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									                                                 State Agriculture Plan – Tamil Nadu        15

temperature ranges from 23° to 42°C and the minimum from 10° to 14°C and being an
interior region, the diurnal range of temperature is large particularly in summer. Western Zone

        The   western     zone   comprises     of   Erode    and    Coimbatore       districts,
Thiruchengodu Taluk of Namakkal district, Karur Taluk of Karur district and northern
part of Dindigul and Madurai districts. The zone is located in between 9°10’ and 12°
North latitude and 70°30’ to 78° East longitude. The altitude of the zone ranges from
160 to 450 m above MSL.

        The zone has undulating topography sloping towards east.              Western and
northern parts of the zone are bound by the Western Ghats bordering Kerala and
Karnataka states with peaks ranging from 1000 to 2750 m above MSL. On the east,
the zone is bordered by Salem, Tiruchirapalli and Dindigul districts. The southern
part of the zone lies in Madurai district having contours of varying altitudes.

        The climate in the zone ranges from semi-arid to sub-humid with frequent
occurrence of drought.       Four distinct seasons are south-west monsoon (June-
September), north-east monsoon (October-December), winter (January-February) and
summer (March-May). The cool months of the year are November to January and the
hot months are March, April and May. The annual rainfall of the zone varies from
524 to 1428 mm with an average of 780 mm. Of the total rainfall, 48.4 per cent is
received during       north-east monsoon and 32.2, 18.6 and 2.8 per cent during south
west, summer and winter seasons respectively. The maximum temperature of the
zone ranges from 26.9 to 42.1°C and the minimum from 16.2 to 24.5°C.                      The
maximum temperature is experienced during the months of March, April and May,
gets reduced gradually and reaches the minimum during the months of December and
January.   Being an interior region, the diurnal variation in temperature is large
particularly in the dry and hot seasons. Cauvery Delta Zone

        Cauvery Delta Zone lies in the eastern part of Tamil Nadu between 10°00 and
11°30 North latitude and 78°15 and 79°45 East longitude. It is bound by the Bay of
                                               State Agriculture Plan – Tamil Nadu    16

Bengal on the east, the Palk Straight on the south, Tiruchirapalli and Perambalur
districts on the west and north-west, Cuddalore district on the north and Pudukkottai
district on the south-west.     This zone comprises the entire revenue taluks of
Thanjavur, Thiruvarur and Nagapattinam districts, Musiri, Kulithalai, Lalgudi and
Tiruchi taluk of Tiruchirapalli district, Chidambaram and Kattumannarkovil taluks of
Cuddalore district and Aranthangi taluk of Pudukkottai district.

       It is a deltaic zone. Cauvery is the river traversing the delta. A fair width of
sandy beach occurs including the sand bars on the sea surface of the river delta, stiff
clay seashores and marshy tidal swamps with mangroves. The terrain is an open plain
sloping gently towards east and devoid of any hills or hillocks. The altitude ranges
from 6 to 250 m above MSL.

       The Cauvery delta zone has diverse climatic conditions as the zone includes
coastal belt as well as inland area. Cyclonic storms and high humidity occur in
coastal belts. The coastal belt is favoured by high rainfall and when it proceeds to the
interior, the rainfall intensity decreases. The mean annual rainfall is 1,192 mm.
North-east monsoon alone contributes about 52.5 per cent of the total followed by
south-west monsoon with 30.5 percent. Hot weather season accounts for 11.4 per
cent while, the winter season has only 5.6 per cent. The mean maximum temperature
reaches 38.6°C in the month of May and the minimum of 21.0°C in December. April
to August is the hot months and November to February is the cool months. Southern Zone
       The southern zone is located between 8 and 10°.55’ North latitude and 79° 50
East longitudes. It is bound on the north by Tiruchirapalli and Thanjavur districts of
Cauvery delta zone, on the south by Kanyakumari district of heavy rainfall zone and
the Indian Ocean, on the east by Bay of Bengal and on the west by Kerala and part of
Madurai district of the western zone. The southern zone consists of Tiruneveli,
Tuticorin, Virudunagar, Ramanathpuram and Sivagangai districts, Thirumangalam,
Madurai south, Madurai north and Melur taluks of Madurai district, Dindigul and
northern taluks of Dindigul district and Pudukottai district (except Aranthangi taluk).
                                              State Agriculture Plan – Tamil Nadu    17

       This zone comprises of flat plains and intermittent hills at varying altitudes
ranging upto 700 m high. The topography is undulating with the gradient sloping
towards the east. The major river systems are Vaigai, Manimuthar, Sarguni, Gundar
and Arjuna nadhi.

       The climate of the southern zone is generally semi-arid and only a small
portion comes under – sub-humid. Thus, frequent drought occurs. Summer is very
hot. The zone comes under rain shadow area. The rainfall ranges from 700 to 1277
mm with a mean of 876.4 mm. North-east monsoon accounts for 54.9 per cent of
total rainfall and forms the main cropping season. South-west monsoon accounts for
23.9 per cent of total rainfall of this zone. Winter rainfall is negligible and summer
rainfall forms 13.0 per cent. The maximum temperature ranges between 30.0° and
37.5°C, while the minimum temperature is from 20.0° to 27.0°C. The temperature is
more or less similar in most parts of this zone. However, along the Western Ghats,
the minimum temperature tends to be low. High Rainfall Zone
       The High rainfall zone of Tamil Nadu consists of Kanyakumari district,
located between 77°50 and 77°36 East longitude and 8°03 and 8°35 North latitude.
It is bordered by Tirunelveli district in north-east, the Kerala State in the North West
and Arabian Sea in the west and Indian Ocean in the south.

       Kanyakumari district extends from the Arabian Sea to the Western Ghats upto
an elevation of 600 m above MSL. Two distinct physiographyic regions viz., the hill
and ‘else’ region and the plains are identifiable in this district. The climate is sub-
humid influenced by both the south-west and north-east monsoons, because of the
proximity of sea and the Western Ghats. There is not much variation in the mean
monthly temperature, which varies from 23.9°C (minimum) to 36.7°C (maximum). Hilly Zone
       This zone comprises the Nilgiris, the Shervarays, the Yelgiris, the Anamalais
and the Palani hills. The rainfall varies from 1000 mm at the foot of the hills to 5000
mm at the peaks. The maximum temperature varies from 15°C to 24°C and that of
                                                State Agriculture Plan – Tamil Nadu      18

minimum ranges from 7° to 13°C. The soil is mainly lateritic. The major crops are
vegetables, potato and tropical and temperate fruit crops. At the foot of the hills, hill
tribes raise minor millets. At higher altitudes wheat cultivation is common during
winter season.

2.1.3. Agro-Ecological Systems
       Besides, Tamil Nadu can also be classified under four Agro-ecological
systems.    There are 16 zones showing distinct soil characteristics under Hill
Ecosystem, Upland ecosystem, Plain Ecosystem and Coastal ecosystem.

Soils of Agro-Ecological Systems
i) Hill Ecosystem

      Deep to very deep, clayey and gravelly clay soils of the Nilgiris, hot humid to
       per humid (rainfall 1500- 2500 mm) ecosystem with Length of Growing
       Period (LGP) more than 210 days.
      Shallow to medium deep (with rocky phases), loamy to gravelly clay soils of
       south Sahayadris, hot humid / per humid transitional to moist semi-arid (rainfall
       900 – 1700 mm) ecosystem with Length of Growing Period (LGP) of 210 days.
      Shallow to moderately deep (with rock phases) red soils of Eastern Ghats, loamy
       to clayey with gravels, hot moist semi-arid to dry semi-arid transition (rainfall 750
       – 1000 mm) with Length of Growing Period (LGP) between 150 – 180 days.

ii) Upland Eco-system

      Moderately deep to deep gravelly loam to gravelly clay soils of upland, hot
       semi-arid dry ecosystem (rainfall 750 – 1000 mm) with Length of Growing
       Period (LGP) between 150 – 180 days.
      Moderately deep to deep, gravelly loam to gravelly clay soils, semi-arid to arid
       transitional ecosystem (rainfall 750 mm) with Length of Growing Period
       (LGP) between 90 – 120 days.
      Deep to moderately deep, clayey black soils in association with gravelly clay red
       hill soils of upland, hot semi-arid dry to arid transitional ecosystem
       (rainfall<750mm) with Length of Growing Period (LGP) between 90-120 days.

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