High Frequency Irrigation Research Articles

Soil Gaseous Carbon Emissions from Lettuce Fields as Influenced by Different Irrigation Lower Limits and Methods

Lettuce is a water-sensitive stem-used plant, and its rapid growth process causes significant disturbances to the soil. Few studies have focused on the gaseous carbon emissions from lettuce fields under different irrigation methods. Therefore, this study investigated the effect of different drip-irrigation lower limits and methods (drip and furrow irrigation) on greenhouse gas (CO2, CH4) emissions from lettuce fields. Thus, drip irrigation (DI) was implemented using three different lower limits of irrigation corresponding to 75%, 65%, and 55% of the field capacity, and named DR1, DR2, and DR3, respectively. Furrow irrigation (FI) was used as a control treatment. The CO2 and CH4 emission fluxes, soil temperature, and soil enzyme activities were detected. The results showed that the cumulative CO2 emission was highest under DR3 and relatively lower under DR1. For the FI treatment, the cumulative CO2 emission (382.7 g C m−2) was higher than that under DR1 but 20.2% lower than that under DR2. The cumulative CH4 emissions under FI (0.012 g C m−2) were the greatest in the whole lettuce growth period, while DR2 and DR3 treatments emitted lower amounts of CH4. The irrigation method considerably enhanced the activity of urease and catalase, meanwhile promoting CO2 emission. The low irrigation amount each time combined with high irrigation frequency reduced soil CO2 emission while increasing CH4 emission. From the perspective of the total reduction of gaseous carbon, DR1 is the optimal drip irrigation method among all the irrigation lower limits and methods.

Soil legacies of tree species richness in a young plantation do not modulate tree seedling response to watering regime.

Trees have a strong and species-specific influence on biotic and abiotic properties of the soil. Even after the vegetation is removed, the effect can persist to form so-called soil legacies. We investigated the effects of soil legacies of tree species richness on the emergence and growth of tree seedlings, and how these legacy effects modulate the seedling responses to irrigation frequency. We used a 9-year-old tree plantation on former agricultural land in Belgium, which is part of a biodiversity-ecosystem functioning experiment (FORBIO). Soil originating from monocultures and four-species plots, with different species combinations, was translocated to a greenhouse. Five tree species (Betula pendula, Fagus sylvatica, Pinus sylvestris, Quercus robur, and Tilia cordata) were sown and grown for one growing season in these soils. We performed a watering treatment (low and high irrigation frequency) to measure any potential interaction effects between the soil legacies and irrigation frequency. There was no evidence for soil legacy effects of species richness on plant performance or their response to the irrigation frequency. However, the effect of irrigation frequency was dependent on species identity of the tree seedlings. Despite the lack of clear legacy effects, performance measures did show correlated responses that are likely due to species composition effects. We ascribe these patterns to the young age of the forest and the agricultural past land use. At this early stage in forest development, the land-use history likely has a more important role in shaping soil characteristics that affect plant growth and their response to drought, than species diversity.

Climate-ready Landscape Plants: Garden Roses Trialed at Reduced Irrigation Frequency in Utah, USA

Increased urban and suburban populations in the arid western United States have resulted in more water demand; however, water availability in the region has become limited because of inadequate precipitation. Recent droughts have led to restrictions on irrigating landscape plants. Garden rose (Rosa ×hybrida) is commonly used as flowering plants in residential landscapes, but its drought tolerance has not been widely studied. The objective of this study was to determine the impact of reduced irrigation frequency on visual quality, plant growth, and physiology of five garden rose cultivars, including ChewPatout (Oso Easy® Urban Legend®), Meibenbino (Petite Knock Out®), MEIRIFTDAY (Oso Easy® Double Pink), Overedclimb (Cherry Frost™), and Radbeauty (Sitting Pretty™). Twenty-four plants of each rose cultivar were established in a trial plot at Utah Agricultural Experiment Station Greenville Research Farm (North Logan, UT, USA) in Summer 2021. Plants were randomly assigned to one of three deficit irrigation treatments for which irrigation frequencies were calculated using 80% reference evapotranspiration (ETO) (high), 50% ETO (medium), and 20% ETO (low). The total volumes of irrigation water applied to each plant were 345.6, 172.8, and 43.2 L for the high, medium, and low irrigation frequencies, respectively, during the deficit irrigation trial from 12 May to 30 Sep 2022. Root zones were wetted more frequently as irrigation frequency increased from low to high irrigation frequencies. Decreased irrigation frequency increased the number of visibly wilted and damaged leaves on all rose cultivars. However, only ‘Meibenbino’ and ‘MEIRIFTDAY’ exhibited a reduction in overall appearance under decreased irrigation frequency. The relative growth indices of both ‘Meibenbino’ and ‘MEIRIFTDAY’ decreased by 6%, whereas the dry weights of their leaves decreased by 37% and 36%, respectively, as irrigation decreased from high to low frequencies. Roses in this study appeared to decrease stomatal conductance up to 51% when irrigation decreased from high to low frequencies, or when air temperature increased. ‘Meibenbino’ and ‘MEIRIFTDAY’ exhibited unacceptable overall appearance, growth reduction, and higher leaf–air temperature differences, and they were less tolerant to reduced irrigation. Although the ‘Radbeauty’ maintained plant growth under the reduced irrigation frequency, the large leaf size led to a more visibly wilted appearance and the potential for heat stress, thus impairing visual quality. ‘ChewPatout’ and ‘Overedclimb’ were most tolerant to deficit irrigation at 20% ETO and maintained plant growth with acceptable visual quality and lower leaf temperatures when they received one irrigation during the growing season.

Assessing the performance of wheat (Triticum aestivumL.) crop by managing irrigation and nitrogen fertilizer under a semi-arid environment

AbstractUnderstanding the linkage between crop yields, irrigation frequencies, and fertilizer rates is crucial in region-specific agriculture practices. The present study was conducted to assess the effect of nitrogen fertilizer rates and irrigation frequency on wheat crop growth and yield in the semi-arid region of Rajasthan, India. The experiment was laid out in a randomized complete block design with 12 treatments with 4 replicas, combining 4 nitrogen fertilizers quantities (0%, 50%, 100%, and 125% of recommended dose) with 3 irrigation intervals (15, 21, and 25 days after sowing) were used for three consecutive years (2014-15, 2015-16 and 2016-17). Crop responses were recorded for different growth stages. One-way analysis of variance and Fisher's least significant difference tests were applied to determine significant changes in yield. The results showed that the high irrigation frequency and high fertilizer application significantly increased crop growth and yields. Yields observed in the first year of the experiment were higher than those in the second and third years in most treatments. The results showed that water and fertilizer are the key factors that can affect wheat yield in the semi- arid region of Rajasthan and should be managed according to soil and irrigation availability.

Irrigation and Phosphorus Management of Alfalfa Under Semi-Arid Conditions

The frequency of irrigation and deficit irrigation management are drawing attention because water resources are becoming limited year by year, especially in the last decade. Besides, the rate and application time of P fertilization gained more importance just after the researchers found out it is more effective than N-fertilizing for alfalfa cultivation. This study aimed to determine the effects of different irrigation managements (seasonal deficit, intervals of 5, 7, and 9 days), phosphorus application season (autumn and spring), and the rate of P fertilizer (0, 30, 60, 90 kg ha-1) on the yield and forage quality of alfalfa. The experiment was conducted in the 2019-2020 years, which was the 3rd and the 4th years of alfalfa respectively, under semi-arid Mediterranean conditions. The stand height and fiber content (NDF) were higher in the autumn application. However, forage contained more nitrogen in the spring application. A higher amount of water (800 mm) with higher irrigation frequency (5 days – I5d) caused a reduction in yield due to water excess. The yield was the highest (21.34 t ha-1) and the forage quality was better in 448 mm water application with 9 days intervals (I9d). Seasonal deficit water management caused a significant loss in yield and quality. Nevertheless, 18.04 t ha-1 dry matter yield with 24.05 % CP content was recorded at seasonal deficit water management. P fertilization increased the yield and forage quality. The yield was the highest (20.23 t ha-1) at the rate of 90 kg ha-1 P fertilizer, but yield and forage quality characteristics were similar between 30, 60, and 90 kg ha-1 P. The results showed that P fertilization could be done in both autumn and spring at the rate of 30 kg ha-1 and 448 mm water could be applied at 9 days intervals for fulfilling performance under semi-arid Mediterranean conditions. When water resources are very scarce, the seasonal water deficit should be applied, especially in late summer.

Evaluation of irrigation frequency on pineapple plants grown in greenhouse conditions

• Seasons affect the values of all the indicators (LCI, NDVI, SDD, RWC). • The sensitivity of the non-destructive indicator is higher than the destructive. • High and medium irrigation frequency show higher conversion of water into biomass. • High frequency shows higher crop water productivity at the end of vegetative cycle. The objectives of this work are to evaluate the water status and growth variables of pineapple plants under different frequencies of irrigation to optimize the water productivity irrigation in greenhouse conditions in the subtropics. The experiment was conducted during the vegetative cycle for nine months, comparing three frequencies of irrigation: irrigation every three days (High frequency-T1), every seven days (Medium frequency-T2), and every 15 days (Low frequency-T3). The water status was measured using destructive indicators: Relative Water Content (RWC) and non-destructive indicators: Normalized Difference Vegetation Index (NDVI), Stress Degree Day (SDD), and Leaf Chlorophyll Index (LCI). Water productivity indicators (Irrigated water productivity, crop water productivity) and growth variables (plant height, maximum diameter, plant biomass, assimilate partitioning) were also measured. The environmental conditions monitored were temperature, humidity, and incident radiation. The soil moisture depletion and daily depletion rate were also registered and calculated. Destructive indicators of water status did not detect differences between irrigation treatments in this study, while non-destructive indicators statistically differentiated T1 from T3. T2 was the most appropriate irrigation treatment during the cold season. These results suggest that in greenhouse conditions in subtropical environments, a combination of high frequencies in warm seasons and medium frequencies in cold seasons would adjust irrigation management according to the pineapple crop needs, optimizing irrigation water productivity.

Simulation of temperature control and irrigation time in the production of tulips using Fuzzy logic

We are now living in the Intelligent Industry or Industry 4.0 era; therefore, it is very important its application in situations that allow us to simulate and model any necessary process. In this case, we are concerned with tulip production in a greenhouse. Tulip flowering in Holland is one of the most beautiful spring phenomena and everybody in the world is eager to reproduce it. The purpose of this research project is to simulate how to control the temperature and irrigation time in a greenhouse for tulip production in the city of Ilo, Moquegua (Peru). To this end, fuzzy logic and LabView software version 16 from National Instrument were used to simulate temperature control and irrigation time in the production, activating and deactivating the chiller when the sensor informs of any deviation above or below the set temperature (15°C) keeping it constant for the process, as well as for the irrigation variable telling the system when and for how long plants should be irrigated at high, medium or low irrigation frequencies. The expected results were obtained in the simulation to control greenhouse temperature and irrigation time, since the chiller operates activating or deactivating the system to stay at the set temperature and the irrigation time is controlled depending on humidity.

Vegetative and productive responses of tabasco pepper to fertigation and plastic mulching

The use of plastic mulching and high frequency hydroponic drip irrigation (intensive production methods) watering cycle may increase tabasco pepper crop production per unit area. To test this hypothesis, two randomized block experiments were conducted in a greenhouse, using a 2 × 4 factorial scheme with two contrasting soil types (sandy loam and loamy soil), two mulching conditions of soil cover (SC), and no soil cover (NC) at four frequencies: 1, 3, 12, and 24 irrigations every three days. The growth and yield pepper components were evaluated and the water use efficiency (WUE) was calculated. Mulching did increase fruit dry mass percentage (FDMP), WUE, and potassium use efficiency (KUE) in sandy loam soil. The greater frequency fertigation did not increase fruit fresh mass (FFM), number of fruits (NF), fruit average mass (FAM), fruit dry mass (FDM), FDMP, or WUE in sandy loam and loamy soils. Tabasco pepper has a permanent shrub growth habit that is somewhat different from horticultural crops, besides it is usually responsive to high frequency irrigation under vegetative intensive growth.

Impact of Lateral Depth and Irrigation Frequency on Inorganic Nitrogen Distribution, Yield, and Quality of Asparagus Lettuce Utilizing Sewage Effluent under Drip Irrigation

ABSTRACT The utilization of wastewater for agricultural irrigation has been widely accepted in China and other arid and semi-arid regions around the world. Effects of lateral depth and irrigation frequency on inorganic nitrogen yield and quality of Lactuca sativa var. augustana (asparagus lettuce) under drip irrigation with sewage effluent was examined in a solar-heated greenhouse in North China Plain amid two growing seasons of 2014 and 2015. Three pan coefficients of 0.6, 0.8, and 1.0 and three lateral depths of 0, 10, and 20 cm were tested during the 2014 season. In contrast, three irrigation intervals of 4, 8, and 12 days and three lateral depths similar to the 2014 season were utilized in the 2015 season. The groundwater control experiment was applied for treatments with a pan coefficient of 0.8 (2014) and irrigation intervals of 8 days (2015). A higher irrigation frequency increased the yield of asparagus lettuce, while a lower frequency was favorable to the quality parameters of vitamin C and soluble sugar. Generally, compared with surface drip irrigation, subsurface drip irrigation increased inorganic nitrogen distribution in the subsurface soil layer, and also increased the yield, vitamin C, and soluble sugar of asparagus lettuce. When asparagus lettuce was buried laterally 10 cm below the soil surface, highest yield was observed. Sewage irrigation increases the accumulation of nitrogen in the soil, and asparagus lettuce yield is higher compared to groundwater irrigation. Additionally, compared with groundwater irrigation, no destructive effect of sewage irrigation on the quality of asparagus lettuce was found.

Allometry and morphophysiology of papaya seedlings in a substrate with polymer under irrigation with saline water

The availability and quality of the irrigation water are among the limitations for the development of agriculture in the semiarid. Aiming at gathering information on these limitations, this work aimed to evaluate the association between a water-absorbing polymer and water salinity in irrigation frequencies, as well as container volumes on the allometric and morphophysiological indices of seedlings of the papaya (Carica papaya) cultivar ‘Sunrise Solo’. The treatments were obtained from the combination between the water-absorbing polymer (0.0; 0.2; 0.6; 1.0, and; 1.2 g dm-3), the electrical conductivity of the irrigation water (0.3; 1.1; 2.7; 4.3, and; 5.0 dS m-1), and irrigation frequencies (daily and alternate), plus two additional treatments (0.75 and 1.30 dm3) to study the effects of the container volume, distributed in a randomized block design. At 55 days after sowing, the following characteristics were evaluated: ratio between stem height and diameter; ratio between shoot and root dry matter; root density; leaf blade area; ratio between total leaf area and root dry mass; specific leaf area; leaf area ratio; leaf mass ratio; and Dickson quality index. The allometric and morphophysiological indices were damaged by the increase of water electrical conductivity and favored by the application of the polymer and a higher irrigation frequency. In the production of papaya seedlings, a daily irrigation frequency must be prioritized, using containers of 0.75 or 1.30 dm-3, water with electrical conductivity up to 2.6 and 1.9 dS m-1 when irrigated daily or in alternate days, respectively, and 0.6 g dm-3 of polymer.

Water and Air Relations in Propagation Substrates

Greenhouse propagation of unrooted plant cuttings is characterized by short container cell height and high irrigation frequency. These conditions can result in high moisture level and low air content in soilless container substrates (“substrates”), causing delayed growth of adventitious roots and favoring root disease. The objective of this study was to quantify and compare substrate water and air relations for three propagation substrates (peat, rockwool, and phenolic foam) that varied widely in physical characteristics using four methods: 1) evaporation method with a tensiometer, 2) frozen column method, 3) gravimetric analysis, and 4) X-ray computed tomography (CT) analysis. Moisture retention curves based on evaporation (1) and the frozen column (2) resulted in differences for peat, but similar curves for rockwool and foam. The frozen column method was simple and low cost, but was constrained by column height for peat, which had a higher water potential compared with the other two substrates. Substrate porosity analysis at container capacity by gravimetric or CT methods were similar for volumetric water and air content (VWC and VAC) in rockwool and foam, but differed for peat for VWC and VAC. Gravimetric analysis was simple, rapid, and low cost for whole-cell analysis, but CT further quantified spatial water and air relations within the cell and allowed visualization of complex water and air relations in an image. All substrates had high water content at container capacity ranging from 67% to 91% VWC with 5% to 11% VAC in the short propagation cells, emphasizing the need for careful irrigation management.

Effects of Irrigation Amount and Irrigation Frequency on Flue-Cured Tobacco Evapotranspiration and Water Use Efficiency Based on Three-Year Field Drip-Irrigated Experiments

This study aimed to determine the effect of irrigation amount and irrigation frequency on drip-irrigated flue-cured tobacco evapotranspiration (ETa), yield, and water use efficiency. Four irrigation treatment levels were imposed: 100% IRT (fully irrigated treatment, no stress), 85% IRT, 70% IRT, RFT (rainfed treatment), and high, medium, and low irrigation frequencies were set. The relationship between irrigation volume and yield is a quadratic curve. The evapotranspiration had a positive relationship with the irrigation amount. The yield of flue-cured tobacco was the highest in 2016 (wet year), and the corresponding ETa was the smallest. The irrigation water use efficiency (IWUE) in the driest year, 2017, was lower than IWUE in the wet years 2015 and 2016, and the crop water use efficiency (CWUE) had similar results for the three years. IWUE increased with irrigation amount. The effect of irrigation frequency on CWUE was not significant. The CWUE had a positive relationship with yield. No significant differences due to irrigation frequency were found for yield.

Effects of irrigation frequency of organic nutrient solution and irrigation amount on yield, quality, fertilizer and water use efficiency of melon in facility

To investigate the organic cultivation mode for high-yield and high-quality melon, we measured the growth of melon that grown in pots with different conditions of organic nutrient solution and irrigation. There were three irrigation frequencies of organic nutrient solution (8-time application, each time 750 mL per plant, F1; 12-time application, each time 500 mL per plant, F2; 16-time application, each time 375 mL per plant, F3) and two different irrigation amount per single plant (irrigating by 120% daily evapotranspiration (ET) before fruit enlargement, by 140%ET after fruit enlargement, W1; irrigating by 140%ET before fruit enlargement, by 160%ET after fruit enlargement, W2), following a randomized block trial design. The effects of those treatments on photosynthetic characteristics, yield, quality, fertilizer and water use efficiency of melon were investigated. The results showed that photosynthetic rate of melon leaves was significantly increased by more frequent and less amount of organic nutrient solution application. Fruit yield and water use efficiency were significantly improved under low irrigation condition. Fertilizer utilization was optimal under the treatments of high irrigation and medium organic nutrient solution frequency. Fruit quality was improved under less organic nutrient solution and relatively suitable water supply. A mathematical model of exponential function y=0.214e0.18x (R2=0.851) could be used to quantify the relationship between the vitamin C content of melon fruit and frequency of organic nutrient solution application. Considering the variables, such as yield, quality and water use efficiency, F3W1 treatment was recommended with the aim to improve fruit quality and optimal water use efficiency under promising yield, which could achieve high-yield and high-quality cultivation of organic melon in facilities.

Modeling dissolved organic nitrogen dynamics under different N management practices for intensive greenhouse production using an improved WHCNS_veg model

Excess dissolved organic nitrogen (DON) leaching occurs due to manure or fresh organic matter application coupled with high irrigation frequency in intensive greenhouse vegetable production systems (GVPS). Quantifying DON leaching is crucial in developing best management practices for intensive GVPS. The objectives of this study were to develop a DON leaching component for the water and N management model for greenhouse vegetables (WHCNS_veg) and to evaluate nitrate and DON leaching under different N management practices. Two seasons of tomato greenhouse experiments with several N management practices were conducted in Shouguang County, Shandong Province in China. The measured soil water content, soil nitrate and DON concentrations, and tomato yield were used to calibrate and evaluate the improved WHCNS_veg model. Results showed that the WHCNS_veg performed well in modeling soil water content, soil nitrate and DON concentrations, and tomato yield, giving normalized root mean square error values of 4.4%, 37.2%, 45.8% and 3.8%, respectively. Manure application significantly enhanced DON leaching, which accounted for 8.8% to 18.7% of the total N leaching under different N management practices. The simulated and measured tomato yield was not sensitive to different N management practices (except for the no N input treatment). However, the amounts of nitrate leaching, DON leaching, and N gas emission (NxO and NH3) under conventional N management were 2.1, 1.3, and 1.1-fold greater than those in the reduced N management treatment, respectively. Reduced N management practices should be recommended in the greenhouse tomato production in North China, which had a relatively high vegetable yield, less environmental impact, and more sustainability. Results indicated that the improved WHCNS_veg model has great potential to optimize N management and assess the environmental impact of GVPS.

Combined effects of biochar and fertilizer application on maize production in dependence on the cultivation method in a sub-humid climate

ABSTRACT Low, erratic rainfall amounts and restricted accessibility of chemical fertilizer for rural farmers in developing countries may have negative effects on crop production. Agricultural methods like biochar applications, fertilizer microdosing and tied ridging can help to mitigate these constraints, but have rarely been studied in combination and under varying water availability. A field trial was conducted in split-plot design over two contrasting cropping seasons in 2016 and 2017 in Tanzania to study the effect of these agricultural methods on maize grain yield, biomass, leaf area index, plant height and soil moisture content. In both seasons each with contrasting irrigation frequencies, fertilizer microdosing increased the grain yield of maize. Biochar alone affected the yield only at high application rates (10 t/ha) and low irrigation frequency. However, when combined with fertilizer microdosing the yield effect of biochar was more pronounced. For example, combining 5 t/ha biochar with fertilizer microdosing under flat tillage increased yield by 170% compared to the control without biochar and fertilizers. Tied ridges increased soil moisture content and tended to increase maize yield compared to flat tillage, whereas biochar application resulted in significantly higher soil moisture contents. Fertilizer microdosing with biochar application can be recommended to improve maize yields mainly under flat tillage.

The Effect of Irrigation Frequency, Phosphorus Fertigation, and Cultivar on Levels of Phenolic Compounds in Sweet Cherries

This work examined the effect of irrigation frequency and phosphorus (P) fertigation on the levels of phenolic compounds present in two sweet cherry cultivars, ‘Skeena’ and ‘Cristalina’, over three growing seasons (2012–14). Two irrigation treatments were tested: a high irrigation frequency (I1) and a low irrigation frequency (I2). Both irrigation treatments applied the same quantities of water [100% evapotranspiration (ET)], but the high irrigation frequency applied water four times daily (0300, 0900, 1500, and 2100 hr) whereas the low irrigation frequency was applied at one time (0900 hr) every second day. Three soil management treatments were investigated, including 1) an unmulched control receiving no P, 2) a 10-cm waste wood mulch receiving no P, and 3) a treatment involving annual fertigation of 20 g P/tree at full bloom as ammonium polyphosphate. It was determined that cultivar was the most important factor affecting levels of phenolic compounds in sweet cherries, with generally greater levels associated with ‘Skeena’. The effect of different irrigation and fertilization strategies showed less promising results in terms of influencing levels of phenolic compounds. Both severe and mild water stress did not show an appreciable influence on increasing levels of phenolic compounds in cherries. Furthermore, severe water stress, which occurred during 2012, was associated with the lowest annual concentration of phenolic compounds and an economically unacceptable reduction in fruit size. Phosphorus fertigation influenced cherry phosphorus status positively by increasing leaf and fruit P concentrations consistently, yet these fruit exhibited lower levels of phenolic compounds.

Sprinkler Irrigation Frequency Affects Maize Yield Depending on Irrigation Time

Core Ideas Plant Na+ content doubled with daytime sprinkler irrigation. Plant Na+ content increased by 30% with high irrigation frequency. Irrigation frequency was not relevant for nighttime sprinkler irrigation of maize. High irrigation frequency during daytime reduced maize yield and water use efficiency. Sprinkler irrigation with solid‐set systems easily allows changing irrigation frequency. We studied, under field conditions and during 3 yr, the effects of irrigation frequency (two events per week or daily) and daytime vs. nighttime irrigation on microclimatic changes, soil matric potential, growth, yield, and water use of maize (Zea mays L.). Microclimatic changes (decrease of air temperature and vapor pressure deficit, and of canopy temperature) were slightly larger and lasted for more time after the irrigation event with low frequency irrigation. Increasing irrigation frequency during daytime resulted in a lower soil matric potential. Irrigating at nighttime resulted in higher maize height (+3%) and yield (+10%) than irrigating at daytime. The high irrigation frequency decreased maize height (−7%) and yield (−5%) compared with the low irrigation frequency when irrigation was performed at daytime but not at nighttime. The Na+ content of the plant was doubled with daytime sprinkler irrigation compared with nighttime irrigation, and was increased by 30% when the irrigation frequency was increased. Water use efficiency (WUE) was not affected by irrigation frequency when irrigating at nighttime, but it decreased with the increase of irrigation frequency when irrigation was applied during daytime. Sprinkler irrigation with solid‐set must be applied at night to obtain the maximum maize yield and WUE. Irrigation frequency is not relevant for sprinkler irrigation of maize applied at night, but high irrigation frequency should be avoided when maize is sprinkler irrigated during daytime to avoid yield and WUE decreases.

Alternate partial root-zone irrigation with high irrigation frequency improves root growth and reduces unproductive water loss by apple trees in arid north-west China

Alternate partial root-zone irrigation (APRI) can improve water use efficiency in arid areas. However, the effectiveness and outcomes of different frequencies of APRI on water uptake capacity and physiological water use have not been reported. A two-year field experiment was conducted with two irrigation amounts (400 and 500 mm) and three irrigation methods (conventional irrigation, APRI with high and low frequencies). Root length density, stomatal conductance, photosynthetic rate, transpiration rate, leaf water use efficiency, midday stem and leaf water potentials were measured. The results show that in comparison with conventional irrigation, APRI with high frequency significantly increased root length density and decreased water potentials and stomatal conductance. No differences in the above indicators between the two APRI frequencies were detected. A significantly positive relationship between stomatal conductance and root length density was found under APRI. Overall, alternate partial root-zone irrigation with high frequency has a great potential to promote root growth, expand water uptake capacity and reduce unproductive water loss in the arid apple production area.

Development of an irrigation scheduling software based on model predicted crop water stress

Modern irrigation scheduling methods are generally based on sensor-monitored soil moisture regimes rather than crop water stress. Crop water stress is difficult to measure in real-time, but can be computed using agricultural system models. In this study, an irrigation scheduling method and its facilitate software based on RZWQM2 model (Root Zone Water Quality Model) predicted crop water stress were developed and evaluated. The timing of irrigation was based on the occurrence of model-simulated water stress, while the depth of irrigation was based on the fraction of the soil moisture deficit (K) needed to replenish the soil water content (θ) at any given time to field capacity (θfc), i.e., from θt0 to θt0+K(θfc-θt0). The predicted water stress for different K values was tested based on RZWQM2 scenarios calibrated against data collected in a drip-irrigated corn (Zea mays L.) field near Greeley, Colorado, USA between 2008 and 2010, and in a sprinkler irrigated soybean [Glycine max (L.) Merr.] field in Noxubee, Mississippi, USA in 2014. For the Colorado site, the simulated full irrigation (K =1) using this newly developed water stress-based irrigation approach saved 30.5%, 17.3% and 7.1% in total irrigation depth in successive years, whereas higher frequency with 60–90% of full irrigation at each event (0.6 ≤ K ≤ 0.9) provided water savings of as much as 35%, 30%, and 16%, respectively. The water stress-based irrigation scheme showed that crop yield was not affected, with a negligible change about 0.03–3.81% decrease. These water savings were a result of the water stress-based irrigation regime maintaining sufficient water to meet crop root water uptake requirements without constantly fully rehydrating the soil, thereby minimizing evaporation from the soil surface and soil water storage after grain filling. For the Mississippi site, this newly developed water stress-based irrigation software could improve crop yield by 291 kg ha−1 though consume 3.43 cm more water than field irrigation regime. Similarly, high frequency irrigation (lower K) under water stress-based regime resulted in higher water use efficiency. This study suggested that the water stress-based irrigation scheme could save water use and maintain crop yield in semi-arid region, while in humid region it could increase crop yield while consume more water. Further work is needed to install this system in an irrigated field and test its performance under different climate and soil conditions.

Effect of irrigation frequency on growth and production of a cucumber crop under soilless culture

Three irrigation frequencies were applied on a soilless cucumber crop, in a greenhouse located in the coastal area of southern Cyprus. Irrigation scheduling was based on solar radiation and performed whenever accumulated solar radiation energy outside the greenhouse reached 1.3 MJ m-2 [High Irrigation Frequency (HIF)], 1.9 MJ m-2 [Medium Irrigation Frequency (MIF)] and 3.0 MJ m-2 [Low Irrigation Frequency (LIF)]. The amount of water applied was 0.192 Kg m-2, 0.288 Kg m-2 and 0.448 Kg m-2 for high, medium and low irrigation frequencies, respectively. Appropriately, the total volume of water applied was identical in each of the three cases. In order to study the effects of irrigation frequency on cucumber crops, multiple measurements were taken; the fresh and dry weight of plant organs (i.e. leaves, stem and fruit), marketable fresh yield production, and microclimate variables for a 75 day period, beginning in April and ending in June. The results revealed that the irrigation frequency did not influence the cucumber crop’s growth and production. Plants at LIF were facing water stress conditions, as estimated from leaf temperature and stem micro variation measurements. However, HIF increased the transpiration rate of the plants, resulting in less water and nutrient losses.