Long‐term application of different organic and inorganic fertilizers in no‐tillage crops changes the soil microstructural viscoelasticity and shear resistance to transient stresses

The processes involved in deformation, internal strength and stability of soils with long‐term application of fertilizers (organic and inorganic sources) remain poorly investigated and hence understood, particularly in agricultural systems under subtropical climatic conditions. We investigated how long‐term fertilizer management with organic and inorganic amendments in no‐till crops affects the microstructural stability of a sandy Alfisol under oscillatory shear. The study was conducted in southern Brazil on a 17‐year completely randomized block experiment with five fertilizer treatments: pig slurry (PS), cattle slurry (CS), pig deep litter (PDL), mineral fertilizer (MF) and control, i.e. unfertilized (CL). Soil samples were collected from two layers (0–5 and 5–15 cm) for physical and chemical analyses and evaluation of soil rheological properties under oscillatory shear at two matric potentials (0 and −10 kPa). Organic matter accumulation in soil provided by the PDL and CS fertilizers resulted in higher soil stability and elasticity under oscillatory shear, especially in the 0–5 cm layer. Conversely, MF and PS enhanced the soil susceptibility towards deformation under transient stresses, mainly in the 0–5 cm layer under saturated conditions. The PDL significantly increased soil shear resistance under low‐shear strain conditions. Significant differences ceased under high‐shear strain conditions, though PS and MF yielded at significantly lower strains. Hence, under subtropical conditions, long‐term application of organic fertilizers with fibrous components promoted soil microstructure strengthening, reducing soil susceptibility to erosive processes and compaction.