Monday, July 18, 2011

Land Preparation for tea Cultivation

Tea may be replanted in old lands after the removal of old cultivation or in new lands. In either operation, there are many factors that should be considered to minimize the soil and nutrient losses and to protect the soil structure. Regardless which one you are going to do, almost all the operations are the same. Therefore, we consider it as replanting tea after uprooting the old cultivation.

Uprooting of Old Tea Cultivation

When your tea cultivation gives poor yield and with debilitated bushes, and cannot be corrected with agronomic practices such as fertilizer, pruning, etc. tea has to be uprooted and re-planted. In some estates, up-rooting is a manual practice but, it is always better to use a winch (lifter/puller) since it will remove the whole root system. All the roots must be pulled out to remove all Poria and Nematode infested roots, so that they would not infest into new clearing.

At the time of old tea up-rooting, it is advisable to remove all the shade trees. It is a well known fact that, when we cut down shade trees at once, the reserved carbohydrates in the root system would not be depleted. In such situation, remaining carbohydrates will facilitate root disease like Charcoal root, etc. Ring balking (removal of Phloem) stops the translocation of synthesized carbohydrates in leaves into roots without damaging the vascular bundles in the Xylem. This makes water & nutrient supply to the upper parts of the plant continue, and hence, plant dies gradually depleting all carbohydrates in the root system. Therefore, it is always advisable to ring balk the high-shade trees (Albizia) 2 – 2.5 years prior to up-rooting of old tea, to a width of approximately 45 – 60 cm from the base.

If root diseases or Nematode infestations could be seen in up-rooting old tea, treat the soil immediately to prevent their spread. Fork the field and remove all roots in pencil thickness, or even smaller, to prevent re-infestations. All infected roots must be burned in an incinerator and destroyed.

When land preparation is done in a large and hilly area, start it from the upper most sections, in a block-wise manner. This will prevent cleared blocks from re-infestation with pests/diseases and damage to new clearing by rolling rocks, etc.

Always thoroughly keep in your mind that, soil is the utmost priceless component in your land, specially the top 30 cm layer. If you are too haste and didn’t apply measures to minimize erosion during land preparation, it is not only the soil created during millions of years you miss, but also a huge amount of money that you would earn from your tea yield in future. The following paragraphs will briefly explain you on the practices to be done and how to do them with minimum erosion of soil.

Land preparation should always be done avoiding heavy rains. Always try to minimize the time gap between up-rooting and establishment of rehabilitation grass. Finish the job in blocks and complete it up to planting of rehabilitation grass immediately as possible preventing exposed and loosen soil from rain. Never level the land into a very fine texture. It will make falling rain water runoff fast without leaving much time to soak it into the soil and ultimately soil particles will be washed off severely making land eroded. Therefore, it is always better to maintain somewhat rugged soil surface, decreasing the speed of runoff water. It will decrease erosive power of runoff water, and allow spread and percolate into soil pores.

Drains and terrains are then built to maintain the flow of water and save soil from erosion. Drains, terraces and planting of rehabilitation grass and planting of tea are done along the contour lines.  Therefore, marking of contour lines is very important in the field.

Next step is to build up of drains. Sometime, people are used to build drains after several months from the establishment of rehabilitation grass, since it is easier and no collapses of the banks. But that practice is not advisable since it will allow the soil to be washed off with rain water and priceless top soil layer would be lost. Drains are very important to manage the flow of water and minimize erosion. There are two main types of drains, viz. Lateral drains and Main (Leader) drains.

Lateral Drains

Width and depth of the lateral drains are 45 X 45 cm (18 inch) and the slope is maintained 1:120 towards the main drain.  That means if we consider two points each 120 units (m, cm, ft, inch, etc.) apart from other, the difference of vertical elevation between two points is one unit.

Now you might be having a problem, if the depth is 45 cm without changing, and slope is 1:120 how these two conditions come together. Although it is technically said that lateral drains are made along the contour, practically it is not. They are made crossing the contours so that the slope is maintained at 1:120 ratio. We can use the road tracer or clinometers in this purpose.

There are two modifications for lateral drains to control the displacement of silt (soil) from the field, viz.;
  • Lock and Spill drains and
  • Drains with Silt pits

Surface View of a Lock & Spill Drain

Surface View of a Drain with Silt Pits

Lateral drains should not cut open to the main/leader drain directly opposing each other, but in slightly different elevations to minimize collapse of drain banks and erosion.

The spacing between two lateral drains is dependent on the slope and amount of approximate rainfall received. It ranges from 6 m to 12 m. When the slop reduces, and lower rainfall is received, spacing can be made wider (12 m) and vice versa.

Brim or the banks of the drain should be cultivated along sides of the drain with Vetiver Grass (Vetiveria zizanoides) or African Love Grass (Eragrostis curvula) to minimize erosion and collapse of the brim.

Drains should de-silted and clean regularly. Silt removed from drains should always be put upper side of the drain, but not the lower side.

Leader Drains

Leader (Main) drains (Neththi) are cited in the naturally occurring drain lines to carry away the water from lateral drains in non-erosive velocities. Width and depth of the main drain or leader drain is dependent on the amount of water that has to be carried away.

Leader drains are made in step-wise structure with reverse slope and sides and bottom paved with stones to prevent gullies by eroding. Check dams are made in frequent intervals to collect silt carried away with runoff water and sides or banks are planted with Vetiver grass. Leader drains must always be cleaned and de-silted in frequent intervals as done in the lateral drains.

Reverse Slope in Step-wise Leader Drain
Well Maintained Leader (Main) Drain
Stone paved terraces area built along the contour lines to minimize soil erosion and reduce the slope. The upper brim of the terrace must be above the ground/soil level and slope towards the hill side.

Planting of Rehabilitation Grass

Rehabilitation of new clearings prior to the establishment of tea is a compulsory practice. This helps in soil conservation, enhancing soil fertility and structure, minimize erosion and ultimately very important to get a sustainable high yield from tea.

There are only two rehabilitation grasses to re-gain the soil conditions after uprooting the old tea bushes. They are;
  • Guatemala (Tripsacum laxum) and

  • Mana (Cymbopogon confertiflorus)
Just after drains are being constructed rehabilitation grass must be planted, Guatemala in 20 x 60 cm spacing. Planting material for Guatemala is 4 – 6 node stem. Plant stem 3 – 4 nodes below ground using a crowbar. Mana is planted in 10 x 60 cm spacing. Planting material is little tillers separated from large bushes. Rehabilitation grass must be maintained at least 1.5 years to improve soil conditions after uprooting old tea. Grass is frequently (3-4 month interval) cut and put between the rows to increase organic material. Roots of the grass penetrate into the soil and bind soil particles minimizing erosion. On the other hand, such organic matter content incorporated into soil will help in enhancing cation exchange capacity (ability of soil to hold fertilizer in it), water holding capacity, soil aeration, soil micro & macro organisms, etc.

If the land is reported to be infested with Nematodes (Radopholus similis) it is better not to use Guatemala, but Mana for rehabilitation, since roots Guatemala grass found to be hosting that nematode species.

It is always advisable to apply Dolomite to the land prior to establishment of rehabilitation grass. The amount of dolomite to be applied is given below, according to the pH level of soil. This also helps to prevent Magnesium deficiency in young tea. Therefore, you need to know the pH level of your land as well.

Below 3.9 pH                      2500 kg/ha
3.9 – 4.2                               2000 kg/ha
4.2 – 4.5                               1500 kg/ha
4.5 – 5.5                               1000 kg/ha

Lop the grass regularly in 3 – 4 month interval. Fertilizer (U 625) application is done when the plants having sufficient foliage beginning from 160 kg/ha, next the dosage is increased to 210 kg/ha after lopping. After 2 – 3 lopping it is further increased to 310 kg/ha.    

Wednesday, July 13, 2011

Land Selection for Tea

Tea is economically cultivated in a wide range of soils. In tropical, sub-tropical and temperate climatic conditions, tea grows in soils derived from Gneiss or Granites, Flat Alluvial lands, Peat Soils, Volcanic Ashes and Residual Formations.

Albizia moluccanais the best indicator plant that shows the suitability of a soil for the cultivation of tea, especially  in South-East Asian region, i.e. countries like India and Sri Lanka, etc. Tea is a plant that love to grow in acidic soils. It is considered that it can grow in a range of pH 4 - 6.5, where the optimum range is pH 4.5 - 5.5. If the pH of the soil is out of that optimum level, it should be corrected with Aluminum Sulphate or elemental Sulphate, before the planting. Lands naturally grown with Bracken fern (Gleichenia linearis), generally known as in this optimum pH range. Red-Yellow Podzolic Soils (RYP) is the best tea growing soil. These are the dominant soils in the low country and upcountry wet zone in Sri Lanka.
Albizia moluccana Leaves & Flowers

Gleichenia linearis Plant

If you are planning to replant old tea cultivation, it is always better to select lower “B” category and upper “C” category fields for that. Generally, tea estates have categorized their tea fields as A, B & C based on the yield (kg/ha/yr) over a period of not less than 2-3 years. Highest yielding lands come under category “A” while lowest in “C”.

The lands selecting must be undulating terrains, well drained and with a good soil depth and un-eroded. It is always advisable to avoid eroded lands with slab rock, concentrated boulders, surface rocks and gravel. In Sri Lankan conditions well drained lands less than 70% (31.5o) of slope (Mid elevations 55% of slope or 24.75o), more than 60 cm of soil depth, less than 20% of surface rockiness and less than 50% of gravel in top 90 cm layer of soil are considered as generally accepted parameters in land selection for ea cultivation. Flat lands adjoining paddy fields, water bodies or boggy areas are advisable to avoid due to poor drainage and soil aeration.

Land slope can be easily measured (either in percentage or degrees) with Clinometers. Otherwise, it could be simply measured with a rope. One end of the rope is wedge to the slope while a person below to that point raise the other end so that the rope would remain in the horizontal pane. Vertical height to the hand of the man at the point which the rope is held (A) divided by the horizontal length of the rope from the wedge to man’s hand (B), multiplied with 100 will give you the slope in percentage.

Simple way of finding Land Slope in percentage

Simple Home-made Clinometer, its Mechanism, Pocket Clinometer and Hand-held Clinometer in use

Soil depth is measured after preparing soil pits. Number of soil pits dig will be depended on the variation of the land. But generally, there should be at least 12 – 15 soil pits made to cover a one hectare land. The soil pit is 1 m X 1 m X 1 m in dimension and one wall should directly face the sunlight. Soil depth is measured with the meter tape from the upper brim of the pit to the parent rock. Apart from the soil depth, we can inspect for any hard layers underneath the soil surface, type & structure of the soil, depth of the gravel layer, depth of the top soil layer, soil color, etc. in the same location. At least 60 cm of soil depth is considered compulsory for commercial tea cultivation while 60 cm – 90 cm is moderately suitable and more than 90 cm will be the optimal.   

Duly Prepared Soil Pit for Inspection
In determining gravel percentage, take samples from the top 90 cm layer of the soil pit. Air-dry the sample and carefully break any soil aggregations with hand and weigh (Initial weight) it. Then sieve it through 10 mm mesh & collect what is remained in the sieve and weigh (Weight of Gravel). The following equation gives the percentage gravel content.

Set of Siever for partical size analysis
Surface rockiness is measured visually. Visually inspect the land from a distance and determine how much surface area covered with rocks and approximate percentage of that.

Avoid steep rocky clayey or gravelly patches even in a good land you have selected. Such bad patches of land can be easily identified by the growth of rehabilitation grass (Guatemala & Mana). If rehabilitation grass noticed retarding or wilting like symptoms, such land pockets may be having some kind or limitation for tea as well. Therefore, use such areas continue with grass as thatch banks, or diversify them into fuel or timber crops, rather than cultivating tea.

Apart from above discussed land and soil parameters, climatic factors such as rainfall & its distribution, prolonged drought conditions, desiccating wind areas should be avoided from tea cultivation. In Sri Lanka, only wet and intermediate zones could be cultivated with tea. The Agro Ecological Regions (AER,) suitable for tea cultivation, are as follows. (W – Wet zone, I – Intermediate zone, U – Up Country, M – Mid Country, L – Low Country)

  • Wet zone -                    WU1, WU2a, WU2b, WU3
WM1a, WM1b, WM2a, WM2b, WM3a, WM3b
WL1a, WL2a

  • Intermediate Zone -       IU1, IU2, IU3a, IU3b, IU3c, IU3d, IU3e
IM1a, IM2a, IM2b, IM3c