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 shoo t processes in agricultural crop systems. The facility is composed of 48 dr ainage lysimeters, from which 24 can be in use at the same time. These were equipped with horizontal minirhizotrons (for non-destructive root observat ion), suction cups (to sample the soil solution), thermistors (for the cont rol and monitoring of the temperature), time-domain reflectometry (TDR) pro bes (to control and measure the volumetric soil water content) and leachate samplers (to measure the leachate and to monitor nutrient leaching). Toget her with non-destructive shoot data measurements, the instrumentation can b e used to study the dynamics of above- and below-ground crop growth, as wel l as the leaching of nutrients (like nitrate) and the water budget. The res ults 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 synchronize d in the upper soil horizons, while in deeper horizons time of maximum root density was delayed. Nitrate leaching was high throughout the season, alwa ys exceeding the 'safe limit' for drinking water (10 mg l(-1)). It was espe cially high during early season, exceeding the rather tolerant 'EC limit' f or drinking water (50 mg l(-1)). As a consequence, 90% of the nitrogen leac hing losses were observed within 50 days after planting. Intensive water pe rcolation 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 tasselin g is reflected by the extensive exploitation of soil water reserves. The co incidence of minimum soil water storage and maximum leaf area, as well as t he maximum rooting density in the upper soil layers, is remarkable and demo nstrates the close relationship between demand (shoot activity), supply (ro ot activity) and the exploration of soil water reserves. The facility was d emonstrated to be suitable for the investigation of complex interactions be tween two plant components (shoots and roots) and between the plants and th e environment, as are expected to occur during the growth of an agricultura l crop. It will be most useful to evaluate present and alternative agronomi c strategies in relation to their environmental feasibility.