Evaluation of Yield and Yield Components of Leek (Allium porrum L.) in Intercropping with White Clover (Trifolium repens L.)

Leek, Allium porrum L. is one of the most important vegetables in Europe. Open canopy up to harvest in leek field raises problem in weed management and increase nutrient leaching during vegetation period. Intercropping in leek fields causes better weed control along with the other benefits of this type of method. Intercropping leek with White clover Trifolium repens L. as a cover crop is considered, because it is known to have high ability to fix nitrogen in the soil biologically and prevent nutrient leaching during the growing season. In this study, intercropping ofleek A. porrum L. and white clover T. repens L. is evaluated.
Materials and Methods This experiment was conducted in 2011 and located at the research farm Hessian State Estate Frankenhausen, Germany (51° 27′ 0″ N, 9° 25′ 0″ E),249 meter above sea level. The goal of this experiment was based on comparison between leek in intercrop system with white clover (The factors included different date of sowing composed early undersowing, sowed right after transplanting leeks and late undersowing, one month later) and leek in monoculture system. In addition, different cover crop management by cutting and without cutting the clovers has been considered. In monoculture system, applying hand weeding and no-weeding was evaluated. Therefore, this experiment consisted of 6 treatments (1 and 2: early undersowing of clovers with and without cut, 3 and 4: late undersowing of clovers with and without cut, 5 and 6: monoculture with and without hand weeding) with three replications and performed as a complete randomized block design. Analysis of variance, Duncan tests (P≤0.05) and orthogonal analysis wasapplied for comparison between the treatments.
The comparison between treatments with cover crop indicated a significant difference (P ≤ 0.01) among treatments with early and late sowing time for clovers. Treatments with late sowed clovers (with and without cut) produced significantly higher dry matter in comparison with treatments with early sowed clovers (with or without cut). It seems late existence of clover at the early stages of development created more dry matterin leeks. Comparison indicated that treatments with clover but without cut, significantly created more dry matterin comparison with treatments, which clover cut. Existence of clover as mulch prevents weed growth and also biological Nitrogen fixation can be a reason for such observation. The results indicated that stem diameter for leeks in monoculture system and without hand weeding was significantly less than other treatments. Moreover, leek diameter in monoculture treatments with hand weeding was one of the greatest values. The largest amount of leek diameter was created in treatments with late sowing of clover, 48 days after transplanting leeks, whether clover has or not been cut. It seems despite all benefits of clover in Nitrogen fixation and prevention of weeds, that clover itself can be a considerable competitor with leeks as well.
The results of this experiment indicated that intercropping leek and clover can have a positive effect on dry matterproduction and quality of leek with proper timing of undersowing. We should consider that weeding was not possible for the whole growing season. Therefore, weeding at the beginning of the growing season and applying late cover crop could create more benefits of intercropping with a few competing effects on leek. In fact, weeding at the beginning of growing season establishes a good potential for nutrient absorption during the critical primary growing period of leek.