In this article we will discuss about the management of saline and sodic soils.
Management of Saline Soils:
Flooding and draining the flooded water after 3 to 4 days of flooding can leach down the soluble salts below root zone depth. Two to three such treatments can make the soil suitable for most crops.
Leaching requirement (LR) is that fraction of water that must be leached through the soil root zone depth to control the salinity at a specified level. This is simply the ratio of equivalent depth of drainage water to the depth of applied water which can be expressed as fraction or per cent.
If the ECd in root zone is to be maintained below 4 dS m-1 and ECa is 2 dS m-1,
LR = 2/4 = 0.5 or 50 per cent
Fifty per cent of applied water must pass through the root zone for maintaining desired salt balance in the root zone depth. However, several other factors need consideration at field level.
Provision of adequate drainage can minimise the adverse effects of salinity. Sowing the seed on the sides of ridges rather than on the top, application of acid forming fertilisers, use of organic manures and proper irrigation schedule can reduce the risk of crop production on saline soils.
Management of Sodic Soils:
Basic principle in reclamation of sodic soils is replacement of exchangeable sodium by calcium and leaching out the released sodium salt from the root zone. Availability and low cost makes gypsum an important amendment for reclamation.
Since the process is reversible, sodium sulphate should be leached out from the sphere of exchange. The amount of gypsum required to lower the ESP of a sodic soils to a desired level is known as gypsum requirement (GR). It depends on purity and solubility of gypsum, clay minerals present in the soil and the extent to which the exchange process takes places in the soil.
Laboratory method is used for assessing the GR of sodic soil. Weighed quantity of sodic soil 5 g is shaken with 100 ml saturated gypsum solution of known Ca2+ concentration and the filtrate analysed for Ca2+ and Mg2+.
where, Q is the concentration (meq l -1) of Ca2+ in gypsum solution and C2 is the concentration of Ca2+ plus Mg2+ in the filtrate.
Elemental sulphur and sulphuric acid can also be used where sodium carbonate content is more. Sulphur upon biological oxidation yields sulphuric acid which not only changes sodium carbonate to less harmful sodium sulphate, but also decreases the alkalinity.
Several other materials are also used for reclaiming sodic soils.
Gypsum equivalents of amendments used for reclamation of sodic soils as per Central Soil Salinity Research Institute, Karnal are given below:
Effective management practices are essential in the early state of exploitation of saline and alkali soils, such as:
1. Growing salt tolerant crops.
2. Using higher seed rate.
3. Growing shallow rooted crops that tolerate high soil moisture conditions.
4. Planting on the bottom side of the furrow.
5. Heavy irrigation before planting.
6. Heavy rates of organic manures application.
7. Using fertilisers containing calcium.
8. Keeping the land under cultivation without leaving it fallow for long, especially in hot, dry climates.