Agronomic Water Use Research Articles

Physiological Indices for the Selection of Drought-Tolerant Safflower Genotypes for Cultivation in Marginal Areas

Safflower is known as a tolerant plant to abiotic stress factors. This study was conducted to introduce some physiological indices to improve drought-tolerant safflower genotypes for cultivation in marginal and arid areas. Six safflower genotypes were studied for two years (2017–2019) in the East Azarbaijan Agricultural and Natural Resources Research and Education Centre of Iran under non-stressed and low-water conditions from flowering to seed maturity. The occurrence of water deficits led to a significant decrease in relative water content (RWC), stomatal conductance (gs), osmotic adjustment (Oadj), water potential (WP) and agronomic water use efficiency (WUEa) and an increase in the water stress index (CWSI). In addition, the values of these traits differed significantly between the safflower genotypes. The correlations between the physiological traits and seed yield were significant. The regression relationships between seed yield and the above traits showed that CWSI, WP and WUEa had a strong relationship with seed yield under normal (R2 = 0.854, 0.801 and 0.856, respectively) and water deficit conditions (R2 = 0.931, 0.877 and 0.900, respectively). It can be concluded that the CWSI, WP and WUEa indices are able to select high-yielding and drought-tolerant safflower genotypes for the late season. Among the components of seed yield, the number of capitula per plant (r = 0.86) and seeds per capitula (r = 0.92), which were positively and significantly correlated with seed yield, played the main roles in the formation of seed yield. The Golemehr and Mec.295 genotypes achieved higher seed yields under normal (4676 and 4961 kg h−1, respectively) and water deficit conditions (3211 and 3385 kg h−1, respectively) and can be recommended for cultivation in marginal and arid areas.

A simple method for evaluating the relative water uptake rate of drip‐irrigated crops

AbstractDrip irrigation is widely acknowledged for its water use efficiency, yet evaluating relative water uptake rates (RWURs, ratios between the water uptake rates and the irrigation rates) remains pivotal for effective system design and management. This article presents a novel method employing straightforward measurements of wetted soil surfaces around emitters or perpendicular to driplines, both with and without water uptake, emphasizing simplicity and practicality. The proposed method offers valuable insights into agronomic water use efficiency, facilitating the optimization of drip irrigation for both annual and perennial crops. While effective for intensively irrigated crops, the method does have limitations for smaller wetted areas and longer irrigation cycles, depending also upon a reasonable determination of the active root zone depth and the soil capillary length. Despite relying on a simplified water uptake model, the accessibility and cost‐effectiveness of the method render it a valuable tool for assessing RWURs in diverse agricultural settings, contributing to the sustainable utilization of water resources in drip irrigation.

Benefits of a robotic chamber system for determining evapotranspiration in an erosion-affected, heterogeneous cropland

Abstract. In the light of the ongoing global climate crisis and the related increases in extreme hydrological events, it is crucial to assess ecosystem resilience and – in agricultural systems – to ensure sustainable management and food security. For this purpose, a comprehensive understanding of ecosystem water cycle budgets and spatiotemporal dynamics is indispensable. Evapotranspiration (ET) plays a pivotal role in returning up to 90 % of incoming precipitation back to the atmosphere. Here, we studied the impacts of soil types and management on an agroecosystem's seasonal cumulative ET (ETsum) and agronomic water use efficiency (WUEagro, the dry matter per unit of water used by the crop). To do so, a plot experiment with winter rye (17 September 2020 to 30 June 2021) was conducted in an eroded cropland which is located in the hilly and dry ground moraine landscape of the Uckermark region in northeastern Germany. Along the experimental plot (110 m × 16 m), two closed chambers were mounted on a robotic gantry crane system (FluxCrane as part of the AgroFlux platform) and used to determine ET. Three soil types representing the full soil erosion gradient related to the hummocky ground moraine landscape (extremely eroded: Calcaric Regosol; strongly eroded: Nudiargic Luvisol; non-eroded: Calcic Luvisol) and additional topsoil dilution (topsoil removal and subsoil admixture) were investigated (randomized block design, three replicates per treatment). Five different modeling approaches were used and compared in the light of their potential for reliable ETsum over the entire crop cultivation period and to reproduce short-term (e.g., diurnal) water flux dynamics. While machine-learning approaches such as support vector machines (SVMs) and artificial neural networks (with Bayesian regularization; ANN_BR) generally performed well during calibration, SVMs also provided a satisfactory prediction of measured ET during validation (k-fold cross-validation, k=5). We found significant differences in dry biomass (DM) and small trends in ETsum between soil types, resulting in different WUEagro. The extremely eroded Calcaric Regosol showed an up to 46 % lower ETsum and up to 54 % lower WUEagro compared to the non-eroded Calcic Luvisol. The key period contributing to 70 % of ETsum spanned the beginning of stem elongation in April to the harvest in June. However, differences in the ETsum between soil types and topsoil dilution resulted predominantly from small differences between the treatments throughout the cultivation rather than only during this short period of time.

Guar resilience in water‐restricted production

AbstractGuar [Cyamopsis tetragonoloba (L.) Taub] is an alternative crop in the Southern High Plains that thrives in semi‐arid regions, due to its low water input requirements. Field experiments were conducted in 2017 and 2018 at New Deal, TX, to evaluate the response of guar (‘Matador’) to four levels of deficit irrigation (DI; extreme, 51 mm; severe, 127 mm; moderate, 203 mm; and mild, 279 mm). Soil moisture extraction patterns, plant height, leaf area index, yield components, seed yield, harvest index (HI), agronomic water use efficiency (AWUE), and irrigation WUE (IWUE) were measured among the irrigation levels. In both years, guar grown under extreme and severe DI extracted a major portion of the water from the 50‐to‐100‐cm soil depth. Water deficit reduced plant height, leaf area index, and number of pods per plant in both years. However, the IWUE and 1,000‐seed weight increased with reduced irrigation. There were no significant differences in seed yield, HI, and AWUE among treatments as a result of a tradeoff between increased seed weight with low pod production under lower DI treatments and increased pod production with low seed weight under higher DI treatments. Guar extracted water deeper in the soil and produced adequate numbers of pods per plant in balance with the source organ capacity to allocate resources toward optimal seed development. Our research offers valuable information about root exploration and development of larger seeds as compensatory mechanisms that can be further explored to improve the adaptability of guar under water‐restricted production conditions.

Reduced plant water use can explain higher soil moisture in organic compared to conventional farming systems

Conventional high-input farming systems in Europe are often regarded as unsustainable with severe environmental impacts on biodiversity, soils, water and climate. Low-input farming approaches, such as organic farming, have been proposed to reduce environmental impacts while further improving soil properties such as soil organic matter content and aggregate stability. Whether these changes also influence ecohydrological properties and improve the water relations of organically grown crops remains unclear. In this study we assessed the long-term effects of conventional and organic farming systems on the water relations of soils and crops in the “DOK” (bio-Dynamic, bio-Organic & ‘Konventionell’ = conventional) trial. In particular, we tested if organic and conventional farming lead to marked differences in soil moisture, soil water evaporation, as well as root water uptake depth and stomatal conductance of winter wheat and soybean during the growing seasons 2017 and 2018. Stable isotope analyses and ecophysiological measurements revealed that organic compared to conventional farming did not affect soil water evaporation or root water uptake depths. Instead, we found higher soil moisture in the rooting zone and reduced stomatal conductance (gs) in organically grown wheat. Treatment effects on soil moisture and gs of soybean were smaller but showed similar tendencies as observed in wheat. Also, leaf area, and grain and straw yield of wheat decreased under organic farming while yields of soybean were not affected by the treatments. Based on our data we suggest that reduced plant water use observed under organically managed farming lead to the observed higher soil moisture in organically compared to conventionally managed farming systems in the DOK trial. These results suggest advantages of organic farming regarding agronomic water use as well as for the resistance of farming systems to current or future drought scenarios.

AGRONOMIC PERFORMANCE OF IRRIGATED CROP ROTATIONS UNDER CONVENTIONAL AND NO-TILLAGE SYSTEMS IN THE SEMIARID REGION OF MINAS GERAIS, BRAZIL

ABSTRACT The objective of this work was to evaluate the agronomic performance and water use efficiency of crop rotations under conventional system (CTS) and no-tillage system (NTS) through two experiments conducted in the Semiarid region of the northern state of Minas Gerais, Brazil. Experiment 1 consisted of a grain corn-common bean rotation, and experiment 2 consisted of a sorghum-sweet corn rotation. The treatments, in both experiments, consisted of two tillage systems (CTS and NTS) arranged in strip-plots, in two crop years, with ten replications. Yield and production components of all crops and water use efficiency (WUE) of crops grown in the autumn-winter seasons were evaluated within each crop rotation. The data obtained were subjected to analysis of variance and, when significant, the means were subjected to the F test at 5% significance level. The results obtained showed that the NTS increases corn yield in 21.45% in the grain corn-common bean rotation; however, the common bean yield present no difference between tillage systems. NTS increases the sorghum fresh and dry matter yields in 39.65% and 84.26%, respectively, in the sorghum- sweet corn rotation, and the sweet corn total and commercial ear yield in 11.99% and 21.80%, respectively. The NTS increases the WUE of crops grown in the autumn-winter season, in both crop rotations.

Water Use Efficiency in Popcorn (Zea mays L. var. everta): Which Physiological Traits Would Be Useful for Breeding?

To ensure genetic gains in popcorn breeding programs carried out under drought conditions knowledge about the response of morphophysiological traits of plants to water stress for the selection of key traits is required. Therefore, the objective was to evaluate popcorn inbred lines with agronomically efficient (P2 and P3) and inefficient (L61 and L63) water use and two hybrids (P2xL61 and P3xL63) derived from these contrasting parents, cultivated under two water regimes (WW watered—WW; and water-stressed—WS) in a greenhouse, replicated five times, where each experimental unit consisted of one plant in a PVC tube. Irrigation was applied until stage V6 and suspended thereafter. Individual and combined analyses of variance were performed and the genotypic correlations and relative heteroses estimated. The water use efficient inbred lines were superior in root length (RL), root dry weight (RDW), and net CO2 assimilation rate (A), which were the characteristics that differentiated the studied genotypes most clearly. High heterosis estimates were observed for RL, SDW, leaf width (LW), leaf midrib length (LL), and agronomic water use efficiency (AWUE). The existence of a synergistic association between root angle and length for the characteristics A, stomatal conductance (gs), and chlorophyll concentration (SPAD index) proved most important for the identification and phenotyping of superior genotypes. Based on the study of these characteristics, the higher AWUE of the previously selected inbred lines could be explained. The results reinforced the importance of root physiological and morphological traits to explain AWUE and the possibility of advances by exploiting heterosis, given the morphophysiological superiority of hybrids in relation to parents.

Partial root-zone drying in field-grown papaya: Gas exchange, yield, and water use efficiency

Partial rootzone drying (PRD) is an irrigation technique that usually applies less water (than well-watered control treatments) to only part of the rootzone (the irrigated side) and alternates the irrigated and non-irrigated sides. However, an incomplete understanding of the effects of its components (decreased water application versus frequency of alternating the irrigated side) on physiological responses of fruit crops such as papaya, is considered to be a constraint for its adoption under semiarid conditions. Therefore, a study was performed to determine effects of PRD on soil water dynamics, leaf gas exchange, yield, water use efficiency and water footprint in field-grown papaya. Yields and physiological measurements were evaluated under control (Full Irrigation - FI) and restricted (50 % and 35 % reduction in irrigation water depth - IWD) irrigation with the irrigated side alternated every 0, 7, 14 and 21 days. A drip irrigation system with three emitters on each side of the plant was used to apply surface drip irrigation as needed to supplement natural rainfall during the study period. Physiological functions, including stomatal conductance (gs), transpiration (E) and net photosynthesis (A) did not differ among treatments, but resultant differences in plant height and diameter growth rates were found to be significantly and positively related to yield. Decreasing the irrigation applied at moderate alternate frequency (PRD7 35 % and PRD14 35 %) increased agronomic water use efficiency of papaya (AWUE) without compromising its yield and gas exchange. Therefore, PRD strategy with irrigated side alternation frequency of every 7–14 days with a 35 % reduction in the irrigation depth could become a viable technique to reduce the water footprint of papaya, thus increasing the effective use of water under semiarid conditions.

Drought tolerance is determined by species identity and functional group diversity rather than by species diversity within multi-species swards

Abstract Low-input grasslands depend on the presence of grasses and legumes for the provision of nitrogen and a sufficient amount and quality of herbage for livestock. Increasing variability in the amount and distribution of rainfall, associated with climate change, is a major factor affecting production from permanent grassland and particularly grass-clover swards. Previous work has shown that introduction of deep-rooting dicotyledonous forbs into grass-legume mixtures increases functional trait diversity (FTD), which facilitates the resistance and resilience of grassland to drought. It also increases species diversity and functional group diversity (FGD). However, the role of species diversity at a given level of FGD and associated FTD for the resistance and resilience of low-input grassland towards drought remains unclear. This knowledge is required to design forage mixtures adapted to drier climatic conditions. We conducted a drought-stress experiment with 16 different sown sward types, grown in cylindrical mesocosms, combining three levels of species diversity (one, three, five) and three levels of FGD (one, two, three) all being associated with FTD in terms of phenology, rooting depth and nitrogen fixation to determine whether maximum levels of species diversity or FGD promote adaptation to drought. The study was conducted over three drought-stress cycles in an open-sided greenhouse where the climate followed ambient natural conditions. Over the duration of 685 days, we found no clear species diversity effect but a distinct species identity effect on biomass production and agronomic water use efficiency. A positive species identity effect depended largely on white clover presence and on the FGD within mixtures. The best performing mixtures for resistance and resilience combined FGD and FTD in a complementary way, irrespective of whether the swards contained three or five species, as FGD and FTD were already maximized within the best-performing three-species swards. Increasing complementarity of traits by species grown in carefully designed mixtures is one measure to achieve diversity effects and facilitate future sustainable grassland production. We propose to exploit the benefits of species identity and functional group diversity in designing future mixtures to cope with drought.

Agro-physiological response of potato to “sustainable” deficit irrigation in the plain of Saïs, Morocco

Morocco is one of the countries who’s facing an insufficient water supply for irrigation, therefore it is seeking for new technologies allowing irrigation management evolution. Deficit irrigation is for this reason one of the recommended approaches to deal with this alarming situation. This study deals with the assessment of Sustainable Deficit Irrigationon potatoes production (Var. Desiree). The experiment was conducted on an experimental plot in open field in Morocco. Three water regimes were applied: T1control (100%), T2 (75%) and T3 (50%) of crop evapotranspiration ETc. This is a complete random block device with four repetitions. Measurements focused on monitoring vegetative, ecophysiological and yield parameters. The results obtained show that: (i)the irrigation regime did not significantly affect the eco-physiological parameters nor the vegetative parameters, except for the height of the plants; (ii) in terms of yield, a deficit of less than 25% of ETc did not lead to a significant difference compared to the control treatment and reached 41, 17 tones/ha compared to the 100% ETc with 42, 51 t/ha; (iii) irrigated treatments at less than 50% of daily ETc revealed extreme yield loss (20, 96 Tonnes/ha);(iv) finally, the best agronomic water use efficiency was recorded for irrigated treatments at 75% of Etc.

Stomatal response in soybean during drought improves leaf-scale and field-scale water use efficiencies

Diminishing water resources and an expected increase in frequency of extreme water stress events necessitate tools to diagnose and improve the drivers of variability in agronomic water use efficiency. The objective of this study was to determine if leaf-scale water use efficiency (measured as intrinsic water use efficiency and transpiration efficiency) is expressed at the field scale as yield or agronomic water use efficiency variability. We measured grain yield, total aboveground biomass, and carbon isotope discrimination and estimated evapotranspiration using a mass balance approach for field-grown Glycine max (soybean) over five years. We found that the high agronomic water use efficiency in years characterized by high vapor pressure deficit was caused by a large reduction in evapotranspiration and a relatively smaller reduction in yield. This has implications for developing drought tolerance in soybeans without compromising yield. We observed a positive relationship between transpiration efficiency and agronomic water use efficiency, with the leaf scale explaining 68% of the variability at the field scale. Through this analysis, we infer that increasing transpiration efficiency at the leaf scale will likely improve agronomic water use efficiency at the field scale in rain-fed soybean systems.

YIELD AND AGRONOMIC EFFICIENCY OF SUNFLOWER IN RESPONSE TO NITROGEN FERTILIZER APPLICATION AND SOWING SEASON

ABSTRACT Agronomic responses to the use of agricultural inputs have been used in agriculture to identify the optimal level of nutrients to be supplied for high yield. This strategy helps to avoid economic losses and excessive application of fertilizers that has caused pollution of aquifers and soil degradation. The aim of the study was to evaluate water use efficiency, agronomic efficiency of nitrogen, heat units and use of evapotranspiration in yield and its components in sunflowers under hot climate conditions in function of nitrogen fertilizer application during two sowing season. The experiment was conducted in the field. The treatments were two sowing seasons and three levels of nitrogen fertilizer application and one control: 0, 60, 80 and 120 kg N ha-1. The nitrogen source was urea. The experimental design was complete random blocks with factorial array and four replications. The occurrence of cv. Cobalto sunflower phenological stages were not modified by the treatments. Urea favored agronomic efficiency and water use efficiency. Yield components were modified positively, with increasing receptacle area, 100-grain weight, and grain yield per receptacle. Application of nitrogen fertilizer favored sunflower development, although environmental conditions are of critical importance as demonstrated by a clear interaction between the yield response to fertilizer application and the environment where the plants grew.

Wheat agronomic parameters and water use efficiency under different bioclimatic stage in the North of Tunisia

Improvement of water use efficiency (WUE) in wheat is important for almost all agricultural practices, so Water use efficiency (WUE), is the ratio of grain yield to crop water use, provides a simple means of assessing whether yield is limited by water supply or other factors. Limited precipitation restricts yield of wheat grown in Tunisia, so supplement irrigation will be paramount in Mediterranean agriculture in the future where wheat is a major crop. The present study was carried out in two stations of the Regional Filed Crop Research Center of Béja, Tunisia, in sub humid climatic stage and Oued Miliz in semi arid, in sub humid experiment was conducted rainfed whereas three irrigations levels were used in semi arid condition. The aim of this work was to study effect of biocliamtic stage and supplemental irrigation on yield and water use efficiency. There was a significant difference (p < 0.05) in biological water use efficiency between two climatic stages for all varieties; whereas in the same condition there no significant difference between varieties.

Dry-season deficit irrigation increases agricultural water use efficiency at the expense of yield and agronomic nutrient use efficiency of Sacha Inchi plants in a tropical humid monsoon area

Application of deficit irrigation (DI) will be problematic in tropical humid monsoon areas, since high relative air humidity during growth there leads to stomata malfunctioning. A field split-plot experiment was used to evaluate the physiological features, growth and seed and oil yield of Sacha Inchi (Plukenetia volubilis Linneo) plants, a tropical promising woody oilseed crop, responded to DI and fertilization in southwest China. The field experiment consisted of a factorial combination of five irrigation levels applied in the dry season [rainfed; DI20, DI50, DI100 (i.e., with irrigation amount of 20, 50 and 100% crop evapotranspiration, respectively); and full irrigation (irrigation of water saturated soil)] combined with two levels of compound fertilizer (0 and 200kgha−1) over two growing seasons, in a randomized complete block design with three replicates.Results showed the growth and root to stem mass ratio had lower sensitivity responded to DI, probably owing to their extremely low root mass fraction and seasonal short-term effect of DI on leaf photosynthetic traits. Irrigation affected the seasonal variations in seed size, seed oil concentration and seed yield, depending on the harvest date; whereas, with constant mean seed size and mean seed oil concentration across irrigation and fertilization treatments, the total seed and seed oil yield over the growing seasons were largely determined by the seed numbers per unit area. The soluble sugar and nitrogen storages as the active process, are related to effective flower formation, fruit (seed) development and enhance productivity of Sacha Inchi plants, which was indicated by the positive relationships between total seed yield and total nitrogen pool in the vegetative tissues or sugar pool in stems across all treatments. Fertilization increased total seed and seed oil yield, but no interaction between irrigation and fertilization was found. Compared with DI100, DI50 and DI20 had significant lower total seed yield, especially under the fertilized condition, although having higher agronomic water use efficiency (WUEagr, yield divided by irrigated water applied) but lower agronomic nutrient use efficiency (NUEagr, increased yield divided by fertilization rate). As a water-demanding crop species, Sacha Inchi plants under DI100 with the similar values to full irrigation had the highest total seed yield and NUEagr, but at the expense of water use efficiency. The maximum seed yield and maximum WUEagr, or maximum WUEagr and maximum NUEagr of Sacha Inchi plants are not compatible because the negative relationships existed between each of them. The polynomial regression relationships between total seed or seed oil yield and relative evapotranspiration could help to develop appropriate water-saving techniques for Sacha Inchi plantation in the tropical humid monsoon region.

Effects of tillage practices on water consumption characteristics and grain yield of winter wheat under different soil moisture conditions

A serious water shortage is threatening agricultural sustainability in the Huang-Huai-Hai Plain of China. Long-term reduced tillage (shallow rotary tillage) has led to thickening of the plough pan, which prevents the infiltration of precipitation and inhibits the root growth of wheat. Moreover, the topsoil was usually too loose to retain soil moisture. These conditions were not conducive to the highly efficient use of limited water for wheat production. The experiment was conducted from 2011 to 2013 using a split plot design. The main plots contained five different tillage treatments, and the subplots consisted of the two following different irrigation treatments: rain fed and supplemental irrigation (SI). Subsoiling promoted soil water consumption and crop evapotranspiration as well as significantly increased the water potential (ψL), transpiration rate (Tr) and net photosynthesis rate (Pn) of the flag leaves. Furthermore, subsoiling increased the 1000-grain weight and grain yield of winter wheat under both the rain fed and SI conditions compared with long-term rotary tillage. Subsoiling could even increase spike number under SI conditions, but could not increase the agronomic water use efficiency (AWUE). Harrowing or moderate topsoil packing before seeding increased the water content of the topsoil, the water consumption from the deep soil layers, the Pn of the flag leaves, and the 1000-grain weight, grain yield and AWUE in plots that were subsoiled. However, excessive topsoil packing significantly decreased the ψL, Tr, Pn and water use efficiency (WUEleaf) of flag leaves as well as the 1000-grain weight, grain yield and AWUE under both the rain fed and SI conditions.

Improving agronomic water use efficiency in tomato by rootstock-mediated hormonal regulation of leaf biomass

Water availability is the most important factor limiting food production, thus developing new scientific strategies to allow crops to more efficiently use water could be crucial in a world with a growing population. Tomato is a highly water consuming crop and improving its water use efficiency (WUE) implies positive economic and environmental effects. This work aimed to study and exploit root-derived hormonal traits to improve WUE in tomato by grafting on selected rootstocks. Firstly, root-related hormonal parameters associated to WUE were identified in a population of recombinant inbred lines (RILs) derived from the wild tomato species Solanum pimpinellifolium. A principal component analysis (PCA) revealed that some hormonal traits were associated with productivity (plant biomass and photosynthesis) and WUE in the RIL population. Leaf ABA concentration was associated to the first component (PC1) of the PCA, which explained a 60% of the variance in WUE, while the ethylene precursor ACC and the ratio ACC/ABA were also associated to PC1 but in the opposite direction. Secondly, we selected RILs according to their extreme biomass (high, B, low, b) and water use (high, W, low, w), and studied the differential effect of shoot and root on WUE by reciprocal grafting. In absence of any imposed stress, there were no rootstock effects on vegetative shoot growth and water relations. Finally, we exploited the previously identified root-related hormonal traits by grafting a commercial tomato variety onto the selected RILs to improve WUE. Interestingly, rootstocks that induced low biomass and water use, ‘bw’, improved fruit yield and WUE (defined as fruit yield/water use) by up to 40% compared to self-grafted plants. Although other hormonal factors appear implicated in this response, xylem ACC concentration seems an important root-derived trait that inhibits leaf growth but does not limit fruit yield. Thus tomato WUE can be improved exploiting rootstock-derived hormonal signals which control leaf growth.

Partial rootzone drying (PRD) and regulated deficit irrigation (RDI) effects on stomatal conductance, growth, photosynthetic capacity, and water-use efficiency of papaya

Papaya (Carica papaya, L.) is an important economic crop in tropical and subtropical countries. It is a giant herbaceous species; maintaining adequate tissue turgidity and water availability is necessary to maintain the rigidity of the stem as well as increase productivity. Water-saving irrigation techniques for papaya will be needed in the future due to the possibility of water shortages related to climate change. The morphological and physiological responses of ‘Grand Golden’ papaya to partial root drying (PRD), regulated deficit irrigation (RDI) and no irrigation followed by re-hydration (NI-gh) in a greenhouse study or no irrigation (NI-field) in a field study were compared with full irrigation (FI). In the greenhouse study, plants were grown in pot with roots split equally between two soil columns. In the field study, drip emitters on opposite sides of the plant delivered irrigation water. In FI, the whole root system was irrigated at 100% of water use; in RDI 50% or 70% of FI water use was supplied to the whole root system (greenhouse and field study, respectively); in PRD 100% of FI was supplied to half the root zone while the other was allowed to dry to 50% or 70% of FI (greenhouse, and field study, respectively). In the field study, PRD was achieved by applying different amounts of irrigation water to alternate sides of the root system within the plant row. The application of 50% water use in PRD and RDI in the greenhouse study decreased shoot and root dry weight production, with a more pronounced effect on root dry weight compared to FI. This decrease in biomass was associated with a decrease in the net photosynthetic rate in the day of most intense water stress for the plants in NI-gh. In the field study, a 30% water deficit in both PRD and RDI treatments did not significantly reduce vegetative growth or yield components (number fruitplant−1, average weight (g)fruit−1, kgfruitha−1, kgfruitplant−1), compared to FI. In greenhouse conditions there was evidence of a non-hydraulic signal in the PRD treatments decreasing Gs compared to RDI at comparable soil water tension but it was insufficient to affect shoot growth or yield components in field conditions. There was no difference in the instantaneous leaf water use efficiency (WUE, A/E) of PRD or RDI treatments in the greenhouse or the agronomic water use efficiency (AWUE) (kgfruitL−1 and number fruitL−1) in the PRD and RDI treatments in the field but both treatments improved AWUE compared to FI. It appears that papaya can tolerate some water deficits without a significant reduction in yield components indicating that <100% ET0 irrigation replacement can be scheduled but there is little or no benefit to PRD.

Partial rootzone drying in sugarcane (Saccharum officinarum L.): effects on gas exchange, growth and water use efficiency

Sugarcane (Saccharum officinarum L.) is an effective crop for biomass production and is used mainly for sugar production and bio-fuel. Irrigation water has become less available in many regions due to global climate change and domestic. To confront the challenge of water utilization, there is a need to develop water-saving irrigation techniques in order to maximize crop water use efficiency. Partial rootzone drying (PRD) is a water-saving irrigation strategy that involves irrigating only part of the rootzone while leaving the other portion to dry to a predetermined level before the next irrigation. The objective of this study was to examine whether PRD affects photosynthetic capacity and growth in young sugarcane plants (48-day old). The experiment was conducted from January to April, 2011 in a greenhouse. Sugarcane mini-stalks were transplanted with divided root systems at 20 days of age into two pots. The pots were filled with soil (oxisol), sand and manure (1:1:1). The sugarcane plants were well-watered in the first 10 days after transplanting. Thereafter, the plants were exposed to three irrigation regimes: (1) Full irrigation (FI) (control); in which both soil compartments were watered to 100 % field capacity; (2) PRD; in which one soil compartment was watered to the field capacity while the other was allowed to dry for 17 days, then the plants were re-irrigated; (3) no irrigation (NI); in which both compartments were allowed to dry for 17 days, then re-irrigated. Net photosynthetic rate, stomatal conductance, transpiration, predawn leaf water potential, leaf area, shoot dry weight, root dry weight, root volume, and intrinsic water use efficiency were measured. PRD did not significantly reduce growth and gas exchange in comparison to FI, yet there was a 17.6 % reduction in water application. In addition, the agronomic water use efficiency was higher in PRD (4.1 g l−1) and FI (3.6 g l−1) than NI (2.9 g l−1). In this study, PRD irrigation reduced water consumption by 17.6 % with a total biomass reduction of 11.3 % as compared with fully watered plants. In conclusion, PRD may be an efficient irrigation strategy and promising for application in drought-prone regions for saving water where sugarcane is produced.

Effects of supplemental irrigation with micro-sprinkling hoses on water distribution in soil and grain yield of winter wheat

The development of water-saving irrigation techniques is required for future food and ecological security in the Huang-Huai-Hai Plain of China, which suffers from severe water shortage. Field experiments were performed over two years (2010/2012) with the high-yielding winter wheat cultivar Jimai22 to examine the effects of supplemental irrigation (SI) with micro-sprinkling hoses on water distribution in soil and grain yield of winter wheat. Five irrigation treatments were tested: rainfed (T0), and irrigated with micro-sprinkling hoses with minimum sprinkling angles (i.e. the angle between the tangent of the initial water jet and the horizontal) of 35° (T1), 50° (T2), 65° (T3) and 80° (T4). The SI brought soil water content in the 0–140cm profile to 75% field capacity (FC) at jointing and 70% FC at anthesis in 2010/2011, and 70% FC at both jointing and anthesis in 2011/2012. The distribution uniformity of irrigation water (Cμ) in soil after irrigation at jointing and anthesis was increased by increasing sprinkling angle from 35° to 80°. The increase in the soil water content in the 0–40cm soil layer of the inter-rows decreased significantly with increasing distance from the micro-sprinkling hose in T1, T2 and T3, but there was no significant difference between inter-rows in T4. As sprinkling angle was increased from 35° to 80°, the amount of SI required (CIR), soil water consumption (ΔW) and crop evapotranspiration (ETc) decreased. The grain filling rate at the later filling stage, 1000-kernel weight, dry matter accumulation (DM), grain yield, and agronomic water use efficiency (AWUE) were significantly higher in T4 than in T1, T2 and T3. The CIR, ΔW and ETc had significant, negative, linear relationships with Cμ. However, DM, grain yield, and AWUE had significant, positive, linear relationships with Cμ with mean correlation coefficients of 0.60, 0.91 and 0.91, respectively. In this study, the optimum sprinkling angle of micro-sprinkling hoses for irrigating wheat after jointing was 80°.

Root growth, yield, and fruit quality responses of reticulatus and inodorus melons (Cucumis melo L.) to deficit subsurface drip irrigation

Water scarcity associated with intense and frequent droughts has increased the need for the implementation of drought adaptation strategies that can save water and sustain crop productivity in water limited environments. A two season (2011 and 2012) study evaluated root growth, yield and fruit quality responses of cvs. Mission (muskmelon; reticulatus), Da Vinci (tuscan; reticulatus) and Super Nectar (honeydew; inodorus) of melon (Cucumis melo L.) to two irrigation rates (100% and 50% crop evapotranspiration (ETc)) on a silty clay soil under the semi-arid conditions of Texas. Deficit irrigation (50% ETc) increased root length density (RLD) in Mission, decreased in Da Vinci and did not affect in Super Nectar. Marketable fruit yield at 100% ETc irrigation was 77.1tha−1 in 2011 and 78.7tha−1 in 2012, but deficit irrigation caused a 30% decrease in marketable yield in both seasons, mainly due to a reduction in fruit size. Yield responses to deficit irrigation also varied with cultivar. A significant yield reduction of 43% in 2011 and 33% in 2012 was measured in Super Nectar, while for cvs. Mission and Da Vinci the reduction in yield was 24% and 30%, respectively in 2012. Deficit irrigation had no adverse impact on melon fruit quality; rather it increased total soluble solids content (23%) in Mission and β-carotene content (25%) in Da Vinci in 2011. At 50% ETc, agronomic water use efficiency (WUE; kgha−1mm−1) was improved in Mission (13%) in 2012 while it decreased in Super Nectar (21%) in 2011. These results showed that deficit irrigation can save 37–45% of irrigation water in Mission and Da Vinci cultivars (reticulatus) with a moderate reduction in economic yield. This practice may not be applicable for cv. Super Nectar (inodorus), as it reduced yield without improving water use efficiency.