热带亚热带酸性土壤硝化作用与氮淋溶特征

通过室内好气培养和土柱模拟淋洗培养试验,研究了氨基氮肥加入对热带亚热带4种不同性质和利用方式酸性土壤硝化、氮及盐基离子淋溶、土壤及淋出液酸化的影响。4种土壤分别为采自花岗岩发育的海南林地砖红壤(HR)、玄武岩发育的云南林地砖红壤(YR)、第四纪红黏土发育的江西旱地红壤(RU)和第四纪下蜀黄土发育的江苏旱地黄棕壤(YU)。结果表明:4种土壤硝化作用大小表现为YURUYRHR。HR主要以可溶性有机氮(DON)和NH_4~+-N形态淋失,YU土壤的氮淋溶形态以NO_3~–-N为主,YR和RU土壤的氮淋溶形态NO_3~–-N、NH_4~+-N和DON兼而有之。盐基离子总淋失量与NO_3~–-N淋失量显著正相关,但各盐基离子淋失由于离子本性和土壤性质差异并不完全一致。Ca~(2+)在缓冲外源NH_4~+-N硝化致酸和平衡NO_3~–-N淋失所带负电荷过程中起重要作用。在阳离子交换量小、盐基饱和度低的土壤(如RU土壤),外源NH_4~+-N的硝化和淋失不仅导致盐基离子淋失,而且引发NH_4~+-N、甚至是H~+淋失。综上,热带亚热带地区土壤上外源氮输入的增加可能会在更短的时间内导致氮素向系统外的流失,引发环境问题。

Nitrification and Nitrogen Leaching in Tropical and Subtropical Acid Soils

To investigate the effects of urea addition on nitrification; nitrogen(N) leaching; base cations leaching and soil/leachate acidification in four tropical and subtropical acid soils included latosols in Hainan (HR, granite, forest land), latosols in Yunnan (YR, basalt, forest land), red soil in Jiangxi (RU, quaternary red earth, upland field) and yellow-brown soil in Jiangsu (YU, quaternary Xiashu loess, upland field), an laboratory aerobic incubation and simulated leaching soil column study were conducted. Results showed that nitrifying activity in four soil types was in the rank of YU>RU>YR>HR. Dissolved organic N(DON) and ammonium N(NH4+-N) were the predominant forms of N leaching, while nitrate N(NO3--N) dominated N form of YU leachate. In YR and RU, both NO3--N, NH4+-N and DON existed in each leachate. A significant positive linear correlation was observed between total base cations and NO3--N in leachates. Nevertheless, leaching of each base cation varied with ionic innate qualities and soil properties. Ca2+ played a key role in both buffering H+ produced by nitrification and balancing the negative charges of leaching NO3--N. Nitrification of exogenous NH4+-N in soil with low cation exchange capacity(CEC) and base cations saturation like RU caused not only base cations leaching but also NH4+-N and H+ leaching. Overall, urea addition might cause N leaching in a shorter time in tropical and subtropical soils and thus trigger environmental issues.