Abstract
The conversion of forest areas to grain cropping has promoted a decrease in soil organic matter stocks in the Amazon. This process is most striking when the conventional cultivation system is used. In order to evaluate the changes in soil carbon and nutrient stocks resulting from the time of adoption of the no tillage system in a dystrophic Yellow Oxisol of the Brazilian Amazon biome, a study was conducted in a grain producing area in the northeastern of Pará, Brazil. The treatments corresponded to the following systems: CT6- conventional tillage system with six years of implementation; No-tillage system with 3 (NT3), 4 (NT4) and 7 (NT7) years of implementation. All systems were always cultivated in corn / soybean rotation. Deformed and non-deformed soil samples were collected on a the 2013 crop year at 0-10, 10-20 and 20-40 cm depths. Stocks of carbon (SC) and phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) were calculated by using the equivalent soil mass methodology. Regardless of depth, the NT showed higher SC values than the CT. The adoption of NT showed a tendency of increasing SC of the soil over time. Such increases were up to 36% of the NT7 compared to the CT6. In NT7, the stocks of K, Ca and Mg were higher in relation to PC6. The EC correlated positively with the stocks of K, Ca and Mg in the areas under NT, regardless of the time of system adoption, up to 40 cm deep, indicating improvements in the soil fertility.
Highlights
Conversion of forests into grain farming in the Amazon has promoted changes in soil organic matter stocks (Deon, 2013)
This behavior was observed by Pragana et al (2012), who attribute to the few years of cultivation under no-tillage system (NT), mentioning that there was not enough time for recovery of the soil previously cultivated under conventional tillage (CT)
At seven years of adoption of NT, there was a reduction in soil density values in the topsoil, reaching values close to the system with shorter land use (NT3), which may be associated with higher accumulation of matter over the period in which the system has been adopted
Summary
Conversion of forests into grain farming in the Amazon has promoted changes in soil organic matter stocks (Deon, 2013). Soil management practices based on less tillage and maintenance of residue stand out as a strategy to increase carbon levels by promoting the physical protection of organic matter, with greater aggregate stability (Sáet al., 2004). In this context, the no-tillage system (NT) represents one of the primary advances in the productive process of Brazilian farming as the dynamics of the processes of transformation and accumulation of organic matter as well as the nutrient cycling differ from the conventional cultivation system (Anghinoni, 2007)
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