Composition of phosphorus pool and the consumption and transformation characteristics of accumulated phosphorus in fluvo-aquic soil
[Objectives]Long-term application of phosphate fertilizer resulted in the accumulation of a large amount of phosphorus(P)in fluvo-aquic soil.We studied the composition and consumption characteristics of phosphorus pool after cessation of phosphorous application,to provide a theoretical base for the P nutrient management.[Methods]The research was based on the"National Long-term Monitoring Station of Fluvo-aquic Soil Fertility and Fertilizer Effects",where P was applied in different rates for 26 years and the soil P accumulation amounts in different treatments varied greatly.The top layer soils from a single treatment or a mixture of two treatments were used to prepare the test soils with different Olsen-P contents for a P exhausting micro-plot trial,under wheat-maize rotation.The soils with Olsen-P content 6.7 mg/kg was defined as P deficient(L1),14.3 and 27.6 mg/kg as moderate(L2,and L3),and 55.4 and 72.3 mg/kg as sufficient(L4,and L5),respectively.During the five years of exhausting,the total P(TP),Olsen-P content,and P fractions were analyzed.[Results]Inorganic P accounted for more than 90%of total P in fluvo-aquic soil.The Resin-P,NaHCO3-Pt and NaOH-Pt in L5 soil were 5.0,3.5 and 2.8 times of those in L1 soil,respectively.The proportion of labile and difficult-utilization P fractions were 10.4%and 24.0%of TP in L1 soil,and the proportion were 20.6%and 14.3%in L5 soil.The proportion of moderately labile P fraction was basically maintained at 66%of TP in all the test soils.Resin-P content would not increase until the Olsen-P level was higher than the agronomic threshold(L2 soil),and the increase contributed 17.3%-22.6%of the total increase of labile P pool.During the depletion process,crops absorbed the labile P fractions first and in order of Resin-P,NaHCO3-Pi and NaOH-Pi.For each 1 mg/kg of Resin-P,NaHCO3-Pi,and NaOH-Pi consumption,the soil Olsen-P content was reduced by 1.3,0.7,and 1.0 mg/kg,respectively.The P pools with different availability converted with each other.After five years of depletion,18.0 mg/kg of difficult-utilization P fractions converted into moderately labile P(D.HCl-Pi)in L1 soil,and 22.3 and 7.2 mg/kg of moderately labile P converted into labile P in L2 and L3 soils,showing a trend of activation of accumulated P.While in L4 and L5 soils,29.9 and 43.1 mg/kg labile P converted into moderately labile P,showing a trend of immobilization of accumulated P.[Conclusions]With the increase of Olsen-P level in fluvo-aquic soil,the proportion of labile P pool(Resin-P,NaHCO3-Pt,and NaOH-Pt)is increased,the proportion of difficult-utilization P pool is decreased,and the proportion of moderately labile P pool keeps stable.When the Olsen-P exceeds the agronomic threshold,the Resin-P content will begin to increase.Crop absorption drive the conversion of P pools,depending on the soil Olsen-P levels.In P deficient soil,the conversion is mainly from difficult-utilization P to moderately labile P,and in moderate P level soils,the conversion is from moderately labile P to labile P,the accumulated P in phosphorous deficient and moderate soils are in procession of activation,and will be used by crops at last.In high P soil,however,more than 30%of labile P fractions will be converted to moderately labile ones,and luxury P absorption of crops is common,resulting in the waste of phosphorus fertilizer nutrients.Moderate P level in soil is the most favorable for efficient utilization of phosphorus resources and high yield of crops.
fluvo-aquic soilavailability of accumulated phosphorusconversion of phosphorus fractionmoderately labile P phosphorusbiological depletionsoil phosphorus fertility
万方数据
维普
