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BACKGROUND: Biochar addition strongly alters net carbon (C) balance in agroecosystems. However, the effects of biochar addition on net C balance of maize field under various irrigation water quantities and qualities remains unclear. Thus, a field experiment combining two irrigation levels of full (W1) and deficit irrigation (W2 = 1/2 W1), two water salinity levels of fresh (S0, 0.71 g L−1) and brackish water (S1, 4 g L−1), and two biochar addition rates of 0 t ha−1 (B0) and 60 t ha−1 (B1) was conducted to investigate soil carbon dioxide (CO2) emissions, maize C sequestration and C budget. RESULTS: Compared with W1, W2 reduced average cumulative CO2 emissions by 6.5% and 19.9% for 2020 and 2021, respectively. The average cumulative CO2 emissions under W1S1 treatments were 5.4% and 22.3% lower than W1S0 for 2020 and 2021, respectively, whereas W2S0 and W2S1 had similar cumulative CO2 emissions in both years. Biochar addition significantly increased cumulative CO2 emissions by 17.8–23.5% for all water and salt treatments in 2020, and reduced average cumulative CO2 emissions by 11.9% for W1 but enhanced it by 8.0% for W2 in 2021. Except for W2S1, biochar addition effectively increased total maize C sequestration by 6.9–14.8% for the other three treatments through ameliorating water and salt stress over the 2 years. Compared with W1S0, W1S1 did not affect net C sequestration, but W2 treatments significantly decreased it. Biochar addition increased net C sequestration by 39.47–43.65 t C ha−1 for four water and salt treatments for the 2 years. CONCLUSION: These findings demonstrate that biochar addition is an effective strategy to increase both crop C sequestration and soil C storage under suitable water‐saving irrigation methods in arid regions with limited freshwater resources. © 2023 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Climate change presents a challenge for plants to acclimate their water relations under changing environmental conditions, and may increase the risks of hydraulic failure under stress. In this study, maize plants were acclimated to two different CO2 concentrations ([CO2]; 400 ppm and 700 ppm) while under either water stress (WS) or soil salinity (SS) treatments, and their growth and hydraulic traits were examined in detail. Both WS and SS inhibited growth and had significant impacts on hydraulic traits. In particular, the water potential at 50% loss of stem hydraulic conductance (P 50) decreased by 1 MPa in both treatments at 400 ppm. When subjected to elevated [CO2], the plants under both WS and SS showed improved growth by 7–23%. Elevated [CO2] also significantly increased xylem vulnerability (measured as loss of conductivity with decreasing xylem pressure), resulting in smaller hydraulic safety margins. According to the plant desiccation model, the critical desiccation degree (time×vapor pressure deficit) that the plants could tolerate under drought was reduced by 43–64% under elevated [CO2]. In addition, sensitivity analysis showed that P 50 was the most important trait in determining the critical desiccation degree. Thus, our results demonstrated that whilst elevated [CO2] benefited plant growth under WS or SS, it also interfered with hydraulic acclimation, thereby potentially placing the plants at a higher risk of hydraulic failure and increased mortality. [ABSTRACT FROM AUTHOR]

BACKGROUND: Increasing crop yield per unit area by increasing planting density is essential to ensure food security. However, the optimal combination of planting density and nitrogen (N) application for high‐yielding maize and its source–sink characteristics need to be more clearly understood. RESULTS: A 2‐year field experiment was conducted combining three planting densities (D1: 70 000 plants ha−1; D2: 100 000 plants ha−1; D3: 130 000 plants ha−1) and three nitrogen rates (N1: 150 kg hm−2; N2: 350 kg hm−2; N3: 450 kg hm−2). The results showed that increasing planting density significantly increased leaf area index and grain yield but negatively affected ear traits. The Richards model was used to fit the dynamic changes of dry matter accumulation of maize under different treatments, and the fitting results were good. Increasing planting density increased population yield while limiting the development of individual plants, bringing the period of rapid dry matter accumulation to an early end and accelerating leaf senescence. An appropriate nitrogen rate could prolong the period of rapid accumulation of dry matter in maize, and increase the 100‐kernel weight. Increasing planting density enhanced post‐silking dry matter accumulation to a lesser extent, and the source–sink relationship of the maize population gradually developed from sink limitation to source limitation with increasing planting density. CONCLUSION: The decrease in yield due to the insufficient source strength to meet the sink demand at too high densities was the reason that limited further improvement of the optimal planting density. An appropriate nitrogen rate facilitated the realization of yield potential at high density. © 2023 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Stomata regulate leaf CO2 assimilation (A) and water loss. The Ball–Berry and Medlyn models predict stomatal conductance (gs) with a slope parameter (m or g1) that reflects the sensitivity of gs to A, atmospheric CO2 and humidity, and is inversely related to water use efficiency (WUE). This study addressed knowledge gaps about what the values of m and g1 are in C4 crops under field conditions, as well as how they vary among genotypes and with drought stress. Four inbred maize genotypes were unexpectedly consistent in how m and g1 decreased as water supply decreased. This was despite genotypic variation in stomatal patterning, A and gs. m and g1 were strongly correlated with soil water content, moderately correlated with predawn leaf water potential (Ψpd), but not correlated with midday leaf water potential (Ψmd). This implied that m and g1 respond to long‐term water supply more than short‐term drought stress. The conserved nature of m and g1 across anatomically diverse genotypes and water supplies suggests there is flexibility in structure‐function relationships underpinning WUE. This evidence can guide the simulation of maize gs across a range of water supply in the primary maize growing region and inform efforts to improve WUE. Summary Statement: Parameter values for models simulating stomatal conductance were unexpectedly consistent for anatomically and physiologically diverse genotypes of the model C4 crop maize when they were grown across a range of water supplies in the field. [ABSTRACT FROM AUTHOR]

Plants can modify xylem anatomy and hydraulic properties to adjust to water status. Elevated [CO2] can increase plant water potential via reduced stomatal conductance and water loss. This raises the question of whether elevated [CO2], which thus improves plant water status, will reduce the impacts of soil water deficit on xylem anatomy and hydraulic properties of plants. To analyse the impacts of water and [CO2] on maize stem xylem anatomy and hydraulic properties, we exposed potted maize plants to varying [CO2] levels (400, 700, 900, and 1,200 ppm) and water levels (full irrigation and deficit irrigation). Results showed that at current [CO2], vessel diameter, vessel roundness, stem cross‐section area, specific hydraulic conductivity, and vulnerability to embolism decreased under deficit irrigation; yet, these impacts of deficit irrigation were reduced at elevated [CO2]. Across all treatments, midday stem water potential was tightly correlated with xylem traits and displayed similar responses. A distinct trade‐off between efficiency and safety in stem xylem water transportation in response to water deficit was observed at current [CO2] but not observed at elevated [CO2]. The results of this study enhance our knowledge of plant hydraulic acclimation under future climate environments and provide insights into trade‐offs in xylem structure and function. We demonstrate the hypothesis that the impact of soil water deficiencies on xylem anatomy and hydraulic properties of plant stem would be alleviated by elevated [CO2]; moreover, we also demonstrate that these impacts of elevated [CO2] are not direct but indirect. [ABSTRACT FROM AUTHOR]

• The dual crop coefficient and the multisource model were used for heterogeneous canopy. • The performance of dual crop coefficient and the multisource model was evaluated. • An accurate model that predicts ET for a heterogeneous canopy was determined. Accurately modeling evapotranspiration (ET) and its components of maize grown for seed production is essential for precision irrigation management. In this study, a dual crop coefficient method and a multisource model based on radiation interception by adjacent crop varieties were used to estimate ET and its components in the arid region of northwest China. The dual crop coefficient method and multisource model were validated using observed ET (ET EC), transpiration (T) of female (T sf) and male (T sm) parents and evaporation (E s). Observations were made using the eddy covariance system, sap flow measurements, and micro-lysimeter in 2013 and 2014. Results showed that ET estimated by the dual crop coefficient method was close to ET EC at the midseason stage, and was higher than ET EC both at the initial and the development stage due to the constant value of initial basic crop coefficient and linear interpolation at the development stage. The estimated T of female and male parents was greater than T sf and T sm in both years. Soil evaporation estimated by the dual crop coefficient method was greater than measured soil evaporation in the late growth stage. While the ET , T of female and male parents and E predicted by the multisource model were closer to the measurements. Estimated ET was 2% less (2013) and 4% greater (2014) than ET EC , T of male parents was 8% and 3% less than T sm , T of female plants was 8% and 6% less than T sm , and E was 6% and 3% less than E s. Thus the multisource model based on radiation interception by neighboring species is suitable for estimating ET and its components of maize grown for seed production in the arid region of northwest China. [ABSTRACT FROM AUTHOR]

Highlights • New non-linear dynamic WP* models were developed. • New insight of crop water production functions to develop new HI models. • Newly developed WP* and HI models improved yield simulation accuracy. Abstract Simulating yield response to different irrigation scenarios is important for agricultural production, especially in the arid region where agriculture depends heavily on irrigation. To better predict yield under different irrigation scenarios, the variation of normalized water productivity (WP*) over the whole growing period of maize for seed production and the effect of different irrigation treatments on harvest index (HI) were investigated using field experiments from 2012 to 2015 in an arid region of northwest China. Two new non-linear dynamic WP* (WP* KR-L and WP* KR-S) models derived from the Logistic and Sigmoid equations, and four new HI (HI KR-J , HI KR-M , HI KR-B and HI KR-S) models developed on the basis of water deficit multiplicative or additive models at different growth stages were compared with the measurements and the WP* (WP* AC) and HI sub-model (HI AC) in the original AquaCrop model (Version 4.0). In addition, the WP* AC and HI AC models in the original AquaCrop model were replaced by the optimal WP* and HI models to build the AquaCrop-KR model. Then the yield simulated by the AquaCrop-KR model was compared with the measured yield and the yield simulated by the original AquaCrop model. The results show that both WP* KR-L and WP* KR-S models improved the simulation of final biomass, especially for the WP* KR-L model. The tested HI sub-models, namely HI KR-J , HI KR-M , HI KR-B and HI KR-S models had good performance to simulate HI under different irrigation scenarios, and the HI KR-M model was the best among all tested sub-models. When both WP* KR-L and HI KR-M sub-models were embedded into Aquacrop, the performance of the AquaCrop model was improved significantly to simulate yield, especially under severe water stress condition, with R2 increased from 0.496 to 0.653, NRMSE decreased from 26.2% to 16.1% and EF increased from 0.055 to 0.642. [ABSTRACT FROM AUTHOR]

Flowering Model, can accurately simulate the kernel number of maize based on the flowering characteristics and is very suitable for hybrid maize seed production where the number of pollen grain is always the main strain for kernel formation. However, it isn’t suitable for the water deficit condition. Therefore, the Water-Flowering Model was built by incorporating the seed-set capacity of female plant into Flowering Model and simulating the effect of water deficit on flowering characteristics in the form of water production function. The experiment conducted at Shiyanghe Experimental Station of China Agricultural University in 2014 and 2015 was used to calibrate and validate the Water-Flowering Model, respectively. The regression coefficient (b), determination coefficient (R 2 ), relative root mean square error (RRMSE), Nash and Sutcliff modelling efficiency (EF), average relative error (ARE) and concordance index d of Willmott between the measured data and simulated results of 2015 was 0.78, 0.78, 0.2787, 0.29, 0.2501 and 0.84, respectively. To some extent, the model can be used to simulate kernel number in hybrid maize seed production under different water regimes in this area. But the key parameter, pollen density threshold (PD min ), is heavily influenced by meteorological factors. Therefore, PD min should be related to meteorological factors instead of using an average value during the flowering stage to accurately simulate kernel number using Water-Flowering Model. [ABSTRACT FROM AUTHOR]

Highlights: [•] ET and K c with different plant densities were compared. [•] The relationship between K c and LAI was investigated. [•] A relatively simple and accurate method with density ratio (K density) to calculate K c and ET was developed. [•] The performance of four methods calculating K c was evaluated. [Copyright &y& Elsevier]

The partition of available energy into evapotranspiration affected by environmental and physiological factors is critical in understanding the water cycle and optimizing the water management in the field. Our study attempted to accurately quantify the environmental and physiological control on variability in evaporative fraction ( EF) based on the Penman-Monteith model. The eddy covariance method was used to measure water flux over a canopy and then calculate the EF above a maize field in northwest China in 2007. Results indicate that the EF was lower in other growth stages than in the heading stage, so the EF value in the heading stage was taken as the standard value. The decreases in EF caused by canopy conductance and environmental factors were 0.176 and −0.026, accounting for 117% and −17% of the total difference in EF, respectively. Such results were mainly due to the following: (1) the variation of maize canopy conductance was greater than that of the environmental factors, such as air temperature, air humidity, wind speed and radiation; (2) the EF of the maize was more sensitive to variation in canopy conductance than the environmental factor. Our study revealed that crop physiological factor played an important role in determining the energy partition processes and reducing the sensible heat flux in the maize field. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Highlights: [•] An adjusted SW (MSW) model was proposed after considering mulching effect on ET. [•] The original SW model overestimated maize ET significantly over the whole season. [•] PM model performed well when canopy fully covered the substrate. [•] MSW model can simulate ET and Es well under film mulch without non-water stress. [ABSTRACT FROM AUTHOR]

The physiological basis for the advantage of alternate partial root-zone irrigation (PRI) over common deficit irrigation (DI) in improving crop water use efficiency (WUE) remains largely elusive. Here leaf gas exchange characteristics and photosynthetic CO2–response and light–response curves for maize (Zea mays L.) leaves exposed to PRI and DI were analysed under three N-fertilization rates, namely 75, 150, and 300 mg N kg−1 soil. Measurements of net photosynthetic rate (An) and stomatal conductance (gs) showed that, across the three N-fertilization rates, the intrinsic WUE was significantly higher in PRI than in DI leaves. Analysis of the CO2–response curve revealed that both carboxylation efficiency (CE) and the CO2-saturated photosynthetic rate (Asat) were significantly higher in PRI than in DI leaves across the three N-fertilization rates; whereas the N-fertilization rates did not influence the shape of the curves. The enhanced CE and Asat in the PRI leaves was accompanied by significant decreases in carbon isotope discrimination (Δ13C) and bundle-sheath cell leakiness to CO2 (Φ). Analysis of the light–response curve indicated that, across the three N-fertilization rates, the quantum yield (α) and light-saturated gross photosynthetic rate (Amax) were identical for the two irrigation treatments; whilst the convexity (κ) of the curve was significantly greater in PRI than in DI leaves, which coincided with the greater CE and Asat derived from the CO2–response curve at a photosynthetic photon flux density of 1500 μmol m−2 s−1. Collectively, the results suggest that, in comparison with the DI treatment, PRI improves photosynthetic capacity parameters CE, Asat, and κ of maize leaves and that contributes to the greater intrinsic WUE in those plants. [ABSTRACT FROM PUBLISHER]

Abstract: Accurate determination of evapotranspiration (ET) is useful to develop precise irrigation scheduling. Although eddy covariance (EC) is a direct method which is widely used to measure ET, its performance in arid region of northwest China is not clear. In this study, ET measured by EC (ETEC) was compared with that by large-scale weighing lysimeter (ETL) during the whole growing season of maize in 2009. Energy balance ratio was 0.84 for daytime fluxes, indicating that lack of energy balance closure occurred, so daytime ETEC was adjusted by Bowen-ratio forced closure method. Compared to the corresponding ETL, half-hourly daytime ETEC was underestimated by 21.8% without the adjustment and 4.8% with the adjustment. Furthermore, nighttime ETEC was adjusted using filtering/interpolation method. Mean error between half-hourly nighttime ETEC and ETL decreased from 30.2% without the adjustment to 10.3% with the adjustment. After such adjustment of day and night measurements, daily ETEC was underestimated by 6.2% compared to ETL. These results indicated that the adjusted ETEC well matched with the ETL. Moreover, the discrepancy of adjusted total ETEC and ETL was decreased to 3.2% after subtracting the overestimated ET by lysimeter resulting from irrigation and heavy rainfall events. Thus, after appropriate adjustments of observations, eddy covariance method is accurate in estimating maize ET in the arid region of northwest China. [ABSTRACT FROM AUTHOR]

Effects of alternately applying osmotic and nitrogen (N) stresses to partial root zone were studied on maize seedlings. The maize seedlings were grown in Hoagland's nutrient solution with the roots divided equally into two containers. Half of the root system was subjected to an osmotic stress (W) using PEG 6000 added in the solution at -0.2 MPa and/or nitrogen stress (N) with the N-free Hoagland's solution. After 6 days, four of such treatments, C (control), W, N, and WN were shifted to the other halves of the root systems. Results showed that when compared to the control, total root dry weight and the root/shoot ratio increased markedly for all the stress treatments. There were no statistically significant differences in shoot biomass and N accumulation of the whole plant among all the treatments. Nitrogen use efficiency for the N and WN was significantly enhanced when compared to the C and W treatments, and the shoot N concentrations were less for N and WN than for C and W. The root vitality of the non-treated halves under the W, N, or WN treatments increased by 21.1–65.6% when compared to the other halves of the same root system or by 19.7–68.9% when compared to the control roots. Such a compensation of root function was evident during our days 1, 3, and 5 observations. After each alternation, rates of biomass accumulation of all previously stressed half root systems were significantly higher than the other halves or the controls. Our results suggested that significant compensation mechanisms of growth and functions in the root system occurred both when N and osmotic stresses were localized in part of the root system and during the subsequent recovery from either of such stresses. [ABSTRACT FROM AUTHOR]

Accurate simulation of yield under different irrigation and fertilizer conditions is the basis of precise water and nitrogen management, which is the determining factor for agricultural sustainable development. To find out the responses of actual water consumption (ET a), dry mass (DM) and yield(Y) of drip-fertigated hybrid maize to different water and nitrogen levels, three-year continuous field experiments were conducted in Hexi Corridor, Northwest China from 2016 to 2018. Three irrigation levels CK, W1, W2 (100%, 75% and 50% of full irrigation) at four growth stages S1, S2, S3 and S4 (seedling, jointing, tasseling and grain filling stage) combined with seven nitrogen rates (50, 150, 200, 250, 300 kg/ha in 2016, 0, 50, 100, 150, 200, 250, 300 kg/ha in 2017 and 2018) were set. The results showed that in addition to S1W1 treatment, the yield of CK was higher than the yield under deficit irrigation of the same nitrogen level. When the nitrogen application was 150 kg/ha, the average yield of S1W1 increased by 6% compared with CK. When nitrogen application increased from 150 kg/ha to 300 kg/ha, the yield of CK, S1W2 and S3W2 decreased in different extent, by 18%, 22%, and 17% respectively. Based on the parabolic relationships between yield and nitrogen rate, we modified Jensen model by introducing a new water sensitive index which considered the response of crop water sensitivity to the nitrogen application and background mineral in soil. Comparing the modified Jensen model (W*N−Jensen model), to Jensen model and N-Jensen model, which considering the parabolic relationship between the yield and nitrogen application only, we found that W*N−Jensen model can better simulate the yield under different combinations of irrigation and nitrogen levels, with higher determination coefficient (R2), higher affinity index (d), lower normalized root mean square error (NRMSE), and lower Akaike information criterion (AIC). W*N−Jensen model has higher accuracy and consistency, and can be used to provide scientific basis for water and nitrogen management and yield forecasting in the field. • Nitrogen application rate had a parabolic effect on the grain yield of hybrid maize, and the effect was influenced by water conditions. • The water sensitive index in Jensen model was affected by both nitrogen application rate and the background value of soil mineral. • Modified W*N−Jensen model based on the response of water sensitivity to nitrogen application rate and background value of soil mineral had a better performance in simulating yield of hybrid maize. [ABSTRACT FROM AUTHOR]

• The strengths and weaknesses of DSSAT-CERES-Maize and AquaCrop were identified. • DSSAT-CERES-Maize with the two evapotranspiration (ET) options was tested. • DSSAT-CERES-Maize was inferior to handle ET simulation with drought than AquaCrop. • DSSAT-CERES-Maize showed greater potential to simulated maize yield than AquaCrop. • Both crop models had greater uncertainties under severe drought conditions. As water scarcity becomes more acute in many parts of the world, crop modeling tools that effectively simulating crop response to deficit irrigation strategies to help investigate management improvement are needed. Identifying the strengths and weaknesses of the crop models with different growth-engines are therefore of great importance. The objective of this study was to investigate the capability and improvements of the new version of a solar energy-driven crop model (DSSAT-CERES-Maize, v4.7.5.0) in simulating water consumption and yield of hybrid seed maize under different soil water conditions, and its comparison with a water-driven crop model (AquaCrop, v4.0). Data obtained from a 4-year (2012–2015) field trial on maize grown under different irrigation treatments at Wuwei, Northwest China, was used for this assessment. These models were calibrated and validated using measured daily evapotranspiration (ET), leaf area index (LAI), aboveground biomass, yield (Y), harvest index (HI) and soil water content (SWC). Daily ET was measured using a combination of an eddy covariance (EC) system, sap flow sensors, and micro-lysimeter cylinders. The ability of DSSAT-CERES-Maize using the two different ET options, i.e., Priestley-Taylor/Ritchie (PT) and FAO-56 Penman-Monteith (PM) was analyzed. The results showed that DSSAT-CERES-Maize with the PT approach had fair agreement with measured daily ET of maize under non-water stress condition (R2=0.85; NRMSE=26.7%), but poor agreement with ET under water stress conditions (R2=0.51; NRMSE=43.8%). DSSAT-CERES-Maize with the PM approach systematically underestimated ET by up to 13% under non-water stress condition, which was mainly attributed to that the maximum static CERES-Maize crop coefficient (EORATIO) was currently hard coded to 1.0. Using the PT or FAO-56 PM approach as ET input in DSSAT-CERES-Maize showed no different effect on final biomass (B) and Y simulation for full irrigation. But for water stress conditions, DSSAT-CERES-Maize with the FAO-56 PM approach simulated B and Y with higher overestimation to the measured data than those simulated using the PT approach. The simulated LAI, biomass and SWC by DSSAT-CERES-Maize using the PT approach generally well followed the trend of the measured values for most irrigation treatments. The model with the PT approach showed acceptable prediction for B and Y of different irrigation treatments across years, with NRMSE of 15.5% and 26.2%, respectively, but the accuracy decreased with an aggravation of water stress. Furthermore, the strengths and weaknesses of DSSAT-CERES-Maize and AquaCrop, and their different cores of growth-engines, i.e. RUE and normalized water productivity (WP*) were carefully discussed. It was concluded that DSSAT-CERES-Maize was a superior estimate of maize yield than was AquaCrop, especially when the climate varied dramatically between years. But DSSAT-CERES-Maize, for the simulation of maize water consumption in an arid region where drought often occurs, was inferior to AquaCrop. These results contribute to recommend the appropriate crop model for specific modeling goals. [ABSTRACT FROM AUTHOR]

• The inter-annual evapotranspiration (ET) increased significantly. • The annual mean ET was 521.68 mm and the water demand pressure was severe. • The dominant factors of the trend and fluctuation of annual ET were different. • The mean annual total potential water saving amount was 2.2 billion m3 in Northwest China. To alleviate the contradiction between crop evapotranspiration (ET) and available water resources, and to develop agricultural production, mulched irrigation, as a water saving technology, is popularized in arid areas of China. However, the observations of ET in long-term mulched farmlands are scarce, so the inter-annual variation and controlling factors of ET after mulching remain uncertain, and the overall water saving effect of mulching in arid areas has not been quantified. Therefore, we conducted the observation experiments (2007–2021) on a mulched maize field, applied the modified Shuttleworth-Wallace model and obtained multi-source data statistics to fill in the gaps in the previous research. The results showed that the mean ET in the past 15 years was 521.68 mm, and the arid areas faced more severe water demand pressure. The inter-annual ET trend of the mulched maize field increased significantly, mainly caused by the reference evapotranspiration (ET 0), while the inter-annual fluctuation was mainly attributed to the crop coefficient (K c). The contribution of plant transpiration (T r) to ET was always greater than that of soil evaporation (E s), and the contribution of solar radiation (Rs) to ET was the largest among environmental factors. In addition, based on observation data and model simulation, it was revealed that the water saving amount and ratio of the long-term mulched maize field were estimated to be 83.8 mm and 13.3 %, respectively. Furthermore, the statistical results from 49 sites in five provinces (regions) in Northwest China showed that compared with the agricultural water use in the recent 10 years, the mean annual total potential water saving amount and ratio of the mulched maize field were 2.2 billion m3 and 2.5 %, respectively. Our study will provide important guidance for understanding the variation of crop ET and water resources allocation. [ABSTRACT FROM AUTHOR]

Abstract: The effects of alternate partial root-zone drying (PRD) irrigation as compared with conventional deficit irrigation (DI) and full irrigation (FI) on leaf nitrogen (N) accumulation were investigated in maize (Zea mays L.) grown under three N-fertilization rates (1.5, 3.0, and 6.0gNpot−1). The plants were grown in split-root pots in a glasshouse and were exposed to FI, PRD, and DI treatments from the seventh leaf to tasselling/silking stage. The results showed that neither irrigation nor N-fertilization treatments influenced shoot biomass and plant leaf area; while PRD plants had the highest root biomass and root to shoot ratio compared to DI and FI plants. Increase of N rate significantly increased leaf N accumulation; across the N-fertilization rates, PRD and FI plants accumulated significantly greater amount of N in leaves than did DI plants. Leaf δ15N decreased significantly with increasing N-fertilization rate, and was significantly higher in PRD and FI than in DI plants. Water use efficiency (WUE) was the highest in PRD, followed by DI and the lowest in FI; while N-fertilization rate had no effect on WUE. It was concluded that an enlarged root system and an enhanced soil N availability under PRD might have contributed to the greater N accumulation in maize leaves. [Copyright &y& Elsevier]

• The average K c of maize under film mulch was 0.88 over 12 years. • K c was basically stable with an interannual coefficient of variation of only 12.18%. • In arid regions, K c-FAO reflected the trend of the K c-loc. • LAI or GDD can be used to estimate the K c of spring maize in an arid area. Water resource is an irreplaceable natural resource for the development of human society. As a key parameter of irrigation scheduling, crop coefficient has an important reference value for precision irrigation and water-saving in agriculture. Although crop coefficient method proposed by FAO has been verified in many areas and crops, how the crop coefficient varied during a long period and whether it was stable during different years remain uncertain. We investigated the maize evapotranspiration (ET c), reference evapotranspiration (ET 0) and crop coefficient (K c) under film mulch in northwest China through a 12-year crop evapotranspiration observation by using the eddy covariance system. From 2007 to 2018, the annual average ET c was 481.68 mm and the annual average ET 0 was 551.48 mm. To our surprise, not only the interannual variation in ET c and ET 0 was small over a 12-year period, the average crop coefficient remained more stable over a long period. The mean annual K c was 0.88, and the coefficient of variation was only 12.18%. In the whole process of crop growth and development, crop coefficient advised by FAO (K c-FAO) can reflect the variation of observed crop coefficient (K c-loc), and K c-FAO is only 7% higher than K c-loc. The K c , LAI and GDD were fitted by cubic polynomials, and the determination coefficient (R2) were 0.74 and 0.75 respectively. Our study demonstrates the stability of maize crop coefficient, the close relation between crop coefficient with LAI and GDD, and the high reliability of the crop coefficient modelling method advised by FAO. This study provides an important scientific basis for the practice of agricultural irrigation management. [ABSTRACT FROM AUTHOR]

• Joint optimization of Irrigation and planting pattern (JOIPP) were built for hybrid maize seed production. • JOIPP can guarantee seed quality, maximize yield and save water. • The optimal planting pattern increased yield by 10%, and WUE by 7.3%. Severe water scarcity necessitates the development of a scientifically informed basis for efficient crop irrigation. Both irrigation and crop planting pattern (the planting dates and the planting ratio for male to female maize inbred lines) affect the yield components in hybrid maize production. A high kernel weight, which affects seed germination, is critical in maize seed production. Therefore, the aim of this study was to build a system that jointly optimizes irrigation and planting pattern (JOIPP) to guarantee a suitable kernel weight, maximizes yield, and saves water. The JOIPP was based on a model which could simulate flowering, predict kernel number and estimate the upper and lower limits of kernel weight based on the evapotranspiration and planting pattern. Parameters in JOIPP were calibrated and validated using data from experiments conducted from 2014 to 2016 in Hexi Corridor, northwestern China. A weighted sum method was used to maximize yield and minimize irrigation. A genetic algorithm with a modified initial population generation module was used to solve this optimization problem. Results showed that when the minimum lower limit of kernel weight (LowKWmin) increased, there was decreased irrigation at the flowering stage, increased irrigation at the grain-filling stage, less optimal yield and water use efficiency when the available water insufficient. However, the associated risk of seed germination failure decreased. The optimized planting pattern, compared with the crop planting pattern used by local farmers, increased yield by about 10% and water use efficiency by about 7.3% when LowKWmin was 260 mg/kernel. JOIPP is a useful tool that enables farmers and seed companies to save water and improve yield and seed quality when planting and irrigating maize for hybrid seed production. [ABSTRACT FROM AUTHOR]

Over-irrigation to ensure high crop yields in North China Plain (NCP) has led to a sharp groundwater table decline over the past decades. We conducted a scenario analysis from1980 to 2017 with 12 irrigation strategies from T1W0M0 to T12W3M2 (T is treatment and numbers of irrigation times in wheat (W) and maize (M) seasons, 75 mm each) for the dominant winter wheat-summer maize rotation using the soil-water-atmosphere-plant (SWAP) model in the NCP. After model calibration and validation with 4-year experimental data, we analyzed the long-term simulated annual crop yield, actual evapotranspiration (ET a), water productivity (WP), groundwater table change and economic benefit to the different irrigation practices. The optimized irrigation strategy is based on an integral analysis for different precipitation year-types. Results showed that annual yield and WP increased with increased irrigation until these reached a plateau. Treatment T4W2M1 was the turning point with an annual yield of 15335 kg·ha-1, significantly higher than T2W1M1 (26 %) and T1W0M0 (63 %), but not significantly different from 4 to 5 irrigations in wet and normal years. ET a increased with increased irrigation from 456 to 644 mm yr-1. The annual WP followed a similar trend as annual crop yield for all irrigation schedules. T4W2M1 had an annual WP of 2.47 kg cm-3, significantly higher by 15 % than T2W1M1 and 24 % higher than T1W0M0, with no significant difference seen with 4–5 irrigations. The rainfed treatment mitigated groundwater table decline the best, even reversing the trend during the past four decades to 0.11 m yr-1 rise. This was followed by two irrigation treatments (−0.30 m yr-1), three irrigations (−0.55 m yr-1), four irrigations (−0.72 m yr-1), and five irrigations (−0.86 m yr-1). The latter corresponds to typical farmer practice. Using the productivity indicators, including irrigation WP, marginal benefit and economic index, T4W2M1 showed the best performance. Therefore, we recommend T4W2M1 (two irrigations at pre-wintering and jointing stages for wheat and one irrigation at maize sowing stage) as the best irrigation strategy for the wheat-maize rotation to mitigate groundwater table decline, and sustain grain yields and water productivity in the NCP; another anthesis irrigation for winter wheat is recommended during extreme dry years to sustain grain yield. • Twelve irrigation strategies for wheat-maize from 1980 to 2017 were evaluated. • Three targeted irrigations per year mitigated the groundwater table decline by 40 %. • 225 mm total for three irrigations per year is best to increase water productivity. [ABSTRACT FROM AUTHOR]

Water and nitrogen (N) supply are the two main factors limiting crops productivity. However, physiological mechanisms of crop responses to water and nitrogen stress remain to be elucidated. We examined stomatal conductance (g s), water use (ET), yield, and water productivity (WP c) of maize and analyzed the relationships between g s with ET , growth and yield under three growth stage-based deficit irrigation (mild, moderate and severe) and two nitrogen supplies (high and low nitrogen). Drought reduced g s as exacerbated by nitrogen stress. Coordination of g s by soil water content (SWC) and vapor pressure deficit (VPD) was affected by nitrogen supply. Controlling of transpiration by stomata was intensified by nitrogen stress in drought conditions. Yield was indirectly driven by g s through ET and aboveground biomass and directly by harvest index, but excessive water consumption did not result in higher yield instead reduced WP c. Field management optimization based on g s can promote the efficient use of water and fertilizer and the sustainable development of agriculture. • Drought reduced g s as exacerbated by nitrogen stress. • Coordination of g s by SWC and VPD was affected by nitrogen supply. • Controlling of transpiration by stomata was intensified by nitrogen stress. • Variations of yield and ET were driven by g s. [ABSTRACT FROM AUTHOR]

Abstract: Antioxidation responses of maize roots and leaves to water deficit and rewatering under partial root-zone irrigation (PRI) were investigated using a pot system. Plants were cultured using three irrigation methods, i.e. conventional irrigation (CI), alternate PRI (APRI) and fixed PRI (FPRI) with three different water regimes including W1 (70% field capacity, FC), W2 (50% FC) and W3 (35% FC). Compared to CI, root peroxidases (POD) activity was enhanced in the irrigated root zone of FPRI and both root zones of APRI during mild water deficit. After rewatering, POD activity was increased in the dry root zone under FPRI but reduced in the roots under APRI. Roots in the dry zone and leaves under FPRI remained high superoxide dismutase (SOD) activity after rewatering. In contrast, SOD activity decreased in the roots and leaves under CI and APRI. Malondialdehyde (MDA) contents were increased in leaves and two sub-roots under FPRI during water deficit and remained higher after rewatering compared to those under CI and APRI. MDA contents in the tissues under APRI showed similar levels to those under CI. Compared to CI, APRI showed the same biomass production, achieving significantly higher water use efficiency under mild water deficit. The results suggested that plants under APRI experienced less oxidative stress or damage induced by water deficit. [ABSTRACT FROM AUTHOR]