Plant-soil interactions in changing rice cropping systems and their influence on C and N dynamics
Final Report Abstract
Rice is the major crop sustaining food supply in almost all Asian countries. While it is currently frequently grown in double cropping or even triple cropping systems, there is an increasing shift towards the use of a non-flooded crop like dry rice or maize in the dry season, with chances and risks for soils and environment. We therefore investigated the impact of introducing maize and dry rice during the dry season into a continuous paddy rice cropping system on water losses via drainage as well as on carbon (C) and nitrogen (N) cycling with a focus on leaching losses to groundwater. We especially addressed the role of preferential flow paths in soil such as desiccation cracks, as well as the effect of cover cropping and straw management. For this purpose, different field experiments with different upland - paddy rice cropping systems were established at the International Rice Research Institute (Los Baños, Philippines). We conducted a dye tracer experiment in a maize – paddy rice system with and without rice straw application, followed by a soil crack monitoring experiment. The comparison between dyed soil areas (preferential flow pathways) and non-dyed soil areas (matrix soil), showed that preferential flow paths are “hot spots” for nutrient cycling because they were enriched in total C and plant nutrients (N, Ca2+, K+, Mg2+). Larger fertilizer N incorporation into residual microbial biomass along the flow paths, as well as tendentiously elevated copy numbers of 16S rRNA, pointed to higher microbial activity and larger nutrient availability in flow paths compared to the surrounding matrix soil. Monitoring the cracks over time revealed that desiccation cracks exhibited larger microbial activities than in the surrounding bulk soil. The increased activity fostered microbial uptake of fertilizer 15N along the cracks, which was detected mainly in fungal residues and only in the fields receiving additionally rice straw. Furthermore, a lysimeter experiment was continued to quantify water flux and leaching losses during and after the transition phase of a maize – paddy rice system with straw application (during the wet-to-dry fallow phase) and cover cropping (during the dry-to-wet fallow phase). The lysimeter experiment showed large initial percolation, C and N losses due to leaching, after maize was introduced. These losses were independent of surface desiccation crack appearance because they were not connected to the groundwater in greater soil depth. Adapted management such as straw application and cover cropping could not reduce the C and N losses, triggered by the switch to maize - paddy rice cropping system, to a level that was observed after a transition period several years following the initial cropping if maze. In summary, the work of this research unit shows that introducing upland crops into continuous paddy rice systems results in large initial N losses, which are not solely triggered by crack formation, but generally by preferential flow paths. However, these initial losses of N diminish in the long term, probably because of clogging of macropores, which form during the first maize growing season.
Publications
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2015. Carbon release from rice roots under paddy rice and maize–paddy rice cropping. Agric. Ecosyst. Environ. 210: 15-24
He, Y., Siemens, J., Amelung, W., Goldbach, H., Wassmann, R., Alberto, M.C.R., Lücke, A., Lehndorff, E.
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2017. Leaching losses of water, nitrogen, and dissolved organic carbon after introducing maize into a continuous paddy rice crop rotation. Agric. Ecosyst. Environ. 249: 91-100
He, Y., Lehndorff, E., Amelung, W., Wassmann, R., Alberto, M.C.R., von Unold, G., Siemens, J.
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2018. Nitrogen fertilizer fate after introducing maize and upland-rice into continuous paddy rice cropping systems. Agric. Ecosyst. Environ. 258: 162-171
Fuhrmann, I., He, Y., Lehndorff, E., Brüggemann, N., Amelung, W., Wassmann, R., Siemens, J.
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2019. Introducing non-flooded crops in rice cropping systems – impacts on soil nitrogen dynamics. Dissertation, Landwirtschaftliche Fakultät, Universität Bonn
Fuhrmann, I.
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2019. Preferential flow pathways in paddy rice soils as hot spots for nutrient cycling. Geoderma 337: 594-606
Fuhrmann, I., Maarastawi, S., Neumann, J., Amelung, W., Frindte, K., Knief, C., Lehndorff, E., Wassmann, R., Siemens, J.
