Before starting the farming, cultivating a greem manuring crop like Sesbania, Cortolaria, Soybean etc. is often very beneficial. After 4 - 5 weeks of vegetative growth, the crop is plowed down in the soil and allowed to decompose in-situ. It greatly helps in enhancing soil fertility, water holding capacity and soil drainage. Green manuring also improves all over nutrient availability.
Stevia Farming - Demystifyed
I have worked with many different organizations, who are engaged in stevia plantations – and I found an almost universal pattern. In most of the cases, the plantation is started without proper planning and without appropriate assessment of local agro-climatic conditions.
During identification of a land for stevia farming, generally, very little effort is invested on proper assessment of its fertility status, inherent soil problems, topography and water availability. Selection of wrong stevia cultivars, improper irrigation planning and sub-optimal nutrient management are the other factors which contributes to underperformance of stevia plantations.
All these mistakes in the early phases of plantation may lead to very costly rectifications in later stage, on in worst case, may make the farming unsustainable altogether.
In this article, I am trying to demystify the basics of Stevia farming….in simple language, without resorting to technical jargons.
The Three Pillars of Success
The leaf biomass yield and steviol glycoside yield from a farm is a function of three variables – the breed, the existing soil and agro-climate and the crop management. I shall discuss about the breeds in some later article. Now, let me present my brief notes about the farming operations with specific reference to soil and agro-climate, as well as crop management.
Stevia grows well on most soils, but prefers a sandy loam or loam, high in organic matter. Its native soils are on the acid side, but stevia tolerates a wide range of soil pH, and pH 6.0 to 7.5 is the optimum condition. Stevia likes consistently moist soil, but not waterlogged. Standing water can cause plant rot. Except in the case of very sandy soils, raised growing beds provide Ideal conditions. Stevia does not grow well in saline soils.
The soil texture class is determined by the percent of sand, silt and clay in the soil. The USDA classifies soil types according to a soil texture triangle chart which gives names to various combinations of clay, sand, and silt. The chart at the left-hand side indicates the range of the textural classes suitable for Stevia cultivation.
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Soils suitable for Stevia cultivation
Gray Alluvial Soils – but soils with high clay content and low drainage should be avoided
Red Soils – but highly acidic soils with aluminium and iron in toxic level shuld be avoided
Black Soils – The charnozem black soil with high organic matter is suitable. The highly clayey volcanic black soils have drainage and hardness issue and not favoured.
Soils not suitable for Stevia cultivation
Black peaty soils
Marshy peat bog soils
Chalky soils with high phosphate binding capacity
Infertile desert soils
Highly eroded soils, specifically when the surface horizon is lost
Saline and sodic soils
Gravelly and rocky soil
Soils with low water-holding capacity
Soils with very hard structure i.e. clod formation
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For assessment of suitability of a soil for Stevia cultivation, soil fertility test is indispensible. The soils should be fertile enough to nutritionally sustain a high yielding Stevia crop. I am providing here a rough guideline about the required soil test values for soil capable of economically sustaining high yielding stevia crop.
How to Take a Soil Sample
The reliability of a soil test is only as good as the sample you submit. The small amount of soil in the sample bag you send to the Agricultural Testing Lab must represent the entire area to be fertilized. Avoid unusual areas such as those where fertilizer or lime has spilled. Take samples before lime, fertilizer, or manure are added. Use only clean equipment for collecting soil samples.
Where to sample
The area to be sampled should be as uniform as possible in terms of soil type and cropping and fertilizing history. For practical purposes it should be an area you expect to fertilize as a unit. If you have a problem on part of the production field, you may wish to determine if soil fertility is the cause by taking one sample to represent the “good” and the other to represent the “poor” area.
Take a good sample
Collect a number of cores or slices by walking in a zig-zag pattern over the area. Mix cores thoroughly in a clean pail for a composite lab sample. The greater the number of collected cores mixed together, the better the sample will represent the average condition of the sampled area. Choose one of the following tools:
Soil Probe or Auger –
A soil probe or auger is the best tool for sampling. An auger will be needed if the soil is very stony or gravelly. Simply push the probe (or push and turn the auger) into the soil to the desired depth, lift up to remove the core, and place it in the clean pail. Sampling depth should be 6 inches deep.
Garden Trowel or Shovel –
If a soil probe or auger is not available, collect your sample by pushing the blade of a garden trowel, shovel, or spade into the soil to the desired depth. Cut out a triangular wedge of soil and set it aside (to be replaced after sampling). Now slide your blade into the soil again taking a thin (half inch) slice from one side of the hole. With a knife, trim the slice to about a 1-inch strip of soil down the center of the spade – top to bottom. Save this “core” as part of your composite lab sample.
Mix the sample and fill the sample bag
Make sure that all the cores are thoroughly mixed together. Your soil test mailer contains a plastic bag intended for one lab sample. Fill plastic bag about 1/2 full (approximately 1 cup) with the mixed sample.
Good Agricultural and Environmental Conditions
It is always a good idea to follow the Good Agricultural and Environmental Conditions (GAEC) especially if maintenance of environment is one of the objectives of the farming operations. The guidelines for maintenance of GAEC are as follows :
Main issue – Water
Establishment of buffer strips along water courses
Where use of water for irrigation is subject to authorisation, compliance with authorisation procedures
Protection of ground water against pollution: prohibition of direct discharge into groundwater and measures to prevent indirect pollution of groundwater through discharge on the ground and percolation through the soil of dangerous substances.
Main issue - Soil and carbon stock
Minimum soil cover
Minimum land management reflecting site specific conditions to limit erosion
Maintenance of soil organic matter level through appropriate practices including ban on burning arable stubbles, except for plant health reasons
Main issue - Landscape, minimum level of maintenance
Retention of landscape features, including where appropriate, hedges, ponds, ditches, trees in line, in group or isolated, field margins and terraces, and including a ban on cutting hedges and trees during the bird breeding and rearing season and, as an option, measures for avoiding invasive plant species
Stevia grows as a wild plant in semi-humid, sub-tropical climates where temperatures typically range between -6°c to 43°c. It is a long day plant and requires 12-16 hours of sunlight per day and is sensitive to excessive heat and low temperature. Long spells of higher temperature may inflict heat stress to the plants and they may wilt. The plant can withstand mild frost but heavy frost may adversely affect the roots. The optimal temperature for growing Stevia is between 15°C to 30°C. Long cold spells are also undesirable as it can affect the growth rate and can make the plants dormant. The day temperatures should not exceed 48°C and the night temperatures should not fall below 4°C.
Annual average rainfall of 140 cm per year has been found optimum for its good growth. Higher annual rainfall promotes fungal leaf diseases. Higher cloud cover also promote flowering and decrease in steviol glycoside content in the leaves.
It is a photophilous plant and doesn’t grow in shady locations. The growth rate of the plant is reduced at a photoperiod of less than 12h. The increase in the photoperiod to 16h and the high intensity of solar radiation increase the vegetative growth of the plant, and the levels of stevioside.
The flowering is directly linked to the duration of the photoperiod and accelerates during short days. Flowering always decreases steviol glycoside and biomass yield.
Meanwhile, the atmospheric moisture appears to play an important role in the plant development, as cases of wilt have been mentioned in crops sufficiently provided with water, when dry and warm conditions prevailed.