Nitrogen use efficiency in grain production and the estimated nitrogen input/output balance in China agriculture.

BACKGROUND: Understanding the nitrogen (N) use efficiency and N input/output balance in the agricultural system is crucial for best management of N fertilisers in China. RESULTS: In the last 60 years, N fertiliser consumption correlated positively with grain production. During that period the partial factor productivity of N (PFPN ) declined greatly from more than 1000 kg grain kg⁻¹ N in the 1950s to nearly 30 kg grain kg⁻¹ N in 2008. This change in PFPN could be largely explained by the increase in N rate. The average agronomic efficiency of fertiliser N (AEN ) for rice, wheat and maize during 2000-2010 was 12.6, 8.3 and 11.5 kg kg⁻¹ respectively, which was similar to that in the early 1980s but lower than that in the early 1960s. Estimation based on statistical data showed that a total of 49.16 × 106 t of N was input into Chinese agriculture, of which chemical N, organic fertiliser N, biological fixed N and other sources accounted for 58.2, 24.3, 10.5 and 7.0% respectively. Nitrogen was surplus in all regions, the total N surplus being 10.6 × 106 t (60.6 kg ha⁻¹). CONCLUSION: The great challenge is to balance the use of current N fertilisers between regions and crops to improve N use efficiency while maintaining or increasing crop production under the high-intensity agricultural system of China.

Changes in the efficiency of fertiliser use in China.

Results of three nationwide fertiliser efficiency studies in recent history in China are reviewed. The results indicate that after a long history using organic recycling to maintain soil fertility in China, nitrogen (N) became the first yield-limiting nutrient in the first national fertiliser efficiency study in 1935-1940. With N fertilisation being used, phosphorus (P) and potassium (K) deficiencies were gradually revealed and developed in the following national fertiliser efficiency studies in 1958-1962 and 1981-1983. Research conducted through the International Plant Nutrition (IPNI) cooperative network in China in 2000-2006 indicates that agronomic efficiencies of N fertiliser (yield increase per kilogram from the application of 1 kg N) for rice, wheat and maize are 11.7 kg, 10.8 kg and 12.2 kg grain per kilogram of N, respectively, while crop recovery efficiency of N (percentage of N taken up by plant in total N applied) with rice, wheat and maize were 24.8%, 35.7% and 30.5%, respectively. Both agronomic efficiency and crop recovery efficiency of N are significantly lower than the average N use efficiency reported in international literature for other countries. Current agronomic efficiency of P and K are also discussed. Measures to improve fertiliser use in China are discussed.

[Potential of organic manures nutrient resources and their environmental risk in China].

Based on the data from China Agriculture Yearbook 2006 and other documents, the amounts of crop straws and of the excreta from human, livestock, and poultry in China in 2005 were estimated, with the potential and the environmental risk of their nutrient resources analyzed. In 2005, the total amount of crop straws in this country was 643 million tons, and that of the excreta from human, livestock, and poultry was 4625 million tons. The amounts of N, P2O5, and K2O from the straws and the excreta were 28.24, 12.82, and 29.48 million tons, being 1.08, 0.86, and 4.56 times of the inputs from chemical fertilizers in the same year, respectively. There was a great regional difference in the distribution of the organic manures nutrient resources. The total amount of N, P2O5, and K2O in the excreta was more than 4 million tons in Henan, Shandong, and Sichuan provinces, but less in Beijing, Tianjin, Shanghai, and northwest China, while the total amount of these nutrients in crop straws was more than 1.5 million tons in Henan and Shandong provinces, the main grain production areas, but less in northwest China. The per unit farmland load of N, P2O5, and K2O from the excreta was the highest (787.26 kg x hm(-2)) in Beijing, followed by in Tianjin (515.31 kg x hm(-2)) and Shanghai (505.35 kg x hm(-2)), where the environmental risk could be more serious.

Status of heavy metals in agricultural soils as affected by different patterns of land use.

This study was conducted to determine status of heavy metals in agricultural soils under different patterns of land use. A total of 38, 40 and 45 soil samples for bare vegetable field, greenhouse vegetable field, and grain crop field were respectively taken from surface layer (0-20 cm) from selected experimental areas away from suburbs of ten counties (or districts or cities) in four provinces or municipalities of Huabei plain in north China. Information of crop production history, including varieties, rotation systems and fertilizer use, at the corresponding sampling sites was surveyed. Soil total Cu, Zn, Cd, Pb, Cr, As and Hg were measured. The results showed that the contents of total Cu, Zn, Cd, Pb, Cr, As, and Hg in the soil samples, especially soil total Cu and Zn contents, were higher in the bare vegetable field and the greenhouse vegetable field than that in the grain crop field. Long-term use of excessive chemical fertilizers and organic manures in the bare vegetable field and the greenhouse vegetable field contributed to the accumulation of Cu, Zn, and other heavy metals in the soils. The contents of total Cu, Zn, and other heavy metals in soils increased with increasing vegetable production history of the research areas. In comparison with the grain crop field, the comprehensive pollution indices of the seven soil heavy metals and the single-factor pollution indices of soil Zn, Cu, Cd, Cr, and Hg based on the second criterion of Environmental Quality Standard for Soils were significantly higher in the bare vegetable field and the greenhouse vegetable field. Soils from the greenhouse vegetable field were slightly contaminated according to the comprehensive pollution index, and soils from the bare vegetable field and the grain crop field were at the warning heavy metal pollution level. The soils were contaminated with Cd according to the single-factor pollution index. The Cd pollution was relatively more serious in the bare vegetable field and the greenhouse vegetable field than that in the grain crop field. The soils selected with different land use patterns were not contaminated with Zn, Cu, Pb, Cr, As and Hg.

Capitalizing on multi-element interactions through balanced nutrition--a pathway to improve nitrogen use efficiency in China, India and North America.

A viable option for increasing nitrogen (N) use efficiency and mitigation of negative impacts of N on the environment is to capitalize on multi-element interactions through implementation of nutrient management programs that provide balanced nutrition. Numerous studies have demonstrated the immediate efficacy of this approach in the developing regions like China and India as well as developed countries in North America. Based on 241 site-years of experiments in these countries, the first-year N recovery efficiency (RE) for the conventional or check treatments averaged 21% while the balanced treatments averaged 54% RE, for an average increase of 33% in RE due to balanced nutrition. Effective policies to promote adoption are most likely those that enable site-specific approaches to nutrient management decisions rather than sweeping, nation-wide incentives supporting one nutrient over another. Local farmers, advisers and officials need to be empowered with tools and information to help them define necessary changes in practices to create more balanced nutrient management.

[Effects of phosphate-dissolving fungi on transformation, fixation and efficiency of fertilizer 32P].

By using a radioactive 32P-labeled technique, this paper studied the effects of P-dissolving Penicillium oxalicum P8 inoculum on the transformation, fixation and efficiency of fertilizer P. The results showed that the inoculum could prevent available P from fixation by soil, and promoted the uptake of applied P by maize and peanut. Additionally, it reduced the amount of Ca10-P fraction derived from available P, increased the pool of available P, and maintained more 32P in forms of Ca2-P and Ca8-P. With time extending, the ratio of Ca10-P fraction in soil was gradually increased, and the treatment with P. oxalicum P8 showed the lowest ratio of Ca10-P form, compared with treatment without P. oxalicum P8. The inoculum not only prevented available 32P from turning into Ca10-P form, but also had a longer effective period.