Aggregate strength and mechanical behaviour of a sandy loam soil under long‐term fertilization treatments

Abstract

Summary Current concern for soil quality has stimulated research on soil biological and chemical properties. In contrast, the mechanical behaviour of soil is somewhat neglected. We have examined the effects on soil mechanical properties of more than 100 years of contrasting fertilization employing three treatments from the Askov long‐term experiment: UNF (unfertilized), NPK (mineral fertilized) and AM (animal manured). We have measured tensile strength of aggregates when air‐dry and when adjusted to −10, −30 and −100 kPa pressure potential. Four aggregate size classes were investigated (1–2, 2–4, 4–8 and 8–16 mm diameter). Soil fragmentation was characterized in the field using a drop‐shatter test. Bulk soil strength was determined in the field using a shear vane and a torsional shear box. Soil texture, pH, cation exchange capacity and microbial biomass were measured. The unfertilized soil has little soil organic matter and microbial biomass and is dense. Its aggregates were strong when dry and weak when wet. In contrast, the manured soil had strong aggregates when wet and rather weak ones when dry. The NPK soil generally had intermediate properties. The differences between the soils when dry seem to be related to differences in dispersible clay content, whereas the differences when wet are related to differences in the amount of organic binding and bonding material. The optimal water content for tillage as well as the tolerable range in water content was largest in the manured soil and smallest in the unfertilized soil. Our results indicate that soil mechanical properties should be measured over a range of water regimes to determine the effects of various long‐term fertilization treatments.

Soil Infrastructure, Interfaces & Translocation Processes in Inner Space ("Soil-it-is"): towards a road map for the constraints and crossroads of soil architecture and biophysical processes

“…Relation between the content of clay and OC for a range of Danish surface soils with different soil management. Results on soil physical characteristics were reported for the Group I through Group III soils by Munkholm et al (2001) and Schjønning et al (2002a), the Askov B2 and B4 fields were studied by Munkholm et al (2002), and the Askov B5 soil by Schjønning et al (1994). Soils with poor tilth conditions are shown by closed symbols.…”

“…Low levels of soil OM (NCC>0) may create aggregates that are unstable in wet conditions but become hard and strong in dry conditions (Watts and Dexter, 1997;Munkholm et al, 2001Munkholm et al, , 2002Schjønning et al, 2002a). This has major impacts on agronomic aspects like tillage but also on clay dispersibility/colloid mobilization and hence colloidfacilitated transport of environmental pollutants (de Jonge et al, 2004ab).…”

Effects of Agriculture on Climate Change: A Cross Country Study of Factors Affecting Carbon Emissions

“…After 30 years of crop rotations, annual SOC gains ranged from 60 to 220 kg per ha per year for fields in Canada (Campbell et al, 2000). Nutrient management through fertilization and manure application generally increases SOC concentration (Haynes and Naidu, 1998;Schjonning et al, 2002;Munkholm et al, 2002;Hao et al, 2002). Manure application increases SOC concentration (Martens and Frankenberger, 1992;Haynes and Naidu, 1998;Nyamangara et al,1999;Aoyama et al, 2000).…”

Soil Aggregate Stability and Associated Structure Affected by Long-Term Fertilization for a Loessial Soil on the Loess Plateau of China

“…Simansky et al [11] even reported that chemical fertilization (NPK) did not have statistically significant influence on increasing the soil structure stability of orthic luvisol. In addition, organic matter was a major contributor to aggregate stability because it provided important biological binding agents, which decreased the breakdown of aggregates by slaking, swelling, or even osmoting stress [7,[12][13][14]. Some studies have reported that aggregate stability was higher in soil fertilized with manure than in soil fertilized with chemical fertilizers [15][16].…”