放牧家畜排泄物N转化研究进展

Nitrogen turnover from grazing livestock excreta: a review

放牧家畜排泄物氮转化是草原生态系统氮循环的关键。自 2 0世纪 70年代以来 ,以提高氮利用效率和减少温室气体排放为目的的家畜排泄物氮转化的研究越来越受到人们的重视。放牧家畜排泄物氮的转化研究主要包括 3个方面 :氮的矿化、硝化与反硝化 ,氮的氨化。家畜粪氮矿化速度慢 ,持续时间长 ;尿氮矿化速度快 ,持续时间短。氮矿化与家畜排泄物 C∶ N比、木质素/氮素比、木质素含量和纤维素含量呈负相关关系 ,而与全氮含量和水溶性氮含量呈正相关 ;土壤动物和微生物可以显著促进氮的矿化过程 ;高温和相对干燥、砂质土壤较壤土和粘土有利于氮的矿化。 4～ 4 0℃氮硝化作用与温度呈正相关 ;硝化作用的底物和产物浓度、土壤溶液渗透压和氯化物浓度的增加对硝化作用有强烈的抑制效应 ;p H6 .0～ 8.0条件下硝化作用强度随着土壤p H值的升高而增加 ,而 p H值高于 8.0或低于 6 .0时硝化作用受到抑制 ;硝化作用与土壤氧气含量呈正相关关系 ,而与土壤含水量呈负相关 ;温暖湿润较干燥炎热的气候条件有利于硝化过程的进行。反硝化作用与土壤氧气浓度呈负相关关系 ,而与土壤含水量和可利用有机碳含量呈正相关 ;0～ 6 5℃反硝化作用强度随温度升高而增大 ,10～ 35℃条件下温度成为影响反硝化作用的关键因素 ;

Nitrogen turnover from grazing livestock excreta is the key process in the nitrogen cycle of pasture ecosystems. Since the 1970s, many studies of nitrogen turnover from grazing livestock excreta have been conducted in order to improve nitrogen use efficiency and reduce greenhouse gas emission. Nitrogen turnover research mainly includes three related aspects: (i) Nitrogen mineralization, (ii) Nitrification and denitrification, and (iii) Nitrogen ammonification. Differences exist between the nitrogen mineralization of livestock urine and manure. The rate of manure nitrogen mineralization is very slow and continues for a long time, but for urine ,the rate is fast and is completed quickly. The factors that influence nitrogen mineralization mainly include excreta properties and biotic and soil variables. Negative correlations between nitrogen mineralization and C:N ratio, lignin to nitrogen ratio, lignin and fibre content of livestock excreta; and positive correlations between nitrogen mineralization and total nitrogen, water-soluble nitrogen and microbial nitrogen content of livestock excreta have been reported. Soil animals and microorganisms, high temperature, relatively dry soil and sandy soil can promote the nitrogen mineralization process. Nitrification shows significantly positive correlations with soil temperature and oxygen content, and significantly negative correlations with soil water, substrate and production content, soil osmotic pressure and chloride content. In the range pH 6.0~8.0, nitrification rate increases as pH increases, however nitrification will be inhibited if pH is higher than 8.0 or lower than 6.0. Nitrification increases under warm and wet climate conditions. Denitrification has significantly negative correlations with oxygen content, and positive correlations with soil water and available organic carbon. In the range 0~65℃, denitrification rate increases as the temperature increases.Between 10℃ and 35℃, the rate of denitrification is very dependent on temperature, often doubling with a 10℃ increase over this range. Denitrification is inhibited by strongly acidic conditions (pH<4), but soil pH has little effect on denitrification in the range pH 6~8. The presence of plants can both promote and inhibit denitrification. Nitrogen ammonification is positively correlated with soil NH^+_4 content, solar radiation, temperature, soil pH and plant litter quantity, but negatively correlated with soil cation exchange capacity(CEC), the buffering capacity of soil pH, soil organic matter content, plant biomass, plant growth yield and vegetation cover.The moisture content of the soil has little effect on nitrogen ammonification, unless the soil is so dry that urease activity is inhibited. Hot, dry, windy climate conditions favor ammonification whereas cool, moist, windless conditions inhibit ammonification.