To answer these questions, a combined evaluation of these agricultural production systems was done by Dr. LU Hongfang et al. at Vegetation and Landscape Ecology Research Group, South China Botanical Garden, using emergy (i.e. the available energy of one kind of previously used up directly and indirectly to make a service or product), energy and economic methods.

An economic analysis clearly showed that the reason for this conversion was simply that the economic output/input ratio and the benefit density of the vegetable production system were greater than those of rice. However, both energy and emergy evaluations showed that long-term rice was the best choice for sustainable development, followed by rotation systems. The current price of rice is lower than the em-value of rice produced from the long-term rice system, but higher than that of rice produced from the rotation system.

Scenario analysis showed that if the government increases the price of rice to the em-value of rice produced from the long-term rice system, and takes the value of soil organic matter into account, the economic output/input ratios of both the rice and rotation systems will be higher than that of the vegetable system. The three methods, energy, emergy and economics, are different but complementary, each revealing a different aspect of the same system. Their combined use shows not only the reasons behind a system’s current state or condition, but also the way to adjust these systems to move toward more sustainable states.

The relative research results have been published on the Journal of Environmental Management (2010.91:2727-2735).