Selection of suitable legumes for relay intercropping with durum wheat in mediterranean cereal-based cropping systems

The increased interest in sustainable agricultural systems has led to significant developments in cropping practices that allow to preserve crop productivity and reduce the reliance on herbicides and nitrogen fertilizers. Relay intercropping of legumes in wheat may represent a proficient practice to maintain crop productivity, improve soil fertility and support weed control at crop rotation level, if appropriate associated legumes are used. The objective of this study is to select suited legumes for relay intercropping with durum wheat in central Italy among a wide range of taxa (Medicago sativa, Medicago varia, Medicago lupulina, Trifolium repens, Hedysarum coronarium, Trifolium alexandrinum, Trifolium incarnatum, Trifolium resupinatum, Vicia villosa, Medicago polymorpha, Medicago rotata, Medicago scutellata, Medicago truncatula, and, 3 subsp. of Trifolium subterraneum). This study was carried out at the Centre for Agro-Environmental Research “Enrico Avanzi” in Pisa (Italy) in 2017/18 and repeated in the 2018/19 cropping season. According to the results obtained during 2017/18, legumes were reduced in 2018/19 excluding the least performing ones. The experiment was organized in a randomized complete block design with four replicates and the sole wheat crop as control. No pesticides or fertilizers were used. The evaluation was focused on i) legume establishment in the already developed wheat, ii) grain production and quality, iii) weed control before and after the wheat harvest, iv) legume persistence and growth after wheat harvest and, v) effects on the following crop. Legumes, indeed, were incorporated into the soil the following spring and forage sorghum was seeded. Results of this study showed that relay intercropped legumes preserved wheat production and reduced weed biomass up to the 70% in comparison with the control. After wheat harvest legumes persisted in the field, as dead mulch or cover crop according to the different life cycle of the tested legumes, until the sowing of sorghum. Dead mulch of annual legumes resulted unsuitable to contrast weeds while, perennial and annual self-seeding legumes as M.polymorpha and T.subterraneum, showed overall good weed control and biomass accumulation. Legume biomass at spring soil incorporation, was the most important factor related with sorghum production. Sorghum, preceded by T. subterranum, H. coronarium and T. repens, had a higher biomass production than the control and was comparable with the productive level that can be obtained under conventional systems. The overall assessment of legumes used in this study, allows to select the most suited ones for relay intercropping with durum wheat for the local environmental condition.