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Crop canopy temperature and Crop Water Stress Index (CWSI) are used for assessing plant water status and irrigation scheduling, but understanding management interactions is necessary. This study evaluated whether nutrient deficiencies would confound interpretation of plant water status from leaf temperature. Leaf temperature and CWSI in maize (Zea mays L.) were evaluated with different irrigation strategies and varying nitrogen (N) supply for replicated glasshouse and field studies. Glasshouse treatments consisted of well-watered or simulated drought and sufficient, intermediate, or deficient N. Field study treatments consisted of well-watered, controlled deficit irrigation, or simulated drought and sufficient, sufficient delayed, or deficient N. Average CWSI values varied across irrigation treatments, with 0.37 and 0.54 for glasshouse well-watered and drought and 0.34, 0.47, and 0.51 for field well-watered, drought, and controlled deficit treatments, respectively. Nitrogen levels created widely different leaf chlorophyll contents without affecting leaf temperature or CWSI. Canopy water stress measurements were robust across varying N levels, but CWSI did not correlate well with leaf area due to confounding effects of irrigation timing and nitrogen levels. Leaf temperature and CWSI are useful for evaluating crop water status, but nutrient status and timing of water stress must also be considered for crop growth prediction.

Vegetative growth and water relations of Thompson Seedless grapevines in response to applied water amounts at various fractions of measured grapevine ETc were quantified. Treatments ranged from no applied water up to 1.4 times the water used by vines growing in a weighing lysimeter. All treatments were irrigated at the same frequency as the vines in the lysimeter (whenever they used 2 mm of water), albeit at their respective fraction. Soil water content and midday leaf water potential (Ψl) were measured routinely in four of the irrigation treatments across years. The amount of water depleted in the soil profile ranged from 190 mm for the 0.2 treatment in 1993 to no water depletion for the 1.4 treatment in 1992. The irrigation treatments significantly affected midday Ψl, total shoot length, leaf area per vine, pruning weights and trunk diameter; as applied water decreased so did vegetative growth. Pruning weights were a linear function of the seasonal, mean midday Ψl across growing seasons. The application of water amounts in excess of evapotranspiration negatively affected vegetative growth some of the years. A companion paper will demonstrate that over-irrigation can negatively affect reproductive growth of this grape cultivar due to excess vegetative growth.

The decrease of annual irrigation application rate observed since 1950 was reversed in 1988 as a result of a sudden increase of the amount of treated effluents used for irrigation. Intensification of research on irrigation with effluents and marginal water starting in 1994 resulted four years later in the renewal of the decrease of irrigation application rate.

Stress degree days (SDD) and canopy-air temperature differential summation procedures were used to quantify the response of crops of chickpea (Cicer arietinum L.) to soil water availability and atmospheric demand over a four year period on a deep and medium-deep Vertisol in India using different irrigation treatments and planting dates. Canopy temperatures measured between 13.00–14.00 h provided a good index of the daily mean canopy temperature. Differences in the diurnal variation in the canopy-air temperature differentials between irrigated and non-irrigated chickpea reflected clearly the differential response of the crop to soil water availability. Total water use of chickpea decreased with increasing SDD. Data pooled over three growing seasons showed a close relationship between SDD and yield of chickpea. Calculated water stress index (WSI) which includes the vapor pressure deficit term showed a similar relationship with yield to that with SDD.

Water status directly affects yield and crop quality in grapevines. Precision viticulture demands the application of new available technologies and methodologies for accurate irrigation management in vineyards. The objective of this work was the development of an on-the-go thermal imaging application for the assessment and mapping of vineyard water status, building a dataset from a commercial Tempranillo (Vitis vinifera L.) vineyard over two consecutive seasons and validating it in another commercial vineyard from a different winegrowing region. Thermal imaging was performed with a thermal camera mounted in an all-terrain vehicle, moving at 5 km/h and operating at a distance from the canopy of 1.20 m. Stem water potential (Ψstem) was used for validation as the grapevine water status reference method, using a Scholander pressure chamber. Crop Water Stress Index (CWSI) and Stomatal Conductance Index (Ig) from a 4-day dataset were computed and correlated with Ψstem, delivering significant (p < 0.0001) determination coefficients R2 up to 0.71. The prediction capability of this dataset was also validated in another commercial vineyard, achieving a prediction R2 up to 0.82 (RMSE of 0.123 MPa). The predicted values of both indices were thus employed for mapping vineyard water status in the second plot. These results evidence the potential applicability of on-the-go thermal imaging for assessing and mapping water status in commercial vineyards required for precision viticulture.

Different irrigation regimes were performed on container-grown early-season peach trees (cv. Alexandra) during stage III of fruit growth. In the first experiment, three water treatments were applied: T1, control irrigation; T2, light water restriction; T3, high water restriction. In the second experiment, T4, a light water restriction, was compared to T5, the same total amount of water as T4 but with alternating periods of water withholding and subsequent re-irrigation. Compared to T1 and T2, leaf photosynthesis was limited under T3. Fruit yield and quality did not differ between T1 and T2, while fruit yield, average weight and percentage in the higher commercial grade decreased and total soluble solids (TSS) increased under T3, compared to T1 and T2. Comparing T5 to T4, yield, fruit firmness and average weight did not vary, but heterogeneousness of fruit diameter and TSS at the lower fruit grade tended to be higher. Peach sensitivity to brown rot was likely to decrease under T3 compared to T1 and T2. Peach water loss and brown rot incidence after contamination in conidial suspensions were enhanced under T5 compared to T4, implying that re-irrigation after water withholding should be avoided in order to limit brown rot incidence.

This work studies the feasibility of using automated drip irrigation based on the volumetric soil water content measured with capacitance probes in early maturing nectarine trees (Prunus persica L. Batsch, cv. ‘Flariba’) grown in a clay–loam soil in Mediterranean conditions. An automated irrigation treatment (AUTO), based on the management allowed depletion (MAD) concept (with a feed-back control system), was compared with an irrigation-scheduling method based on the conventional crop evapotranspiration (100% ETc) as Control, under high (HWA) and low (LWA) water availability scenarios, each during three consecutive growing seasons. With HWA (no water restriction), the AUTO treatment maintained the soil water content at near field capacity (α = 10% depletion of available soil water content), and there were no significant differences between treatments in terms of the plant–soil water status, nectarine yield, or fruit quality parameters. Under LWA conditions (water deficit), the AUTO treatment (α = 10% during pre-harvest and 30% post-harvest) provided 43% less water than the Control, promoting a moderate plant water deficit, which led to a decrease in vegetative growth (winter pruning and tree canopy cover) but no significant differences in total yield and fruit quality parameters (although the total soluble solid content increased). The water use efficiency values in the AUTO treatment increased by an average of 34%. It was concluded that automated irrigation, based on MAD seasonal threshold values and monitored by means of real-time soil water content sensors, could be considered a promising tool for application in semi-arid Mediterranean agro-systems subjected to water scarcity.

The study of the micro-physical characteristics of spray droplets provides crucial insights into the impact of sprinkler water on soil erosion, leaf impact, and the microclimate of agricultural environments. However, the variability in measurement outcomes across different technologies due to their distinct measurement principles is a significant challenge. This research aims to evaluate and compare the droplet diameter, velocity, application rate, and kinetic energy rate using four distinct measurement technologies: the paper stain method (PS), flour pellet method (FP), laser precipitation monitor (LPM), and two-dimensional video disdrometer (2DVD), alongside a rain gauge (RG) in the context of sprinkler irrigation conditions. The results reveal that: (1) The FP method struggled to capture small droplets under the same spray conditions, while the PS method recorded a maximum droplet diameter exceeding 7 mm. The LPM registered the highest droplet count per unit area and time, notably capturing a significant number of small droplets (< 1 mm). Conversely, the 2DVD provided a more uniform distribution of droplet sizes, with the LPM’s mean equivalent droplet diameter (dv) being 0.86 times that of the 2DVD. (2) Although droplet diameters and velocities measured by the 2DVD, LPM, FP, and PS, decreased with increased working pressure, these technologies concurred when assessing low-velocity and small-diameter droplet. (3) The 2DVD’s larger sampling area compared to other methods enables the acquisition of more representative droplet characteristics, including their irregular shapes, suggesting its utility in measuring the micro-physical properties of sprayed droplets. (4) Based on the kinetic energy rate measured by the 2DVD under identical conditions, kinetic energy rate calibration factors of 0.88, 1.15, and 1.10 are suggested for the LPM, FP, and PS, respectively. This study provides essential data for calibrating and applying various droplet measurement technologies.

The distribution of a crop rooting system can be defined by root length density (RD), root length (RL) per soil layer of depth Δz, sum of root length (SRL) in the soil profile (total root length) or rooting depth (z r . The combined influence of these root system parameters on water uptake is not well understood. In the present study, field data are evaluated and an attempt is made to relate a daily “maximum water uptake rate” (WUmax) per unit soil volume as measured in different soil layers of the profile to relevant parameters of the root system. We hypothesize that local uptake rate is at its maximum when neither soil nor root characteristics limit water flow to, and uptake by, roots. Leaf area index and the potential evapotranspiration rate (ET p ) are also important in determining WUmax, since these quantities influence transpiration and hence total crop water uptake rate. Field studies in Germany and in Western Australia showed that WUmax depends on RD. In general, there was a strong correlation between the maximum water uptake rate of a soil layer (LWUmax) normalized by ET p and RL normalized by SRL. The quantity LWUmax · ET was linearly related to (RL/SRL)1/2. The data show that the single root model will not predict the influence of RD on WUmax correctly under field conditions when water-extracting neighboring roots may cause non-steady-state conditions within the time span of sequential observations. Since the rooting depth z r was linearly related to (SRL)1/2, the relation: LWUmax · ET = f (RL1/2/z r ) holds. Furthermore it was found that the maximum “specific” uptake rate per cm root length URmax was inversely related to RD1/2 and to SRL1/2 or z r of the profile. Observed high specific uptake rates of shallow rooted crops might be explained not only by their lower RD-values but also by the additional effect of a low z r . The relations found in this paper are helpful for realistically describing the “sink term” of dynamic water uptake models. Growing plants extract water from the soil to meet transpiration needs. Rates of transpiration and of water uptake are set by evaporative demand and by plant and soil factors which influence capacity to meet that demand. These factors include crop canopy size and leaf characteristics, root system characteristics and hydraulic properties of the soil and the soil-root interface. Soil and root system properties vary with depth and all factors vary in time, so that parameters related to them require constant updating over a crop season. Dynamic simulation models describe water uptake by root systems under field conditions as a function of soil depth and time. Many of these simulation approaches are based on Gardner's (1960) single root model (Feddes 1981). These simulation procedures follow the assumption that water uptake is proportional to a difference in water potential between the bulk soil and the root surface or the plant interior, to the hydraulic conductivity of the soil-plant system and to the “effectiveness” of competing roots in water uptake. The effectiveness factor accounts more or less empirically for the influence of various root system parameters on water uptake such as percentage of “active” roots absorbing water, root surface permeability, root length density determining the distance between neighbouring roots, or total root length and depth of the root system. Such models however, will not always reflect correctly the influence of root system characteristics on water uptake since these assumptions have rarely been tested under field conditions. In many instances, there is better agreement between simulated and measured total water use of plants than between predicted and observed water depletion by roots within individual layers of the soil profile (Alaerts et al. 1985). Water uptake by an expanding root system as a function of depth and time has been studied under field conditions for several crops (listed in Herkelrath et al. 1977a; Feddes 1981; Hamblin 1985). They show that the dynamics of water uptake depend on root length density and the “availability” of soil water. However, the combined influence of root length density, total root length and rooting depth on the water uptake pattern has not been assessed. An evaluation of root system parameters with respect to soil water extraction should aid our understanding of how roots perform under field conditions and may assist our efforts to formulate the water uptake function of roots in dynamic simulation studies more realistically. The aim of the present investigation is to develop an approach that relates measured water uptake rates to relevant parameters of the root systems. This approach will be confined to situations where water uptake in a soil layer is not restricted by unfavorable soil conditions, such as in wet soil, by insufficient aeration and, in dry soil, by reduced water flow towards roots or by increased contact resistance (Herkelrath et al. 1977b). We will define a maximum water uptake rate WUmax that is neither soil-limited nor appreciably limited by the decreasing permeability of aging roots. This WUmax will be related to relevant root system parameters as they exist when WUmax is observed. Hence, water uptake by roots in a very wet, as well as in a dry soil, has been excluded from consideration.

The agronomic implications of growing rice under sprinkler irrigation on a duplex soil in inland south east Australia were examined by comparing 3 sprinkler irrigation regimes applied once, twice and three times a week (S1W, S2W and S3W) with continuous flood irrigation (CF). Each sprinkler irrigation treatment was managed to replace evaporative loss since the previous irrigation. Each irrigation main plot was split into subplots receiving 3 levels of nitrogen (N) fertilizer −0, 80 or 120 kg N ha−1 (0N, 80N and 120N). Grain yield on all sprinkler-irrigated treatments was reduced by 50% or more when compared with CF. There was a slight decline in grain yield with lower frequency of sprinkler irrigation. The main factors contributing to the lower yields were reductions in the number of spikelets per panicle and in floret fertility. Panicle density was not significantly influenced by the irrigation treatments. Sprinkler irrigation delayed anthesis by at least 8 days, and the duration of anthesis was extended by 5 to 7 days. The lower yields under sprinkler irrigation did not appear to be due to greater N deficiency and it is uncertain whether any or all irrigation treatments suffered from P deficiency. Irrigation treatment had little effect on plant N concentration, but P concentration in the plant tops was reduced by sprinkler irrigation during the vegetative and reproductive stages. Low night temperatures throughout the reproductive phase reduced floret fertility, but all irrigation treatments at the same N rate (except SlW/120N) were affected to a similar extent. Water stress, as evidenced by leaf rolling in response to high evapotranspiration rates in this semi-arid environment, was considered to be the main factor contributing to the decline in yield on the sprinkler-irrigated treatments. The irrigation and N rate treatments did not interact significantly in their effect on any important parameter measured. Increasing the rate of applied N from 0 to 80 kg N ha−1 increased yield by about 1 t ha−1 by producing more panicles, but 120N was of no further benefit and was associated with increased floret sterility. Nitrogen fertilizer increased both the N uptake and N concentration in the plant material. We conclude that sprinkler irrigation for rice production is unlikely to be a viable strategy for water management on duplex soils in inland south east Australia. Conventional dry-seeded culture with permanent flood delayed until panicle initiation is probably a preferable alternative to sprinkler irrigation for increasing water-use efficiency.