Suboptimal fertilisation compromises soil physical properties of a hard-setting sandy loam

Abstract

Nutrient management affects not only crop productivity and environmental quality, but also soil physical properties related to soil tilth. Previous studies on soil physical properties have focussed on effects of fertiliser type, whereas the effect of fertiliser rate has been neglected. We examined the impact of no fertilisation (UNF) and different rates of mineral fertiliser (½NPK and 1NPK) and animal manure (1½AM) on an ensemble of soil physical characteristics, with the amount of fertiliser added at level 1 corresponding to the standard rate of plant nutrients for a given crop. Soil was from the Askov long-term field experiment, initiated in 1894 on a hard-setting sandy loam. We assessed clay dispersibility, wet-stability of aggregates, aggregate strength, bulk soil strength and soil pore characteristics. The soils receiving 1NPK and 1½AM had similar soil physical properties, the only differences being a wider range in the optimum water content for tillage and more plant-available water in the soil amended with 1½AM. Suboptimal fertiliser rates (UNF and ½NPK) increased clay dispersibility, soil cohesion and bulk density, and reduced aggregate stability. The physical properties of soils exposed to suboptimal fertilisation indicate that the level of soil organic matter, including active organic binding and bonding materials, has become critically low due to reduced inputs of crop residues. While long-term suboptimal fertilisation compromises soil physical properties, crop-yield-optimised rates of mineral fertilisers and animal manure appear to sustain several soil physical properties equally well.