Impact of Water Regime and Growing Conditions on Soil-Plant Interactions: From Single Plant to Field Scale

Global water resources quantities and qualities are declining, but at the same time, a strong demand for higher agricultural productivity continues to emerge due to population growth. This calls for a significant increase of irrigation and fertilization efficiencies and requires improving our understanding of the interactions between plants and their physical environment. The main objective of this study is to analyze the combined effect of varying drip irrigation management techniques and growing conditions (media properties and container volumes) on soil-plant interactions. In a series of experiments, irrigation flow rates and intervals ranging from 2 d to 10 min were applied to the vegetative stage of a test crop (bell pepper [Capsicum annuum L. 'Selika']) cultivated under different growing conditions-sand and perlite in buckets, perlite in containers, and loamy sand under field conditions. Data on soil water regime, plant water uptake, and plant development were monitored in each setup. Large differences were observed both in terms of root and canopy development in response to the different application rates and frequencies. The prevailing irrigation management reflects on the soil water content dynamics, and consequently, on the plant water uptake and growth. Sap flow rates measurements indicated that higher irrigation frequency or lower water application rates increased plant water uptake rates. However, in most of the cases (except for the sand) it also led to a lower root mass and a smaller root mass/leaf area ratio. Interestingly,in the single plant per bucket experiments, a larger leaf area seemed conditioned on a larger root mass, while the opposite was the case in those two experiments where plants were grown in rows (perlite in containers and loamy sand field), where most prolific canopy development was supported by the smallest root mass. Integrating findings across the different experiments, we introduce the concept of mean daily available water volume per plant as the product of container/bucket volume and mean daily water content in the medium to express the joint effect of constraints imposed by the physical volume of growing medium and their specific hydraulic properties. Mean daily available water volume per plant was found to be positively correlated with the dry root mass to leaf area ratio.