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Title: EXTRACTABLE SOIL WATER AND TRANSPIRATION RATE OF SOYBEAN ON SANDY SOILS

Author
item Sinclair, Thomas
item HAMMOND, L. - UNIV. OF FLORIDA
item HARRISON, J. - UNIV. OF FLORIDA

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/29/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: A substantial problem in understanding the response of crops to drying soils has been a quantification of the severity of the drying stress on plants. Early in this century, it was recognized that the behavior of plants was closely linked to the amount of water that could be extracted from the soil by plants. For heavy soils, stable relationships were developed for plant behavior in response to the amount of extractable water remaining in the soil expressed as a fraction of the total amount of water that could be extracted from the soil. For sandy soils, such stable relationships remained elusive. This research documented that the problem in using these relationships for sandy soils was in defining the total amount of water that was available in the soil for plant extraction. It was found that the best approach for sandy soils would be to identify in absolute terms the soil water content for the point at which plant behavior changes in response to drying soil. The more useful expression of response to relative amount of extractable soil water would need to be developed for each field situation for sandy soils.

Technical Abstract: Substantial consistency has been obtained in describing plant response to drying soil by expressing plant performance as a function of the fraction of soil water that can be used by the plants. There is, however, ambiguity whether this relationship is appropriate for sandy soils. The objective of this research was to compare the descriptions of extractable soil water by soybean (Glycine max L. Merr.) plants grown in pots with soils of different sand content. Extractable soil water was determined based both on thermodynamic and on physiological definitions of the upper and lower endpoints of extractable soil water. Large differences existed in defining the volumetric soil water of the upper endpoint either thermodynamically (commonly assumed to be -10 kPa for sands) or physiologically ('pot capacity'). As a consequence, there were large differences in the response curves obtained based on the two expressions of extractable soil water. For sandy soils it may be necessary to use directly the absolute volumetric soil water content determined under controlled conditions to interpret crop response under any particular field situation.