Steady state nutrition by transpiration controlled nutrient supply

Abstract

Programmed nutrient addition with a constant relative addition rate has been advocated as a suitable research technique for inducing steady state nutrition in exponentially growing plants. Transpiration controlled nutrient supply is proposed as an alternative technique for plants with a short or no exponential growth phase. A two-weeks experiment with transpiration controlled nitrogen supply to Pennisetum americanum was carried out to evaluate this method.After an adaptation phase a constant plant N-concentration was maintained, while the relative growth rate decreased rapidly. The transpiration coefficient was almost constant in time and insensitive to moderate N-stress, but increased sharply when plant N-concentration dropped below 1760 mmol/kg DW. Relative growth rate and nitrogen productivity showed a steep decline at the lowest Nconcentrations (about 1000 mmol/kg DW). Nitrogen productivity was optimal at about 1760 mmol/kg DW.The results show that transpiration controlled nutrient supply is applicable in research and gives accurate results in growth analysis. When the transpiration coefficient is known, the nutrient solution can be adjusted to give any desired plant N-concentration, except for the lowest concentrations.

Utilization of the ambient concentration as a criterion for steady state after exponential growth: Some culture experiments with optimum or suboptimum N nutrition

“…Normal maturation was favoured by this treatment, and the internal accumulation of nitrate was less than in plants grown at a constant RAR. In other studies to establish stable suboptimal regimes, a fixed proportion of the decreasing amounts of N that were absorbed by roots in the optimum treatment was added (Asher and Blamey, 1987;Braakhekke and Labe, 1990;Freijsen and Veen, 1990). Attainment of steady state in either of these culture methods is dependent on an expectation of ontogenetic drift of the N content in the stressed plants.…”

Controlling growth and chemical composition of saplings by iteratively matching nutrient supply to demand: a bootstrap fertilization technique

“…Nutrient flux rates across the root surface are often more rapid than those found in nature; root development and architecture are different from that found in soils; the necessary equipment is expensive; and the size and number of plants that can be grown are limited (e.g., Lund 1986, Koch et al 1987). Applying exponentially increasing rates of nutrients to plants in solid media is problematic because plants will not always be growing at constant exponential rates (e.g., Braakhekke andLabe 1990, Freijsen andOtten 1993), and therefore, exponential additions will not maintain steady-state growth and nutrition.…”