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Water table contribution to plant water use is a significant element in improving water use efficiency (WUE) for agricultural water management. In this study, lysimeter experiments were conducted in a controlled greenhouse environment to investigate the response of soybean water uptake and growth parameters under four different water table depths (WTD) (30, 50, 70, and 90 cm). Soybean crop water use, WUE, and root distribution under the different WTD were examined. For 30, 50, 70, and 90 cm of WTD treatments, the average water table contributions were 89, 83, 79, and 72%; the grain yields were 15.1, 10.5, 14.1, and 17.2 g/lys.; and the WUEs were 0.22, 0.18, 0.25, and 0.31 g/lys./cm, respectively. Further analysis of the root mass and proportional distribution among the different soil layers illustrated that the lysimeters with 70 and 90 cm WTD had greater root mass with higher root distribution at 40-75 cm of the soil layer. The results indicated that 70 and 90 cm of constant WTD can yield higher grain yield and biomasses with greater WUE and better root distribution than the irrigated or shallow WTD treatments.Water 2019, 11, 931 2 of 12 contribution to plant water use can be a significant element in crop production by reducing drainage and surface irrigation water volumes, and by enhancing crop water uptake from water table [6]. Thus, water table contributions to crop growth have gained attention recently, with research in controlled environments (i.e., laboratories and greenhouses) using weighed lysimeters and in the field using controlled drainage practices [5,[7][8][9].When an optimal water table depth is maintained for a crop, the water table can be considered as accessible water source to support the crop water requirement. Hence, the higher performance of the crop can be obtained with a lower amount and frequency of surface irrigation. Besides, the optimum water table depth can supply the necessary respiration and aeration for plant roots [10]. Most of the irrigation scheduling programs assume that the water table is too deep and only surface irrigation water is required to meet the plant water demand [11]. However, shallow water table can be a water source that helps to decrease the need for irrigation water [12,13]. Several researches showed that the water table can contribute to crop production through capillary rise and provide sufficient moisture for the crop root zone [6,14,15]. Meyer et al. [16] investigated the effect of soil type on soybean water use from shallow water table, and they found that 24% and 6.5% of the contribution to soybean water use in loam and clay loam soils was supplied from the water table, respectively. They found the soybean root length to be two times denser in the loam soil compared to the clay loam soil. Luo et al. [17] reported that 75% of the wheat water requirements could be met from a water table depths (WTD) of 100 cm, but that contributions from water table decreased with increasing WTD from 30 to 90 cm. This showed an inverse relationship between WTD and water tab...

Core Ideas Hydromulch was applied to disturbed, bare soil at two rates. Micro‐Bowen ratio systems quantified soil temperature and evaporation. Hydromulch moderated temperature fluctuations, especially daily maximums. Hydromulch application reduced evaporation following rainfall. North Dakota State Univ., Dep. of Soil Science, Fargo, ND 58108. Soil disturbance reduces plant‐residue cover and can leave bare soil susceptible to erosion, extreme temperature fluctuations, and increased evaporation. Under such conditions, establishing vegetation is difficult. To overcome these difficulties, managing disturbed lands by applying surface cover may be a good step toward soil reclamation. Hydromulch is often applied to stabilize soil after disturbance, but its influence on soil temperature and evaporation has not been described. This study assessed soil temperature over time and used the surface energy balance to quantify evaporation from bare soil (0×), and two rates of hydromulch application, 1× and 3× (by weight) of manufacturer's recommended rate. Diurnal temperature extremes were highest in the 0× and least in the 3×. Evaporation was highest in the 0× during the final 18 d of data collection and lowest in the 3×. These findings indicate that temperature fluctuations decrease and evaporation is reduced when hydromulch is applied to bare soil, suggesting it may aid in soil reclamation.

Core Ideas Soil moisture is needed in defining well‐watered turfgrass condition in evapotranspiration measurement. Deep soil moisture supports turfgrass growth when surface soil moisture is not sufficient. The ETa can be estimated from 0.96 ETo using the ASCE‐EWRI standardized method for well‐watered turfgrass. The ASCE‐EWRI standardized reference ET equation can be used for water management of turfgrass in northern cool climates and during drought periods. Turfgrass actual evapotranspiration (ETa) measurements are critical for water management and irrigation scheduling. With no historical ETa measurements in eastern North Dakota, turfgrass ETa rates were measured with the residual method using eddy covariance instrumentation and two arrays of soil moisture sensors on unirrigated turfgrass under natural conditions in the 2011, 2012, and 2013 growing seasons. An on‐site weather station provided weather data to calculate the standardized grass‐based reference evapotranspiration (ETo) (Allen et al., 2005). The daily ETa/ETo ratios were screened using the criteria of soil moisture ≥50% of available water for the top 30 cm of the root zone, rain amounts ≤10 mm, and a recovering period after drought. The screened monthly average ETa/ETo ratios for the unirrigated turfgrass were 1.03, 0.98, 0.94, 0.90, 0.82, and 1.18 from May to October. The mean ETa/ETo ratio for the entire growing seasons was 0.96, implying that the American Society of Civil Engineering–Environmental and Water Resource Institute ETo method was valid for guiding the turfgrass ETa calculation even in unirrigated and cold climate conditions. Because this is the first reported study on ETa measurement of a turfgrass site, the limited data can provide a baseline on water management for turfgrass under various weather conditions in this region. The results indicated that a monthly refinement of ETa/ETo values might be required to maintain the landscape turfgrass quality more precisely in terms of water management.