养殖场污水灌溉土壤渗出液磷特征分析

Phosphorus Characteristics in Leachate from Soils Irrigated with Livestock Wastewater

养殖场污水田间处理会引起土壤表面径流和渗出液中的磷组分流失.磷组分中有机磷比无机磷酸盐迁移能力强,构成地表水体富营养化重要的磷源.本文通过一组实验来探讨养殖场污水灌溉条件下土壤渗出液有机磷成分和数量特征.实验设计9个地块,其中一组4个地块加入45kg·(hm2·a)-1的过磷酸钙(以P计,下同),然后4次分别加入100、200、300、400t·(hm2·a)-1猪场污水,相应地施磷量分别为6.2、12.4、19.2、24.8kg·(hm2·a)-1;另一组4个地块只加入同样猪场污水.渗出液物化分析表明渗出液中颗粒态难反应磷居多,占TP的77%～90%.31P的核磁共振波谱分析表明难反应P主要以有机磷的单酯和二酯形式存在.在磷酸酶活性实验中,渗出液自身含有的磷酸单酯酶和磷酸二酯酶可以水解9%～29%有机磷,这表明P在迁移过程中,部分磷酸单酯和二酯可以水解成无机磷.对于施肥处理P45+F200而言,有机磷组分酶水解显示难反应磷主要含有33%的易反应单酯磷、17%的肌醇磷和9%磷酸二酯(磷脂和核酸).易反应单酯磷、肌醇磷和磷酸二酯是渗滤液有机磷流失过程能矿化的重要成分.

Phosphorus fractions could enter water body from surface runoff and leachate due to excessive irrigation of centralized farm wastewater. Organic P is more mobile than inorganic P in the soil profile and represents a significant proportion of P present in leachate from irrigated farm soils. A set of parallel experiments were conducted to compare the characteristics of organic phosphorus in leachate. The experiment was established in a complete randomized block design with nine replicates. The plots received different combinations of P fertilizer and different rates of pig slurry, i.e. 100, 200,300, 400t·（hm^2·a）^-1, accordingly, the phosphorus was added to the plots was 6.2,12.4,19.2,24.8kg·（hm^2·a）^-1, respectively. Leachate was collected over a year period and analyzed for different P fractions. Physico-chemical fractionation of P in leachate indicated that the majority of the P loss from the irrigated soil occurred in unreactive particulate （77%-90%） P forms. ^31P nuclear magnetic resonance analysis of eight leachate samples indicated that unreactive P was mainly comprised of monoester and diester forms of organic P. The presence of phosphomonoesterase and phosphodiesterase activity in leachate resulted in hydrolysis of 9%-29% of total unreactive P （TUP）, indicating that some of the monoesters and diesters can be eventually hydrolyzed into inorganic P forms during P transport. To the treatment P45＋F200, enzyme hydrolysis showed that 33% of the TUP was present as labile monoester P （LMP）, followed by 17% as inositol hexakisphosphate （IHP） and 9% as diesters （phospholipids and nucleic acids）. The results suggest that LMP, IHP and diesters are an important component of organic P leaching from the irrigated soil. The identification of these organic P forms will improve our understanding of the mechanisms responsible for their release from soils, so that specific mitigation strategies can be implemented at the P source.