Response of phosphorus uptake by rape and bioavailability of soil phosphorus to carbon and phosphorus addition
[Objectives]We studied the effects of carbon and phosphorus additions on phosphorus uptake of rape and the bio-availability of soils under different phosphorus P levels,to explore the pathway of improving phosphorous fertilizer use efficiency.[Methods]A rape pot experiment was carried out,the high-P purple soil was taken from vegetable field,where available and total P content were 163.23 mg/kg and 1.72 g/kg,and the low-P purple soil was taken from a maize growing field,with available and total P content 3.93 mg/kg and 0.31 g/kg.Four treatments were set up,including:no carbon or phosphorus added(CK),adding phosphorus(+P),adding carbon(+C),and added carbon and phosphorus(+C+P),glucose was used as carbon source.After 30 days of growth,rape plants were harvested for measurement of aboveground biomass,and P content,the soil was sampled for measurement of microbial biomass P content(MBP),and phosphatase activity.Additionally,we analyzed the contents of four phosphorus components in the soil—CaCl2-P,Citrate-p,Enzymatic-P,and HCl-P,using the bioavailability-based phosphorus classification method(BBP).[Results]In low-P soil,adding P favored the growth and P uptake of rape,the rape biomass in+P and+C+P treatment was 6.48 and 4.21 g/pot,which was 2.39 and 1.20 times higher than the CK,and the P contents were increased by 71.43%and 58.33%.In high-P soil,addition of C and P(+P、+C、+C+P)did not significantly increase rape growth,but enhanced the plant P content,with increment of 30.55%,33.45%,and 42.52%in+P,+C,and+C+P treatment,respectively.In low-P purple soil,the addition of carbon and phosphorus significantly increased Enzyme-P levels by 2.76 times on average,+P and+C+P treatment increased CaCl2-P content by 24.76%and 27.72%,and+C enhanced Citrate-P content,but no any treatment showed significant effect on HCl-P.In high-P purple soil,all the treatments decreased CaCl2-P content,especially+C treatment resulted in 34.45%of drop,relative to that of CK;and compared to CK,+P,+C,and+C+P treatment increased Citrate-P significantly by 12.50%,17.43%and 24.47%.In low-P soil,+P,+C,and+C+P treatment increased soil MBP and phosphatase activity by 28.80%-59.39%and 5.96%-6.69%,while in high-P soil,only+C and+C+P treatment increased MBP by 35.65%and 37.08%,phosphatase by 5.33%and 7.76%.[Conclusions]In low-P soil,adding P could increase the growth and P uptake of rape,while in high-P soil,adding P could only lead to the luxurious P uptake of rape.Adding phosphorus and carbon could improve phosphorus bioavailability of low-P soil.However,the response of soil phosphorus bioavailability to external carbon is more significant in high-P soil.Therefore,in low phosphorus soils,both carbon and phosphorus should be added to enhance the effect of fertilizer,while in high phosphorus soils,organic carbon should be supplemented to improve the bioavailability of phosphorus.
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