Soil compaction distribution under tractor traffic in almond ( Prunus amigdalus L.) orchard in Almería España

Abstract

Almond orchards in Almería require frequent traffic with farm machinery, about 1–8 times a year. Our main objective was to evaluate the vertical distribution of soil compaction induced by traffic of two tractors with different weights, one light (LT = 15 kN) and one heavy (HT = 50 kN), passing 0, 1, 3, 5 and 8 times over the same track on Aridisol soil. The work was performed in the Vélez Blanco District of Almería in southeast Spain. Outlined hypothesis were: (a) subsoil compaction distribution due to tractor traffic on recently tilled soils in almond orchard depends on total axle load and tractor passes, (b) topsoil compaction produced by tractor traffic depends on tractor passes and ground pressure. Variables measured were (CI) cone index, (BD) bulk density, (TSP) total soil porosity and (RD) rut depth. The relevant results were: in topsoil (0–200 mm), 1, 3, 5 and 8 passes of a LT caused mean values of CI of 1420, 1825, 1950 and 2050 kPa respectively, while for the HT with the same number of passes the values were of 1235, 1520, 1630 and 2510 kPa respectively. BD mean values had a similar behavior: 1.35, 1.38, 1.51 and 1.55 Mg m −3 for 1, 3, 5 and 8 passes of a LT and 1.30, 1.32, 1.41 and 1.52 for the HT with the same number of passes. In the subsoil (200–600 mm) the HT caused higher CI and BD values than the LT. CI mean values of the LT were between 1705 and 2490 kPa, while the HT produced 2100–2790 kPa of CI. BD mean values were between 1.58 and 1.7 Mg m −3 for the LT and 1.65–1.77 Mg m −3 for the HT. Hence, the data support both hypotheses. No significant differences were found in RD between HT and LT when they passed 1, 3 or 5 times, but there was a difference when traffic raised up to 8 passes (143 mm RD for HT). The main conclusions were: (a) this work has shown that soil compaction resulting from tractor traffic increases CI and BD and decreases total soil porosity. The data of CI and BD indicated that Almond orchard soil is unable to limit subsoil compaction under moderate traffic intensity. (b) Up to the fifth pass of either a FWA or 2WD tractor, ground pressure is responsible for topsoil compaction.