Nitrogen Fixation Capacity in Contour Hedgerow Systems: How Important?

TitleNitrogen Fixation Capacity in Contour Hedgerow Systems: How Important?
Publication TypeJournal Article
Year of Publication1994
AuthorsGarrity D, Mercado AR,
JournalAgroforestry Systems
Keywordsagroforestry, agroforestry systems, agrosilvicultural systems, Alley cropping, biomass production, crop yield, fodder plants, fuelwood, Gliricidia sepium, green manures, intercropping, maize, mulching, multipurpose trees, Nitrogen fixation, nitrogen fixing trees, nutrients, oryza, Oryza sativa, pennisetum purpureum, plant competition, plants, poles, rice, senna spectabilis, trees, woody plants, yields, Zea mays
AbstractThe choice of an appropriate hedgerow species is one of the most critical decisions in exploiting the value of a contour hedgerow (alley cropping) system. The implications of hedgerow species with nitrogen (N)-fixation capacity on hedgerow-crop competition and crop productivity have been widely debated. An examination was made of the agronomic significance of N-fixation by comparing the performance of species representing three classes of hedgerow vegetation at an on-farm upland research site at Claveria, northern Mindanao, Philippines. The species tested were: a nitrogen-fixing tree legume (Gliricidia sepium), a non-nitrogen fixing tree (Senna spectabilis syn. Cassia spectabilis), and a forage grass (Pennisetum purpureum). The 4-year study (1988-91), which was laid out on a farmer's field on an Ultic Haplorthox soil (pH 4.8; organic C, 1.9%; total N, 0.18%), investigated hedgerow biomass and nutrient yields from leaf and green stem prunings, and their relative effects on the performance of two annual crops commonly grown in alley farming systems (upland rice and maize), with emphasis on hedgerow-crop interference. Pruning started in June 1989, ten months after the trees were established; prunings (leaves and green stems) were all applied as a surface mulch except for material from the first pruning, which was ploughed in as a green manure. C. siamea produced 46% more pruning biomass on an annual basis than did G. sepium; N supplied to the alley crops was similar to that supplied by G.sepium in the first year of observation, but 20-30% higher in the succeeding years (because of the greater pruning biomass). Data are also tabulated on woody stem biomass production in prunings (used for bean poles or fuelwood) by each tree species. Upland rice and maize grain yields and total dry matter were unaffected by tree species, but the nitrogen-fixing tree exerted less competitive effects on the annual crops growing in adjacent rows. Grass hedgerows reduced maize yields 86% by the second year, indicating an unsustainable drawdown of nutrients and water. It is concluded that hedgerow systems composed of a nitrogen-fixing tree did not exert significant advantages compared with a non-fixing tree species, and that factors other than N-fixation were more important determinants in the choice of hedgerow species.