Crop Growth Effects on Variability of Tensiometer Measurements.

Two of the major problems in feedback irrigation management are where to place the sensors and how many sensors are needed. The spatial variability of agricultural systems is influenced mainly by roots, soil, climate, and irrigation method. As a result, many sensors are needed in order to acquire a representative value for the field. In this work we used an experimental plot with high spatial variability of soil properties. Drip lines were installed perpendicular to three strips of different soils (sand, loam, clay). In each soil we installed 17 tensiometers near the drippers in a synthetic material that enhances root growth within it. In addition, 13 tensiometers were installed in each soil at a distance of 10 cm from the drip lines. Variability of tensiometer measurement was calculated throughout the growth season of corn plants. The results indicate a strong influence of root water uptake on measurement variability. As plants grew and their root system expanded towards the dripper, measurement variability decreased. After harvest, measurement variability increased again to the values at the beginning of the season. Tensiometers located 10 cm from the drip lines showed much higher variability, especially at the end of the season. After harvest, their variability decreased because of the rise of average water content. Root water uptake has a significant influence of matric head patterns in the field. Since it reduces variability of matric head in the root zone, there is an advantage of installing tensiometers near the dripper in a synthetic material for irrigation management.