Fertiliser for tea: Improve soil organic matter
A farmer with his stock of fertiliser in Puttalam. Pic by Hiran Priyankara
Vegetatively Propagated Tea are clonal hybrids which requires high and correct nitrogen ratios to reach its potential yield of over 3000 kg per hectare made tea per annum. I have fields that are achieving over 4000 kg per hectare on several small estates under my management.
The norm of nitrogen is 10 kg nitrogen for every 100 kg of made tea. If soil carbon ratios are good and with a high cation exchange capacity it is possible to reduce the N ratio from 10 N to 07 N per 100 kg made tea.
Most soil where tea is grown is eroded and the organic matter in soil is so poor that the tea is fertiliser dependent.
A field yielding 3000 kg of made tea per hectare will require 300 N; less if the soil carbon is good. The N per 01 Ton of compost is believed to be low at 7.1 kg nitrogen. Based on it, one hectare of tea yielding 3000 kg per hectare will require 42 tons of compost each year. Cost is prohibitive and so will be cost of application. It is not practical.
Quality of compost to be supplied to the industry requires to be closely monitored, particularly if being imported as we could introduce nematodes and other pest and diseases that we currently do not have.
When compost is being produced locally it has to ensure proper C:N ratios and give a standard of 20:1 or below. Quality control is a must or there will repercussions as with high ratios the bacteria in the compost will draw nitrogen from the soil.
If nitrogen is reduced, production will take a huge dip and leaf supplied to the tea factory will not be healthy for processing a good tea. Succulent leaf is required for a good tea manufacture but with less nitrogen the leaf will be yellowish and leathery. This will result in a brownish tea and high percentage of off grades. Poor quality tea will not fetch good prices at the auctions and the overall average will dip with both the factory and the green leaf supplier getting severely affected. The tea factories will run into issues not being able to achieve the desired out-turn from green leaf to made which should be 21.50 percent. Even a loss of 0.50 percent will mean a huge loss to the factory in monetary terms.
When nitrogen is reduced over a long period of time, the tea will become weak and casualty rate will be very high after pruning.
Dependence on artificial fertiliser can be reduced but cannot be completely stopped. It cannot be done overnight, but the stage has to be set by the cultivators. Suggest the following:
a. Encourage the grower to establish Gliricidia and Albizzia shade and maintain it correctly. A good cover of both type of shade ensures improving the soil carbon over a period of time. 50 kg of gliricidia leaves adds 01 kg nitrogen into soil.
b. Tea with a poor cover of tea, due to erosion most of the soil carbon will be lost and the grower must be encouraged to infill. Bright sun light striking directly on the soil burns up the soil organic matter very fast and also leads to loss of ammonia in the soil when the soil temperature increases. Therefore, establishing of shade and infilling vacant tea patches is essential.
c. By changing the method of fertilising, efficiency can be improved. Currently, the method of fertiliser application is to apply on the surface of the soil popularly known as broadcasting. This I consider the most inefficient method leading to loss of ammonia. I have over a decade adopted a different method being placement of fertiliser. Placement of fertiliser is expensive but the method is very successful and less fertiliser can be used. An alavangoe hole is made 6 inch deep 1 ½ ft away from the bush on the upper side of the slope and the fertilizer is placed in the alavangoe hole and covered. The cost of placement works out to 3 ½ workers per acre as opposed to one when broadcasting. It is a crime at today’s cost of fertiliser (more to the government as the fertiliser is heavily subsidised) to waste fertiliser by broadcasting and giving a high rate of application to compensate for volatisation.
d. R & D is required to invent a fertiliser applicator for placement of fertiliser.
Good agricultural practices dependent on artificial fertiliser can be reduced but cannot go 100 percent organic. It is important in educating the farmer, 70 percent of whom are smallholders. Smallholders use much more fertiliser than the recommended amount. They are of the belief that when fertiliser is applied the crop will increase overnight. They apply as much as 5 to 6 applications per year when only four would suffice timing it correctly. What the smallholder does not understand is that we have only to replace N that has been removed from the soil. This is why we go on a replacement ratio of 10 kg N to 100 kg of made tea which could be reduced to 7 percent if the soil organic matter is good. If a study is done of the fertiliser usage by the smallholder and work out the N replacement ratio, I am sure it will be astronomical. This is where lot of money is going waste that needs to be corrected. With proper usage of fertiliser imports can be reduced and save the much-needed dollars for the country.
Reducing rate of N application with artificial fertiliser in my view does not require addition of compost if proper agricultural practices are followed. If the estate I work on is visited one can see that the soil is very rich in organic matter on account of a good cover of Albizzia and Gliricidia. No soil is exposed but one could see a lot of Albizzzia leaf litter, twigs, gliricidia lopping on the soil quietly disintegrating and into colloids that will attract a negative iron to bind the ammonia and other elements such as K, Calcium etc.
I wish to take the opportunity to discuss another subject which is not related to fertiliser. I have successfully mastered the technique of mechanical harvesting and adopted new techniques in planting to achieve high yields. 70 percent of the 37-acre property is on mechanical harvesting.
(The writer is a senior planter with 48 years in the industry).