Variability of soil water tension in a trickle irrigated Chile pepper field

Summary

Soil-water tension variability in a 0.15 hectare drip irrigated chile pepper field was evaluated in order to determine the number of tensiometers required for scheduling irrigations in such a field. Four plots were irrigated with a trickle irrigation system. Fifty tensiometers were installed in each plot and monitored on 13 days using a handheld pressure transducer (tensimeter). The standard deviations of the soil-water tensions were relatively high (30 cm at 50 cm tension) and increased when the soil became drier (180 cm at 400 cm tension). The variability of the log-transformed soil-water tension values did not increase as the soil became drier. Forty-eight out of 52 sets of soil water tension measurements were approximately log-normally distributed. Therefore, it appears that the log-transformed soil-water tension values should be used for statistical inference about the mean soil water status of the field. Temporal stability of the soil-water tension readings persisted for one irrigation interval. Using a previously determined production function (yield versus soil-water tension) it is shown for this field that about seven tensiometers are needed to determine the threshold tension value above which yields start to decrease.