1.2 Determination method
The chloroform fumigation extraction method was used for the
determination of soil microbial biomass carbon and nitrogen. The
chloroform-fumigated and non-fumigated soils were extracted with
0.5mol/L K2SO4 solution at the
soil/liquid ratio of 1: 4. The organic carbon content in the extraction
solution was determined by FeSO4 solution titration with
a conversion coefficient of 0.38, and the organic nitrogen content in
the extraction solution was determined by ninhydrin colorimetric method
with a conversion coefficient of 5.00(Li et al.,2008).The measurement of
fumigation and non-fumigation was repeated 3 times, and the mean value
was taken.
Soil enzyme activity was determined by referring to Soil Enzyme and Its
Research Method(Guan et al.,1986).Catalase (Cat) was measured by
KMnO4 titration as a ml number of
1g.h-1 soil consuming 0.1 mol.L-1KMnO4.Urease (Ure) using phenol-sodium hypochlorite
colorimetric method, in 1g of soil after 1d culture generated
NH3-N mg number said urease activity; Sucrase (Sue) was
colorimetric with 3,5-dinitrosalicylic acid and expressed as sucrase
activity in milligrams of glucose formed in 1g of soil after 1d of
culture. Acid Phosphatase (Acp) activity was determined using a disodium
phosphate colorimetric method using milligrams of phenol released from
1g of soil 1d later. Each soil sample was measured three times, and the
average value was taken. The soil moisture water content was determined
by the drying method.
Soil microbial biomass
carbon and nitrogen and enzyme activity evaluation calculation
In this paper, the entropy method is used to determine the weight of
each index. Due to the differences between each index, in order to
eliminate the dimension of index data and the positive and negative
effects of the index, the original data is standardized to form a new
data column. The following formula is the entropy method to calculate
the index weight (Huang et al.,2021;Lu et al.,2019):
(1) Data standardization
(1)
Where: is the value of indicator of its sample (=1,2…,n;
=1,2…,n);,are the maximum and minimum values of indicator ,
respectively, and is the normalized ,which were the standardized
indicators of soil microbial carbon and nitrogen content and enzyme
activity under different water and fertilizer optimal management.
(2)Calculate the weight of thesample data under theindicator for that
indicator :
(2)
①Construction of original evaluation matrix:
There are m evaluation objects, nevaluation indicators,the indicators
and the corresponding entropy weightsmultiplied,the data are represented
as the original matrix,is the original data of the jth indicator of the
ith treatment,is the original data of the jth indicator of the ith
treatment:
(3)
Where:i=(1,2,…,m),j=(1,2,…,n), m=13,are 13 water
and fertilizer treatment trials.n=7,are indicators of soil enzyme
activity, microbial load carbon and nitrogen, and water content。
②Normalization matrix.The maximum and minimum values of each column
constitute the optimal and inferior vectors respectively:
(4)
③The distance between the ith treatment and the optimal and inferior
solutions are:
(5)
④The ith treatment fits to the optimal solution Ci are:
(6)
Microsoft Excel 2016 and SPSS26.0 were used for statistical analysis of
the data, and one-way ANOVA was used to test the differences of soil
microbial biomass carbon and nitrogen content and enzyme activity under
different water and fertilizer optimal management (=0.05). The entropy
method was used to calculate the weight and rank the soil microbial
biomass carbon and nitrogen content and enzyme activity. Mantel analysis
was performed using R language, and Origin2020b software was used for
mapping.
2 Result analysis