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The main objectives of the present study were to assess the water demand for heavy fruit load of ‘Hass’ avocado throughout the growth periods and to investigate the effects of deficit irrigation during sensitive phenological phases on yield. The experimental set-up allowed the comparison between trees responses to three irrigation strategies during the entire growth period (no water stress; excessive irrigation; constant water stress) as well as the comparison between regulated deficit irrigation (RDI) managements applied during the early or the late growth period. The yield of no water stress treatments during three experimental years was very high (25–31 t ha−1) while the yields of water-stressed trees were significantly lower (16–21 t ha−1). More importantly, the yield of no water stress trees was not susceptible to alternate bearing while the yield of water-stressed trees was considerably reduced during off-crop years. Irrigation rates and the actual evapotranspiration coefficient KL = ET/ET0 for the no water stress treatment may serve as a reasonable guide for irrigation management. Fruit load should be taken into account while planning irrigation and fertilization management and plant-based methods should be used for controlling the irrigation management (scheduling and quantities). Analyses of trunk diameter variation data that lead to evaluation of trunk growth rate and maximum daily shrinkage reflect phenological stages and periodicity of shoot, fruit and root growth, and also may provide an integrative, “holistic viewpoint” of overall tree status.

High-frequency drip irrigation supplies water and nutrients at a rate that is close to plant uptake, thus enhancing growth and production. In light of water scarcity in arid regions, marginal water is increasingly considered as a resource for agricultural production. The objective of this study was to investigate the combined effects of pulsed irrigation and water salinity on the response of the soil–plant system. As a test crop, bell pepper (Capsicum annuum L.) was cultivated in a screenhouse and drip irrigated daily (D) and at high frequency (P) with saline (S) and fresh (F) water. Simultaneous monitoring of meteorological, physiological, soil physical, plant and soil chemical, and yield data was performed during the experiment. Most physiological parameters were negatively affected by high water salinity. No consistent effect of the irrigation frequency was found on the overall season, although pulsed irrigation led to higher plant weight and leaf area at the early stages of plant growth. The distinct patterns of soil water content for the two irrigation frequencies are presented. Salinity in the root zone was higher under pulsed irrigation, an observation that is supported by measured leaf chloride content and tensiometer readings indicating that the once daily application may have more efficiently removed salts from the top soil. Yield, fruit weight, and irrigation water use efficiency (IWUE) were highest under once daily irrigation with fresh water. High-frequency irrigation led to higher Mn concentrations in leaves and fruits and increased concentrations of Cl, N, and P in leaves, confirming earlier conclusions on improved P mobilization and uptake under pulsed irrigation.

The increasing reuse of treated wastewater (WW) for irrigation brings with it a need to reconsider irrigation water quality criteria because of the expected lower quality of WW. In particular, the impacts of higher sodium and dissolved organic carbon (DOC) concentrations on soil permeability must be evaluated in practical field settings over long periods of WW reuse. Here we report the long-term impact of WW reuse for irrigation on soils at three different semiarid-zone field sites under row crop or orchard agriculture. The soils contain about 60% clay, dominated by smectite, and present an order of magnitude variation in calcite content (1–11%). In two of the sites, parcels irrigated with freshwater (FW) are available for comparison. Our results show an increasing sodicity hazard and a decreasing saturated soil hydraulic conductivity ( K s ) from WW irrigation, although the depth profiles of soil chemical and physical properties were highly site-specific. Despite this spatial variability, all of the data on sodicity hazard, represented by the relationship between exchangeable sodium percentage (ESP) and the soil sodium adsorption ratio (SAR), could be incorporated into a single Gapon constant for calcium–sodium exchange whose values depended uniformly on the ratio of soil DOC concentration to calcite content. Moreover, all of the data on K s , for both FW and WW irrigation, could be incorporated into a single power-law relationship involving the ratio of ESP to soil DOC. These two relationships unify complex interactions between sodicity and organic matter (OM) that influence soil permeability to yield simple correlations with predictive power. The main detrimental effect of WW application was related to sodicity hazard. Therefore, effort should be invested in reducing the SAR of WW for irrigation. This could be achieved, for example, by mixing WW with FW, including desalinized water, when and if available.

Global water resources quantities and qualities are declining, but at the same time, a strong demand for higher agricultural productivity continues to emerge due to population growth. This calls for a significant increase of irrigation and fertilization efficiencies and requires improving our understanding of the interactions between plants and their physical environment. The main objective of this study is to analyze the combined effect of varying drip irrigation management techniques and growing conditions (media properties and container volumes) on soil–plant interactions. In a series of experiments, irrigation flow rates and intervals ranging from 2 d to 10 min were applied to the vegetative stage of a test crop (bell pepper [ Capsicum annuum L. ‘Selika’]) cultivated under different growing conditions—sand and perlite in buckets, perlite in containers, and loamy sand under field conditions. Data on soil water regime, plant water uptake, and plant development were monitored in each setup. Large differences were observed both in terms of root and canopy development in response to the different application rates and frequencies. The prevailing irrigation management reflects on the soil water content dynamics, and consequently, on the plant water uptake and growth. Sap flow rates measurements indicated that higher irrigation frequency or lower water application rates increased plant water uptake rates. However, in most of the cases (except for the sand) it also led to a lower root mass and a smaller root mass/leaf area ratio. Interestingly, in the single plant per bucket experiments, a larger leaf area seemed conditioned on a larger root mass, while the opposite was the case in those two experiments where plants were grown in rows (perlite in containers and loamy sand field), where most prolific canopy development was supported by the smallest root mass. Integrating findings across the different experiments, we introduce the concept of mean daily available water volume per plant as the product of container/bucket volume and mean daily water content in the medium to express the joint effect of constraints imposed by the physical volume of growing medium and their specific hydraulic properties. Mean daily available water volume per plant was found to be positively correlated with the dry root mass to leaf area ratio.

[1] The increasing demand for freshwater (FW) for domestic use turns treated wastewater (WW) into an attractive source of water for irrigated agriculture. The main goal of this study was to evaluate the impact of 15 yrs of irrigation with WW on hydraulic properties and flow processes in a clayey soil, compared to FW use. It also quantitatively addressed the distribution with depth along the soil profile of that impact on soil hydraulic properties. Standard methods used in soil physics at the laboratory scale, and numerical solutions of the flow equations on the basis of HYDRUS, were applied to define fundamental soil hydraulic properties of disturbed soil samples from 0–20, 20–40, and 40–60 cm layers in the root zone. Results showed that saturated hydraulic conductivity, sorptivity, and infiltration rates are consistently lower in the WW irrigated soil samples at all depths. Water retention and hydraulic conductivity functions were affected by the use of WW, leading to a smaller, simulated-wetted volume below a dripper for the WW-irrigated soil case. These results illustrate the combined and complex effect of WW use on soil-exchangeable sodium percentage, and suggest changes in contact angle and pore size distribution. They also suggest that WW application will affect differently different zones in the soil profile, depending on irrigation management parameters and plant uptake characteristics.

[1] Reservoirs enhance availability and temporal stability of water resources, however, water losses due to evaporation may significantly reduce their operational efficiency. Studies have evaluated the efficacy of various types of chemical or physical evaporation barriers often on a qualitative basis. Certain design and maintenance advantages are offered by self-assembling modular floating covers especially for large reservoir surfaces. Evidence suggests that evaporation suppression efficiency of these floating covers is not proportional to the covered surface fraction. Capitalizing on recent experimental results carried out on small vessels, we show that evaporation suppression efficiency of floating covers in much larger reservoirs (3 to 5 order of magnitude in volume) is proportional to the square root of open area. Thermal effects of evaporation from open and partially covered surfaces on surface water temperature are proportional to evaporation rate and thus provide a potential mean for real-time monitoring of cover performance. Floating covers seem to suppress evaporation more effectively than other suspended evaporation barriers. For a fixed covered surface fraction, larger “holes” suppress evaporation more efficiently than many smaller and distributed openings. The concepts and relationships developed in this study provide quantitative means for engineering design and economical evaluation of evaporative barriers for water reservoirs in terms of cover geometry and water saving efficiency.