Effect of Enhanced Soil Fertility and Weed Control On Nutrient Partitioning Between Crop and Weeds, for Corn and Soybean in a Northeast Nebraska Organic Corn-Soybeans Rotation.

Organic grain crop producers face limited options for maintaining soil fertility, while still needing to sell cash crops to make a living--which exports nutrients from their farms.   Two years of data from 2010 and 2011 will be presented from a certified organic corn-soybeans rotation in northeast Nebraska that focused on the interaction effects of beef cattle manure application and multiple weed control treatments on weed, corn (Zea mays), and soybean (Glycine max) growth.  Measurements were taken that focused on soil fertility as well as nutrient partitioning between crop and weeds.  Variables measured include leaf color at two stages (SPAD), crop height, soil nitrate, yearly soil testing to 48" depth, crop biomass production, weed biomass production, grain yield and yield components.  By ANOVA, following two preseason spring applications of beef feedlot manure at 101 and 96 t/ha, the effect of manure on corn grain yield was significant in 2011 only, at p=0.2049 and p<0.001 for 2010 and 2011 respectively. Manure increased mean corn yields by 7.1% to 8.83t/ha in 2010 and 71.3% to 6.91t/ha in 2011.  The effect of manure on weed dry matter production in corn was insignificant both years, and weed DM ranged from 236-634 g/m² (excluding the weed-free check plot).  The effect of manure on soybean grain yield was insignificant in 2011, at p=0.063.  Manure increased soybean yields by 12.7% to 2.7t/ha in 2011. A manure*weed control method interaction(p=0.002) did exist for 2011 for soybean grain production, but interactions among factors were generally infrequent.