R. M. Harish Selvanathan
Salim Ali School of Ecology and Environmental Sciences, Pondicherry University, Pondicherry 605 014, INDIA.
The objective of the study is to conduct a holistic study of the land resources and utilization in Pondicherry and its environs. This was studied integrating all the parameters that contribute to land utilization.
The physical parameters studied were landform, soil, water and climate. Also other factors such as dynamics of land use over the years, population, agriculture, irrigation and other associated factors were studied.
As a first step, the landform was studied. The portion of the study area south of river Gingee is a flat alluvial plain with two major rivers flowing across; throughout the alluvial plain about 140 tanks were found, out of which 86 occur in the Pondicherry region. There are two elevated highlands of about 30-40 metres above mean sea level in the northern and north eastern portion of the study area. The elevated lands occur in the form of red broken mound with gently to very gently sloping lands. Gullies and ravines are common in this land form. Adjacent to the mound on the north western side, small charnokitic hillocks occur with gently sloping lands.
In between the two elevated mounds the uplands plain with very gently sloping land with flat low ayacut cultivated land occur.
To the south of the river Gingee occurs the alluvial plain which is the major landform in the study area. The marine/coastal land extends as a narrow stretch bordering the Bay of Bengal on the eastern side.
In the study area about five major landforms and 16 subunits (physiographic units) were identified. The alluvial land form occupies about 60% of the total extent followed by the elevated uplands (23%), upland plains (9%), marine landform (24) and water bodies and settlements occupy (6%). Out of the various landforms the alluvial plains are extensively cultivated.
The soil of the study area exhibited a lot of variations and were found typical to the landform where they occurred. About twenty two soil unit/series were identified totally. In the alluvial plain nine types of soils were identified; out of which five soils (OP1, OP2, OP3, OP4, and OP5) occurred in the old plain and two in the recent flood plain and very recent flood plain respectively. The soils in the old plain were medium to heavy textured and were intensively cultivated with paddy and sugarcane. The soils in the recent flood plain and very recent flood plain were light to medium textured and were cultivated with paddy, sugarcane, cotton, groundnut, tapioca and millets.
The soils of the coastal plain (MN1) was mainly of sandy texture and only a few crops like casuarina, groundnut were cultivated. The beach soil MN3 were found unsuitable for agriculture. The soils in the coastal creek(MN,)were of medium texture and fit for only paddy cultivation.
The red soils in the elevated landforms (SS1, SS2 and SS3) are light textured and are suitable for horticulture crops and Agri-horti-silvi-pastoral cultivation.
About four soils were identified in the upland plain (LL1, LL2, LL3, and LL4). The LL3 and LL4 occur in low lying ayacut lands are heavy textured and are fit for paddy and sugarcane cultivation. The LL1 & LL2 soils in the slightly undulating lands are light to medium textured and have moderate potentiality for cultivation of crops.
The soils (CK1, CK2 & CK3) in the north western portion with hillocks and undulating landforms have poor to moderate potential for agriculture.
The soils composition were found to establish a strong relationship with the physiographic units. The landform and soil resources were mapped and studied by adopting the procedure outlined by Seghal et al. (1987) and the method was found to be ideal and suitable for the study area.
Fertility status of the study area was also studied. Soil samples from 721 sample points were analysed and it was observed that the soils were generally low status for available nitrogen, high status of phosphorous and medium status of potash. The soils were mildly to moderately alkaline in general and sometimes strongly alkaline in localized patches.
The climate resource comprising of the main parameters viz., rainfall and temperature were analysed for their variability and fluctuations. The north east and south west monsoon operating from October to December and June to September respectively were mainly responsible for bringing rainfall to the study area. Both the monsoons were found to be variable and differed only in the intensity of rainfall, though the north east monsoon brought 62% of the rainfall the difference in the number of rainy days between the two monsoons was very meagre. Frequency classes and monthwise frequency classes for a period of 80 years (1911-1990) were analysed and presented. The period October to December were the months of maximum rainfall. The temperature also revealed variations in the mean maximum and mean minimum temperature. However the variations were not very abrupt to make significant climatic changes. The water balance study revealed the growing period as ranging from 150-210 days. The months July to December were the periods of recharge & surplus, January & February were utilization period and from March upto July it was deficit period. Overall, the temperature and rainfall was favourable for the cultivation of crops.
The water resource study revealed the potential of surface and sub surface water for irrigation and other purposes. The surface water resource comprises of river Gingee and river Ponnaiyar which feed the numerous storage tanks through a net work of canals and channels. The tanks and rivers also get water flow from the adjoining lands. The rivers are seasonal and are dependant upon the monsoon for their flow. The surface resource was having a command area of 6700 ha in Pondicherry region only but by 1986 the area got reduced to nil. The reason was due to the bad maintenance of the tanks and canals resulting in siltation and reduction in storage capacity. At present the entire load of water supply for irrigation and other purpose is met by only the ground water resource. The ground water supply for the region is mainly from three aquifers namely, Alluvium, Cuddalore Sandstone and Vanur-Ramanathapuram formation. Initially only the Alluvial aquifer was tapped but due to over exploitation this aquifer has depleted and from the middle of seventies the Cuddalore Sandstone aquifer was tapped, and in the early eighties the Vanur-Ramanathapuram aquifer was tapped. However over the years due to over exploitation, all the aquifers have started declining indicating the depletion of groundwater resources.
At present there is no scope for further development of tube wells and it is now only a question of monitoring and enhancing the recharge of the aquifer. With the intrusion of sea water at several places the situation is alarming and there is an urgent need to conserve and improve the resource.
Therefore it is necessary to desilt and reinstate or even increase the capacity of the storage tanks and canals so as to not only increase the storage capacity but also to enhance the recharge of the ground aquifer. The simple regression analysis showing the relationship between rainfall received and water depth showed that the depth of water level did not increase with increased quantum of rainfall. This may be due to the heavy drawal from the surrounding places of the observation tube wells.
The analysis and dynamics of general land use over the past revealed that the barren and uncultivated land has declined due to land reclamation. The area under non agricultural use has increased mainly due to conversion of good agricultural lands. Net area sown has been gradually declining over the years. The cultivable waste land area has increased and the net cropped area has also gradually declined. Above all the agricultural lands are converted for non agricultural purposes which is due to the rapid urbanization and the spurt in industrialization witnessed in the Pondicherry region since the last decade. This trend in land use change is not in the right direction because the decrease in area under age old agriculture will affect the region in many ways.
The agricultural and cropping pattern showed the diversity of crops, dominance of food crops, increase of area under paddy which is the principal crop. Sugarcane ranks first among commercial crops followed by groundnut as an oil seed crop. The area under pulse has been fluctuating over the years and in the last few years the area under pulse has increased significantly. Overall the area under different crops and cropping pattern did not show any pattern or trend the whole scenario was haphazard with dominance in paddy and sugarcane cultivation.
The land evaluation were conducted by adopting the Land Capability Classification Riquier model, F.A.0, model and land evaluation by predicting optimal crop using statistical model. The Land Capability classification revealed that about 57% of the land were under Class II, 25% under Class III and 0.18 under Class IV, other lands unfit for agriculture. According to Riquier parametric method 6 soils were under the class 'Good', 11 were average and 4 were poor. The land suitability classification for various crops revealed that more than 55% of the land were highly suitable for paddy and sugarcane cultivation, 23% for millets, 23% for groundnut, 40% for vegetable and 37% for flower cultivation besides the other lands which were moderately suitable, marginally suitable, currently not suitable and permanently suitable.
The prediction of optimal crop profitability based on soil properties and yield brought two distinct informations, sugarcane was the most profitable crop occupying about 74% of the sampling point. Also, increase in prices of inputs with various levels did not alter the status of sugarcane excepting when the proposed water levy was considered.
However when the income of crop was considered on monthly basis, groundnut occupied the major place. It continued to remain on top even when prices were hiked including water levy thereby demonstrating its profitability under all circumstances and also showing less consumption of inputs like water, power and labour.
The optimal crops prediction gives an overview of the most profitable crops to be grown so as to plan the suggested land use or cropping pattern to augment the revenue from the agricultural sector.
From the land evaluation for predicting optimal crop using statistical model and the decision maker approach model for precasting the profitability of crop due to increase in prices of inputs; the following was observed:
1) Sugarcane was the most profitable crop when the profit/income was considered for a single crop.
2) Groundnut was the most profitable crop when income/profit was considered on a monthly basis and it continued to be high compared to other crops even when all the input prices were increased.