Article

Reducing Environmental Risk by Improving N Management in Intensive Chinese Agricultural Systems

Key Laboratory of Plant and Soil Interactions, Ministry of Education, China, and College of Resources and Environmental Sciences, China Agricultural University, Beijing 100193, China.
Proceedings of the National Academy of Sciences (Impact Factor: 9.81). 03/2009; 106(9):3041-6. DOI: 10.1073/pnas.0813417106
Source: PubMed

ABSTRACT Excessive N fertilization in intensive agricultural areas of China has resulted in serious environmental problems because of atmospheric, soil, and water enrichment with reactive N of agricultural origin. This study examines grain yields and N loss pathways using a synthetic approach in 2 of the most intensive double-cropping systems in China: waterlogged rice/upland wheat in the Taihu region of east China versus irrigated wheat/rainfed maize on the North China Plain. When compared with knowledge-based optimum N fertilization with 30-60% N savings, we found that current agricultural N practices with 550-600 kg of N per hectare fertilizer annually do not significantly increase crop yields but do lead to about 2 times larger N losses to the environment. The higher N loss rates and lower N retention rates indicate little utilization of residual N by the succeeding crop in rice/wheat systems in comparison with wheat/maize systems. Periodic waterlogging of upland systems caused large N losses by denitrification in the Taihu region. Calcareous soils and concentrated summer rainfall resulted in ammonia volatilization (19% for wheat and 24% for maize) and nitrate leaching being the main N loss pathways in wheat/maize systems. More than 2-fold increases in atmospheric deposition and irrigation water N reflect heavy air and water pollution and these have become important N sources to agricultural ecosystems. A better N balance can be achieved without sacrificing crop yields but significantly reducing environmental risk by adopting optimum N fertilization techniques, controlling the primary N loss pathways, and improving the performance of the agricultural Extension Service.

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    • "Moreover, the worldwide demand is projected to increase from 112 million tons in 2011 to greater than 135 million tons in 2030, and N 2 O emissions are expected to increase in the future (FAOSTAT, 2011). Optimal N fertilization can maintain crop yields while reducing nitrate leaching (Liang et al., 2011) since reactive N is primarily lost by leaching and not by N 2 O emissions (Ju et al., 2009). However, the increasing N fertilizer application rate inevitably increased N 2 O emissions (Pelster et al., 2011); thus, modifying the N fertilizer in some cases is effective for reducing N 2 O emissions (Venterea et al., 2012). "
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    ABSTRACT: Agricultural activities are an important source of atmospheric nitrous oxide (N2O). Excess nitrogen (N) fertilization in the Taihu Lake region, southeast China, has resulted in a series of environmental issues such as N2O emissions and water body eutrophication. Optimal fertilization can reduce the loss of surplus N with a penalty of no or low yield. The conversion of plant residues to biochar is an attractive strategy for mitigating atmospheric carbon dioxide emissions and for enhancing carbon storage in soil. A field experiment was conducted to investigate the effect of biochar on N2O emissions, crop yield, and global warming potential (GWP). Five treatments were conducted with four replicates: no nitrogen fertilizer (Control), locally conventional N fertilizer (RN), optimal N fertilizer (ON), optimal N fertilizer plus low amount of biochar [3.75 t ha−1; (ONC1)], and optimal N fertilizer plus high amount of biochar [7.50 t ha−1; (ONC2)]. Results showed that both N2O and NO emissions increased exponentially with the N fertilizer application rate during the wheat growth season, and cumulative N2O emissions were significantly (P < 0.05) reduced in the ON treatment. Biochar amendment at 3.75 and 7.50 t ha−1 did not notably reduce N2O emissions. A significant negative correlation was observed between N2O flux and the soil water-filled pore space (WFPS) in biochar amendment, and the NO/N2O ratio was almost lower than 1, except for tillering fertilization when the soil WFPS was lower, indicating that N2O was primarily produced by denitrification. The GWP was significantly mitigated in the ON treatment compared with the RN treatment, which was significantly lower in the biochar treatment (P < 0.05). The greenhouse gas intensity (GHGI) also decreased from 0.039 to 0.031 kg CO2-eq kg−1 yield after biochar addition. GWP and GHGI results indicated that the application of biochar could significantly mitigate GWP compared with the ON treatment. Our results suggest that the application of biochar slightly reduced N2O emission, which might contribute to promote the reduction N2O to N2. Optimal N fertilization, especially, combined with biochar will exercise a greater effect for mitigating global warming.
    Journal of Cleaner Production 10/2015; 104. DOI:10.1016/j.jclepro.2014.12.038 · 3.84 Impact Factor
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    • "There are 13 million hectares of rice–wheat crop rotation systems in China, which are predominantly located in the provinces of Jiangsu, Anhui, Hubei and Sichuan along the Yangtze River Valley (Ma et al., 2009). The high level of crop production in China has been obtained by increasing the use of fertilizers (Ju et al., 2009), and the input of chemical nitrogen (N) fertilizer in the rice–wheat rotation system is as high as 550–600 kg N ha À1 yr À1 (Zhang et al., 2012). "
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    ABSTRACT: A 3-year field experiment was conducted to investigate the effects of different organic fertilization strategies for rice–wheat annual rotation systems on net global warming potential (net GWP) and greenhouse gas intensity (GHGI) by incorporating methane, nitrous oxide emissions, the changes in soil organic carbon (SOC) derived from the net ecosystem carbon budget (NECB), and the CO2 equivalent emissions from manure and chemical nitrogen (N) fertilizer manufacturing. Six fertilization strategies were studied, including control (CK), N fertilizer (CF), pig manure compost + N fertilizer (MC), straw + N fertilizer (SC), straw + pig manure compost + N fertilizer (SM), and straw + straw-decomposing inoculant + N fertilizer (SI). The results indicated that the application of organic amendments did not change the seasonal pattern of GHG emissions but significantly affected their seasonal quantities. Averaged over the 3 cycles, the annual SOC sequestration rates contributed significantly to the net GWPs and were estimated to be 1.01 t C ha−1 yr−1 for the control and 1.13–1.27 t C ha−1 yr−1 for the fertilized plots. Compared to CF, the MC strategy significantly increased SOC while had similar size of net GWP and GHGI, thus deserving recommendation regarding sustainable soil productivity and GHGs mitigations. However, the other proposed organic strategies of SC, SM, and SI significantly increased net GWP and GHGI as well as SOC thus requiring further researches for GHGs mitigations. Therefore, we recommend that the application of manure substituting half chemical fertilizer be an effective strategy while straw returning in any currently studied strategies should be re-examined in the rice–wheat annual rotation system.
    Ecological Engineering 08/2015; 81. DOI:10.1016/j.ecoleng.2015.04.071 · 3.04 Impact Factor
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    • "Addition of N fertilizers to modern cropping systems increased yields dramatically (Tilman et al. 2002). However, excessive N fertilizer usage has led to a series of environmental problems including water eutrophication, soil acidification, greenhouse gas emissions and air pollution (Tilman et al. 2002; Ju et al. 2009; Guo et al. 2010). Improving nitrogen use efficiency (NUE) in crops could help to reduce these problems. "
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