Evaluation of ecological and economic benefits of pomelo orchards with different grass growing systems based on emergy analysis

Honey pomeloCitrus. grandis (L.) Osbeck. cv. Hongroumiyou is the dominant crop in Pinghe County, Fujian Province; however, this historically fruit is facing production challenges. The practice of grass cultivation, rather than grass clearing, in the pomelo orchards is an important method to promote sustainable development in the honey pomelo industry. In order to clearly evaluate the effects of grass management pattern on the ecosystem, the economic and ecological benefits, two cultivation techniques, grass cultivation and grass clearing, were compared in orchards growing honey pomelo located in Qianlin Village, Wuzai Town, Pinghe County in 2017-2018. An emergy methodology was used to compare the two systems by calculating indices of emergy self-sufficiency ratio (ESR), emergy investment value (EIV), emergy yield ratio (EYR), environmental load ratio (ELR), efficient emergy yield ratio (EEYR), and emergy feedback rate (EFR). Results of the emergy indicators for orchards with grass cultivation or with grass clearing were:ESR, 0.003 for both; EIV, 339.291 and 295.763; EYR, 1.003 for both; ELR, 0.348 and 0.321; EEYR, 4.57 and 2.90-7E J·sej^-1; and EFR, 0.002 and 0.000; respectively. Compared to grass clearing, grass cultivation had a lower total energy input of 9.21%, a smaller non-renewable natural resources input of 76.71%, and a higher EIV resulting from the rapid decrease of natural energy input and the relatively low cost of purchased emergy input. The grass cultivation pattern showed better economic vigor with an increase of the commercial emergy of 1.00+E sej·hm^-2(versus 4.60+10E J·hm^-2 for grass clearing). The ratio of labor emergy input to the total was 70.45%-72.90%. The main contributors to labor input were fruit picking, daily management, and water-soluble fertilizer spraying. Although labor for weeding increased under grass cultivation, with a value of 1.31+16E sej·hm^-2, total labor energy input decreased by 3.30+16E sej·hm^-2 and labor efficiency rose by 17.50% through improvements in daily management and labor savings on pesticide spraying, fertilizing, and organic fertilizer transport. The environmental loading ratio in the cultivated grass system rose, with a value of 0.027 because of purchasing resource savings on organic fertilizers and labor. This study demonstrated that honey pomelo production incorporating a cultivated grass regime had the potential to improve commercial fruit production, increase farmer incomes, and provide a more sustainable production system, and such a management pattern would benefit supply-side reform.