Journal of Irrigation and Drainage Engineering

The root water uptake (RWU) process plays an important role in the terrestrial water cycle by connecting the soil environment to the atmosphere. Inaccurate representation of RWU functions (RWUFs) in land surface models (LSMs) has been one of the principal causes of error. Various RWUFs have been proposed for application in LSMs to simulate surface water–heat fluxes within diverse ecosystems. However, none have proven suitable for maize farmland ecosystems where vegetation differs from perennial plants, maize being a typical annual crop with significant human intervention. This study evaluated the performance of the common land model (CoLM) to reproduce energy and water-vapor fluxes during the growing season measured with an eddy covariance system in a maize farmland ecosystem of northeastern China. The simulation performance of the default CoLM differed with the interannual diversity of precipitation: it was relatively poor in the low rainfall year with underestimation of latent heat flux and overestimation of sensible heat flux, but was excellent in the high rainfall year. The effects of two different RWUFs were compared: RWUFZ, an empirical approach to represent a dynamic RWU efficiency by introducing two thresholds; and RWUFL, modifying the original RWUF with a linear function of soil water potential to one with an exponential function. The CoLM performance for simulating water and heat exchanges was significantly improved when the default RWUF was replaced with RWUFL and RWUFZ, respectively, using reasonable parameter assignments. The improvements of modified model performance demonstrated obvious interannual and intermonthly variations, which were more significant for RWUFZ than RWUFL. Thus, RWUFZ is recommended for use in the CoLM in northeast China’s maize farmland ecosystems and possibly for other similar agriculture ecosystems.

Water is the major factor limiting crop production in the Ogallala Aquifer Region of the U.S. Central High Plains. Seasonal precipitation is highly variable, low in amount, and not enough to meet full corn water needs. The Ogallala Aquifer is the major source of irrigation water for commercial agriculture in the region. However, groundwater levels of the aquifer have declined drastically due to water withdrawals for irrigation exceeding mean annual recharge. The purpose of this study was to (1) determine optimum irrigation water allocation and planting dates under various growing season precipitation scenarios for corn using AquaCrop and (2) evaluate the impact of spreading versus concentrating water based on corn yield and crop water productivity in western Kansas. Corn needed on average 450, 300, and 150 mm of irrigation for dry, normal, and wet growing seasons, respectively, assuming initial soil water at planting as 70% of field capacity. There were differences in corn yield among evaluated planting dates. Late planting produced the lowest yield. Yield and biomass were optimum at seasonal evapotranspiration (ET) of 675–703 mm for early, 664–702 mm for normal, and 623–675 mm for late planting, respectively, in sandy clay loam soils. Similarly, ET values for silt loam soils were 679–709 mm, 662–714 mm, and 625–687 mm, respectively. The highest and lowest ET in the range corresponded to wet and dry growing season precipitation scenarios, respectively. Assuming a limited well capacity of $68.1{\mathrm{m}}^3/\mathrm{h}$, planting 50% of 46.8 ha produced the highest yield and crop water productivity on both sandy clay loam and silt loam soils compared to planting 100% of the area. However, for comprehensive assessments of limited irrigation strategies, further analysis of the different land–water allocation combinations with economic analysis of net income is recommended. The results of this analysis could be useful for other semiarid regions where water for irrigation is limited.

Within the context of global warming, climate extremes, including heavy rainfall events, have become one of the most significant and attractive themes around the world. The target region of this study is confined to Huaibei Plain, an important agricultural production base in China, where the wet climate extremes can cause considerable damages to the economy, particularly to agriculture. In this study, lysimeter measurements at the Wudaogou Hydrological Experiment Station in Huaibei Plain region were used for analyzing the effects of the water table on crop growth and production. The crops studied included summer maize, winter wheat, and summer soybean. From the interannual and intraseasonal scale, temporal and spatial distributions of heavy rainfall events for 49 stations in Huaibei Plain over the period 1951–2012 were examined rigorously by means of the Fortran language. The results demonstrate that an optimum groundwater depth range in which crop yields were highest was observed for all three crop species analyzed (0.8–2.5 m for maize, 0.8–1.5 m for wheat, and 0.8–1.2 m for soybean). As groundwater levels become shallower than these depth bands, crop yields declined sharply, suggesting negative effects of waterlogging and root anoxia. Groundwater levels greater than these depth bands were associated with gradually declining yields because deeper groundwater could not compensate (through phreatic evaporation) for rainless periods of moisture stress during the growing season. Heavy rainfall events have shown an increased and spreading trend since 1950s, especially in the 1990s. The frequency, duration, and precipitation of heavy rains in Huaibei Plain show a tendency of spreading from some areas to the whole region during the 1950s–2000s, and the number of heavy rains entered into a period of increase during the 1990s–2000s. The waterlog disaster is still one main factor that strains local agricultural production due to the incomplete drainage system in Huaibei Plain.

Baffle sluice modules are used as onfarm volumetric water delivery structures. Several methods for module design have been presented so far to limit the discharge variations to the nominal design value for the variation range of a specified water surface. All methods were on the basis of assumptions to analytically determine the baffle dimensions; hence experimental studies are inevitable for choosing the most appropriate one. Initially in this paper, the performances of current theoretical design methods were evaluated experimentally. On the basis of the obtained results, the common fundamental assumptions of the flow controls through the module were revised. Then, new design criteria of using the baffle modules in parallel were proposed. The new design scheme was on the basis of installing a low delivery module in parallel with a high delivery one. The modules’ dimensions then were determined to minimize the discharge variations. Finally, the performance of the new design scheme was verified experimentally, which shows that the discharge deviation from the nominal design discharge was less than that of all design methods available in the literature.