A method of fertility evaluation - to understand the capacity of the soil for crop production - helps for the efficient and economic use of fertilizers - helps for increased production of crops - to maintain the soil health in a sustainable manner - helps for adopting integrated nutrient management system for increased crop production and soil health - soil test values are of little value if they are not calibrated against nutrient rate experiments conducted in green houses.

Fertiliser use projects were initiated in India in 1953 based on the work carried out by Stoward.

All India soil-testing programme was started in 1955-56
Soil fertility rating with respect to the available N, P & K was proposed by - Ramamoorthy and Bajaj (1969)
Plant nutrient index concept was introduced by - Pasker et-al (1951)

Sampling- a composite sample to represent a particular area - important factor. Steps - to traverse the area to separate out the difference in slope, colour, structure, type of crop, type of management, etc. Group similar areas having same characters - then take representative samples from these areas at the rate of 10-20 samples (at least 8-16) from each locality - tools soil auger (for wet soils) soil tubes, spade, trowel, etc., remove suface litters stubbles and stoney portion- depth of sampling 15 cm. for wetlands (paddy fields) and25 cm. For dry lands (garden land).

Make a 'V' shaped cut using spade and collect soil from the sides of the 'V' cut at a thickness of 2cm. Pool the collected sample together and take only 500 gm of soils as the test sample by 'quartering' method. Then dry the soil under shade and bag using cloth or polybag. Furnish full details regarding the farmer and field as required in the prescribed form to be sent along with the submitted sample.

Testing - usually 1-10gm of the soil is subjected to testing. According to the result obtained, the soil is fist rated and classes assigned. There are 10 classes (0 to 9) for each parameter. Based on the result of the soil test, i.e., whether low, medium or high and also on the assigned class, organic manures, fertiliser and lime recommendations are given.

Soils with average fertility values - 100% of the general fertiliser recommendation, e.g., soil with 10kg/ha of available P2 O5 is considered to be average and requires 100% of the general fertiliser recommendation.
For K it is considered to be average if it contains 115kg per ha of available K2O
For N: sandy soils - average value is 0.05% (organic carbon 0.3%). For loamy and clayey soils the average value is 0.05% (organic carbon 0.05%). For low rated soils the recommendation is increased and for high the recommendation is lowered (for N 54 to 128% and for P and K 25 to 128% of the general recommendation).

Soil Test Results- Contain 3 parts.

First part contains the:(i) pH of the soil (ii) organic carbon (as a measure of available N), (iii) total soluble salts (as a measure of salinity), available P, (v) available potassium, (iv) any other pertinent information.

Second Part - Fertiliser recommendation based on the analytical results, history of the field and recent research work - indicates quantities of N2 P2 O5 and K2O. Lime and organic manures to be applied for the crops.

Third Part - The methods and time of application of fertilisers and other practices required to make the fertiliser use more efficient and effective.

Soil Testing Facilities in Kerala - There are 14 soil-testing labs in Kerala, i.e., one for each district. A central soil testing labs is functioning at Parottukonam, Nalanchira to supervise, coordinate and control the activities of the different soil testing labs in the state. There are 9 mobile soil-testing labs with a testing capacity of 50 samples per day one each in 9 districts (except districts of Ernakulam, Pathanamthitta, Idukki, Wayanad and Kasargodu).

Soil Test Crop Response correlation Studies

Interpreted S.T. Data - best basis for fertiliser recommendation. But the response of the crop depends on other factor like plant population, crop variety, soil moisture, etc.- many methods were suggested to improve ST interpretations. The all India Coordinated Project for investigation on ST - crop response - started in 1967. The studies have indicated significant regression equation for different soil types for predicting crop response and for preparing suitable fertiliser schedules based on ST data. The purpose of ST crop response studies is securing and selecting the best ST method and the calibration of ST values for fertiliser recommendation - the studies enable to know the type of response curve operating in a set of soil-crop-agro-climaric condition, e.g., of each curves - linear, mitscherlich-bray, sigmoid, etc - curves are useful to determine fertiliser does to obtain economic yield - different approaches - critical level approach, percentage yield approach, targeted yield/prescription method .

Soil Test Summaries and Soil Fertility Map

Soil test data can be summarized to provide information on overall fertiliser requirements for specific areas and on the kinds of fertiliser materials and mixture most suitable for those areas. Helpful for planners and administrators in determining policies of fertiliser production, distribution and consumption - useful for researchers also - can be prepared soil wise, village wise, block wise or district wise. State wise or Country wise maps have also been attempted. Many ST summaries include tables giving the percentage of the total number of samples falling in different categories of classification - Low, medium and high. The nutrient index concept introduced by Parker et-al (1951) is particularly useful in formulating area wise fertiliser recommendation and in comparing the fertility levels of two areas.

For preparing village wise nutrient indices analytical data on about 50-200 samples for every 20-30 ha of evaluated area would be required. The analysis values of these samples should be summarized into percentage in each category for each nutrient and the percentage in category 'low' 'medium' 'high' multiplied by 1,2 and 3 respectively, the sum of the figures thus obtained should be divided by 100 to give the index or weighted average. An index below 1.66 is low, between 1.67 and 2.33 medium and above 2.34 is high - using these indices the current State wise or region wise fertiliser recommendation for each crop can be modified to suit the village better. These modified recommendations will be of use to farmers whose fields have not been individually tested.

Soil erosion - is the process of detachment and displacement of soil particles from land surface. Agencies involved - water, wind, sea waves and animals. 2 broad categories - (i) The Natural erosion or the geologic erosion or the normal erosion; (ii) Accelerated erosion or soil erosion - By soil erosion we mean accelerated soil erosion only. Reasons (1) Destruction of forests, (2) unscientific cultivation practices, (3) Heavy grazing in pasture and grass lands. Harmful effects - (1) Convert the fertile lands to barren and unproductive, (2) causes frequent floods and diversion of course of flow of rivers through fertile river banks due to deposition of soil in river basins, (3) silting of dams due to deposition of sand and silt. Types of Erosion - (1) Rainwater erosion includes - splash erosion, sheet erosion, hill erosion and gully erosion - out of these Gully erosion is the most serve for. (2) Land slides erosion - Earthquakes, heavy rainfall, etc., are the major factors - Heavy destruction of forests also (takes places is sloppy and mountainous areas). (3) Stream Bank Erosion - due to torrential rains in hilly areas causes flooding of rivers and streams causing large scale erosion throughout the stream banks. (4) Sea shore erosion - due to turbulent waves in the sea during heavy rains and winds. (5) Wind erosion - in low rainfall areas - due to strong winds - soil particles are deposited on fertile soils of far of places. Causes expansion of deserts to fertile areas. Winds cause movement of soil particle in 3 ways - (i) Saltation, (ii) Suspension, (iii) surface creep.

Saltation - soil particles having a size of between 0.1 to 0.5 mm diameters are directly hit by wind which lead to a bouncing action of the particles- this bouncing action is called Saltation.

Suspension - The soil particles having a size of less than 0.1 mm are carried in suspension and transported to long distances - causing permanent loss of surface soil.

Surface Creep - Soil particles larger than 0.5mm diameter but smaller than 1mm which may not be carried by the Saltation movement, move on the ground surface as a soil creep.

Factors Influencing Erosion
(1) Rainfall,
(2) Wind,
(3) The type of soil,
(4) The slope of the land,
(5) the ground cover and land use pattern
(6) Human factor.

Soil and Water Conservation Measures - Two measures
(1) Agronomic measures,
(2) Engineering of mechanical measures.

Agronomic Measures:
(1) Contour Farming: Cultivation of crops across the slopes - along the contour lines,
(2) Strip cropping planting crops in different strips across the slope of land. Alternate strips are to be constituted by erosion resisting and erosion permitting crops (leguminous crops - erosion protecting crops),
(3) Stubble Mulching - Mulching with different materials,
(4) Cover cropping - Leguminous crops like Calapagonium, etc can be used.
(5) Alley Cropping Planting of certain erosion resisting crops in hedges at intervals across the slope of the land along the contours-Planting subabul (Leucaena leucocephala) is an effective alley cropping plant.
(6) Crop Rotation - Introducing erosion resisting crops in rotation with erosion permitting crops. Leguminous crops grown in rotation with crops like tapioca, cereals, etc.
(7) Conservation Tillage - Minimum tillage or zero tillage, etc, can be adopted,
(8) Mixed cropping - Helps to protect the soils from the beating action of raindrops.

Mechanical or Engineering measures - To reduce the run off velocity by dividing the lengthy slopes into short compartments. This includes
(1) Basin listing - Making a large number of small basins across the slope along the contour. They act as storage basins for the rainwater and retain it for a fairly long time- increases infiltration and reduces the run off,
(2) sub soiling - the process of breaking the hard pans and impermeable sub-soil layers. Makes the soil more permeable and helps in reducing the runoff and erosion,
(3) Contour bunding - Making narrow and broad based embankments or bunds along the contour lines. Most commonly adopted mechanical soil conservation measure. Since the slope exceeds 33% we have to reinforce the bunds by some means - usually by rubbles and hence known as rubble pitched contour bunding.
(4) Contour Trenching - Trenches are taken along the contour lines - intercept run off of water and thereby prevent water and soil loss - Commonly adopted in coffee gardens of Wayanad.
(5) Terracing - has to be practiced in areas having a slope of more than 10% - Terraces are of different types - channel terraces, graded terraces, diversion type terraces, bench terraces, etc. Bench terraces are taken in areas having slope of even more than 33% - sloppy areas are divided into a large number of platform. They help to retain water, manure, fertiliser, etc. Though initial cost is very high this is the only effective practice that can be followed in steeps slopes.

AGRO-ECOLOGICAL ZONES OF KERALA
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 summarised in Table 27. 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).

Agro-ecological zones
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 summarised in. 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.