (Miscanthus × giganteus Greef et Deu.) are two perennial rhizomatous grasses (PRGs), considered as promising sources of lignocellulosic biomass for renewable energy production. Although the agronomic performance of these species has been addressed by several studies, the literature dedicated to the crop water use of giant reed and miscanthus is still limited. Our objective was thus to investigate giant reed and miscanthus water use by assessing crop evapotranspiration (ET_c), crop coefficients (K_c) and water use efficiency (WUE). The study was carried out in central Italy and specifically designed water-balance lysimeters were used to investigate the water use of these PRGs during the 2010 and 2011 growing seasons. Giant reed showed the highest cumulative evapotranspiration, with an average consumption of approximately 1100 mm, nearly 20% higher than miscanthus (900 mm). Crop evapotranspiration rates differed significantly between the species, particularly during the midseason (from June to September), when average daily ET_c was 7.4 and 6.2 mm in giant reed and miscanthus respectively. The K_c values determined in our study varied from 0.4 to 1.9 for giant reed and 0.3 to 1.6 for miscanthus. Finally, WUE was higher in miscanthus than in giant reed, with average values of 4.2 and 3.1 g L⁻¹ respectively. Further studies concerning water use under nonoptimal water conditions should be carried out and an assessment of the response to water stress of both crops is necessary to integrate the findings from this study.     

Deficit irrigation affects seasonal changes in leaf physiology and oil quality of Olea europaea (cultivars Frantoio and Leccino)

The olive tree is a traditionally nonirrigated crop that occupies quite an extensive agricultural area in Mediterranean-type agroecosystems. Improvements in water-use efficiency of crops are essential under the scenarios of water scarcity predicted by global change models for the Mediterranean region. Recently, irrigation has been introduced to increase the low land productivity, but there is little information on ecophysiological aspects and quality features intended for a sagacious use of water, while being of major importance for the achievement of high-quality products as olive oil. Therefore, deficit irrigation programmes were developed to improve water-use efficiency, crop productivity and quality in a subhumid zone of Southern Italy with good winter–spring precipitation. The response of mature olive trees to deficit irrigation in deep soils was studied on cultivars Frantoio and Leccino by examining atmospheric environment and soil moisture, gas exchange and plant water status, as well as oil yield and chemical analysis. Trees were not irrigated (rainfed) or subjected to irrigation at 66% and 100% of crop evapotranspiration (ET_C), starting from pit hardening to early fruit veraison. Improvements in the photosynthetic capacity induced by increasing soil water availability were only of minor importance. However, plant water status was positively influenced by deficit irrigation, with 66% and 100% of ET_C treatments hardly differing from one another though consistently diverging from rainfed plants. The effect of water stress on photosynthesis was mainly dependent on diffusion resistances in response to soil moisture. Leccino showed higher instantaneous water-use efficiency than Frantoio. Crop yield increased proportionally to the amount of seasonal water volume, confirming differences between cultivars in water-use efficiency. The unsaturated/saturated and the monounsaturated/polyunsaturated fatty acid ratios of the oil also differed between cultivars, while the watering regime had minor effects. Although irrigation can modify the fatty acid profile, polyphenol contents were scarcely affected by the water supply. Irrigation to 100% of ET_C in the period August–September might be advisable to achieve high-quality yields, while saving consistent amounts of water.     

Effects of N application frequency on nitrogen uptake efficiency in Citrus trees

Two irrigation systems were used to compare nitrogen uptake efficiency in citrus trees and to evaluate the NO₃⁻ runoff in «Navelina» orange trees [Citrus sinensis (L.) Osbeck] on Carrizo citrange rootstock (Citrus sinensis × Poncirus trifoliata Raf.). These were fertilized with 125 g N as labelled K¹⁵NO₃ and grown outdoors in containers filled with a sand-loamy soil. Two groups of 3 trees received this N dose either in five equally split applications by a flooding irrigation system or in 66 applications by drip. Trees were harvested at the end of the vegetative cycle (December) and the isotopic ratios of ¹⁵N/¹⁴N were measured in the soil-plant system. The N uptake efficiency of the whole tree was higher with drip irrigation (75 percnt;) than with flooding system (64 percnt;). In the 0-90 cm soil profile, the N immobilized in the organic fraction was similar for both irrigation methods (around 13 percnt;), whereas the N retained as NO₃⁻ was 1 percnt; of the N applied under drip and 10 percnt; under flooding. In the last case, most of NO₃⁻ remained under root system and it could be lost to leaching either by heavy rainfalls or excessive water applications. These results showed that a drip irrigation system was more efficient for improving water use and N uptake from fertilizer, in addition to potentially reduced leaching losses.     

Lychee tree parameters for water balance modeling

Lychee (Litchi chinensis Sonn.) is widely grown under irrigation in the tropical northern Thailand highlands. Water efficient irrigation requires sound irrigation scheduling for which the requisite soil moisture information can be obtained from water balance modeling. A prerequisite for water balance predictions are plant parameters which describe interception, root distribution evaporation and transpiration. These parameters depend on climate, soil, as well as plant physiology, variety and age. This study investigated the plant parameters for 7-year-old lychee trees in tropical granite landscapes, as they are as yet unavailable. Interception could be satisfactorily predicted with the modified Gash model. The Gash parameters (canopy capacity per canopy cover area (S _c), canopy cover factor (c)) were determined to be 21.8 mm and 0.22, respectively. The spatial distribution of lychee tree roots depended on slope inclination. On the level plateau position, root length density (RLD) distribution was trunk-symmetrical and could be predicted with an empirical function. On the slope, the asymmetrical and irregular root development was not predictable. The suitability of the dual crop coefficient approach predicting daily potential evaporation (E _pot) and daily potential transpiration (T _pot) rates for water balance modeling was limited due to the weak correlations of E _pot and T _pot with the potential reference evapotranspiration (ET_o). As a result, no universal values for the potential evaporation coefficient (K _e,max) and the potential transpiration coefficient (K _cb) could be determined. Hence, E _pot and T _pot measurements are mandatory if accurate E _pot and T _pot data are necessary. In the case of missing measurements, K _e,max values of 0.6 and 1.6 are recommended for rough E _pot estimates underneath and in-between the lychee tree canopies. For T _pot predictions in irrigation scheduling, a relatively high K _cb of 0.8 is recommended in order to ensure a water stress free fruit development within the irrigation season. Section Editor: R. E. Munns     

Evaluation of Phragmites australis (Cav.) Trin. evapotranspiration in Northern and Southern Italy

The design, operation, pollutant removal as well as hydraulic modeling of wetland systems for wastewater treatment can be improved by better understanding and simulating the evapotranspiration process. To this purpose, two experiments were carried out in Northern (Veneto region) and Southern (Sicily region) Italy to measure evapotranspiration (ET) and determine the crop coefficient of Phragmites australis (Cav.) Trin. using the FAO 56 approach. The experimental set-up consisted of a combination of vegetated and unvegetated plastic tanks (Veneto) or pilot sub-surface flow beds (Sicily). The ET values were obtained by measuring the amount of water needed to restore the initial volume in the tanks and in the beds after a certain period. All the needed climatic variables were measured and taken into account in the ET measurements. In the two experimental sites cumulative reference evapotranspiration (ET₀) was similar to the cumulative ET measured in the control tanks and beds (without vegetation, ET_con), while ET measured for P. australis (ET_phr) was significantly higher, underlining the strong effect of vegetation. From June 2009 to September 2009 the cumulative ET₀, ET_con and ET_phr in Veneto were 455, 424 and 3048 mm, in Sicily 653, 556 and 3899 mm, respectively. The plant coefficient trend of P. australis (K_p) estimated in Veneto was similar to that in Sicily, suggesting that the role of the plant in dispersing water is similar under different environmental conditions. Additional measurements made in the Veneto plant showed that K_p assumes different patterns and values in relation to plant age and growth stage. These results highlight the importance of the plants in regulating water losses from a wetland system, above all from small-scale constructed wetlands where the effect of the advection in ET rates is evident.     

Leaf water potential and leaf conductance during the growing season in almond trees under different irrigation regimes

Seasonal changes in leaf water potential (Φ) and leaf conductance (g₁) were determined in almond trees under different irrigation regimes. The development of water stress in the rainfed treatment induced a specific seasonal dynamics of Φ values and an important reduction in g₁ values. A decrease in g₁ values occurred independently of the irrigation treatment through the growing season. No statistically significant differences were obtained in g₁ values within the drip irrigated treatments.     

Effect of Irrigation Type on Inoculum Density of Macrophomina phaseolina in Melon Fields in Arizona

Charcoal rot, caused by Macrophomina phaseolina, has become increasingly problematic for melon growers using subsurface drip irrigation in Arizona; but has rarely been observed in fields with furrow irrigation. Since the relationship between increasing incidence of charcoal rot on melon and irrigation type is unknown, studies were initiated to determine the effects of edaphic factors on inoculum density. Soil samples were collected once from fields irrigated by subsurface drip, with and without plastic mulch, and by furrow at 10, 20 and 30 cm depths. Samples were analysed for percentage soil moisture, pH, salinity and inoculum density. Percentage soil moisture was significantly higher at 20 and 30 cm depths in the furrow‐irrigated field compared with the drip‐irrigated field with plastic mulch, but not in the field without plastic mulch. Average minimum and maximum temperatures and inoculum density were significantly lower at all three depths in the furrow‐irrigated field compared with both types of drip irrigation. pH was significantly higher in the furrow‐irrigated field compared with both types of drip irrigation at 20 and 30 cm depths but not at 10 cm depth. Differences in inoculum densities of M. phaseolina suggest that drip irrigation may contribute to higher disease incidences.     

Water relations of citrus exocortis viroid-infected grapefruit trees in the field

Citrus viroids (CVds) were used to limit citrus tree size ('dwarfing'). It is hypothesized that changes also occur in the hydraulic properties of the conducting system, thereby affecting water relations. Grapefruit trees (var. Star Ruby on Troyer Citrange rootstock) in northern Israel were infected with citrus exocortis viroid (CEVd). The orchard was drip irrigated. The infected (I) and apparently healthy (H) control plots were subdivided into wet (W) and dry (D) irrigation treatments receiving 100% and 70% of the recommended irrigation quantity for the region. Soil water content, soil temperature, water uptake, leaf and stem water potential, and leaf conductance were measured in addition to climatic variables. Water uptake response to increasing spring-time soil temperatures was greater in healthy than in infected trees. Leaf conductance in the infected trees was lower than the non-infected trees only in the sixth year after inoculation. Stem water potential was significantly lower in the CEVd-infected trees than in the control trees. Water uptake was lower and hydraulic resistance higher in infected than in healthy trees. It was concluded that CEVd causes a reduction in the water uptake ability of the root and canopy system. Possible mechanisms for this are discussed.     

Tomato root distribution, yield and fruit quality under subsurface drip irrigation

Tomato rooting patterns were evaluated in a 2-year field trial where surface drip irrigation (R0) was compared with subsurface drip irrigation at 20 cm (RI) and 40 cm (RII) depths. Pot-transplanted plants of two processing tomato, `Brigade' (C1) and `H3044' (C2), were used. The behaviour of the root system in response to different irrigation treatments was evaluated through minirhizotrons installed between two plants, in proximity of the plant row. Root length intensity (L _a), length of root per unit of minirhizotron surface area (cm cm^–2) was measured at blooming stage and at harvest. For all sampling dates the depth of the drip irrigation tube, the cultivar and the interaction between treatments did not significantly influence L _a. However differences between irrigation treatments were observed as root distribution along the soil profile and a large concentration of roots at the depth of the irrigation tubes was found. For both surface and subsurface drip irrigation and for both cultivars most of the root system was concentrated in the top 40 cm of the soil profile, where root length density ranged between 0.5 and 1.5 cm cm^–3. Commercial yields (t ha^–1) were 87.6 and 114.2 (R0), 107.5 and 128.1 (RI), 105.0 and 124.8 (RII), for 1997 and 1998, respectively. Differences between the 2 years may be attributed to different climatic conditions. In the second year, although no significant differences were found among treatments, slightly higher values were observed with irrigation tubes at 20 cm depth. Fruit quality was not significantly affected by treatments or by the interaction between irrigation tube depth and cultivar.     

The effect of deficit irrigation on seasonal variations of plant water use in Olea europaea L.

A field experiment on olive trees (Olea europaea L.) was designed with the objective to search for an optimum irrigation scheduling by analyzing the possible effects of deficit irrigation. Treatments were: a non-irrigated control (rainfed) and three treatments that received seasonal water amount equivalent to 33 and 66% of crop evapotranspiration (ET_C) in the period August–September (respectively 33II and 66II), and 66% of (ET_C) from late May to early October (66I-II). Atmospheric evaporative demand and soil moisture conditions were regularly monitored. Irrigation effects on plant water relations were characterized throughout a growing season. Whole-plant water use, in deficit irrigated (66I-II) and rainfed olive trees, was determined using a xylem sap flow method (compensation heat-pulse technique). The magnitude of variations in water use and the seasonal dynamic of water relations varied among treatments, suggesting that olive trees were strongly responsive to both irrigation amount and time. Physiological parameters responded to variations in tree water status, soil moisture conditions and atmospheric evaporative demand. All measurements of tree water status were highly correlated with one another. There was a considerable degree of agreement between daily transpiration deduced from heat-pulse velocity and that determined by calibration using the water balance technique. Deficit irrigation during the whole summer (66I-II) resulted in improved plant water relations with respect to other watering regimes; while, severe regulated deficit irrigation differentiated only slightly 33II treatment from rainfed plants. Nevertheless, regulated deficit irrigation of olive trees after pit hardening (66II) could be recommended, at least in soil, cultivar and environmental conditions of this study.     

Analysis of soil moisture variations in an irrigated orchard root zone

Soil moisture and suction head in an irrigated orchard were continuously monitored by time domain reflectometry (TDR) probes and gypsum blocks, respectively, during and between successive irrigation events. On each side of the trees in the plot, two 30-cm long probes were installed vertically 10 cm below the soil surface (denoted as shallow) and another two probes were installed vertically 40 cm below the soil surface (denoted as deep). The variation in moisture content measured by the TDR probes between successive irrigation events was qualitatively divided into four stages: the first was during water application; the second initiated when irrigation stopped and the moisture content in the layer sharply decreased, mainly due to free drainage. The succeeding moderate soil-moisture decrease, caused by the simultaneous diminishing free drainage and root uptake, was the third stage. During the fourth stage, moisture depletion from the layer was solely by root uptake. The slopes of moisture content variation with time throughout this stage enabled the monitoring of water availability to the plant. The range of moisture content variations and moisture depletion rates between subsequent irrigation events was higher in the shallow (10–40 cm) than in the deeper (40–70 cm) layer. Irrigation nonuniformity and spatial variability of soil hydraulic properties contributed to the unevenness of the moisture distribution in the soil profile. However, as soon as moisture content within a layer reached field capacity, namely the free drainage had stopped, irrigation uniformity had a negligible effect on water flux to the plant roots. The measured data indicate that soil moisture is fully available to the plant as long as the momentary moisture flux from the soil bulk to the soil–root interface can replenish the moisture being depleted to supply, under non-stressed conditions, the atmospheric water demand. This flux is dominated by the local momentary value of the soil's bulk hydraulic conductivity, K _r, and it stays constant for a certain range of K _r values, controlled by the increasing root suction. A decrease in water availability to the plant appears for longer irrigation intervals as a break in the constant soil-moisture depletion rate during stage 4. This break is better correlated to a threshold K _r value than to threshold values of moisture content or suction. Therefore, it is suggested that moisture content or suction used to measure water availability or to control irrigation first be alibrated by K _r() or K _r() curves, respectively.     

Water productivity evaluation for grain crops in irrigated regions of China

Improving crop water productivity is necessary for ensuring food and ecological security. To quantify the water utilization in grain production from multiple perspectives, gross inflow water productivity (WP_g), generalized water productivity (WP_u), evapotranspiration water productivity (WP_ET) and irrigation water productivity (WP_I) were screened in this study. Then, we calculated and analyzed the temporal and spatial variation of the water productivity indices (WPs) in the irrigated land of 31 provinces of China based on the data collected from 459 irrigation districts. The results show that the national values of the four indices were 0.694, 0.860, 1.314, and 1.361 kg/m³, and almost all of the provincial WPs increased from 1998 to 2010. The Moran's I analysis shows all of the WP indices were significantly clustered, both globally and locally, in the study years. WPs of the provinces in and around Huang-Huai-Hai Plain are high, while provinces in the northeast, south of the Yangtze River and the northwest of China showed lower water use efficiency. There is a large difference among the four indices in the scientific connotation and numerical performance, and the degree of the spatial difference was WP_I > WP_ET > WP_u > WP_g. It is necessary to promote WP in the irrigated land of China, and the provinces in the northeast should be chosen as the key regions to develop water-saving agriculture because of the high production of grain and the low value of WP. Policy decision-making based on the spatial pattern of WP and their relationships among indices for specified regions are also discussed in this paper.     

Daily variations in water relations of apricot trees under different irrigation regimes

Mature apricot (Prunus armeniaca L. cv. Búlida) trees, growing under field conditions, were submitted to two drip irrigation treatments: a control (T1), irrigated to 100 % of seasonal crop evapotranspiration (ETc), and a continuous deficit (T2), irrigated to 50 % of the control throughout the year. The behaviour of leaf water potential and its components, leaf conductance and net photosynthesis were studied at three different times during the growing season, when they revealed a diurnal and seasonal pattern in response to water stress, evaporative demand of the atmosphere and leaf age. The deficit-irrigated trees showed, among other effects, a pronounced decrease in leaf water potential (ψ_w), decreased in leaf conductance (g_s) and no osmotic adjustment. For this reason, g_l and ψ_w can be considered good indicators of mature apricot tree water status and can therefore be used for irrigation scheduling.