Abstract

STUDDERT, Guillermo Alberto et al. Carbono orgánico del suelo bajo sistemas de cultivo contrastantes y su relación con la capacidad de proveer nitrógeno. Cienc. suelo [online]. 2017, vol.35, n.2, pp.285-299. ISSN 1850-2067.

Soil total (COT) and particulate (COP) organic carbon (C) contents decrease over the years under cropping. Its variation affects many soil processes that determine soil productivity (e.g. nitrogen (N) supply). COT and COP changes depend on the balance between C input and loss. For mollisols of the southeastern region of Buenos Aires province, it was hypothesized that: 1) COT and COP content decrease in the arable layer and vary as a function of the crop sequence regardless of the tillage system (SL), ii) COP content depends on the immediate preceding crop residue characteristics, and iii) changes in COT and COP are related to the soil N supplying capacity, regardless of the SL and crop sequence. Total organic C and COP were determined in soil samples taken annually at 0-5 cm and 5-20 cm depths in a long-term experiment in Balcarce between 2005 and 2011. The experiment comprised two SL (conventional (LC) and no-till (SD) and three crop sequences (with three alternatives (Series) for each one), including corn (M), wheat (T) and soybean (S): MMT, MST y SST. Corn and T were fertilized with N (FN). There were differential decreases in COT and COP among SL (no decrease under SD and decreases of 0.34 and 0.39 Mg ha^-1 yr^-1 under LC, respectively) only at the 0-5 cm layer. In the whole arable layer COT and COP decreased over the years under cropping (0.30 and 0.26 Mg ha^-1 yr^-1, respectively), regardless of the SL. No differential COT nor COP decrease was detected related to crop sequences, regardless of the SL. Neither was there an effect of the immediately preceeding crop residue characteristics on COP content. Likewise, COT and COP showed similar dynamics than reported for NAN. Relationships between NAN and COT and NAN and COP were significant although with low R² (0.55 and 0.57 (0-5 cm), 0.09 and 0.10 (5-20 cm), 0.18 and 0.17 (0-20 cm), respectively). Frequency and rate of FN may have masked the expected effects of the amount of residue C input on COT and COP and, besides, on the relationship of these two variables and NAN. Nitrogen fertilization affects organic material decomposition and transformation dynamics. The experimentally obtained evidences did not support the posed hypotheses.

Keywords : Crop rotations; Tillage systems; Carbon input; Particulate organic matter; Anaerobic nitrogen.

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