Observation of root behavior in a controlled soil water retention zone

Abstract

This study aimed to observe root behavior at a dry and wet soil boundary by applying a precisely controlled water supply method. In this method, a soil water retention zone (SWRZ) is formed in the plant root zone, and the volume of the SWRZ is controlled during growth of the plant in order to realize a system using a minimal amount of water for irrigation. In this study, a point water source was designed and positioned at the center of the assumed spherical shape of the SWRZ. In order to control the shape of the SWRZ easily, soil was oven dried and sieved to obtain uniform physical properties. Several soil moisture sensors were placed at 3-cm intervals from the water source in vertical and horizontal directions to confirm the existence of the SWRZ. Distilled water (10 mL at a time) was manually supplied to the plant root zone through the water source. Water supply was conducted several times a day by observing the appearance of the plant. Two tomato samples were used from seeding to fruiting stage. This experiment was conducted in an environmentally controlled growth chamber from September 2016 to January 2017. During this period, observations were conducted according to plant growth status by digging up a small amount of dry soil. As a result, root tip distribution was observed at the wet-dry boundary. At the end of the experiment, the SWRZ was taken out to analyze the root distribution on the dry and moist sides. We observed that several roots had elongated into the dry soil, accounting for 6% of the total weight of the root biomass. We also observed roots bend towards the water source, and a shape of vertex architecture was observed at the cross-section of the spherical SWRZ.