Tillage effects on physical characteristics and crop yield of a silt loam soil under five years of continuous cropping

This paper is part of a sequence of studies on a long-term tillage trial at Massey University. Selected soil physical properties including soil penetration resistance, soil bulk density, water infiltration rate, soil water content, and crop dry matter (DM) were measured and compared under no-tillage (NT), moldboard plough (MP) and permanent pasture (PP) management. The soil type is Ohakea silt loam, representing youngest yellow-grey earth with poor natural drainage on fine texture material, and topsoil moderately to strong acid encleached soils. Soil penetration resistance significantly decreased in the MP plots soon after cultivation compared to the NT and PP plots. However, this trend was reversed within six months, following winter grazing and spring fallow when soil was recompacted. In the 0-5 cm topsoil, the penetration resistance increased from 1.2 to 1.6, 0.6 to 2.9, and 1.3 to 1.7 MPa in the PP, MP, and NT fields respectively. Bulk density measured during the early oats growing season indicated a remarkably higher density in the top 0-5 cm soil layer under the NT (1.31 g cm-3) than under the MP treatment (1.12 g cm-3). These data suggest that NT soils had higher compaction and lower total porosity at the time of planting than soils in the MP plots. On the other hand, water infiltration rates were significantly higher under the NT (1.6 mm min-1) and PP (1.2 mm min-1) treatments than the MP plots (0.7 mm min-1). These data reflect an improved macropore continuity, water-filled porosity and hydraulic conductivity under NT. The NT soils may have relatively higher resistance to penetration and high soil bulk density, but these soils conserved more water and produced comparable winter oats and summer maize DM to those under MP treatment.