Optimization of wheat residue rate and sunflower (Helianthus annus L.) density on weed control and crop growth using surface analysis regression method

A combination of plant residues and increased crop density would play an important role in enhancing crop growth through weed suppression in organic agriculture. In order to attain the best level of wheat residue amount and sunflower density, a factorial experiment based on RCBD with three replications was conducted at research field of the Faculty of Agriculture of Birjand University (Amirabaad campus) in 2008 growing season. Treatments were 5 different rates of wheat residue including 0, 250, 1250, 3750 and 5000 kg ha-1 and 3 sunflower densities including 50000, 70000 and 90000 plants ha-1. Results showed that the maximum crop growth as well as the lowest weed growth was observed at the density of 70000 plants ha-1 and 3000 kg ha-1 of wheat residue. Increasing crop density and residue amount to the levels above these limits would have no effect, or even in some cases reduce crop growth.