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 26o 47’ 45’’ to 26o 48’15’’ latitude and 80o 46’ 7” to 80o 46’ 45” longitude was prepared and used for detailed soil survey. This base map served the role of cadastral map very well.
|
