Karst rocky desertification is one of the most serious eco-environmental issues in southwest China. Hybrid napiergrass (Pennisetum hydridum), also known as elephant grass, has been cultivated as an energy crop for raising livestock and for the production of ethanol in this area. In addition, hybrid napiergrass develops a large root system and has been increasingly grown to reduce soil erosion in this area. Given these properties, hybrid napiergrass is considered as an excellent plant for the restoration of degraded karst ecosystems. However, unsound management practices of napiergrass could reduce forage yield, forage quality, and soil quality.

Soil nematodes are the most abundant metazoa and occupy key positions at most trophic levels (bacterivore, fungivore, plant parasite, omnivore andpredator) in soil food webs. The composition of the soil nematode community can indicate ecosystem processes and environmental conditions. Therefore, soil nematodes were employed as bioindicators to assess the soundness of the management practices of hybrid napiergrass. Specifically, nematode communities with relatively high diversity, low herbivore densities, and/or high trophic links of food web are considered as indicators of a ‘healthy’ soil. The experiment included four levels of the each of the following main factors: nitrogen fertilization, cutting frequency, cutting intensity, and irrigation. The cultivar studied was ‘Guimu-1’.

This study was carried out at the Huanjiang Observation and Research Station for Karst Ecosystems, Chinese Academy of Sciences (CAS), Guangxi Province, China. A team of researchers from Institute of Subtropical Agriculture (CAS) designed the experiment; the hybrid napiergrass (Guimu-1) seedlings were planted in late April 2011. Soil was sampled in September 2012 and soil nematode community of each soil sample was analyzed.

The soil nematode community was affected more by nitrogen fertilization and irrigation than by cutting frequency and cutting intensity. The responses to fertilization indicated that fertilization had both positive and negative effects on the soil community and that the net effect (the trade-off between positive and negative effects) depended on the level of fertilization. Additional water applied in irrigation was detrimental to soil nematode communities in that it might reduce the oxygen content of soil and also increases the potential for the leaching of nutrients from soil. Additionally, we suggest that moderate N fertilization (460 kg ha?1 yr?1), moderate irrigation (one time yr?1 during the dry season), and cutting (three times per year at 20 cm height) will maintain soil health and provide substantial hybrid napiergrass yields.

This study was supported by the Chinese Academy of Sciences Action Plan for the Development of Western China (KZCX2-XB3-10), the National Key Technology Research and Development Program of the Ministry of Science and Technology of China (2010BAE00739-02), two National Natural Science Foundation of China (31270555 and 31300448), and a Western Light Program from CAS.

The study entitled “Responses of the soil nematode community to management of hybrid napiergrass: The trade-off between positive and negative effects” has been published in Volume 75 of Applied Soil Ecology, details could be found at http://www.sciencedirect.com/science/article/pii/S0929139313002539