The impact of Desmodium spp. and cutting regimes on the agronomic and economic performance of Desmodium–maize intercropping system in western Kenya

Low soil fertility, stemborers (particularly, Chilo partellus) and Striga weeds (Striga hermonthica and Striga asiatica) are major limitations to production of maize in western Kenya. The “Push–Pull” technology (“PPT”) has been described as an appropriate innovative technology capable of addressing these constraints. The technology involves intercropping maize with Desmodium and planting Napier grass (Pennisetum purpureum) around the intercrop, but in the current study a modified PPT was used and Napier grass was not included. Field trials were conducted in two locations in western Kenya during 4 subsequent seasons to test the hypothesis that maize yield, the degree of Striga suppression and economic benefits of intercropping maize with Desmodium are affected by: (i) the related biomass production by different Desmodium species and (ii) the cutting regime of the Desmodium. Maize was intercropped with Desmodium uncinatum (Jacq.) DC, cv Silverleaf or Desmodium intortum (Mill.) Urb. cv Greenleaf, and treatments with sole maize (with and without urea) were included for comparison. To eliminate phosphorus (P) deficiency, all treatments received basal P. The first two Desmodium cutting events were fixed at land preparation i.e. at the start of every season, and 4 weeks later, following the recommended practice, while the third cutting was varied and conducted at 9, 12 or 18 weeks after planting maize. Maize yield in the Desmodium–maize intercropping system was only higher than sole maize without urea from the third season. This implies that when P is not limiting inclusion of Desmodium spp. into the maize cropping system would provide a substitute for inorganic N fertilizers to enhance crop growth and yield after Desmodium becomes well established. Cumulative maize grain yield over the four seasons with the D. intortum and D. uncinatum intercrops were 6.3 and 7.0, and 10.9 and 11.6 t ha−1 in Busia and Siaya, respectively, and significantly higher than or comparable to a maize monocrop (5.8 and 11.8 t ha−1). Average net benefits from Desmodium intercropping over the four seasons were increased by 1290 and 918$ ha−1 relative to the maize monocrop in Busia and Siaya, respectively. Biomass yields were significantly higher for D. intortum than for D. uncinatum. Varying the time of the third Desmodium cutting had little effect on Desmodium biomass yields or maize grain yields in Busia, while in Siaya, D. intortum biomass yields were highest when cut at 12 weeks after planting. In the Desmodium intercropping systems, Striga counts were reduced by 95% in Busia and by 65–90% in Siaya with higher reductions when Desmodium was cut at 18 weeks after planting. In summary, the use of PPT provides robust and high economic benefits to smallholder farmers in western Kenya. The use of D. uncinatum with the third cutting at 18 weeks after planting is recommended, but can be modified according to the need for fodder without much effect on maize yield or revenue.

► When phosphorus is not limiting, maize yield in Desmodium–maize intercropping system is enhanced when the system is well established.
► Varying the time of cutting Desmodium has little effect on maize yield, but affects Desmodium biomass production.
► Desmodium intercropping is a profitable enterprise for western Kenya in comparison with a sole maize system.
► Desmodium intercropping is effective in reducing Striga weed compared to sole maize system.