E3 Journal of Environmental Research and Management

E3 Journal of Environmental Research and Management Vol. 4 (4) pp. 0234-0241, May 2013; © E3 Journals; ISSN 2141-7466

Nitrogen cycling in seasonally dry coffee (Coffea arabica L.) agroecosystem of southern Ethiopia

Abstract

Nitrogen (N) cycling is presumed to be closed in most low input agroecosystems. This is because N cycles in a short circuit between vegetation, soil and microorganisms. However, information is lacking with this regard in low input coffee soils of Ethiopia. To this end, two experiments were conducted; the first experiment assessed carbon (C) and N mineralization in laboratory incubation under different moisture regimes (25%FC, 50%FC, 75%FC and 100%FC), whereas the second experiment investigated N mineralization via unconfined in-situ soil sampling. The soil revealed low bulk density, good aggregate fraction and higher aggregate stability (82%). Drought stress significantly reduced the rates of C (89%) and N (75%) mineralization, suggesting low N cycling in dry season. The net N mineralization and nitrification rates tended to be greater under in-situ than laboratory incubation. Average in-situ nitrification rate was about 30-40% of mineral N, despite the fact that the soil is relatively acidic. Hence, leaching and denitrification loss of N might be possible as the soil moisture in the wet season was found to be higher. This finding suggests that the anticipated climate change that results in reduction of rainfall may substantially reduce the rates of SOM decomposition and N cycling.

Keywords: Carbon mineralization, climate change, carbon sequestration, denitrification, drought stress, nitrate leaching