Contribution of nitrogen from litter and soil mineralization to shade and sun coffee (Coffea arabica L.) agroecosystems

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Coffee (Coffea arabica L.) production is important for its economic, ecological and social values in tropical areas. Whether coffee is grown under shade (SHD) or full sunlight (SUN), may have a direct impact on soil nitrogen (N) cycling, which can affect yield and agroecosystem sustainability. We studied N cycling in coffee farms in three municipalities in Puerto Rico and evaluated three ecosystem types in each: SUN coffee, SHD coffee and secondary forest (FOR). Aboveground litter dry matter and litter N inputs were quantified. Litter dry matter inputs (t ha-1year-1) were higher in SHD (2.15) and FOR (1.83), and were significantly greater than SUN (1.40). Litter N inputs (kg N ha-1year-1) were significantly lower in SUN (31) than in SHD (52) and FOR (43). Cycling of N was evaluated in detail in the municipality of Las Marias in SHD and SUN coffee. Litter N inputs (kg N ha-1year-1) to soil were significantly different between FOR (41) and SHD (56). The standing stock of N in aboveground biomass SHD was ∼3 times that in SUN, and total N input was twice that in SUN. However, soil N standing stocks were similar in SHD and SUN, indicating faster litter N turnover in SUN than in SHD ecosystems. By contrast, net soil N mineralization rates (kg N ha-1year-1) were ∼2 times higher in SHD (96) than in SUN (49), indicating that soil N turnover is greater in SHD than SUN. Our results suggest that litter N is mineralized at a slower rate in SHD than in SUN, whereas soil N is mineralized at a slower rate in SUN than in SHD. Higher inputs of N to soil, and soil N turnover in SHD may result in improved coffee production and associated forest biomass N uptake. Higher soil N mineralization rates in SHD coffee suggest improved ecosystem sustainability than in SUN coffee, presumably due to higher microbial activity, greater microbial diversity and substrate availability.

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Tropical Ecology





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