Physical quality of sandy soils under orange orchards in Southern Brazil

Abstract

Sandy soils are characterized by low organic matter content and soil water retention and availability. Conventional tillage has been used for the implementation of orange orchards, but it exposes the soil to erosion and promotes accelerated oxidation of organic matter with negative impacts on the soil’s physical quality. The objective of this study was to evaluate the soil physical quality of sandy soils influenced by two soil tillage practices for planting the orange trees in areas after long-time under pastures. Soil sampling was carried out in three experimental areas (one under Lixisol and two under Ferralsol) where the planting of orange trees had been carried out using two tillage practices: (i) conventional tillage in total area; and (ii) localized conventional tillage in a strip corresponding to the orange tree planting lines. A complete randomized design was used with two treatments (total or strip tillage) and four replications. Disturbed and undisturbed soil samples were taken in 2011 (8 to 18 years after the establishment of the treatments) from the 0.00-0.10 and 0.10-0.20 m layers in transects crossing: (i) under canopy projection below orange trees; (ii) under machine wheel tracks in the interrow of the orange trees; and (iii) under grass groundcover between the wheel tracks in the interrow of the orange trees. The following determinations were made for these samples: texture analysis, total organic carbon, soil bulk density, reference bulk density obtained with saturated soil subjected to a 200 kPa, soil resistance to penetration, soil water content, and water retention curves and the least limiting water range. The results suggest that total tillage for the implantation of orange orchards is unnecessary; however, after a long time of establishing orange orchards occurs soil physical quality discontinuity under wheel tracks compared to the other sampling positions. A positive correlation between organic carbon and soil physical quality was identified under the canopy of trees and grass groundcover in the interrow of the orange trees. For similar sand content, the higher soil organic carbon in the Ferralsol provided better physical quality than in Lixisol.