The Effect of Cover Crops and Time of Sowing on Weed Population and Corn Yield in Two Minimum and Conventional Tillage Systems

In order to study the effect of cover crops and sowing time on weed population and corn yield in minimum an conventional tillage systems, an experiment was conducted in the Seed and Plant Improvement Research Institute, Karaj, using Vicia villosa (V), Trifolium resupinatum (T) and Secale cereale (S) as cover crops, plus control (no cover crops, allowing weeds to grow). The cover crops were planted at three different dates of September 23rd, October 7th and October 27thin a corn field. In the first year (2013-2014) early ripening corn (Var. 108) was planted under minimum tillage. In the second year (2014-2015) late ripening corn (Var. 704) was planted under conventional tillage. Results indicated that the first cover plant sowing time was favorable in both years. This was mostly due to nitrogen availability of the soil which resulted in higher grain yield and better weed growth. Under minimum tillage, S reduced weed biomass by 34%. Under conventional tillage system, all the cover crops reduced weed biomass by 53%. Generally, percentage of organic carbon was higher in minimum tillage than in conventional system. S showed highest nitrogen uptake among the three cover crops in both tillage systems. In minimum tillage, the highest corn yield was under S cover crop with 5.304 t/ha. In conventional tillage, the highest corn yield was under T cover crop with 9.298 t/ha.