Effect of intercropping and ploughing on Mediterranean managed grasslands invaded by Oxalis pes-caprae

Intercropping can increase crop productivity and control invasion by alien plants, giving at times more effective results than mechanical control. Oxalis pes-caprae L. (soursob) a South African perennial geophyte reproducing vegetatively by bulbs is invading Mediterranean communities around the world. Two adjacent field experiments were conducted in a grassland infested for a long time by soursob in Menorca (Balearic Islands) to test whether intercropping using the grass Lolium multiflorum Lam. (ryegrass) or the legume Hedysarum coronarium L. (sulla) alone or in combination increased crop production and reduced invasion by soursob. Winter aboveground biomass removals were also conducted to test whether intercropping was more effective in controlling soursob invasion than mechanical control. Mixed crops did not have higher production than monospecific crops. Ryegrass plots had the lowest soursob cover. However, this decrease in soursob cover was low and only lasted one season. Aboveground biomass removal by ploughing the plots in January, when the soursob parent bulb is almost depleted and further bulb production has not yet occurred, reduced the soursob cover by more than 70%. Overall, contrary to expectations, intercropping neither increased crop production, nor decreased invasion. Mechanical control was notably more effective than cropping and had a legacy effect.