Coffee-growing regions of southern India are a part of the Western Ghats. This area has exceptional biodiversity attested by the fact that it is designated as a biodiversity hotspot. This indicates both a high level of endemism, and a high threat from human activity.
Multi-storeyed coffee horti-forestry estates in Karnataka, Tamil Nadu and other parts of Western Ghats are a successful soil-management module that has been in place for decades now. This system may also be termed as “cultivation in forests''. Developed and sustained by farmers based on their local knowledge, this system is one of the most diverse production systems in the world, and maintains soil-health besides providing ecosystem services. In addition to its contribution to employment and economic development, the coffee plantations prevent soil loss, sustain soil health, sustain biodiversity in the form of flora and fauna and, in turn, contribute to valuable ecosystem services such as carbon sequestration and hydrological services. In addition to contributing to employment and economic development of the region, soils present in these cultivated forests qualify, in every respect, for a sustainable system.
The system generally consists of cardamom–coffee-pepper–vanilla-citrus–banana-shade trees of diverse nature. People of the region have developed and sustained this system on Class III and Class IV soils of land-capability classification, based on their local knowledge of the region. Natural landscape of the region (Class III and Class IV of land-capability classification) provides an excellent opportunity for promotion of the recently-emerging concept of ‘green economy’. The soil health is expressed in terms of total carbon sequestered under this system. In one of the regions, analysis found that while evergreen forest had a slightly lower carbon pool of 170 t/ha, the sacred coffee groves had 207 t/ha (Devagiriet al., 2012). Unlike heavy-sediment loads in the waters of river systems like that of the Beas, Ganga or Narmada, theKaveririver system (which drains from these coffee systems), contains very low amounts of sediments; this is surely an index of the health of the soil under a coffee system. The contribution of riverKaveritowards the economic development of agricultural productivity in Karnataka and Tamil Nadu and, the dependence of Bengaluru on Kaveri water, is well-known. Ecosystem services provided by the ‘Green landscape’ of the coffee system of Western Ghats are not only confined to the region, but also, a range of life-supporting and sustaining benefits are provided to communities downstream the river (Kaveri) in terms of water, climate regulation, and timber and fuel wood needs.
Multi-storeyed coffee-cardamom-Pepper-orange system in Kodagu District of Karnataka
Ecosystem services
The presence of a tree cover in coffee-based horti-forestry farms on what are often very steep mountainous landscapes in high-rainfall areas, helps stabilize slopes and minimize soil erosion. The roots of trees, leafy canopy-cover, and leaf litter on the ground, all help do this.
Coffee based horti-forestry farms can act as a possible buffer to future temperature increases brought on by climatic change, for the simple reason the compounded ecosystem services that the system provides. In addition, as with natural forests, the presence of the trees helps protect water supplies in both quantity and quality.
On a per hectare per year basis, leguminous (nitrogen-fixing) shade-trees such as Erythrina spp. can increase the soil nitrogen content by 30% to 35%. With nitrogen fertilization (a common practice in non-organic coffee production), coffee farms in the Western Ghats leach very little nitrate into the groundwater supply than most other systems of the region, contributing least to contamination of the water bodies of the region.
The sheer biomass associated with the shade-tree component of the coffee horti-forestry system can be easily seen as a carbon sink, where carbon is bound in the trunks, limbs, and leaves (above-ground biomass) as well as roots (below-ground biomass). As with natural forests, carbon sequestered by coffee and the shade-trees within a shade-grown coffee farm is locked up in the wood (as opposed to being in the atmosphere and adding to global warming), until the trees are removed. Moreover, the soil itself incorporates carbon from the organic matter that accumulates and is broken down over time. Presence of trees in the shade-grown coffee farms, then, can help keep carbon out of the atmosphere. In addition, as with natural forests, the presence of trees can help protect water supplies in both quantity and quality, iterated above.
Expansion of coffee cultivation is encouraged, keeping the increasing demand and economic benefit the farmers get from this crop. Modern coffee estates are raised using silver oak as a single-species shade tree. This is disastrous to the proven multiple-species shade tree systems. A comparison between the two systems shows the following differences:
The mere presence of shade trees of different species, canopy structure and heights within coffee plantations, has been associated with increase in soil carbon, soil nitrogen, and enzyme activity (all of which are important factors contributing to soil fertility and plant health)
An increase in glomalin content (a glycoprotein that helps in soil aggregation) and the presence of ‘water-stable aggregates’ (a soil-structure feature that inhibits erosion)
A comparison made between coffee system and agriculture systems showed that shade-grown coffee lost 0.2 metric tons of soil per hectare per year, compared to the paddy system which lost 1115 metric tons, and a maize field lost 1340 metric tons per hectare per year. Natural-forest erosion rates can range between 0.03 and 0.3 metric tons per hectare per year, making shade-coffee comparable to these natural systems
Modern coffee plantations with systematic planting of shade-trees using silver oak suffer three- to four-fold soil loss from erosion compared to natural shaded systems
Carbon content in the soil (an indicator of soil fertility) of multi-species shaded coffee was found to be 23% higher than that found in coffee with little shade under silveroak
Fertility measurement (expressed at cation exchange capacity) in shade-grown coffee farms revealed 25% increase when compared to plantations with little shade
Infiltration rates (important for soil-moisture and plant growth) in silver oak-coffee systems decreased by as much as 52% in 10 years, over the natural-shaded coffee plantations
Soil moisture in silver oak-coffee plantations is 37% lower compared to naturally-shaded coffee plantations that have leafy foliage as canopy
These scientific facts allow us to conclude that multi-storeyed coffee horti-forestry systems on Alfisols and Ultisols are a sustainable module of soil management.
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