Temporal stability of the spatial distribution of water storage in a soil under citrus cultivation

The objective of this work was to quantify and characterize the spatio-temporal variability and the temporal stability of water storage in a yellow Latosol under citrus cultivation. The experimental plot was installed on a soil under a 10 years old citrus crop, consisting of 40 observation points along two transects in a 4 m x 7 m spacing, that is, two parallel transects 1 and 2 (two plant rows) spaced 7 m with 20 points each 4 m apart, encompassing a 80 x 14 m land area (40 plants). Each point was located in-between two plants (2 m from the stem) in the row. Transect 1 points were enumerated from 1 to 20 and those of transect 2 from 21 to 40 in the opposite direction. At each observation point an aluminum tube accessing the neutron probes was installed down to the depth of 1.20 m. Weekly measurements were made over two years from November through July of the following year. Disturbed soil samples were also taken from each observation point for a soil mechanical analysis along the profile. All 40 points showed temporal stability for the measured parameter, that is, they kept their characteristics independent of sampling time; this was proven by means of the Pearson correlation coefficient among data. By means of the relative difference technique it was possible to identify the points that, independently of time, estimate the real field mean, the driest points and the moistest points. This technique identified point 28 as the representative for the mean and point 15 as the driest and point 05 as the moistest point.