Tea industry concerned over effects of global warming

" Many individual plantations have undergone three planting cycles. "

Dr. N. Yogaratnam, Consultant, National Institute of Plantation Management

The Tea industry's concern over the need for sustainable crop production and environmental protection has heightened in the recent past, with agronomists and environmental consultants reporting that tea plantations are at a risk of being severely damaged by the anticipated climate change now popularly referred as "Global warming".

Plantations in the low and mid-country are the most vulnerable areas that have to survive the wrath of global warming. Coinciding with this thinking, it appears that the Ministry of Plantation Industries has also announced plans to launch a programme of reforestation in small holdings and corporate sector plantations in vulnerable areas.

Fluctuating weather patterns had been a major contributory factor for the inconsistency in tea production.

Water and temperature, whether too little / low or too much / high, are constraints to crop production. Tea, known to be very sensitive to these conditions recorded a decrease of 12.7 percent in production in the period Jan / June 2007 over the same period in 2006, 143.6 MnKg in 2007 as against 164.5 MnKg achieved in 2006. Changes in weather pattern appear to be the main reason for this decline.

It has, therefore, become necessary to look for cropping systems that would minimize the adverse effects of climate change, a phenomena which seems to be going out of control.

Agro-forestry

Agro forestry involves complex and diversified croppings as it combines the growing of agricultural and forestry crops in one area. In any cropping system, a balance is always struck between the productive and protective functions of the resulting eco-system.

A desirable agro-forestry cropping system, therefore is one that gives a good yield while conserving soil, water and nutrients. It is now becoming clearer that plantation agriculture is more efficient and sustainable when integrated with forestry.

Reforestration with rubber

As is well-known the rubber tree Hevea brasiliensis was first introduced as a crop for plantation agriculture several years ago from the wilderness of the Amazon jungles. Hence, one can expect Hevea to behave as a typical tropical rain-forest tree.

It is a known fact that typically luxuriant rain-forests often behave as a closed, self sufficient, steady-state ecosystems being nutritionally sustained by the relatively thin organic top-soil layer overlying somewhat impoverished soils.

The performance of rubber plantations as a sustainable eco-system is linked to the history of the rubber plantation industry in the south and south east Asia, from the period the first rubber plantations were established in Sri Lanka, Malaysia and Indonesia at the beginning of the century.

Now, many individual plantations have undergone three planting cycles of approximately 30 years per cycle without adverse effects on the natural environment. In the meantime, commercial yields of rubber have also risen from about 250 kg per ha to the present level of modern high-yielding trees of approximately 2,500 kg per ha, a ten-fold increase, providing immense economic benefits.

Forests opened up for agriculture exposes the soil to damage from high rainfall and high temperatures typical of the humid tropics. Unprotected soils are subjected to excessive erosion and leaching and changes detrimental to the environment occurs.

Over the years, the planters of rubber in newly-cleared forest lands have taken into consideration the need to practise various soil conservation measures, in order to protect and preserve soil fertility. Some of the measures include : terracing, silt pitting and surface coverage, all based in scientific research by agronomists.

Study on the ecological impact of rubber plantations on soils degraded by shifting cultivation demonstrated an improvement of soil properties after the establishment of Hevea.

It has also been observed that rubber plantations adopting proper agro-management practices, were helped by the enrichment of organic matter which consequently improved the soil's physical properties such as bulk density, soil porosity, moisture retention and infiltration.

An increase in organic matter in the surface layer was also recorded in Sri Lanka. It was noted that under Indian conditions, soil's physical properties in denuded forests as well as in areas subjected to continuous shifting cultivation are considerably improved once a rubber plantation is established.

Environmental conservation

While conservation measures are being pursued to minimise deterioration of the native fertility status of the soil, other agronomic practices, i.e., biological nitrogen fixation via legumes and regular fertilizer applications are simultaneously introduced to sustain high crop performance through soil nutrient enrichment.

The rate of soil erosion dramatically increases as soon as the forest is cleared and the soil exposed. Increase in the gradient of the land also enhances erosion, both under forest and bare situations.

Land clearing also drastically reduces the rate of saturated infiltration in some soils, but later with the establishment of a full legume cover, infiltration again increases to reach levels which were even higher than the original levels under forests.

On steep hilly terrain, rubber is planted on contour terraces to prevent soil erosion. Soil erosion along terraces and on gentle slopes is minimised by digging of silt pits and construction of bunds which check the flow of water during heavy rains.

Rapid coverage of the exposed soil surface was encouraged by sowing rapidly spreading creeping legume cover plants. In addition to plant covers, soil surface exposure is also avoided by applying mulches around the base of young rubber trees.

Rubber husbandry practices include soil nutrient enrichment by biological nitrogen fixation through legume cover cropping, while regular fertilizer application to sustain rapid growth of immature trees and high yields in mature rubber.

Nutritionally self-sustaining

Rubber plantations are also known to behave as an environmentally acceptable closed ecosystem from planting to replanting, with a constant cycle of uptake and return of nutrients from and to the soil. This concept of nutritionally self-sustaining forestry type eco-system has long been accepted by Tree Crop Agronomists who have been of the opinion that the limiting factors of rubber are not necessarily nutritional.

During the early rubber manuring investigations, when the potential value of manuring rubber trees was being seriously considered, from a slightly different view point, the raising of rubber trees was investigated on the basis of agro forestry system.

This so called Bikemorse Forestry System involved initial sowing of rubber seeds, periodic removal of noxious competing weeds (which are expected to impoverish the soils) and allowing the regeneration of succulent "beneficial" plants. The area, contain mixed population of rubber trees of varying age, was exploited by tapping trees of appropriate growth (girth).

The harvested crop latex, which containing the contains the economic crop, the rubber hydrocarbon, which is unique, contains a variety of nutrients besides rubber particles. The amount of these nutrients which are ultimately removed from the ecosystem via the latex crop, are relatively small in comparison to the amount of nutrients in the harvested products from other tree crops, such as oil palm, tea, coconut, etc.

Between rubber and forest ecosystems, nutrient storage value for rubber stands at and beyond 24 years of age, is comparable to those of the forest ecosystem. In the case of biomass accumulation, comparable biomass levels are attained only when the rubber trees reach 33 years of age.

The comparatively higher nutrient storage levels in rubber stands at a relatively younger age is most likely due to the regular application of fertilizer which results in an accelerated enhancement of the tree nutrient bank.

However, nutrients are added to the forest ecosystem only by natural means and take relatively longer to build up. It thus appears that the Hevea stand can accumulate nutrients in amounts similar to or higher than those found in forest ecosystems.