Determination of evapotranspiration for maize and berseem clover

Maize and berseem are among the most important crops in India and several other countries in the world. Irrigation is provided to these crops to get higher production; hence, determining the water requirements of these crops is important for irrigation planning. Improved water management of these crops requires accurate scheduling of irrigation, which in turn requires accurate measurement of crop evapotranspiration (ET_c). Thus, the first objective of this study was to measure daily, weekly and seasonal ET_c of maize and berseem directly from weighing type lysimeters. Experiments were conducted in a set of two electronic weighing-type lysimeters of 7.82 m³ to measure the hourly ET_c of maize and berseem from June 1996 to April 1998 at Karnal, India. The average daily ET_c of maize varied from <2.8 mm day^-1 in the early growing period to >4 mm day^-1 at development and reproductive stages. The peak daily ET_c of maize was 7.7 mm day^-1 and this occurred 9 weeks after sowing (WAS) at the silking stage of maize when leaf area index (LAI) was 5.5. The measured seasonal ET_c of maize was 354 mm. In the case of berseem, the average daily ET_c was 0.9 mm day^-1 at the initial stage, achieved a peak value of 6.9 mm day^-1 between 25 and 26 WAS during the fifth cut. The measured seasonal ET_c of berseem was 480 mm. Precise information on the crop coefficient, which is required for regional-scale irrigation planning, is lacking for semi-arid climates such as those found in north India. Therefore, the second objective of this study was to develop crop coefficients (K_c) for maize and berseem from ET_c measurements and weather data. The estimated values of K_c for maize by the Penman-Monteith method at the four crop growth stages; namely, initial, crop development, mid-season and maturity, were 0.55, 1.00, 1.23 and 0.64, respectively, and the corresponding values for berseem were 0.76, 0.82, 1.11 and 1.24, respectively. In the case of these two crops, actual K_c values determined from this study are different from those suggested by the FAO (Allen et al. 1998), indicating the need for generating these values at the local/ regional level.     

Water use efficiency of irrigated wheat in the Tarai region of India

Experiments were conducted during the winter seasons of 1983–1984 and 1984–1985 to identify suitable irrigation regimes s for wheat grown after rice in soils with naturally fluctuating shallow water table (SWT) at a depth of 0.4 to 0.9 m and medium water table (MWT) at a depth of 0.8 to 1.3 m. Based on physiological stages, the crop was subjected to six irrigation regimes viz., rainfed (I₀); irrigation only at crown root initiation (I₁); at only crown root initiation and milk (I₂); at crown root initiation, maximum tillering and milk (I₃); at crown root initiation, maximum tillering, flowering and milk (I₄); and at crown root initiation, maximum tillering, flowering milk and dough (I₅). Tube-well water with an EC <0.4 dsm^–1 was used for irrigation. Based on 166 mm effective precipitation during the cropping season, 1983–1984 was designated as a wet year and 1984–1985 with 51 mm as a dry year. The change in profile soil water content W (depletion) in the wet year was less (23%) under SWT and 10% under MWT as compared to the dry year. The ground water contribution (GWC) to evapotranspiration (ET) was 58% under SWT and 42% under MWT conditions in both the years. The GWC in the wet year was 20% under SWT and 23% under MWT. Of the total net water use (NWU), about 85% was ET and 15% drainage losses. The NWU was highest (641 and 586 mm) in I₅ under SWT and MWT conditions, respectively, but not the yield (5069 kg ha^–1). Compared to I₅, NWU in I₂ treatment decreased by 10% in the wet and 25% in the dry year. A similar trend was observed in the I₃ treatment under MWT condition. However, there was no statistically significant difference between yields of the I₁ to I₅ treatments of either water table depth during the wet year. This was also true during the dry year for the I₂ to I₅ treatments. Under SWT, in I₂, the grain yield was 5130 kg ha^–1 and under I₃ regime, 5200 kg ha^–1. Under MWT in I₃, the yield was 5188 kg ha^–1 and under I₄ regime, 5218 kg ha^–1. Thus it appears that in the Tarai region where the water table remains shallow (<0.9 m) and medium (<1.3 m) for most of the wheat growing season applications of more than 120 and 180 mm irrigation under SWT and MWT conditions, respectively were not necessary. Irrigation given only at crown root initiation and milk stages under shallow water table conditions, and at crown root initiation, maximum tillering and milk stages under medium water table conditions, appears to be as effective as frequent irrigations.     

Potato water use and yield under furrow irrigation

Field experiments were conducted to study the effects of plant-furrow treatments and levels of irrigation on potato (Solanum tuberosum L.) water use, yield, and water-use efficiency. The experiments were carried out under deficit irrigation conditions in a sandy loam soil of eastern India in the winter seasons of 1991/92, 1992/93, and 1993/94. Two plant-furrow treatments and two levels of irrigation were considered. The two plant-furrow treatments were F₁ - furrows with single row of planting in each ridge with 45 cm distance between adjacent ridges, and F₂ - furrows with double rows of planting spaced 30 cm apart in each ridge with 60 cm distance between adjacent ridges. The two levels of irrigation (LOI) were I₁ - 0.9 IW/CPE and I₂ - 1.2 IW/CPE, where IW is irrigation water of 5 cm and CPE is cumulative pan evaporation. Treatment F₂ produced highest tuber yield in all years with average value of 10,610 kg ha ^-1 and 12,780 kg ha ^-1 at LOI of I₁ and I₂, respectively. On average, six irrigations with a total of 25 cm, and seven irrigations with a total of 30 cm were required for both treatments F₁ and F₂ at LOI of I₁ and I₂, respectively. Treatment F₂ resulted in a significantly higher number of branches and tubers per plant, foliage coverage and water-use efficiency for both irrigation levels than treatment F₁. Average daily crop evapotranspiration was found to range from 1.1 to 3.4 mm and from 1.2 to 3.9 mm for treatment F₁ and from 1.1 to 3.6 mm and from 1.2 to 4.0 mm for treatment F₂ at LOI of I₁ and I₂, respectively.     

Comparison of water status indicators for young peach trees

We measured a series of physiological and physical indicators and compared them to xylem sap flow, to identify the most sensitive and reliable plant water status indicator. In the growing season of 1998, 4-year-old peach trees (Prunus persica Batsch cv. 'Suncrest', grafted on 'GF 677' rootstock) were studied under two irrigation treatments, 25 l day^у and no irrigation, and during recovery. Trials were conducted near Pisa (Italy) in a peach orchard situated on a medium clay loam soil and equipped with a drip-irrigation system (four 4 l h^у drippers per tree). Measurements of leaf water potential (ƒ_W), stem water potential (ƒ_S), and leaf temperature (T_l) were taken over 5 days (from dawn to sunset) and analyzed in conjunction with climatic data, sap flow (SF), trunk diameter fluctuation (TDF) and soil water content (SWC). Physiological indicators showed substantial differences in sensitivity. The first indication of changes in water status was the decrease of stem radial growth. TDF and SF revealed significant differences between the two irrigation treatments even in the absence of differences in pre-dawn leaf water potential (pdƒ_W), up until now widely accepted as the benchmark of water status indicators. Irrigated trees showed a typical trend in SF rate during the day, while in non-irrigated plants the maximum peak of transpiration was anticipated. Measurements of water potential showed ƒ_S to be a better indicator of tree water status than ƒ_W. T_l was found to have poor sensitivity. In conclusion, we found the sensitivity of the indicators from the most to the least was: TDF >SF rate >SF cumulated = pdƒ_W=ƒ_S>mdƒ_W>T_l.     

Water requirements of subsurface drip-irrigated faba bean in California

A 3-year study was done in central California to determine the water requirements for growing faba bean (Vicia faba L.) as a winter cover crop using subsurface drip irrigation (SDI). Water was applied at 0, 50, and 100% of the estimated crop evapotranspiration (ET_c) the first 2 years and 50, 100, and 150% ET_c the third year, with drip laterals installed 0.30, 0.45, or 0.60 m deep. Rainfall was above normal the first year (>330 mm) and irrigation had no effect on crop production. Irrigation improved production and water-use efficiency the following years, however. Production was higher when drip laterals were located at 0.30 or 0.45 m than at 0.60 m depth, even though roots tended to be concentrated near the laterals (later in the season) regardless of depth. Overall, well-irrigated faba bean required 231-297 mm of water to produce 3.0-4.4 t ha^у of dry vegetative biomass.     

Soil evaporation from drip-irrigated olive orchards

Evaporation from the soil (E_s) in the areas wetted by emitters under drip irrigation was characterised in the semi-arid, Mediterranean climate of Córdoba (Spain). A sharp discontinuity in E_s was observed at the boundary of the wet zone, with values decreasing sharply in the surrounding dry area. A single mean value of evaporation from the wet zone (E_sw) was determined using microlysimeters. Evaporation from the wet zones of two drip-irrigated olive orchards was clearly higher than the corresponding values of E_s calculated assuming complete and uniform soil wetting (E_so), demonstrating the occurrence of micro-scale advection in olive orchards under drip irrigation. Measurements over several days showed that the increase in evaporation due to microadvection was roughly constant regardless of location and of the fraction of incident radiation reaching the soil. Thus, daily evaporation from wet drip-irrigated soil areas (E_sw) could be estimated as the sum of E_so and an additive microadvective term (T_MA). To quantify the microadvective effects, we developed variable local advective conditions by locating a single emitter in the centre of a 1.5 ha bare plot which was subjected to drying cycles. E_sw increased relative to E_so as the soil dried and advective heat transfer increased evaporation from the area wetted by the emitter. The microadvective effects on E_s were quantified using a microadvective coefficient (K_sw), defined as the ratio between E_sw and E_so. A model was then developed to calculate T_MA for different environmental and orchard conditions. The model was validated by comparing measured E_sw against simulated evaporation (E_so+T_MA) for different soil positions and environmental conditions in two drip-irrigated olive orchards. The mean absolute error of the prediction was 0.53 mm day^-1, which represents about a 7% error in evaporation. The model was used to evaluate the relative importance of seasonal E_s losses during an irrigation season under Córdoba conditions. Evaporation from the emitter zones (E_sw) represented a fraction of seasonal orchard evapotranspiration (ET), which ranged from 4% to 12% for a mature (36% ground cover) and from 18% to 43% of ET for a young orchard (5% ground cover), depending on the fraction of soil surface wetted by the emitters. Estimated potential water savings by shifting from surface to subsurface drip ranged from 18 to 58 mm in a mature orchard and from 28 to 93 mm in a young orchard, assuming daily drip applications and absence of rainfall during the irrigation season.     

The effect of saline irrigation on lucerne production: shoot and root growth, ion relations and flowering incidence in six cultivars grown in northern Victoria, Australia

The effect of irrigation with saline (0.1-7.6 dS m^-1) water on the growth of six cultivars of lucerne was assessed over four irrigation seasons at Tatura, Victoria, Australia. Measurements made in the study included shoot dry matter production, shoot ion concentrations, flowering incidence, root distribution and soil salinity and sodicity levels. After four seasons, soil EC_e levels had risen to 4.2 dS m^-1 at the beginning of the irrigation season and this increased to around 6 dS m^-1 at the end of the season for the highest salinity irrigation treatment (7.6 dS m^-1). The soils in the two most saline irrigation treatments also became sodic (SAR_1:5>3) by the third and fourth seasons. By the second season, cultivars differed significantly in salt tolerance as defined by the rate of decline in dry matter production. The cultivars CUF 101 and Validor were consistently the most salt-tolerant cultivars, although cv. Southern Special produced the greatest amount of dry matter over all salinity treatments. Root densities at depths from 0 to 60 cm were greater under saline (2.5 and 7.6 dS m^-1) than under non-saline conditions (0.1 dS m^-1). Flower production was increased by salinity. It was concluded that, despite the presence of intraspecific variation for salt tolerance, it is detrimental to irrigate lucerne with water at electrical conductivities greater than 2.5 dS m^-1 on a red-brown earth in southern Australia.     

Water use of mature Thompson Seedless grapevines in California

Water use of Thompson Seedless grapevines was measured with a large weighing lysimeter from 4 to 7 years after planting (1990-1993). Above-ground drip-irrigation was used to water the vines. Vines growing within the lysimeter were pruned to four and six fruiting canes for the 1990 and 1991 growing seasons, respectively, and eight fruiting canes in the last 2 years. Maximum leaf area per vine at mid-season ranged from 23 to 27 m² across all years. Reference crop evapotranspiration (ET_o) averaged 1,173 mm between budbreak and the end of October each year, with a maximum daily amount of approximately 7 mm each year. Maximum daily vine water use (ET_c) was 6.1, 6.4, 6.0, and 6.7 mm (based upon a land area per vine of 7.55 m²) for 1990, 1991, 1992, and 1993, respectively. Seasonal ET_c was 718 mm in 1990 and ranged from 811 to 865 mm for the remaining 3 years of the study. The differences in water use among years were probably due to the development of the vine's canopy (leaf area), since they were pruned to differing numbers of fruiting canes. These differences were more pronounced early in the season. Soil water content (SWC) within the lysimeter decreased early in the growing season, prior to the initiation of the first irrigation. Once irrigations commenced, SWC increased and then leveled off for the remainder of the season. The maximum crop coefficient (K_c) calculated during the first year (1990) was 0.87. The maximum K_c in 1991, 1992, and 1993 was 1.08, 0.98, and1.08, respectively. The maximum K_c in 1991 and 1993 occurred during the month of September, while that in 1992 was recorded during the month of July. The seasonal K_c followed a pattern similar to that of grapevine leaf area development each year. The K_c was also a linear function of leaf area per vine using data from all four growing seasons. The decrease in K_c late in the 1991, 1992, and 1993 growing seasons, generally starting in September, varied considerably among the years. This may have been associated with the fact that leafhoppers (Erythroneura elegantula Osborn and E. variabilis Beamer) were not chemically controlled in the vineyard beginning in 1991.     

Root growth, water potential and yield of irrigated wheat

Root length density (LV), mid-day leaf water potential (Ψ _leaf) and yield of wheat were studied in 1983 – 1984 and 1984 – 1985 on a Phoolbagh clay loam (Typic Haplaquoll) and on a Beni silty clay loam (Aquic Hapludoll) in the Tarai region of Uttar Pradesh under naturally fluctuating shallow (0.4 – 0.9 m, SWT) and medium-depth (0.8 – 1.3 m, MWT) water table conditions with six water regimes: rainfed (I₀); irrigation at cown root initiation (I₁); at crown root initiation and milk (I₂); at crown root initiation, maximum tillering and milk (I₃); at crown root initiation, maximum tillering, flowering and milk (I₄); and at crown root initiation, maximum tillering, flowering, milk and dough (I₅). Maximum rooting depth (0.8 m under SWT and 1.05 m under MWT conditions) was attained at the dough stage (115 days after sowing, DAS) and was more strongly influenced by fluctuations in water table depth than by the water regime. For wet regimes (I₂– I₅), roots were concentrated at and above the water table interface and had greater horizontal development, whereas in dry regimens (I₀ and I₁), due to deficient moisture conditions in the upper soil layer (0.45 m) they invaded lower horizons and had a greater vertical distribution Ψ _leaf was not significantly affected by water regime (I₁– I₅) up to 94 DAS during a wet year (1983 – 1984) and up to 74 DAS during a dry year (1984 – 1985), but was significantly affected thereafter. Grain yields with water regimens I₁– I₅ during a wet year and for the I₂– I₅ treatments during a dry year at either water table depth were not significantly different, but there was a (non-significant) trend to lower yield with increasing soil water deficit. Under SWT in I₂, the average grain yield wsa 5130 kg ha^–1 and under the I₃ regime, 5200 kg ha^–1. Likewise, under MWT in I₃, it was 5188 kg ha^–1 and under the I₄ regime, 5218 kg ha^–1. The results indicate that application of irrigation of more than 120 and 180 mm under SWT and MWT conditions, respectively, did not raise yield. Irrigation given as per schedule I₂ under SWT and I₃ under MWT conditions in the Tarai situation, appears to be more effective than a very wet regime (I₅). Received: 9 December 1997     

An improved water use efficiency of cereals under temporal and spatial deficit irrigation in north China

Water shortage is the major bottleneck that limits sustainable development of agriculture in north China. Crop physiological water-saving irrigation methods such as temporal (regulated deficit irrigation) and spatial (partial root zone irrigation) deficit irrigation have been tested with much improved crop water use efficiency (WUE) without significant yield reduction. Field experiments were conducted to investigate the effect of (1) spatial deficit irrigation on spring maize in arid Inland River Basin of northwest China during 1997–2000; (2) temporal deficit irrigation on winter wheat in semi-arid Haihe River Basin during 2003–2007 and (3) temporal deficit irrigation on winter wheat and summer maize in Yellow River Basin during 2006–2007. Results showed that alternate furrow irrigation (AFI) maintained similar photosynthetic rate (P_n) but reduced transpiration rate (T_r), and thus increased leaf WUE of maize. It also showed that the improved WUE might only be gained for AFI under less water amount per irrigation. The feasible irrigation cycle is 7d in the extremely arid condition in Inner River Basin of northwest China and less water amount with more irrigation frequency is better for both grain yield and WUE in semi-arid Haihe River Basin of north China. Field experiment in Yellow River Basin of north China also suggests that mild water deficit at early seedling stage is beneficial for grain yield and WUE of summer maize, and the deficit timing and severity should be modulated according to the drought tolerance of different crop varieties. The economical evapotranspiration for winter wheat in Haihe River Basin, summer maize in Yellow River Basin of north China and spring maize in Inland River Basin of northwest China are 420.0 mm, 432.5 mm and 450.0 mm respectively. Our study in the three regions in recent decade also showed that AFI should be a useful water-saving irrigation method for wide-spaced cereals in arid region, but mild water deficit in earlier stage might be a practical irrigation strategy for close-planting cereals. Application of such temporal and spatial deficit irrigation in field-grown crops has greater potential in saving water, maintaining economic yield and improving WUE.     

Comparison of flooded and furrow-irrigated rice on clay

In some situations, potential water savings or relatively steep slopes make furrow irrigation a useful management practice for rice (Oryza sativa L.). Furrow-irrigated and flooded rice were compared in a field study conducted during three growing seasons: 1990, 1991, and 1992, at the University of Arkansas Northeast Research and Extension Center, Keiser, Ark., USA on a Sharkey silty clay soil. Excessive levee seepage greatly affected the water-use data for flooded rice production; however, there appeared to be potential for water savings on the Sharkey soil with furrow irrigation. Yields for flooded production consistently exceeded those for furrow-irrigated, with 3-year averages of 7.04, 6.02, and 5.88 Mg ha^-1 for flooded and two furrow-irrigated treatments, respectively. The yield difference appeared due to greater individual grain weight for the flooded treatment. Attempts to compensate for the yield reduction through additional nitrogen applications were unsuccessful. These results are consistent with findings of reduced rice grain yield associated with sprinkler irrigation. Furrow irrigation at an estimated 19 mm soil water deficit had a 3-year average of 11 kg ha^-1 of rice produced per mm of irrigation water applied.     

Impact of fertilisation practices on nitrogen leaching under irrigation

Field experiments were carried out over a 2-year period on a loamy soil plot under corn in Montpellier (south-east France). The effectiveness of improved irrigation practices in reducing the adverse impact of irrigation on the environment was assessed. Different irrigation and fertiliser treatments were applied to identify the best irrigation and fertilisation strategy for each technique (furrow and sprinkler) to ensure both good yields and lower NO₃^- leaching. No significant differences in corn yield and NO₃^- leaching were found for the climatic scenario of 1999 between sprinkler and furrow irrigation during the irrigation season. Following the rainy events occurring after plant maturity (and the irrigation season), differences in N leaching were observed between the treatments. The study shows that both the fertiliser method, consisting of applying a fertiliser just before ridging the furrows, and the two-dimensional (2D) infiltration process, greatly influence the N distribution in the soil. N distribution seems to have a beneficial impact on both yield and N leaching under heavy irrigation rates during the cropping season. But, under rainy events (particularly those occurring after harvesting), the N, stored in the upper part of the ridge and not previously taken up by plants, can be released into the deeper soil layers in a furrow-irrigated plot. In contrast, the 1D infiltration process occurring during sprinkler irrigation events affects the entire soil surface in the same way. As a result the same irrigation rate would probably increase N leaching under sprinkler irrigation to a greater extent than under furrow-irrigation during an irrigation period. In order to assess the robustness of these interpretations derived from soil N-profile analysis, a modelling approach was used to test the irrigation and fertilisation strategies under heavy irrigation rates such as those occurring at the downstream part of closed-end furrows. The RAIEOPT and STICS models were used to simulate water application depths, crop yield and NO₃^- leaching on three measurement sites located along the central furrow of each treatment. The use of a 2D water- and solute-transport model such as HYDRUS-2D enabled us to strengthen the conclusions derived from the observations made on the N distribution under a cross-section of furrow. This model helped to illustrate the risk of over-estimation of N leaching when using a simplified 1D solute-transport model such as STICS.     

Irrigation strategies to improve the water use efficiency of wheat-maize double cropping systems in North China Plain

Water is the most important limiting factor of wheat (Triticum aestivum L.) and maize (Zea mays L.) double cropping systems in the North China Plain (NCP). A two-year experiment with four irrigation levels based on crop growth stages was used to calibrate and validate RZWQM2, a hybrid model that combines the Root Zone Water Quality Model (RZWQM) and DSSAT4.0. The calibrated model was then used to investigate various irrigation strategies for high yield and water use efficiency (WUE) using weather data from 1961 to 1999. The model simulated soil moisture, crop yield, above-ground biomass and WUE in responses to irrigation schedules well, with root mean square errors (RMSEs) of 0.029 cm³ cm⁻³, 0.59 Mg ha⁻¹, 2.05 Mg ha⁻¹, and 0.19 kg m⁻³, respectively, for wheat; and 0.027 cm³ cm⁻³, 0.71 Mg ha⁻¹, 1.51 Mg ha⁻¹ and 0.35 kg m⁻³, respectively, for maize. WUE increased with the amount of irrigation applied during the dry growing season of 2001-2002, but was less sensitive to irrigation during the wet season of 2002-2003. Long-term simulation using weather data from 1961 to 1999 showed that initial soil water at planting was adequate (at 82% of crop available water) for wheat establishment due to the high rainfall during the previous maize season. Preseason irrigation for wheat commonly practiced by local farmers should be postponed to the most sensitive growth stage (stem extension) for higher yield and WUE in the area. Preseason irrigation for maize is needed in 40% of the years. With limited irrigation available (100, 150, 200, or 250 mm per year), 80% of the water allocated to the critical wheat growth stages and 20% applied at maize planting achieved the highest WUE and the least water drainage overall for the two crops.     

不同灌溉模式对黄淮海平原区夏玉米生产性状及水分利用率的影响

为了探明黄淮海平原区不同灌溉模式对夏玉米生产性状和水分利用效率的影响,2018-2019连续2年设置覆膜浅埋滴灌(T4)、浅埋滴灌(T3)、覆膜滴灌(T2)、地表滴灌(T1)和传统畦灌(CK)等5种灌溉方式实施大田对比试验,测定了玉米株高、叶面积指数(LAI)、地上部干物质累积量、产量及产量构成因素以及水分利用效率(W...     

Water use of young Thompson Seedless grapevines in California

Water use of Thompson Seedless grapevines during the first 3 years of vineyard establishment was measured with a large weighing lysimeter near Fresno, California. Two grapevines were planted in a 2ǸǶ m deep lysimeter in 1987. The row and vine spacings in the 1.4-ha vineyard surrounding the lysimeter were approximately 3.51 and 2.15 m, respectively. Vines in the lysimeter were furrow-irrigated from planting until the first week of September in 1987. They were subsequently irrigated with subsurface drip-irrigation whenever they had used 2 mm of water, based upon the area of the lysimeter (equivalent to 8 liters per vine). The trellis system, installed the second year, consisted of a 2.13 m long stake, driven 0.45 m into the soil with a 0.6 m cross-arm placed at the top of the stake. Crop coefficients (K_c) were calculated using measured water losses from the lysimeter (ET_c) and reference crop evapotranspiration (ET_o) obtained from a CIMIS weather station located 2 km from the vineyard. Water use of the vines in 1987 from planting until September was approximately 300 mm, based on the area allotted per vine in the vineyard surrounding the lysimeter. Daily water use just subsequent to a furrow-irrigation event exceeded ET_o (>6.8 mm day^у). Water use from budbreak until the end of October in 1988 and 1989 was 406 and 584 mm, respectively. The initiation of subsurface drip-irrigation on 23 May 1988 and 29 April 1989 doubled ET_c measured prior to those dates. Estimates of a 'basal' K_c increased from 0.1 to 0.4 in 1987. The seasonal K_c in 1988 increased throughout the season and reached its peak (0.73) in October. The highest K_c value in 1989 occurred in July. It is suggested that the seasonal and year-to-year variation in the K_c was a result of the growth habit of the vines due to training during vineyard establishment. The results provide estimates of ET_c and K_c for use in scheduling irrigations during vineyard establishment in the San Joaquin Valley of California and elsewhere with similar environmental conditions.     

Plant indicators for scheduling irrigation of young olive trees

The sensitivity of several water status indicators was determined in irrigated young olive trees subjected to two drought periods at Cordoba, Spain. Trunk diameter fluctuations (TDF) were monitored continuously and stem water potential (N), leaf photosynthesis (P_n) and conductance (g_l) were measured periodically on trees where irrigation was interrupted or which were fully irrigated. During the first period of water deprivation in late spring, only some of the TDF-derived parameters were able to detect significant differences caused by water deficits, while there were no differences in stem N, P_n and g_l. All water stress indicators responded during the second drought period in midsummer. However, differences in maximum trunk diameter were detected several days before significant stem N differences of about 0.2 MPa were established between treatments. Stem N differences declined further to 0.6 MPa before differences in leaf P_n and g_l became significant. Of all TDF-derived indices, trunk growth rate was the most sensitive to water deficits while treatment differences in maximum daily shrinkage were insignificant in the young trees. It is concluded that continuous monitoring of trunk diameter provides the most sensitive indicator for accurate, automated irrigation scheduling of young olive trees under intensive production.     

Macromanagement of deficit-irrigated peanut with sprinkler irrigation

Precision irrigation management and scheduling, as well as developing site- and cultivar-specific crop coefficient (K_c), and yield response factor to water deficit (ky) are very important parameters for efficient use of limited water resources. This study investigated the effect of deficit irrigation, applied at different growth stages of peanut with sprinkler irrigation in sandy soil, on field peanut evapotranspiration (ETc), yield and yield components, and water use efficiencies (IWUE and WUE). Also, yield response factor to water deficit (ky), and site- and cultivar-specific K_c were developed. Four treatments were imposed to deficit irrigation during late vegetative and early flowering, late flowering and early pegging, pegging, and pod formation growth stages of peanut, and compared with full irrigation in the course of the season (control). A soil water balance equation was used to estimate crop evapotranspiration (ETc). The results revealed that maximum seasonal ETc was 488 mm recorded with full irrigation treatment. The maximum value of K_c (0.96) occurred at the fifth week after sowing, this value was less than the generic values listed in FAO-33 and -56 (1.03 and 1.15), respectively. Dry kernels yield among treatments differed by 41.4%. Deficit irrigation significantly affected yields, where kernels yield decreased by 28, 39, 36, and 41% in deficit-irrigated late vegetative and early flowering, late flowering and early pegging, pegging, and pod formation growth stages, respectively, compared with full irrigation treatment. Peanut yields increased linearly with seasonal ETc (R² = 0.94) and ETc/ETp (R² = 0.92) (ETp = ETc with no water stress). The yield response factor (ky), which indicates the relative reduction in yield to relative reduction in ETc, averaged 2.9, was higher than the 0.7 value reported by Doorenbos and Kassam [Doorenbos, J., Kassam, A.H., 1979. Yield response to water. FAO Irrigation and Drainage Paper 33, Rome, Italy, 193 pp.], the high ky value reflects the great sensitivity of peanut (cv. Giza 5) to water deficit. WUE values varied considerably with deficit irrigation treatments, averaging 6.1 and 4.5 kg ha⁻¹ mm⁻¹ (dry-mass basis) for pods and kernels, respectively. Differences in WUE between the driest and wettest treatment were 31.3 and 31.3% for pods and kernels, respectively. Deficit irrigation treatments, however, impacted IWUE much more than WUE. Differences in IWUE between the driest and wettest treatment were 33.9 and 33.9% for pods and kernels, respectively. The results revealed that better management of available soil water in the root zone in the course of the season, as well as daily and seasonal accurate estimation of ETc can be an effective way for best irrigation scheduling and water allocation, maximizing yield, and optimizing economic return.     

Different irrigation methods and water stress effects on potato yield and yield components

This research was conducted during the spring seasons of 2000 and 2002 in Hatay province located in the East Mediterranean Region of Turkey. The research investigated the effects of two drip irrigation methods and four different water stress levels on potato yield and yield components. The surface drip (SD) and subsurface drip (SSD) irrigation methods were used. The levels were full irrigation (I₁₀₀), 66% of full irrigation (I₆₆), 33% of full irrigation (I₃₃) and un-irrigated (I₀) treatments. Five and three irrigation were applied in 2000 and 2002 early potato growing seasons, respectively. Total irrigation amount changed from 102 to 302 mm and from 88 to 268 mm in 2000 and 2002, respectively. Seasonal evapotranspiration changed between 226 and 473 mm and 166 and 391 mm in 2000 and 2002, respectively. SD and SSD irrigation methods did not result in a significant difference on yield. However, SD method has more advantages than SSD method, which has difficulties in replacement and higher system cost. Irrigation levels resulted in significant difference in both years on yield and its components. Water stress significantly affected the yield and yield parameters of early potato production. Water deficiency more than 33% of the irrigation requirement could not be suggested.Water use efficiency (WUE) of SD irrigation methods had generally higher values than SSD irrigation methods. Treatment I₃₃ gave maximum irrigation water use efficiency (IWUE) for both years. SSD irrigation method did not provide significant advantage on yield and WUE, compared to SD irrigation in early potato production under experimental conditions. Therefore, the SD irrigation method would be recommended in early potato production under Mediterranean conditions.     

Varying irrigation rates effect on yield and yield components of chickpea

This study was conducted to determine the effect of different supplemental irrigation rates on chickpea grown under semiarid climatic conditions. Chickpea plots were irrigated with drip irrigation system and irrigation rates included the applications of 0 (I ₀) 25 (I ₂₅), 50 (I ₅₀), 75 (I ₇₅), 100 (I ₁₀₀), and 125 % (I ₁₂₅) of gravimetrically measured soil water deficit. Plant height, 1,000 seed weight, yield, biomass, and harvest index (HI) parameters were determined in addition to yield-water functions, evapotranspiration (ET), water use efficiency (WUE), and irrigation water use efficiency (IWUE). Significant differences were noted for plant height (ranging from 24.0 to 37.5 cm), 1,000 seed weight (ranging from 192.0 to 428.7 g), and aboveground biomass (ranging from 2,722 to 6,083 kg ha^?1) for water applications of I ₀ and I ₁₂₅. Statistical analysis indicated a strong relationship between the amount of irrigation and yield, which ranged from 256.5 to 1,957.3 kg ha^?1. Harvest index values ranged between 0.092 and 0.325, while WUE and IWUE values ranged between 1.15–4.55 and 1.34–8.36 (kg ha^?1 mm^?1), respectively.     

不同灌溉方式对制种玉米产量及水分利用效率的影响

通过田间试验,研究了畦灌、常规沟灌、隔沟交替灌3种灌溉方式对制种玉米产量及水分利用效率的影响,结果表明,不同灌溉方式下,制种玉米产量为8.73~10.87 t/hm~2,耗水量为349.7~625.0 mm,WUE为1.40~3.01kg/m~3。隔沟交替灌溉方式耗水量最低,畦灌方式最高,常规沟灌居中。相同灌溉定额条件下,隔沟交替灌制种玉米产量较常规沟灌增减幅度在-2.43%~10.24%。常规沟灌方式若能保证作物需水关键期的灌溉,适度减少灌水不会造成制种玉米减产。产量构成要素结果表明,行粒数、出籽率、穗长、穗粗、秃尖长、千粒重产量构成要素对产量的累积贡献率达85.54%。在甘肃河西地区,制种玉米全生育期灌水8次(苗期1次,拔节期2次,抽穗期1次,灌浆期2次,乳熟期2次),灌溉定额2 250 m~3/hm~2的隔沟交替灌溉方式(T6处理)能稳定提高产量和水分利用效率。