PREDICTION OF PHOSPHORUS UPTAKE BY WHEAT AND ITS DEPLETION IN THE RHIZOSPHERE USING A MECHANISTIC MODEL

Abstract

A green house experiment was conducted on a sandy loam soil (pH 8.2, clay 5.0%, silt 20%, sand 75%, and organic carbon 0.35%) varying in soil solution phosphorus (P) concentration from 4.2 to 412 μM. Wheat (Triticum aestivum L.) plants were grown in polyethylene lined pots containing 3.5 kg soil. Plants were harvested after 12 and 24 days of growth. Nutrient uptake model (NST 3.0) was run to predict P uptake by wheat using soil and plant parameters determined from the pot experiment. Nutrient uptake model satisfactorily predicted P uptake by wheat. However, at low P levels there was under prediction and at high P levels there was over prediction of P uptake by wheat. When root hairs were included, model calculations gave better prediction of P uptake by wheat. The effect of root hairs in P uptake was more pronounced in low P soils than in high P soils. Sensitivity analysis had shown that at low P levels, soil supplying parameters were more sensitive in controlling P uptake, whereas at high P levels, maximum influx and mean root radius were the most sensitive parameters. Model could also predict P depletion in the rhizosphere of wheat. In low P soil, soil solution P concentration decreased by 42, 62, and 77% of the original soil solution P concentration after 1, 7, and 12 days of growth, respectively, at a distance of 0.2 mm away from the root cylinder. In medium P, the depletion pattern was the same as in low P soil. But in high P soils, depletion of P was less compared to low and medium P soils.

ACKNOWLEDGMENT

The authors thank Dr. Professor Nobert Claassen, Institut fu"r Agrikultur-chemie, George-August-Universita"t, Go"ttingen, Germany for providing a copy of the latest version of the model (NST 3.0).