Relative Competitiveness of Spring Crops In Eastern Washington Dryland Organic Systems.

Weed control in certified organic grain production in Eastern Washington presents many challenges. Spring crops, in particular, are weak competitors against weeds and often fail due to weed pressure. In the spring of 2010 and 2011 organic spring crop trials were initiated near Pullman, WA. The study addressed the relative competitiveness of spring barley, wheat, lentils, garbanzos, and peas against oats. The experiment was a randomized complete block design with strip plots with four replications. Main plots included each crop planted at two different seeding rates (a recommended and a doubled rate) and subplots were two oat density treatments (22 kg ha^-1 and 88 kg ha^-1) and a weed free control. The growth and development of crops and weeds were measured by height, leaf area index (LAI), biomass, and yield. Barley heights across oat density treatments were greater than all other crop heights. An increase in seeding rate, increased LAI for all crops, however, barley LAI values were greater than all crops. Barley and wheat biomasses were greater than total weed biomass, while broadleaf crop biomasses were less. Barley and wheat yields decreased as oat density increased whereas oat presence in the broadleaf crops resulted in a complete yield loss. Doubled seeding rates increased barley and wheat yields. Barley and wheat were competitive against oats while the broadleaf crops were poor competitors. Wild oat will likely continue to be a challenging weed in dryland organic systems in Eastern Washington, and when selecting a spring crop, barley and wheat planted at high densities are the most competitive choices.