Kenya Trial Links Push–Pull Cropping and Insect Frass to Higher Farm Output

A two-year field trial in western Kenya found that diversified push–pull cropping systems produced substantially more combined food and forage than untreated maize or cowpea monocultures, while the addition of black soldier fly frass fertilizer improved several of the strongest-performing systems. The result is not a blanket prescription for African farms, but it offers unusually detailed evidence on how crop design and recycled organic nutrients can work together under real agroecological conditions.

The study, published on September 2, 2026 in npj Sustainable Agriculture, tested 12 systems across Busia, Homa Bay and Kisii counties during the 2024 and 2025 long- and short-rain seasons. Researchers compared sole maize and cowpea plots with conventional fertilizer-and-pesticide treatments, frass-fertilized plots, standard push–pull arrangements, and a vegetable-integrated push–pull design that combined maize, cowpea, Desmodium and Brachiaria.

Push–pull systems use companion crops as part of pest and weed management. Desmodium is planted within the cereal field and Brachiaria around its edge; together they alter pest behavior, suppress some weeds and provide livestock forage. The vegetable-integrated version adds a food legume, widening the system from cereal protection into a mixed food-and-feed production model.

The most important result is the land-use comparison. Every diversified system recorded a land equivalent ratio above one, meaning that the mixture produced more from a given area than the component crops grown separately. Ratios ranged from 2.0 to 3.3. The highest value occurred in maize push–pull plots receiving frass, while the maize-and-cowpea vegetable-integrated system with frass reached 3.0.

Maize grain yield more than doubled in diversified and amended plots relative to untreated monocropping, and cowpea responded positively to the frass treatment. Much of the large increase in total harvested biomass came from the companion forages: Desmodium yielded roughly 10.3 to 12.4 tonnes per hectare in the detailed results, while border-grown Brachiaria produced about 2.3 to 2.4 tonnes per hectare. That distinction matters because total-system gains cannot be read as an equivalent increase in maize alone.

The authors also converted output into wheat-equivalent yield so that unlike products could be compared on one economic basis. Untreated maize and cowpea monocultures scored about 1.1 and 1.2 respectively. Push–pull maize reached 3.2 and rose to 3.6 with frass; the most diversified maize-and-cowpea system reached 3.6 without frass and 4.0 with it. Protein production was highest in the diversified systems, with cowpea contributing to human-food protein and Desmodium supplying much of the feed-protein gain.

Economic estimates followed the productivity pattern. The researchers calculated average annual benefits of $6,864 for maize push–pull without frass and $7,528 with it. Vegetable-integrated systems ranged from $7,238 to $8,340, with the maize-and-cowpea version plus frass at the top. Those figures reflect study prices and trial conditions rather than guaranteed farm income; labor requirements, input availability, market access and establishment costs will determine whether the economics travel.

The trial also measured above-ground biomass carbon, not changes in total soil carbon. Diversified plots stored more carbon in plant material than untreated monocultures, especially where frass was added, but the paper does not establish a long-term soil-sequestration rate. The authors reported meaningful variation among sites, seasons and years, showing that rainfall, temperature and baseline fertility still shaped the outcome.

For producers and development programs, the practical lesson is that the components should be evaluated as one production system. Frass can recycle organic waste into nutrients; legumes can add food and biologically fixed nitrogen; companion crops can contribute pest management and dry-season feed. The Kenyan results justify larger farm-scale and longer-term tests that account for labor, local input supply and market prices. They do not eliminate the need for location-specific agronomy, but they strengthen the case for testing diversified food-and-forage systems instead of judging each crop in isolation.