| In southern area of China,there are many disadvantageous factors for sustainable development of red soil,such as soil acidification,lower soil organic carbon(SOC)and potassium(K)deficiency.Long-term combined application with organic and inorganic fertilizers could affect mineral K release and K-dissolving bacteria through alleviate soil acidification,increase SOC,and then improve soil K content.However,it is unclear about the mechanism of K forms and transformation under different SOC and acidification conditions.Therefore,the two long-term field experiments of red soil were employed in this study,which was belong to Jiangxi Institute of Red Soil in Zhanggong Town,Jinxian county of Jiangxi province(since 1986)and Experimental Station of Red Soil of Chinese Academy of Agricultural Sciences in Wenfushi Town,Qiyang county of Hunan provice(since 1990),respectively.Then,the undisturbed surface soil(0–20 cm)were sampled from different treatments in 2015,which including CK(no fertilizer),NP(application of chemical nitrogen and phosphorus fertilizers),NPK(application of chemical nitrogen,phosphorus and K fertilizers),NPKM(application of chemical nitrogen,phosphorus and K fertilizers plus pig manure),and NPKS(application of chemical nitrogen,phosphorus and K fertilizers plus returning half of straw).First of all,total K(TK),non-exchangeable K(NEK)and exchangeable K(EK)of soil aggregates were analyzed.Secondly,the relationships of K stock in different soil aggregates with soil pH and SOC levels were explored.Thirdly,the K-solubilizing bacteria were analyzed under different fertilization treatments.The end,the K release rate and the dissolution in white mica by K-solubilizing bacteria under different pH and organic carbon levels were revealed.The conclusion was following as:(1)There was different for the soil aggregate distribution in the two long-term fertilization experiments.It was found that the proportion of >2 mm aggregate was less than 10% in Jinxian site,while the proportion of >2 mm aggregate was 18.8%-35.6% in Qiyang site.It also suggested that NPKM treatment could increase the proportion of >2 mm and 0.5-1 mm aggregates.However,the soil aggregate distribution in NPKS treatment were not significant different than NPK treatment.(2)Long-term K fertilization improved EK and NEK content or stocks of most aggregates in red soil,compared with no K fertilization.NPKM treatment raised EK stocks in most aggregates mainly due to higher carbon input.However,the NEK and EK stocks of soil aggregates in NPKS treatment was significantly lower than that of NPKM treatment.Moreover,the turnover rate of K in >2 mm aggregate was faster for meeting crop K uptake than other aggregates.(3)For Jinxian site,soil p H improvement can significantly increase NEK content of >2 mm aggregate in NP soils.However,the NEK content of >2 mm aggregate was not significantly increased by soil pH adjusting,while the proportion of >2 mm aggregate was 18.8%-35.6% in Qiyang site.(4)The proportion of >2 mm aggregate and its EK and NEK stocks could be increased significantly along with the SOC improvement by glucose addition.It was shown that the growth rates of EK and NEK stocks in >2 mm aggregate along with SOC increasing in Qiyang site were significantlyhigher than those of Jinxian site through linear fitting equation.(5)The properties of K-solubilizing bacteria were varied in different treatment of Jinxian and Qiyang sites.Further analysis showed that the length and surface area of maize root were the key factors affecting the K-solubilizing bacteria in rhizosphere soil under long-term fertilization conditions.The dissolution of K-containing minerals and the amount of K released by K-solubilizing bacteria could be promoted significantly,while the pH and organic carbon content were increased moderately.It was found that the suitable pH was 5.0-5.5,and organic carbon content was 10%-20% for K-solubilizing bacteria(Microbacterium). |
PDF Full Text Request