Effects of subsoil loosening and irrigation on soil physical properties, root distribution and water uptake of potatoes (Solanum tuberosum)

Abstract The effects of irrigation and subsoil loosening to 0.45-m depth on potato (cv. ‘Record’) root growth and water uptake in a sandy loam soil are reported. Root length was measured by destructive core sampling, and the penetration of roots into the subsoil monitored using glass minirhizotrons. Subsoil loosening resulted in an increased root length below ploughd depth, but only in irrigated plots. Despite large reductions in soil penetration resistance, the maximum depth of rooting was little affected by the loosening operation. In the summer of 1984, soil drying occurred to 1.2-m depth, with the depth of water extraction consistently 0.3–0.4 m below the observed rooting depth. It was inferred that up to 13% of the total water uptake was supplied by capillary rise to the root zone. Root water uptake in unirrigated treatments was limited by soil water deficits in excess of 50 mm, resulting in significant reductions in tuber yield. However, no differences in water uptake and yield were observed between loosened and unloosened plots. Evidence from several sources suggested that soil shrinkage on drying allowed sufficient roots to penetrate the compact, unloosened subsoil. This may have been sufficient to maintain water uptake rates similar to those found in loosened treatments.