The Effect Different Types Of Phosphate Sources On Autorotrophic/Heterotrophic Nitrification Of Paddy Soil In Zhejiang Yuhang

Nitrification is the key process of soil nitrogen cycle.Different types of phosphate sources effect the circle in soil.In this study,paddy soil in two different locations of Zhejiang Yuhang was investigated by laboratory incubation experiment using ¹⁵N stable isotope labeled and acetylene suppression technique.The concentration gradients of commonly used exogenous phosphate supply?inorganic phosphate source,organic source and biochar?included:no fertilizer?M0,0 g/kg?,low amount of fertilizer?Low,3.1 g/kg?,medium amount of fertilizer?Medium,6.2 g/kg?and high amount of fertilizer?High,12.4 g/kg?.The influence of different addition on the physicochemical properties,gas loss and the nitrification process was observed.The results obtained in this study were as follows:?1?Different phosphate sources have significant influence on NH₄⁺-N and NO₃^-N concentration in soil.Without C₂H₂,the NH₄⁺-N concentration decreased with the increase of inorganic P source and biochar application;In S₁,the average NH₄⁺-N concentration were 13.51,12.38 and 11.13 mg/kg with the applied amount of inorganic P source increasing from low to high;while in S₂,the average NH₄⁺-N concentration were 12.83,11.12 and 10.06 mg/kg.When added bichar,in S₁ and S₂,the average NH₄⁺-N concentration were 13.51,12.38,11-13 and 12.83,11.12,10.06mg/kg,respectively.When added organic P source,compared to control group,the samples in S₁ increased 4.25,8.45and 11.32 mg/kg,respectively;the samples in S₁ increased 5.51,10.00 and 13.39 mg/kg,respectively.The NH₄⁺-N concentration increased with the increase of three kinds of phosphate sources.In S₁,the average NO₃^--N concentration were 15.48,16.49 and 15.44 mg/kg with the applied amount of inorganic P source increasing from low to high;while in S₂,the average NO₃^--N concentration were 15.48,16.49 and 19.65mg/kg.When added organic P source,compared to control group,the samples in S₁ increased 16.03,17.62 and 19.84 mg/kg,respectively;the samples in S₂ increased 16.78,17.99and 20.09 mg/kg,respectively.When added bichar,in S₁ and S₂,the average NO₃^--N concentration were 15.01,16.03,17.29 and 15.87,16.91,17.81 mg/kg,respectively.In the presence of C₂H₂,the NH₄⁺-N concentration in soil showed no obvious change after applying the three types of P sources,there were also no significant changes of NO₃^--N concentration after applying the three types of P sources.The total-nitrogen concentration increased with the application amount of organic P source,it increased 1.62 and 1.92 g/kg in S₁ and S₂.While the biochar and inorganic sources showed less significant effection.The C/N ratio increased after appllied inorganic P source and biochar,while decreased after appllied organic P source.Both total-P and Olsen-P increased during the experiment.?2?After the applying of different exogenous phosphate sources,the N20 flux of S₂ is greater than S₁;after applying inorganic phosphorus source,N20 release flux in S₁ and S₂ increased 1.72 and 2.51 mg/m2 h respectively.After applying organic phosphorus source,N₂O release flux in S₁ and S₂ increased 2.25 and 2.72 mg/m2 h respectively.The C02 and N20 in soil have the similar release situation,and there was a significant positive correlation between the release rate of CO₂ and N₂O.In this study,inorganic phosphate and organic phosphorus facilitate the emission of CO₂ while biochar inhibited soil C02 release.The addition of phosphate will promote the increase of NH3.The high dose of inorganic phosphate source promote the emission of NH3;the application of organic phosphate source facilitate the emission of NH3,it increased 0.58 and 0.80 mg/m2 h,respectively in S₁ and S₂;the facilitation of biochar to the emission of NH3 was not as good as organic fertilizer and has a positive relationship with the addition amount.?3?Autotrophic nitrification is dominant in this experiment and the contribution of heterotrophic nitrification is 2%.The gross nitrification rate in soil S₁(25.39 mg kg^-1d^-1)and S₂(35.23 mg kg^-1d^-1)have a obvious dissimilarity.The effects of exogenous phosphorus on the soil S₁ is greater than S₂.The gross nitrification rate increased with the addition of exogenous phosphate.The changes of soil autotrophic nitrification rate is basically the same as gross nitrification rate.Compared with the other two kinds of P sources,the influence of organic P source is more significant,the gross nitrification value after applied organic P source in S₁ and S₂ were 49.66 and 59.26.mg kg^-1d^-1.After the addition of exogenous phosphate sources,the heterotrophic nitrification rate increased.Among the three additions,biochar had the most significant influence on heterotrophic nitrification rate.The influence of organic P source was inferior to biochar.However,the heterotrophic nitrification rate of S₁ and S₂ were slightly decreased after the addition of inorganic phosphate fertilizer.The difference between heterotrophic nitrification rate of S₁(0.32 mg kg^-1d^-1)and S₂(0.39 mg kg^-1d^-1)was not significant different.Inorganic fertilizer and organic fertilizer have no effect on heterotrophic IV nitrification contribution rate,meanwhile,after the addition of biochar,the heterotrophic nitrification contribution rate is higher than that in blank group.And the incremental values in S₁ and S₂ were 0.20 and 0.23,respectively.