Sustainable weed control by allelochemicals from rye cover crops: from the greenhouse to field evidence

The allelopathic potential of rye crop to inhibit the weeds growth may reduce the herbicide use in Agriculture. In pot culture, four rye (Secale cereale L.) cultivars (Fasto, Forestier, Nikita, Primizia) were grown in open with two nitrogen rates (0 and 50 kg N ha⁻¹) to determine their weed suppressiveness on three warmseason weeds (Chenopodium album L., Amaranthus retroflexus L., and Portulaca oleracea L.) in greenhouse. The contents of benzoxazinoids, DIBOA and DIBOA-Glucose were determined in rye cultivars tissues. Total benzoxazinoid content ranged from 80 to 450 μg g⁻¹ d.m. and differed between the cultivars. Nitrogen application increased the benzoxazinoid content, 50 kg N ha⁻¹ produced more benzoxazinoid content than 0 kg N ha⁻¹ (258 vs. 154 μg g⁻¹, i.e. +41% higher). The rye mulch obtained from different cultivars and from two N fertilisation levels (0 and 50 kg N ha⁻¹) inhibited the growth of test weed spp. There was no correlation between the total benzoxazinoid content and the number of weed seedlings suppressed. The field study determined the allelopathic effects of rye cover crop on weeds (grass and broadleaf) in maize grown with two tillage systems (no-tillage, conventional tillage) at three nitrogen rates (0, 250, 300 kg N ha⁻¹). The mulching significantly reduced the density of grass and broadleaf weeds by 61% and 96%, respectively. In no-tillage, residual nitrogen drastically reduced the broadleaf weeds density (83–90%), but the conventional tillage, increased their population (61–65%). Linear regressions between DIBOA and DIBOA-Glucose in the mulch and weed inhibition (%) were statistically significant, with R² of 0.59 and R² of 0.65 for grass and broadleaf weeds, respectively.