Determination of soil available phosphorous

Estimate soil available phosphorous

4. Log I
0/I
t=KC
WhereI
oistheintensityoftheincidentradiationandI
tisthetransmitted
radiation.
C: Concentration of solution
k: Constant

5. UV-Visible Spectrophotometer

7. 6. Activated charcoal -DarcoG-60.
7. 2.4 p-nitrophenol(0.25%)
5 N
(5 N) 148 ml

8. (5 N)

9. Preparation of std. curve
Prepare a series of standards by taking 0, 1, 2, 3, 4, 5 and 10 ml of 2
ppm P solutionin 25 ml volumetric flask .
Add 5ml NHCO3 sol. To each flask and adjust pH as above.
Develop colourand record the reading as above.
Construct a graph by plotting readings on X-axis and P on Y-axis.

10. Available P Total vol. of extract 1 2.24 X 10
6
(Kg/ha) = R X --------------------------X ---------------X --------------------------
Vol. of aliquot taken Wt. of soil 10
6

11. Result:
Sr. No.Particulars Rating ofsoil (kg/ha)
1. Very low Less than 7
2. Low 7.1-14
3. Medium 14.1-21
4. Moderately High 21.1-28
5. High 28.1 -35
6. Very high More than 35
Rating of soil for phosphorous:
Theavailablephosphorousstatusofthesoilis------------
kg/ha,thereforesoilis------------inphosphorous.