Can no-till restore soil organic carbon to levels under natural vegetation in a subtropical and tropical Typic Quartzipisamment?

摘要

Sandy soils are widely distributed in Brazil and occur in most states. However, they have serious limitations for agricultural use due to low natural fertility, low water retention capacity, low resilience, and high susceptibility to erosion. Management of these soils through a no-till (NT) system following its basic principles (i.e., elimination of plowing, diversification of crop rotation, retention of crop residues, and maintenance of permanent soil cover) is a practice that can restore the soil organic carbon (SOC) stock, and restore productivity and economic viability of these soils. We hypothesized that: (a) we can recover the carbon (C) stock in Typic Quartzipisamment in subtropical and tropical climates to the level of native vegetation; (b) the adoption of NT during the initial phase, in conjunction with intensive cropping systems with high plant biomass input, is an efficient strategy to recover SOC in Typic Quartzipisamment soils; and (c) long-term NT (over 20 years-the maintenance phase), and low/medium input of plant biomass, is an efficient strategy for SOC recovery in Typic Quartzipisamment soils. Thus, the present study aimed at assessment of the recovery of SOC stocks in soil profile (0-1.0 m depth) in a Typic Quartzipisamment in subtropical and tropical climates, in comparison with the neighboring soil under native vegetation (NV). The sites selected for this study are located in two Brazilian grain-producing regions: (a) Manoel Viana City-Rio Grande do Sul State (MV-site 1) that represents the subtropical climate condition, and (b) Luiz Eduardo Magalhaes City-Bahia State (LEM-site 2), which represents the tropical climate. Soil samples were collected from soil profile for 0-1.0 m depth. At site 1, the predominant crop rotation over the years was wheat/soybean/oats + forage turnip/soybean. At site 2, the crop rotation includes cultivation in two periods designated as the crop and off-seasons, and the succession consisted of soybean/Brachiaria/cotton/millet/soybean/maize-Brachiaria. In both sites, soils under the neighboring NV were also sampled. SOC content was determined by the dry combustion method using an elemental C and N analyzer. Soil C stock was calculated based on the equivalent soil mass. Approximately 31 and 23% of the SOC stock was stored in the surface at 0-0.20 m, compared with 69 and 77% in 0.20-1.0 m layer of a Typic Quartzipisamment with high and low/medium input of crop residues, respectively. The Typic Quartzipisamment with low/medium input of crop residues fully recovered the stock of C in the surface soil layer (0-0.05 m). The Typic Quartzipisamment with high input of crop residues fully recovered the stock of C in the cultivated (0-0.20 m) and also in deeper soil layers (0-0.40 m). Thus, adoption of NT associated with intensification of cultivation systems and high addition of biomass-C is an effective strategy for C restoration in a Typic Quartzipisamment, while also playing a crucial role in restoring ecosystem productivity, soil quality, and environment.