纳米羟基磷灰石作为新型磷肥的可行性和机理研究

Using currently-available fertiliser technology and agronomic methods, only 10-25% of the P which is applied as fertiliser to soils is actually absorbed by plants, with the remaining 75-90% rapidly transformed into forms that are of low availability, or lost through their movement into water bodies, resulting in low fertiliser efficiency and adverse environmental outcomes. Previous studies about slow/controlled release fertilisers and nano-fertilisers are mainly focused on nitrogen (N), and seldomly addressed P. In the present study, hydroxyapatite nanoparticles (HA-NPs) is proposed as a novel phosphorus (P) fertiliser that can provide increased efficiency and minimise adverse environmental impacts. In our previous studies, application of HA-NPs with modified surface significantly reduced the fixation of P by soil particles and increased P mobility, thus enhancing the fertiliser utilising efficiency. However, the influential factors are not clear. In this project, the effect of particle size (especially small size: <10 nm), surface charge and soil type on behaviour of HA-NPs in soils will be analysed, through examining release dynamics, transformation, and movement of P. Accordingly, the performance and potential of applying HA-NPs as a novel P fertiliser will be systematically evaluated, and mechanism of the process will be elucidated. The results of this research are expected to help to optimise the usage of P, thus relieving the pressure of P scarcity and lessening environmental risks, by providing theoretical basis and technical guidance for developing P fertiliser with higher efficiency.

传统磷肥的当季利用率极低，施入土壤后大部分（75-90%）磷被土壤颗粒吸附、固定，或淋溶进入水体中，造成磷的流失，引起环境污染。目前已有缓/控释肥、纳米肥的研究，但主要集中在氮素营养的利用。本研究率先提出纳米羟基磷灰石作为新型磷肥的可行性分析，前期工作发现表面改良后的纳米羟基磷灰石显著减少了磷在土壤中的固定，提高了磷肥利用率，但其适用范围及影响因素仍不明晰。本项目拟探究纳米羟基磷灰石作为高效磷肥时，颗粒尺寸（尤其是小尺寸：<10 nm）、表面电荷、土壤生化环境因素对磷的释放、转化、迁移行为的影响，并检测其肥效。从而系统地评估纳米羟基磷灰石作为一种新型磷肥的性能和潜力，阐述其作用机理，为解决磷资源紧缺而磷污染严重的难题提供科学依据与技术支撑。

纳米羟基磷灰石(HA-NPs)作为一种新型磷肥，不仅可以通过控释磷来提高磷肥效率，还可以减少传统磷肥施用对环境的不良影响。在本项目中，我们采用湿式沉淀法合成了纳米羟基磷灰石（HA-NPs），比较了不同改性剂对HA-NPs表面性质的影响。接着通过土壤培养实验，考察了不同类型HA-NPs在不同土壤里的磷释放动力学规律及磷的形态分布，揭示微观形态（颗粒尺寸和表面电荷）对HA-NPs在土壤中作为缓释磷肥的影响特点和机制。结合土壤类型和理化性质，提出了纳米羟基磷灰石作为新型高效磷肥的适应场景。然后通过温室盆栽实验评估了不同类型HA-NPs对向日葵(Helianthus annuus)的施肥效果，并通过柱淋实验探究了这几种HA-NPs在沙子和两种土壤中的磷移动性能，解析其肥效机制。另外，探究了HA-NPs作为新型磷肥施用时与菌根的相互影响，并研究了在硅灰石稳定土壤Cd过程中，施用HA-NPs对植物吸收Cd的影响，从而揭示HA-NPs的施用与土壤生化环境和植物生长之间的关系。结果表明：在酸性土壤Ultisol (pH 4.7)中，相比传统磷肥三过磷酸钙(TSP)，添加HA-NPs的土壤中磷的释放保持相对稳定，降低了溶解态磷向Fe/Al结合态磷转化比例。通过薄膜扩散梯度(DGT-P)测算，45 d后HA-NPs处理的土壤有效磷含量高于TSP。与中性和正电荷HA-NPs相比，带负电荷HA-NPs处理的土壤有效磷含量更高。在温室栽培试验中，带表面负电荷的HA-NPs(-)促进植物生长效果显著高于其他几种含P化合物(包括TSP，HA-NPs(+)、HA-NPs(0)和微米级磷酸钙RP)，使向日葵的鲜生物量增加16.5倍，根增加8倍。通过柱实验还发现，尽管磷在土壤中的整体迁移率较低，但Ultisol中HA-NPs(-)的施用提高了磷的迁移率，将5%的磷移动到柱的100 mm深度。因此，对于酸性Ultisol，表面电荷改变的HA-NPs是有潜力的新型磷肥。在碱性土壤Vertisol中，由于HA-NPs溶解度较低，磷供给效果不佳。这一信息对于HA-NPs作为新型肥料的开发具有重要意义。