Carbon and nitrogen stocks and soil health indices in subtropical soils of Argentine

Abstract

The objective of this study was to evaluate the effect of deforestation and the subsequent cultivation of tea (Camellia sinensis L.) on the potential accumulation of carbon and nitrogen and to evaluate the soil health through biological quality indexes in subtropical soils of Argentine. A completely randomized design was used, with twelve plots under subtropical rainforest (S) and twelve plots under tea plantation of 40-60 year-old in red soils of Misiones (Argentine). For each plot, composite samples were collected at 0-0.10; 0.10-0.20 and 0.20-0.30 m depths. The following variables were measured: texture, silt+clay (Li+Arc) pH, bulk density (Bd), total porosity (TP), equivalent humidity (HE), air space (Ea), soil organic carbon (SOC), total organic matter (OM) and total nitrogen (Nt), respiration of soil (RES), particulate organic matter (POM), cation exchange capacity (T), and potentially mineralizable nitrogen (PMN). Carbon and nitrogen stocks (CS and NS) as well as POM and organic matter associated of mineral fraction soil (MOM) stocks were calculated (with masses correction) from 0 to 0.30 m. Then, ten biological indices were developed to 0-0.10 m: PMN /Nt, PMN / POM, PMN /RES, POM /RES, POM /OM, POM /Li+Arc, MOM/Li+Arc, MOM/OM, T/OM and T/RES. The results obtained were analyzed through ANOVA, LSD Test (P < 0.05), and a Pearson correlation. Removal of the subtropical rainforest and subsequent tea cultivation reduced CS and NS by 31% and 37%, respectively. The biological indicators and their indices indicated that tea land-use over average 50 years disturbed the natural balance of native red soils. Land-use changes resulted in a negative organic balance, a decrease in NPM (65%), in RES (41%) indicators to 0-0.10 m, and it also affected the functioning of the system, as observed in POM /Li+Arc, MOM/Li+Arc, PMN /RES, PMN /Nt, and PMN/POM. The indicators more sensitive were Bd, HE, CS, NS, PMN, RES and MOM. The correlation of RES with OM, POM, Nt, HE, Ea, and TP, as well as the MOP/Li+Arc index were shown to be positive and significant across, but negative with Bd. The PMN were shown to be positive and significant with T, OM, Nt and MOM. In the future research on MOM structures are necessary. The subtropical rainforest elimination for Tea land-use resulted in a decrease of CS and NS, degradation of biological soil quality, and modification of soil functionality.