Improve Irrigation Water Use Efficiency Research Articles

The use of alternative irrigation and cropping systems in forage production may alleviate the water scarcity in semi-arid regions.

Strategies to enhance the efficient use of irrigation water require a major shift in irrigation and cropping systems. It was hypothesized that (i) replacing water-demanding crops such as corn silage with more drought-tolerant forages species, (ii) adoption of intercropping instead of monoculture, and (iii) use of alternative irrigation methods, may alleviate the water shortage in semi-arid regions, while producing high-quality forage. Adoption of drip irrigation (DRIP) and alternate furrow irrigation (AFI) reduced water consumption by 43% and 20%, respectively. Additionally, DRIP produced 11% more biomass than the conventional furrow irrigation. The intercropped ratio of 50% sorghum and 50% amaranth under DRIP maximized forage production and improved irrigation water-use efficiency (IWUE). Principal component analysis indicated that the DRIP increased the dry matter yield and IWUE, whereas the AFI improved the forage quality. The intercropped ratio of 75% sorghum and 25% amaranth demonstrated the highest yield stability and was considered superior cropping system regardless of the irrigation strategies. DRIP and AFI strategies were effective in reducing water consumption, with DRIP being the most water-efficient method. Intercropping sorghum and amaranth at a ratio of 50:50 under DRIP resulted in the highest forage yield and IWUE. While sole amaranth had the highest forage quality, intercropping sorghum and amaranth increased dry matter production with better forage quality than sorghum monoculture. Overall, the combination of DRIP and intercropping sorghum and amaranth at a ratio of 50:50 considered as a suitable strategy for improving forage yield and quality, as well as IWUE. © 2023 Society of Chemical Industry.

Spatio-Temporal Study on Irrigation Guarantee Capacity in the Northwest Arid Region of China

Irrigation guarantee capacity is the critical factor in evaluating the development level of irrigated agriculture and is also a future development trend. It is necessary to carry out scientific planning and reasonable allocation of irrigation water resources to ensure the sustainable development of irrigated agriculture and improve the efficiency and effectiveness of water resource utilization. This study is based on remote sensing meteorological data and the principles of the Miami model and water balance. We calculated the annual irrigation water requirement and effective irrigation water, and used the ratio between the effective irrigation water and irrigation water requirement as the basis for evaluating an irrigation guarantee capability index. By using irrigation guarantee capability evaluation indicators from multiple years, we evaluated and assessed the irrigation guarantee capability in the arid region of northwest China. In addition, we analyzed three indicators (i.e., irrigation water requirement IWR, effective irrigation water EIW, and irrigation guarantee capacity index IGCI) to explore the rational allocation of water resources in the northwest arid area. IWR, EIW, and ICGI in northwest China from 2001 to 2020 were analyzed, and the average values were 379.32 mm, 171.29 mm, and 0.50, respectively. Simultaneously, an analysis was conducted on the temporal and spatial distribution of IWR, EIW, and IGCI in the northwest region of China from 2001 to 2020. The results indicated that the rainfall in the southwestern edge of the Yellow River Basin and the eastern part of the Qaidam Basin could meet the irrigation water demand. The northwest edge of the Yellow River Basin, the central Hexi Inland River Basin, most of Northeast Xinjiang, central and southeastern Xinjiang, and other regions mainly rely on irrigation to meet agricultural water requirements. The rest of the region needs to rely on irrigation for supplementary irrigation to increase crop yield. All districts in the ‘Three Water Lines’ area of northwest China should vigorously develop sprinkler irrigation, micro-irrigation, pipe irrigation, and other irrigation water-saving technologies and support engineering construction. Under the premise of ensuring national food security, they should reduce the planting area of rice, corn, and orchards, and increase the planting area of economic crops such as beans and tubers in the ’Three Water Lines’ area. That is conducive to further reducing the agricultural irrigation quota and improving the matching degree of irrigation water resources. It provides a scientific reference for optimizing water resource allocation and improving irrigation water-use efficiency in northwest arid areas.

Effects of water and NPK fertigation on watermelon yield, quality, irrigation-water, and nutrient use efficiency under alternate partial root-zone drip irrigation

Alternate partial root-zone drip irrigation (APRD) is efficient in improving irrigation water use efficiency (IWUE). However, little is known about the coupling effects of irrigation and NPK fertilisers on watermelon performance and resource use efficiency under APRD. This study investigated the effects of drip irrigation modes (conventional drip irrigation [CDI], APRD) coupled with NPK fertilisation rates on watermelon growth, IWUE, nutrient use efficiency, yield, and fruit quality. There were five treatments coded as CSH, CDH, CDL, ADH and ADL. The capital letters in the codes indicate drip irrigation modes as CDI (C) or APRD (A), irrigation amount as sufficient (S) or deficit (D, 60% of the total amount of S), and NPK fertilisation rates as high (H) or low (L, 60% of the amount of H). The results showed that compared with CDI at the same fertigation level, APRD increased the photosynthetic rate by 10.1%, plant growth by 25.5%, and NPK absorption by 29.1% across all growth stages, respectively. The promotion effect of APRD was more prominent at early growth stages. APRD increased watermelon yield by 10.4%, thus increased IWUE and fertiliser partial productivity at the same extent, while decreased the NPK use efficiency by 7.0% compared with the CDI counterparts. Compared with CSH, APRD increased vitamin C, total soluble solids (TSS), and the ratio of TSS to total organic acids by 63.2%, 6.2% and 17.2%, respectively. Additionally, the yield didn’t decrease in ADL whereas it increased in ADH, leading to an increase in IWUE of 67.8–78.7% under APRD treatments compared with CSH. Conclusively, APRD could save 40% of total irrigation water and NPK fertilisers without yield reduction while improving fruit quality. Thus, it is suggested as a sustainable practice for watermelon production.

Exploring the optimisation of mulching and irrigation management practices for mango production in a dry hot environment based on the entropy weight method

Rational application of field-management technology can not only improve mango (Mangifera indica L.) fresh fruit yield and quality but also improve irrigation water use efficiency (IWUE). However, few studies have involved the simultaneous use of mulch and irrigation-management techniques in hot and dry environments to achieve a relatively good level of performance. We used the entropy weight method (EWM) to explore an optimal mulching and irrigation-management technology for mango production in a dry hot environment. Three irrigation levels [FI, 100% mango evapotranspiration (ETC); DI75, 75% ETC; DI50, 50% ETC] were designed with (SM) and without (NM) sugarcane leaf mulching in 2018 and 2019 in a dry hot environment. The results showed that the photosynthetic rate, stomatal conductance, transpiration rate, leaf water-use efficiency, and carboxylation efficiency in the SM treatment were 12.5% to 83.7% higher than those in the NM treatment in both years. Compared with the NM treatment, the SM treatment increased the fresh fruit yield and IWUE by 45.7% and 49.7% in 2018 and by 46.1% and 63.2% in 2019. The solid-to-acid ratio and sugar-to-acid ratio in the SM treatment were 48.5% and 50.4% higher than those in the NM treatment, respectively, but the titratable acid content decreased by 31.3%. Compared with FI, DI75 increased carotenoid content, total soluble solids, solid-to-acid ratio and sugar-to-acid ratio by 8.4%–40.7%, while it reduced titratable acid by 22.8%. Compared with FI, DI50 reduced fresh fruit yield by 24.3% and 21.9% in 2018 and 2019, respectively, while it increased IWUE by 13.6% and 17.7%. The fresh fruit yield of SMDI75 was the highest, which was 1.42 and 1.44 times that of NMFI in both years, respectively. A comprehensive evaluation by EWM also showed that the SMDI50 treatment had the highest comprehensive scores of mango yield, quality and water-use efficiency, which could provide a basis for the scientific management of mango fertiliser in dry and hot areas of China.

Determining optimal deficit irrigation and fertilization to increase mango yield, quality, and WUE in a dry hot environment based on TOPSIS

Rational application of water and fertilizer management practices can not only improve mango (Mangifera indica L.) yield and quality but also improve irrigation water-use efficiency (IWUE). However, few studies have addressed the use of water and fertilizer management practices in hot, dry environments with the aim of achieving relatively favorable levels of these parameters concurrently. We used the technique for order preference by similarity to an ideal solution (TOPSIS) method to identify optimal water and fertilizer management practices that resulted in high fruit yields and high IWUE in Southwest China. A randomized block design study with four irrigation levels [full irrigation throughout the growth period (FI), regulated deficit irrigation during flowering (RDIFS), regulated deficit irrigation during fruit expansion (RDIES), and regulated deficit irrigation at maturity (RDIMS)] and three fertilization levels [FH, a water-soluble compound fertilizer (N:P2O5:K2O = 12:8:40) applied at 129.0 kg ha−1; FM, 103.2 kg ha−1; and FL, 77.4 kg ha−1] was implemented in 2018 and 2019 to investigate these relationships. The net photosynthesis rate (Pn), transpiration rate (Tr) and stomatal conductance (Gs) of mango under the different water deficit treatments were significantly lower than those under the FI treatment with the same fertilization conditions, but the instantaneous water-use efficiency (WUEi) of the leaves increased. The fresh fruit yield, solids:acid ratio (SOAR), sugar:acid ratio (SUAR), and IWUE under the RDIFS treatment were significantly lower than those under the FI treatment at the same fertilization rates. Averaged over all fertilization rates, the fruit yield under RDIES was 8.6–22.3% lower than that under FI in both years, but the IWUE significantly increased from 3.7% to 18.6%. Compared with the FI treatment, the RDIMS treatment had no significant effect on fruit yield but significantly increased the IWUE (35.5–44.7%), total sugar (TS) content (3.7–8.5%), and carotenoid content (CC) (1.5–13.1%) in both years. At the same irrigation level, the Pn, Gs and Tr increased with an increasing fertilization rate, while the fruit yield, IWUE, TS, and vitamin C (VC) content of fresh fruit first decreased but then increased with increasing fertilization rate. IWUE was more closely related to photosynthesis characteristics at the flowering stage than at the mature stage, but fruit quality was more closely related to photosynthesis characteristics at the mature stage than at the flowering stage. Compared with the FIFH treatment, the RDIMSFM treatment significantly increased the fruit yield by 10.1% and 6.6% in 2018 and 2019, respectively, and increased the IWUE by 28.1% and 35.6%, respectively. On the basis of the TOPSIS method, the multi-target optimum scheduling of mango was achieved under the RDIMSFM treatment. The identified optimum combination of water and fertilizer can provide a scientific basis for irrigation and fertilization optimization and management in the hot, dry environment of Southwest China.

Leaf physiological impedance and elasticity modulus in Orychophragmus violaceus seedlings subjected to repeated osmotic stress

Leaf water status is always influenced by plant growth and environment and dynamically changes over time. Rapid measurement of leaf physical characteristics helps to timely determine the plant water needs, in order to prevent inhibition of photosynthesis in plants and improve irrigation water-use efficiency (WUE) under water deficit conditions. The present study determined leaf electrophysiological and mechanical properties, water content (LWC), water potential (ΨL), carbonic anhydrase (CA) activity, net photosynthesis, and re-watering WUE (WUER) in relation to osmotic stress and following drought hardening in Orychophragmus violaceus seedlings. The study established a coupling model between gripping force and physiological impedance according to the Nernst equation, and the leaf water dissipation rate (LWDR) was defined and determined. Changes of cell stiffness and LWDR altered the intracellular water status, which affected the photosynthetic capacity and WUER. Photosynthesis was inhibited by the 40 g L−1 PEG (polyethylene glycol) treatment due to the reduction of intracellular water, and leaf cells were severely damaged at the higher, 80 g L‒1 PEG. Plants transferred from 20 to 10 g L‒1 PEG had the highest WUER. We have found that the physiological impedance provides more reliable information of plant water status compared with ΨL, which can help improve the irrigation WUE.

A sustainable strategy of managing irrigation based on water productivity and residual soil nitrate in a no-tillage maize system

No-tillage with limited supplementary irrigation is promising for improving crop growth and ensuring sustainable crop yield in semi-arid and semi-humid areas defined by their water scarcity and uneven seasonal precipitation distribution. Choosing effective irrigation methods and scheduling to improve irrigation water use efficiency (IWUE) and reduce the risk of soil nitrate leaching has become increasingly necessary for crop management. Field experiments were conducted on no-tillage summer maize over four consecutive years from 2014 to 2017 in a semi-humid and drought-prone region of Northwest China. Four irrigation strategies were used, i.e. rain-fed (RF, no irrigation), conventional flood irrigation (CK), full drip irrigation (FI) and deficit drip irrigation (DI, 75% FI). The results indicated that supplemental irrigation mitigated the drought stress resulting in improving maize growth and a stable, sustainable yield. Plant height, leaf area index and aboveground biomass of the DI treatment were lower than those of the CK and FI treatments, while the DI treatment produced insignificantly lower grain yield and increased grain nitrogen content. The DI treatment promoted the transfer of nutrients from vegetative organs to reproductive organs. The IWUE of the DI treatment was increased by 22.1%–27.3% and 28.4%–48.6% compared with the CK and FI treatments during the four growing seasons, respectively. Soil NO3−-N of the CK treatment was mainly distributed below 40 cm soil depth, while most soil NO3−-N remained above 40 cm in the FI and DI treatments, implying lower levels of nitrate leaching compared with the conventional flood irrigation. In conclusion, deficit drip supplementary irrigation is a sustainable agricultural production strategy that improves water use efficiency, maintains stable yield and alleviates the risk of soil nitrate pollution in the no-tillage agrisystem of arid and semi-arid regions.

Efficient irrigation water allocation and its impact on agricultural sustainability and water scarcity under uncertainty

Agriculture is a key economic sector in developing countries that are facing challenges of low efficiency of water resources utilization and of shrinking water supply. This study develops an optimization model for the allocation of agricultural irrigation water to improve irrigation water use efficiency (IWUE), considering uncertainties of fluctuating water supply. Then, it assesses the impact of efficient water allocation on the sustainability and water scarcity under different levels of water supply. This study can help answer questions as to how to optimal allocate limited water supplies to different crops and different subareas under uncertainty to improve IWUE, how water shortage affects economic, social, and environmental aspects, and what the relationship between system sustainability and water shortage is. To demonstrate its feasibility, the proposed models are applied to an irrigation district in northeastern China. These models can also be applied to other regions that suffer from water scarcity. Results of application are found to be satisfactory for explaining the impact of agricultural irrigation water allocation on net economic benefit, water resources allocation equity, total greenhouse gas emissions, and water scarcity footprint under different water supply conditions. This study provides insights into tradeoffs amongst resources, economy, society, and environment in irrigated agricultural systems under uncertainty.

Evaluation of a Decision Support System for Variable-Rate Irrigation in a Humid Region

HighlightsAn Irrigation Scheduling Supervisory Control and Data Acquisition (ISSCADA) system was tested against a soil electrical conductivity (EC) based method for variable-rate irrigation (VRI).Soil EC was used to create irrigation prescription in EC-based VRI.ISSCADA generated VRI prescriptions using canopy temperature, soil water content, and weather data.ISSCADA-based VRI reduced irrigation water use and increased irrigation water productivity.Abstract. Use of variable-rate irrigation (VRI) technology has the potential to improve irrigation water use efficiency (IWUE). VRI hardware is commercially available and can be implemented in any center pivot or lateral move irrigation system. However, practical methods and algorithms for creating VRI prescriptions have become the bottleneck in accelerating the adoption of VRI. An Irrigation Scheduling Supervisory Control and Data Acquisition (ISSCADA) system for VRI was evaluated for two years in a humid region in the Mississippi Delta. The ISSCADA system was used to manage irrigation of soybeans for two seasons. In field practice, the ISSCADA system scanned the field for canopy temperature and collected soil water data from time domain reflectometers and weather data from a nearby weather station. The ISSCADA system automatically generated VRI prescription maps. The maps were modified to include plots managed using soil electrical conductivity (EC) based VRI prescriptions. Test results indicated that there was no difference in crop yield between EC-based VRI and ISSCADA-based VRI management. However, ISSCADA-based VRI management reduced irrigation water use and increased irrigation water productivity in comparison with EC-based VRI. There is great potential for the use of ISSCADA for VRI in humid regions. Keywords: Canopy temperature, Soil electrical conductivity, Soil moisture sensor, Soil water sensor, Soybean, Variable rate irrigation.

Deficit Irrigation as a Sustainable Practice in Improving Irrigation Water Use Efficiency in Cauliflower under Mediterranean Conditions

Water shortage is one of the major constraints in vegetable production. Deficit irrigation is a sustainable technique that improves irrigation water use efficiency. Field studies were conducted during two growing seasons to evaluate the effects of deficit irrigation on plant growth, plant water status, productive response (curd yield and quality), irrigation water use efficiency (IWUE), and crop profitability of cauliflower. Nine irrigation treatments were used, applying 100%, 75% (moderate), or 50% (severe) of the irrigation water requirements (IWR) during the entire growing season (Continued Deficit Irrigation, CDI), or 75% and 50% of IWR during one of the following stages (Regulated Deficit Irrigation, RDI): Juvenility, curd induction, and curd growth. Severe deficit irrigation applied during juvenility and curd induction reduced the plant size, but it only led to a significant reduction of marketable yield (22%), and average curd size and weight if it was maintained throughout the crop cycle, supposing the highest IWUE (43.6 kg m−3). Moderate CDI or severe RDI during juvenility did not reduce significantly the curd yield compared to fully irrigated plants (4.4 kg m−2), thereby obtaining similar gross revenues (16,859 € ha−1) with important water savings (up to 24.3%), improving IWUE (up to 34.2 kg m−3).

Effects of straw returning on rice growth and yield under water-saving irrigation

ABSTRACT Straw returning (SR) is an important means of straw utilization, which has been tested and is helpful for improving soil fertility and crop production. However, the effects of SR on plant growth and yield of paddy rice (Oryza sativa L. subsp. japonica Kato) under water-saving irrigation (WSI) are rarely investigated. In the 2015 and 2016 rice seasons, field experiments were conducted with four treatments, namely controlled irrigation with conventional fertilization (CI- CF), controlled irrigation with straw returning (CI-SR), flooding irrigation with conventional fertilization (FI-CF), and flooding irrigation with straw returning (FI-SR). The objective of the present study was to investigate the response of plant height, number of tillers, biomass, and yield to SR and irrigation management. Results indicated that SR enhanced rice yield on average by 7.9% and 7.5% and improved irrigation water use efficiency (IWUE) by 6.3% and 8.3% in 2015 and 2016, respectively. The CI-SR combination significantly increased IWUE compared with FI-CF. These results suggested that SR could offset the inhibition of rice growth caused by CI, and the CI-SR combination could be an effective measure to enhance soil fertility, maintain the rice field, and increase IWUE. Furthermore, rice growth (plant height, number of tillers, and biomass) was slightly inhibited by SR during the first 20 d of the rice season, but increased after the jointing stage (approximately 40 d after transplanting). This implied that diverting some top-dressed chemical N fertilizer into basal application may be necessary for fertilizer management to better meet crop nutrient uptakes in rice fields with SR application, especially with CI.

Integrating deficit irrigation into surface and subsurface drip irrigation as a strategy to save water in arid regions

Development of sustainable and efficient irrigation strategies is a priority for producers faced with water shortages. A promising management strategy for improving irrigation water use efficiency (IWUE) is deficit irrigation, which attempts to optimize yield and IWUE. Soil water use, crop yield and IWUE of tomato were evaluated for two consecutive years under two types of irrigation methods (subsurface and surface drip irrigation) and three irrigation strategies: 1.0 of full irrigation supply (T1), 0.8 of full irrigation supply (T2) and 0.6 of full irrigation supply (T3). The results showed that the highest yields were found in the plots irrigated by subsurface drip irrigation at T1 (94.1 ton/ha) and T2 (81.4 ton/ha). Conversely, the fully stressed treatment (T3) reduced the amount of irrigation water by 40%, but significantly decreased mean tomato yield by 25.6% and 26.1% under subsurface and surface drip irrigation, respectively, as compared to T1. The maximum IWUE tended to be higher for subsurface drip than for surface drip irrigation system. The greatest IWUEs were obtained from subsurface drip and surface drip at T3 (19.7 kg/m3 and 18.3 kg/m3), whereas the lowest IWUEs were those estimated in T1 (15.9 kg/m3 and 14.8 kg/m3, respectively). The primary conclusion is that deficit irrigation strategies present certain advantages to crop water management with minimal effects on production and quality, thus contributing to crop sustainability.

Deficit irrigation and planting patterns strategies to improve maize yield and water productivity at different plant densities in semi-arid regions

Field research was done in two consecutive years to optimize deficit irrigation under different crop densities (low, medium, and high) using the ridge and furrow rainfall harvesting (RFRH) system. We demonstrate that applying deficit irrigation (375 m3 ha−1) at the flowering stage of maize grown at medium density (M: 75000 plant ha−1) under the RFRH system (MIF) can improve soil water storage (0–200 cm) at the bell, filling and flowering stages. MIF increased biomass by 10% and grain yield by 21%, thereby achieving a 17% increase in water use efficiency (WUE) and a 22% increase in precipitation use efficiency (PUE) compared with conventional flat planting (CKM). MIF also improved irrigation water use efficiency (IWUE) (9%) and irrigation water productivity (IWP) (46%) compared with no-irrigation under the RFRH system (MI0). We observed that applying deficit irrigation (750 m3 ha−1) at the bell and flowering stage (IBF) had positive effects on dry matter, leaf area, and evapotranspiration, but there were no significant increases in IWUE, IWP, WUE, biomass and grain yield compared with maize grown under IF at low, medium and high plant densities. The average net profit over the two years was 34% higher for MIF compared with the CKM treatment.

Alternate furrow irrigation affects yield and water-use efficiency of maize under deficit irrigation

Shortage of fresh water and drought stress are important factors limiting crop productivity in semi-arid and arid regions. Irrigation management needs to be optimised to improve irrigation water-use efficiency (IWUE), and thus, agricultural sustainability in these climates. A field experiment was conducted at two semi-arid locations in Iran to evaluate the impact of irrigation regime (applied after crop evapotranspiration of 70 mm (I70), 100 mm (I100) or 130 mm (I130)) and irrigation method (applied to every furrow (EFI) or variable alternate furrow (AFI)) on yield and IWUE of maize (Zea mays L.). Yield response to irrigation rate was quadratic. Kernel yield was 8476 kg ha–1 under I70, and this reduced by 12.3% under I100 and 27.7% under I130. Yield reduction due to water stress was attributed to decline in both kernel number and kernel weight. Implementation of AFI resulted in a significant saving in irrigation water. At I70, 31% less water was used with AFI than with EFI. Irrigation water saving was even greater under I100 and I130 when AFI was implemented. Regardless of irrigation regime, IWUE under AFI was always greater than under EFI (1.32 vs 1.03 kg m–3 for grain and 3.30 vs 2.47 kg m–3 for biomass production). In addition, plants were shorter with a longer root system under AFI, and the role of carbohydrate remobilisation in kernel filling was greater under AFI consistently among irrigation regimes. The results indicated good potential of AFI for development of water-saving strategies for maize production in semi-arid climates.

Mitigated CH4 and N2O emissions and improved irrigation water use efficiency in winter wheat field with surface drip irrigation in the North China Plain

Effects of different irrigation methods on greenhouse gas (GHG) emissions in winter wheat field are poorly understood. In this study, emissions of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) were investigated in winter wheat field irrigated with surface drip irrigation (SDI), sprinkler irrigation (SI) and flood irrigation (CK) from 1 April to 31 May of 2014 in the North China Plain. The results showed that SDI increased CH4 uptake by 22.9%, reduced N2O emission by 14.6%, improved irrigation water use efficiency (IWUE) by 44.2%, and could keep yield steady. IWUE and yield of winter wheat in SI was greater than that in CK by 28.2% and 8.5%, respectively. These combined results indicated that SDI may not only guarantee yield stability, but also mitigate GHG (CH4 and N2O) emissions and improve IWUE. Therefore, more attention should be paid to apply SDI in winter wheat field in the North China Plain.

Effect of spatio-temporal deficit irrigation and nitrogen supply on water and nitrogen use of tomato

For sustainable water use in protected agriculture,crop-specific and water-saving irrigation techniques that do not negatively affect crop productivity must be developed.Globally,successful attempts have been documented regarding the use of deficit irrigation methods.Regulated deficit irrigation(RDI) and controlled alternate partial root-zone irrigation(CRAI) have been used to improve irrigation water use efficiency(IWUE) of various crops.Because nitrogen(N) has been the most widely used fertilizer,N demand was likely to grow in the future.Thus the optimization of water and fertilizer use in vegetable production was a critical water/fertilizer-saving strategy.Four irrigation treatments under CRAI and three N levels were explored for optimum modes of water and fertilizer supply in vegetable production under water-saving irrigation in a pot tomato experiment.The irrigation treatments were WH WH(high water level through out growth period),WH WL(high water level at flowering and fruit-setting stages with low water level at full-fruit stage),WL WH(low water level at flowering and fruit-setting stages with high water level at full-fruit stage) and WL WL(low water level through out growth period).Then the N levels included NH [high N,0.45 g(N)·kg-1],NM [medium N,0.30 g(N)·kg-1] and NL [low N,0.15 g(N)·kg-1].Using conventional irrigation(CI) as control experiment,the effect of spatio-temporal of deficit controlled deficit irrigation(STCDI),which combined RDI and CRAI,and N rates on the vegetative parts of tomato dry matter accumulation(DMA),irrigation water use efficiency(IWUE),N accumulation(NA) and soil water and mineral N distribution were studied.Compared with CI,the results showed that WH WH,WL WH,WH WL and WL WL under CRAI decreased tomato DMA by 4.52%,11.93%,17.76% and 23.94%,respectively.They respectively decreased NA by 1.74%,12.86%,15.50% and 22.47%.The four irrigation treatments decreased N dry matter production efficiency(NDMPE) by 2.24%,3.93%,2.55% and 0.89% and increased IWUE by 12.39%,8.99%,15.02% and 12.96%,respectively.DMA,IWUE and NA of NM were highest under CRAI.Compared with NL,NM and NH decreased tomato NDMPE by 6.87% 12.70% and 17.81% 24.38% while increasing soil NO3-N content by 31.64% 159.58% and 57.37% 297.37%,respectively.High DMA,IWUE and NA were obtained under WH WH,CRAI and NM.The optimum mode for water and N supply under CRAI was 80% of CI irrigation(which was 70% 85% of soil field capacity) and nitrogen rate of 0.30 g(N)·kg-1(dry soil).

Yield, water-use efficiencies and root distribution of soybean, chickpea and pumpkin under different subsurface drip irrigation depths and oxygation treatments in vertisols

Most trickle irrigation in the world is surface drip yet subsurface drip irrigation (SDI) can substantially improve irrigation water use efficiency (IWUE) by minimizing evaporative loss and maximizing capture of in-season rainfall by the soil profile. However, SDI emitters are placed at depths, and in many soil types sustained wetting fronts are created that lead to hypoxia of the rhizosphere, which is detrimental to effective plant functioning. Oxygation (aerated irrigation water) can ameliorate hypoxia of SDI crops and realize the full benefit of SDI systems. Oxygation effects on yield, WUE and rooting patterns of soybean, chickpeas, and pumpkin in glasshouse and field trials with SDI at different emitter depths (5, 15, 25, and 35 cm) were evaluated. The effect of oxygation was prominent with increasing emitter depths due to the alleviation of hypoxia. The effect of oxygation on yield in the shallow-rooted crop vegetable soybean was greatest (+43%), and moderate on medium (chickpea +11%) and deep-rooted crops (pumpkin +15%). Oxygation invariably increased season-long WUE (WUEsl) for fruit and biomass yield and instantaneous leaf transpiration rate. In general, the beneficial effects of oxygation at greater SDI depth on a heavy clay soil were mediated through greater root activity, as observed by general increase in root weight, root length density, and soil respiration in the trialed species. Our data show increased moisture content at depth with a lower soil oxygen concentration causing hypoxia. Oxygation offsets to a degree the negative effect of deep emitter placement on yield and WUE of SDI crops.