Intercropping lablab with maize increases grain production and soil cover, and reduces pest pressure in Tanzania

Background

East African farmers and researchers are sharing a renewed interest in Lablab purpureus (L.) Sweet, a multipurpose leguminous cover crop. Lablab can produce food and fodder, fix nitrogen, scavenge resources, protect the soil, and tolerate drought. To capitalize on its potential, lablab requires more research into its basic agronomy, particularly under intercropping situations in which it is usually grown by small-holder farmers in East Africa.

Objectives

The study aimed to understand the effects of lablab-maize intercropping through three measured ecosystem services: 1) grain production of lablab and maize, assessed in yield and land equivalent ratio; 2) late season soil cover of living plant material; and 3) major lablab insect pests: pod boring caterpillars (Maruca vitrata, Helicoverpa armigera, Etiella zinckenella) and pod sucking coreid bugs (Riptortus pedestris, Clavigralla tomentosicollis).

Methods

In this study, lablab was intercropped with maize across two agro-ecozones in northern Tanzania over three years. Yield data was collected from both crop species, while late season soil cover and insect pressure focused on lablab. A simple economic analysis examined net return of sole and intercropping as a response to the costs of seed and harvesting.

Results

Over the six environments, intercropping reduced lablab grain yields by 35 % (p = 0.009); intercropping reduced maize yields marginally though this was not found to be significant (p = 0.087). The land equivalent ratio of maize and lablab, ranged from 1.36 to 1.96 across environments. Under adequate moisture conditions lablab grown with maize produced 58 % more late season ground cover than when lablab was sole cropped (p = 0.039), whereas in the driest environments, the opposite trend was observed (p = 0.011). The number of pod boring caterpillars (p = 0.052) and pod sucking coreid bugs (p < 0.001) were reduced by 34 % and 57 % respectively by intercropping. Intercropping produced a higher net return than sole cropping lablab or maize.

Conclusions

These results demonstrate the diverse benefits of growing maize with lablab allowing for greater food production, increased soil protection, and reduced pest pressure. Of particular importance was the negligible effect of lablab grown with maize, on maize grain yield, highlighting that the detractions of intercropping in smallholder agriculture are outweighed by the advantages. Continued lablab research to identify best agronomic practices and new cultivars will encourage its adoption and help East African farmers diversify and strengthen their cropping systems.