Phosphorus sorption isotherm for evaluating phosphorus requirements of lettuce at five temperature regimes

Abstract

A study was conducted to determine the influence of temperature on solubility and subsequent availability of P to plants. Phosphorus sorption curves were used to fertilize the soil with six P rates corresponding to initial sorption equilibrium solution P levels in the range of 0.03 to 0.72 ppm. Yield response to P measured for temperatures was in controlled environment chambers. Growth temperatures ranged 12.7°C to 29.4°C. Sorption of added P and desorption of sorbed P increased with increase in temperature. Yields of lettuce increased with the increased sorption equilibrium solution P levels at all the temperatures. Initial sorption-equilibrium solution P levels necessary for 95% yield had to be increased from 0.20 to 0.64 ppm when temperature was lowered from 29.4° C to 12.7°C. Desorption-equilibrium solution P levels for 95% yield were nearly constant at all temperatures. The log of initial sorption equilibrium solution P as a function of temperature for 95% yield was linear between 17.2°C and 29.4°C. Comparison of the data for 95% yield in solution cultures showed that critical nutrient solution P levels were very close to the desorption equilibrium P levels for 95% yield of plants grown in soil at similar temperatures. Relative yields of lettuce and desorption equilibrium solution P levels showed the same trend to changes in temperature. The study suggests that the major role of temperature on P uptake between 17.2°C and 29.4°C is due to desorption of P from the soil. Physiological influences of temperature on plant growth and consequent P requirement play a minor role.