Use of GPS for Farm level Mapping of Salt Affected Soils


R. C. Sharma
Central Soil Salinity Research Institute
Karnal, Haryana 132 001

Salt affected soils (SAS) are an important entity of irrigated lands in arid and semi arid regions of the world. Lying barren, they occupy 6.65 mha area in India. Development of reclamation technologies by Central Soil Salinity Research Institute, Karnal (CSSRI) has raised their agricultural productivity manifold. Due to varied nature of salts, mineralogy and climatic conditions the location specific technologies need testing and modifications to suit new areas. Recently CSSRI Karnal has opened an experimental farm at Shivari village in Lucknow district of Uttar Pradesh.This Centre will test and modify reclamation technologies to suit SAS of the eastern parts of Indo-Gangetic Plain. The first step in the establishment of experimental farm was to map and characterize SAS. For the sake of characterization and mapping of such areas one has to depend on the cadastral maps which are very rare due to lack of maintenance.

In our research work since the survey of SAS of CSSRI research farm, Karnal and other projects in seventies, we faced some major problems that made us realize how much difficult field based agricultural researches are, which greatly depend upon cadastral mapping. Since there has been no regular upgradation of fragmentation of parcels of lands through Cadastral Surveys, the land records do not display the correct ground realities. Secondly, the SAS that have long been abandoned to agricultural operations had become bereft of structures or permanent land features those could serve reference points in survey operations.

In such surveys, the practice others and we adopted was to mark the distance and direction of a nearby village or a road to indicate the location of soil profile or sampling site. As a result of soil reclamation, the landscape feature of alkali soils undergoes complete transformation to the extent that relocation of profile sites becomes extremely difficult. Identification of exact location of sampling site of an experimental farm survey is very important for undertaking monitoring and change detection studies. In order to improve upon the reproducibility of sampling sites for future reference, Global Positioning System (GPS) was introduced in the farm level survey of CSSRI experimental farm Shivery.

Site Characteristics of the area
Located at village Shivari, in Lucknow district, the experimental farm has an area of 24 ha. Formed on old alluvium, the farmlands have gentle slopes between contours of 99.0 m in the NE to 97.6 m in the SW direction. The climate is seasonal and monsoonic. Salt infestation and fertility loss has rendered the soils unproductive. Due to long abandonment the soils have undergone a dramatic change in ground realities. The field bunds and field boundaries are lost, trees and plants are destroyed, on farm structures like tube wells, shelters, water channels have disappeared and the ground is covered with coarse grasses and bushes. The land is used mainly for zigzag village passages and serves as a resting and grazing place for village cattle.

Base map of the farm
For planning field survey of the farm, the cadastral map and Survey of India toposheet no.63B/13 didn’t prove of much help. The farm site in the form of open tract has two reference points a culvert and a seasonal nala. While the position of culvert was missing both in the cadastral map and toposheet, the position of nala understandably had shifted. In order to prepare a base map, a contour map of the farm was conducted. Prismatic compass survey was used to determine north direction of the farm and also farm boundary was drawn by angles of vertices of the traverse. Dumpy level was used to determine vertical ground level. During prismatic compass survey local magnetic declination error occurring due to nearby power lines was corrected. Exact locations of the culvert and nala were marked. A contour map of the farm on 0.2m contour interval was prepared. Lowrance Global Map 100 GPS was used to know the coordinates of the four corners of the farm. Thus a base map of the farm located within 26^o 47’ 45’’ to 26^o 48’15’’ latitude and 80^o 46’ 7” to 80^o 46’ 45” longitude was prepared and used for detailed soil survey. This base map served the role of cadastral map very well.

Application of GPS in field survey
Field traverse and land contours formed the basis of selecting profile sites representing all categories of alkali soils occurring in the farm. A total of eight soil profiles were studied for their site characteristics and soil morphology. From each soil profile, horizon wise soil samples were collected for laboratory analysis and characterization. A number of intervening soil auger bore tests was performed to establish extensiveness of profile boundary. For better reproducibility of the sampling sites, longitude and latitude of each soil profile was recorded with the help of GPS, which are given in the table along with their land use and soil characteristics. The location of soil profiles was marked in the Farm map (Figure 1).

Usefulness of GPS in survey of SAS
Spatial distribution of SAS is patterned in the form of scattered patches of less than 1 hectare to more than 50 hectares amidst fertile soils. Besides, crop growth properties of SAS differ greatly from surrounding soils. These two unique characteristics makes it necessary to mark their sampling site in such a manner that it could be easily and accurately relocated in the post reclamation period. GPS marked location of sampling sites are easily and accurately identifiable. Thus various monitoring studies based on point data can be conducted with greater degree of precision. Use of GPS in surveys of SAS would definitely improve the quality of studies leading to; comparable study to monitor the improvement of soil properties in the post–reclamation period, precise detection of hot spots of salinity emergence & expansion and identification and establishment of benchmark sites of SAS.

Location of soil profiles marked with GPS, land use and characteristics of alkali soils at Shivari Farm, Lucknow Uttar Pradesh

Soil Profile	Location as per GPS Value in Coordinates	Land use and soil characteristics*
P1	26o 48’4. 0”N, 80o 46’10. 3”E	Alkali soil, reclaimed with gypsum for 4 years, Under sugarcane crop. Soil pHs 8.7, ECe 0.6
P2	26o 48’ 04”N, 80o 46’ 21”E	Alkali soil, barren, pHs 10.1, ECe 1.4
P3	26o 47’58”N, 80o 46’24” E	Alkali soil biologically reclaimed with Accacia for 4 years. PHs 8.9, Ece 0.9
P4	26o47’51. 3”N, 80o46’32. 5”E	Alkali sol, barren, pHs 9.5, ECe 1.6
P5	26o47’50. 5”N, 80o 46’29. 2”E	Normal soil, low lying topography, pHs 8.0, Ece 0.7
P6	26o 47’56. 5”N, 80o 46’21. 7”E	Alkali soil, barren, pHs 10.7, ECe 10.7
P7	26o48’1. 6” N, 80o 46’16. 0” E	Alkali soil, barren, pHs 10.7, ECe 15.2
P8	26o48’9. 3” N, 80o 46’22. 0” E	Alkali soil, reclaimed with gypsum for 4 years. Under rice-wheat crops, pHs 8.8, ECe 0.9

* For surface 15 cm soil, pHs = pH of the saturated soil paste, ECe = Electrical conductance of saturated soil solution in dS/m