Suction Index Research Articles

Comparison of Indexes Relating Plant Response to Soil Moisture Status1

AbstractThe response of container‐grown sunflowers and snapbeans to soil moisture status was measured in a growth chamber and related to four soil moisture indexes. Drymatter yield was related to pre‐irrigation and to mean integrated soil moisture content and capillary suction. When related to moisture content indexes, yield appeared as a continuously rising function of moisture content, with a fairly constant slope. When related to moisture suction indexes, yield decreased very sharply with increasing capillary suction in the low‐suction range. When the maximum capillary suction index was used, most of the yield depression occurred at suctions lower than two bars, after which yield decreased at a much lower and constant rate to the 15‐bar suction. Among the four indexes examined, the maximum capillary suction index was found to be the most convenient for current control of soil moisture regimes. Application to results of fleld irrigation experiments indicates that it may be used under field conditions as well as with container‐grown plants. Since plant performance is a result of interaction between many factors in addition to soil moisture suction, an index based on a single factor cannot uniquely relate plant response to this factor. The maximum capillary suction index can, however, serve as a practical and simple tool when the effect of modifying factors is known or can be held constant.