Effects of alley cropped Calliandra calothyrsus and Gliricidia sepium hedges on weed growth, soil properties, and taro yields in Western Samoa.
Field experiments were conducted on a tropical Inceptisol in Western Samoa to evaluate the effects of alley cropping on soil characteristics, weeds and taro yield. Taro yields were compared from Calliandra calothyrsus and Gliricidia sepium alleys (spaced at 4, 5 and 6 m) and a control (no trees). Measurements were made for soil moisture and temperature, weed growth, hedge biomass production and taro growth and yield over 4 years (1988-1991). The hedge biomass yield ranged from 5.1 to 16.1 t/ha/year dry weight over the 4 years of the trial, with Calliandra and Gliricidia performing equally well. Biomass yields decreased by about 2 t/ha with increasing alley width from 4 to 6 m alleys. Weed populations were significantly lower in the 4 m alleys than the 5 m, 6 m and control plots. The 6 m alleys supported the highest weed populations. Soil from alley plots held significantly more water in the 0.3-1.0 bar range than soils from the control plots. Four years of mulch application measurably improved the soil waterholding capacity and bulk density. However, no improvement was seen in the N, P, K, Ca Mg and organic C content in the alley plot compared with the control plots. There was no positive yield effect of alley cropping on the taro yield. Yields in the 5 m and 6 m alleys were not significantly different from the control, while the 4 m alleys produced significantly lower yields than the control. Authors' summary. KEYWORDS: TROPAG | Colocasia esculenta Calliandra calothyrsus Gliricidia sepium | Miscellaneaous Crops and Forestry | agroforestry | hedges | Calliandra | Gliricidia | Colocasia esculenta | weeds | nutrient availability | trees | South Pacific Islands | Western Samoa.