Irrigation Volume Research Articles

Biochar-Induced Mitigation Potential of Greenhouse Gas Emissions Was Enhanced under High Soil Nitrogen Availability in Intensively-Irrigated Vegetable Cropping Systems

Intensive irrigation coupled with excessive nitrogen (N) fertilizer input has resulted in high soil greenhouse gas (GHG) emissions in vegetable cropping systems. Biochar as a soil amendment has been advocated as a desirable option to reduce GHG emissions in agricultural systems, but its interactive effects with soil N availability in vegetable systems have yet to be clarified. We performed a field study to examine how biochar interacts with N fertilizer in driving annual methane (CH4) and nitrous oxide (N2O) emissions from an intensively-irrigated greenhouse vegetable cropping system acting as both sources of atmospheric CH4 and N2O in subtropical China. Biochar amendment significantly increased soil CH4 emissions by 33% and 85%, while it decreased soil N2O emissions by 22% and 12% with and without N fertilizer input, respectively. Fertilizer N combination weakened the positive response of CH4 to biochar while it enhanced the mitigation potential of biochar for N2O. Annual direct emission factors of fertilizer N for N2O were estimated to be 1.35% and 1.94% for the fields with and without biochar amendment, respectively. Annual flux-sustained global warming potential (SGWP) and greenhouse gas intensity (GHGI) were significantly decreased by biochar amendment, and this mitigation effect was enhanced with fertilizer N combination. Altogether, we highlight that biochar can reconcile higher yield and lower climatic impact in intensive vegetable cropping systems in subtropical China, particularly in vegetable soils with high N availability.

Semi-supervised machine learning analysis of crop color for autonomous irrigation

Agricultural irrigation wastage, especially from inefficient infrastructure in developing nations, is among the leading causes of the global water shortage epidemic, which affects an estimated 2.8 billion people worldwide. In this project, a three-component cloudless internet-of-things (IoT)-based irrigation network is designed and constructed to affordably integrate into existing irrigation infrastructure and approach zero water wastage while maintaining crops at a perceived healthy threshold. A Raspberry Pi-based electrical circuit of sensors and drone are constructed to collect environmental data and extract brightness-adjusted HSV crop color using k-means clustering-based computer vision algorithms. A semi-supervised approach is used to train a bidirectional Recurrent Neural Network, which enables long-term and working memory analysis within hidden layers for time-sensitive outputs. The resulting predicted irrigation volume is executed by an Arduino Nano-based irrigation micropiece to dynamically adjust the water flow to each crop for individualized irrigation. Induction from water flow through irrigation pipes generates current, yielding complete and scalable power self-sufficiency at an excess margin of 25.8%. Empirical data collection reflects a 68.8% increase in irrigation effectiveness for crop growth. Model testing on various African nation crop yields and corresponding satellite images (n = 10,301) reflects an accuracy rate of 89.1% and a binary classification success of 96.0% after a single growth cycle. The ability to cost-effectively integrate into existing irrigation infrastructure and minimize irrigation resource wastage enables the constructed network to be a viable solution to mitigate the negative impacts of water scarcity on agriculture yields.

Optimal Sprinkler Application Rate of Water–Fertilizer Integration Machines Based on Radial Basis Function Neural Network

The application rate for sprinkler irrigation of water–fertilizer integration machines is an important technical parameter for efficient operation. If the value is too large, the equipment will produce runoff; if it is too small, the equipment will run too long and waste energy. Therefore, it is necessary to provide a feasible scientific and theoretical basis for developing a reasonable application rate. In this study, a mathematical model of soil infiltration for sprinkler irrigation with water and fertilizer integration machines was developed. Soil water accumulation time for different soil’s initial water content, bulk density, sprinkler application rate and soil texture were derived by the finite element method, and these data were used as a training database for the neural network. To make the neural network convenient for predicting the optimal application rate of sprinkler irrigation (the maximum application rate of sprinkler irrigation without runoff) in practice, the time of waterlogging, was multiplied by the optimal application rate of sprinkler irrigation to obtain the total irrigation volume. The optimal application rate of the sprinkler irrigation prediction model of radial basis function (RBF) neural network was constructed with total irrigation water, soil bulk density, initial water content and soil texture as inputs and compared with BP neural network and generalized regression neural network. The highest prediction accuracy of RBF neural network was obtained, and its average relative error was 0.11. To verify the accuracy of the RBF neural network application rate of sprinkler irrigation prediction model in real life, a sprinkler experiment was conducted in the laboratory of Guangzhou University, and the collected soil and lawn of Guangzhou University were used to simulate the actual environment. The results showed that the relative error between the RBF neural network prediction results and the actual values was generally around 10%, while for a total irrigation volume of 58 mm, the optimal application rate of sprinkler irrigation calculated with the model was 42 (mm/h), which can save 70% of irrigation time compared to the case of using the stable infiltration rate of soil as the application rate of sprinkler irrigation without water and fertilizer. Water and fertilizer losses were not observed. This indicates that the model proposed in this study is of practical value in determining the optimum application rate of sprinkler irrigation for water–fertilizer integration machines.

ANALISIS KEMAMPUAN SISTEM IRIGASI TETES BERTINGKAT DALAM PEMBERIAN LENGAS TANAH PADA POLYBAG

In increasing the supply of food in residential areas, it is necessary to encourage the use of land and water sources in the yard even though the land area is limited. The design of multilevel drip irrigation may be an option in these housings, and therefore it is necessary to test and determine the ability of the irrigation to discharge, uniformity and soil moisture produced. This study aims to determine the effect of using inch PVC pipe as a secondary network on discharge, uniformity (CU) and soil moisture (w) in a multilevel drip irrigation system. Experiments were carried out with a 150 liter reservoir water source 3 m high, soil moisture test with a test duration of 5 minutes, 10 minutes and 15 minutes. Data analysis was carried out on discharge data (Q), irrigation volume and soil moisture. The research results are presented in tables, graphs and concluded descriptively. The results showed that the secondary pipe flow rate was Q1 822.54 cm3/sec, Q2 107.47 cm3/sec and Q3 15.39 cm3/sec. Irrigation uniformity in TSK irrigation operations obtained CU of 72.67% and in SK obtained CU of about 51.49% to 89.34%. Soil moisture produced at a duration of 5 minutes, 10 minutes and 15 minutes with an initial soil moisture condition range of 14%-28%, the results on the 1st floor (w1) ranged from 41%-50%, for the second floor w2 it was around 31%-45 % and on the third floor w3 around 25%-40%

Influence of furrow irrigation regime on the yield and water consumption indicators of winter wheat based on a multi-level fuzzy comprehensive evaluation.

Irrigation regimes should be chosen to maximize crop yield and water use efficiency. To realize high yield and efficient water use with the appropriate furrow irrigation regime, the effects of two regimes (alternate furrow irrigation and conventional furrow irrigation) and three lower soil moisture limits (60, 70, and 80%) were studied on winter wheat yield and water consumption using a multi-level fuzzy comprehensive evaluation method. The results show that under the two regimes, alternate furrow irrigation and conventional furrow irrigation, when the lower limit of the soil moisture is 70%, the harvest index (0.45 and 0.39, respectively) and crop water productivity of winter wheat (1.86 and 1.90 kg m−3, respectively) are highest. The comprehensive fuzzy evaluation model considers multiple measures, including yield, harvest indices, irrigation volume, total water consumption, and crop water productivity – the index values are highest at the 70% condition, which are 0.3468 and 0.3432, respectively. Therefore, it can be concluded that a moderate water deficit is conducive to saving water resources and improving water use efficiency. In conclusion, a multi-level and multi-factor indices system of furrow irrigation regime was constructed based on ensuring winter wheat production. Conventional furrow irrigation is recommended in areas with sufficient irrigation water, while alternating furrow irrigation, which can reduce the total amount of irrigation required, is suitable for areas with water shortages.

Modelling Soil Water, Salt and Heat Dynamics under Partially Mulched Conditions with Drip Irrigation, Using HYDRUS-2D

Drip irrigation under mulch is a widely used technique in the arid region of northwest China. The partially mulched soil and the bare strips between mulched areas may complicate the migration of water, salt, and heat in soils, and cause lateral salt accumulation on bare soil surfaces. For investigating hydrothermal dynamics and salt distribution patterns under such circumstances, tank experiments with drip irrigation under plastic film on partially mulched soil were conducted under two intensities of drip irrigation (i.e., low (W1) and high (W2)) with the same total irrigation amount. The spatial distributions of soil water, temperature, and electrical conductivity were monitored accordingly. The two-dimensional (2D) model of soil water, salt, and heat transport under drip irrigation and partially mulched soil conditions was established using HYDRUS-2D, and kinetic adsorption during salt migration was considered. The results of the experiments showed that the uneven distribution of the hydrothermal state led to the accumulation of salt on the un-mulched soil surface. Water migrated from where the dripper was located, and heat accumulated mainly in the mulched soil. HYDRUS-2D matched reasonably well with the observed data, with an R2 higher than 0.54. Under the partially mulched conditions, lower intensity of drip irrigation (W1) show higher desalination efficiency in root zones, with less even lateral salt distribution. Scenario simulations further demonstrated that a larger total irrigation amount would result in a larger desalination zone, and drip irrigations with appropriate incremental intensity could improve salt leaching in the root zone with increased lateral migration of water.

Bite Wounds Should not be Irrigated by Syringe. An Anatomic Study

In eight cadavers, artificial bite wounds were produced in typical locations. These wounds were irrigated by syringe and button cannula using diluted ink. The pressure of irrigation was limited to "no noticeable pressure". In all cases, more than half of the irrigation volume remained inside the victim´s organism, following anatomic structures and spreading over large areas. Irrigation fails to clean the wound but increases the risk of contaminating the surrounding structures. Hence, the authors recommend that bite wounds should not be irrigated by syringe and button cannula.

Determining Soil Available Water Capacity and Reasonable Irrigation Volume in Dryland Pasture

Among the methods used to describe soil-available water in terms of yield, field water capacity and permanent wilting coefficient were considered as the upper and lower boundaries, respectively, for normal plant growth. This study investigated the soil properties and groundwater resources of the Hailiutu pasture in Inner Mongolia, China. Soil water characteristics and hydraulic conductivity function curves of the pasture soil were measured based on filter paper method. Experimental results showed that air-entry and residual value were determined to be 34.6% and 13.1%, corresponding to the field water capacity and permanent wilting coefficient, respectively, and the available water capacity was 218.0 mm. The downward velocity of the soil wetting front in the silt is 3.0 mm/h. Site investigation revealed that the pasture was a natural capillary barrier, and its critical suction could optimize the upper boundary of irrigation. Considering the limited underground water resources, shallow water level, and the transpiration of Caragana Korshinskii in the pasture, an available drip irrigation method was designed. The spacing between drip irrigation pipes is 60 cm, the spacing between drip holes is 60 cm, the drip irrigation volume per hole is 475.2~838.8 mL/d, the drip irrigation time is 110~200 min at each night. Each hectare pasture exhausts 13.5~22.5 m3 water each day. Field tests showed that the proposed method is feasible and can be used for irrigation in dryland pastures.

Significance to the Horticulture Industry

Significance to the Horticulture Industry

Water-temperature controlled deformation patterns in Heifangtai loess terraces revealed by wavelet analysis of InSAR time series and hydrological parameters

Loess deposits are widely distributed in western and central China. Because loess is wet-collapsible, loess mass is prone to failure after water infiltration. Heifangtai, composed of two adjacent typical loess platforms located in the Loess Plateau beside the Yellow River, has experienced hundreds of landslides in the past few decades. Here, we derived surficial time-series deformation, velocity, and amplitude of seasonality from the Sentinel-1 SAR images acquired from October 2014 to March 2021 in the Heifangtai region and studied their relation with precipitation, temperature, and irrigation applying wavelet analysis. The decomposed velocities show that not only a large amount of along-slope deformation occurred surrounding the terrace but also a significant subsidence in the residential area in the middle of the platform was observed. The high-seasonality areas are distributed along the Yellow River and on the terrace consistent with other water sources, e.g., springs and irrigation, revealing a promotion of a periodic water-involved process on deformation in loess. Through the wavelet analysis, we found that the temperature is almost in phase with the uplift velocity when the temperature is below the freezing point. The precipitation precedes the surface displacement of ∼1 to 2 months for water penetration. The comparison between irrigation volumes and averaged displacements suggests that irrigation also plays a role in promoting subsidence from March to October but uplift in winter due to frost heave. We highlight that the retrogressions of the terraces in this region may be accelerated by both natural and anthropogenic factors. Careful monitoring and water management are highly recommended for the safety of local residences and infrastructures.

Occurrence and behavior of arsenic in groundwater-aquifer system of irrigated areas.

Groundwater arsenic pollution has received much attention worldwide for decades as a serious threat to public health, but the mechanisms responsible for arsenic mobilization are not fully understood. Groundwater and bore drilling sediment samples from Qiji county, a small geographical agricultural area with endemic arsenicosis, are collected for demonstrating the occurrence and speciation of arsenic in groundwater and sediments, and arsenic release between solid-liquid phase influenced by human activities. Results show that arsenic concentrations in groundwater vary from 5 μg/L to 19.6 μg/L, with 80% exceeding the maximum permissible limits required by WHO (10 μg/L) for drinking water and therefore constituting a health risk for humans. In a weak oxidizing environment (oxidation-reduction potential (ORP): 12.9 mV-151 mV), inorganic As(V) accounts for 85% of total dissolved As, which to some extent alleviates the harm of As pollution on humans. Total As content in the sediments is in the range of 6.98 mg/kg and 14.34 mg/kg (median of 10.71 mg/kg), three times higher than the average value of many countries. Sequential chemical leaching indicates that 11% of arsenic in sediments is labile bound and may be closely related to the arsenic in groundwater. Additionally, irrigation intensity contributes to arsenic release with diverse As3+/As5+ by dissolving weakly bound arsenic rapidly. Subsequently part of As(III) is oxidized to As(V). Competitive and/or alkaline desorption of As(V), which had been adsorbed by FeMn (hydrous)-oxides and carbonates in the unsaturated zone and the aquifer, exerts a significant role in releasing arsenic into the groundwater. Our study indicates that systematic management and regulation of irrigation intensity are required to prevent further deterioration of groundwater resources.

Modeling Soil Profile Salinity with HYDRUS-1D

Salt accumulation within the root zone significantly effects plant growth and development in arid and semi-arid regions. Today, use of low-quality irrigation water in agricultural production is increasing rapidly, because of continuous depletion and pollution of water resources. This means more salt transferred to the soil profile. It is of great importance to predetermine the effects of irrigation practices for sustainable crop production. For this purpose, models and tools that can produce reliable and fast results should be used. In this study, soil profile salinity was modeled with the HYDRUS-1D software. In present study, Three different irrigation water salinity levels (S1=0.25 – control/municipal tap water, S2=1.5, S3=3.0 dS m-1) and 4 different irrigation volumes (leaching ratio) (LR1=10%, LR2= 20%, LR3=35%, LR4=50%) were modeled in a randomized plots factorial experimental design with 3 replications. Each treatment was carried out in individual PVC lysimeters with a length of 115 cm and a diameter of 40 cm in open-field to determine the efficiency of the model at different salinity levels and leaching rates. Alfalfa (Medicago sativa L.) was preferred as a plant due to its economic value, effective root depth and being a perennial plant. During the growing period, a total of 7 irrigations were practiced and five soil samples were taken from 20, 40, 60, 80 and 100 cm depths at the last day of each month. Present findings revealed that values modeled with the HYDRUS-1D software were sufficient to determine the soil profile salinity. Relative error values (RE) ranged from 0.048 to 0.307. Increase in salinity and irrigation applications reduced the accuracy of the model. However, it can be said that the values produced by the model were sufficient even under the mentioned conditions. Especially for academic studies, the HYDRUS-1D software can be used to obtain fast and reliable results.

A New Method to Map Spring Irrigated Areas Using MODIS LST Products and Ancillary Data in an Agricultural District of Northwest China

Irrigation alleviates drought in croplands and maintains or increases crop yields. The accurate monitoring of irrigated areas is important to regional water resource management, food security, climate change, drought monitoring, and emergency disaster relief. Based on field experiments that demonstrate the feasibility of irrigated area mapping using land-surface temperature, we propose a method to map spring irrigation areas using historical meteorological data, main crop phenological characteristics, irrigation regimes, and MODIS land-surface temperature (LST) products. The distribution of irrigation intensity, spring irrigated areas (SIA, considering the irrigation intensity), and total area of spring irrigation (STIA, regardless of irrigation intensity) were monitored by the proposed method for the Donglei Irrigated District (Phase II) in northwestern China from 2011 to 2018. The spring irrigation of the study area was divided into three periods (16 January–23 February, 24 February–24 March, and 25 March–31 May). Then, the temperature threshold of the irrigated area in each period was determined by the diurnal temperature range (DTR) of the rain-fed plots and precipitation data; for the three periods, this was 12 °C, 15 °C, and 11 °C, respectively. The results showed that most of the croplands in the study area were irrigated once or twice. The SIA in most years varied between 55,900 and 73,100 ha, but in 2016, the irrigation area reached 100,200 ha. The STIA accounted for 60–70% of the irrigated area except 2016. The average accuracy of SIA monitoring was satisfactory and above 94% for years when sufficient and reliable data was available.

Irrigation Method and Volume for Korla Fragrant Pear: Impact on Soil Water and Salinity, Yield, and Fruit Quality

A field study in an orchard of Korla fragrant pear tested three levels of irrigation (as varying proportions of evapotranspiration; namely, W1: 70% ETC, W2: 85% ETC, and W3: 100% ETC) and four methods of applying such irrigation; namely, F1: surface drip, F2: subsurface, F3: root zone infiltration, and CK: flood irrigation (as the control or check). The effects of the different treatments were evaluated in terms of plant growth (shoot length and leaf area), fruit yield and quality, and the distribution of water and salt in soil. For a given method of irrigation, soil moisture content, wet-front displacement, the length of new shoots, and leaf area under W3 were significantly higher than those under W1 and W2. The salt content under W3 was also significantly lower than that under W1 and W2, whereas the yield was significantly higher—by 5.89–13.85% compared to that under W2 and by 4.08–13.13% compared to that under W1. For a given volume of irrigation, yield, water-use efficiency, and fruit quality were significantly higher under F3 and F2 than those under F1. Soil water was more uniformly distributed and its content was significantly higher under F3 than the corresponding values under F1 or F2. The salt content of the root zone was the lowest under F3, and most of the soil salt was in soil layers deeper than 80 cm, but there was no significant difference between F3 and F2 (p < 0.05). There were also no significant differences in shoot length and leaf area among the three irrigation methods (F1, F2, and F3) (p < 0.05). Compared to that under F1, root zone infiltration under W1 was 3.61% greater, that under W2 was 6.58% greater, and that under W3 was 5.43% greater. The irrigation water-use efficiency and production factor efficiency for nitrogen under F3 and F2 were significantly higher than those under F1 (p < 0.05). Principal component analysis showed that the comprehensive score for fruit quality under different volumes of irrigation was the highest under W3, was intermediate under W2, and was the lowest under W1. The corresponding ranking of different irrigation methods was F2, F3, F1, and CK. Comprehensive analysis showed that yield, quality, and the efficiency of utilization of water and fertilizer were higher under the combination W3F3 than under any other combination—therefore, irrigation at 100% of evapotranspiration applied through root zone infiltration is recommended for Korla fragrant pear. The research results can provide a theoretical basis for the optimal use of water and for salt control in pear in Korla, Xinjiang.

Improvement in potassium budget with water outflow reduction through reducing excessive irrigation in a paddy field

ABSTRACT Countermeasures to reduce radiocesium uptake by crops have been implemented in farmlands affected by the accident at Tokyo Electric Power Company’s Fukushima Daiichi Nuclear Power Plant in 2011. A widely practiced countermeasure is the application of K. Long-term maintenance of soil K is crucial due to the long physical half-life of 137Cs (30 years). Plant-available K budgets can be used as an indication of sustainable maintenance. Our previous study found that large water outflow, especially percolation, associated with excessive irrigation caused major K outflow and a negative K budget in a paddy field in Fukushima in 2018. The present study evaluated whether decreasing the water outflow by reducing the irrigation volume from 6300 to 1900 mm reduced K outflow and improved the K budget in the field during the cropping period in 2019. K concentrations in soil solution were comparable in both years, and the percolation water volume decreased to 37% that of 2018, resulting in a 53% reduction in the K output from 392 to 184 kg ha–1. The input via irrigation also decreased (−35 kg ha–1), but the output via surface runoff showed a greater reduction (−58 kg ha–1) owing to a 70% decrease in the water volume compared with 2018. Consequently, the K budget was substantially improved (from −289 to −57 kg ha–1), highlighting the importance of controlling water outflow, particularly percolation, for soil K maintenance in paddy fields with high permeability.

Unveiling microbial community and function involved in anammox in paddy vadose under groundwater irrigation

The extensive application of nitrogen fertilizer in intensive irrigation areas poses a potential threat to groundwater. Given that the vadose zone acts as a buffer zone for the underground entry of surface pollutants, an in-depth understanding of its microbial community structure and function was crucial for controlling groundwater nitrogen pollution. In this study, soil samples from paddy vadose under groundwater irrigation with different depths (G1: 6.8 m, G2: 13.7 m, G3: 15.6 m, and G4: 17.8 m) were collected to unravel the differences in microbial community structure and function at different vadose depths (0–250 cm), as well as their relationship with soil properties. Results showed some differences among soil physicochemical factors under groundwater irrigation with different depths and that some electron acceptors were more abundant than others under deep groundwater irrigation (G2–G4). Remarkable differences in microbial communities under shallow- and deep-groundwater irrigation were found. The high abundances of anammox bacteria Candidatus_Brocadia in G2 and G3 indicated that deep groundwater irrigation was beneficial to its enrichment. Iron-reducing bacteria Anaeromyxobacter and sulfate-reducing bacteria Desulfovibrio were widely distributed in vadose zone and possessed the potential for anammox coupled with Fe(III)/sulfate reduction. Norank_f_Gemmatimonadaceae had nitrate- and vanadium-reducing abilities and could participate in anammox in vadose zone. Dissimilatory nitrate reduction to ammonia (DNRA) bacteria Geobacter facilitated Fe(II)-driven DNRA and thus provided electron donors and acceptors to anammox bacteria. Soil nutrients and electron donors/acceptors played important roles in shaping microbial community structure at phylum and genus levels. Microorganisms in vadose zone under groundwater irrigation showed good material/energy metabolism levels. Deep groundwater irrigation was conducive to the occurrence of anammox coupled with multi-electron acceptors. Our findings highlight the importance of understanding the structure and function of microbial communities in paddy vadose under groundwater irrigation and reveal the potential role of indigenous microorganisms in in-situ nitrogen removal.

Evaluation of the multifunctionality of a vertical greening system using different irrigation strategies on cooling, plant development and greywater use

Vertical greening systems (VGS) are implemented in the building envelope to address challenges such as the urban heat island effect, energy reduction, air purification, support of biodiversity and recently greywater treatment (wastewater without urine and faeces) for reuse purposes. In this context, providing and using treated wastewater is a crucial point, as generally VGS are irrigated with tap water and thereby increase urban water depletion and pollution. In this study, we evaluate the multifunctionality of a pot-based VGS irrigated with untreated greywater and capable, as well, of acting as a greywater treatment system. The full-scale experimental system uses a low-tech irrigation technique and was investigated for different irrigation water volumes to identify the needed water demand to maximize local cooling by evapotranspiration and suitable plants for the different water conditions and water types. Plant development and greywater treatment capabilities were monitored from April 2020 until September 2021. Based on the highest irrigation volume, a local air temperature reduction of up to 3.4 °C was measured. The removal efficiencies for treating greywater were COD 80 %, TOC 74 %, TNb 70 %, NH4-N 81 % and Turbidity 79 %, respectively, and showed a decrease in the second year of operation. Therefore, the results support the need to develop more robust systems, since up to now mainly short-term experiments have been reported in literature.

Can rainwater harvesting replace conventional irrigation for winter wheat production in dry semi-humid areas in China?

The plastic-mulched ridge and furrow rainwater harvesting (PRFRH) planting practice is widely used in rain-fed arid and semi-arid areas. However, it remains unknown whether PRFRH can replace or reduce irrigation to achieve a high and stable wheat yield in dry semi-humid areas. In this study, two cultivation practices (PRFRH and conventional flat planting [CK]) were used in combination with three irrigation regimes (0, 75, and 150 mm) to evaluate the efficacy of PRFRH in different precipitation year types (dry, normal, and wet years). Results showed that PRFRH increased soil temperature and pre-jointing soil water storage at 0–80 cm depth, whereas irrigation increased post-anthesis soil water storage at 0–80 cm depth. Furthermore, PRFRH prolonged the duration of the jointing–anthesis stages and thereby increasing the kernel number. Both PRFRH and irrigation increased dry matter accumulation and the leaf area index. PRFRH accelerated the grain-filling rate but shortened the effective grain-filling duration, while irrigation extended the effective grain-filling duration. PRFRH did not significantly influence kernel weight, whereas irrigation increased kernel weight. Overall, PRFRH reduced the effective wheat planted area and thereby reducing spike number, although it increased the kernel number, resulting in yields that were 13.7% lower than those under CK. The yield under PRFRH was significantly higher than that under CK only in the dry year but lower in the normal and wet years. Irrigation increased the yield; however, the yield did not significantly differ between the 75 and 150 mm irrigation regimes. The water productivity and net profit under 75 mm irrigation were relatively high. In conclusion, in dry semi-humid areas, PRFRH combined with a 75 mm irrigation volume could mitigate drought stress to improve yield, water productivity, and net profit in dry years only.

Subsurface irrigation with ceramic emitters: Evaluating soil water effects under multiple precipitation scenarios

China's Loess Plateau is the optimal and largest region of growing apple trees in the world. Subsurface irrigation with ceramic emitters (SICE) is an energy-efficient and water-saving approach for fruit trees in arid and semi-arid regions. Climate change, which is shifting annual precipitation regimes, is challenging the existing irrigation scheduling. However, little is known about how annual precipitation change affect the irrigation scheduling with SICE. Therefore, simulations with HYDRUS-2D and validation experiments in apple orchard were used to study the effects of the event- and annual-scale precipitation and ceramic hydraulic conductivity of emitter (CHC) on soil water dynamics. Results indicated that annul precipitation slightly affected the irrigation volume, however precipitation events had a significant effect on emitter discharge; the outflow was 22.7% and 49.7% lower in soil than in air with CHC of 0.017 and 0.077 m d−1. There was a significant positive correlation among CHC, irrigation volume and deep percolation. Precipitation and CHC both have a significant effect on the soil water content in apple orchards, the average SWCs of wet year were 17.8%− 24.7% higher than normal and dry year, the average SWC was 0.154 and 0.191 cm3 cm−3 with emitter hydraulic conductivities of 0.017 and 0.077 m d−1, respectively, in 2010. SICE could provide a stable soil water environment for apple trees in different precipitation years. Apple trees could be continuously irrigated by SICE until July, and irrigation could be stopped when the average SWC exceeds 0.20 cm3 cm−3 after July in Loess Plateau. This work may assist orchard managers in adapting their orchards by SICE to meet apple growth under future climate change conditions.

Effects of controlled release potassium chloride application on rhizosphere bacterial community and metabolites under reduced irrigation volume

Though controlled-release potassium chloride (CRK) has been widely used, its effects on the response of microbial community to soil deficit irrigation remain unclear. Here, a three-year greenhouse pot experiment was conducted from 2018 to 2020 to investigate the effects of CRK application under different irrigation levels (conventional irrigation (90 %–100 % field capacity) and 40 % irrigation reduction) on rhizosphere bacterial community and metabolites. The results showed that rhizosphere bacterial richness, diversity, and Alphaproteobacteria, Saccharimonadaceae, Rhizobiaceae, Sphingomonas, Sphingomonadales and Sphingomonadaceae relative abundance was increased by CRK application compared with potassium chloride (KCl) application. Especially under drought conditions, the application of CRK significantly increased bacterial 16S rDNA gene copy number, Chao1 index and Shannon index by 14.1 %, 5.5 % and 0.4 % compared with potassium chloride (KCl) application. Compared with conventional irrigation plus KCl, deficit irrigation plus KCl leads to the dominance of Firmicutes and Actinobacteria. The effects of CRK plus deficit irrigation resulted in a declined relative abundance of the three phyla, e.g., Gemmatimonadales, Frankiales, Nocardioidaceaeand and enrichment of other bacterial phyla, e.g., Proteobacteria, Sphingomonadales, Sphingomonadaceae, Burkholderiaceae, and Alphaproteobacteria compared with deficit irrigation plus KCl. Metabolomic analysis showed that compared with KCl application, CRK application altered soil metabolites. The significantly changed metabolites were those involved in N-glycan biosynthesis, atrazine degradation, retinol metabolism, cutin, suberine and wax biosynthesis, and sphingolipid metabolism. This unique study provides new insights into the mechanism of rhizosphere bacteria adapting to deficit irrigation by the application of CRK.