Study On Phosphorus Accumulation And Leaching In Loess Soil Under Long-term Fertilization Condition

The effect of phosphorus leaching losses to be an environmental rather than an agronomicalproblem has been extensively concerned worldwide, particularly in developed countries. Thepossibility of occurring of phosphorus leaching on loess soil, possible mechanism andfractions of phosphate leaching, the dependence of P movement on irrigation and rates offertilization, phosphorus accumulation and balances, and microbial biomass phosphorus andits relationships with soil biological and chemical properties were studied based on 3 longterm fertilizer experiments that lasted for 12,12 and 22 years, respectively. Following resultshave been obtained:Long-term application of phosphorus containing fertilizers in either super-phosphate orfarmyard manure exceed the crop needs lead to P accumulation that predominantly in theplough layer (0-20cm), significant correlations were observed between net P balances(net Pinput)and soil total P and Olsen P or their increments in plough layers. Linear correlationsbetween Olsen P and total P, or between their increments were also observed; 100 mg/kgincrease in total P made approximately 18 mg/kg Olsen P increase. Phosphorus accumulationdecrease P use efficiency and probably cause leaching losses, a mass P balance sheet for 12years experiment revealed that apparent cumulative phosphorus use efficiencies were lessthan 17% for unbalanced fertilization (PK and MNPK), and exceed 40% for balancedtreatments; there are 4- to 37% of cumulative P inputs can not be accounted for in 0-100cmsoil profile.As expected, distribution of phosphorus in soil profile was strongly dependent on irrigation(or precipitation). Under rain-fed condition, deeper P enrichments were found to 100 cmdepth of soil profiles for plots received chemical fertilizers (PK and NPK treatments) and to300cm for that treated with manure combined with NPK(MNPK); The same trends werefound under irrigation condition, the total and Olsen-P contents of PK & MNPK in 0-300cmsoil profiles were not only higher than that of CK and NPK , but also higher than that of sametreatments under rain-fed condition.Phosphorus movement in soil profile was also dependent upon soil P status of top 20cmsoil layer; the results from 22 years long-term fertilizer experiment indicated that markedly摘 要 ·v·linear correlations between Olsen P contents of plough layers and amount of cumulativeOlsen P in 20-100,100-200,and 200-300 cm soil depth, these strongly suggested P leachingoccur in loess soil.The possible mechanism for P leaching is preferential flow pathway, gypsum coated soilparticles can be seen reaching to nearly 90 cm along the macro-pore and 55 cm along rootsurface in gypsum experiment which with a P content of 200 mg P /kg ; Olsen Pconcentrations of soil sampled along inner surface of macro-pore were increased obviously, incontrast, it remain unchanged in bulk soil sample, indicated phosphorus movement probablythrough macro-pore.A intact soil core column experiment was carried out with different Olsen P gradient,results from 13 leaching events shown that concentrations of molybdate reactive phosphorus(MRP), total dissolved phosphorus (TDP) and total P (TP) in leachates were positively relatedto soil Olsen P contents of plough layers; a predominant part of the total phosphorus (P) inleachates can be present as dissolved phosphorus, in average, total dissolved phosphorusand particulate phosphorus (PP) comprised of 82.5- and 17.9% of total P in leachates; of TDP,molybdate reactive phosphorus and dissolved organic phosphorus constituted 77.1- and13.8% of TP. The maximum concentration of TP in leachates was 3.95 mg/kg.Microbial biomass phosphorus (MBP) and its relations to soil biological and chemicalproperties were also studied, the result revealed that microbial biomass C (MBC) increased by4-15, 26 and more than 60% respectively, microbial biomass nitrogen increase by 4-20, 54and 85% respectively; MBP by 86-122, 122 and exceed 450% for application of ino...