Effect Of Olsen P Levels On Phosphorus Use Efficiency And Phosphorus Fractions In Black Soil Northeast Of China

Phosphorus(P)is one of the essential macronutrients for crop growth and development,but the continuous excessive application of P containing fertilizer has dramatically increased soil Olsen P(OP).The level of soil OP is an important influencing factor for P use efficiency(PUE),crop production,and environmental safety.Investigating the crop response,P fractions and P adsorption and desorption characteristics in soils with different OP levels are essential for guiding rational fertilizer P application,enhancing PUE and decreasing soil P leaching risk.Based on P fertilization experiment in black soil at Jilin Province,Northeast of China,six soil OP levels(16,20,28,38,43,49 mg kg^-1,and we named them OP1,OP2,OP3,OP4,OP5 and OP6)were chosen;and six rates of P fertilizer were applied for each soil OP level using micro-plots with randomized complete block design.Crop yield was measured,P uptake and PUE were calculated.Meanwhile,P adsorption and desorption characteristics were measured with isothermal sorption experiment and P fractions were analyzed with Hedley(1992)sequential method.The main results are as follows:1.The response of crop yield to OP levels could be portioned into two parts.The first part,the OP level less than 28 mg kg^-1 the crop yield increased significantly with the OP level increased,it was significantly related to the amount of P fertilizer.The second part more than 28 mg kg^-1 there was no response to P fertilizer application,the crop yield was stable along with the increase of OP level and P application rates.The change point between the two parts was determined as the agronomic critical level.The PUE(%)increased with soil OP levels and decreased with P fertilizer application rates.At the same P application rate(P2),compared with PUE at low OP level(OP1),PUE significantly increased with soil OP levels increase.The PUE increased at OP6(high OP level)in 2017,2018 and2019 by 49.5%,40.1%and 32.4%when compared with that at OP1(low OP level)respectively.While,at the same OP levels,when compared PUE at low P application rate(P2),PUE at high P application rate(P6)decreased significantly in the range 62.8 to 78.7%during the study period in all three years.Under an average deficit of 100 kg ha^-1P,the soil Olsen P level at all three years decreased by 3.9 mg kg^-1 in the treatment without P addition(P1)and increased by 2.4?3.5 mg kg^-1 in the P treatments for each 100 kg ha^-1 P surplus.In the black soil with relatively high Olsen P content,with P application rate44 kg P ha^-1 and OP levels 28 mg kg^-1(critical level)will meet the demand for high yield,maintains the soil Olsen P level and effective supply ability of P,increase the PUE and reduce the environmental risk while reducing the use and loss of excessive P in the study area at the northeast of China.2.The result showed was a good correlation between the P adsorption curve and Langmuir equation R² in rang 0.95-0.99,(P<0.01)with six OP levels.P adsorption constant(K),Degree of P saturation(DPS),the maximum P desorption(Dm)increased;and the maximum amount of P adsorbed(Qm),P adsorption index(PSI)decreased with the increase of OP level(P<0.01).Mehlich-3Aluminium(M3-Al)showed a significant negative correlation with Qm and PSI(R²=-0.94**and-0.95**),and positive correlation with readily desorbable P(RDP),DPS_M3-Pand DPS_{Olsen P}(R²=0.93-0.98),and M3-Al was the main influencing factor to affect P adsorption and desorption characteristics.The OP levels affected the P availability in black soil by changing P adsorption and desorption characteristics,the higher OP level,the weaker the adsorption capacity of soil to P and high availability to plant.Also,when the OP level was higher than 38 mg kg^-1 in the black soil,the DPS_M3-P value exceeded the critical environmental value,which could cause risk of P loss to water,suggesting that the amount of P fertilizer application must be controlled in the study area.3.The result showed that the P fractions and P activation coefficient(PAC)were affected by different OP levels.Compared to low OP level,different OP levels in the field resulted in a significant increase of Pi fractions(Resin-P,Na HCO₃-Pi,Na OH-Pi,Dil.HCl-Pi and Conc.HCl-Pi),and the largest increases were from highest OP level.Among the six OP level,the highest mean concentration of all Pi fractions was Residual Pi.We observed the three Po fractions(Na HCO₃-Po,Na OH-Po and C.HCl-Po),also were the highest with high OP level.The Po concentrations were ordered Na OH-Po>Na HCO₃-Po>C.HCl-Po for almost all of the OP level.The fractionated total P(sum of all P fractions)content among the six OP levels decreased as follows:OP6>OP5>OP4>OP3>OP2>OP1.4.The proportions of labile P pools were increased with the OP level increase and the proportions of non-labile P pool were decreased with the OP level decrease,whereas the proportion of moderately labile P pools showed small variations among the six OP levels.The mean proportion of non-labile P pool accounted for 53%of the sum P fraction content.5.Correlation analysis revealed that the PAC was positively correlated with the proportions of Pi fractions and the proportion of labile P moderately labile P pools(P<0.01).In Redundancy analysis(RDA),the first(RDA 1)and second(RDA 2)ordination axes accounted for 80.8%and 7.7%of the total variation between the soil P fractions and chemical properties,respectively.According to the order of interpretation rate of soil properties factors,the order from high to low was total P,PAC,M3-Al,M3-Ca,M3-Fe and M3-Mg.A rational P fertilizer use led to optimum crop production and minimizing P surplus,where the PUE was more than 30.0%.The PUE showed a positive trend with OP levels and negative trend with the P application rates.So,improving soil OP level by rational P fertilizer application which an important approach to obtaining maximum crop production and sustainably.Moreover,the soil properties like(Ca,Mg,Al and Fe concentration)were the most important factors affect in P transformations.