A global meta-analysis on yield gain in intercropping was publised in Nature Plants on June 1st, 2020.
It describes two syndromes of production in intercropping, one based on maize, strip intercropping, adequate fertilizer input and temporal complementarity between species. The other syndrome is a low input syndrome, with legumes and low input of fertilizer, usually with crop species sown in full mixture and with the same or similar growing season. A team of Dutch and Chinese researchers found that both syndromes of production provide major savings of land and fertilizer input per unit product compared to pure stands at the same input level, but the yield gain, measured as the difference between observed total grain yield and expected grain yield, was four times as high in the high input syndrome as in the low input syndrome. They conclude that intercropping offers opportunities for the sustainable intensification of both high- and low-input agriculture.
The full paper can be read here