Evaluation of production efficiency and sustainability for straw-sheep-cropland recycling agroecosystems based on emergy analysis

Ecological recycling agriculture is an effective practice to solve the pollution from large-scale livestock farming. This study evaluated the production efficiency and sustainability of the straw-sheep-cropland integrated agroecosystem. This integrated system included four subsystems, as the sheep raising subsystem, the organic composting subsystem, the cropping subsystem and the feed producing subsystem. For the sheep raising subsystem, the emergy input of renewable resources was 2.33×1012 Sej, accounting for <0.01%; the emergy input of non-renewable resources was 9.68×1015 Sej, accounting for 0.24%; the purchased economic resource emergy was 4.03×1018 Sej, accounting for 99.76%, in which feed and labor were two main components, with a proportion of 84.22% and 10.06% respectively. The emergy output of the sheep husbandary subsystem was 2.65×1019 Sej, including the sheep and manure, accounting for 17.70% and 82.30% respectively. For the organic composting subsystem, the emergy input of renewable resources was 7.69×1012 Sej, accounting for <0.01%; the purchased economic resource emergy input was 2.44×1019 Sej, accounting for >99.90%; in which the raw materials for producing organic fertilizers accounted for the most, including the manure and straw residues with a proportion of 89.31% and 8.81% respectively. The emergy output for the organic compost subsystem was 2.06×1019 Sej, including two sections with equal proportion, one for inside using and the other for outside selling. For the cropping subsystem, the emergy input of renewable resources was 1.12×1017 Sej, accounting for 6.16%; the non-renewable resource emergy input was 7.06×1015 Sej, accounting for 0.38%; the purchased economic emergy was 1.46×1018 Sej, accounting for 93.46%, in which the chemical fertilizer, labor, electricity, machinery and diesel were the main components with a proportion of 33.60%, 26.86%, 15.99%, 12.78% and 8.61%, respectively. The emergy output was 2.57×1018 Sej, including two parts, grain accounted for 54.08% and straw residues accounted with 45.91%. For the feed-production subsystem, the renewable resource emergy input was 1.95×1013 Sej, accounting for <0.01%; the purchased economic resource was 1.23×1019 Sej, accounting for >99.99%, in which the soybean meal and straw residues were two main components, with a proportion of 20.31% and 50.32%, respectively. The only emergy output was feed of 2.11×1019 Sej, with two parts with the inside using of 16.13% and outside selling of 83.87%. Results of evaluation for the integrated system showed that the unit emergy value (UEV) was reduced by 96.09%, which was suggested that the emergy use efficiency was greatly increased comparing to the single sheep husbandry. The emergy investment ratio (EIR) and environment loading ratio (ELR) were decreased by >67.66%, respectively, while the emergy sustainability index (ESI) was evidently enhanced, suggesting that the integrated agroecosystem has a good sustainable potential with low environmental pressure. However, the net emergy yield ratio (EYR) and emergy yield-investment ratio were decreased by 70.32% and 70.43%, respectively, suggesting that the production efficiency and economic benefit were reduced in the integrated agroecosystem. This was caused by increasing cost from raw materials (i.e. bean dregs or straw residues), buildings and equipment. Therefore, the ecological compensation is needed for the positive externality of ecosystem services from the integrated agroecosystem. The compensation standard was estimated as ￥380.76/sheep per year based on the net emergy benefit difference. Nonetheless, once the current integrated system is optimized, EYR will be increased in theory and the integrated system can achieve self-compensation for its positive environmental benefits. © 2019, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.