Species dynamics in modified hill farming systems in north eastern India – a comparative analysis

Abstract

In north-eastern India, the hot humid climate favours luxuriant weed growth that results in reduction of crop yield. Field evaluation was carried out for two consecutive years in four agroforestry systems on the occurrence and distribution dynamics of weed flora. The four systems were compared simultaneously with the traditional abandoned jhum (AJh) and agricultural crops (sole). The four agroforestry systems (AFS) investigated were – mandarin (Citrus reticulata), alder (Alnus nepalensis), cherry (Prunus cerasoides) and albizia (Paraserianthes falcataria) with different cropping systems. Among the six systems compared, it was observed that the number of weed species remained consistently higher in the abandoned jhum, followed by the sole crop and was least in the four AFS with the number of perennial weed species being higher in the former than in the latter. Annual weeds (therophytes) dominated the four AFS and sole crop situations with the density of weeds like Ageratum conyzoides, A. haustonianum, Bidens pilosa and Galinsoga parviflora being high during the cropping season. In the abandoned jhum situation, perennial grass species like Arundinaria bengalensis, Imperata cylindrica and Digitaria sanguinalis were dominant. Weed biomass was lower in the AFS due to regular soil working, intercultural operation and competition of resources with the associated crops. Species diversity (H’) of both grasses and herb species was highest in the AJh situation over the four seasons. Among the four AFS, the mandarin based AFS had a higher species diversity compared with the sole crop situation. Ordination by Correspondence Analysis (COA) indicated that the occurrence of weeds across seasons varied among the systems due to the higher abundance of one or more weed species. The weed species showed fluxes in their abundance patterns which are linked with the spring and rainy season. The study indicates that weed infestation could be greatly reduced under suitable agroforestry systems in north-eastern India which in turn can contribute to enhancement of crop yields and provide additional benefits to farmers by way of fruits, firewood, and soil amelioration and at the same time protect the environment.