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Procedure for determining fertilizer requirement for Stevia

Determine the fertilizer use efficiency under the prevailing crop management system

 

The whole amount of nutrients applied to the soil in the form of fertilizers cannot be utilized by the crop, because a large portion of the nutrients are lost from soil before it is utilized by the plants. Some nutrients are also added to the soil from other sources during the cropping period. Apart from fertilizer application, the routes through which major nutrients (NPK) are lost and added to the soils are as follows.

A detailed study of soil physico-chemical study gives an idea about its fertilizer use efficiency. So, we can assess, apart from the amount removed by the crop, how much excess quantity nutrients are to bbe applied to maintain steady state adequate nutrient level in the soil.     

After working out an ad hoc fertilizer schedule, There are two processes for fine tuning the fertilizer doses. The processes are (1) Field trials and (2) Pilot farming. The processes are briefly described below.

4. Apply fertilizers in judicious splits

 

If we consider a target yield of about 6.0 metric tons of dry leaves per ha. per year ( total of four harvests in an year) then the annual nutrient removal per ha. will be approximately 84 Kg nitrogen, 18 Kg phosphorus and 144 Kg potash. If we consider 50% fertilizer use efficiency, then we have to apply 168 Kg nitrogen, 36 Kg phosphorus and 288 Kg potash per year.  For much less biomass yield, Brandle et al (Brandle, J. E., Starratt, A. N. and Gijzen, M. 1998. Stevia rebaudiana: Its agricultural, biological, and chemical properties. Can. J. Plant Sci. 78: 527–536) suggested an annual application of 105 kg N, 23 kg P and 180 kg K.    

 

For sustained availability of all the nutrients, the nutrients are to applied in small doses, either through fertigation or through several split doses if they are applied as solid.

3. Build up the organic matter 

 

For building up the organic matter in the soil, which in turn helps in sustained nitrogen nutrition of the crop as well as improved availability of other nutrients, a pre-plantation green manure crop is very helpful. Leguminous plants like Sesbania aculeata, Sesbania rostrata, Crotolaria juncea, Clover, Vetch, Soybean, Alfalfa or Cow-pea are good choices as green manure crop. The crop is grown on the farm land, either with irrigation or in rainy season. The plants are allowed to grow for 3 to 4 weeks and then they are incorporated into soil by tilling. Then they are allowed to decompose in the soil for an adequate period before transplantation of Stevia.

Sesbania

Crotolaria

Clover

Vetch

Soybean

Cow pea

Alfalfa

2. Correct the phosphate status 

 

If the soil is deficient in available phosphate, to build up the phosphate reserve, rock phosphate can be applied. Finely ground soft rock phosphate (oxy-, hydroxy- or carbonate apatite) is generally the best option. Rock phosphate application in alkaline soils and in soils with very low organic matter is not very helpful. Generally 2 to 5 metric tons of rock phosphate is applied for a sustained phosphate supply for a 5 year Stevia crop.

1. Correct the pH of the soil 

 

The best pH for Stevia is 6.0 to 7.5. If the soil is acidic, the pH should be corrected with lime or dolomite. The dose of lime or dolomite will depend on the soil pH, soil texture (relative proportion of sand, silt and clay) and soil cation exchange capacity (CEC). The dose of lime or dolomite for increasing pH by 1.0 unit varies between 0.5 metric tons per ha to 3.5 tons per ha. The required amount of lime or dolomite is to be incorporated into the soil during tillage operations.

 

If the soil is alkaline, its pH can be lowered by application of elemental sulphur or gypsum. Here also, the dose will depend on soil pH, soil texture and CEC. For decreasing pH by 1.0 unit 0.2 – 1.3 metric tons of sulphur or 1.0 – 6.0 tons of gypsum is to be applied per ha. The required amount of sulphur or gypsum is to be incorporated into the soil during tillage operations.

Field Experiments

 

Stevia is cultivated with different fertilizer doses in experimental trial plots. The different fertilizer doses are based on rational variations of the worked out ad hoc dose. The performance of the plant is monitored in terms of biomass and glycoside yield and the best fertilizer combination is identified. The field trial is carried out in statistically laid experimental plots with multiple replications of different fertilizer combinations. The experimental results, i.e. the leaf biomass and glycoside yield at different fertilizer doses are also analyzed statistically for working out optimal fertilizer doses.  

Pilot Farming

 

In a new location, stevia is first cultivated in pilot plots with the ad hoc fertilizer dose. The performance of the crop is monitored continuously according to the following procedures -    

Nutrient hunger signs on growing crops (deficiency symptoms)

 

The plants are monitored for any visible nutrient deficiency symptoms and required specific dose for correction of the nutrient deficiency is standardized. Thus, optimal fertilizer dose for vigorous crop growth is identified. Identification of nutrient deficiency is difficult in some cases. The deficiency symptoms of two different nutrients can be nearly identical or deficiency of one nutrient can mask the symptoms of another deficiency. sometimes the plants can suffer from invisible latent deficiency (“hidden hunger”). Care should be taken not to confuse hunger signs with disease symptoms or damage caused by  pests.

Plant and/or plant tissue tests in the field

 

 

With plant testing you are “asking the plant” if the soil and fertilizer supplied enough of each tested nutrient and whether the different essential nutrients are in correct proportion to each other. The plant will give you reliable information on its total nutritional status at the date of sampling and thus indicate any actual supplementary fertilizer needs (of the current crop).  If a nutrient is below the minimum concentration (“critical value”), which is different for each nutrient, it is likely that the application of a fertilizer containing that nutrient will increase yield. 

Nutritional Management

Stevia needs proper balanced nutrition for proper growth and glycoside production. Though stevia was originally portrayed as a crop with little external nutritional support requirement, but it was discovered later that it responds very well to fertilizer application. The nutritional management program for stevia depends on local soil and agroclimate, farming system, variety and target yield. The fertilizer requirement for stevia for a specific farm cannot be guessed and there is no universal fertilizer recommendation. There are also several myths about fertilizer requirement of stevia, which are listed below.

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Calculation of precise location and variety specific fertilizer schedule

A typical ad hoc nutrient management scheme

 

After the land preparation and tilling, the following steps are to be undertaken

Fertigation

 

Fertigation is a method of fertilizer application in which fertilizer is incorporated within the irrigation water by the drip system. In this system fertilizer solution is distributed evenly in irrigation. The availability of nutrients is very high therefore the efficiency is more. In this method liquid fertilizer as well as water soluble fertilizers are used. By this method, fertilizer use efficiency is increased from 80 to 90 per cent.

 

Advantages of fertigation

 

  • Nutrients and water are supplied near the active root zone through fertigation which results in greater absorption by the crops.

  • As water and fertilizer are supplied evenly to all the crops through fertigation there is possibility for getting 25-50 per cent higher yield.

  • Fertilizer use efficiency through fertigation ranges between 80-90 per cent, which helps to save a minimum of 25 per cent of nutrients.

  • By this way, along with less amount of water and saving of fertilizer, time, labour and energy use is also reduced substantially.

 

Fertilizer used in fertigation

 

  • Urea, potash and highly water soluble fertilizers are available for applying through fertigation.

  • Application of super phosphorus through fertigation must be avoided as it makes precipitation of phosphate salts. Thus phosphoric acid is more suitable for fertigation as it is available in liquid form.

  • Special fertilisers like mono ammonium phosphate (Nitrogen and Phosphorus), poly feed (Nitrogen, Phosphorus and Potassium), Multi K (Nitrogen and Potassium), Potassium sulphate (Potassium and Sulphur) are highly suitable for fertigation0 as they are highly soluble in water.   Fe, Mn, Zn, Cu, B, Mo are also supplied along with special fertilisers.

N fertigation 


Urea is well suited for injection in micro irrigation system. It is highly soluble and dissolves in non-ionic form, so that it does not react with other substances in the water. Also urea does not cause precipitation problems. Urea, ammonium nitrate, ammonium sulphate, calcium ammonium sulphate, calcium ammonium nitrate are used as nitrogenous fertilizers in drip fertigation. 

 

P fertigation


Application of phosphorus to irrigation water may cause precipitation of phosphate salts. Phosphoric acid and mono ammonium phosphate appears to be more suitable for fertigation.

 

K fertigation


Application of K fertilizer does not cause any precipitation of salts. Potassium nitrate, Potassium chloride, Potassium sulphate and mono potassium phosphate are used in drip fertigation.

 

Micro nutrients 


Fe, Mn, Zn, Cu, B, Mo could be used as micro nutrients in drip fertigation

Micronutrient Nutrition for Stevia

 

Since Stevia prefers acid soils with low pH, this condition itself ensured adequate availability of micronutrients. However, even in acid soils response was noticed. The decreasing order of response of Stevia: to microelements when sprayed on the crop grown on an acidic soil in terms of plant fresh weight was as follows: 0.1% Mn > 0.05% Mo > 0.02% Mo > 0.05% Zn > 0.1% B > 0.05% Mn > 0.02% Cu > 0.25% B > 0.2% Zn. (1)

 

Experiments conducted in nutrient solutions indicated that Boron supplied at 10 ppm reduced growth, flowering, root weight, and caused leaf spotting also. (2).

 

In an experiment in Brazil it was found that shortly before or at flowering the production of 1 ton of dry leaves, demanded in g: 89g boron, 26g Copper, 638 g iron, 207g manganese, and 13g zinc. (3)

 

Plants grown in nutrient solutions containing four concentrations of nutrients revealed following interactions before flowering. Mn, Fe, and Cu showed synergistic effects between N and P, P and Cu, and P and Fe; antagonistic effect between N and K, N and Zn, K and Mg, and K and S; and either synergistic or antagonistic interaction between Zn and B, and Mn and Mg. (4)

 

  1. Zhao, YG :1985, The effect of microelements on Stevia rebaudiana; Zhejiang Agricultural Science Zhejiang Nongye Kexue 1, 44-45

  2. Sheu, BW, Tamai, F and Motoda, Y; 1987; Effects of boron on growth, yield and contents of stevioside and rebaudioside A od Stevia rebaudiana; J. Agricultural Sc. (Japan), 31, 265-272

  3. Filho, LOF, Malavilta, E, De Sena, JOA and Carneiro, JWO; 1997; Uptake and accumulation of nutrients in Stevia (Stevia rebaudiana), II , Micronutrients, Scientica Agricola, 54, 23-30

  4. Lima, FOF and Malavolta, E; 1997; Nutritional interactions in Stevia – Stevia rebaudiana Bertoni; Arquivos de Biologia e tecnologia Curitiba; 40; 351-357

Nutritional Management and Glycoside Content

 

There is a close association between nutrient supply and stevioside accumulation as evident from the studies all over the world. Though the requirements of micronutrients are lesser than macronutrients, experiments conducted in nutrient solutions indicated that Boron supplied at 5 ppm registered higher contents of stevioside and rebaudioside (1). Among secondary nutrients, only severe Ca deficiency caused reduction in the glycoside concentration (2). Besides, the role in growth and development, deficiencies of K, Ca, and S decreased the concentration of stevioside in the plant on dry weight basis while all deficiencies, except that of P, decreased the stevioside content in the plant (3). Supporting these results, research at Egypt showed a gradual and significant increase in stevioside content as nitrogen fertilizer increased from 10 to 30 kg N to the tune of 1.99% at the higher dose (4).

 

 

  1. Sheu, BW, Tamai, F and Motoda, Y; 1987; Effects of boron on growth, yield and contents of stevioside and rebaudioside A od Stevia rebaudiana; J. Agricultural Sc. (Japan), 31, 265-272

  2. Filho, L. o. F., Malavolta, E., and Filho, o. F. D. L. (1997b). Symptoms of nutritional disorders in stevia (Stevia rebaudiana). Scientia Agricola 54, 53-61.

  3. Utumi, MM, Monnerat, PH, Pereira, PRG, Fontes, PCR, Godinho, V de PC (1999). Macronutrient deficiencies in Stevia rebaudiana: Visual symptoms and effects on growth, chemical composition and stcvioside production. Pesquisa  Agropecuria  Brasiliena, 34, 1039—1043.

  4. Allam, A.I. , A. M.  Nassar and S.Y.Besheit (2001). Nitrogen fertilizer requirements of Stevia rebaudiana Bertoni under Egyptian condition . Egyptian Journal of Agricultural  Research 79(3):1005-1018

 

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