Assessment For Typical Modes Of Circular Agriculture In The Guanzhong Plain

As the foundation of the national economy industry, agriculture is facing the increasingly prominent resource constraints and environmental problems. At present, realizing a more sustainable form of agricultural development is a necessity for improving the livelihood of people in China.Circular agriculture is based on the principle of a circular economy and sustainable development. This concept organizes an agricultural production activities along a pathway “resources- agricultural products- renewed resources”emphasizing the recycle and reuse of wastes and byproducts in place of the conventional extensive linear production mode. Circular agriculture requires reducing the input of resources and energy, maximizing the utilization rate of materials and energy accessible to the production- consumption system, decreasing waste production and pollutant emissions from sources, and improving the efficiency of using natural resources and wastes, ultimately achieving a win-win situation of economic effectiveness along with an environmentally friendly production system. Based on the theory of circular agriculture, a variety of agricultural production practices have recently been carried out in complex agricultural systems. But it is still lacke of quantitative assessment and empirical research for providing insight into its actual performance regarding resource utilization, environmental emission mitigation, and sustainability. We selected three circular agriculture modes as the study objects including the integrated production system of cattle, biogas, and greenhouse vegetables(IPSCBV), the “five in one” apple production system and the three-dimensional complex system for planting and raising(TCSPR), which were built based on local agricultural industry characteristics. We performed an in-depth analysis using emergy synthesis, economic analysis and life cycle environment impact assessment to compare the circular agriculture modes with conventional farming systems with regard to the efficiency of resource use, the reduction of environmental load, increasing sustainability, economic benefits and greenhouse gas(GHG) emission mitigation by follow-up survey and information collection from farmers; to give insight into the superiority of circular agriculture compared to conventional agriculture and identify the potential of the studied systems for optimizing the production mode and promoting the development of circular agriculture. The results show that:(1) The purchased emergy, especially the non-renewable purchase had the largest contribution to the total input of the IPSCBV. Overall, cattle feeds contributed most to the total emergy(68.43%). The IPSCBV had improved values of joint emergy-based indices, i.e., lower transformity(Tr) and environment load ratio(ELR) and higher renewbility(%R), emergy sustainability index(ESI), and emergy index for sustainable development(EISDYI) compared to the weighted averages of the corresponding indices for the independent production systems of fatted cattle and greenhouse vegetables. The reduced and avoided inputs from the materials replaced by recycling is 3.2 times of increased inputs for recycling. In other words, the IPSCBV had better emergy efficiency, waste resource use efficiency and higher sustainability, which resulted in less environmental stress than the independent production systems for cattle and greenhouse vegetables. But the calculated joint emergy yield ratio(EYR) for the IPSCBV was about equal to 1.0, indicated that the process of integrated production had no advantage in exploiting and making local resources available by investing the outside resources. The calculated value of emergy exchange ratio(EER) for the IPSCBV was lower than 1, showing that the IPSCBV received less emergy than it had used for production. The economic analysis showed that largest economic cost of the IPSCBV was calves. The economic output-input ratio of the IPSCBV was higher than the independent fatted cattle system but lower independent greenhouse vegetable production system. The total greenhouse gas emission mitigation of the IPSCBV was 5.57×105 kg CO2-eq/yr, in which the excrement utilization made the most contribution.(2) In the “five in one” apple production system, the purchased resources was the most important emergy inputs, accounting for approximately 97.16% of total emergy input, in which pig feed and piglets contributed most(57.58%). The “five in one” apple production system had improved values of joint emergy-based indices, i.e., lower Tr and ELR and higher %R, ESI, and feedback ratio of yield emergy(FYE) compared to the weighted averages of the corresponding indices for the independent production systems of fatted pig and conventional(clean) tillage-based apple production system. That means the “five in one” apple production system had better emergy production efficiency, self-organization ability, lower environment stress and higher sustainability. But the calculated joint EYR for the IPSCBV was close to 1.0, indicated that the process of integrated production had a weak advantage in exploiting and making local resources available by investing the outside resources. In addition, the calculated recycle benefit ratio(RBR) was low only with a value of 1.36. The economic analysis showed that largest economic cost of the “five in one”mode was hired labor. The economic output-input ratio of “five in one”mode(3.02) was higher than the independent production systems. The total greenhouse gas emission mitigation of the “five in one” mode was 2.72×103 kg CO2-eq/yr, in which the excrement utilization made the most contribution.(3) Corn had the largest contribution to the total input of the TCSPR, accounting for approximately 30% of total emergy input.The TCSPR had improved values of joint emergy-based indices, i.e., lower Tr and ELR and higher %R, EYR, ESI, and EISD compared to the weighted averages of the corresponding indices for the independent production systems of animals, walnut and grains. The reduced and avoided inputs from the materials replaced by recycling and nature biomass is more than 14 times of increased inputs for recycling. In other words, the TCSPR had better emergy production efficiency, waste recource use efficiency, self-organization ability, lower environment stress and higher sustainability. The economic analysis showed that the net income of the TCSPR was increased 1.22×104 $ than the sum of that of the independent production systems, but the economic output-input ratio of the TCSPR was lower than the independent production system of walnut and grains. The total greenhouse gas emission mitigation of the TCSPR was 9.33×104 kg CO2-eq/yr, in which the replaced feed by recycling of crop residues and nature biomass made the most contribution.(4) Nitrogen had the largest contribution to the total input of the straw returned mode. The mode had improved values of joint emergy-based indices, i.e., lower transformity(Tr) and environment load ratio(ELR) and higher transformity, %R, FYE, ESI, and lower ELR compared to the conventional mode. The recycle benefit ratio(RBR) of the straw returned mode is 2.35. In the straw-returned mode, raw material subsystem and agricultural product subsystem was a main role on the global warming, whereas plant system became the main potential factor on eutrophication, environment acidification and toxicity. The impact potential indexes of global warming, environmental acidification, eutrophication and water toxicity of the control model were higher than those of straw returned mode. The total greenhouse gas emission mitigation of the straw-returned mode was 2.10×103 kg CO2-eq/yr. The economic output-input ratio of the straw returned mode was higher than the conventional mode.(5) Compared to the three modes, although the EERI and FYE of TCSPR was not the highest, the RBR of the TCSPR was 4.6 times that of the IPSCBV, 11 times that of“five in one”mode,6.3 times that of the straw returned mode. In addition, other emergy indices of the TCSPR and economic output-input ratio were obviously better than those of the other two modes. The GHGs emission mitigation intensity of the TCSPR was 16.8 times that of the IPSCBV, 5.6 times that of the“five in one”mode, 3.5 times that of the straw returned mode. We can say that the TCSPR is the best circular agricultural mode from an ecological, economic and environmental point of view.