Carbon, nitrogen, and aggregation index in Ultisol with 11 years of application of animal manures and mineral fertilizer

Abstract

Soil erosion in Brazil is very high, and there is need to promote aggregate stability technics to increase the soil organic matter and the soil water infiltration, with a consequent decrease in erosion processes. Applications of animal manure on sandy loam soil may increase carbon (C) and nitrogen (N) contents in soil aggregates, causing increased aggregate stability. This study aimed to evaluate the contents of total organic carbon (TOC) and total nitrogen (TN) as well as the physical properties of a sandy loam soil subjected to 11 years of application animal manure and mineral fertilizer. The experiment was conducted under no-tillage (NT) system with corn (Zea mays L.)/black oat (Avena strigose Schreb.), bean (Phaseolus vulgaris L.)/black oat, and corn/wheat (Triticum spp.) crops. The following treatments were used: control (no fertilization), pig slurry (PS), pig deep litter (DL), cattle slurry (CS), and mineral fertilizer (NPK). Soil aggregates were obtained from undisturbed soil samples collected at soil depths of 0 to 5, 5 to 10, and 10 to 20 cm. Applications of PS, DL, and CS on soil increased TOC and TN contents, and increasing weighted mean diameter (WMD) and geometric mean diameter (GMD) in the topsoil. Use of DL and CS increased TOC at 0 to 5 cm in comparison to PS, NPK, and control. The use of animal manure also resulted in higher TN contents at 0 to 5 and 10 to 20 cm compared to control. The use of animal manure for 11 years under NT reduced the amount of mesoaggregates (2.0 > Ø ≥ 0.25 mm) and microaggregates (Ø < 0.25 mm) and increased GMD in the topsoil in comparison to the NPK and control. The animal manure promoted the dispersion of clays at 5 to 10 and 10 to 20 cm, resulting in lower soil aggregation in depth. Principal component analysis confirmed that animal manure reduced the degree of flocculation, with a consequent decrease in aggregation indexes, as it grouped the manure treatments in opposition to the NPK and control treatments.