Ricardo O. Bordonal a b c , Maoz Dor d , , Andrey K. Guber b , , Maurício R. Cherubin c e , , Alexandre F. Nascimento f , , Sarah Tenelli a e , , Newton La Scala g , , Carlos E.P. Cerri c e , , João L.N. Carvalho a c , , Alexandra N. Kravchenko b ,
- aBrazilian Biorenewables National Laboratory, Brazilian Center for Research in Energy and Materials (LNBR/CNPEM), Rua Giuseppe Máximo Scolfaro 10000, Polo II de Alta Tecnologia, Campinas, SP 13083-100, Brazil
- bDepartment of Plant, Soil, and Microbial Sciences, Michigan State University (MSU), 1066 Bogue St, East Lansing, MI 48824, USA
- cCenter for Carbon Research in Tropical Agriculture – University of São Paulo (CCARBON/USP), Av. Pádua Dias 11, Piracicaba, SP 13418-900, Brazil
- dFrench Associates Institute for Agriculture and Biotechnology of Drylands, The Jacob Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Sede-Boker, Israel
- eDepartment of Soil Science, “Luiz de Queiroz” College of Agriculture – University of São Paulo (ESALQ/USP), Av. Pádua Dias 11, Piracicaba, SP 13418-900, Brazil
- fBrazilian Agricultural Research Corporation (EMBRAPA), Embrapa Agrossilvipastoril, Rodovia MT-222, km 2.5 Zona Rural, Sinop, MT 78550-000, Brazil
- gCollege of Agricultural and Veterinarian Sciences, São Paulo State University (FCAV/UNESP), Via de Acesso Prof. Paulo D. Castellane s/n, Jaboticabal, SP 14884-900, Brazil
Highlights
- Presence of Urochloa grass in ICL and MP enhanced microbial biomass and soil C.
- ICL and MP shaped pore structure with positive effects on soil C gains.
- Urochloa grass in ICL and MP increased the volume of medium-sized pores (70–150 μm Ø).
- Formation of medium-sized pores appears to be a major determinant of soil C gains.
- Decreased CO2-C emissions in MP contributed to greater soil C gains.
Abstract
Integrating well-managed grass into agricultural systems is a management target for enhancing soil carbon (C) storage in tropical agroecosystems. Yet, the mechanisms behind physical protection of soil C are not sufficiently lucid. Here we analyzed pore structure and particulate organic matter (POM) characteristics in structurally intact soil using synchrotron X-ray computed micro-tomography (μCT). We combined these analyses with bulk measurements and CO2 respiration data to explore the interactions between pore structure and soil C characteristics in a mid-term experiment in the Southern Amazon, Brazil. The farming systems were: (i) crop succession (CS) with annual production of soybeans followed by corn; (ii) integrated crop-livestock (ICL) with soybeans and then corn intercropped with palisade grass; and (iii) well-managed pasture (MP) with continuous monoculture of palisade grass. Soils of ICL and MP exhibited higher soil C (18–27 %) and N (27–29 %) contents, along with increased microbial biomass C (25–45 %) compared to CS. Additionally, ICL and MP showed higher μCT-based porosity (26–30 %) than CS and a greater volume of pores in the 70–150 μm range, which are regarded as optimal microbial habitats. Image-determined POM fractions in ICL and MP were 71 % and 51 % higher compared to CS. The spatial distribution patterns of soil pores and POM influenced the magnitude of soil C decomposition. Greater distances to medium pores and to POM fragments in MP are likely associated with lower soil C losses via CO2 emission, suggesting more effective soil C protection. We surmise that the intricacies of pore networks and their association with the spatial distribution of POM dictate C accrual in soils with greater presence of well-managed grass, thus providing the basis for target-oriented development of management strategies to rebuild soil C in Brazilian agriculture.
Keywords
Soil organic matter, Carbon stabilization, Physical protection, Soil pore structure, Tropical soils, Managed pasture, Integrated crop-livestock, Crop succession
