Kraals or bomas increase soil carbon and fertility across several biomes

Abstract

Knowledge about how pastoralism and kraaling may contribute to desired global objectives, such as soil fertility, is in danger of being lost. We tested whether short duration kraaling increases soil fertility across various biomes and countries via a meta-analysis (random effects model, n = 12 studies). Kraaling approximately doubled soil concentrations of carbon (C), nitrogen (N), phosphorus (P), potassium (K), and slightly increased pH compared to non-kraaled areas (p ≤ 0.0158, all meta-analyses). Results support the idea of persistent nutrient hotspots post kraal abandonment as a generalizable phenomenon. Anecdotes from a case study, the Herding 4 Health Model, supported findings. However, inconsistency scores (I² ≥ 90%) indicated that while the average effect size was positive, in some cases the true outcome may in fact be negative. Kraal age did not predict soil fertility in our analysis, possibly due to coarse time intervals. Some studies nevertheless found kraal age to be important, with relatively immobile elements such as P persisting over time while N and K decreased. Using kraals to achieve ‘desirable states’ such as wildlife-livestock coexistence, land restoration, and crop fertilisation will require monitoring, and maintenance of fertility within ecological bounds, ideally with inputs from scientists and pastoralists alike as part of global partnerships.