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Sodic or ‘Usar’ soils are characterized by the presence of sufficient exchangeable sodium that adversely affects the growth of most crop plants. In these soils, exchangeable sodium percentage (ESP)> 15 and this high ESP has an adverse effect on the both physical and nutritional properties of the soil, thereby reducing crop growth significantly. Besides this, there are salts capable of alkaline hydrolysis viz. carbonates and bicarbonates of sodium. In order to improve the productivity of these soils, the soil needs to be reclaimed. Mineral gypsum is used to replace excess soil sodium with calcium and thereafter flushing sodium out. 

Gypsum being the cheapest, easily available and easy to handle have been widely used. However, the amount of gypsum (CaSO4.2H2O) required to reclaim sodic soil depends upon various factors such as degree of Na-saturation, texture, degree of improvement desired, water quality, crops intended to grow etc.

Estimation of gypsum requirement of sodic soil is a tedious laboratory process and most of the labs lack expertise and facility for estimation. Thus using soil pH2 for calculating appropriate amount of gypsum for sodic soil reclamation is easy. Soil pH2 is normally determined in all testing laboratories and is component of soil health cards. The gypsum requirement dose is evaluated from the pH2 of the sodic soil.
Based on large number of soil sample analysis from 7 sodic soil dominant districts of Uttar Pradesh viz. Raebareilli, Unnao, Hardoi, Sultanpur, Barabanki, Faizabad, Lucknow and 2 sodic districts of Bihar viz. Muzaffarpur and Samastipur, in order to assess the nature and extent of sodicity. The information about soil related constraints and average crop yields were recorded.
Soil pH2, ESP and Gypsum requirement (GR) was determined for all the samples and then the relationship was drawn between soil pH2 and GR. Further the average crop yield from each sampled site was equated to predict the yield based on the soil pH for traditional as well as tolerant varieties.

This App is user friendly and can be useful for field functionaries, researchers, line department officials as well as farmers desirous of chemical reclamation of sodic soil for optimizing crop production in Indo-Gangetic plains by calculating the gypsum requirement in bags (of 50 Kg). It also estimates exchangeable sodium percentage of the sodic soil. It also calculates total depth of water required for leaching to flush out salts. Expected yield of salt tolerant as well as traditional varieties of rice-wheat after chemical reclamation is also predicted. 
In the input parameter, the requirement is only soil pH2, depth of soil to be leached and dimension of the field to be reclaimed. The output generated shall provide the gypsum quantity required in bags for heavy, medium and light textured soil. Also the output information includes the depth of water required for leaching soluble salts in cm and expected yield of crops (rice and wheat) both for salt tolerant as well as traditional cultivars. This software application will allow straightforward decision support for reclamation of sodic soil following standard protocols and optimize crop yields in Indo-Gangetic plains of North India. The mobile application has been developed that calculates the gypsum requirement on the basis of the mathematical equations obtained through curve fitting. The Mobile App is compatible with all the smart phone handsets with Android operating system commonly available in markets.


GypCal -Sodic Soil Reclamation

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