Before planting tea in such an area, the area needs to be rehabilitated for the proper growth and development of tea plants and the sustained productivity of the area. Soil rehabilitation is needed in areas where the soil structure is destroyed due to burning of the organic matter and the soil being compact. The objectives of soil rehabilitation are:
- to increase soil aeration,
- improve the soil physical condition and
- increase the organic matter content.
Then, how to rehabilitate the soil?
The most convenient method of improving the organic matter status in the soil is by growing one or more green crops in situ. The crop selected for the purpose should be easy to grow in the particular locality and should produce luxuriant growth to provide a large amount of organic matter. The species should also be amenable to repeated lopping. It should preferably possess a robust and deep root system which can penetrate to the lower depth of the soil. Normally, soil rehabilitation can be done by growing some suitable species, mostly grasses, for a reasonable period (period ranging from 18 to 24 months). The grasses are most preferred because they, besides providing large amount of biomass to the soil by way of loping, make the soil aerated by penetrating their roots into the deeper layer.
Soil Rehabilitation Crops
A large number of plants, grasses, twining creepers, shrubs have been tried as mulch crop in different parts of the world to provide organic matter to the soil. Amongst the grasses Guatemala (Tripsicum laxum), a prolific grower, is extensively used as a rehabilitation crop in many parts of the world. Pusa Giant Napier grass (Pennisetum purpureum) is used in N.E. India and Africa. Another grass, Citronella (Cymbopogan wintarianus) is also used in N.E. India. Mana grass (Cybopogan confertiflorus) is widely used in Sri Lanka and Eragrostis curvula,in Africa.
Growing of Soil Rehabilitation Crop
In case of replanting of tea in the uprooted tea areas, first step of rehabilitation programme is to plough the land properly and, if required, sub soiling should be done. Sub soiling is needed in case of heavy soils by means of which the compact sub-soil is broken without inverting the soil with a narrow cultivator shovel or chisel. The next phase is the incorporation of organic matter into the soil. The status of the organic matter in the soil is improved by addition of lopping of rehabilitation crops.
The rehabilitation crops should be planted in future tea rows after properly ploughing the land. At the time of planting of the rehabilitation crops, 15 – 20 tones of cattle manure per hectare should be applied as basal dressing, if possible. If not, NPK @ 60:30: 60 kg per ha as 10:5:10 YTD mixture may be applied. The crop can be lopped three times a year at 8-10 weeks intervals and the lopping should be placed in situ. If the soil is very acidic (pH less than 4.5), 2-3 tons of powdered slacked lime per hectare is suggested at the time of soil preparation.
The period of rehabilitation depends on the state of the soil. The land can be considered properly rehabilitated only when there is satisfactory growth of the rehabilitation crop itself. Apart from raising the fertility of uprooted soil, there is another aspect of rehabilitation which also requires a minimum period of rest for the soil. The soil borne pests and diseases which parasitize on tea cannot thrive for long, after uprooting and removal of the host plant. When grasses like Guatemala is used, the rehabilitation period may be two years since the grass is not susceptible to root rot fungi. However, the period of rehabilitation has to be prolonged if the growth of the rehabilitation crop is not satisfactory. The growth of the crop gives an indication of the success of the rehabilitation operation.
On satisfactory completion of rehabilitation, the crop is cut at ground level and the litters are kept in situ as mulch.