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Soil Carbon Dynamics in Soybean Cropland and Forests in Mato Grosso, Brazil
Author(s) -
Nagy R. Chelsea,
Porder Stephen,
Brando Paulo,
Davidson Eric A.,
Figueira Adelaine Michela e Silva,
Neill Christopher,
Riskin Shelby,
Trumbore Susan
Publication year - 2018
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
eISSN - 2169-8961
pISSN - 2169-8953
DOI - 10.1002/2017jg004269
Subject(s) - environmental science , soil water , deforestation (computer science) , soil carbon , soil organic matter , agronomy , carbon cycle , organic matter , agroforestry , soil science , ecosystem , ecology , biology , computer science , programming language
Climate and land use models predict that tropical deforestation and conversion to cropland will produce a large flux of soil carbon (C) to the atmosphere from accelerated decomposition of soil organic matter (SOM). However, the C flux from the deep tropical soils on which most intensive crop agriculture is now expanding remains poorly constrained. To quantify the effect of intensive agriculture on tropical soil C, we compared C stocks, radiocarbon, and stable C isotopes to 2 m depth from forests and soybean cropland created from former pasture in Mato Grosso, Brazil. We hypothesized that soil disturbance, higher soil temperatures (+2°C), and lower OM inputs from soybeans would increase soil C turnover and deplete C stocks relative to nearby forest soils. However, we found reduced C concentrations and stocks only in surface soils (0–10 cm) of soybean cropland compared with forests, and these differences could be explained by soil mixing during plowing. The amount and Δ 14 C of respired CO 2 to 50 cm depth were significantly lower from soybean soils, yet CO 2 production at 2 m deep was low in both forest and soybean soils. Mean surface soil δ 13 C decreased by 0.5‰ between 2009 and 2013 in soybean cropland, suggesting low OM inputs from soybeans. Together these findings suggest the following: (1) soil C is relatively resistant to changes in land use and (2) conversion to cropland caused a small, measurable reduction in the fast‐cycling C pool through reduced OM inputs, mobilization of older C from soil mixing, and/or destabilization of SOM in surface soils.