PHOSPHATE IN MALAYSIAN ULTISOLS AND OXISOLS AS EVALUATED BY A MECHANISTIC MODEL

ABDUL-AZIZ BIDIN, Purdue University

Abstract

Phosphate uptake from soil by plant roots depends on the phosphate supply characteristics of the soil, the phosphate absorption kinetics of the roots and the extent of the root system. A mathematical model describing phosphate uptake has been successfully tested for phosphate uptake on Indiana soils but not on tropical soils. The objective of this research was to determine if the model accurately predicts phosphorus uptake on Malaysian Ultisols and Oxisols and if root hairs play a significant role in phosphorus uptake from these soils. The models used were the Cushman model which does not measure root hair effects, and the Itoh and Barber model which does. Sorghum which has root hairs and carrot which has few root hairs were used as the test plants. Phosphate adsorption experiments used to obtain parameters for the model showed that Malaysian soils were higher in P adsorption than Indiana soils. The plant parameters showed that in the same solution phosphate concentration carrot roots had higher influx than sorghum roots. Root hair surface was 10 times greater on sorghum than on carrot roots. The model predicted phosphorus uptake by main roots, without root hair effects, that was 50% of observed uptake for sorghum and 81% for carrot. When the contribution of root hairs was included, the predicted uptake was 10 to 15% greater than observed uptake for both plant species. This showed that the more prominent root hairs on sorghum gave a significant contribution to phosphorus uptake. High correlation between predicted and observed values was obtained in all cases and there was no indication of any effect due to soil differences. Thus the model could be used to predict phosphate uptakes on tropical soils providing the role of root hairs is included.

Degree

Ph.D.

Subject Area

Agronomy

COinS