360-3 Soil and Environmental Impacts of Excessive Nitrogen Use in China.



Wednesday, October 19, 2011: 9:05 AM
Henry Gonzalez Convention Center, Room 213B, Concourse Level

Fusuo Zhang, Department of Plant Nutrition, College of Resources and Environmental Sciences, China Agricultural University, Beijing, China and Mingsheng Fan, Department of Plant Nutrition, College of Resource and Environmental Sciences, China Agricultural University, Beijing, China
China’s economy has made great strides since 1949, and especially since China initiated economic reforms and the open-door policy in the 1980’s. The growth in agricultural production has been one of the main national accomplishments. This has created the so-called ‘Miracle in China’ with 9% of the world’s arable land feeding 22% of the world’s population(Fan et al., 2011). The use of fertilizers has played a crucial role, accounting for about 50 % of the yield increase. The consumption of fertilizer in China has increased linearly since 1961. Total consumption of chemical fertilizers exceeded 64 Mt in 2009, and this was nearly 35% of total global fertilizer consumption. Use of nitrogen (N) fertilizer has increased from 0.5 Mt in 1961 to 46.6 Mt in 2009 (Consumption = production + import - export, Revised from National Bureau of Statistics of China, 1950-2010).

Unfortunately, since about 1990 the increase in grain production has been associated with a major decline in fertilizer nutrient use efficiency, especially N, and with widespread environmental damage. According to yearly data for grain yield and synthetic N consumption (National Bureau of Statistics of China, 1950-2010), the partial factor productivity of applied N (PFP, the ratio of yield to the amount of applied N) has been halved over the last 30 years. Recovery efficiency of N (% fertilizer N recovered in aboveground crop biomass, REN) for cereal crops was 35% on average in the 1990’s. However, this value has gradually reduced since then and the current REN is 28.3 % for rice, 28.2 % for wheat and 26.1 % for maize (Zhang et al., 2008), all of which are lower than the world values (40-60%). The low nutrient use efficiency may be attributed to fertilizer overuse and high nutrient loss resulting from inappropriate timing and methods of fertilizer application, especially in high yielding fields.

Decreasing N use efficiency indicated that more fertilizer N was being lost to the environment, causing further negative environmental impacts. For example, losses of N through leaching and run-off have led to drinking water pollution which affects 30 % of the population and results in eutrophication of 61% of lakes in the country. Annual synthetic fertilizer N-induced N2O emission from Chinese croplands has increased from 120 Gg N2O-N yr-1 in the 1980s to 210 Gg N2O-N yr-1 in the 1990s (Zou et al., 2010). Another case study showed that soil pH in the major Chinese crop-production areas has declined significantly from the 1980s to the 2000s because of excessive N fertilizer inputs (Guo et al., 2010).

Therefore, rationalisation of N application to deliver greater N use efficiency and reduced environmental risks is urgently required in China. There is now overwhelming evidence that quantities of N fertilizer applied could be reduced with no detrimental effect on yield. Crop yields might even be increased by reduced use of fertilizer (Wilkinson et al., 2007; Fan et al., 2008). The great challenge ahead is to determine how crop productivity can be further increased to feed a growing population while minimizing N loss and its subsequent environmental damages for China. In reality, achieving such a target represents one of the greatest scientific challenges facing humankind (Tilman et al., 2002).

See more from this Division: S04 Soil Fertility & Plant Nutrition
See more from this Session: Symposium--Synthetic Fertilizer Use In Sustainable Cropping Systems: Benefits and Consequences