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Agronomic Services — Soil Testing

Mehlich Buffer Acidity
Table 1. Factors for calculating lime rates*
Current
Soil pH
Target pH
6.5
6.2
6.0
5.7
5.5
5.0
3.2
.971
.882
.824
.735
.676
.529
3.3
.970
.879
.818
.727
.667
.515
3.4
.969
.875
.813
.719
.656
.500
3.5
.968
.871
.806
.710
.645
.484
3.6
.967
.867
.800
.700
.633
.467
3.7
.966
.862
.793
.690
.621
.448
3.8
.964
.857
.786
.679
.607
.429
3.9
.963
.852
.778
.667
.593
.401
4.0
.962
.846
.769
.654
.577
.385
4.1
.960
.840
.760
.640
.560
.360
4.2
.958
.833
.750
.625
.542
.333
4.3
.957
.826
.739
.609
.522
.304
4.4
.955
.818
.727
.591
.500
.273
4.5
.952
.810
.714
.571
.476
.238
4.6
.950
.800
.700
.550
.450
.200
4.7
.947
.789
.684
.526
.421
.158
4.8
.944
.778
.667
.500
.389
.111
4.9
.941
.765
.647
.471
.353
.059
5.0
.936
.750
.625
.438
.313
0
5.1
.933
.733
.600
.400
.267
 
5.2
.929
.714
.571
.357
.214
 
5.3
.923
.692
.538
.308
.154
 
5.4
.917
.667
.500
.250
.083
 
5.5
.909
.636
.455
.182
0
 
5.6
.900
.600
.400
.100
 
 
5.7
.889
.555
.333
0
 
 
5.8
.875
.500
.250
 
 
 
5.9
.857
.428
.143
 
 
 
6.0
.833
.333
0
 
 
 
6.1
.800
.200
 
 
 
 
6.2
.750
0
 
 
 
 
6.3
.667
 
 
 
 
 
6.4
.500
 
 
 
 
 
6.5
0
 
 
 
 
 

* The factors in this table are derived from this formula:
        FACTOR = [(target pH - current pH) ÷ (6.6 - current pH)].

The lime requirement (LR) in U.S. tons per acre = (acidity × FACTOR) - residual credit.   Residual credit = 8% per month for MIN soils and 16% per month for M-O and ORG soils.
        Example: If soil pH = 5.0; desired pH = 6.0; acidity = 1.2; and residual credit = 0,
        then LR = (1.2 × 0.625) - 0 = 0.76 ton/acre.

Acidity is calculated from the formula: (6.6 - BpH) × 4 = meq Ac/100 cm³, where BpH = the buffer pH reading determined in the lab.


Last Update April 24, 2013

 

 

NCDA&CS Agronomic Services Division, Colleen M. Hudak-Wise, Ph.D., Director
Mailing Address: 1040 Mail Service Center, Raleigh NC 27699-1040
Physical Address: 4300 Reedy Creek Road, Raleigh NC 27607-6465
Phone: (919) 733-2655; FAX: (919) 733-2837