Residue removal from maize (Zea mays) fields offers an opportunity to increase farmer profits, but potential tradeoffs for water dynamics and crop performance merit further evaluation. This study, established in 2014, compared the effects of two tillage practices (no-till and conventional) and two residue management practices (harvested vs. kept in place) on maize grain yields, water infiltration, evapotranspiration, and soil physical attributes. On average, maize grain yields under limited irrigation increased with residue retention by 1.1 Mg ha−1 year−1 between 2016 and 2018, but tillage had no significant effect. Total infiltration (over 30 min) was higher with residue retention. Neither tillage nor residue management had a significant impact on evapotranspiration during the vegetative growth stage. However, there was a significant residue by tillage interaction where vegetative evapotranspiration was reduced by no-till and residue retention. Conversely, penetrometer resistance was significantly reduced by both tillage and residue retention. Volumetric water content in the soil profile at planting was higher with residue retention. These results suggest that plots with residue removal would on average require 60 mm year−1 of additional irrigation to attain the same yields as fields with residue retention. In summary, our findings suggest that high rates of crop residue removal under limited irrigation in a semiarid environment can negatively affect water conservation and yields, and that tradeoffs surrounding residue export need to be fully considered in land management and policy decisions.

The main goal of this work was to evaluate the potential of the Shuttleworth–Wallace (SW) model for mapping actual crop evapotranspiration (ET) over complex surface located in the foothill of the Atlas Mountain (Morocco). This model needs many input variables to compute soil $$({r}_{\mathrm{s}}^{\mathrm{s}})$$ and vegetation ( $${r}_{\mathrm{s}}^{\mathrm{v}})$$ resistances, which are often difficult to estimate at large scale particularly soil moisture. In this study, a new approach to spatialize $${r}_{\mathrm{s}}^{\mathrm{s}}$$ and $${r}_{\mathrm{s}}^{\mathrm{v}}$$ based on two thermal-based proxy variables was proposed. Land Surface Temperature ( $$\mathrm{LST}$$ ) and Normalized Difference Vegetation Index (NDVI) derived from Landsat data were combined with the endmember temperatures for soil ( $${T\mathrm{s}}_{\mathrm{min}}$$ and $${T\mathrm{s}}_{\mathrm{max}}$$ ) and vegetation ( $${T\mathrm{v}}_{\mathrm{min}}$$ and $${T\mathrm{v}}_{\mathrm{max}}$$ ), which were simulated by a surface energy balance model, to compute the soil ( $$T\mathrm{s}$$ ) and the vegetation ( $$T\mathrm{v}$$ ) temperatures. Based on these temperatures, two thermal proxies ( $${\mathrm{SI}}_{\mathrm{ss}}$$ for soil and $${\mathrm{SI}}_{\mathrm{sv}}$$ for vegetation) were calculated and related to $${r}_{\mathrm{s}}^{\mathrm{s}}$$ and $${r}_{\mathrm{s}}^{\mathrm{v}}$$ , with an empirical exponential relationship [with a correlation coefficient (R) of about 0.6 and 0.5 for soil and vegetation, respectively]. The proposed approach was initially evaluated at a local scale, by comparing the results to observations by an eddy covariance system installed over an area planted with olive trees intercropped with wheat. In a second step, the new approach was applied over a large area which contains a mixed vegetation (tall and short) crossed by a river to derive $${r}_{\mathrm{s}}^{\mathrm{s}}$$ and $${r}_{\mathrm{s}}^{\mathrm{v}}$$ , and thereafter to estimate ET. A Large aperture scintillometer (LAS) installed over a line transect of 1.4 km and spanning the total area was used to validate the obtained ET. The comparison confirmed the ability of the proposed approach to provide satisfactory ET maps with an RMSE, bias and R2 equal to 0.08 mm/h, 0.06 mm/h and 0.80, respectively.

Laboratory experiments were conducted to investigate the hydraulics and discharge characteristics of sharp-crested weir culverts with downstream ramps for hydraulically smooth wall boundary and for free, partially submerged, and fully submerged-flow conditions. Four weir-culvert models were tested with different weir heights, ramp lengths, and culvert heights. The partially submerged-flow conditions were created when a slight increase in tailwater caused the headwater to rise due to partial submergence of the culvert. In this flow regime, supercritical flow over the ramp interacted with culvert outflow and this flow regime was classified as Supercritical Jet Interaction Regime or SJIR. Once tailwater reached the weir crest, the weir flow regime became submerged indicating fully submerged-flow condition. Based on the variations of water surface profiles, submerged flows were further classified into Surface Jump Regime (SJR), Surface Wave Regime (SWR), and Deeply Submerged Regime (DSR) and the boundaries between each flow regime were defined by regime plots. To predict discharge of weir culverts with downstream ramps, variations of discharge coefficient with weir geometry and flow regimes were studied and empirical formulations were developed. In addition, free and partially submerged flow discharges were predicted by implementing the interaction factor. It was found that the interaction factor was independent of the Froude number in SJR, while it correlated with the Froude number in SJIR. Under submerged-flow conditions, evaluation of the discharge characteristics of the proposed weir-culvert model showed correlations with water surface flow regimes and a three-stage prediction formula was proposed for estimation of submerged flow. The energy losses over weir-culvert models were also calculated and it decreased with submergence.

Crop nitrogen (N) status is known to affect crop water status and crop water use. To investigate further the N effects on soil water changes and on canopy temperature, three water levels × four N levels were imposed on two growing seasons of maize in west central Nebraska, USA. Soil water changes were measured using a neutron probe, whereas canopy temperature was measured using infrared thermometers on a ground-based mobile platform. At all water levels, soil water losses over month-long intervals were generally greater as N levels increased. Given equal water levels, early afternoon canopy temperatures were usually lower with higher N levels, but no trend or even the opposite trend was occasionally observed. Jointly considering canopy reflectance and soil water depletion shows potential to explain much of the variation in estimated instantaneous water use among plots. However, determining the relative contributions of the canopy and soil factors on a particular day may require season-to-date knowledge of the crop. Further research on assimilating such sensor data for a combined stress coefficient would improve crop modeling and irrigation scheduling when variable water sufficiency and variable N sufficiency are simultaneously significant.

Rational parameterization of the soil water stress reduction function in root water uptake model is crucial for accurate description of root water uptake and simulation of soil water dynamics in a soil–plant system. In this study, we propose three improvements to a popular transpiration-based approach to parameterize the water stress reduction function in a widely used macroscopic root water uptake model. The improvements are based on the interdependent relationships between soil and plant water status and consideration of effects of (1) relative distribution of soil water to roots on transpiration; (2) differences in growth levels of plants exposed to different levels of water stresses on potential transpiration; and (3) hysteresis of water stress on parameter optimization through identifying and discarding the data involved in the recovery periods when the discrepancy between soil and plant water availability is significant. Lysimetric experiments with winter wheat planted alternatively in greenhouse soil columns and in a field were conducted to test the proposed improvements. Through minimizing the residuals between the measured and estimated actual transpiration, the optimized parameterization was used to set up the root water uptake model. Thereupon, actual transpiration and relative transpiration were estimated and soil water content distributions were simulated. The estimated actual (RMSE ≤ 0.09 cm day−1) and relative (RMSE = 0.06) transpiration agreed well with the measurements. The simulated soil water content distributions also matched the measured values well for both experiments (RMSE ≤ 0.023 cm3 cm−3). Omitting any of the three proposed improvements reduced the estimation accuracy of relative transpiration, as the individual contribution ratio for each improvement was between 21.2 and 51.2%. The improvements should be reasonable in providing rational parameter estimation for the water stress reduction function, from which root water uptake models can be established to accurately evaluate plant transpiration and simulate soil water flow in a soil–plant system. The parameterization strategy for the water stress reduction function of root water uptake not only benefits accurate evaluation of plant transpiration under drought conditions but also contributes to further study and description regarding the apparent hysteresis of root water uptake after re-watering.

The irrigating winter wheat one or two times each season was practiced in Huanghuai Winter Wheat Region in order to reduce the over-exploitation of groundwater. In this study, plant height (PH) and its relationship with yield were analyzed in a field study conducted over three growing seasons with 102 wheat varieties irrigated zero to two times at different growth stages. Here, we found that irrigation at the jointing stage increased wheat PH by 6.60–9.70%. Whereas irrigation at the early milking stage had almost no effect on it. Against the wildtype alleles Rht-B1a and Rht-D1a, the genetic background of Rht-B1b and Rht-D1b significantly reduced PH by 14.40–15.50% and 16.90–19.10%, respectively. The combined Rht-B1b and Rht-D1b can reduce PH by 29.10–32.50%. PH was strongly, negatively correlated with grain yield in jointing irrigation (W1) or jointing + milking irrigation (W2) over three growing seasons. In contrast, a significant positive correlation was detected in no-irrigation (W0) in the 2012/2013 wheat growing season, yet no correlation was found in 2013/2014 and 2014/2015. PH was positively correlated with drought coefficient (DRC) in W1 and W2. These results augment our understanding of the relationship between PH and grain yield in different irrigation regimes and provide PH traits for wheat improvement on water saving.

Surface irrigation, particularly furrow irrigation, is the most common method of water application into agricultural lands. Despite all its advantages, furrow irrigation has some demerits, such as a potential large volume of runoff losses. In this research, an approach was proposed to reduce runoff losses and to improve water flow characteristics by creating micro-dams, barriers inside the irrigated furrows. To control water flow and increase infiltration into the soil, experimental micro-dams were created at distances of 10 and 20 m, with a height of 5 cm. Field experiments were conducted at the research farm of the College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran in summer of 2018. Two erosive inflow rates (0.6 and 0.9 L/s) were considered. Furrow length and spacing were 100 and 0.75 m, respectively. Results indicated that micro-dams increased the advance time, leading to increased infiltration. Micro-dams also increased the recession time, due to the increase in overland water volume. Moreover, results showed that in treatments with micro-dams, runoff was reduced by up to 45.3% in comparison to the control treatment. The change in furrow cross-sectional area during the irrigation event was also reduced. Micro-dams showed a great potential to reduce irrigation runoff losses, and should be considered as a management practice aiming at water and soil conservation.

As groundwater levels continue to decline in the Ogallala Aquifer, stakeholders, policymakers, and producers encourage the adoption of new irrigation technology in an effort to conserve groundwater, extend the economic life of the aquifer, and enhance profitability. One such technology currently receiving attention in the Central Ogallala region is the mobile drip irrigation (MDI) application system. This study compares MDI to low elevation spray application irrigation by evaluating the changes in variable cost per hectare to calculate the payback period for a MDI system under three levels of investment cost for grain and fiber crops representing three levels of water use while holding yield constant. Using a 3% discount rate, under the medium level of investment cost ($371 per hectare), a discounted payback period of 4.9, 9.0, and 6.3 years is required for corn, cotton, and sorghum/wheat, respectively. As the cost per hectare to convert an existing center pivot drops to $185 per hectare, the payback period also drops to 2.3, 4.2, and 3.0 years, respectively. Thus, producers growing higher water use crops are able to recover the costs of the conversion to MDI through increased water use efficiency quicker than producers growing medium and lower water use crops.

Water retention θ(h) and hydraulic conductivity K(h) are mandatory soil hydraulic properties (SHP) for consistent hydrological modeling and for an efficient irrigation management. Most commonly, SHP are determined by conventional methods (CM), based on hydrostatic equilibrium and the independent measurement of saturated hydraulic conductivity, which is used as a matching point for K(h) function. Alternatively, inverse-modeling experiments allow simultaneous parameter estimation using data from transient water flow conditions. This study aims to investigate the implications of these two protocols on simulations of soil water content (θ) and crop evapotranspiration (ET), and how they affect irrigation management and scheduling for different irrigation systems and crops. The SHP obtained from CM and IM were used in simulations with the Richards equation-based SWAP hydrological model. ET and θ were simulated for passion fruit under high-frequency drip irrigation and for pasture under conventional sprinkler irrigation. The simulation performance was evaluated using measured θ and ET obtained with passion fruit under drip irrigation. Both methods (CM and IM) gave similar results in the wetter range, while in the drier soil, CM estimated higher θ than IM. These differences affected the simulated ET and irrigation scheduling. Regarding the ET and θ simulations, for the drip irrigation scenario, in which the water content in the root zone remains near saturation, both SHP determination methods produced similar results. On the other hand, for scenarios with larger irrigation intervals such as sprinkler irrigation, simulations were affected significantly, with CM likely biasing irrigation frequency and depth.

In this study, the volume balance equation and Elliott and Walker’s two-point method were employed to estimate the Kostiakov–Lewis (KL) infiltration equation parameters. The volume balance equation has a maximum point, whose location (distance) is a function of two parameters, r (constant parameter in advance equation) and fo. (final infiltration rate). If the length of the field is less than the distance of maximum point, then parameters of the infiltration equation obtained by the two-point method will have appropriate values. Otherwise, the values of infiltration parameters would depend on the values of r and fo, and there would be a possibility of their values being inappropriate. In this method, the soil texture of the field is assumed to be homogeneous; so, the relationship between r and fo is ignored, which may render the two-point method unsuitable in heterogeneous soils. By investigating the effect of soil heterogeneity on the values of r and fo, it was found that in the two-point method, point information is used for the estimation of parameters of the KL infiltration and that there is no clear relationship between these two points. As a result, a novel method was developed in this study to estimate the KL infiltration equation parameters and applied in three irrigation fields. The infiltration parameters obtained by the proposed method had appropriate values. The infiltration depth computed with the use of parameters so obtained was in close agreement with observed infiltration depth. Thus, the proposed method is potentially useful for estimating the KL infiltration equation parameters.