Modelling population dynamics of Sinapis arvensis in organically grown spring wheat production systems

Although we know that alterations in crop density, crop spatial pattern and inclusion of more selective weed control can improve weed suppression for organic growers, it is unknown whether these result in changes to the weed seedbank that increase cropping system profitability over time. Data collected from field trials conducted in 2009 and 2010 in Maine, USA, comparing regional grower practices (Standard) with management that aimed to (i) facilitate better physical weed control through the use of wide row spacing and inter-row cultivation (Wide) or (ii) enhance cropweed competition through increased seeding rate and narrow inter-row spacing (Narrow HD), were used to construct a matrix population model with an economic sub-model. Using field measurements of grain yield and weed survival and fecundity, we investigated the lasting implications of employing alternative organic spring wheat (Triticum aestivum) production practices on Sinapis arvensis population dynamics. In most scenarios, the model indicated that regional production practices were not sufficient to prevent an increase in the weed seedbank, even with excellent weed control. The two alternative methods, on the other hand, were able to limit weed population growth when initial densities were low or cultivation efficacy was >80%. Due to higher seed costs in the Narrow HD system, net returns were still lower after 10years of simulation in this system compared with wide rows with cultivation, despite a lower weed seedbank.