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THE POSSIBILITY OF PREDICTING SOLUTE UPTAKE AND PLANT GROWTH RESPONSE FROM INDEPENDENTLY MEASURED SOIL AND PLANT CHARACTERISTICS: V. THE GROWTH AND PHOSPHORUS UPTAKE OF RAPE IN SOIL AT A RANGE OF PHOSPHORUS CONCENTRATIONS AND A COMPARISON OF RESULTS WITH THE PREDICTIONS OF A SIMULATION MODEL

J. L. BREWSTER, K. K. S. BHAT and P. H. NYE
Plant and Soil
Vol. 44, No. 2 (APRIL 1976), pp. 295-328
Published by: Springer
Stable URL: http://www.jstor.org/stable/42932988
Page Count: 34
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THE POSSIBILITY OF PREDICTING SOLUTE UPTAKE AND PLANT GROWTH RESPONSE FROM INDEPENDENTLY MEASURED SOIL AND PLANT CHARACTERISTICS: V. THE GROWTH AND PHOSPHORUS UPTAKE OF RAPE IN SOIL AT A RANGE OF PHOSPHORUS CONCENTRATIONS AND A COMPARISON OF RESULTS WITH THE PREDICTIONS OF A SIMULATION MODEL
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Abstract

Rape plants were grown under controlled environment conditions in a sandy loam soil fertilised to different levels of P. Other nutrients and water were regularly replenished. The growth and uptake were followed by successive harvests of replicate plants. Measurements at harvest included the mean length and number of root hairs. Growth and uptake were very similar at all levels of soil P; only towards the end of the experiment did some differences between treatments become apparent. Relative growth rates were large (0.5 g/gd) and equalled those measured earlier in solution culture. Soil solution concentrations and desorption isotherms were determined, and these data were used together with plant parameters obtained from growth in solution culture to simulate uptake and growth in the soils. The simulation aimed to take precise account of the uptake by root hairs. Simulations satisfactorily predicted growth and uptake in the well fertilised soils (soil solution concentrations 56 and 800 × 10⁻⁶ M). However in the poorer soils, experimental uptake was greater than the simulated uptake by a factor of about ten. The effects of pH changes in the rhizosphere on P mobility did not account for this discrepancy. An increase in the P concentration in the solution phase in the rhizosphere seems necessary to account for the observed uptakes. The results showed a great difference between rape and onions in their responsiveness to the level of soil P. These differences were explicable only in terms of the transport of P from the soil to the root; both species responded to a similar concentration range in solution culture. The greater ability of rape to extract P from poor soil appears to be related to its long and abundant root hairs, but uptake cannot wholly be explained by the roots and their hairs acting as simple sinks for P.

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