Vehicular traffic effects on hydraulic properties of a Crosby silt loam under a long-term no-till farming in Central Ohio, USA

Changes in soil properties have been reported under several long-term no-till (NT) studies, however, the magnitude of changes in soil hydraulic properties with the use of new generation heavy machinery under NT farming is not widely documented on a long term basis. Therefore, a site under long-term NT production system was selected, where a known compaction force of 0 Mg axle load (control, C-0), two (C-2) and four (C-4) passages of 2.5 Mg water wagon axle load was applied to cover the entire plot for 20 consecutive years to assess changes in soil hydraulic properties at a site in the Central Ohio, USA. The field was under NT-based corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] rotation since 1997. An additional three plots were established in a natural woodlot (30 m adjacent from the compaction field plots) as the baseline to compare the impact of compaction under a NT managed agricultural soil. Total of 24 (three per treatment for each depth) undisturbed soil cores was collected in November 2016 from 0 to 10 cm and 10 to 20 cm depths by using a hammer based manual core sampler for determination of soil hydraulic properties (soil water retention-SWR, plant available water), and to measure pore size distribution and air porosity. Results revealed that vehicular traffic induced significant changes in SWR at 0 and -6 kPa soil water potential (psi). A reduction of SWR by 7.9 to 3.2% under C-2, by 6.6 to 0% under C-4 and by 2.4 to 0.8% under C-0 was observed at -6 to -300 kPa compared to that for the wooded soil. The soil under C-4 treatment had the lowest air porosity. Furthermore, the volume of pores with diameter> 10 mu m under C-4 was reduced by 8.3% compared to C-0 and by 7.6% compared to the wooded soil. Soil water content (transmission, plant available and residual water) followed a trend similar to that of the pore volume distribution for soil subjected to vehicular traffic-induced compaction. The data supports the conclusion that two or four passages of 2.5 Mg axle load of vehicular traffic under NT farming moderately changed SWR, plant available water, pores size distribution and air porosity compared to that of the wooded soil. However, the magnitudes of changes in soil hydraulic properties due to vehicular passages of 2.5 Mg axle load were not consistent under the NT production system. Thus, further monitoring of the impacts of compaction on soil hydraulic properties particularly on some other properties (e.g., water infiltration and air permeability) across the years is needed for better assessment of the relationships between crop production and soil hydraulic properties as well as soil resilience.