Soil pH:-
Soil pH is an excellent chemical indicator of soil quality. Farmers can improve the soil quality of acid soils by liming to adjust pH to the levels needed by the crop to be grown. Benefits of liming include increased nutrient availability, improved soil structure, and increased rates of infiltration.
Understanding soil pH is essential for the proper management and optimum soil and crop productivity. In aqueous (liquid) solutions, an acid is a substance that donates hydrogen ions (H+) to some other substance.
Soil pH is a measure of the number of hydrogen ions in the soil solution. However, the actual concentration of hydrogen ions in the soil solution is actually quite small. For example, a soil with a pH of 4.0 has a hydrogen ion concentration in the soil water of just 0.0001 moles per liter. (One mole is equal to the number of hydrogen atoms in 1 gram of hydrogen). Since it is difficult to work with numbers like this, pH is expressed as the negative logarithm of the hydrogen ion concentration, which results in the familiar scale of pH ranging from 0-14. Therefore, pH = 4.0 = - log (0.0001). Because the pH scale employs the use of logarithms, each whole number change (for example from 5.0 to 4.0) represents a 10-fold increase in the concentration of H+ ions. Note that as the amount of hydrogen ions increases, pH decreases. A pH of 7 will have a hydrogen ion concentration 100 times less than a soil with pH of 5. Table 1 shows descriptive terms for various pH ranges.
Table 1. Descriptive ranges for pH in soils
Ultra acid
|
<
3.5
|
Neutral
|
6.6-7.5
|
Extremely
Acid
|
3.5-4.4
|
Slightly
alkaline
|
7.5-7.8
|
Very
strongly acid
|
4.5-5.0
|
Moderately
alkaline
|
7.9-8.4
|
Strongly
acid
|
5.1-5.5
|
Strongly
alkaline
|
8.5-9.0
|
Moderately
acid
|
5.6-6.0
|
Very
strongly alkaline
|
>
9.0
|
Slightly
acid
|
6.1-6.5
|
· an indicator for potential plant growth,
· an indicator of required lime, but does not tell how much lime is needed.
Liming Benefits
Liming will provide the following benefits:
· reduces the possibility of Mn2+ and Al3+ toxicity;
· improves microbial activity;
· improves physical condition (better structure);
· improves symbiotic nitrogen fixation by legumes;
· improves palatability of forages;
· provides an inexpensive source for Ca2+ and Mg2+ when these nutrients are deficient at lower pH;
· improves nutrient availability (availability of P and Mo increases as pH increases at 6.0 – 7.0, however, other micronutrients availability increases as pH decreases).
Lime Requirement for differnet pH and different texture of soils Lime(K.g/Ropani)
Note:- Lime should be applied before 2-3 weeks of seed sowing.
· improves symbiotic nitrogen fixation by legumes;
· improves palatability of forages;
· provides an inexpensive source for Ca2+ and Mg2+ when these nutrients are deficient at lower pH;
· improves nutrient availability (availability of P and Mo increases as pH increases at 6.0 – 7.0, however, other micronutrients availability increases as pH decreases).
Lime Requirement for differnet pH and different texture of soils Lime(K.g/Ropani)
Soil pH
|
Hills (Pahad)
|
Terai
|
||||
Sandy Loam (Balaute Domat)
|
Loamy(Domat)
|
Clayey Loam(Chimtaelo
domat)
|
Sandy Loam(Balaute Domat)
|
Loamy(Domat)
|
Clayey Loam(Chimtaelo
domat)
|
|
6.4
|
15
|
20
|
24
|
8
|
14
|
22
|
6.3
|
29
|
40
|
48
|
15
|
24
|
44
|
6.2
|
43
|
60
|
72
|
23
|
34
|
64
|
6.1
|
58
|
78
|
98
|
30
|
44
|
86
|
6.0
|
71
|
92
|
120
|
38
|
52
|
106
|
5.9
|
85
|
110
|
146
|
45
|
62
|
128
|
5.8
|
97
|
128
|
166
|
52
|
72
|
146
|
5.7
|
108
|
142
|
188
|
58
|
82
|
166
|
5.6
|
119
|
158
|
208
|
64
|
90
|
184
|
5.5
|
130
|
170
|
230
|
70
|
100
|
200
|
5.4
|
140
|
188
|
252
|
76
|
110
|
220
|
5.3
|
150
|
204
|
274
|
81
|
118
|
238
|
5.2
|
160
|
218
|
294
|
86
|
126
|
254
|
5.1
|
169
|
228
|
314
|
91
|
136
|
270
|
5.0
|
176
|
240
|
334
|
96
|
142
|
286
|
4.9
|
184
|
252
|
354
|
101
|
150
|
302
|
4.8
|
191
|
262
|
374
|
106
|
158
|
316
|
4.7
|
199
|
272
|
390
|
111
|
166
|
330
|
4.6
|
205
|
280
|
406
|
115
|
174
|
340
|
4.5
|
210
|
290
|
420
|
120
|
180
|
350
|