Speciation,formation,and Transformation Of Occluded Phosphorus In Red Soils

Phosphorus is one of the essential nutrient elements in the process of plant growth,which takes part in various metabolism activities in the plant.Phosphorus deficiency will promote slow growth and development of the plant,leaves and fruits,which are easy to fall,etc.,so phosphorus is very important for the normal growth of the plant.Because a large amount of P fertilizer is applied to the soil every year,the accumulated P content in the soil is very considerable.But the available P content of plants is very low.Due to the high content of Fe and Al in red soil,the utilization rate of fertilization is only about 10%in the current season,and most of them are fixed in the soil.Most of the phosphorus fixed by the soil is slowly transformed into occluded phosphorus?O-P?which can not be absorbed and utilized by crops.The content of occluded phosphorous in the soil is huge,which can reach more than 60%of the total soil phosphorus in the red soil.Therefore,it is of great significance to study the speciation,formation and transformation mechanism of occluded phosphorus in the red soil to slow down the formation and activation of occluded phosphorus.In this study,the morphology,formation mechanism and influencing factors of occluded phosphorus were studied by continuous chemical extraction,X-ray near edge structure spectroscopy and Raman spectroscopy.The main results of this study are as follows:?1?Different fertilization levels can change the basic physical and chemical properties of soil,including p H,organic matter,iron and aluminum content,phosphorus content,etc.the application of inorganic fertilizer will lead to the decrease of soil p H and increase the acidification of red soil.The application of P fertilizer can increase the content of P in each component of the soil,and the application of inorganic and organic fertilizer can significantly enhance the level of P supply,alleviate soil acidification and improve the soil.?2?The basic physical and chemical properties of soil,such as p H,organic matter,clay mineral content,etc.,have a certain impact on the proportion of the content of occluded phosphorus.The content of Fe and Al is directly related to the content of occluded phosphorus,and the content of amorphous Fe and Al is directly proportional to the content of occluded iron and aluminum phosphorus.?3?Occluded phosphorus can be synthesized in artificial environment by using amorphous iron oxide pyrite,inorganic phosphorus and Fe²⁺.The proportion of occluded phosphorus in the minerals formed in the simulated system increases with time,and increases with the increase of iron ions.the less phosphorus adsorbed in the early stage,the higher the degree of O-P in the later stage.?4?The formation process of the occluded phosphorus:firstly,inorganic phosphorus is adsorbed on the surface of iron oxide,part of the phosphate is converted to the precipitated state of iron phosphate on its surface,and then the free iron ion will be adsorbed on the surface of these iron phosphate.As the free iron ion in the system is oxidized,the iron oxide coating will be formed on the surface of iron phosphate.This process is the the occluded process,the phosphorus coated by iron oxide It is called the occluded phosphorus.