Agro-Ecological Zones

Four parameters that together evolve distinct agronomic environments wherein a distinct cropping pattern flourishes are altitude, rainfall pattern, soil type and topography. The parameters and their levels used for delineating agro-climatic zones are summarized below. The levels of each parameter are broadly determined to avoid complexity in the process of land evaluation. In reality, there can be several more levels for each parameter (For example, there are 38 soil associations identified in Kerala, at 1:250,000 scale).

Altitude: Altitudinal variations influence the temperature regime. High altitude generates temperate climatic conditions in a tropical area like Kerala. Sizeable areas in the high ranges of Idukki and Wayanad districts fall under this category, even though high altitude areas are found all along the Western Ghats. The low altitude region, endowed with humid tropical climate is spread over the entire length of the state.

Rainfall: The State is relatively rich in rainfall endowment; with an annual precipitation around 2600 mm. Ninety percent of this precipitation is during the two monsoons, June to August (southwest) and October to November (northeast). About 60% of annual rainfall is received during southwest monsoon period and about 30% during northeast monsoon. From December to March there is very little rainfall, but the occasional rainfall during this period is a very critical requirement for cultivation as we still depend upon rainfall for raising many of the crops. The spread of rainfall is relatively better with 6-7 months having rainfall above or nearly around the monthly average. The quantum of annual precipitation is concentrated around lesser periods towards the northern part of the state while it is spread over longer periods in the southern parts. The co-efficient of variation of the annual rainfall is below 20% and hence, agriculture is expected to flourish under relatively stable conditions. However coefficient of variation of monthly rainfall is high. As a result, stability in production can be ensured only with the support of irrigation at least for most of the major crops so as to increase their production and productivity. The state was divided into two halves namely the areas south and north of lION latitude (approximately south and north of Thrissur) with rainfall pattern i and II respectively. The southern region is having relatively well distributed rainfall and June maxima for SW monsoon while the northern region has relatively ill distributed rainfall and July maxima for SW monsoon.

Soil Types: Soil type is the third factor for distinguishing specific zones. The major group under the soils of Kerala is laterite and its variations. In the traditional midland region the dominant soil type is typical laterite with the B-horizon present. The areas skirting the Western Ghat and the high ranges which together form the traditional highland region has lateritic soil where the B-horizon is absent. Red loam is found in the southern most tip of the state. All these variability constitute distinct homogeneous agro-ecological zones, though the rainfall pattern is the same. Distinct zones have been identified based on special soil types such as riverbank alluvium, peaty soil (kari) as in Kuttanad and 'sandy soils, though the rainfall pattern and topographic models are the same. In the coastal area, the texture of the soil- especially of the garden lands is considered as a distinguishing feature in identifying two separate zones one with sandy loam and the other with sandy soil. The soil characteristics of the paddy land such as peaty (kari) and saline soils (pokkali) have also been associated in delineating the zones.

Topography: Areas having similar rainfall pattern and soil type are further delineated into zones based on topographical features. For instances, the midland region north of II _ latitude has a common rainfall pattern and the soil is of typical laterite with B-horizon. It is further delineated into two zones based on the differences in topography with one zone having topographic Model II-b and the other Model II-c. Similarly the midland region south of II "N has been delineated into two zones based on the differences in topographic features as models II-a and II-b.

Following the above approach and using a matrix built upon altitude, rainfall, soil and topography, the state has been delineated into thirteen agro-climatic zones. Block Panchayat has been taken as the unit for purposes of delineation. All the Blocks, Municipalities and Corporations have been grouped into appropriate agro-ecological zones. Whenever a Block or Municipality was found to fall in more than one agro-climatic zone, it was assigned to that zone which has the largest area. Though 13 agro-climatic zones have been identified, no Block was assigned to one zone viz. the Riverbank alluvium as it is found scattered in several blocks. This zone is found generally all along the banks of the major rivers. It is found relatively extensively in the lower basins of the Periyar and Pampa river systems. Further, such alluvium deposits are generally found in the paddy fields that form the valley portions of the undulating landscape, which is interspersed with mildly sloping hills. The principal characteristics of each zone are summarized.. Each of the zones identified is assigned a popular name. Many of them are currently in vogue and are associated with areas having singular agro-climatic features and cropping patterns.

Parameters for identifying agro-ecological zones

Parameter	Level	Description
I Altitude	Type I	Altitude Up to 500 m above MSL (Low altitude zone- hot humid tropics, spread over the entire state)
	Type II	More than 500 m above MSL
II Rainfall	Pattern I	Both the southwest and northeast monsoons are active and moderately distributed. Southwest monsoon with June maximum (South of 11ºN latitude)
	Pattern II	Poorly distributed rainfall; southwest monsoon with July maximum and concentrated in 3-4 months. Northeast monsoon relatively weak (North of 110 N Latitude).
III Soil Type	1	Alluvial soil (Spread over river banks)
	2	Sandy soil (Coastal areas)
	3	Sandy loam soil (Coastal areas)
	4	Laterite soil with well defined B horizon (Natural midlands)
	5	Laterite soil without B-horizon (Natural highlands).
	6	Red soil (Southern-most Kerala)
	7	Black soil (Chittur taluk of Palakkad district)
	8	Peat (kari) soil (Kuttanad)
	9	Acid-saline soil (Pokkali and Kaipad areas)
IV Topology		Vallyes	Hill Tops	Slopes
	Model I	Extensive valleys with level but raised garden lands
	Model II a	Valleys less extensive	Hills with moderate gradients	Slopes having mild gradients
	Model II b	Valleys less extensive	Hills with moderate gradients and top with egg shaped hump	Steep slopes
	Model II c	Valleys less extensive	Hills with table tops	Steep slopes
	Model IIII	Narrow valleys	Hills with steep gradients	Steep slopes

No	Zones	Attribute type	Rainfall Pattern	Topography	Soil Type
I	Onattukara	I	I	I	Sandy loam
II	Coastal Sandy	I	I	I	Sandy loam
III	Southern midlands	I	I	III	Laterite without B-horizon
IV	Central midland	I	I & II	IIa	Laterite
V	Northern midlands	I	II	IIb	Laterite
VI	Malappuram type	I	II	IIc	Laterite
VII	Malayoram	I	I	III	Laterite without B
VIII	Palakkad plains	I	II	II	Red loam
IX	Red loam	I	I	III	Red loam
X	Chittoor black soil	I	II	IIa	Black soil
XI	Kuttanad	I	I	I	Peat (kari)
XII	Riverbank alluvium	I	I	I	Alluvium
XIII	High ranges	II	I&II	III	Red loam

Distribution of agro-ecological zones of Kerala

No	Zones	Description
I	Onattukara	Quilon ©, Chavara, Karunagappally, Ochira, Kayamkulam (M), Mavelikkara, Mavelikkara (M), Muthukulam1, Haripad2
II	Coastal Sandy	Ambalapuzha2, Alleppey (M)2, Aryad3, Kanjikuzhy3, Cherthalai(M), Pattanakad3, Thykkattussery3, Vaikom (M), Vaikom3, Vyttila4, Edappally4, Palluruthy4, Kochi ©4, Vypeen4, Parur4, Parur (M), Kodungallur, Thalikkulam, Mathilakom, Chavakkad, Andathode5, Ponnani5
III	Southern midlands	Trivandrum ©, Trivandrum Rural, Kazhakkuttam, Chirayinkeezh, Attingal (M), Varkala, Kilimannoor, Ethikkara, Mukhathala, Anchalummude, Chadayamangalam, Kottarakkara, Vettikkavala, Chittumala, Sasthamkotta, Elanthur, Pandalam, Kulanada, Bharanikkavu, Chengannur7, Koippuram7, Thiruvalla (M)7, Mallappilly7, Changanacherry (M), Madappally2, Pallom, Kottayam (M), Ettumannur2, Kaduthurithy
IV	Central midlands	Pampakuda, Vadavucode, Koovappady, Perumbavoor (M), Vazhakkulam, Aluva (M), Alangad7, Parakadavu7, Angamaly, Mulanthuruthy, Mala, Vellangallur5, Irinjalakkuda (M), Irinjalakkuda5, Cherpu5, Anthikkad5, Thrissur ©, Puzhakkal5, Mullassery, Kunnamkulam (M), Chowannur, Trithala, Pattambi, Ottappalam.
V	Northern midlands	Pandalayani8, Balusseri, Perambra, Meladi, Vadakara (M), Thodannur, Kunnummel, Tuneri, Badagara, Thalassery6, Thalassery(M), Kuthuparamba, Edakkad, Cannanore (M), Irikkur, Cannanore6, Taliparamba, Payyannur
VI	Malappuram type	Tirur, Kuttipuram, Tanur, Tirurangadi, Vengara, Malappuram, Manjeri, Kondotty, Kozhikode8, Kozhikode ©, Chevayur, Kunnamangalam, Koduvally, Nileshwar8, Kanhangad9, Kasargod9, Manjeshwar9
VII	Malayoram	Perumkadavila, Vellanad, Nedumangad, Vamanapuram, Anchal, Pathanapuram, Parakode, Konni, Ranni, Vazhoor, Kanjirappally, Pampady, Erattupetta, Lalam, Pala (M), Uzhavoor, Thodupuzha, Elamdesam, Muvattupuzha, Muvattupuzha(M), Kothamangalam, Chalakudy7, Kodakara7, Ollukkara, Pazhayannur, Mannarkkad, Sreekrishnapuram, Perinthalmanna, Mankada, Vandur
VIII	Palakkad plains	Alathur, Palakkad, Palakkad (M), Kuzhalmannam, Nemmara10
IX	Red loam	Nemom, Neyyattinkara (M), Athiyannur, Parassala
X	Chittoor black soil	Chittur, Kollengode
XI	Kuttanad	Chambakulam, Veliyanad, Pulikeezhu 7
XII	Riverbank alluvium	Distributed as narrow stretches in the river banks all over Kerala
XIII	High ranges	Arudai, Devikulam, Attapadi, Kalpetta, Sultan Battery, Mananthavady

M-Municipality; ©-Corporation; 1-Kayal land; 2-Kuttanad; 3-Kariland; 4-Pokkali land; 5-Kole land; 6-Kaippad lands; 7-River bank alluvium; 8-Brown sands; 9-Sandy; 10-High ranges

Source: KISSAN KERALA