Evaluation of grapevine water status from trunk diameter variations

We evaluated the usefulness of short-term trunk diameter variations (TDV) as water stress indicator in field-grown grapevines cv. Tempranillo. Two indices were calculated from TDV, maximum daily trunk shrinkage (MDS), and trunk growth rate (TGR). The seasonal evolution of both indicators was compared with occasional determinations of pre-dawn leaf water potential and stem water potential, measured at early morning (Ψ_s^em) and at midday (Ψ_s^md) in irrigated and non-irrigated vines. In the second season, the effect of crop load on the vine water status indicators was also studied. Crop load did not affect either the vine water relations or the TDV. All water potential determinations had much lower variability and were more sensitive than both MDS and TGR to water restrictions. The ability of both indices to detect plant water stress varied largely depending upon the phenological period. In fact, MDS and TGR were only able to detect vine water stress during a short period of time before veraison. During this period, TGR was linearly related to both Ψ_s^em and Ψ_s^md, while for MDS a curvilinear, quadratic equation, better described the relationship with plant water status. After veraison no apparent relationship existed between plant water status and MDS or TGR. Hence, our results question the practical use of both MDS and TGR as variables to automate irrigation scheduling for grapevine.     

A method for spatial prediction of daily soil water status for precise irrigation scheduling

Available water holding capacity (AWC) and field capacity (FC) maps have been produced using regression models of high resolution apparent electrical conductivity (EC_a) data against AWC (adj. R² = 0.76) and FC (adj. R² = 0.77). A daily time step has been added to field capacity maps to spatially predict soil water status on any day using data obtained from a wireless soil moisture sensing network which transmitted hourly logged data from embedded time domain transmission (TDT) sensors in EC_a-defined management zones. In addition, regular time domain reflectometry (TDR) monitoring of 50 positions in the study area was used to assess spatial variability within each zone and overall temporal stability of soil moisture patterns. Spatial variability of soil moisture within each zone at any one time was significant (coefficient of variation [% CV] of volumetric soil moisture content (θ) = 3-16%), while temporal stability of this pattern was moderate to strong (bivariate correlation, R = 0.52-0.95), suggesting an intrinsic soil and topographic control. Therefore, predictive ability of this method for spatial characterisation of soil water status, at this site, was limited by the ability of the sensor network to account for the spatial variability of the soil moisture pattern within each zone. Significant variability of soil moisture within each EC_a-defined zone is thought to be due to the variable nature of the young alluvial soils at this site, as well as micro-topographic effects on water movement, such as low-lying ponding areas. In summary, this paper develops a method for predicting daily soil water status in EC_a-defined zones; digital information available for uploading to a software-controlled automated variable rate irrigation system with the aim of improved water use efficiency. Accuracy of prediction is determined by the extent to which spatial variability is predicted within as well as between EC_a-defined zones.     

Effects of canopy size and water stress over the crop coefficient of a “Tempranillo” vineyard in south-western Spain

This paper describes the assessment of the crop coefficient of an irrigated Tempranillo vineyard measured in a weighing lysimeter during 5?years in south-western Spain. During the first year of the study (2006), young vines displayed a different canopy growth compared to the subsequent years. From 2007 to 2010, vines experienced 2?years with no restriction in water supply, and two other years with short periods of crop water stress. Basal crop coefficient (K _cb) started from 0.2 at bud-break until 1.0 at full development in every year, being this maximum management-dependent. K _cb showed a good correlation with canopy size indices, which allows to interpolate these results to a wide range of commercial vine systems that are usually managed with lower vegetation size. Moreover, a simple linear model of crop evapotranspiration reduction with relative water content is presented, allowing the estimation of consumptive water use under deficit irrigation conditions.     

Could trunk diameter sensors be used in woody crops for irrigation scheduling? A review of current knowledge and future perspectives

The use of trunk diameter fluctuations and their derived parameters for irrigation scheduling in woody crops is reviewed. The strengths and weaknesses of these continuously measured plant-based water stress indicators compared with other discretely measured indicators for diagnosing plant water status in young and mature trees are discussed. Aspects such as sensor reading variability, signal intensity and the relationship between trunk diameter fluctuations and plant water status are analyzed in order to assess their usefulness as water stress indicators. The physiological significance of maximum and minimum daily trunk diameter and maximum daily trunk shrinkage (MDS) are also considered. Current knowledge of irrigation protocols and baselines for obtaining maximum daily trunk shrinkage reference values is discussed and new research objectives are proposed. We analyze the response of woody crops to continuous deficit irrigation scheduled by maintaining MDS signal intensity at threshold values to generate mild, moderate and severe water stress and assess the possibility of using linear variable displacement transducer (LVDT) sensors in trunk as a precision tool for regulated deficit irrigation scheduling. Finally, the possibility of using MDS signal intensity as a tool to match the irrigation regime to tree water requirements is also reviewed.     

Using EM and VERIS technology to assess land suitability for orchard and vineyard development

Orchard and vineyard producers conduct preplant site evaluations to help prevent planting permanent tree and vine crops on lands where the crop will not perform to its highest potential or attain its full life expectancy. Physical soil characteristics within specific soil profiles and spatially throughout an orchard influence decisions on land preparation, irrigation system selection, horticultural choices, and nutrient management. Producers depend on soil surveys to help them understand the soil characteristics of the land and may be interested in technology that provides additional information. Electromagnetic induction (EM38) and four-probe soil resistance sensors (VERIS) are being used in combination with global positioning systems to map spatial variability of soils using apparent soil electrical conductivity (ECa). The hypothesis evaluated in this study is whether rapid, in situ, and relatively low-cost methods of measuring ECa (EM38 and VERIS) can effectively identify and map physical soil variability in non-saline soils. The supposition is that in non-saline soils, ECa levels will relate well to soil texture and water-holding capacity and can be used to map physical soil variability. In turn, the information can be used to guide decisions on preplant tillage, irrigation system design, water and nutritional management, and other horticultural considerations. Two sites in the Sacramento Valley were mapped each with EM38 and VERIS methods. Site-specific management zones were identified by each provider on ECa maps for each site, and then soil samples were collected by University of California researchers to verify these zones. Results showed that on non-saline soils, ECa measured with both EM38 and VERIS correlate with physical soil properties such as gravel, sand, silt, and clay content but the relationship between conductivity and these physical soil properties varied from moderately strong to weak. The strength of the correlation may be affected by several factors including how dominant soil texture is on conductivity relative to other soil properties and on methods of equipment operation, data analysis and interpretation. Overall, the commercial providers of ECa surveys in this study delivered reasonable levels of accuracy that were consistent with results reported in previous studies. At one site, an ECa map developed with VERIS provided more detail on physical soil variability to supplement published soil surveys and aided in the planning and development of a walnut orchard. At a second site, almond yield appeared to correlate well with distinctly different soil zones identified with EM38 mapping.     

Evaluation of the sap flow determined with a heat balance method to measure the transpiration of a sugarcane canopy

Sap flow measurements based on the heat balance method offers the opportunity to evaluate directly and quite easily the mass flow rate of water in plants. However, extrapolation of measurements of water use by individual stems to that for a canopy is tricky. In the present study, 14 sugarcane stems, out of a canopy of nearly 200 000, were equipped with Dynamax sap flow gauge. We extrapolated these individual measurements to determine the transpiration of the canopy and compare this transpiration to the crop evapotranspiration calculated on the basis of the Penman–Monteith method. The method used for the extrapolation assumes that the transpiration of a sugarcane plant is proportional to its leaf area. Transpiration of the canopy determined by this method was overestimated by more 35% as compared to the reference evapotranspiration results. Different sources of possible errors were examined and lead to suppose that it is very difficult to determine the transpiration of a heterogeneous canopy in growth by using the sap flow measurement technique.     

坡耕地主要土壤参数的空间变异特征

以松嫩平原北部黑土区坡耕地进行的田间采样为基础,将经典统计学与地统计学相结合,在大豆生长过程中,对土壤含水量、土壤饱和含水量、土壤干容重、土壤有机质、以及表征土壤机械组成的土壤砂砾含量、粉粒含量、粘粒含量几项主要参数进行了空间统计分析。得出了各主要参数的最佳半方差理论模型以及空间分布图,并据此对试验区主要参数的空间变异特征进行了分析,为该地精准农业的研究提供了一定的参考。     

Relations between relative evapotranspiration and predawn leaf water potential in soybean grown in several locations

Summary The measurement of water consumption in the field is normally restricted to research purposes, although the development of practical field criteria for timing water application is required to improve crop productivity. To develop such criteria irrigation experiments on Soybean were conducted from flowering to grain filling at four locations which differed in their soil properties and the convective contribution of their climates to potential evapotranspiration. The energy balance, predawn leaf water potential (PLWP), soil moisture depletion, and a crop water stress index (CWSI) based on foliage temperature were measured. The range of soil, atmospheric, phenological and irrigation conditions, produced a common, linear relation between relative evapotranspiration (rET) and the logarithm of -PLWP. Correlation with the temperature based CWSI was weak. A similar relation with PLWP for other C₃ plants was also derived from data in the literature. This relation could be helpful for irrigation scheduling once the critical values of rET for crop productivity are known.     

Assessment of vine development according to available water resources by using remote sensing in La Mancha, Spain

The relevance of growing vines under semiarid conditions is universally accepted because of its impacts on social, economic and environmental aspects. Improving the knowledge of the soil–plant–atmosphere system related to the expression of vine growth allows the study of vine cover in wide areas. Several aspects of vine growing under semiarid conditions, related to weather, soil, and plant cover are analysed in this paper. Once the ground truth is achieved, multitemporal studies by remote sensing are especially useful for vine growth monitoring. The purpose of this work is focussed on determining changes of vine cover development according to available water resources in relation to present remote sensing methods. The method is based on using multitemporal masking classification techniques based on the ground truth knowledge achieved during previous research.     

土壤紧实度估算G-A模型参数的空间变异分析

为了分析土壤入渗空间变异特征并为灌溉系统设计和管理提供依据,基于土壤初始重量含水率、土壤紧实度、土壤黏粒含量和入渗过程数据,利用多元线性回归方法,分析选用土壤紧实度对简化的G-A入渗模型参数进行估算的合理性;通过半方差函数分析,进一步探讨了不同畦田规格下土壤入渗空间变异特征.结果表明:土壤紧实度与土壤质地、结构和含水率关系密切,在与土壤入渗参数的回归关系中达到了系统的显著性要求,采用其对简化的G-A入渗模型参数进行估算是可行的;畦田规格由0.5 hm2扩展到3.0 hm2时,简化的G-A入渗模型参数的变异系数均在0.1~1.0,空间变异程度呈中等,空间结构具有中等相关性,且都可用球状模型进行描述,畦田规格差异对G-A入渗模型参数空间变异程度和空间结构影响不具有统计学意义.     

土壤空间变异对水氮淋失和产量影响的模拟研究

基于CERES-Maize模型,研究了土壤空间变异和水文年型对半干旱地区土壤水氮淋失和玉米产量的影响.结果表明,土壤空间变异对作物产量和土壤水氮淋失的影响程度与降雨密切相关.丰水年水氮淋失量显著高于平水年和枯水年.降雨对作物产量和农田尺度水氮淋失的空间变异有明显影响,并能在一定程度上减弱土壤空间变异对产量和农田尺度水氮淋失的影响.随着土壤空间变异程度的增大,产量降低,产量的空间变异程度增加.水分渗漏和氮淋失量随土壤空间变异的增加呈增加趋势.当土壤黏粒和粉粒含量变异系数CV≥0.2时,在水氮管理中考虑土壤空间变异有利于提高作物产量,减轻水氮淋失.     

Yield components and grape composition responses to seasonal water deficits in Tempranillo grapevines

A field experiment was carried out over three seasons on Vitis vinifera cv. Tempranillo in order to compare pre-veraison and post-veraison water restrictions on vine performance and fruit composition. Rain-fed vines were compared with a treatment named MAX that was constantly irrigated at 75?% of the estimated crop evapotranspiration (ETc). In addition, an early (pre-veraison) water deficit strategy (ED) was applied by withholding irrigation until plant water stress experienced by vines surpassed a threshold value of midday stem water potential of ?1.0?MPa. After that, 75?% of ETc was applied. A late season deficit (LD) treatment was irrigated as per the MAX up to veraison, and thereafter, water application was reduced to approximately 37?% of ETc. All irrigation regimes increased vine yield up to 58?% with respect to the rain-fed treatment, and no differences in yield among the irrigated treatments occurred. However, there were differences in berry composition among the different irrigation strategies. The ED strategy was more effective than the LD one in reducing berry growth leading to more concentrated berries in terms of sugars and anthocyanins. The LD water shortage impaired berry sugar accumulation due to the detrimental effect of water stress on leaf photosynthesis.     

Maximum diurnal trunk shrinkage is a sensitive indicator of plant water, stress in Diospyros kaki (Persimmon) trees

Persimmon tree (Diospyros kaki L.f.) is a deciduous fruit tree included in the so-called group of minor fruit tree species. Worldwide, it is not widely grown but, nowadays, Kaki culture is of some importance in the south-east of Spain because of the high fruit commercial value. Currently, neither it is known about Kaki trees water needs, nor crop responses to the irrigation regime. The objective of the present research was to assess the feasibility of using maximum diurnal trunk shrinkage (MDS) as a plant water stress indicator for Kaki trees. During two drought cycles, in trees under either full or deficit irrigation, the MDS obtained by means of LVDT sensors was compared with a reference indicator of fruit trees water status, the midday stem water potential (Ψ_stem). In addition, stomatal conductance and fruit diameter variations were also followed. As water restrictions began, there was an immediate increase in MDS, in correspondence with a decrease in Ψ_stem. Pooling data from both drought cycles and irrigation regimes, MDS and Ψ_stem were linearly correlated (r² = 0.77***). The magnitude of differences between well watered and deficit irrigated trees was much larger in the case of MDS than for Ψ_stem. However, the tree-to-tree variability of the MDS readings was three times higher than for Ψ_stem; average coefficient of variation of 14% and 38% for Ψ_stem and MDS, respectively. Overall, results reported indicated that MDS is a sensitive indicator of Kaki water status and it can be further used as an irrigation scheduling indicator for optimum irrigation management of this crop. However, the large MDS tree-to-tree variability should be taken into account when selecting the number of trees to monitor within an orchard.     

新疆维吾尔自治区参考作物腾发量时空变异性研究

研究参考作物腾发量的时空变化特征,有助于了解新疆维吾尔自治区农牧业及生态需水的分布与演变规律。选择新疆吾尔自治区范围68个气象站的气象观测资料,应用Penman-Monteith公式,计算得出不同气候分区的历年参照作物腾发量ET0,分析了不同气候分区不同年份ET0的变化情况。采用ArcGIS空间插值技术绘制新疆维吾尔自治区参考作物腾发量的分布图,结果表明:各站ET0变化在660~1 800mm,其空间分布总体表现为南疆大于北疆、东部大于西部、盆地大于山区的分布格局。     

The inherent variability of water stress indicators in apple, nectarine and pear orchards, and the validity of a leaf-selection procedure for water potential measurements

The following two topics were examined: (1) The variability in the measurement of leaf water potential (LWP), stem water potential (SWP), maximum daily trunk shrinkage (MDS), and soil water tension (SWT) in apple, nectarine and pear orchards; and (2) The validity of a leaf-selection procedure for SWP measurements in commercial apple orchards. 27 trees were selected in an apple orchard, 27 in a nectarine orchard, and 30 in a pear orchard. The trees were close to each other. The measurements comprised of: midday SWP in apple, nectarine and pear; midday LWP in apple; MDS in apple and nectarine; and SWT in pear. The mean and standard errors (SEs) of each water status indicator in each species were calculated for an increasing sample size. The sample sizes required for stable averages were: SWP – 4, 5, and 8 trees for apple, nectarine and pear, respectively; MDS – 17 and 16 trees for apple and nectarine, respectively; SWT – 21 for pear trees. The relative SEs (i.e. percent of population mean) were 2.4, 6.1 and 10.1% in SWP/LWP, MDS and SWT, respectively. Possible explanations for the differing variability of the various water status indicators are discussed. The results show that smaller samples were sufficient to represent SWP and LWP properly than what was required for MDS and SWT. 9 commercial apple plots were selected and about 25 randomly selected leaves were used for midday SWP measurements in each plot (i.e. experimental sets). About 5 leaves on closely adjacent “representative” trees were selected in each of the commercial plots (i.e. commercial sets) and midday SWP was measured. The average difference in SWP between the experimental and the commercial sets was –0.127 MPa. The choice of closely adjacent trees increased the deviation from the experimental sets. The use of a reasonable sample size (n=7) may enable midday SWP to be measured within ±0.15 MPa in most commercial orchards.     

Evaluation of partial root-zone drying for potential field use as a deficit irrigation technique in commercial vineyards according to two different pipeline layouts

The use of partial root-drying (PRD) irrigation implies doubling pipelines instead of using a conventional single pipeline. However, pipelines can be spaced a short distance apart (e.g. 1 m) along the vine row (“D” layout) or joined with cable ties and laid as a single pipeline (“S” layout). Pipelines in “S” configuration are laid under the vine row, and in “D” at both sides of the vine row. These two different layouts can change the wetted soil zone and affect grapevine response to irrigation. The focus of this study was therefore on establishing the role of pipeline layout in vine-grape (cv. ‘Tempranillo’) response under semi-arid conditions in which PRD is managed as a deficit irrigation technique. Six irrigation treatments were applied, which resulted from the combination of Control (C, full irrigation), PRD and seasonal sustained deficit irrigation (SSDI), and “S” and “D” pipeline layouts. SSDI and PRD were irrigated to 50% C throughout the irrigation season, and C irrigation was scheduled according to a crop water balance technique. Midday stem water potential (Ψ_stem) and leaf conductance (g_l) indicated that, on the whole, PRD treatments had a slightly higher water status than SSDI treatments, but a substantially lower status than C treatments. Use of the “D” pipeline layout significantly reduced Ψ_stem in both PRD and SSDI treatments and in some instances for Control conditions, too. Berry yield, vine intercepted radiation, leaf abscisic acid (ABA) and g_l were highly correlated with Ψ_stem. Differences in water status between PRD-S and SSDI-S, according to a sub-surface irrigation test, seemed to be more related to changes in soil evaporation losses and irrigation efficiency than to any intrinsic PRD effect. PRD-S accounted for water savings equivalent to 10% according to the ratio between applied water and grape production for the SSDI-S treatment, whereas PRD-D berry yield was not significantly different from that associated with the SSDI-S treatment. In conclusion, under the growing conditions of this experiment, PRD-S offered the possibility of slightly improving water conservation when irrigation was applied to the soil surface.     

猕猴桃果园不同采样密度下土壤含水率空间变异性研究

为揭示小区尺度乃至微尺度土壤含水率的空间变异性,在杨凌地区猕猴桃果园选取40 m×40 m区域,并在此基础上再以8、2 m为间距进行网格划分,基于经典统计学和地统计学理论,对不同采样密度条件下0~60 cm土层土壤含水率的空间分布特征及其空间变异性进行了研究。结果表明,对于40 m×40 m(L)、8 m×8 m(M)和2 m×2 m(S)3种尺度,0~60 cm深度各土层土壤含水率在水平方向上的变异强度表现为弱变异至中等(偏弱)变异,且随尺度减小和土层深度增加而减小,且所有取样点处0~60 cm深度内土壤含水率在垂直方向上的变异强度表现为弱变异至中等(偏弱)变异。在3种尺度中,土壤含水率存在强烈的空间相关性,表征土壤含水率空间分布形态的半方差函数因尺度不同存在较大差异,L尺度可采用球状和指数模型,M尺度可采用线性模型,S尺度可采用高斯、指数、线性模型。L尺度合理取样数较实际少,而M和S尺度合理取样数较实际多,对于3种尺度,基本表现出0~30 cm土层合理取样数较实际多、30~60 cm土层合理取样数较实际少,表明取样点的合理性分布有待进一步优化。由于地形原因导致当地果园内南北侧土壤含水率空间分布存在较大差异。     

调亏灌溉下酿酒葡萄耗水特性及水分生产函数研究

为了确定酿酒葡萄的水分生产函数,以酿酒葡萄"梅鹿辄"为供试品种,采用滴灌的方式,以不同生育期土壤水分水平为试验因素,对酿酒葡萄不同生育期进行亏水处理,测定不同生育期土壤含水率、耗水量、产量及水分利用效率,研究了不同生育期、不同土壤水分状况对酿酒葡萄耗水量和产量的影响。结果表明,土壤水分对酿酒葡萄产量的影响规律为浆果膨大期最大,其次是开花期、着色成熟期、抽蔓期,萌芽期最小;通过对Jensen模型与Blank模型进行计算比较,发现在该试验中Jensen模型更为合理,且得出不同生育期水分生产函数的敏感指数为:浆果膨大期开花期着色成熟期抽蔓期萌芽期,与酿酒葡萄耗水规律一致;在萌芽期、抽蔓期及着色成熟期的土壤水分保持在田间持水率的60%~65%左右不会造成酿酒葡萄减产,而在浆果膨大期进行充分供水,既可获得高产,也使水分利用效率达到较高水平。     

Grapevine cv. ‘Riesling’ water use in the northeastern United States

Vine water use was measured in a Vitis vinifera cv. Riesling vineyard located in New York. Vines were fully irrigated and were trained via vertical shoot positioning giving a narrow curtain intercepting about 30% of the incident light during the sunlight hours. Vine water use was estimated on six vines by sap flow gauges directly calibrated with whole canopy transpiration measurements. The regression analysis between estimates of transpiration showed that there were large differences between vines in the calibration values obtained. Sap flow monitoring started late in June, about 2 weeks after bloom, when the canopy already filled the trellis system, and continued until October. Results showed that vine water use during most of the summer days was between 1.0 and 2.0 mm day⁻¹, with peak values around 2.5 mm. The basal (e.g. vine transpiration/reference evapotranspiration) crop coefficient (K _cb) varied somewhat between days, but it was quite stable during the whole season. Averaged over the entire experimental period, the K _cb was 0.49. Some of the day-to-day variation in the K _cb was negatively related with daily average air vapour pressure deficit. This suggests that reference evapotranspiration models on grass may not be fully accurate for vines under these experimental conditions.