Maintaining exponential growth, solution conductivity, and solution pH in low-ionic-strength solution culture using a computer-controlled nutrient delivery system.

Abstract

Studies of plant nutrient requirements in solution culture have often used nutrient concentrations many-fold higher than levels found in fertile soils, creating an artificial rooting environment that can alter patterns of nutrient acquisition. The relative addition rate (RAR) technique addresses this problem by providing nutrients in exponentially increasing quantities to plant roots in solution culture. A computer-controlled RAR nutrient delivery system has been developed to reduce workload and to facilitate more frequent nutrient additions (4x daily) than is possible with manual additions. In initial experiments, a minimum background solution containing 500 microM nitrogen and all other essential nutrients in optimal proportions was required for the healthy growth of Triticum aestivum. This requirement was reduced to 50 microM nitrogen when calcium in the background solutions was increased to 400 microM. Varying the abundance of ammonium and nitrate in both background and delivery solutions provided a means of controlling plant-induced pH changes in growth solutions. In optimized solutions, plant relative growth rates (RGR) in the order of 0.2 g g(-1) plant d(-1) were maintained over a 22 d experimental period. Variation in RARs provided a means of growing plants with varying RGRs under relatively constant conditions of solution electrical conductivity and pH.