Assessing the effects of 17 years of grazing exclusion in degraded semi-arid soils: Evaluation of soil fertility, nutrients pools and stoichiometry

Grazing exclusion (GE) has been used as a strategy to restore degraded pastures worldwide. In this study, the effects of 17 years of GE on a) soil fertility, b) stoichiometric ratios between soil nutrients and c) carbon (C) and nitrogen (N) storage in particulate and mineral-associated organic matter soil fractions were assessed in an area degraded by overgrazing (OG) in a semi-arid region in Brazil. For this purpose, three sites with two treatments (exclusion and overgrazing) were studied at three sampling depths (0-10, 10-20 and 20-40 cm). Our results showed that pH, total organic carbon, particulate organic carbon, total N, particulate organic nitrogen, Ca2+ and K+ increased, whereas the Al3+ content decreased with GE. Conversely, the available P content, Mg2+ and Na+ showed no significant variations as a function of GE. A relatively constant C:N:P ratio (30:4:1) was observed, with little variation as a function of GE or OG, indicating a high total P content in the soil. Labile fractions (particulate) of C and N increased with GE. According to our results, GE can be used as a strategy to restore degraded natural pastures in arid and semi-arid ecosystems.