Poultry litter and liquid swine slurry applications stimulate glomalin, extraradicular mycelium production, and aggregation in soils

Abstract

In addition to their ability to alter chemical attributes, poultry litter and liquid swine slurry applications in agricultural lands can improve soil physical structure by acting on aggregate formation and stability, in particular via glomalin and extraradicular mycelium production. The aim of this study was to evaluate the effects of different rates of poultry and swine manure on microbiological (glomalin and extraradicular mycelium) and physical (aggregation) parameters and to establish a relationship between them. The experiment was conducted in a very clayey Oxisol, in a randomized block design with four replications. The design consisted of a 2 x 4 + 2 factorial scheme combining two types of manure, poultry and swine, at four rates corresponding to 67, 100, 133 and 200% of the amount of nitrogen (N) required for oat crops, as well as two control treatments, where, in one, no N was applied, and, in the second, urea was applied to provide the recommended N rate. After six years with semiannual applications, in no-tillage system, soil samples were collected within 0.00-0.10 and 0.10-0.20 m depths. Compared with applications of liquid swine slurry, chemical fertilizer or no fertilizer, application of poultry litter, mainly at the 133% N rate, stimulated the production of active and total extraradicular mycelium and total glomalin, and both increased and stabilized the soil aggregates within the 0.00-0.10 and 0.10-0.20 m soil layers. In both layers, the production of active and total extraradicular mycelium was positively correlated to the formation of aggregates of relatively large diameter (> 8.00 mm) and, consequently, to increases in the geometric and weighted mean diameter. The production of easily extractable and total glomalin was positively correlated with the aggregate stability index and the formation of aggregates with an intermediate diameter (between 1.00 and 8.00 mm). These results indicate that manure application can be used to maintain or improve soil aggregation in addition to chemical fertility, but this benefit depends on the type of the manure used.