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• Modified biochar decreased pH of salt-affected soils in an intercropping system. • Oversupply of biochar had negative impact on soil water and crop yield. • A 10 t ha−1 biochar application rate was recommended to improve soil and yields. Biochar application in agricultural salt-affected soils has shown strong potential to amend soil and promote production. The effect of biochar on soil properties and crop yield varies with crop, soil, biochar properties and climate. Thus, it is critical to select suitable biochar and their application amounts for ameliorating salt-affected soils while improving its conditions and crop yields. The objectives of this study were to investigate the effect of biochar application rates on soil properties, water and temperature conditions and crop yields in saline-alkali soils under cotton-sugarbeet intercropping. We used a three-year (2018–2020) field experiment with biochar application rates of 0, 10, 50 and 100 t ha−1 in 2018, 0, 10, 25, 50 and100 t ha−1 in 2019 and 0, 10, 25 and 30 t ha−1 in 2020. Soil bulk density decreased and thus porosity increased with application of biochar. Soil pH decreased with increasing biochar application amount and the rate of change ranged from −0.003 to −0.004 per ton of biochar. Biochar application at 10 t ha−1 increased soil water content (SWC) and weighted planar soil water storage (WPSWS) in all three experimental years, while oversupply of biochar decreased SWC. Application of biochar moderated soil temperature fluctuations. The yield of cotton and sugarbeet first increased and then decreased with increasing amount of biochar. Considering the effects of biochar on soil water, temperature, and crop yields, 10 t ha−1 biochar amount was proposed as an appropriate application rate for saline-alkali soils. The results provided valuable information on appropriate biochar rates to amend salt-affected soils and their properties while increase crop yields. [ABSTRACT FROM AUTHOR]

• Irrigated pasture had greater SWRP than dryland pasture and irrigated crop. • Soils with SOC < 2% tended to be wettable and soils with SOC > 4% repellent. • SWRP curve described by a Gaussian model with three physically meaningful parameters. • Model parameters and SWRPC could be predicted by SOC. Soil water repellency (SWR) affects hydrological processes such as water infiltration, preferential flow, run-off, and evapotranspiration. Understanding the relationship between SWR and volumetric soil water content (θ) is critical for predicting hydrological processes in hydrophobic soils. In this study, water droplet penetration time (WDPT) was used to investigate the SWR persistence (SWRP) in three soil types with contrasting drainage levels, namely a well-drained Lismore (LIS) stony silt loam, a moderately well-drained Templeton (TEM) silt loam, and a poorly drained Waterton/Temuka (WAT) clay loam under three long-term (>20 years) land uses (irrigated pasture [IP], dryland pasture [DP], and irrigated crop [IC]) in Canterbury, New Zealand. The three soils belong to different soil orders (i.e., Brown, Pallic, and Gley, respectively) in the New Zealand soil classification. Within each land use, 9, 12, and 9 sites were sampled in the LIS, TEM, and WAT soils respectively. There was strong evidence of SWR in all three soil types under three land uses. The maximum SWRP (WDPT max), ranging from 6 to 1470 s with the median value of 56 s, differed with land use by following descending order of IP > DP > IC. The effects of land use on SWRP differed with soil type. Compared with other two soils, LIS soil had higher differences in WDPT max between IP and DP, but lower differences in WDPT max between DP and IC. Most of the SWRP parameters were significantly correlated with soil organic carbon (SOC) content. In soils with higher SOC content, SWR usually developed under drier conditions and declined as soils were maintained under wetter conditions. This study suggests that the WDPT max appears at soil water contents of 0.17 to 0.19 cm3 cm−3 (equivalent to 0.15 to 0.16 g g−1). Soil water repellency persistence was positively related to SOC content. Soils with SOC content < 2% tended to be wettable, while soils with SOC content > 4% tended to be water-repellent. A Gaussian model with three physically meaningful parameters was developed to successfully fit the SWRP curve (SWRPC, LnWDPT as a function of θ). Our study also showed the possibility to predict the model parameters and SWRPC using SOC content. The model needs to be tested across other soil types, land uses, and climates before it can be widely applied to predict the SWR occurrence from SOC data. Future work should also focus on the impacts of SOC composition on SWRP parameters and other hydrological properties for predicting soil water processes in water-repellent soils. [ABSTRACT FROM AUTHOR]

• Different scenarios of soil water stress remarkably influenced the plant height and aboveground biomass of winter wheat. • The returning-green stage was a critical stage for winter wheat irrigation. • The current CERES-Wheat model had large simulation errors under soil water stress at early vegetative stages. • The current CERES-Wheat model was unable to simulate the phenology discrepancy caused by soil water stress. • The uncertainties in permanent wilting point could introduce large simulation errors under severe stress conditions. Soil parameters related to soil water holding capacity could play an important role in simulating winter wheat growth under severe soil water stress, which could heavily influence the simulated soil water contents, and then biomass and final yield. In this study, a field experiment of winter wheat (Triticum aestivum L.) was conducted in two consecutive growing seasons (2012–2014) under rainfall shelter in arid areas of China, with the purpose to identify to what extent the soil parameters could influence the simulated output variables in the DSSAT-CERES-Wheat model under water stress conditions. The permanent wilting point (PWP), which were initially indirectly measured based on soil sampling, were manually tuned through a trial-and-error method based on field observations of soil water content and aboveground biomass. The results showed that the maximum advancing of maturity date was about five days under water stress conditions. The stages of returning green and grain-filling were critical periods for agricultural water management of winter wheat in arid areas. The relative mean absolute error (RMAE) of simulated and observed variables were almost all less than 20% when water stress occurred at the heading and grain-filling stages. However, there were relatively large simulation errors when water stress occurred at the wintering and returning green stages. In addition, the CERES-Wheat model did not correctly simulate the discrepancies in phenology dates of winter wheat. The overall averaged root mean square error of all treatments for total water storage in 0−100 cm soil layer and winter wheat biomass decreased to 0.3 mm and 750 kg ha−1 after manually tuning the initially indirectly measured value of PWP. In general, the CERES-Wheat model showed some limitations to simulate winter growth under complicated arid conditions. Meanwhile, the measurement uncertainty in soil parameter PWP could introduce large simulation errors in simulating crop growth response to severe water stress conditions. We suggest the soil parameter PWP should be more carefully calibrated based on relevant field observations since it is related to crop type and difficult to be directly and precisely measured. In general, it is necessary to further research into the responding mechanism and simulation of winter wheat growth to water stress in liable-drought areas. [ABSTRACT FROM AUTHOR]