NUTRIENT UPTAKE: A Microcomputer Program to Predict Nutrient Absorption from Soil by Roots.

Soil nutrient uptake by plant roots can be described mathematically. Computer programs (Claassen-Barber, BarberCushman) have been developed to solve the mathematical model and predict nutrient uptake. The Barber-Cushman model uses the initial nutrient concentration in solution, the buffer power, the effective diffusion coefficient, and the mean water influx to describe the kinetics of nutrient supply through the soil to the root. The initial root length, the mean root radius, the rate of root elongation, and the half distance between roots are used to describe the root system. Michaelis-Menten kinetics with the maximal influx at high concentration (/max), the nutrient concentration below which influx ceases (Cmjn), and the nutrient concentration in solution minus Cmjn where net influx is onehalf /max (*m)» describe influx into the root. For each problem, the program gives the parameter values, a table of relative nutrient concentration with distance from the root and a plot of these data at the final time, a table of nutrient influx with time and a plot of these data, and the calculated nutrient uptake by the plant. Previously only mainframe computer programs were available. The objective of this article is to describe a user-friendly personal computer version of the BarberCushman model describing plant nutrient uptake. Additional index words: Phosphorus, Potassium, Nitrogen, Diffusion, Soil solution, Ion concentration. P depend on nutrient uptake by the root system to supply nutrients needed for growth. Knowledge about the mechanisms involved in nutrient movement from the soil into the plant has progressed to the point where the process can be mathematically described (Barber, 1984). Computer programs have been developed to numerically solve the mathematical relations involved (Claassen and Barber, 1976; Barber and Cushman, 1981) and predict nutrient uptake by plants grown in soil. These models use parameters and equations that describe the size and morphology of the root system and its change with time, the influx kinetics that describe the relation between nutrient concentration in soil solution at the root surface and net influx, and the nutrients supplied by mass flow and diffusion (Crank, 1956) through the soil to the root surface. Radial geometry is used to calculate the nutrient supply to the root by mass flow and diffusion from a cylinder of soil with a radius equal to the mean half-distance between root axes. Net influx of nutrients as related to their concentration in solution at the root surface is described by Michaelis-Menten kinetics (Epstein, 1972). The model combines the effect of soil nutrients supplied to the root with the Michaelis-Menten kinetics for nutrient uptake by the root to determine the relation between net influx and time. The solution of this relation is nonlinear and is solved numerically using the Crank-Nicolson and Newton-Ralphson techniques (Barber and Cushman, 1981). This relationship can then be 'Journal paper no. 11073, Purdue Univ. Agric. Exp. Stn. , W. Lafayette, IN 47907. Contribution from the Dep. of Agronomy. Received 4 Mar. 1987. Post-doctoral research associate and professor of agronomy, Purdue Univ., respectively. Published in J. Agron. Educ. 16:65-68 (1987). 66 JOURNAL OF AGRONOMIC EDUCATION, VOL. 16, NO. 2, FALL 1987 used with root growth to give calculated nutrient uptake with time. The models have been verified in both pot and field experiments. Close agreement has been obtained between observed and predicted uptake (Barber, 1984). The initial programs were written to use on a mainframe computer. They have not been easily accessible because the complexity of the program has made it difficult to transfer the program to other mainframe computers; hence, the programs have not been available for educational use. The goal of this article is to briefly describe a user-friendly personal computer version of the Barber-Cushman (1981) program, one that can be used for educational instruction as well as research. Specific objectives are to: 1. Briefly review the mechanistic approach concept 2. Define the parameters used and briefly describe how they are measured 3. Describe user inputs and options available 4. Present an example of input data and output results 5. Discuss some applications of the program The program is on a diskette and can be readily used on any IBM PC-compatible microcomputer.