Responses Of Phosphorus Use Efficiency To Soil Phosphorus Fertility Under Winter Wheat-Summer Maize Cropping On Loess Soil

Understanding the relationship between phosphorus use efficiency and soil phosphorus fertility is of great importance to quantify the optimum soil phosphorus level on which the best management strategy of phosphorus resources is based.The judicious phosphorus management can help to achieve high crop production and meanwhile to minimize the potential risk of P losses to environment.In this thesis,we studied the response of phosphorus use efficiency（PUE）to soil phosphorus fertility levels from experiment under controlled condition（pot experiment）and field experiment under winter wheat-summer maize cropping system on Loess soil.We conducted the experiment under controlled condition（pot experiment）with 5 sets of soils（labeled as F1,F2,F3,F4 and F5 in turn）.The soils used were collected from the plots subjected to diverse fertilization treatments for 25 years in a long-term experiment on Loess soil.And the field experiment selected 4 sets of soils（labeled as F1,F2,F3 and F4 in turn）.Five rates of 0,30,60,90 and 120 kg P₂O₅/ha were applied for each soil.The main results are as follow:1.Experiment under controlled condition（pot experiment）For the low phosphorus fertility soil（Olsen-P<15 mg/kg）,the application of phosphorus significantly increased the grain yield of winter wheat by 52.2%-119.7%and summer maize by 94.6%-212.7%compared with P0 where receiving no phosphorus containing fertilizers,but showed no significant effects in the other soils where Olsen-P contents are above 15 mg/kg.After two crop harvested,no significant increases in soil total P content were observed for treatments except for at P rates of 60,120 kg P₂O₅/ha in F2 and 120 kg P₂O₅/ha in F5.In general,the application of phosphorus can significantly increased the soil Olsen-P contents by-4.08%-434.69%,26.49%-112.77%,6.74%-48.24%,4.07%-43.65%and-4.84%-28.29%,respectively,on soils of F1,F2,F3,F4 and F5 over the corresponding P0 treatments.At the P application rates of 30,60,90 and 120 kg P₂O₅/ha,the PUE of wheat were found positively and significantly increased in linear with the increase of soil initial Olsen-P level（P<0.05）.The PUE of wheat reached 100%at the soil Olsen-P of 33 mg/kg at P application rate of 60 kg P₂O₅/ha.At P30,the PUE of maize was increased followed a pattern of parabola of soil initial Olsen-P dependent,and the PUE reached 100%at the soil Olsen-P content of 12mg/kg and maximum of 155.24%at soil Olsen-P content of 34 mg/kg;at P60,P90 and P120,the PUE of maize increased significantly and linearly with the soil Olsen-P contents and reached the maximum at Olsen-P of 12 mg/kg,17 mg/kg and 14 mg/kg,respectively,and then kept constant.The soil initial Olsen-P dependent PUE for the entire winter wheat-summer maize cropping system was much like that of summer maize.The PUE of system reached 100%at the soil Olsen-P of 18 mg/kg at annual P application rate of 60 kg P₂O₅/ha and the maximum value of PUE reached 131.51%at Olsen-P of 40 mg/kg.Under the same soil phosphorus level,the PUE of wheat and maize decreased significantly with the increase of P application rate,especially when the P application rate was higher than 60 kg P₂O₅/ha.From the viewpoint of the whole winter wheat-summer maize cropping system,the soil Olsen-P content should be maintained at the range of 17-40 mg/kg,and annual phosphorus application rate of 60-120 kg P₂O₅/ha was recommended.2.Field experimentIn the low phosphorus fertility soil（Olsen-P 10 mg/kg）,whether wheat or maize,the application of phosphate fertilizer significantly increased the grain yield（wheat is not significant）,but show no significant effects in the other soils.The results obtained from the two-year field experiments showed that there was a significant and positive linear correlation between the phosphorus use efficiency（PUE）of winter wheat and the initial Olsen-P level of soil（P<0.05）.At P60,the PUE of wheat reached100%at the soil Olsen-P content of about 31-33 mg/kg.The relationship between the PUE of summer maize as a function of soil initial Olsen-P level could be described with linear or linear plus plateau models,the PUE of maize reached 100%at the soil Olsen-P content about 18mg/kg for P application rate of 60 kg P₂O₅/ha.The soil Olsen-P dependent PUE for the entire wheat-maize cropping system was much like that of winter wheat.When the total P application rate was 120 kg P₂O₅/ha,the annual PUE of the two-year wheat-maize system reached 80%-83%at soil Olsen-P reached the critical soil Olsen-P level for summer maize（Olsen-P 13mg/kg）;the annual PUE reached 85%⁸7%at the critical soil Olsen-P level for winter wheat（Olsen-P 17 mg/kg）;the annual PUE reached 100%at the soil Olsen-P about 28 mg/kg;the annual PUE reached 115%at the soil Olsen-P level reached the critical soil P of environment（Olsen-P 40 mg/kg）at which the exhaustion of P fertility emerged.In summary,from the viewpoint of the whole winter wheat-summer maize cropping system,the soil Olsen-P content should be maintained at the range of 17-28 mg/kg,and annual phosphorus application rate of 120 kg P₂O₅/ha was recommended.