Analysis of soil/ Soil test correlation with soil extractants (reagents)

• Several kinds of extracting solutions are used to correlate soil test results with plant growth. Correlation is to find suitable extracting solution.
• An assay crop is grown in greenhouse. All the factors are controlled except the nutrients in question. After the harvest of the crops, the uptake of nutrient by plants is determined.
• Different extractants are selected to extract that nutrient which is in question. The uptake of that nutrient is correlated statistically with those extracted by different extractants.
• A best correlation between the nutrient and the extractant is selected. An extractants with high correlation coefficient is selected as a suitable extractant for soil tests. After selecting the extractant, a field calibration study must be carried out.
• Different extractants are used based on several factors such as acidic condition, alkaline condition, temperature condition, weather condition, temperature condition, weather condition, topography, soil texture and soil type etc.

Some suitable extractants are

➢ Brays p-1 for neutral to acid soil for available P

➢ 1N ammonium acetate for available K

➢ DTPA for Cu, Mn, Fe, Zn.