According to the second national soil survey and related standards, the soil nutrient content is divided into the following levels (see the following table).
Table 1 Soil nutrient grading standards
project
Organic matter
%
Total nitrogen
%
Fast-acting nitrogen
PPM
Fast-acting phosphorus
PPM (P2O5)
Available potassium
K2O
level
content
1
>4
>0.2
>150
>40
>200
2
3~4
0.15~0.2
120~150
20~40
150~200
3
2~3
0.1~0.15
90~120
10~20
100~150
4
1~2
0.07~0.1
60~90
5~10
50~100
5
0.6~1
0.05~.075
30~60
3~5
30~50
6
<0.6
<0.05
<30
<3
<30
The soil nutrient grading standards are mainly used to classify the contents of organic matter, total nitrogen, available nitrogen, available phosphorus, and available potassium, and the content of different components is different for each grade. In actual work, we can compare or reference this standard and test and analyze the land to be fertilized to understand the real fertility of the soil.
Soil nutrients refer to the essential nutrients that are present in the soil. Including carbon (C), nitrogen (N), oxygen (O), hydrogen (H), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulfur (S), iron (Fe) Mn, Mo, Zn, Cu, B, and Cl are 16 types. In the natural soil, in addition to the first three, the soil nutrients mainly come from the soil minerals and soil organic matter, followed by atmospheric precipitation, slope seepage and groundwater.
Organic matter is a symbolic substance of soil fertility. It is rich in nutrients needed by plants and regulates soil physical and chemical properties. It is an important indicator of soil nutrients. It is mainly derived from organic fertilizers and plant roots, stems, branches, leaves of corruption and various microorganisms, etc. The basic components are mainly cellulose, lignin, starch, sugars, oils and proteins, etc., providing a wealth of plants C, H, O, S, and trace elements can be directly absorbed and utilized by plants. The classification of organic matter can be used as soil nutrient grading. The soil nutrient grading standard is a total of six grades, and the sixth grade is the lowest, and the first grade is the highest.