Effect of Different Planting Dates of Cover Crops Soybean (Glycine max L.), Fenugreek (Trigonella foenum graecum L.) and Cowpea (Vigna unguiculata L.) on Weed Seed Bank and Population Dynamic in Corn (Zea mays L)

To investigate the effect of different planting date of cover crops on weed seed bank and population dynamic in corn a field experiment based on randomized complete blocks design with three replications was conducted in Sari Agricultural Sciences and Natural Resources University during growth season of 2010. Treatments consisted of three cover crops, soybean, fenugreek and cowpea in two different planting date (simultaneous with corn and 21 days after planting of corn), along with two control (no weeding and weeding). The results showed that weed seed bank was influenced by cover crops, so that soybean, fenugreek, and cowpea at first and second planting date, and control treatment (no weeding) decreased the numbers of seeds in soils by 49, 52, 26, 27, 49, 51 and 5%, respectively. The results showed that dominant weed populations such as velvetleaf and johnsongrass were also affected by planting date of these cover crops in contrast with control (no weeded). All three cover crops and weeding check increased corn yield significantly as compared with no weeding check. The highest corn yield obtained under weeding check treatment and cowpea cover crop at second planting date. Weed seed bank density at some species was significantly reduced at second sampling stage as compared with first sampling stage.