Each vegetable plot was planted in both alley-cropped and control subplots. Subplot size was 20m by 4 m. Various fertilizer was applied to each of the vegetable crops, except for the last Chinese cabbage crop, which was not fertilized. Fertilizer was not a treatment variable. Crops were sprinkle-irrigated when needed. The leucaena hedgerows were pruned to a height of 0.25 m above ground. First pruning took place at 145 days after planting the seedlings, and subsequently at 8-to10-week intervals. The weight of the prunings was determined and sub-samples used for estimating pruning dry weights and nutrient yield.
Prunings were retained and spread in only the alley-cropped plots. The total accumulated dry weight of the hedgerow prunings during the 14 months of the experiment totaled 5.3 t/ha. The nutrient yield from these prunings in kg/ha were: 223 N, 13 P, 157 K, 59 Ca, and 38 Mg. The various cropping patterns did not have any distinct affect on soil nutrient levels. Addition of leucaena prunnings in the alley-cropped plots resulted in slightly higher nutrient status, particularly organic carbon level.
Despite the better growth apprearance of the alley-cropped plants (data not shown), statistical analysis of the yields of the vegetable crops from the different plots did not show any significant differences. Total yield for the various cropping patterns with and without alley cropping also showed no significant difference. Yield differences may have been masked by fertilizer application. It was therefore decided not to fertilize the last test crop, Chinese cabbage, in either the control or alley-cropping plots.
Table 1 shows the improved Chinese cabbage yield and crop nutrient status as affected by alley cropping with Leucaena. The differences between the control and alley cropped plots were statistically significant.
The presence of leucaena hedgerows and mulch appeared to have had another beneficial effect- they minimized rain splash and soil erosion which reduced the plant stand of the direct-seeded Chinese cabbage. The photo illustrates the beneficial effect of alley cropped leucaena: a control plot is in foreground and an alley-cropped plot is in the background. On average,76% of the Chinese cabbage planted in alley-cropped plots survived, while only 31% of the Chinese cabbage in the control plot survived.
For more information contact:
Dr. B.T. Kang
International Institute of Tropical Agriculture
PMB 5320, Ibadan