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.     

Water and nitrate movement in drip-irrigated onion under fertigation and irrigation treatments

Frequent fertigation of crops is often advocated in the technical and popular literature, but there is limited evidence of the benefits of high-frequency fertigation. Field experiments were conducted on an Indo-American Hybrid var., Creole Red, of onion crop during three winter seasons of 1999–2000 through 2001–2002 in coarse-textured soil of Delhi under the semi-arid region of India. Three irrigation levels of 60, 80 and 100% of the crop evapotranspiration (ET) and four fertigation frequencies of daily, alternate day, weekly and monthly comprised the fertigation treatment. Analysis of soil samples indicated considerable influence of fertigation frequency on NO₃-N distribution in soil profile. NO₃-N in lower soil profiles (30.0–60.0 cm soil depth) was marginally affected in daily, alternate day and weekly fertigation. However, fluctuations of NO₃-N content in 0.0–15.0, 15.0–30.0, 30.0–45.0 and 45.0–60.0 cm soil depth was more in monthly fertigation frequency. The level of soil NO₃-N after the crop season shows that more NO₃-N leached through the soil profile in monthly fertigation frequency. Amounts of irrigation water applied in three irrigation treatments proved to be too small to cause significant differences in the content of NO₃-N leached beyond rooting depth of onion. Yield of onion was not significantly affected in daily, alternate day and weekly fertigation, though there was a trend of lower yields with monthly fertigation. The highest yield was recorded in daily fertigation (28.74 t ha⁻¹) followed by alternate day fertigation (28.4 t ha⁻¹). Lowest yield was recorded in monthly fertigation frequency (21.4 t ha⁻¹). Application of 56.4 cm irrigation water and 3.4 kg ha⁻¹ urea per fertigation (daily) resulted in highest yield of onion with less leaching of NO₃-N.     

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.     

Irrigation rate and plant density effects on yield and water use efficiency of drip-irrigated corn

The efficient use of water by modern irrigation systems is becoming increasingly important in arid and semi-arid regions with limited water resources. This study was conducted for 2 years (2005 and 2006) to establish optimal irrigation rates and plant population densities for corn (Zea mays L.) in sandy soils using drip irrigation system. The study aimed at achieving high yield and efficient irrigation water use (IWUE) simultaneously. A field experiment was conducted using a randomized complete block split plot design with three drip irrigation rates (I₁: 1.00, I₂: 0.80, and I₃: 0.60 of the estimated evapotranspiration), and three plant population densities (D₁: 48,000, D₂: 71,000 and D₃: 95,000 plants ha⁻¹) as the main plot and split plot, respectively. Irrigation water applied at I₁, I₂ and I₃ were 5955, 4762 and 3572 m³ ha⁻¹, respectively. A 3-day irrigation interval and three-way cross 310 hybrid corn were used. Results indicated that corn yield, yield components, and IWUE increased with increasing irrigation rates and decreasing plant population densities. Significant interaction effects between irrigation rate and plant population density were detected in both seasons for yield, selected yield components, and IWUE. The highest grain yield, yield components, and IWUE were found for I₁D₁, I₁D₂, or I₂D_1, while the lowest were found for I₃D₂ or I₃D₃. Thus, a high irrigation rate with low or medium plant population densities or a medium irrigation rate with a low plant population density are recommended for drip-irrigated corn in sandy soil. Crop production functions with respect to irrigation rates, determined for grain yield and different yield components, enable the results from this study to be extrapolated to similar agro-climatic conditions.     

Crop coefficients for drip-irrigated processing tomato

Drip irrigation of processing tomato is increasing in the San Joaquin Valley of California (USA), a major tomato production area. Efficient management of these irrigation systems requires reasonable estimates of crop evapotranspiration (ET_c) between irrigations. A common approach for estimating ET_c is to multiply a reference crop evapotranspiration (ET_o) by a crop coefficient. However, a review of literature revealed mid-season crop coefficients for processing tomato to range from 1.05 to 1.25. Because of this variability, uncertainty exists in the crop coefficients appropriate for drip irrigation in the San Joaquin Valley. Thus, a study was initiated to determine the ET_c of processing tomato for drip irrigation in commercial fields and then calculate crop coefficients from the ET_c and ET_o data for the west side of the San Joaquin Valley. Crop ET_c was determined at five locations using the Bowen Ratio Energy Balance Method (BREB). Canopy coverage was also measured using a digital infrared camera. Average crop coefficients ranged from about 0.19 at 10% canopy coverage to 1.08 for canopy coverage exceeding about 90%. A second order regression equation reasonably described a relationship between crop coefficient and canopy coverage. Generic curves describing crop coefficient versus time of year were developed for various planting times.     

Water use by an irrigated almond orchard

The evapotranspiration rate of a high-yielding (4.3 t/ha) almond orchard was measured by the eddy covariance technique. The site was subject to advection (LE/Rn > 1) for one-third of the mid-season. The slope of energy balance equation calculated from half-hourly flux data was 0.87. Flux data were transformed by forcing closure of the energy balance to give a seasonal ET of 1,450 mm (ETo 1,257 mm). This value could be reconciled with ancillary measures of soil salinity and water content, and plant water status. The mid-phase crop coefficient was 1.1 which was 0.1 higher than a recently published value. Use of the transformed value of ET in calculations of field application efficiency and annual drainage gives values of 98% and 24 mm, respectively.     

Characterisation of water use by Sultana grapevines (Vitis vinifera L.) on their own roots or on Ramsey rootstock drip-irrigated with water of different salinities

Seasonal evapotranspiration (ET) was determined for Sultana grapevines grown on their own roots (Own-rooted) or grafted onto Ramsey rootstock (Grafted), and irrigated with water of three salinity levels – low (0.4 dS m^–1), medium (1.8 dS m^–1) and high (3.6 dS m^–1) – during the 1994/1995 growing season in south-eastern Australia. Transpiration (T) was determined from sap flux, soil evaporation (E _s) with a model, and soil water (S) with a neutron probe. Total ET for the season was similar for both Own-rooted and Grafted, averaging 382 mm. However, Grafted partitioned a mean of 193.5 mm (50.8%) of the ET through T compared to 146.7 mm (38.4%) by Own-rooted. Daily rates of T were generally low and attained peaks of 1.2 mm (9.9 l per vine) for Grafted and 0.9 mm (7.5 l) for Own-rooted in late November, and changed very little until after harvest in February. In contrast to T, the E _s rate was consistently higher for Own-rooted than for Grafted from November onwards, and at the end of the season totalled 237 mm for Own-rooted compared to 187 mm for Grafted. Differences between Own-rooted and Grafted in their partitioning of ET into T and E _s were associated with their canopy development. Grafted had a higher rate of canopy development than Own-rooted, and in mid-season, the former intercepted about 50% more incident radiation than Own-rooted. The crop factors, i. e. ratio of water use to evaporative demand, based on ET were similar for both vine types with an average seasonal value of 0.25, but when based on T were 0.12 for Grafted and 0.10 for Own-rooted. The ratio of fresh fruit weight to total water used at harvest, i. e. crop water use efficiency (CWUE), based on ET, had a mean of 86 kg mm^–1 ha^–1 for Grafted and 43 kg mm^–1 ha^–1 for Own-rooted, and when based on T, was 165 and 115 kg mm^–1 ha^–1, respectively; however, supplementary data obtained during the 1993/1994 season, indicated a CWUE based on T of 294 and 266 kg mm^–1 ha^–1 for Grafted and Own-rooted, respectively. Salinity did not have significant effects on canopy development and water use for most of the 1994/1995 growing season. The study shows ET and crop factors for the drip-irrigated grapevines to be much lower than previously reported for this district. Received: 6 May 1996     

Crop coefficient for drip-irrigated cotton in a Mediterranean environment

A 3-year study was conducted in the eastern Mediterranean region of northern Syria to develop crop coefficient, K _c, for drip-irrigated short-season cotton (Gossypium hirsutum L.). Two sets of K _c curves were determined, the generalized K _c published by the UN’s Food and Agriculture Organization (FAO) that was adjusted for local climate, and the locally developed K _c as the ratio of measured cotton evapotranspiration to calculated reference evapotranspiration. The adjusted FAO K _c curves were the same for the 3 years. However, the locally developed K _c curves not only differed among the 3 years, but also from the adjusted FAO K _c. During the mid-season stage, the adjusted FAO K _c was 24% higher than the locally developed value of 1.05. Variations in locally developed K _c values were caused by normal year-to-year variations in irrigation timing and amount, suggesting sensitivity of K _c that cautions against the use of locally developed K _c based on limited data (i.e., a single season). On the season, the overestimation of crop evapotranspiration by using adjusted FAO K _c was substantial and equivalent to 150 mm water or about two additional irrigations per season. Results caution against blind application of published FAO K _c curve, suggesting some local or regional calibration for increased accuracy.     

Interaction between water and nitrogen management in peaches for processing

A three-year field experiment (2006–2008) on clingstone peach cv. Andross was conducted in a commercial orchard under mechanical harvesting for the processing industry. Three irrigation strategies were evaluated: full irrigation throughout the growing season; restricted irrigation during stage-II (~70% restriction) and restricted irrigation during stage-III (~30% restriction), combined with three nitrogen fertilization treatments: 0, 60 and 120 kg N/ha. Trees were fertigated on a daily basis. Daily patterns of soil moisture were monitored with capacitance probes. Irrigation restriction strategies and nitrogen dose affected yield and fruit quality at commercial harvest. As well as the individual effects of applying irrigation strategies and N doses, interactions between the two factors were analyzed. In the second year, there was a nitrogen × irrigation interaction for fruit yield. A positive yield effect for N applied to fully irrigated trees occured, while the opposite was observed when the irrigation restrictions were applied during stage-III.     

Water use by alfalfa,maize, and barley as influenced by available soil water

The availability of soil water is one of the most important determinants of crop production. Field studies were conducted to examine the relationships between relative evapotranspiration ($\text{E}\text{E}{}_{\mathrm{<mtext>max</mtext>}}$) and available water (W) for alfalfa, maize, and barley. Line source sprinkler irrigation systems were used to provide the variations in soil moisture. Actual evapotranspiration (E) was determined using the water balance method. Maximum evapotranspiration (E_max) was the highest E observed among all irrigation levels. Potential evapotranspiration (E₀) was estimated using Penman's equation to characterize the evaporative demand.The results show that the relationships between $\text{E}\text{E}{}_{\mathrm{<mtext>max</mtext>}}$ and W were different for the three crops. For alfalfa, the relationship was dependent on the physical properties of the soil and on E₀. In a clay loam soil, the decline in E from E_max commenced at a higher value of W than in a sandy loam soil. Furthermore, the rate of decline in E from E_max was dependent on E₀ and was greater as E₀ increased. In the sandy loam soil, the relationship between $\text{E}\text{E}{}_{\mathrm{<mtext>max</mtext>}}$ and W was not dependent on E₀. For maize and barley in clay loam soils, $\text{E}\text{E}{}_{\mathrm{<mtext>max</mtext>}}$ as a function of W was linear, and was not dependent on E₀. This study was compared to results reported in the literature, and it was hypothesized that differences were related mainly to the way variation in soil moisture was introduced over the measurement period.     

调亏灌溉对大棚滴灌甜瓜生长发育的影响

在大棚滴灌条件下对厚皮甜瓜伊丽莎白不同生育期进行不同程度的亏缺灌溉,研究调亏灌溉对其植株生长、产量、品质及水分利用效率的影响.以土壤相对含水量为标准,在营养生长期和生殖生长期分别设置不同的土壤水分灌溉下限处理,分别是T1(75%~75%),T2(75%~55%),T3(65%~65%),T4(55%~75%),T5(55%~55%)5个试验处理.结果表明:在营养生长期,随着水分亏缺程度的加大,株高、茎粗、叶面积均呈减小趋势.在果实发育阶段,营养生长期及生殖生长期的水分亏缺对果实的生长、产量都有影响,均随亏缺程度的加大而降低,产量以处理T1和T2的最高,T5的最低,T3的大于T4的,各处理间差异具有统计学意义.水分利用效率为处理T2的最高,T1和T4的较低,T2与T4相比,在灌水基本相同的条件下,产量增加了26.2%,水分利用效率提高了27.7%.品质方面,水分亏缺提高了TSS含量;在营养生长期充分灌溉、生殖生长期亏水灌溉可以提高可溶性蛋白、游离氨基酸、维生素C的含量;而营养生长期亏水灌溉、生殖生长期充分灌溉有利于可滴定酸的合成.经综合分析,认为处理T2的灌溉下限设置可以作为武汉地区大棚滴灌条件下的甜瓜灌溉制度.     

Effect of full and limited irrigation amount and frequency on subsurface drip-irrigated maize evapotranspiration,yield, water use efficiency and yield response factors

The objectives of this study were to: (1) to evaluate the effects of subsurface drip irrigation amount and frequency on maize production and water use efficiency, (2) develop production functions and quantify water use efficiency, and (3) develop and analyze crop yield response factors (Ky) for field maize (Zea mays L.). Five irrigation treatments were imposed: fully irrigated treatment (FIT), 25 % FIT, 50 % FIT, 75 % FIT, rainfed and an over-irrigation treatment (125 % FIT). There was no significant (P > 0.05) difference between irrigation frequencies regarding the maximum grain yield; however, at lower deficit irrigation regime, medium irrigation frequency resulted in lower grain yield. There was a decrease in grain yield with the 125 % FIT as compared to the FIT, which had statistically similar yield as 75 % FIT. Irrigation rate significantly impacted grain yield in 2005, 2006 and 2007, while irrigation frequency was only significant during the 2005 and 2006 growing seasons (two dry years) and the interacting effect was only significant in the driest year of 2005 (P = 0.006). For the pooled data from 2005 to 2008, irrigation rate was significant (P = 0.001) and irrigation frequency was also significant (P = 0.015), but their interaction was not significant (P = 0.207). Overall, there were no significant differences between irrigation frequencies in terms of grain yield. Ky had interannual variation and average seasonal Ky values were 1.65, 0.91, 0.91 and 0.83 in 2005, 2006, 2007 and 2008, respectively, and the pooled data (2005–2008) Ky value were 1.14.     

Water use assessment in muskmelon by the Penman-Monteith “one-step” approach

The use of the “one-step” approach of Penman-Monteith (P-M) to assess crop water use has its limit in the lack of user friendly methodologies for a daily assessment of crop canopy resistance, r_c. The model proposed by Monteith [Monteith, J.L., 1965. Evaporation and environment. In: Fogg, G.E. (Ed.), The State and Movement of Water in Living Organism. Soc. Exp. Biol. Symp. 19, 205-234] to estimate r_c (r_c = 100/LAI), although it is simple, requires the knowledge of LAI value during growing cycle. This work aims to propose an easy-to-use methodology for irrigation scheduling, to assess the values LAI gets during the growing cycle and thus for canopy resistance assessment. In muskmelon crop, grown with and without plastic film mulching, canopy resistance was measured by P-M formula inversion, clarifying the unknown resistivity term, being crop evapotranspiration known by lysimeter-based measurements. Measured canopy resistance was compared with the one estimated by Monteith model (1965), both in its original version and in the form we simplified in terms of LAI value during crop cycle. Thus, we compared the evapotranspiration assessed by the “one-step” use of P-M equation, with those estimated by the classical “two-step” approach, using crop coefficients, and with that directly measured by lysimeters. In particular in the mulched crop the “one-step” approach of P-M overestimates water use only by 4%, while the “two steps” approach underestimates water use by 17%.Despite both the methodologies proposed for LAI calculation and the Monteith model to assess canopy resistance extremely simplify more complex processes, they were able to give a good accuracy to assess muskmelon water use by the P-M “one-step” equation. Comparing the “one-step” and the more used “two-step” approaches it came out that, despite the latter is better correlated to the data measured by a lysimeter, it does not achieve a more accurate assessment compared to the “one-step” approach; in particular, in the mulched crop, the “two-step” approach significantly underestimates water use, while its estimation is reliable with the “one-step” approach.     

河西地区滴灌春玉米对不同灌溉决策方法的响应

基于3种灌溉决策方法(土壤水分、蒸散量、土水势),设置10个灌溉处理(CK,W₁,W₂,E_P100,E_P80,E_F100,E_F80,P₂₅,P₄₅,P₆₅),研究不同灌溉决策方法对河西地区春玉米生长、产量及水分利用效率WUE的影响.结果表明:基于土壤水分、蒸散量、土水势调控灌溉下产量最高的处理分别为CK,E_P100和P₂₅;处理CK的产量比E_P100和P₂₅分别增大6.90%和8.28%.CK的春玉米生长和干物质积累最优,但是耗水量最大,为718.54 mm,比E_P100增大26.13%和11.57%.处理E_P100的产量显著低于CK,但WUE显著高于CK.处理P₂₅较CK和E _P100灌水次数多,产量和水分利用效率表现均不突出.处理E_P80和E_P100的产量和WUE差异不具有统计学意义.综合考虑产量、水分利用效率和灌溉决策方法的适用性,基于过去蒸散量调控灌溉,每周灌水定额为80%ET₀(E_P80)是最适合河西地区春玉米高效稳产的灌溉决策方法.     

Water use efficiency of narrow row cotton

Summary A field experiment was conducted on the west side of the San Joaquin Valley in California to determine water use, crop growth, yield and water use efficiency of Acala (SJ-2) cotton (Gossypium hirsutum L.) grown in 0.5 m spaced rows on a Panoche clay loam soil (Typic Torriorthents). Evapotranspiration was determined by water balance techniques utilizing neutron soil moisture measurements. All neutron measurements were made within a 3 m soil profile in 0.20 m increments. The measured evapotranspiration was compared to climatic estimates of potential evapotranspiration, and to calculations using a one-dimensional soil water balance model that separately computed soil water evaporation and plant transpiration. Crop growth was determined by weekly destructive plant sampling. Leaf area was determined along with dry matter components of leaves, stems, fruiting parts (flowers and squares) and bolls. Final yield was determined by machine harvesting (brush stripper) 720 m² from each plot. Lint yields and fiber quality were determined by sample ginning and fiber analysis at the U.S. Cotton Research Station at Shafter, California. Three irrigation regimes were established that resulted in an evapotranspiration range from a high deficit condition to full irrigation at the calculated atmospheric demand.The measured evapotranspiration of narrow row cotton under a full irrigation regime was 778 mm, 594 mm under a limited irrigation regime and 441 mm under a regime with no post-plant irrigation. The evapotranspiration from these irrigation treatments was accurately simulated by a water balance model. that used inputs of potential evapotranspiration, leaf area index, soil water holding capacity and root development.The average lint yield from narrow row cotton with a full irrigation regime was 1583 kg/ha, the average lint yield from a limited irrigation regime was 1423 kg/ha and the average lint yield from a treatment with no postplant irrigation (fully recharged soil profile at planting) was 601 kg/ha. The full irrigation regime resulted in a dry matter production of approximately 16 t/ha while the limited irrigated regime produce 11 t/ha and the no-postplant irrigation regime produced 7 t/ha of dry matter. The fiber quality results indicated significant (0.05 level) differences only in 50% span length and micronaire, with the 2.5% span length, uniformity index, elongation and strength indicating no difference.Cotton lint yield was found to be directly related to total evapotranspiration although the relationship was slightly non-linear while dry matter yield was found to be linearly related to evapotranspiration. Both lint and dry matter yield were found to have a linear relationship to estimated transpiration from the water balance model calculations.Contribution from the Unived States Department of Agriculture, Agricultural Research Service, Western Region and the University of California     

Modeling soil water dynamics in a drip-irrigated intercropping field under plastic mulch

Intercropping, drip irrigation, and the use of plastic mulch are important management practices, which can, when utilized simultaneously, increase crop production and save irrigation water. Investigating soil water dynamics in the root zone of the intercropping field under such conditions is essential in order to understand the combined effects of these practices and to promote their wider use. However, not much work has been done to investigate soil water dynamics in the root zone of drip-irrigated, strip intercropping fields under plastic mulch. Three field experiments with different irrigation treatments (high T1, moderate T2, and low T3) were conducted to evaluate soil water contents (SWC) at different locations, for different irrigation treatments, and with respect to dripper lines and plants (corn and tomatoes). Experimental data were then used to calibrate the HYDRUS (2D/3D) model. Comparison between experimental data and model simulations showed that HYDRUS (2D/3D) described different irrigation events and SWC in the root zone well, with average relative errors of 10.8, 9.5, and 11.6 % for irrigation treatments T1, T2, and T3, respectively, and with corresponding root mean square errors of 0.043, 0.035, and 0.040 cm³ cm^?3, respectively. The results showed that the SWC in the shallow root zone (0–40 cm) was lower under non-mulched locations than under mulched locations, irrespective of the irrigation treatment, while no significant differences in the SWC were observed in the deeper root zone (40–100 cm). The SWC in the shallow root zone was significantly higher for the high irrigation treatment (T1) than for the low irrigation treatment, while, again, no differences were observed in the deeper root zone. Simulations of two-dimensional SWC distributions revealed that the low irrigation treatment (T3) produced serious severe water stress (with SWCs near the wilting point) in the 30–40 cm part of the root zone, and that using separate drip emitter lines for each crop is well suited for producing the optimal soil water distribution pattern in the root zone of the intercropping field. The results of this study can be very useful in designing an optimal irrigation plan for intercropped fields.     

The effect of drip line placement on yield and quality of drip-irrigated processing tomatoes

Subsurface drip irrigation of processing tomatoes is increasing in California. The common design approach is to bury drip lines 0.2–0.36 m deep in the middle of the plant row, which places drip lines directly beneath plant rows. This design limits the use of the drip irrigation system to only those crops compatible with this drip line and bed spacing, and thus, other design approaches are being investigated to increase the flexibility of the drip systems. These approaches are installing drip lines in alternate furrows and installing drip lines in every furrow, both of which place drip lines midway between plant rows. The furrows are the result of the cultural practices used to form beds for planting.This study investigated the effect of the different drip line placements on crop yield and quality. Results showed that the highest yields occurred for the buried placement and the smallest yields for the alternate furrow placement. For the buried placement, soil water content and root density were concentrated around the drip lines, directly beneath the plant rows, while for the furrow placements, zones of high soil water content and root density did not coincide with the plant rows. However, some growers have found the furrow placement to reduce some of the disease problems normally experienced with the traditional furrow irrigation methods.     

Estimation of actual evapotranspiration for a drip-irrigated Merlot vineyard using a three-source model

A study was performed in order to evaluate the three-source model (Clumped model) for direct estimation of actual evapotranspiration (ET_a) and latent heat flux (LE) over a drip-irrigated Merlot vineyard trained on a vertical shoot positioned system (VSP) under semi-arid conditions. The vineyard, with an average fractional cover of 30%, is located in the Talca Valley, Region del Maule, Chile. The performance of the Clumped model was evaluated using an eddy covariance system during the 2006/2007 and 2007/2008 growing seasons. Results indicate that the Clumped model was able to predict ET_a with a root mean square error (RMSE), mean bias error (MBE), and model efficiency (EF) of 0.33, −0.15 mm day⁻¹ and 74%, respectively. Also, the Clumped model simulated the daytime variation of LE with a RMSE of 36 W m⁻², MBE of −8 W m⁻², and EF of 83%. Major disagreement (underestimated values) between observed and estimated values of ET_a was found for clear days after rainfall or foggy days, but underestimated values were less than 10% of the data analysis. The results obtained in this study indicate that the Clumped model could be used to directly estimate vine water requirements for a drip-irrigated vineyard trained on a VSP. However, application of the Clumped model requires a good characterization of the drip-irrigated vineyard architecture.     

Crop coefficients and actual evapotranspiration of a drip-irrigated Merlot vineyard using multispectral satellite images

A field experiment was carried out to evaluate the METRIC (mapping evapotranspiration at high resolution with internalized calibration) model to estimate the actual evapotranspiration (ET_a) and crop coefficient (K _c) of a drip-irrigated Merlot vineyard during the 2007/2008 and 2008/2009 growing seasons. The Merlot vineyard located in the Talca Valley (Chile) was trained on a vertical shoot positioned system. The performance of METRIC was evaluated using measurements of ET_a and K _c from an eddy covariance (EC) system. METRIC overestimated ET_a by about 9?% with a root mean square error (RMSE) and mean absolute error (MAE) of 0.62 and 0.50?mm?d^?1, respectively. For the main phenological stages of the Merlot vineyard, METRIC overestimated the K _c by about 10?% with RMSE?=?0.10 and MAE?=?0.08. Furthermore, the indexes of agreement were 0.70 for K _c and 0.85 for ET_a. Mean values of K _c measured from EC were 0.41, 0.53, 0.56, and 0.46, while those estimated by METRIC were 0.46, 0.54, 0.59, and 0.62 for the bud break to flowering, flowering to fruit set, fruit set to veraison, and veraison to harvest stages, respectively.