Peer review

Intercropping is a common practice in low productivity (low input–low output) small-scale farming systems. However, as the level of productivity increases due to technological improvements whether intercropping – compared to sole cropping – remains the most productive and resource efficient cropping system is not well understood. Here we hypothesize that inter-crops outperform sole crops at low levels of resource availability because of improved resource capture and resource use efficiency; and answered whether this advantage decreases with increasing levels of resource availability. The performance of three cropping systems i.e. maize intercropped with navy bean, sole maize and sole navy bean were evaluated at three levels of resource input i.e. a low water/nitrogen (low W/N), a medium water/nitrogen (medium W/N), and a high water/nitrogen (high W/N), in three independent experiments, conducted over two consecutive years. The performance of the cropping systems was evaluated in terms of land equivalent ratios (LER), total grain yield, protein and energy productions as well as resource (water, nitrogen, and solar radiation) capture and use efficiency. Our results indicate that maize productivity (grain yield, protein and energy productions) was not significantly affected by the intercrop at any level of resource availability. However, irrespective of the level of resource input, intercropping significantly reduced the productivity of navy bean. The advantage of the intercropping, in terms of LER, tended to decrease with increasing the level of water and nitrogen supply i.e. decreased from 28% to 6% for above ground biomass, from 40% to 7% for grain yield, from 41% to 0.3% for protein production and from 40% to 9.2% for energy production. Intercropping was therefore more efficient in terms of LER under low W/N than under high W/N conditions. The LER was directly related to improved capture of nitrogen and to higher water use efficiency. Here we conclude that in terms of LER, intercropping systems are more resource efficient and suitable for lower productivity environments. As more productive technologies are adopted by smallholder farmers, agricultural development projects and extension services need to consider under what conditions sole cropping become a more productive system.

This work is part of the ACIAR funded sustainable intensification of maize-legume cropping systems for food security in eastern and southern Africa (SIMLESA) project.

Text in English