Crop Evapotranspiration Requirements Research Articles

Gas exchange and yield of yellow passion fruit under different irrigated depths, planting hole volumes, and hydroretentive polymer application

Passion fruit cultivation relies on irrigation to increase yields in the semiarid of northeastern Brazil. Water scarcity is one of the factors that most affect crop physiology, leading to lower yields. Therefore, this study aimed to assess the influence of planting hole volume and application of a hydroretentive polymer on physiological and productive aspects of irrigated yellow passion fruit cv. BRS GA1 in the Northeast semi-arid region of Brazil. The experiment was conducted in randomized blocks, in a split-plot design 2 × (2 × 2). Treatments consisted of irrigation depths (100% and 70% of the crop's evapotranspiration requirement - ETc), planting hole volumes (64 dm3 and 128 dm3), and soil with and without application of hydroretentive Polymer (1.5 g dm3), with four replicates and three plants per plot. The analyzed variables included chlorophyll a and b indices, gas exchange, and yellow passion fruit yield. The findings showed that hydroretentive polymer application to the soil increases chlorophyll content and gas exchange in yellow passion fruit. Moreover, photosynthetic rates were not limited by a 30% reduction in irrigation depth and increased in plants grown in 128-dm3 planting holes with hydroretentive polymer. Based on yield results, irrigation depths can be reduced to 70% of the ETc by applying hydroretentive polymer in 64-dm3 planting holes.

Evaluating deficit irrigation scheduling strategies to improve yield and water productivity of maize in arid environment using simulation

Water scarcity and rising temperatures are creating serious concerns over the sustainability of agriculture systems in arid regions of the Middle East and North Africa. The aims were (i) to calibrate and evaluate the Decision Support System for Agrotechnology Transfer (DSSAT) model using detailed experimental datasets on maize (Zea mays L.) yield and water productivity in an arid Mediterranean environment and (ii) to determine the impacts of various irrigation scheduling strategies on maize yield and water productivity in arid sandy soils and produce irrigation scheduling recommendations that maximize the marginal benefit per unit water applied. The goodness-of-fit statistics comparing the observed and simulated crop phenology, grain yield, dry matter, evapotranspiration (ET), and soil water content indicate that the model simulates these crop and soil variables reasonably well for a medium-maturity maize hybrid (~ 110 days to physiological maturity) commonly grown in the study region. Long-term simulations (1984–2018) using the well-calibrated model were performed and included three irrigation scheduling strategies: (i) soil water-based irrigation scheduling, (ii) ET-based threshold irrigation scheduling, and (iii) growth-stage ET-based irrigation scheduling. In the soil water-based, four levels of maximum allowable depletion (MAD) of available soil water content (AWC) were tested using the auto-irrigation option of DSSAT. Results indicated that MAD 50% is recommended for scheduling irrigation in arid sandy soils for potential irrigation water saving without unacceptable yield loss. The ET-based threshold consisted of a combination of four cumulative net ET threshold (ETH) triggers of 14, 21, 28, and 35 mm and five ET replacement levels of 50%, 70%, 90%, 110%, and 130% ET using the DSSAT ET-based auto-irrigation option. Based on this irrigation strategy, it is more favorable to irrigate at the high frequency of ETH 14 or 21 mm than low frequency of ETH 35 mm, even when replacing 130% ET, as high drought-stress during the crop development and reproductive stages were observed for ETH 35 mm due to the omission of key irrigation events. In the growth-stage ET-based, two levels of irrigation of 100% ET and 60% ET estimated based on the crop coefficient approach were tested with different combinations of targets during the vegetative and reproductive growth stages. Results indicated that meeting crop ET requirements during the reproductive stage is more essential than during the vegetative stage for greater yield and enhanced WUE, particularly when available seasonal irrigation water is less than seasonal full crop ET requirements. In water limited environments, reasonable yield and enhanced WUE can be achieved by applying a deficit rate of 40% ET during the vegetative stage and 80% ET during the reproductive stage or scheduling irrigation based on soil water content to ensure AWC of 30% in the top 0–30 cm soil layer throughout the growing season. Concepts developed in the present study can be adapted to effectively manage irrigation scheduling for medium-maturity maize hybrids in arid sandy soils with low AWC and organic C content.

Comparative evaluation of actual evapotranspiration of capsicum inside and outside of naturally ventilated polyhouse

This study was conducted to study the relationship between capsicum crop evapotranspiration inside (ETCin) and crop evapotranspiration outside (ETCout) the naturally ventilated polyhouse (NVPH) using meteorological parameters. Polyhouse has a straightway impact on air temperature and relative humidity while it indirectly influences soil temperature and soil moisture inside the structure. Under this study, crop evapotranspiration was estimated by conventional method i.e., obtaining reference evapotranspiration from weather data recorded inside the polyhouse and multiplying it with crop coefficient values of capsicum crop. Reference crop evapotranspiration inside and outside the polyhouse found as 745.19 mm and 590.22 mm, respectively whereas capsicum crop evapotranspiration inside and outside the polyhouse was 868.40 mm and 694.16 mm, respectively. The results of the study revealed that the relationship between weekly ETCin and ETCout can be expressed mathematically as ETCin = 0.84 ETCout. This implies that, there was approximately 15 % lower crop evapotranspiration requirement for the capsicum crop inside the naturally ventilated polyhouse as compared to outside the polyhouse.

Simulated deficit irrigation and climate change effects on sunflower production in Eastern Colorado with CSM-CROPGRO-Sunflower in RZWQM2

Sunflower (Helianthus annuus L.) has been used as an alternative summer crop in the traditional wheat (Triticum aestivum L.)-fallow rotation in the Great Plains of the USA. However, few studies have been conducted to quantify sunflower productivity and water productivity (WP) under semi-arid conditions and projected climate change. Experiments were conducted in 2008, 2010, and 2011 on sunflowers under deficit irrigation to meet a fraction of crop evapotranspiration (ETc) as estimated by FAO-56 in eastern Colorado. The field data was used to calibrate and validate the CSM-CROPGRO-Sunflower model that is incorporated in the Root Zone Water Qualify Model (RZWQM2). The calibrated model was then used to simulate sunflower production under projected climate conditions with four Representative Concentration Pathways (RCP) scenarios (2.6, 4.5, 6.0, and 8.5) and four irrigation levels (100%, 60%, 40% ETc and rainfed) in the late 21st century. The results showed that the model was able to adequately simulate sunflower biomass, yield, and soil water storage under the different irrigation treatments in all three years. The corresponding relative root mean square deviation (RRMSD) values were between 0.05 and 0.15 for the simulations of soil water storage, yield, and biomass. Under future climate change conditions, the model simulated greater impact of irrigation treatments than RCP scenarios on sunflower production. For example, yield was 3251.3, 2638.85 and 1937.17 kg ha−1 with 100%, 60% and 40% ETc irrigation under baseline (1992–2013) and was 2932.47, 2360.53 and 1810.65 kg ha−1 with these irrigation treatments under RCP8.5 (2070–2091). Simulation results also showed that scheduling irrigations based on 60% of ETc was the best choice for sunflower WP in eastern Colorado. Climate change did not affect sunflower biomass, yield, and WP. There was an increasing trend of irrigation amount was simulated from the baseline to RCP8.5 scenario to maintain a certain percent of ETc due to high temperature projected. For instance, the irrigation amount for 100%, 60% and 40% of ETc irrigation treatment was 16.4%, 17.3%, and 20.0% higher under RCP8.5 than those under baseline conditions with CO2 fertilization. Finally, our results demonstrated that RZWQM2 can be used to effectively schedule sunflower irrigations based on crop evapotranspiration requirement.

Deficit irrigation and surface residue cover effects on dry bean yield, in-season soil water content and irrigation water use efficiency in western Nebraska high plains

Considering ground water pumping restrictions and unpredictable amount of water available for irrigation from year to year, Nebraska Panhandle producers are facing a challenge to reduce their irrigation water usage and practice deficit irrigation. Among irrigated crops in the region, dry bean (a major cash crop and critical to crop rotation systems) has relatively low water use and is capable to withstand periods of stress. Consequently, two experiments within six consecutive growing seasons (2010–2015) were conducted to determine the impacts of multiple irrigation scenarios (full irrigation, deficit irrigation, and rainfed) and two soil surface conditions (bare soil versus crop residue) on dry bean production, irrigation water use efficiency, and temporal soil water dynamic within the crop root zone. Dry bean yield ranged from 0.41 to 4.07 Mg ha−1 during the six years of the study (2010–2015). The results (2012–2015) indicated that reducing irrigation water by 25% on average increased irrigation water use efficiency (IWUE) by 26% and only caused 6% yield reduction in relative to the full irrigation treatment scenario. However, applying only 50% crop evapotranspiration requirement (ETc) resulted in significant yield reduction (30% reduction on average) in 5 out of 6 years compared to the full irrigation treatment (p < 0.05). Our results indicate that temporal in-season rainfall and ETc demand variabilities along with the per-season soil water content status should be carefully analyzed in order to target the appropriate growth stage(s) for more severe deficit irrigation scenarios. When pre and early season rainfall was abundant deficit irrigation treatments imposed before flowering outperformed treatments targeting after flowering. However, under normal and dry conditions yield decline was more pronounced due to severe early season (before flowering) water stress compared to late season (after flowering) water stress. In two of three years plots with bare soil significantly (p < 0.05) outyielded plots covered with residue. Average yield across irrigation treatments was 14% lower for plots with residue cover (average yield: 2.15 Mg ha−1) compared to bare soil plots (average yield: 2.51 Mg ha−1). Overall, the dynamic of soil water content within root zone and IWUE in plots covered with residue was similar to that in bare soil plots across irrigation treatments throughout the growing seasons.

Supplemental Irrigation for Grain Sorghum Production in the U.S. Eastern Coastal Plain

Abstract. Grain sorghum is one of the top five cereal crops and an important grain crop throughout the world. It is generally considered more drought tolerant compared to other grain crops such as maize. Recently, in the U.S. eastern Coastal Plain region, there was an emphasis on increasing regional grain production in which grain sorghum played an important role. The region’s soils have low water holding capacities that combined with high rainfall variability cause crops frequently to be exposed to water stress. In this research, an experiment was conducted to evaluate the yield response of two grain sorghum varieties at different supplemental irrigation depths and three nitrogen levels. During our 3-year study, seasonal rainfall was adequate to produce acceptable grain sorghum yields. Seasonal rainfall ranged from 421, 365, and 357 mm in 2012, 2013, and 2014, respectively. These rainfall amounts were greater than the seasonal calculated crop evapotranspiration requirement, but rainfall distribution was not adequate to maintain acceptable soil water potentials throughout the growing season. Supplemental irrigation was 51, 38, and 13 mm in 2012, 2013, and 2014, respectively, to maintain soil water potential above -30 kPa. These irrigation amounts did not increase grain sorghum yields. No significant differences were found in grain yield between the two sorghum varieties or for increasing nitrogen applications. This lack of response to nitrogen applications may have been related to adequate supplies in the soil from previous crops. Results from this study suggest that there would be little benefit for supplemental irrigation for sorghum production in the U.S. eastern Coastal Plain. Keywords: Keyword. Grain sorghum, Irrigation, Irrigation management.

Effects of lateral depth and irrigation level on nitrate and Escherichia coli leaching in the North China Plain for subsurface drip irrigation applying sewage effluent

Subsurface drip irrigation is a sound method to apply sewage effluent, but there is a risk of nitrate and pathogen leaching. Field experiments were conducted during the maize growing seasons of 2014 and 2015 in the North China Plain to investigate the effects of lateral depth, irrigation level, and water quality on the deep percolation and the nitrate (NO3–N) and Escherichia coli (E. coli) leaching under semi-humid conditions. The experiments were designed with three lateral depths of 0 cm (D1), 15 cm (D2), and 30 cm (D3) beneath the soil surface along with three irrigation levels of 70% (I1), 100% (I2), and 130% (I3) of crop evapotranspiration requirements. Secondary sewage effluent and groundwater were used as irrigation water. The results indicated that the intensive rainfall caused most of the deep percolation and NO3–N leaching during the maize growing seasons. A high irrigation level usually produced more deep percolation and NO3–N leaching, but no significant difference was found among the treatments. In general, the cumulative NO3–N leaching beyond the root zone increased as lateral depth increased. In addition, the lateral depth obviously influenced the distribution of E. coli in soil, and subsurface drip irrigation usually induced E. coli contamination deeper in the soil. With relatively high nitrate and E. coli concentration, sewage effluent irrigation significantly increased the risk of NO3–N leaching beyond the root zone in the 2014 season, but imposed an insignificant influence on the presence of E. coli in soil. Furthermore, no E. coli was detected in the leachate following an irrigation event with sewage effluent or a rainfall event during the both maize growing seasons. A dripline depth of 15 cm with deficit irrigation can be conductive to reducing NO3 leaching as well as avoiding sewage effluent contact contamination during the maize growing season in the semi-humid region of the North China Plain.

Carbon dioxide emission in relation with irrigation and organic amendments from a sweet corn field

ABSTRACTSoil moisture and organic matter level affects soil respiration and microbial activities, which in turn impact greenhouse gas (GHG) emissions. This study was conducted to evaluate the effect of irrigation levels (75% [deficit], 100% [full], and 125% [excess] of reference crop evapotranspiration requirements), and organic amendments (OA) type (chicken manure [CM] and bone meal [BM]) and OA application rates (0,168, 336 and 672 kg total N ha−1) on (i) soil physical properties (bulk density, organic matter content and soil moisture content) and (ii) soil carbon dioxide (CO2) emissions from a highly weathered tropical Hawai'ian soil. Carbon dioxide readings were consistently taken once or twice a week for the duration of the cropping season. A drip irrigation system was used to apply the appropriate amount of irrigation water to the treatment plots. Treatments were randomly selected and corresponding organic amendments were manually incorporated into the soil. Plots were cultivated with sweet corn (Zea mays ‘SS-16’). Soil moisture content within and below the rootzone was monitored using a TDR 300 soil moisture sensor (Spectrum Technologies, Inc., Plainfield, IL, USA) connected with 12 cm long prongs. Soil bulk density and organic matter content were determined at the end of the cropping season. Analysis of variance results revealed that OA type, rate, and their interaction had significant effect on soil CO2 flux (P < 0.05). Among the OA rates, all CM mostly resulted in significantly higher soil CO2 fluxes compared to BM and control treatment (p < 0.05). The two highest rates of BM treatment were not significantly different from the control with regard to soil CO2 flux. In addition, organic amendments affected soil moisture dynamics during the crop growing season and organic matter content measured after the crop harvest. While additional studies are needed to further investigate the effect of irrigation levels on soil CO2 flux, it is recommended that in order to minimize soil CO2 emissions, BM soil amendments could be a potential option to reduce soil CO2 fluxes from agricultural fields similar to the one used in this study.

Long-term simulation of growth stage-based irrigation scheduling in maize under various water constraints in Colorado, USA

Due to varying crop responses to water stress at different growth stages, scheduling irrigation is a challenge for farmers, especially when water availability varies on a monthly, seasonal and yearly basis. The objective of this study was to optimize irrigation between the vegetative (V) and reproductive (R) phases of maize under different available water levels in Colorado. Long-term (1992–2013) scenarios simulated with the calibrated Root Zone Water Quality Model were designed to meet 40%–100% of crop evapotranspiration (ET) requirements at V and R phases, subject to seasonal water availabilities (300, 400, 500 mm, and no water limit), with and without monthly limits (total of 112 scenarios). The most suitable irrigation between V and R phases of maize was identified as 60/100, 80/100, and 100/100 of crop ET requirement for the 300, 400, 500 mm water available, respectively, based on the simulations from 1992 to 2013. When a monthly water limit was imposed, the corresponding suitable irrigation targets between V and R stages were 60/100, 100/100, and 100/100 of crop ET requirement for the above three seasonal water availabilities, respectively. Irrigation targets for producing higher crop yield with reduced risk of poor yield were discussed for projected five-year water availabilities.

A MODEL FOR PREDICTING DIAMETER OF 'RED SENSATION' PEARS

A MODEL FOR PREDICTING DIAMETER OF 'RED SENSATION' PEARS

Irrigation recommendation in a semi-arid drip-irrigated artichoke orchard using a one-dimensional monthly transient-state model

Irrigation in semi-arid areas can be optimally scheduled using models that maximize accuracy while minimizing data requirements. In this work, the validation of the one-dimensional transient-state SALTIRSOIL_M model able to monthly simulate the soil water content (θ), downward water flux (D), and the electrical conductivity in the saturation extract (ECe) is presented. The θ and the ECe were monthly monitored at 15 and 45cm depth in a plot in commercial production of globe artichoke under semi-arid climate and drip-irrigation in SE Spain during the 2011–2012 growing season. Data on water quality, weather, irrigation management, crop development and soil were also collected and used to simulate the θ, D, and ECe throughout the growing season at both depths with the SALTIRSOIL_M model. Reference and simulations of θ and D reasonably agreed with one another at both depths. ECe at 45cm depth was estimated correctly enough by the model but was underestimated at 15cm depth. The higher concentrations of nitrate, potassium, and hence other cations, which were observed at 15cm as a consequence of fertilization could explain this. The model was subsequently used to estimate the optimum water management in the plot. Use of 325–450mmyr−1 instead of 694mmyr−1, and by means of evenly distributed pulse irrigations instead of continuous ones, would have met the crop evapotranspiration requirements while avoiding excessive drainage, and maintaining soil salinity well below damaging values.

IRRIGATION MANAGEMENT EFFECTS ON YIELD AND FRUIT QUALITY OF HIGHBUSH BLUEBERRY

A study was done to determine the effects of irrigation method and level of water application on yield and fruit quality of 'Elliott' highbush blueberry (Vaccinium corymbosum L.). Plants were grown on mulched, raised beds and irrigated by overhead sprinklers, microsprays, or drip at 50, 100, and 150% of the crop evapotranspiration requirement (ETc). Overall, marketable yield and individual berry weight were higher in plants irrigated by drip than in those irrigated by sprinklers and microsprays. Yield and berry weight were also higher on average when plants were irrigated at 100% ETc than at 50% ETc but were similar between plants irrigated at 100% and 150% ETc. Thus, as expected, plants were generally under-irrigated at 50% ETc and over-irrigated at 150% ETc; however, this was not always the case. Yield did not increase between 50% and 100% ETc when plants were irrigated by drip, and berry weight increased from 100% to 150% ETc when plants were irrigated by microsprays. Interestingly, drip reduced berry firmness and soluble solids relative to sprinkler and microspray irrigation, potentially increasing problems with soft fruit during shipping and storage. Titratable acidity was also lower with drip but only when plants were irrigated at 50% ETc. While irrigation method and the amount of water application affected yield and fruit quality in blueberry, more work is needed to identify the best combinations of each to produce the most marketable fruit.

Implications of Irrigation Method and Amount of Water Application on Phytophthora and Pythium Infection and Severity of Root Rot in Highbush Blueberry

A 2-year study was done in Oregon to determine the effects of irrigation method and level of water application on the development of root rot in northern highbush blueberry (Vaccinium corymbosum L. ‘Duke’). Plants were grown on mulched, raised beds and irrigated by overhead sprinklers, microsprays, or drip at 50%, 100%, and 150% of the estimated crop evapotranspiration requirement. Soil at the site was a silty clay loam. By the end of the first season, plants were largest with drip, intermediate-sized with microsprays and smallest with sprinklers; however, this was not the case the next season. By the end of year 2, plants irrigated by drip had less canopy cover, fewer new canes, lower pruning weights, and only half the shoot and root dry weight as plants irrigated by sprinklers or microsprays. Destructive sampling revealed that the field was infested by root rot. Less growth with drip was association with higher levels of infection by the root pathogen, Phytophthora cinnamomi. Phytophthora infection increased with water application, regardless of irrigation method, but averaged 14% with drip and only 7% with sprinklers and microsprays. Roots were also infected by Pythium spp. Pythium infection likewise increased with the total amount of water applied but, unlike P. cinnamomi, was similar among irrigation methods. Overall, drip irrigation maintained higher soil water content near the base of the plants than sprinklers and microsprays, resulting in conditions more favorable to root rot. Sprinklers and microsprays may be better alternatives than drip at sites prone to problems with the disease.

Long-Term Response of Corn to Limited Irrigation and Crop Rotations

Dwindling water supplies for irrigation are prompting alternative management choices by irrigators. Limited irrigation, where less water is applied than full crop demand, may be a viable approach. Application of limited irrigation to corn was examined in this research. Corn was grown in crop rotations with dryland, limited irrigation, or full irrigation management from 1985 to 1999. Crop rotations included corn following corn (continuous corn), corn following wheat, followed by soybean (wheat-corn-soybean), and corn following soybean (corn-soybean). Full irrigation was managed to meet crop evapotranspiration requirements (ETc). Limited irrigation was managed with a seasonal target of no more than 150 mm applied. Precipitation patterns influenced the outcomes of measured parameters. Dryland yields had the most variation, while fully irrigated yields varied the least. Limited irrigation yields were 80% to 90% of fully irrigated yields, but the limited irrigation plots received about half the applied water. Grain yields were significantly different among irrigation treatments. Yields were not significantly different among rotation treatments for all years and water treatments. For soil water parameters, more statistical differences were detected among the water management treatments than among the crop rotation treatments. Economic projections of these management practices showed that full irrigation produced the most income if water was available. Limited irrigation increased income significantly from dryland management.

Drip Irrigation Configuration Influences Growth in Young Highbush Blueberries

A study was done to determine the effects of irrigation with different drip configurations on growth of newly planted highbush blueberries (Vaccinium corymbosum L. `Duke'). Plants were grown on raised beds mulched with sawdust. Different configurations included two laterals of drip tubing placed on the soil surface on each side of the plants, two laterals buried 0.1 m deep on each side of the plants, and one lateral suspended 1.2 m above the plants. Each treatment was irrigated three times per week (when needed) with enough water to replace 100% of the estimated crop evapotranspiration requirements. During the first 2 years after planting, plants irrigated by buried drip were larger and produced significantly more whips than those irrigated by drip placed at the soil surface. The size and whip number of those irrigated by suspended drip were intermediate. Subsurface drip eliminated water runoff and bed erosion observed with both surface drip configurations. It also maintained lower soil water content near the plant crown. Since plants tested positive for phytophthora and pythium root rot, lower soil water content may have reduced problems with the disease. As plants mature, the next objective will be to determine the effects of each drip configuration on fruit production.

New crop coefficients developed for high-yield processing tomatoes

Processing tomato yields have increased by 53% over the past 35 years, but the current seasonal crop-evapotranspiration requirements that growers use to schedule irrigation are based on 1970s-era data. We updated this data and developed new crop coefficients for processing tomatoes using the Bowen ratio energy balance method in eight commercial fields from 2001 to 2004. Today's evapotranspiration rates are similar to those of the early 1970s, indicating a substantial increase in water-use efficiency by processing tomatoes during the past 35 years. In addition, we collected data in both furrow- and drip-irrigated fields, but no statistical differences were found between them.

Crop evapotranspiration of processing tomato in the San Joaquin Valley of California, USA

Yield of processing tomato has increased by 53% over the past 35 years. Thus, concerns exist about the current seasonal crop evapotranspiration requirements of processing tomato compared to the past published requirements, which were about 645 mm. Also, the mid-season crop coefficient for processing tomato developed 35 years ago with sprinkler irrigation was 1.25, while a mid-season coefficient developed 20 years ago with subsurface drip irrigation was 1.05. Because of the age and variability of crop coefficients and the long-term yield increase, a study was conducted to determine the seasonal crop evapotranspiration and crop coefficients of processing tomatoes using the Bowen ratio energy balance method in eight commercial fields from 2001 to 2004. Measurements were made in both furrow- and drip-irrigated fields. Results showed seasonal crop evapotranspiration to range from 528 to 752 mm with an average of 648 mm. No statistical differences were found between furrow and drip irrigation. Mid-season crop coefficients varied between 0.96 and 1.09 with statistically similar values between furrow- and drip-irrigation for a given year. Current evapotranspiration rates were similar to those of the early 1970s, indicating that the water use efficiency of processing tomato increased substantially with time during the past 35 years.

Soil Salinity under Traditional and Improved Irrigation Schedules in Central Spain

Traditional irrigation management in some semiarid zones waste water relative to crop evapotranspiration requirements. Improved irrigation schedules (irrigation depths were adjusted to seasonal crop consumption), however, may reduce deep percolation and fail to provide adequate leaching of salts. We hypothesized that salt discharge induced by rainfall may partially offset the need for a larger leaching fraction from irrigation water. The experiment was conducted near Madrid, Spain, on a sandy loam Typic Xerofluvent, between February 1993 and May 1997. The crop sequence was corn–wheat–corn–oat (Zea mays L.–Triticum aestivum L.–Z. mays L.–Avena sativa L.), and the irrigation treatments were applied only to corn. The salt concentration of the irrigation water was monitored 23 times in 24 plots and that of the soil solution at 0.5‐m, 0.9‐m, and 1.4‐m depths was monitored 61 times. Net salt losses (salt input through irrigation minus salt removed through drainage) were 1 and 0.64 kg m−2, respectively. In plots under the improved irrigation schedule, 88% of salt discharge occurred after periods of heavier‐than‐usual rainfall against 55% in traditionally irrigated plots. During the experiment, mean electrical conductivity (EC) of the soil solution in the top 0.5 m of soil was 0.61 ± 0.26 S m−1 in plots with the improved irrigation schedule. The corresponding estimate of the EC of the saturated paste extract was 0.34 S m−1, lower than the reported threshold value for corn (0.5 S m−1). These methods can therefore be recommended for semiarid areas where occasional heavy rainfall will remove some of the accumulated salt.

Management of domestic wastewater for reuse in irrigation

Treated effluent from an aerated lagoon and facultative pond system in southern Portugal, was used to irrigate fields planted to maize (Zea mays L.). The effluent was characterised with respect to its nitrogen and phosphorus content and applied by drip irrigation in response to crop evapotranspiration requirements. Nitrification of ammonia in the effluent by soil microorganisms caused a reduced soil pH early in the growing season, but this was reversed as the season continued. For most of the growth season plant nitrogen demand ensured a low soil nitrogen concentration, but towards the end of plant growth the continuous nitrogen supplied in the effluent exceeded crop requirements with a result that nitrate accumulated in the soil. The applied effluent also had a high phosphorus concentration but there was only a slight accumulation of this in the soil. The fertiliser value of the treated effluent was demonstrated by increased yields at physiological maturity and the N yield was within the range of expected values for this crop. The main removal mechanism for N during irrigation was crop uptake whereas P was removed primarily by soil processes. The advantages of wastewater reuse together with the importance of appropriate management practices for re-use are discussed.

Management of domestic wastewater for reuse in irrigation

Treated effluent from an aerated lagoon and facultative pond system in southern Portugal, was used to irrigate fields planted to maize (Zea mays L.). The effluent was characterised with respect to its nitrogen and phosphorus content and applied by drip irrigation in response to crop evapotranspiration requirements. Nitrification of ammonia in the effluent by soil microorganisms caused a reduced soil pH early in the growing season, but this was reversed as the season continued. For most of the growth season plant nitrogen demand ensured a low soil nitrogen concentration, but towards the end of plant growth the continuous nitrogen supplied in the effluent exceeded crop requirements with a result that nitrate accumulated in the soil. The applied effluent also had a high phosphorus concentration but there was only a slight accumulation of this in the soil. The fertiliser value of the treated effluent was demonstrated by increased yields at physiological maturity and the N yield was within the range of expected values for this crop. The main removal mechanism for N during irrigation was crop uptake whereas P was removed primarily by soil processes. The advantages of wastewater reuse together with the importance of appropriate management practices for re-use are discussed.