A rhizolysimeter facility for studying the dynamics of crop and soil processes: description and evaluation

An experimental facility was designed to study simultaneously soil and shoot processes in agricultural crop systems. The facility is composed of 48 drainage lysimeters, from which 24 can be in use at the same time. These were equipped with horizontal minirhizotrons (for non-destructive root observation), suction cups (to sample the soil solution), thermistors (for the control and monitoring of the temperature), time-domain reflectometry (TDR) probes (to control and measure the volumetric soil water content) and leachate samplers (to measure the leachate and to monitor nutrient leaching). Together with non-destructive shoot data measurements, the instrumentation can be used to study the dynamics of above- and below-ground crop growth, as well as the leaching of nutrients (like nitrate) and the water budget. The results of a 1-year maize (Zea mays L.) experiment, in which shoot growth and development were compared to root growth, nitrogen and water dynamics, are presented. Maximum leaf area and maximum root density were well synchronized in the upper soil horizons, while in deeper horizons time of maximum root density was delayed. Nitrate leaching was high throughout the season, always exceeding the 'safe limit' for drinking water (10 mg l(-1)). It was especially high during early season, exceeding the rather tolerant 'EC limit' for drinking water (50 mg l(-1)). As a consequence, 90% of the nitrogen leaching losses were observed within 50 days after planting. Intensive water percolation followed high precipitation early in the crop season. At the end of the crop season, water percolation lagged behind precipitation, as soil water content replenished. The intensive growth of the shoot up to tasseling is reflected by the extensive exploitation of soil water reserves. The coincidence of minimum soil water storage and maximum leaf area, as well as the maximum rooting density in the upper soil layers, is remarkable and demonstrates the close relationship between demand (shoot activity), supply (root activity) and the exploration of soil water reserves. The facility was demonstrated to be suitable for the investigation of complex interactions between two plant components (shoots and roots) and between the plants and the environment, as are expected to occur during the growth of an agricultural crop. It will be most useful to evaluate present and alternative agronomic strategies in relation to their environmental feasibility.