Nurient flow from the forest - source of life for traditional Bhutanese agriculture

Wien

2003

S. 65-72

7 Tab. 6 Lit. Ang.

Unselbständiges Werk

200099716

In spite of constraints given by geology, topography and climate, Bhutanese farmers produce reasonably good crop yields with minimal inputs of chemical fertilizers. This is possible due to continuous flow of plant nutrients from the forest to other parts of the production system. Phosphorus is the most limiting plant nutrient in the higher regions where soils are generally derived from granite gneiss. Methods used to facilitate and to hasten the nutrient flow include: (1) animals as agents for collection and acceleration of nutrient flow; (2) collection of leaves, needles and decomposed litter from the fores and (3) enhancement of nutrient availability through the burning of soil organic matter. Grazing in the forest is the most important source of fodder. Herders have legal grazing rights for some of the forest areas but grazing is not limited to these sites. The P content ranged from 0.07-0.14 % for herbaceous plant biomass of fores or permanent grassland and from 0.22-0.53 % for dung produced by animals grazing these resources. cattle transfer about 300-700 t P per year from the forest to agricultural land. Individual households have registered rights to collect leave/needle litter from forest. The main species in these forests are pine (Pinus roxburghii, P. wallichiana), oak (Quercus girffithii, Q. lanata, and Q. semecarpifolia) and Castanopsis species. The P content for all litter types was </- 0.07 %. at elevations above 2500 m, farmers use a grass fallow system to produce buckwheat. Fallow periods of 6-15 years alternate with cropping periods of 1-2 years. Through the bluepine biomass used to ignite the soil organic matters, about 6 kg P are added to the system. The process exposes 250-500 tons of topsoil to temperatures of 500°C and requires about 150-400 labour days ha®Ü. The main changes induced in the soil are the elimination of all weed seeds, a reduction in organic C and total N and an increase in pH, available K and available P. Although nutrients from the forest are essential to maintain agricultural production, the continuous export of plant biomass may result in a loss of acid buffering capacity and a decreased base saturation of the soil.