Carbon and nitrogen stocks of soils under different land uses in Pernambuco state, Brazil

Acrisols, Ferralsols, Leptosols and Planosols were sampled in layers down to 1 m under dense caatinga, open caatinga, pasture and agriculture. Agricultural Leptosols and Planosols had the lowest C and N concentrations among the land uses, although in some cases differences were not statistically significant. On average, conversion of dense caatinga to agriculture reduced C stocks from 63 to 47 Mg ha−1. Acrisols had the highest concentrations of C and N, and Planosols had the lowest concentrations and stocks. Conversion to pasture did not reduce stocks, but open caatinga also had lower C stocks (50 Mg ha−1) than dense caatinga. Nitrogen stocks did not differ among land uses, implying that losses are greater for C than for N. Despite the fact that the western portion of Pernambuco state covers 3% of the Brazilian semi-arid area, it stocks about 0.20 Pg of C (and 0.019 Pg of N), which represents 2% of the total estimated soil C stock in the semiarid region (8.9 Pg). Therefore, the stock per hectare in the west portion of Pernambuco is about one-third smaller than the stock per hectare in the whole Brazilian semiarid region, probably a consequence of the lower average C concentration in the 20 cm superficial layer, a higher proportion of agricultural fields and shallower depths of some soil classes in western Pernambuco than in the whole semiarid region. •Changes in land use alter soil C and N stocks, but vary in different soil types•Stocks of representative soil types under four land uses were quantified.•Planosols had lowest C and N stocks among soil types; losses were greater for C.•Conversion of dense caatinga to agriculture reduced C stocks to less than half.•The Western portion of Pernambuco state stocks 0.2 Pg of C and 0.019 Pg of N