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Impact of recent large scale conversion of INTENSIVE monoculture coffee systems towards shaded systems on soil fertility in Yunnan province, China

Rigal C., Vaast P., Xu J.. 2019. In : 27th Biennial ASIC Conference, Portland, 16-20 September 2018. Book of abstracts 2019. Portland : ASIC, 1 p.. Biennial ASIC Conference. 27, 2018-09-16/2018-09-20, Portland (Etats-Unis).

RATIONALE The rapid expansion of intensive monoculture in coffee farms, from the 1980's onward, resulted in coffee becoming an important commodity crop in Yunnan Province, China. This expansion was followed by a large-scale transition towards shaded coffee, starting in 2013 with the free distribution of shade tree seedlings by local governments. The current study initiates an early on follow up of this unprecedented large scale conversion by focusing on impacts of shade tree species on soil fertility at a temporally and spatially fine scale. METHODS 124 soil samples were collected in 2017-2018, both in the dry (winter) and rainy (summer) seasons, within and outside of coffee rows, below and outside of the canopy of 3 commonly found shade tree species (Bischojiajavanica, Cinnamomum camphora and Jacaranda mimosifolia). Analysis were run for chemical composition (pH, OM, N, P, K, Ca, Mg), biological communities (nematodes abundance, PLF A) and enzymatic activities (ß-glucosidase , N-acetylglucosaminidase and acid phosphatase). RESULTS 1) There was a marked seasonal effect on soil communities (higher nematodes, bacterial and fungi communities during the rainy season). P cycling also increased during the rainy season, but C and N cycling slowed down. 2) Soils below coffee plants had higher chemical fertility (OM, Ca and Mg) than paired samples outside of coffee rows. During the rainy season, soils below coffee also had more abundant soil communities (nematode, bacteria and arbuscular mycorrhiza fungi) and nutrient cycling rates (C, N and P). 3) Shade trees had a positive impact on soil chemical fertility below coffee plants (pH, OM, N, P and Ca) and a buffering effect on soil communities during the dry season (bacteria and fungi). CONCLUSIONS & PERSPECTIVES This study sets up the baseline (open coffee) and first follow up after the transition to agroforestry (5 years) on soil fertility. Results testify of the high heterogeneity of soil fertility within coffee farms, at a fine temporal and spatial scale. Importantly, shade trees were shown to have a locally positive impact on soil chemical and biological fertility after as little as 5 years, although no significant differences could be found between the 3 shade tree species. Future studies should keep monitoring changes as shade trees grow older.

Mots-clés : coffea; arbre d'ombrage; agroforesterie; propriété physicochimique du sol; faune du sol; cinnamomum camphora; jacaranda; chine; yunnan; bischofia javanica; jacaranda mimosifolia

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