Linear Relationships of Soil Bulk Density and Total Porosity under Machinery Traffic in a Silty Clay Soil of River Nile State, Sudan

Abstract

Machinery traffic can cause soil compaction and alter soil physical properties in mechanized agriculture. This study evaluated the effects of machinery traffic, tillage, and soil moisture on soil bulk density (BD) and estimated total porosity (TP) in a silty clay soil at Nile Valley University, River Nile State, Sudan, during the 2019/2020 and 2020/2021 growing seasons. A split-split plot experiment with three replications included two tillage treatments, two target gravimetric soil-moisture levels (16% and 25%), and four traffic treatments (0, 1, 3, and 6 tractor passes). Soil samples were collected at depths of 0–15 and 15–30 cm. Bulk density increased from 1.261 to 1.400 g cm⁻³ at 0–15 cm and from 1.279 to 1.376 g cm⁻³ at 15–30 cm as traffic increased from zero to six passes, representing increases of 11.0% and 7.6%, respectively. Machinery traffic significantly affected bulk density at both depths (P < 0.001). Linear regression based on individual experimental-unit observations indicated positive relationships between traffic intensity and bulk density, with R² values of 0.9465 and 0.9363 for the upper and lower layers, respectively. The effects of tillage and soil moisture varied with depth, and significant interactions among management factors were observed, particularly at 15–30 cm. Estimated total porosity declined with increasing traffic, reflecting its mathematical dependence on bulk density. These findings indicate that repeated tractor passes were associated with increased soil compaction under the investigated conditions. Minimizing unnecessary machinery passes may help reduce compaction risk in comparable silty clay soils.