Soil Phosphorus Fractions And P Supply Capacity Effected By Long Term Application Of N And P Fertilizer

Phosphorus(P)is indeed the most consumed plant nutrient in the world,essentially required by all plant species for better growth and development.P significance as a key player in environmental degradation increased recently because our agricultural systems are inefficient in P management,which is highly characterized by the paradox fixation of P.Long-term excessive fertilization from calcareous soils are other adverse effects of P on ecosystem.Low output of P has gained as compared with its input in the soil medium and80%of P get fixed in soil which is a great loss for the local farmers.Long-term nitrogen and phosphorus fertilization management may exacerbate the composition and availability of soil phosphorus(P)under long-term fertilized calcareous soils and thus affect long-term plant growth.However,the response of soil P fractions to long-term fertilization remain elusive.Moreover,Purpose of this research was undertaken(I)to evaluate the status of phosphorus fractions distribution in loess soils under fertilized,non-fertilized croplands practices under different rotations of natural fallow(NF)and bare fallow(BF)systems in order to better understand the behavior of different phosphorus forms in soils.As majority of aforementioned P losses from soil,which needs to be addressed and controlled through better fertilization management and affectively the used the P remains in soils.Changes in phosphorus(P)fractions and their availability in soil can be affected by long-term nitrogen(N)fertilizer application,which can subsequently affect plant growth and productivity.The extent of P fixation at different N and P fertilization rates is still unclear and this study focused on highlighting an appropriate N fertilization rate showing minimum P fixation and higher P uptake by the plants.Therefore,we have studied the long-term nitrogen and phosphorus effects on P distribution in response to different rates of application and fallow land and also and its availability to the plants.Hedley modified Tiessen and Moir fractionation scheme was utilized to determine different organic and inorganic P forms.This field study was conducted following a randomized complete block design(RCBD)with following treatments comprising five various N(0,80,160,240,and 320 kg N ha^-1)and P(0,50,100,150,and 200 kg P ha^-1)fertilizer rates represented by N0,N80,N160,N240 and N320,while rates P0,P50,P100,P150,P200 respectively.Moreover,two treatments with no fertilizer application and crops(NF,BF).All treatments were replicated by four times.Main results and conclusion of the studies are stated below:1.A long-term study(12 year)have been conducted to evaluate the changes in soil Pi and Po fractions in response to different P rates(0,50,100,150,and 200 kg P₂O₅ ha^-1)applied to winter wheat.P fractions were determined using the Hedley modified Tiessen and Moir fractionation scheme.Our findings demonstrated that application of different P rates significantly increased the available P,especially the Na HCO₃-P_i in the inorganic P fractions as compared to P0 treatment.Na HCO₃-P_i showed a strong relationship with grain yield(R²=0.91)and P uptake(R²=0.80)respectively.Grain yield were significantly higher in the P100 treatment,but no significant difference was observed between P100 and P200treatments.P200 treatment had a maximum grain P content and plant P uptake.Compared with the P0 treatment,all organic fractions yielded highest P_o with the P rate increase,ranging from 27.3 to 75.6 mg kg^-1,27.2 to 35.6 mg kg^-1,and 58.8 to 124 mg kg^-1for Na HCO₃-P_o,Na OH-P_o,and HCl_c-P_o,respectively.Among all P_i fractions,maximum fraction which is known as apatite(HCl _D--P_i)found in P200 treatment with the range of165 to 245.9 mg kg^-1.HCl _D-Pi accounted for 32%of total P which can be transformed into available P form with the passage of time.An increase of 78%in residual P was found under the treatment of P200.The residual P fraction was positively correlated with correlated with grain yield,P uptake and other inorganic fractions.It can be concluded that application of P increases P availability and grain yield with the increase in its application rate,but too much use of P can cause soil pollution,higher fixation of P.Consequently,a balanced application of fertilizer is recommended to reduce its fixation and increase its availability for the higher crops yield.2.Paradox changes of P into various organic(P_o)and inorganic(P_i)fractions and their contribution in P uptake and yield was evaluated in winter wheat(Triticum aestivum L.)under long-term(12 year)application of different N rates(0,80,160,240,and 320 kg N ha^-1,hereafter,N0,N80,N160,N240,and N320,respectively).Phosphorus fractions were measured using Tiessen and Moir fractionation scheme modified from Hedley method.Our results explained that various N rates significantly decreased available(especially Na HCO₃-P_i)and residual fractions of P,when compared with N0.The Na HCO₃-P_i showed a significant positive relationship with P uptake and grain yield.Grain yield was maximum in N160 treatment with no significant difference between N160 and higher N levels(N240,and N320).Increase in N rates from N0 to N320 increased organic P fractions;Na HCO₃-P_o increased from 64.0 to 69.7 mg kg^-1,HCl-P_o increased from 60.5to 87.1 mg kg^-1,but Na OH-P_o decreased from 46.5 to 31.2 mg kg^-1.Similarly,all P_ifractions were also increased,and maximum contents were observed for apatite(HCl _D--P_i)ranging between 189 to 265 mg kg^-1 from N0 to N320 treatments.HCl _D-Pi was highest contributor(39%)in total P,which is transformable into available P with time.A decrease in residual P by 7.4%was observed in N320.Residual P fraction was positively correlated with grain yield,biomass,P uptake,and with the moderate available fractions(Na OH-P_i,Na OH-P_o,and HCl _D-P_i).It can be concluded that excessive N fertilization does not always result in increased crop yield but can increase P fixation(HCl _D-Pi form)and decreases residual P contents.Therefore,optimum N fertilization should be applied keeping in view the crops requirement,such as N application at 160 kg N ha^-1 can maintain higher wheat yield(5844 kg ha^-1)in Loess Plateau,with no significant increases in P fixation and loss of residual P.3.In this study,results showed that the N0P100 and N160P100 fertilization treatments led to significantly higher total P,Pi,Po and Olsen P concentrations compared with control and un-fertilized treatments.The organic and inorganic fractions of P were affected by the different NP variables and in unfertilized systems.Labile P fractions(Na HCO₃-P_i,Na HCO₃-P_o)were 7.3,11.8-12.4%higher in fertilized treatments compared with control and NF,BF treatments.Moderately labile P fractions(Na OH-P_i,Na OH-P_o,HCl _D-P_i)Na OH-P_i were stable in all treatments but organic(Na OH-P_o)significantly lower in unfertilized treatments NF and BF(2.6,1.4%),however HCl _D-P_i was 59.1%-66%higher treatments in NF and BF compared to the control and fertilized.Non-labile P(HCl _C-Pi,HClc-Po)fractions were non-significant in fertilized and unfertilized treatments.Residual P was significantly higher in fertilized(N0P100)the treatments.The labile(Na HCO₃-P_i,Na HCO₃-P_o)and moderately labile(Na OH-P_i,Na OH-P_o,HCl _D-P_i)organic P fractions showed a significant correlation with Olsen concentrations in SEM analysis.Inorganic NP long-term fertilization effects on labile P fractions(organic and inorganic)and Olsen but influence the HCl _D-P_i which might be the source of inorganic.Unfertilized and natural fallows cycled soil P through plant residues,resulting in increased moderately labile P in soil in the form of increased microbial biomass P immediately after the fallows and the increased P in light fraction of organic matter during the winter wheat growing seasons.