Soil erosion due to settled upland farming in the Himalaya: a case study in Pranmati watershed

SUMMARY

A common concept is that upland agriculture undertaken by local communities is a major factor causing large-scale soil erosion and other environmental problems in the Himalaya. Attempts to measure soil loss from farm fields are limited. This study was undertaken to measure the rate of soil loss from fields sown with crops during the rainy season and to examine the factors determining the erosion rates in the Pranmati watershed which is characterised by settled organic farming on terraced slopes. About 43% of the total agricultural land in the watershed was on low sloping terraces (< 2°), 32% on medium sloping terraces (2-6°) and 25% on highly sloping terraces (6-10°). Potato was the most dominant crop, occupying 50.2% of the total cropped area, followed by Amaranthus paniculatus (22.6%), Eleusine coracana (11.2%), Echinocloa frumentacea (10%) and Oryza sativa (6%). Soil loss from different crop covers was in the range of 0.300-0.658 t/ha/yr on low sloping terraces, 1–7 t/ha/yr on medium sloping terraces, and 6.037-64.39 t/ha/yr on highly sloping terraces. Comparison of different crops revealed the highest soil loss was from potato fields, a cash crop in the watershed. Potato cultivation on highly sloping terraces accounted for 72.6% of the total soil loss from agricultural fields. The area under this crop is rapidly increasing because of increasing emphasis on a monetary economy. Organic manure input in potato fields (28.5 t/ha) was much higher as compared to traditional crops (7.8-15.5 t/ha). Byproducts of potato do not have any fodder value, while the traditional crops do have useful fodder byproducts. The increase in the area under potato also implies more intensive pressure on the forests. The threat of soil erosion causing unsustainability of upland agriculture seems to be due more to the cultivation of potato than to traditional subsistence crops. Factors related to erosion and land-use policy aspects are discussed in the paper.

Key words:

• soil loss
• sustainable agriculture
• high altitude
• Himalaya