Soil shrink–swell behavior is a common phenomenon in farmland, which usually alters the process of water and solute migration in soil. In this paper, we report on a phenomenological investigation aimed at exploring the impact of drying–wetting cycles on the shrink–swell behavior of soil in farmland. Samples were prepared using clay loam collected from farmland and subjected to four drying–wetting cycles. The vertical deformation of soil was measured by a vernier caliper, and the horizontal deformation was captured by a digital camera and then calculated via an image processing technique. The results showed that the height, equivalent diameter, volume and shrinkage-swelling potential of the soil decreased with the repeated cycles. Irreversible deformation (shrinkage accumulation) was observed during cycles, suggesting that soil cracks might form owing to previous drying rather than current drying. The vertical shrinkage process consisted of two stages: a declining stage and a residual stage, while the horizontal shrinkage process had one more stage, a constant stage at the initial time of drying. The VG-Peng model fit the soil shrinkage curves very well, and all shrinkage curves had four complete shrinkage zones. Drying–wetting cycles had a substantial impact on the soil shrinkage curves, causing significant changes in the distribution of void ratio and moisture ratio in the four zones. However, the impact weakened as the number of cycles increased because the soil structure became more stable. Vertical shrinkage dominated soil deformation at the early stage of drying owing to the effect of gravity, while nearly isotropic shrinkage occurred after entering residual shrinkage. Our study revealed the irreversible deformation and deformation anisotropy of clay loam collected from farmland during drying–wetting cycles and analyzed the shrink–swell behavior during cycles from both macroscopic and microscopic points of view. The results are expected to improve the understanding of the shrink–swell behavior of clay loam and the development of soil desiccation cracks, which will be benefit research on water and solute migration in farmland.

Moistube irrigation is an efficient method that accurately irrigates and fertilizes agricultural crops. Investigation into the mechanisms of infiltration behaviors under an adjusted working head (WKH) benefits a timely and artificially regulating moisture condition within root zones, as adapted to evapotranspiration. This study explores the laws of Moistube irrigated soil water movement under constant and adjusted working heads. Lysimeter experiments were conducted to measure Moistube irrigation cumulative infiltration, infiltration rate, and to observe wetting front area and water content distribution using digital image processing and time domain reflectometry, respectively. Treatments of constant heads (0, 1, and 2 m), increasing heads (0 to 1, 0 to 2 and 1 to 2 m) and deceasing heads (1 to 0, 2 to 0 and 2 to 1 m) were designed. The results show that (1) under constant heads, the cumulative infiltration increases linearly over time. The infiltration rate and cumulative infiltration are positively correlated with the pressure head. When WKH is increased or decreased, the infiltration rate and cumulative infiltration curves significantly change, followed by a gradual stabilization. The more the head is increased or decreased, the more evident this tendency will be. (2) When WKH is increased, the wetting front migration rate and the wetted soil moisture content marked increase; when WKH is decreased, the wetting front migration rate sharply decelerates, and the water content of the wetted soil slowly grows. They both tend to equilibrium with time. (3) By regarding the same cumulative infiltration of increased WKH and constant WKH treatments as a similar initial condition, we proposed a cumulative infiltration empirical model for Moistube irrigation under variable working head. Additionally, we treat the Moistube as a clayey porous medium and construct a HYDRUS-2D numerical model to predict the infiltration behaviors under variable WKH. The validity of the two models were well proven, with MRE and NRMSE close to 0 and NSE greater than 0.867, indicating good agreements with the experimental results. This model breaks through the limitation of constant boundary of traditional numerical model and applies variable head boundary to the boundary of the Moistube pipe, which can also effectively simulate the response mechanism of Moistube irrigation to variable WKH. The research results further confirmed the feasibility of manually adjusting the WKH to regulate the discharge of the Moistube pipe and soil moisture state. Based on the HYDRUS-2D numerical model simulation results and the root distribution and water demand of typical facility crops, the selection range of placement depth and the adjustable range of WKH of Moistube irrigation were proposed. The research results provide a theoretical reference for manual adjustment or automatic control of Moistube irrigation WKH to adapt to real-time crop water demand in agricultural production.

In the face of increased competition for water resources, optimal irrigation scheduling is necessary for sustainable development of irrigated agriculture. However, optimal irrigation scheduling is a nonlinear problem with many competing and conflicting objectives and constraints, and deals with an environment in which conditions are uncertain. In this study, a multi-objective optimization problem for irrigation scheduling was presented in which maximization of net benefits and water use efficiency and minimization of risk were the objectives. The presented optimization problem was solved using four different approaches, all of which used the AquaCrop model and nondominated sorting genetic algorithm III. Approach 1 used dynamic climate data without adaption; Approach 2 used dynamic climate data with adaption; Approach 3 used static climate data without adaption; and Approach 4 used static climate data with adaption. The dynamic climate data were generated using the bootstrap resampling of original climate data. A case study of maize production in north Jiangsu Province of China was used to evaluate the proposed approaches. Under the multi-objective scenario presented and other conditions of the study, Approach 4 gave the best results, and showed that irrigation depths of 400, 325, and 200 mm were required to produce a maize crop in a dry, normal, and wet year, respectively.

Investigating the effects of natural rainfall on the soil moisture for sloping farmland is extremely important for comprehending a variety of hydrological processes. Rainfall regimes can elicit different responses to soil moisture at the depth of soil layers, and the responses may differ depending on the landscape position of the sloping farmland. This paper utilized the surface runoff natural rainfall and soil moisture measured on sloping farmland with conventional tillage and contour tillage in the red soil area of China to investigate the influence of natural rainfall events on soil moisture content and to evaluate if the response results were consistent across the four rainfall regimes. Natural rainfall events were classified into different four regimes in line with rainfall duration, rainfall amount, and the maximum 30 min rainfall intensity (I₃₀) by the k-means clustering method, including advanced, intermediate, uniform and delayed regimes. The result showed that the advanced regime was the predominant one in the study area, which represented 45.9% of the total rainfall events. The rainfall regimes influenced the surface runoff coefficient and runoff depth on sloping farmland for conventional and contour tillage, with the uniform regime generating the highest runoff coefficient (5.20% and 5.82%) and runoff depth (2.00% and 2.05%), respectively. For the conventional tillage, soil moisture at a depth of 0–20 cm increased appreciably when the rainfall amount was larger than 20 mm and larger than 30 mm for the advanced regime. For the contour tillage, soil moisture in 20–40 cm layer increased for the advanced regime when the rainfall amount was larger than 15 mm and 30 mm, while the values were modified with rainfall duration and the antecedent dry day (ADD). A longer rainfall duration had a more obvious effect on soil moisture increasing in deep soil. At a depth of 20 cm, the ADD showed an appreciably positive correlation with the increment in soil moisture, which means that a brief ADD produces a compounding effect for a natural rainfall event. The present results underline the complexity of the effect of the rainfall events on soil moisture under two tillage measures for different rainfall regimes and suggest that the advanced regime significantly affects the distinction of soil moisture and the contour tillage can effectively reduce soil water loss and enhance water storage on the sloping farmland with red soil, presenting a theoretical basis for local soil and water conservation research and sloping farmland conservation tillage management.

Preferential pathways in soil lead to nutrient leaching and groundwater contamination. However, the evolution of preferential flow with straw application remains uncertain. This study aims to experimentally determine the hypothesis that, depending on how it is applied, straw will either promote or inhibit the movement of soil preferential flow. Treatments with straw application rates of 0, 5, 10, and 15 t/ha and decomposition time points of 0, 60, and 240 d were set up for the potassium iodide–starch dye-tracer method. The results showed that the straw decomposition rate slowed down in the later stages. At 0 d, the preferential flow coefficients of straw application of 0, 5, 10, and 15 t/ha were 0.13, 0.14, 0.23, and 0.17, respectively. At 60 d, the preferential flow coefficients were approximately 0.17, 0.11, 0.22, and 0.12. Soil properties and irrigation quality improved at 0 d and 60 d. However, a marked increase of 0.31, 0.35, and 0.17 in the preferential flow coefficient was observed at 240 d. Soil properties and irrigation quality deteriorated at 240 d. These results indicate that the effect of straw incorporation and decomposition on preferential flow was initially inhibited and subsequently promoted. Soil properties and irrigation quality were initially improved and subsequently deteriorated. The study serves as a reference for rational utilization of agricultural residuals and scientific irrigation, suggesting that the optimal method of straw incorporation should be adopted based on the growth cycle of the crops.

Predicting soil–water dynamics in Moistube irrigation (ΜΤΙ) favours understanding ΜΤΙ functioning mechanisms and technical parameter design. This study proposed a physically based infiltration (PH) model extending the Green–Ampt (GA) model to a two-dimensional polar coordinate system. We treated Moistube as a clay and considered the infiltration from internal Moistube to surrounding soils. The performances of the PH model, together with a semi-physical–empirical (PH–EM) model and a numerical simulation (NUM) model, were evaluated based on regulated working pressure head (WPH) experiments. A HYDRUS 2D model was used based on experimental design to reproduce the soil–water dynamics by assigning Moistube and soil two sets of hydraulic parameters. WPH increase or decrease treatments were applied to Moistube. The Moistube discharge rate, infiltration volume, and wetting front (WF) advance were analyzed and predicted by three models. The results showed that cumulative infiltration, Moistube discharge, and effective saturation around Moistube were enhanced or abated under WPH increase or decrease, with WF accelerating or decelerating. The modelled effective saturation varied between 0.45 and 0.70, providing suitable moist conditions for crops. Percentage of bias (PBIAS) and mean absolute percentage relative error (MAPRE) were employed to evaluate model performances. Three models well-predicted infiltration characteristics and WF advance but differed in accuracy. The PH model overestimated and underestimated the Moistube discharge rate in early and later phases. The prediction accuracy in WF varied across infiltration phases and WPH modes. The PH–EM model yielded accurate results due to its empirical attribute. The NUM model produced novel phenomena of infiltration characteristics at WPH adjustment points, i.e., the discharge rate exponentially decreased over time after the WPH increased but presented restraining followed by rebounding trends after the WPH decreased. The NUM model strongly depended on the selection of the Moistube hydraulic parameters. Extending the GA model to a two-dimensional polar coordinate system by treating Moistube as a clay was practicable in modelling soil water dynamics, thereby contributing to designing and optimizing MTI technical indexes.