Early effects of temperate agroforestry practices on soil organic matter and microbial enzyme activity
A field experiment was conducted to evaluate the effects of alley cropping systems on microbial activity and soil organic matter (SOM) pools. We hypothesized that enzyme activity and labile pools of SOM are early and sensitive indicators of changes induced by tree introduction in the cropping systems.
Poplar-alfalfa and alder-gramineous (cereal or ryegrass) associations and their respective control systems (alfalfa and gramineous) were compared in terms of soil carbon (C), nitrogen (N) and water contents, SOM labile pools, NIRS-MIRS spectra and microbial enzyme activity in the topsoil (0–15 cm) for 4 years after tree planting.
After 1 year, tree introduction induced a decrease in soil water content, microbial biomass N and some enzyme activities under alfalfa system. After 4 years, tree introduction resulted in higher soil water contents in both systems (alfalfa and gramineous); higher microbial biomass N and lower C:N in alfalfa-poplar plots compared to control plots. MIRS-NIRS analyses showed a greatest differentiation in SOM quality between alfalfa-based systems.
The effects of temperate agroforestry systems on SOC in the topsoil are relatively weak in the first years after tree introduction. Observed effects were more pronounced in the alfalfa-poplar system, probably due to higher tree growth. Further studies will provide insights into the longer-term effects of these systems on soil functioning.
KeywordsAlley cropping N2-fixing species Microbial enzyme activities Soil organic matter pools
The UMR Silva, UR BEF and the experimental site are supported by the French National Research Agency through the Cluster of Excellence ARBRE (ANR-11-LABX-0002-01). This Research was also funded by La Fondation de France and the French Environment and Energy Management Agency (ADEME) through postdoctoral grants to H. Clivot and C. Petitjean. The experiment was supported by the mobile lab (M-POETE) of ANAEE-France. ANAEE-France is an infrastructure of the French Investment for the Future (‘Investissements d’Avenir’) program, overseen by the French National Research Agency (ANR-11-INBS-0001). We thank M.C. Géhin (INRA) for assistance in NIRS-MIRS analyses. We are also grateful to all the people who helped for maintain the experimental site and for field and lab work. This work is dedicated to the memory of our colleague Bernard Amiaud, Professor at the Université de Lorraine (1969-2018).
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