Irrigation of Table Grapes With Refill Lines Set According to Midday Stem Water Potential - Soil Water Content and Seasonal Evapotranspiration

Volumetric soil water content is commonly used for irrigation management in fruit trees. By integrating direct information on tree water status into measurements of soil water content, we can improve detection of water stress and irrigation scheduling. Thermal-based indicators can be an alternative to traditional measurements of midday stem water potential and stomatal conductance for irrigation management of pear trees (Pyrus communis L.). These indicators are easy, quick, and cost-effective. The soil and tree water status of two cultivars of pear trees 'D'Anjou' and 'Bartlett' submitted to regulated deficit irrigation was measured regularly in a pear orchard in Rock Island, WA (USA) for two seasons, 2021 and 2022. These assessments were compared to the canopy temperature (Tc), the difference between the canopy and air temperature (Tc-Ta) and the crop water stress index (CWSI). Trees under deficit irrigation had lower midday stem water potential and stomatal conductance but higher Tc, Tc-Ta, and CWSI. Tc was not a robust method to assess tree water status since it was strongly related to air temperature (R = 0.99). However, Tc-Ta and CWSI were greater than 0°C or 0.5, respectively, and were less dependent on the environmental conditions when trees were under water deficits (midday stem water potential values< -1.2 MPa). Moreover, values of Tc-Ta = 2°C and CWSI = 0.8 occurred when midday stem water potential was close to -1.5 MPa and stomatal conductance was lower than 200 mmol m-2s-1. Soil water content (SWC) was the first indicator in detecting the deficit irrigation applied, however, it was not as strongly related to the tree water status as the thermal-based indicators. Thus, the relation between the indicators studied with the stem water potential followed the order: CWSI > Tc-Ta > SWC = Tc. A multiple regression analysis is proposed that combines both soil water content and thermal-based indices to overcome limitations of individual use of each indicator.

Sustainable table grape production depends on efficient water supply. Water potential is a useful indicator of water constraints in grapevines. In this regard, midday stem water potential (ΨS) is considered to be a better indicator of grapevine water status than leaf water potential (ΨL). The objective of the study was to determine a water potential threshold to set soil water refill lines for table grape irrigation. However, in previous studies carried out locally, only ΨL was measured. The relationship between ΨS and ΨL was determined for ten selected table grape cultivars. Since there were no differences between cultivars, a single equation could be used to convert midday ΨL measured in previous studies with table grapes to ΨS. Vegetative growth, berry mass and colour, as well as juice total soluble solids (TSS) data were pooled, and related to midday ΨS. This showed that -0.8 MPa seems to be a ΨS threshold for water constraints in the pre-harvest period that will allow sustainable growth and berry size for anisohydric table grape cultivars. The optimum ΨS for berry colour is between -0.8 MPa and -1.0 MPa. Consequently, a midday ΨS threshold of -0.8 MPa can be used to set refill points for irrigation where soil water content is measured on a regular basis in table grape vineyards.

Measurements of xylem sap flow (SF) and its response to soil and plant water status and climatic parameters can help to develop better water status indicators, which may help to manage irrigation based on orchard specific conditions. SF was measured with thermal dissipation probes in drip irrigated 12 years old nectarine (Prunus persica var nectarine) trees in Northern Israel. SF probes, automatic sensors for monitoring soil and plant water status, and a meteorological station were installed in standard irrigated plots and in a separate plot for experimental drying and wetting. Mid-day stem water potential (MSWP) was monitored periodically in all plots. SF and leaf conductance increased with leaf area development at the beginning of the season. Variations observed in the drying and wetting plot during four drying cycles before, and one after harvest, were instrumental in finding relationships between SF and canopy conductance and soil and plant water status and climate variables. SF was more variable and less sensitive than other water status measures. During drying, SF decreased by up to 40 % and relative to ET0 it decreased by up to 60%. When expressed relative to the irrigated trees SF decreased by up to 35%, and MSWP by 70%. Similar responses were observed in the post-harvest period. Signal to noise ratios were calculated for the sensors. During the drying cycles SF and conductance were significantly correlated with MSWP, and responses to reduced soil water were quantified. INTRODUCTION Differences in nectarine (Prunus persica var nectarine) sensitivity to water stress at different developmental stages are challenging for irrigation scheduling, similar to other deciduous fruit trees (Ortuno et al., 2004; 2006; Conejero et al., 2007, Fernandez et al., 2011, Biel et al., 2011). For improving agricultural irrigation efficiency it is critical to quantify plant and soil water status. The former can be monitored with manual tools, such as the pressure chamber for measuring leaf water potential, porometry for leaf conductance or with automatic soil and plant sensors (Jones, 2008). For automatic irrigation scheduling it is necessary to replace the manual tools, even though they are believed to be the most precise for setting irrigation timing in fruit trees (Casadesus et al., 2012). The growing shortage of water available for irrigation in many parts of the world increases the need for savings and increased efficiency in water use (Chalmers et al. 1986; Matthews et al., 1990; Fereres et al., 2003; Naor, 2006; Kanety, 2010; Casadesus et al., 2012). For this we need to have better automatic irrigation tools that can quantify water status more precisely (Remorini and Massai, 2003). One automated water status indicator could be the measurement of SF in the tree trunk (Naor and Cohen, 2003; Ortuno et al., 2006; Biel et al., 2012) but few studies have compared the performance of SF and other sensors with tree water status parameters like stem water potential (e.g. Biel et al., 2012).

&amp;lt;p&amp;gt;Irrigation water is an expensive and limited resource. Previous studies show that irrigation scheduling can boost efficiency by 20-60%, while improving water productivity by at least 10%. In practice, scheduling decisions are often needed several days prior to an irrigation event, so a key aspect of irrigation scheduling is the accurate prediction of crop water use and soil water status ahead of time. This prediction relies on several key inputs such as soil water, weather and crop conditions. Since each input can be subject to its own uncertainty, it is important to understand how these uncertainties impact soil water prediction and subsequent irrigation scheduling decisions.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;This study aims to evaluate the outcomes of alternative irrigation scheduling decisions under uncertainty, with a focus on the uncertainties arising from short-term weather forecast. To achieve this, we performed a model-based study to simulate crop root-zone soil water content, in which we comprehensively explored different combinations of ensemble short-term rainfall forecast and alternative decisions of irrigation scheduling. This modelling produced an ensemble of soil water contents to enable quantification of risks of over- and under-irrigation; these ensemble estimates were summarized to inform optimal timing of next irrigation event to minimize both the risks of stressing crop and wasting water. With inclusion of other sources of uncertainty (e.g. soil water observation, crop factor), this approach shows good potential to be extended to a comprehensive framework to support practical irrigation decision-making for farmers.&amp;lt;/p&amp;gt;

A time series of Landsat 8 OLI multispectral images acquired in the period May 2013 - February 2016 was used to investigate vineyard behaviour in terms of vigour and water content. The study site was located in the Castel del Monte DOCG area; a 'Moscato Reale' (syn. 'Moscato Bianco') vineyard was analysed. Normalized difference vegetation index (NDVI) and normalized difference water index (NDWI) were calculated for all images (preventively calibrated and atmospherically corrected) to describe, at pixel level (30×30 m), vigour, plant and soil water status. Spectral indices cyclicity was also assessed to explore dynamics of vines growing season. Satellite-derived information was compared with ground parameters (midday stem water potential and soil water content), correlation tested and regression models for parameter estimation calibrated. Periodicity of vigour (NDVI) and water content (NDWI') along time was described using a Fast Fourier Transform approach, finding that the most vigorous part of vineyard corresponded to the most regular (cyclic) ones. Middle resolution multispectral imagery from satellite can be effectively used, at vineyard level, to describe cyclicity, water status and soil moisture. This is an important issue to focus on since, as Landsat OLI dataset is free, the entire process is economic enough to be consistent with cost and income of the farming system.

In the course of a series of studies conducted to investigate the long-term behavior of 129I (which has a half-life of 16 million years) in the environment, the concentration of stable iodine (127I) in precipitation, irrigation water and soil water to a depth of 2.5 m in a forest plot, an upland field and a paddy field in the upland area of Tsukuba, Japan, was determined. In the forest plot, the mean iodine concentrations in soil water at all the depths ranged from 0.13 to 0.21 μg L−1, about one-tenth of the values recorded in precipitation (weighted mean 2.1 μg L−1). This finding suggests that the major part of iodine in precipitation was sorbed onto the surface soil horizon under oxidative conditions. In the upland field, the mean iodine concentration in soil water was 2.2 μg L−1 at a depth of 0.2 m and it decreased to 0.34–0.44 μg L−1 at a depth of 0.5 m or more; these concentrations were about one-fifth of that in precipitation. This suggested that the major part of the iodine derived from precipitation was sorbed onto the subsurface soil horizon (at depths between 0.2 and 0.5 m). In the paddy field, during the non-irrigation period, the mean iodine concentrations in soil water at all the depths ranged from 1.8 to 4.8 μg L−1, almost the same values as those recorded in precipitation. During the irrigation period, the mean iodine concentrations at depths of 0.2 and 0.5 m were 18.8 and 16.7 μg L−1, values higher than the 10.9 μg L−1 value recorded in irrigation water and the 11.8 μg L−1 value recorded in ponding water. However, at a depth of 1.0 m or more, the mean iodine concentrations in soil water rapidly decreased from 7.3 to 1.8 μg L−1. These data suggested that a significant amount of iodine flowed out from the paddy field by surface runoff and a considerable amount of iodine that leached to a depth of 0.5 m was retained onto the mildly oxidative soil horizon (2Bw) that lay at depths between 0.5 and 1.0 m. At a depth of 2.5 m in the paddy field, the mean iodine concentration in soil water decreased to 1.8 μg L−1, but this level was much higher than those in the forest plot and upland field at the same depth, which suggested that a significant amount of iodine had leached into the groundwater-bearing layer. There was a negative correlation (r=-0.889) between the Eh of soil and the iodine concentration in soil water (0.2 m depth) of the paddy field. Particularly, when the Eh of soil fell below approximately 150 mV, the iodine concentration rapidly increased to above 10μg L−1. As for the chemical forms of iodine in precipitation, irrigation water, ponding water and soil water during the winter irrigation period in the paddy field with oxidative conditions, 58–82% of iodine consisted of IO− 3 and 17–42% of iodine consisted of I−. In the soil water during the summer irrigation period in the paddy field under reductive conditions, 52–58% of iodine consisted of I−, and 42–47% consisted of IO− 3.

To characterize tree responses to water deficits in shallow and deep rooted conditions, parameters developed using daily oscillations from continuously measured soil water content and trunk diameter were compared with traditional discrete monitoring of soil and plant water status in lysimeter and field-grown peach trees [ Prunus persica (L.) Batsch `O'Henry']. Evaluation occurred during the imposition of deficit irrigation for 21 days followed by full irrigation for 17 days. The maximum daily available soil water content fluctuations (MXAWCF) taken at any of the four monitored root zone depths responded most rapidly to the deficit irrigation. The depth of the MXAWCF increased with time during the deficit irrigation. Differences relative to a fully irrigated control were greater in the lysimeter than the field-grown trees. Minimum daily trunk diameter (MNTD) and maximum daily trunk shrinkage (MDS) responded sooner than midday stem water potential (stem Ψ), predawn or midday leaf water potential (predawn leaf Ψ and leaf Ψ), or photosynthesis (A). Parameters based on trunk diameter monitoring, including maximum daily trunk diameter (MXTD), correlated well with established physiological parameters of tree water status. Statistical analysis of the differences in the measured parameters relative to fully irrigated trees during the first 10 days of deficit irrigation ranked the sensitivity of the parameters in the lysimeter as MXAWCF &gt; MNTD &gt; MDS &gt; MXTD &gt; stem Ψ = A = predawn leaf Ψ = leaf Ψ. Equivalent analysis with the field-grown trees ranked the sensitivity of the parameters as MXAWCF &gt; MNTD &gt; MDS &gt; stem Ψ = leaf Ψ = MXTD = predawn leaf Ψ &gt; A. Following a return to full irrigation in the lysimeter, MDS and all the discrete measurements except A quickly returned to predeficit irrigation levels. Tree recovery in the field-grown trees was slower and incomplete due to inadequate filling of the root zone. Fruit size was significantly reduced in the lysimeter while being minimally affected in the field-grown trees. Parameters only available from continuous monitoring hold promise for improving the precision of irrigation decision-making over the use of discrete measurements.

Soil water content criteria for peach trees water stress detection during the postharvest period

Irrigation water is an expensive and limited resource and optimal scheduling can boost water efficiency. Scheduling decisions often need to be made several days prior to an irrigation event, so a key aspect of irrigation scheduling is the accurate prediction of crop water use and soil water status ahead of time. This prediction relies on several key inputs including initial soil water status, crop conditions and weather. Since each input is subject to uncertainty, it is important to understand how these uncertainties impact soil water prediction and subsequent irrigation scheduling decisions. This study aims to develop an uncertainty-based analysis framework for evaluating irrigation scheduling decisions under uncertainty, with a focus on the uncertainty arising from short-term rainfall forecasts. To achieve this, a biophysical process-based crop model, APSIM (The Agricultural Production Systems sIMulator), was used to simulate root-zone soil water content for a study field in south-eastern Australia. Through the simulation, we evaluated different irrigation scheduling decisions using ensemble short-term rainfall forecasts. This modelling produced an ensemble of simulations of soil water content, as well as ensemble simulations of irrigation runoff and drainage. This enabled quantification of risks of over- and under-irrigation. These ensemble estimates were interpreted to inform the timing of the next irrigation event to minimize both the risks of stressing the crop and/or wasting water under uncertain future weather. With extension to include other sources of uncertainty (e.g., evapotranspiration forecasts, crop coefficient), we plan to build a comprehensive uncertainty framework to support on-farm irrigation decision-making.

Wheat growth in response to soil water deficit play an important role in yield stability. A field experiment was conducted for winter wheat (Triticum aestivum L.) during the period of 2002-2005 to evaluate the effects of limited irrigation on winter wheat growth. 80%, 70%, 60%, 50% and 40% of field capacity was applied at different stages of crop growth. Photosynthetic charac- teristics of winter wheat, such as photosynthesis rate, transpiration rate, stomatal conductance, photosynthetically active radiation, and soil water content, root and shoot dry mass accumulation were measured, and the root water uptake and water balance in different layer were calculated. Based on the theory of unsaturated dynamic, a one-dimensional numerical model was developed to simulate the effect of soil water movement on winter wheat growth using Hydrus-1 D. The soil water content of stratified soil in the experimental plot was calculated under deficit irrigation. The results showed that, in different growing periods, evapotranspiration, grain yield, biomass, root water up- take, water use efficiency, and photosynthetic characteristics depended on the controlled ranges of soil water content. Grain yield response to irrigation varied considerably due to differences in soil moisture contents and irrigation scheduling between seasons. Evapotranspiration was largest in the high soil moisture treatment, and so was the biomass, but this treatment did not produce the highest grain yield and root water uptake was relatively low. Maximum depth of root water uptake is from the upper 80 cm in soil profile in jointing stage and dropped rapidly upper 40 cm after heading stage, and the velocity of root water uptake in latter stage was less than that in middle stage. The effect of limited irrigation treatment on photosynthesis was complex owing to microclimate. But root water uptake increased linearly with harvest yield and improvement in the latter gave better root water uptake under limited irrigation conditions. Appropriately controlled soil water contents can improve the root water uptake and grain yield. Consistently high values of root water uptake and grain yield were produced under conditions of mild water deficit at the seedling and start of regrowth to stem-elongation stages, in addition to a further soil water depletion at the physiological maturity to harvest stage. We suggest that periods of mild soil water depletion in the early vegeta- tive growth period together with severe soil water depletion in the maturity stage of winter wheat is an optimum for limited irrigation regime in this oasis. Considerable potential for further improve- ment in agricultural water use efficiency in the arid zone depends on effective conservation of moisture and efficient use of the limited water.

Current irrigation scheduling is based on well-established crop coefficient and reference evapotranspiration procedures to estimate daily crop evapotranspiration (ETc). Effective irrigation scheduling and efficient irrigation water use can occur when ETc is calculated with crop coefficients representative of actual crop water use conditions. The objective of this research was to evaluate irrigation scheduling using two approaches to estimate the basal crop coefficient (Kcb) during wheat experiments conducted in 2003-2004 and 2004-2005 at Maricopa, Arizona. Each Kcb approach (main treatment) included six subtreatment combinations (three plant densities and two N managements) imposed to create spatial and temporal variations in water use among experimental plots. The first approach (NDVI treatment) estimated Kcb separately for each plot based on normalized difference vegetation index (NDVI) data obtained by frequent canopy reflectance measurements. The second approach (FAO treatment) estimated Kcb uniformly for all plots based on a Kcb curve developed for standard wheat conditions. The Kcb estimates were incorporated within the FAO-56 dual crop coefficient procedures to calculate daily ETc and root zone soil water depletion (Dr). Plot irrigations were provided when the predicted Dr reached 45% of the available soil water. During both wheat experiments, considerable variations in measured soil water depletion were observed for subtreatments due to differences in crop water use rates. For the FAO treatment, mean absolute percent difference (MAPD) for predicted Dr was 27% and 40% for 2003-2004 and 2004-2005, respectively. Prediction of Dr was improved significantly for NDVI for both experiments where treatment MAPD was 17% (2003-2004) and 18% (2004-2005). Although mean irrigation application efficiency for NDVI (89%) and FAO (88%) was similar for 2003-2004, it was significantly higher for NDVI (86%) than FAO (77%) for 2004-2005. Differences for irrigation scheduling resulted in significantly lower seasonal irrigation water use for the NDVI than FAO treatment, 8% (2003-2004) and 13% (2004-2005), but did not result in appreciable treatment differences for seasonal ETc, final grain yield, and crop water use efficiency (yield per unit ETc). Consequently, a primary outcome for both experiments was significantly higher irrigation water use efficiency (yield per unit irrigation water) for NDVI than FAO. Incorporating Kcb estimates based on NDVI within existing crop coefficient algorithms provides an opportunity to improve wheat irrigation scheduling strategies for conserving irrigation water while maintaining grain yield potentials.

رشد جمعیت جهان، محدودیت منابع آب و نیاز به تولید محصول بیشتر، به تمایل کشاورزان در مصرف کودهای نیتروژنی بیش از نیاز گیاه و به دنبال آن آبشویی نیترات اضافه به آب های زیرزمینی و آلودگی زیست محیطی منجر شده است. به همین دلیل ارزیابی مدل های جدید با کاربری آسان در برآورد صحیح از توزیع رطوبت و نیتروژن و شناسایی حرکت آب و املاح در خاک منطقه و انتخاب بهترین گزینه مدیریتی با دقت بالا ضروری است. این پژوهش با هدف اعتبارسنجی مدل Eu-Rrotae-N دربرآورد توزیع رطوبت و نیتروژن و شاخص‌های عملکرد گیاه فلفل تحت مدیریت های مختلف کود نیتروژن انجام شد. تیمارهای آزمایشی شامل سه سطح کودی صفر (N0)، نسبت نیترات به آمونیوم 20:80 (N2) و 40:60 (N3) بود که در طرح آماری بلوک های کامل تصادفی در سه تکرار در اصفهان اجرا شد. آبیاری با پایش روزانه رطوبت و به میزان کمبود رطوبت از ظرفیت مزرعه انجام گرفت. عملکرد گیاه فلفل، رطوبت و نیتروژن خاک در طول دوره رشد اندازه گیری شدند. ارزیابی کارایی مدل با استفاده از چهار شاخص ریشه میانگین مربعات خطا (RMSE)، ریشه میانگین مربعات خطای نرمال شده (NRMSE)، ضریب تبیین (r2) و شاخص توافق ویلموت (d) انجام شد. عملکرد گیاه با اختلاف قابل قبولی کمتر از میزان واقعی برآورد شد. برای نیترات و رطوبت خاک، NRMSE به ترتیب برابر 45/11و 08/12، RMSE 89/0 و 022/0، r2 998/0 و996/0 و d برابر با 665/0و66/0 بود. میزان NRMSE کمتر از 20 درصد گویای کارایی خوب مدل و r2 بیشتر از 90 درصد نشان دهنده روند شبیه‌سازی بسیار مناسب مدل بود. همچنین RMSE و d در محدوده قابل قبول قرار داشتند. با توجه به این که نتایج ارزیابی نشان دهنده کارایی مناسب مدل Eu-Rotate-N در شبیه سازی رطوبت، نیترات و عملکرد گیاه بود. پس می توان از این مدل برای شبیه سازی در بهینه‌سازی مدیریت آب و نیتروژن در مزرعه در شرایط گرم و خشک اصفهان استفاده کرد.

Water stress is a major factor affecting grapevine yield and quality. Standard methods for measuring water stress, such as midday stem water potential (ΨSWP), are laborious and time-consuming for intra-block variability mapping. In this study, we investigate water status variability within a 2.42-ha commercial Cabernet Sauvignon block with a standard vertical trellis system, using remote sensing (RS) tools, specifically canopy fraction-based vegetation indices (VIs) derived from multispectral unmanned aerial vehicle (UAV) imagery, as well as standard reference methods to evaluate soil and plant water status. A total of 31 target vines were monitored for ΨSWP during the whole growing season. The highest variability was at véraison when the highest atmospheric demand occurred. The ΨSWP variability present in the block was contrasted with soil water content (SWC) measurements, showing similar patterns. With spatial and temporal water stress variability confirmed for the block, the relationship between the ΨSWP measured in the field and fraction-based VIs obtained from multispectral UAV data was analysed. Four UAV flights were obtained, and five different VIs were evaluated per target vine across the vineyard. The VI correlation to ΨSWP was further evaluated by comparing VI obtained from canopy fraction (VIcanopy) versus the mean (VImean). It was found that using canopy fraction-based VIs did not significantly improve the correlation with ΨSWP (NDVIcanopyr = 0.57 and NDVImeanr = 0.53), however fractional cover (fcover) did seem to show a similar trend to plant water stress with decreasing canopy size corresponding with water stress classes. A subset of 14 target vines were further evaluated to evaluate if additional parameters (maximum temperature, relative humidity (RH), vapour pressure deficit, SWC and fractional cover) could serve as potential water stress indicators for future mapping. Results showed that the integration of NDVIcanopy and NDREmean with additional information could be used as an indicator for mapping water stress variability within a block.

Development and evaluation of drip irrigation and fertigation scheduling to improve water productivity and sustainable crop production using HYDRUS

&lt;p style="text-align: justify;"&gt;&lt;strong&gt;Aim&lt;/strong&gt;: To evaluate the usability of various plant water potentials in table grape irrigation management under a semiarid climate.&lt;/p&gt;&lt;p style="text-align: justify;"&gt;&lt;strong&gt;Methods and results&lt;/strong&gt;: Two water regimes were set up. The « control » water regime was the one usually used in the vineyard. The « 50 % Irrigation » water regime delivered only half the quantity of water to the vines. Predawn leaf (ψ L &lt;sub&gt;PD&lt;/sub&gt;), predawn stem (ψ S &lt;sub&gt;PD&lt;/sub&gt;), midday leaf (ψ L &lt;sub&gt;M&lt;/sub&gt;), and midday stem (ψ S &lt;sub&gt;M&lt;/sub&gt;) water potentials were measured during the growing season. The results show that the four water potentials can accurately measure the vine water status in table grape vineyard at a daily and seasonal time scale. But, ψ L &lt;sub&gt;M&lt;/sub&gt; appeared to be the most reliable indicator to differentiate between the two water regimes with a frequency of 73 %. The « 50 % Irrigation » water regime induced in the ‘Italia’ cultivar an anisohydric behavior and a decrease of 29.4 % in vine vigor and 11.5 % in berry weight. Under the Tunisian climate, ‘Italia’ cultivar may exhibit night time transpiration that decreases ψ L &lt;sub&gt;PD&lt;/sub&gt; by 19.5 %.&lt;/p&gt;&lt;p style="text-align: justify;"&gt;&lt;strong&gt;Conclusion&lt;/strong&gt;: Preliminary minimum ψ L &lt;sub&gt;M&lt;/sub&gt; threshold to produce high quality table grape would be -0.8 and -1.1 MPa for pre- and post-veraison, respectively.&lt;/p&gt;&lt;p style="text-align: justify;"&gt;&lt;strong&gt;Significance and impact of the study&lt;/strong&gt;: The pressure chamber is an effective device for irrigation management in commercial table grape vineyards under semiarid conditions.&lt;/p&gt;