Environmental impacts of a rice-beef-biogas integrated system in the Mekong Delta, Vietnam evaluated by life cycle assessment.

It is essential to increase the production of foods to meet the increasing future food demand, but this should be done in an environmentally sustainable manner. Integrated crop-livestock systems have been suggested to balance the reduction of environmental impacts and the increase in food production. Here we assessed and compared the environmental impacts of specialized (SPC) and integrated (ITG) rice and beef production systems in the Mekong Delta, Vietnam, using a life-cycle assessment (LCA). The productions of rice and beef are separated in the SPC, whereas they are integrated in the ITG: cattle manure is treated by a biodigester for biogas production, its digestate is applied to rice paddy fields as fertilizer, and part of the rice straw is used as cattle feed. We developed an LCA model based on data collected by site investigations of rice and beef farms and the relevant literature and LCA databases. Our evaluation of the ITG and SPC rice-beef production systems using the LCA revealed that among the four environmental impact categories investigated herein, the ITG had less environmental impacts on climate change (22%), energy consumption (22%), and eutrophication (14%) compared to the SPC. With the ITG, the reduction of methane emissions from paddy fields, the avoided energy consumption by the biogas produced, and the lower ammonia, nitrate, and phosphorous emissions from cattle manure and no eutrophying pollutant emissions from grassland were the main contributors to the lower greenhouse gas emissions, energy consumption, and eutrophication potential of this system, respectively. A sensitivity analysis showed that the use of cover for digestate storage resulted in lower environmental impacts of the ITG system compared to SPC system in all of the impact categories investigated here. These results provide helpful information to develop a circular and resource-efficient rice and beef production system that balances increasing productivity with environmental sustainability in rice-producing countries, particularly in Asia.

[Dynamics and ecological significance of nitrogen wet-deposition in Taihu Lake region--taking Changshu Agroecological Experiment Station as an example].

Nitrogen wet deposition was monitored for two years (2001.6-2003.5) at the Changshu Ecological Station in Taihu Lake region. The results showed that the amount of nitrogen wet deposition had a strong seasonal pattern, with higher levels in summer and spring, and low values in autumn and winter. The proportions of NH4(+)-N, NO3(-)-N and DON (dissolved organic nitrogen) to TN (total nitrogen) inputted by wet deposition were 47.6%, 35.1% and 17.4%, respectively. Ammonia volatilization from farmland was the most important source of NH4(+)-N in wet deposition. The monthly NH4(+)-N input from wet deposition increased with monthly rainfall (R2 = 0.3178**), while the monthly NO3(-)-N input from wet deposition had a lower correlation (R2 = 0.1985*) with monthly rainfall but positively related with the time of rainfall (R2 = 0.6757***). The NO3(-)-N concentration in the air was relatively steady in a period of time. Its concentration in wet deposition had a negative correlation with rainfall (R2 = 0.4205***). The annual TN input from wet deposition was 27.0 kg x hm(-2), but its concentration in each rainfall was higher than 0.2 mg x L(-1) (the threshold N concentration for inland water eutrophication). The nitrogen inputted by wet deposition had an ecological significance on both nitrogen balance in agroecosystem and eutrophication.