[Effects of successive incorporation of rice straw biochar into an alkaline soil on soil fertility, carbon sequestration and ammonia volatilization.] / é•¿æœŸç§¸ç§†é»‘ç‚­æ–½åŠ å¯¹çŸ³ç°æ€§æ½®åœŸè‚¥åŠ›ã€å›ºç¢³åŠæ°¨æŒ¥å‘çš„å½±å“.

A five-year successive rice straw-derived biochar (BC) amendment pot trial was conducted to investigate the BC effects on crop growth responses, soil properties and ammonia volatilization in a calcareous alkaline soil from 2010-2015 under the greenhouse condition. We adopted 0 (the control; BC0), 2.25 t·hm-2(BC2.25) and 22.5 t·hm-2(BC22.5) for each wheat/millet crop season with an identical dose of NPK fertilizers. The results showed that BC treatments (BC2.25 and BC22.5) improved soil fertility and crop growth compared to the no BC control. During the five rice/millet rotations, BC22.5 treatment increased the total yields of grain and straw by 24.1% and 74.1%, while the cumulative aboveground uptake amounts of N, P and K were significantly increased by 93.5%, 71.2% and 46.3%, respectively. After the rotations, soil available P, K, and CEC under the BC22.5 treatment were enhanced by 262%, 274% and 58.3%, compared to the control. By contrast, soil bulk density was decreased by 46.6%, while no difference was found in soil pH between the BC treatments and the control. Soil TOC and soil C/N ratio increased by 843% and up to 25 in response to the BC22.5 treatment, respectively. The annual apparent BC loss was 3.5%-5.7% in the BC2.25 and BC22.5 treatments. High level of BC application simulated ammonia volatilization, which increased by 102% in BC22.5 treatment over the course of the crop rotations compared to the control.

Reducing environmental risk by improving N management in intensive Chinese agricultural systems.

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.

[Seasonal variation patterns of NH4(+) -N/NO3(-) -N ratio and delta 15 NH4(+) value in rainwater in Yangtze River Delta].

By using a customized manual rainwater sampler made of polyvinyl chloride plastic, the molar ratio of NH4(+) -N/NO3(-) -N and the natural 15N abundance of NH4(+) (delta 15 NH4(+) in rainwater was monitored all year round from June 2003 to July 2005 at three observation sites (Changshu, Nanjing, and Hangzhou) in the Yangtze River Delta. The results indicated that at the three sites, the NH4(+) -N/NO3(-) -N ratio and the delta 15 NH4(+) value in rainwater had the similar seasonal variation trend, being more obvious in Changshu (rural monitoring type) site than in Nanjing (urban monitoring type) and Hangzhou (urban-rural monitoring type) sites. The NH4(+) -N/NO3(-) -N ratio peaked from early June to early August, declined gradually afterwards, and reached the bottom in winter; while the delta 15 NH4(+) value was negative from late June to mid-August, turned positive from late August to mid or late November, became negative again when winter dominated from December to March, but turned positive again in next May and negative again in next July. These seasonal variation patterns of NH4(+) -N/NO3(-) -N ratio and delta 15 NH4(+) value were found in relation to the application of chemical nitrogen fertilizers during different crop growth periods, and also, the alternation of seasons and the NH3 volatilization from other NH3 emission sources (including excrements of human and animals, nitrogen- polluted water bodies, and organic nitrogen sources, etc.), which could be taken as an indicator of defining the sources and form composition of NH4(+) in atmospheric wet deposition and the intensity of various terrestrial NH3 emission sources.