Sturcture analysis and system dynamics of agroforestry home gardens of southern Kerala

Abstract

A study entitled "Structure analysis and system dynamics of agroforestry home gardens of southern Kerala" was undertaken during the period from 1994 - 1997 in Thiruvananthapuram district of Kerala State. The study comprised of a detailed agroforestry systems inventory description survey of the home gardens in the district, investigations on the system dynamics of two home gardens of the district, laboratory experiments to assess the allelopathic tendencies of some commonly grown multipurpose tree species and linear programming to develop integrated homestead models. The results of the survey revealed that the size of an overwhelming number of holdings was small. The species diversity and average number of plants per home garden was considerably high. Tuber crops ranked first among the crops, followed by fruits, oilseeds, rubber, spices, vegetables, timber and fuel trees and fodder crops. The tree intensity was found to increase as the size of the holding decreased. The frequency of occurrence was highest for coconut, followed by jack, mango, moringa, guava, wild jack and tamarind and lowest for the nitrogen fixing trees. Differences between the agroecological zones of the district with respect to the predominance of crop categories and tree species were also observed. The home gardens presented a multi-tier canopy configuration. There was no specific planting pattern or arrangement. The system, as a whole, was found to be profitable. The two year long field investigation on the dynamics of home gardens revealed that the tree components contributed considerable amounts of nutrients by way of litterfall, stemflow and throughfall. Nutrient addition took place mainly through organic manures at both locations. Harvested biomass accounted for removal of large quantities of nutrients from the systems. Coconut accounted for maximum biomass production and nutrient removal at both sites. The physical, chemical and microbiological properties of the homestead soil were better than that of the control. The soil in the homestead had a lower bulk density, high water holding. capacity, porosity and moisture "Content. An enhanced soil organic carbon content, available N, P and K status were also observed in the home garden. The soil microbial population (bacteria, fungi, actinomycetes and phosphorus solubilizing bacteria) was comparatively higher in the home garden. Nutrient cycling, recycling of crop residues and addition of organic manures helped in improving and maintaining the soil physico-chemical and biological properties of the system in a sustainable manner. The presence of trees lowered the soil temperature in the homestead, whereas relative humidity was maintained at an optimum level when compared to open condition. The light intensities at the floor of all the trees studied were invariably less than that in the open. Both the home gardens were found to be profitable. The tree-crop-livestock integration was a special feature which increased income considerably. Allelopathic inhibition of germination and growth of rice was caused by leaf extracts of all the tree species. Germination of cowpea was inhibited by the leaf extracts of acacia, eucalyptus, casuarina, ailanthus, tamarind, portia and cashew. Growth of cowpea was suppressed by leaf extracts of all the tree species except jack. The powdered leaf litter of all the trees inhibited rice germination and growth. However, jack did not suppress radicle growth. Cowpea germination was inhibited by the powdered litter of all the trees except jack and mange. Cashew, casuarina and jack did not suppress plumule growth of cowpea. Radicle growth of cowpea was inhibited all tree species. The integrated model for the 0.50 ha home garden with 23 enterprises was found to generate a profit of Rs. 10354.21 with an investment of Rs. 3262.30. The coconut-based mixed fanning model developed for the 0.40 ha home garden with 35 enterprises provided a net profit of Rs. 32464.32 on investing Rs. 45000/-.