Spatial variability of soil penetrability and distribution of compaction layer as affected by long-term ploughing at shallow depth in Rambuda irrigation scheme in Vhembe District, South Africa

J. J. O. Odhiambo, D. G. Paterson, L. O. Nethononda

Abstract: The objective of the study was to determine the soil penetrability and distribution of compacted layer as affected by longterm shallow ploughing in Rambuda irrigation scheme. Soil penetrability measurements were made at each node of a 100 m grid using a static electronic penetrometer fitted with an integrated GPS and data logger system. A 130 mm cone was inserted into the soil at 25 mm intervals from 0-750 mm depth at a minimum insertion speed of 0.2 m/min and a maximum speed of 2 m/min. Measurements of cone penetrometer were done when the soil was at field moisture capacity. Data were subjected to descriptive statistical and geostatistical analysis. A compacted layer was detected below 250 mm depth. The coefficient of variation for the topsoil (36%) and subsoil (21%) exhibited moderate variation. Spherical and exponential models were best fit for the semivariogram analysis. Soils displayed a high spatial distribution of compacted layer particularly in the topsoil horizons. Cone penetrometer resistance for the topsoil was generally low to medium but very high for the subsoil varying from 2553 to >3010 kPa indicating that the subsoil is strongly compacted due to continuous shallow tillage. The values were higher than threshold values for root elongation for most crops.

Keywords: compacted layer; cone penetrometer resistance; Rambuda irrigation scheme; semivariograms; soil penetrability; Spatial variability

Date published: 2019-03-25