Interweaving Monitoring Activities and Model Development towards Enhancing Knowledge of the Soil-Plant-Atmosphere Continuum

The study of water pathways from the soil to the atmosphere through plants-the so-called soil-plant-atmosphere continuum (SPAC)-has always been central to agronomy, hydrology, plant physiology, and other disciplines, using a wide range of approaches and tools. In recent years, we have been witnessing a rapid expansion of interweaving monitoring activities and model development related to SPAC in climatic, ecological, and applications other than the traditional agrohydrological, and it is therefore timely to review the current status of this topic and outline future directions of research. The initiative for the special section of Vadose Zone Journal on SPAC emanated from several sessions we recently organized in international conferences and meetings. With a view to the specific research questions covered in this special section, this article introduces and reviews SPAC underlying issues and then provides a brief overview of the invited contributions. We have grouped together the 15 contributions under three main sections related to the local, field, and landscape spatial scales of interests. Within these sections, the papers present their innovative results using different measuring techniques (from classic tensiometers and TDR sensors to more advanced and sophisticated equipment based on tomography and geophysics) and different modeling tools (from mechanistic models based on the Richards equation to more parametrically parsimonious hydrologic balance models). They provide a snapshot of the current state of the art while emphasizing the significant progress attained in this field of research. New technological developments and applications are also highlighted

Short-term watering-distance and symmetry effects on root and shoot growth of bell pepper plantlets

Drip lines were located at distances ranging from 0 to 60 cm from one or both sides of a row of pepper plantlets, and we monitored the effects on their shoot development during 76 days from transplanting to full-size first fruits, on the final root system, and on the areal water and salt distributions in the upper 15-cm soil layer. The experiment was conducted in a greenhouse with a sandy soil, and excess fresh water (1.9 L d-1 per plant) was applied via short daily irrigations. In addition, the effects of watering distance and symmetry on the potential water uptake rate were analyzed with a coupled-source-sink steady flow and uptake model. Initial faster shoot growth with the one-side system and short distances progressively changed to faster growth with the two-side system and longer watering distances, with the optimum at 30-40 cm. These temporal changes are attributed to temporal changes in the root uptake of irrigation water: small plants with small root systems benefit from the larger water supply to a smaller soil volume provided by the one-side system, whereas larger plants with greater water needs could extract more irrigation water when they developed larger, split root systems in the two-side irrigation. Balanced root systems and maximal shoot growth can be obtained by starting the irrigation with a line on each side, near the plants, and moving the lines after a short time.Drip irrigation Water flow and uptake modeling