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Characterization of Potassium Uptake and Translocation in Soybeans¹

ABSTRACT

Nutrients taken up by plant roots are translocated and distributed to plant parts in order for the plant to carry on its normal functions. To understand these functions better, we developed a five compartment mathematical model which describes K translocation within soybean [Glycine max (L.) Merrill] plant parts during vegetative and reproductive growth. The instantaneous rate of change of K contents in the five-compartment soil-soybean system was described using mass balance equations. The seasonal dry matter accumulation, nutrient concentrations, and nutrient contents of the stems, branches, leaves, and pods were used as inputs into the model to determine the effect of growth stage on uptake and translocation parameters. Among the various plant parts, the maximum K fluxes were in the pods (0.257 g m^–2 d^–1) followed by the branches (0.191 g m^–2 d^–1), the stems (0.118 g m^–2 d^–1), and the leaves (0.108 g m^–2 d^–1). The maximum fluxes of K for the stems, branches, and leaves were reached at the same time during vegetative growth. In general, K uptake was higher during vegetative than during reproductive growth. The magnitudes of the transport coefficients were variable during the growing season. During vegetative growth the highest K transport coefficient (15.18 g m^–2 d^–1) was from the stem to the branches indicating that the main transport pathway of K was from the stem to the branch. During reproductive growth the highest transport coefficient (23.26 g m^–2 d^–1) was from the stem to the pods which means that the major movement of K between plant parts during this time was from the stem to the pod. Transport coefficients of K between the branches and pods were low. These results show that the net fluxes of K in soybeans varies with transport pathway within the plant and with plant age.

¹ Contribution from the Dep. of Agronomy and Dep. of Mathematics, Univ. of Arkansas, Fayetteville, AR 72701, and from USDA-ARS Coastal Plains Soil and Water Conservation Research Center, Florence, SC.

² Graduate Assistant, Professor of Agronomy, Associate Professor of Mathematics, Univ. of Arkansas, Fayetteville, AR 72701, and Soil Scientist, USDA, respectively.

Received for publication February 4, 1985. Accepted for publication May 16, 1985.