Spatial distribution of soil water content in potato horizontal-ridge profile under various ridge dimensions

Abstract

Vertical (slopping)-ridge is generally applied to cultivate potato crop in tropical highland area with intensive use of non-organic fertilizer, by which the soil erosion as well as environmental degradation might be significantly accelerated. On the other hand, horizontal (contour)-ridge has been very effective to reduce the soil erosion in potato cropping field, but yet slightly ineffective to support the optimal crop production, due to the waterlogging in the ridge profile. Dimension of the horizontal-ridge is expected to affect water distribution as well as the waterlogged condition, on which a specific study need to be focused, in order to develop an appropriate drainage system on the ridge. This study was aimed to characterize the spatial distribution of soil water in the horizontal-ridge profile under various ridge dimensions. Totally 9-potato-plots of 300 x 300 cm2 with 5% slope were prepared in Serang village, Purbalingga with various dimensions and replications of the horizontal ridges: 30 x 30 x 30 cm3 (G30), 30 x 40 x 30 cm3 (G40), and 30 x 50 x 30 cm3 (G50). Of each plot, the dielectrically (volumetric)-water content of the horizontal-ridge soil within the grid of 80 x 80 cm2 at the depth of 5, 10, and 20 cm were measured every months using EC5 moisture sensors and EM50 data logger, and then averaged. Based on the given grid, the data were plotted in contour pattern and were then analysed using semivariogram (Gstat and GNUplot) to characterize the spatial distribution and variability, respectively. The results showed that the spatial distribution of dielectrically (volumetric)-water contents tended to be inter-correlated within each ridge dimension, and the data were increased with soil depth and ridge dimension increment. Accordingly, the data were spatially-correlated with sill (C, semivariance) ranged from 0.00084-0.00429 cm3 cm-3 and range of influence (a) ranged from 0.624-2.809 m, in which the G50 had most representative and stable trend of the spatial variability (C and a values) among others.