Homegardens, serving as a benchmark of a long term high input
of green manure, determined soil chemical and physical properties
as well as crop productivity. Indeed a continuous high input
of organic matter can reverse soil degradation. This effect was
modified by inclination, and the impact was minimal in the Steep
inclinations. Despite substantial amounts of NPK in Gliricidia green
manure, the impact of mineral fertilizers still boosted crop productivity
much more. Seemingly the chemical fertility of soils was
still much more impaired by previous erosion events than physical
fertility. However, a higher general responsiveness to full mineral
fertilizer addition plus Gliricidia amendment indicates somewhat
reduced physical soil fertility as well. It is a positive sign that
mineral nutrients can really boost the productivity on these soils,
maybe a great chance for farmers in this region if market development
allows matching the nutrient demand which cannot be
fulfilled by green manure alone. Indeed there is no necessity of concentrating
on P sources; while supply of N and K externally should
be guaranteed.
As a very valuable side effect of the mungbean study, the high
economic potential at low climatic risk of modern very short season
cultivars could be highlighted. Application of mineral fertilizers
had a pronounced impact on mungbean yield, indicating that adequate
supply of mineral nutrients is important for commercial scale
production. Mungbean would be benefited from green manure
application due to moisture retention, which becomes critical factor
during minor season may override the fertility implications.
There is no doubt that the extreme inclinations of Meegahakiula
and the adjacent regions require increased efforts to maintain andimprove its agriculture productivity in an ecologically sustainable
way. A similar model could also be applied in steep landscapes in
Asia, Latin America or Africa, which are prone to soil erosion and
degradation, and are farming, by smallholders. As Gliricidia is an
attractive fodder as well, the potential of developing crop-livestock
based systems is a concept which can be applicable in all tropical
regions where the animal husbandry is predominant. Furthermore,
as observed in our study region, additional income can be generated
via fuel-wood for cleaner energy generation with the provisions of
minimizing the climate change and its risks.