P.Masilamani , S.Santhana Bosu and K.Annadurai
Water logging and soil salinity are of great concern all over the world and in India as well; they pose a major limitation to agricultural productivity. Current estimate shows that about 60 per cent of the land in India suffer from soil erosion, water logging and salinity. Approximately, 7.0 million ha is affected by salinity and alkalinity due to water logging in different agro-climatic regions of the country of which about 54,000 ha. is in the Cauvery delta The major reasons for this land drainage problem are low discharge capacity of drainage, rivers, flat longitudinal slope (1 in 2000), silting of bed and channels, meandering of drainage courses, presence of aquatic weed growth in drainage channels and absence of link drains. Management strategies like provision of drainage are to be developed to address the above problems.
Drainage is removal of excess water from the soil surface and the soil profile. Generally, engineering approaches, based on the laws of potential flow, such as deep open ditches, vertical drainage or horizontal sub-surface drainage, are adopted. These approaches require expensive capital investment, operation and maintenance. This will also generate drainage effluent, mainly saline in nature, the disposal of which creates environment problems. A possible alternative is the biological drainage or bio-drainage.
Bio drainage relies on vegetation, rather than engineering mechanisms to remove excess soil water. This happens through evapo transpiration, which is commonly expressed as “letting the vegetation drink itself out of the water logging problem”(Fig: 1). The system of bio-drainage is low cost and does not require installation of any physical structures. However, an initial investment for planting the vegetation is required. When established, the vegetation will also yield marketable products such as fodder, fibre and wood.
To understand the effect of bio-drainage in solving the drainage problems caused by canal seepage, a pilot study was undertaken at Agricultural Engineering College &Research Institute farm at Tiruchirappalli, TamilNadu.
A stretch of a canal of 0.63 km length and 3.0 m width nearing the tank was considered for observation. In addition to the seepage water from the tank, the sewage discharge from the nearby residential area was also discharged into this canal. There was lot of weed growth (Typha sp.) which reduced the free flow of the water disabling its proper use (Plate 1). The stagnation of water resulted in emanating fowl smell, increased mosquito population, and increased soil moisture, thus leading to cultivation problems. The discharge of this water into the Pullambadi canal (Irrigation canal of the Cauvery system) added to environmental problems. Hence, bio-drainage system was introduced to solve the drainage problem and to use the water efficiently.
Half of the canal length was planted with Eucalyptus tereticgrnis (Plate 2) at a spacing of lm and the other half with different varieties of banana ( Poovan, Karpuravalli, Rasthali and Monthan) at a spacing of 3.0 m. Both the crops can be cultivated continuously by ratooning / coppicing. The planting was taken up in March 2002 when the water level in the tank as well as the canal was full.
Among the species planted, survival percentage and biomass production of Eucalyptus tereticornis was higher compared to banana. The survival percentage of Eucalyptus tereticornis was 94 per cent whereas in banana it was 65 per cent. The growth performance of 18 months old eucalyptus in bio-drainage area was better compared to the eucalyptus trees planted in adjacent areas. At the end of first year, leaves, pseudo stem, flowers, and fruits were harvested from the banana crop. Eucalyptus tereticornis can be harvested at the end of fourth year and it can be allowed for coppicing. By coppicing there will be more number of shoots and foliage emanating from the present single stump thus resulting in increased evapotranspiration and biomass.
After the introduction of bio-drainage, it was observed that there was no water stagnation, no fowl smell felt by the residents, no mosquito problem and no harmful weed growth. As there is no stagnation of water, problem of dampness in the nearby fields is reduced and hence the cultivation could be taken as planned.
From this pilot study, it can be concluded that it is very economical and environment friendly to introduce bio-drainage system for the degraded drainage problem lands in low lying delta areas. It is quite common in delta areas that the annual crops like paddy, pulses etc., are washed away during monsoon floods. However, the tree crops used for bio-drainage, can withstand the inundation, quickly drain the water, protect the annual crop nearby and also give revenue in terms of biomass production. Thus, by adopting the low-cost bio-drainage system, the farmers in the delta region can improve their crop productivity.
P.Masilamani , S.Santhana Bosu and K.Annadurai, Agricultural Engineering College & Research Institute, Tamil Nadu Agricultural University, Kumulur, Tiruchirappalli – 621 712, Tamil Nadu.
