Study On Soil Nitrification In Coffee Plantation Of Yunnan

Increasing soil nitrification caused by larger application of N fertilizer has become a major issue in soil areas in Southern China.The process of nitrification of NH₄⁺to NO₃^-,lead to soil acidification,NO₃^-leacing and N loss of denitrification,which cause difficulties in the improvement of the soil.Coffee is one of the important distinctive plants in Yunnan plateau,which is grown in hot areas in the frontier of ecological barrier in Southwest China.Soils from the surface of coffee garden in hot areas of Baoshan and Mangshi used as research materials.The nitrification rates,relative abundance of ammonia-oxidizing microorganism and soil basic physicochemical properties were measured in order to identify nitrification of soil in hot regions in Yunnan province.The main results were as follows:(1)The net nitrification rate of the soil samples was No.4(7.42 mg·kg^-1·d^-1)>No.5(5.91 mg·kg^-1·d^-1)>No.2(5.11 mg·kg^-1·d^-1)>No.3(4.69 mg·kg^-1·d^-1)>No.1(1.83mg·kg^-1·d^-1)at 0-7 days after adding the ammonium solution.Week net nitrification rate was measured in the soil sample(No.1)with low p H(4.44).At the end of incubation experiment,soil p H of all soil samples decreased by 0.04?0.22 p H units.Soil p H of the No.5 with a high net nitrification rate decreased by 0.20 p H units,which was higher0.15 p H units than No.1 sample with a low net nitrification rate.(2)The net nitrification rate was negatively correlated with total nitrogen,organic matter and cation exchange capacity(p<0.05),and positively correlated with p H value(p<0.05).The stepwise regression analysis showed that cation exchange capacity was the important factor for the net nitrification rate(r²=0.465).A significant negative correlation between the gross nitrification rate and available potassium,EC and maximum water holding capacity(p<0.05),and the extremely significant positive correlation between the gross nitrification rate and Olsen-P(p<0.01)was found in this study.The stepwise regression analysis showed that Olsen-P and EC was the important factor for the significant negative(r²=0.978).(3)The dominant bacteria in coffee planting soil were:proteobacteria,acidobacteria,actinomycetes,scimitoids,bacillus,bacteroidetes,scum,verruca,armored fungi and firmicutes.In the genus ranking top 35 in relative abundance,only ammoxoarchaea Group i.1 a-associated(Candidatus Nitrosotalea)was found.The relative abundance of AOA was No.3(0.006675)>No.4(0.004978)>No.5(0.004302)>No.1(0.001247)>No.2(0.000656).(4)In all soil samples,there was negatively correlation between the relative abundance of ammonia-oxidizing archaea and the total nitrogen,organic matter,EC and maximum water holding capacity(p<0.01),and positively correlated with Olsen-P and soil p H(p<0.05).The stepwise regression analysis showed that Olsen-P was the important factor for the relative abundance of ammonia-oxidizing archaea(r²=0.748).In the soil samples with No.2,No.3 and No.5,there was extremely positive correlation between the relative abundance of ammonia-oxidizing archaea and gross nitrification rate(p<0.01),and significantly positive correlation with Olsen-P,available-K(p<0.05),and significantly negative correlation with the EC and extremely negative correlation with the maximum water holding capacity were significantly,respectively.The maximum water holding capacity and EC were the important soil factors affecting relative abundance of ammonia oxidizing archaea calculated by the stepwise regression analysis(r²=0.885).