| The acceleration of urbanization process not only leads to the remarkable reduction in cultivated land resources, but also makes the fragile city ecology worse. Therefore, it is extremely urgent to reallocate the land use patterns and explore low-carbon city lifestyle and new ways of food production. Roof agriculture is an important part of urban space agriculture, and plays a huge role in compensation of land resources and improving local ecology. But as a new agricultural production mode, it remains in the theoretical exploration stage on a global scale, and lacks of systematic research. In this paper, the function of the roof system is refined into three properties of production, life and ecology, and divided into different types according to planting pattern, irrigation method and so on. Taking the roof farm of Chinese Academy of Agricultural Sciences as the main research object, we make a preliminary exploration to the property, the proportion and the future development of the three functions in the roof farming system.(1) Production function: The output of roof agriculture in the North is less than that of fields in terms of production. The total annual output adds up to 1.58kg/m2 in 2014, accounting for about 48.7% of the average of local conventional agriculture. It is equivalent to 14.71kg/m2 reduction of CO2 emission, realizing an economic value of 51.50 yuan/m2.(2) Life function: Comfort evaluation results show that, the occurrence frequency of the comfortable level reaching above all day long for the planting roof is 33.3%, highly coincide with the people’s activity time. Relatively, the occurrence frequency of the comfortable level of the bare roof is far lower and it is only 5.6%, not suitable for life. Furthemore, the existence of roof agriculture can averagely lower the indoor temperature by 2.7℃ or so in summer, thus reduce the cooling load of air-conditioners by over 169.32 k Wh/m2, which is equivalent to 105.0kg/m2 reduction of CO2 emission.(3) Ecological function: Plant carbon sequestration, regulation of regional environmental climate and reduce food miles and casual mileage are calculated respectively. Annual plant carbon sink are 108.27g/m2 and 30.58g/m2 respectively, equal to CO2 emission reduction 0.51 kg/m2. The food mileage of the roof can be reduced by about 0.19kg/m2, equivalent to 8.45×10-2 kg/m2 of CO 2 emission reductions, which only accounts for 2.1% of the total value of ecological functions. The roof agriculture can provide leisure picking service for 206 households, and the CO2 discharge of leisure mileage is reduced by 3,669.5 kg on average annually, which occupies about 74.67% of the ecological function attributes. In summary, the CO2 emission reduction of the roof agriculture system is about 40.95kg/m2.Under ideal conditions, annual output of the northern roof farm is around 2.92kg/m2, and the yield proportions in the system of production, ecology and life are respectively 19.95%, 47.02% and 33.03%. Indirect carbon sequestration value is much higher than direct output value of agricultural products. Because of the local disaster and deficiency of maintenance experience and other reasons in that year, the annual output of the sample plot was only 1.58kg/m2, and the ratio of the three functions is 14.30%, 39.79%, 45.91%. The value of the ecological function is positively correlated with the farm output, which indirectly proves the reasonableness and necessity of roof agriculture in urban environmental system. |
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