Physical and chemical properties of a sandy loam receiving animal manure, mineral fertilizer or no fertilizer for 90 years

Abstract

Summary: Ninety years after the start of the Askov long‐term fertilization experiment on sandy loam, bulk soil was taken from the 0–20 cm and 30–35 cm depths of unfertilized (UNF), animal‐manure (FYM) treated and mineral‐fertilized (NPK) plots and analysed for textural composition, carbon content, pH, CEC, particle density and plasticity limits. Undisturbed soil cores (100 cm 3 ) from the 8–12 cm layer were brought to six different matric potentials and subjected to confined uniaxial compression, drop‐cone penetration and annulus shear tests. Water‐retention curves based on seven matric potentials were produced for undisturbed cores from the 8–12 and 30–35 cm layers. In the field, in situ shear strength of plough‐layer soil was determined by a vane shear tester and a torsional shear box. FYM and NPK treatments increased the soil organic carbon content by 23 and 11% of the amount in UNF, respectively. Corresponding increases observed in CEC were 17 and 11%. The water content at the lower and upper plastic limits both decreased from FYM to NPK to UNF. Soil bulk density in the 0‐20 cm layer was reduced in FYM and NPK treatments relative to UNF, whereas the volume of soil pores larger than 30 μm was unaffected by past fertilization. Soil receiving animal manure showed the greatest soil strength when exposed to annulus shear, drop‐cone penetration and confined uniaxial compression tests, Shear strength measurements indicated that the UNF sandy loam soil reacted like a sand, the increase in soil strength upon drying primarily being due to increased internal friction. In contrast, soil from FYM and NPK treatments showed reactions typical of a loamy soil, the increase in soil strength during drying being caused by increased cohesion in the soil matrix. The field tests employed were unable to detect the management‐induced differences in soil physical parameters found in the laboratory tests. This study shows that physical soil properties related to conditions for tillage and traffic, to crop development and erosion are significantly influenced by differences in soil organic matter levels resulting from contrasting methods of fertilizer management. Exhausting a loamy soil by long‐term lack of fertilizer application severely affects the physical properties of the soil.