Effect of Different Water Treatments in Soil-Plant-Atmosphere Continuum Based on Intelligent Weighing Systems

Abstract

In order to meet the needs of dynamic continuous monitoring of soil-plant-atmosphere continuum (SPAC), a new soil, plant, atmosphere analysis system has been established based on an intelligent weighing system (IWS). Four types of irrigation treatments (90%, 80%, 70%, and 60% of field capacity (FC)) were conducted on lettuce (Lactuca sativa var. ramosa Hort.) for two-season planting experiments. Regarding the soil, the relative system weight of IWS showed a significant linear correlation with the soil volumetric moisture content (SWC) (R2 = 0.64–0.94). When the SWC increased by 1.00%, the soil weight increased by 56–62 g. Regarding plants, the IWS also clearly reflected the changes in plant weight gain, transpiration rate, and stomatal conductance at different growth stages. After verification, the relative errors of the transpiration rate and stomatal conductance measured by the IWS were −9.60–22.30% and −7.20–22.20%, respectively. Regarding the atmospheric environment, the variation trend of the crop evapotranspiration (ETc) based on the IWS and the reference crop evapotranspiration (ET0) calculated with meteorological parameters were consistent. However, the numerical difference was in the uncertainty of the crop coefficient (Kc). The ETc of lettuce under the 80% FC treatment was the highest. Accordingly, a daily online measurement method for Kc was established. The Kc values of lettuce at different growth stages were 0.88, 1.22, and 2.43, respectively. The growth, yield, and water use efficiency (WUE) of crops under 80% FC treatment compared with other treatments significantly increased by 11.07–21.05%, 0.91–9.89%, and 2.16–15.80%, respectively. Therefore, the 80% FC was adopted as the irrigation low limit of potted lettuce. The experimental results provide a theoretical basis for further guiding crop irrigation.