Study On Determining Methods Of Available N, P, K In Chongqing Area Testing Soil For Formulated Fertilization

Determining soil nutrient is the key of testing soil for formulated fertilization.Alkaline hydrolysis diffusion is the conventional method to determine nitrogen,and the results are customarily intituled alkali-hydrolyzable nitrogen.Soil available potassium is extracted by 1mol·1^-1NH₄Ac and determined by flame photometry.And soil available phosphorus is usually determined by Olsen or Black. Although the determining results of conventional methods are reliable and apply extensively, these methods only extract one element at a time and determing process is time-consuming,and the experimental results can not be applied in time and truly reflect field crop nutritive peculiarity and level,so it is too hard to guide formulated fertilization.Mehlich3(M3 for short)and ASI both extract multiple elements simultaneity, except for P,K,they can also extract available Cu,Zn,Fe,Mn and so on,which is quitely advantageous for advancing analysis speed and betimes taking out results to cut down workloads.However, whether these two methods are befitting for our south areas or not is worth approved. Furthermore, these two methods can not determine soil available N.Contrasting to normal bioassary method, this text comparies the results of available P, K determined by conventional methods and M3 and ASI on ChongQing purple soils,which is based on the relativities to ensure these methods' applicability and provide analysis methods for soil testing and fertilizering in ChongQing purple soils and South China.Based upon bioassary method, for available N,it uses NaHCO₃ to extract and colorimetry to determine soluble humic acid, comparies the relativity between soil soluble humic acid and alkali-hydrolyzable nitrogen,and discusses the feasibility to determine humic acid instead of alkali-hydrolyzable nitrogen,and rapidly ensures method to determine soil available N.The study results are as follow:(1) Soluble humic acid extracted by NaHCO₃ is separately remarkable related to organic matter and alkali-hydrolyzable nitrogen of soil, and there are r=0.774^** and 0.714^**(n=83).The humic acid is significantly correlated with alkali-hydrolyzable nitrogen in acid soils and neutral soils,and r are equal to 0.727^**(n=64) and 0.697^**(n=12), and there is no remarkable correlation (related coefficient of 0.666,n=7).Comparing with standard bioassay method,the related coefficient between humic acid extracted by NaHCO₃ and wheat absorbent nitrogen is 0.600^**,n=27,that is,they offer significant correlativity. According to received relational expression, the results of humic acid extracted by NaHCO₃ could be used to estimate the content levels of alkali-hydrolyzable nitrogen.(2) Separately comparing available phosphorus extracted by M3 and ASI with available P extracted by Olsen of 83 soils,the significantly related coefficients are 0.769^** and 0.864^**.On different sour alkalinity of soils,the relevance degree between M3-P and Olsen-p is great and the order of is neutral soil＞acid soil＞calcareous soil,especially calcareous soil is in 0.05 notable level relevance. And available P contents of different acidity-basicity soils determined by ASI and Olsen are extremely notable.Comparing with standard bioassarymethod, on noncalcic purple soils,the phosphorus amounts that the wheat absorbs being extremely notable relation with Olsen-P and ASI-P (r=0.688^**,0.672^**, n=9),and with M3-P are a notable relevance (r=0.915^**,0.871^**, n=9);The bioassay results and Olsen-P, M3-P and ASI-P are extremely remarkable on calcareous purple soil(r=0.765^*,0.831^**,0.761^*, n=9).(3) M3, ASI and routine method determining effective K are extremely notable appearance relation comparatively, that is, r=0.963^** and 0.945^** (n=83). Comparing with standard bioassary method,analysing correlativity between potassium that the wheat absorbs and effective K determined by routine method, M3, ASI: potassium that the wheat absorbs and three kinds of methods determine appearies significantly relevance on acid soils(r=0.871^**,0.875^**,0.890^**, n=9); on neuter soils, reaching notable relevance(r=0.776^**,0.767^**,0.761^*, n=9);however, it can not found notable relevance on calcareous soil.(4) Summarizing above and knowing,in testing soil for formulated fertilization of Chongqing area,the humic acid determined by NaHCO₃ extracting-colorimetry could estimate the content level of soil alkali-hydrolyzable nitrogen;Soil available P,K extracted by M3 and ASI are notable with the results of bioassary method,but pigmented soil filtrate of M3 and ASI influences the results of available phosphorus.And the concentration of NaHCO₃ is upper in M3 and ASI,which results to stop injector of flame photometer when determining effective K.Therefor, this text suggests that soil available P,K should be determined by routine methods in testing soil for formulated fertilization of Chongqing Or all country.