Responses Of Phosphorus And Potassium Absorption Ability In Typical Green Manure Crops And Their Effects On Soil Ecosystem In Sourthen Rice Region China

Cultivation of green manure crops is an effective practice to improve soil fertility in South China.It is meaningful to explore the ability of different green manures on utilization of soil nutrients for the extension of green manures.Traditionally,Chinese milk vetch(Astragalus sinicus L.)has been used commonly as green manure,and other varieties green manure are lack of attention.Additionally,some new milk vetch cultivars have been innovated.It is necessary to understand the ability of nutrients utilization of different green manure varieties and new green manure cultivars.The present study selected three typical rice fields in Nanning of Guangxi,Qiyang of Hunan,and Nanchong of Sichuan,respectively.Pot experiments were conducted in Hunan and Guangxi to evaluate the effects PK fertilization on main popular Chinese milk vetch cultivars,and the treatments include the single application of phosphorus(P1K0),single application of potassium(P0K1),application of phosphorus and potassium(P1K1),and no fertilizer application(P0K0).At all the three sites,also examine the effects of phosphorus(P)and potassium(K)uptake ability of various winter green manure crops as well as their effects on soil properties and soil enzyme activities were explored using micro-plot field experiments.In Hunan and Guangxi,six popular Chinese milk vetch cultivars,i.e.,Minzi No.6,Ningbodaqiao,Wanzi No.1,Xiangzi No.1,Yijiangzi,and Yujiangdaye,together with hairy vetch(Vicia villosa L.)and common vetch(Vicia sativa L.)were compared.In Sichuan site,tested varieties included smooth vetch(Vicia dasycarpa L.),hairy vetch,common vetch,Lathyrus Sativus(Lathyrus Sativus L.),milk vetch and non-leguminous February orchid(Orychophragmus violaceus L.),Chinese radish(Raphanus sativus var.Longipinnatus),and manure radish(Raphanus sativus var.oleiformis Pers.),rapeseed(Brassica napus L.)and perennial ryegrass.In all the 3 sites,perennial ryegrass(Lolium multiforum L.)was planted as a control.The main results were as follows.Phosphorus and potassium application affected the biomass and P and K absorption of Chinese milk vetch and also effects on soil enzymes activities,and significant differences were observed.The highest shoot biomass increased in P0K1 by 22.1% in Guangxi,and in P1K1 by 79.6% in Hunan,compared to control.The P1K1 treatment in Guangxi and Hunan had the highest underground biomass.In term of shoots,P uptake increased in P0K1,i.e.,44.3% and 94.3% in Guangxi and Hunan,respectively,and below-ground P uptake of both sites were showed the highest in P1K1 treatment.In term of K absorption,the P1K0 treatment in Guangxi and the P1K1 treatment in Hunan were the highest in the shoots,which were 35.0% and 122.4% higher than the control,respectively.The highest roots K absorption showed in P1K1 treatment in Guangxi and the P0K1 treatment in Hunan.While in Guangxi P0K1 treatment showed the highest phosphatase activity,and the largest ?-glucosidase and Nacetylglucosaminidase activities were observed in the P1K1 treatment,but the treated soil was significantly reduced the leucine-aminopeptidase activity.In Hunan,the highest activities of ?-glucosidase and N-acetylglucosaminidase were also found in P1K1 treatment.Soil enzyme activity in Guangxi was significantly correlated with soil phosphorus(F = 5.7,p <0.01),while there was no significant relationship between soil enzyme activity and soil properties in Hunan.(2)Field experiments showed that hairy vetch and common vetch revealed higher abilities in terms of biomass accumulation and nutrients uptake.In Guangxi and Hunan,hairy vetch showed the highest biomass accumulation as well as P and K absorption.Moreover,the P,K accumulations of all legumes were higher than ryegrass in Hunan and Guangxi.In Sichuan,common vetch showed the greatest biomass yield,while smooth vetch took the second place,but smooth vetch was observed the highest ability as for P and K absorption.The results led to that hairy vetch,common vetch,and smooth vetch are potential green manures in paddy fields in south China.(3)Green manure cultivation influenced soil available P and K.Soil available P in the treatments of Wanzi No.1 in Guangxi and Ningbodaqiao in Hunan was higher than those of other cultivars or species compared with ryegrass,increasing by 41.2% in Guangxi and 30.6% in Hunan,respectively.The highest soil available K content was found in the treatment of Yujiangdaye in both sites of Guangxi and Hunan,i.e.,59.2% and 50.7%,respectively,higher than that in control.Maximum soil available P and available K contents in Sichuan site were recorded in Chinese radish and February Orchid among all green manure species.(4)Planting of different green manures affected soil enzymes variously.In Guangxi,phosphatase(87.0%)and leucine-aminopeptidase(163.8%)activities were increased by hairy vetch.The ?-glucosidase and N-acetyl-glucosaminidase increased by 143.4% and 283.3% in the treatments of Yijiangzi and Yujiangdaye,respectively,compared to the control.In Hunan,N-acetylglucosaminidase),leucine-aminopeptidase,phosphatase,and ?-glucosidase in Xiangzi No.1 treatment were 352.6%,477.5%,591.0%,and 786.0%,respectively,higher compared to the ryegrass treated soil.In Sichuan,maximum phosphatase,?-glucosidase,N-acetyl-glucosaminidase,and leucineaminopeptidase were found in the manure radish treatment,i.e.126.9%,32.7%,46.8%,and 44.2% respectively higher compared to ryegrass treated soil.The lowest enzymatic activities recorded in rapeseed treatment among all green manure crops.(5)Soil enzymes activities significantly correlated with soil available P and soil available K.Redundancy analysis(RDA)indicated that soil enzyme activities significantly correlated with soil available K both in Guangxi(F = 4.1,p <0.006)and in Hunan(F = 5.6,p < 0.024),as well as with soil total N.In Hunan and Sichuan,soil available P was found significantly relative to soil enzymes activitiesIn conclusion,in paddy fields of south China,PK fertilization could be a beneficial practice to improve the P and K absorption abilities for Chinese milk vetch cultivars.Hairy vetch,common vetch,and smooth vetch have high capabilities for P and K uptake,suggesting that they are potential varieties for improving P and K management in sustainable agriculture.As a mechanism,plantation of hairy vetch,etc.,may improve its ability of nutrient absorption through improving soil enzyme activities.