Alley Cropping in the Tropics...

Scientists of the International Institute of Tropical Agriculture in Ibadan, southern Nigeria, explored the potential of alley-cropping with Leucaena leucocephala for improved vegetable production. They found that alley-cropping with leucaena maintained higher soil and plant nutrient status, reduced soil erosion, and gave better plant stand of the direct-seeded Chinese cabbage crop. It also increased Chinese cabbage yield with no fertilizer application. This study has shown that various vegetable crops can be successfully alley cropped with leucaena.

The Experiment

The trials were conducted from August 1985 to October of 1986. The site has a bimodal rainfall pattern, with a mean annual precipitation of 1250 mm. The soil is an Alfisol classified as Oxic Paleustalf with a sandy loam textured top soil. Leucaena hedgerows were established using 3-month -old seedlings grown in polythelene bags. Seedlings were planted in an inter-row spacing of 0.25 m in the hedgerows and 4 m spacing between the hedgerows. There were two main plot treatment, with and without Leucaena hedgerows. The plots were replicated three times. Main plot size was 20x16 m. The alley-cropped treatment consisted of five hedgrows with four 20 m long alleys between each. There were four vegetable cropping patterns which made up subplot treatments. The vegetable cropping patterns consisted of combinations of five of the following vegetables: Sweet pepper (Capsicum annuum), vegetable cowpea (Vigna unguiculata), Chinese cabbage (Brassica campestris), amaranthus (Amaranthus cruentus), Chinese cabbage (Brassica chinensis), okra (Apelmoschus esculentus), cucumber (Cucumus sativus), Cabbage (Brassica oleracea), tomato (Lycopersicon esculentum), Brocolli (Brassica oleracea), mungbean (Phaseolus radiatus), lettuce (Lactuca sativa). Amaranthus and Chinese cabbage were present in every trial.

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.

Chen, Y.S., Biauw Tjwan Kang, and Fields E. Caveness (1989) Alley Cropping Vegetable Crops with Leucaena in Southern Nigeria. HortScience 24(5):839-840.

For more information contact:

Dr. B.T. Kang
International Institute of Tropical Agriculture
PMB 5320, Ibadan