Effects of different levels of wheat straw and nitrogen fertilizer on the combination, density and population of weeds in garlic

In order to study the impacts of various wheat straw and nitrogen fertilizer levels on the combination, relative density and population of weeds in a garlic field, an experiment was conducted as factorial based on randomized complete block design with three replications at the Agricultural Research Station of Ferdowsi University, Mashhad, during the 2011-2012 growing season. Treatments were four levels of wheat straw (0, 5, 10 and 15 t ha-1) and four nitrogen levels (0, 50, 100 and 150 kg ha-1). The combination, density and dry weight of weeds were measured both before and simultaneously with garlic canopy closure. The results indicated that the simple and interaction effects between wheat straw and nitrogen fertilizer levels were significant on density and dry weight of garlic. By increasing wheat straw from zero to 15 t ha-1 the density and biomass of weeds declined in both sampling stages. Spreading wheat straw on the soil surface reduced the number and density of weeds through preventing their germination by limiting the radiation reaching the soil. Nitrogen weed density and biomass increased due to their vegetative growth. Although nitrogen is one of the essential nutrients for growth improvement but causes changes in soil fertility, it seems that management of nitrogen consumption and use of crop residues are ecological and integrated approaches for decreasing the population and density of weeds in garlic fields.