Management of Acid Soils: 7 Ways

The ways are:  1. Addition of Liming Material 2. Use of Basic Fertilizer 3. Use of Rock Phosphate 4. Soil Management 5. Growing of Acid Tolerant Crops 6. Increasing the Efficiency of Nitrogen and Potassic Fertilizers in Acid Soils 7. Water Management.

Way # 1. Addition of Liming Material:

Soil acidity is the result of the accumulation of a predominance of H ions over OH ions. The bulk of H ions are held in close association with the colloidal complex. When lime is added to moist soil, the soil solution becomes charged with calcium ions.

These active Ca-ions exchange take place with hydrogen ions in the exchange complex. Hydrogen combines with OH-ions to form neutral water or with CO₃ to form unstable H₂CO₃, which is readily changed to H₂ O and CO₂.

The reaction is given below:

Way # 2. Use of Basic Fertilizer:

Use of basic fertilizers like sodium nitrate, basic slag etc. reduces the acidity in soils.

Way # 3. Use of Rock Phosphate:

Phosphate fertilization is almost essential for sustaining crop production in acid soils. As it is known that acid soils fix phosphorus in the soil. Application of rock phosphate in acid soil, soils provide an ideal situation for release of Phosphorus (P) from rock phosphate (RP).

The efficiency of rock – phosphate increase with increasing fineness. A low pH (below 5.0) facilitates release of phosphate from rock phosphate and the effectiveness decreases with increasing pH above 5.0. It is advisable to apply rock-phosphate several months ahead of liming to permit dissolution of rock phosphate at low pH.

Rock phosphates is preferred source of Phosphorous(P) in acid – soils as it is a cheaper source and contains 30 to 50% CaO. CaO increase available calcium (Ca) in the soil, thus raises soil pH and lowers exchangeable Al content.

Way # 4. Soil Management:

Proper soil and water management checks leaching of bases and enhances decomposition of organic matter.

Way # 5. Growing of Acid Tolerant Crops:

In acid soils, acid tolerant crops should be grown. Choice of crops may be done according to soil pH.

Crops can be divided into following groups:

(a) Highly acid tolerant crops:

Rice, potato, sweet potato, oat, castor, Echinochloa, Paspalum etc.

(b)Moderately acid tolerant crops:

Barley, wheat, maize, turnip, brinjal, cow pea, mung beans, pigeon peas, pea nuts etc.

(c) Slightly acid tolerant crops:

Tomato, carrot, red clover etc.

Way # 6. Increasing the Efficiency of Nitrogen and Potassic Fertilizers in Acid Soils:

The need for nitrogen fertilizer can be minimized by introducing acid tolerant N-fixing legumes in the cropping system besides improving the efficiency of fertilizer nitrogen. Higher nitrogen (N) rates are recommended in high rainfall areas to compensate leaching losses. Split application of N definitely improves recovery.

The efficiency of potassium fertilizer can be increased by split application of k- fertilizer. The split application is quite essential in acid soils having sandy texture. The crop residues should not be removed from the field.

Way # 7. Water Management:

Acidification can be prevented by continuous flooding or saturation. Where that is not possible, the soils are drained and leached to remove the acid material. After submergence the soil pH rises due to precipitation of aluminium hydroxide and by the reduction of ferric ion.

Liming Materials:

The common liming materials are:

1. Limestone (Ca CO₃)

2. Quick lime (CaO)

3. Hydrated (Slaked) lime [Ca (OH)₂]

4. Dolomitic limestone [CaMg (CO₃)₂]

5. Blast furnace slag (CaSiO)₃

6. Miscellaneous sources, such as wood ash, ground oyster shell etc.

Lime Requirement (Laboratory Method):

For reasonable crop production on an acidic soil, pH range from 6.0-7.0 is considered good. The amount of lime required to be added to acidic soil to raise the pH to a desired value is known as lime requirement. The buffer method is used for determining lime requirement.

In this method, 5 gm. of soil to which 5 ml of distilled water and 10 ml of the extractant buffer added is stirred continuously for 10 minutes and the pH of the suspension is determined. Lime requirement in terms of pure Calcium Carbonate can be seen from a table. Buffer method for determining lime requirement of soils with appreciable amount of extracted aluminium.

Lime Requirement (Field Method):

The actual dose of liming material is least fixed from field trials on liming and crop response. In a field trial, on different soil textures, lime requirement has been determined (See Table 8.1 and 8.2).

Method of Applying Lime:

The most efficient way to use lime is to apply small amounts every year or alternate, but this liming programme increase the cost of application. Lime can be applied at any stage in the cropping system, but normally it is applied one or two months before the sowing of crop.

It is desirable that newly spread lime be well-mixed with the whole plough layer. When excessively large amounts of lime are applied to sandy soils low in humus, injury to plant growth sometimes occurs due to boron, iron, manganese, copper, zinc etc. Over liming injury may be reduced by application of large amount of compost, farm yard manure, phosphorus, boron etc.

Efficiency of Liming Material:

The efficiency depends on the following:

(a) Chemical composition:

Oxides and hydroxides are the best as it dissolves immediately upon coming in contact with water.

(b) Fineness:

The fine materials are quicker in correcting soil pH.

What Lime does in the Soil?

The main effect of lime on acid soils are:

1. Lime makes phosphorus more available.

2. Lime increases the availability of nitrogen, as increase in nitrification and nitrogen-fixation.

3. Organic matter decomposition increases.

4. Lime makes potassium more efficient on plant nutrition.

5. Beneficial soil bacteria are encouraged.

6. Harmful aluminium and manganese and iron are rendered insoluble and harmless when a soil is well supplied with lime.

7. Calcium and magnesium become available.

8. Flocculating power of soil increases.

9. Improves the physical condition of the soil

10. Checks soil erosion.

11. Fertilizer effectiveness increases.

12. Plant diseases favoured by acid soil decrease.

Loss (or neutralization) of lime in the acid soils:

Lime is neutralized or lost from the soil by the following activities:

(i) Top soil having higher based saturation is lost by erosion.

(ii) Neutralization of lime by the acid formed by carbon dioxide in water.

(iii) Neutralization by acid forming fertilizers (e.g. ammonium fertilizers).

(iv) Neutralization by acids dissolved in rainfall.

(v) Leaching loss of lime (very less loss).

(vi) Removal by crops. Uptake of Ca by crops varies from 20-300 kg/ha.

Crop Response to Lime:

The use of lime on acid soil increases the yield of most crops. Legumes greatly and sugarcane appreciably respond to lime application. Lime application substantially increased the yield of maize, wheat, gram, soybean and groundnut. The response to liming on jowar, moong, arhar, masoor, marua, cotton, barley, linseed and mustard was also encouraging.

Extent of the Problem:

The acid soils in India are located in Kerala, Assam, Manipur, Tripura, some districts of West Bengal, Bihar, Jharkhand and Orissa. In Jharkhand, acid soils are found in Chhotanagpur and Singhbum. In Bihar tarai area of north Bihar, north-east area of Purnea and uplands of south Bihar.