Study of relationship between soybean (Glycine max (L.) Merr.)planting spatial arrangements and velvetleaf (Abutilon theophrasti L.) population dynamic

The velvetleaf is an important annual weed in the Mazandaran province, Iran. Seeds are the only way of propagation and renewal of this weed. More knowledge was gained regarding soil seed bank and its seed production to improve the management of the velvetleaf weed in the future. There is a minimal information concerning the impact of the soybean planting pattern on the dynamics of the velvetleaf population. For this reason two different fields have been studied with the cooperation of the Agriculture Discipline of the Islamic Azad University, in Qaemshahr, Iran, during 2009 and 2012. In this study the effect of two types of soybean row spacing were used, 50 cm-wide and 36 cm - narrow, and three emergences of the velvetleaf weed population (periods 0-10, 10-20 and 20- 30 days after soybean sowing were implemented) were studied. Seed production, leaf area and dry matter increased in each plant population of the velvetleaf weed in the 50-cm soybean rows. Mortality rates were decreased in velvetleaf’s seedling population in the wider spaced rows. By observation it was seen an increased production of seeds in the first batch of seedlings. It appears that we must remove the first weed emergence flushes within three to four weeks after the soybean emergence to prevent reduced yields in the soybean crop and further increase of the velvetleaf seed bank.