AMBI02012,41:370-379 375 Fig.5 Total pesticide 180 (formulation)application rate in China from 1991 to 2008 gunowe 160 140 uonesydde (sauuog 120 20) 100 pnsad 80 60 19911993 19951997199920012003200520072009 Year responded to the rising opportunity cost of their labour. 3.3 million ha in 1980 to about 28 million ha in 2008.An They applied fertilizer in a single application rather than investigation in the late 1990s of 18 provinces(city)showed using split applications which give higher nitrogen use that in all of them except Inner Mongolia,the average efficiency but need more labour. synthetic N fertilizer application rate commonly exceeded Farmers generally fail to take into account of the dif- 200 kg N ha,with the highest rate of 740 kg ha- ferences between the agronomic,economic and environ- occurring in Shandong province(Fig.6)(Ma et al.2000).In mental optimum application rate.Fertilizer trials in China addition,they commonly applied high rates of nitrogen as over many years for different crops,soil types and agro- manure (Li et al.2006).Excessive N inputs are often one of climates have provided good estimates of the agronomic the main reasons for the high incidence of pests and diseases optimum application rate (Yang and Sun 2008).The in vegetable production,and in turn,this commonly leads to average agronomic efficiency of fertilizer N in the 1990s farms using even more pesticide,resulting in high-pesticide when applied to cereals at a rate of 120-150 kg N ha-1 residues on vegetables and in the environment.Insecticide was 8.1-11.8 kg yield per kg of N in over 2700 field application rate are often 2-3 times the recommended experiments(Zhu et al.1997).Farmers,however,generally dosage (Ma et al.2000;Li et al.2006). need to apply higher rates of fertilizer to reach the optimum The excessive and unbalanced inputs of inorganic fer- agronomic efficiency,because of crop varieties developed tilizers can cause the damage to soil structure and soil in recent years commonly require more nutrients and quality.Although the ratio of N:P:K increased from higher management levels.The economic optimum N input 1:0.20:0.11in1991to1:0.28:0.21in2008,the proportion (the balance between the income from increased yield and of potassium fertilizer commonly needs to be increased. the cost of increased fertilizer used to achieve it)will be Nitrogen ratios have been too high in most of regions in less than the agronomic optimum.Finally,the environ- China since the 1970s,especially in eastern areas.Phos- mental optimum N input will generally be comparable or phorus ratios have changed from a deficit to small surplus less than the economic optimum because the latter fail to (with a large surplus in some vegetable areas),but potas- take account of the costs to the public at large of the sium is generally still in deficit (Shen et al.2005). environmental damage caused by NPS pollution.These Unbalanced nutrient ratios in mixed synthetic fertilizers costs (depending primarily on the extent of overuse)are can cause both biological and physicochemical damage to difficult to estimate and are not known with precision but in soils,leading to acidification,secondary salinization and the case of rice in the mid-1990s were estimated to be in reduction of microbial activity (Cao et al.2004;Ge et al. the range of 2.0-7.4 thousand million USD per year for 2009;Guo et al.2010).This damage lowers crop yields and whole China (Norse et al.2001). may lead to farmers applying even more fertilizers to try to The fast development of vegetable production has added compensate for the reduced soil productivity and thereby considerably to the overuse of fertilizer and pesticide.The intensify NPS pollution and the cycle of environmental total area planted with vegetables in China increased from degradation. Royal Swedish Academy of Sciences 2012 www.kva.se/en ②Springerresponded to the rising opportunity cost of their labour. They applied fertilizer in a single application rather than using split applications which give higher nitrogen use efficiency but need more labour. Farmers generally fail to take into account of the dif￾ferences between the agronomic, economic and environ￾mental optimum application rate. Fertilizer trials in China over many years for different crops, soil types and agro￾climates have provided good estimates of the agronomic optimum application rate (Yang and Sun 2008). The average agronomic efficiency of fertilizer N in the 1990s when applied to cereals at a rate of 120-150 kg N ha-1 was 8.1-11.8 kg yield per kg of N in over 2700 field experiments (Zhu et al. 1997). Farmers, however, generally need to apply higher rates of fertilizer to reach the optimum agronomic efficiency, because of crop varieties developed in recent years commonly require more nutrients and higher management levels. The economic optimum N input (the balance between the income from increased yield and the cost of increased fertilizer used to achieve it) will be less than the agronomic optimum. Finally, the environ￾mental optimum N input will generally be comparable or less than the economic optimum because the latter fail to take account of the costs to the public at large of the environmental damage caused by NPS pollution. These costs (depending primarily on the extent of overuse) are difficult to estimate and are not known with precision but in the case of rice in the mid-1990s were estimated to be in the range of 2.0-7.4 thousand million USD per year for whole China (Norse et al. 2001). The fast development of vegetable production has added considerably to the overuse of fertilizer and pesticide. The total area planted with vegetables in China increased from 3.3 million ha in 1980 to about 28 million ha in 2008. An investigation in the late 1990s of 18 provinces (city) showed that in all of them except Inner Mongolia, the average synthetic N fertilizer application rate commonly exceeded 200 kg N ha-1 , with the highest rate of 740 kg ha-1 occurring in Shandong province (Fig. 6) (Ma et al. 2000). In addition, they commonly applied high rates of nitrogen as manure (Li et al. 2006). Excessive N inputs are often one of the main reasons for the high incidence of pests and diseases in vegetable production, and in turn, this commonly leads to farms using even more pesticide, resulting in high-pesticide residues on vegetables and in the environment. Insecticide application rate are often 2–3 times the recommended dosage (Ma et al. 2000; Li et al. 2006). The excessive and unbalanced inputs of inorganic fer￾tilizers can cause the damage to soil structure and soil quality. Although the ratio of N:P:K increased from 1:0.20:0.11 in 1991 to 1:0.28:0.21 in 2008, the proportion of potassium fertilizer commonly needs to be increased. Nitrogen ratios have been too high in most of regions in China since the 1970s, especially in eastern areas. Phos￾phorus ratios have changed from a deficit to small surplus (with a large surplus in some vegetable areas), but potas￾sium is generally still in deficit (Shen et al. 2005). Unbalanced nutrient ratios in mixed synthetic fertilizers can cause both biological and physicochemical damage to soils, leading to acidification, secondary salinization and reduction of microbial activity (Cao et al. 2004; Ge et al. 2009; Guo et al. 2010). This damage lowers crop yields and may lead to farmers applying even more fertilizers to try to compensate for the reduced soil productivity and thereby intensify NPS pollution and the cycle of environmental degradation. Fig. 5 Total pesticide (formulation) application rate in China from 1991 to 2008 AMBIO 2012, 41:370–379 375 Royal Swedish Academy of Sciences 2012 www.kva.se/en 123