337-8 Winter Annual Weeds Effect On Nitrogen Dynamics in No-till Corn.

See more from this Division: S08 Nutrient Management & Soil & Plant Analysis
See more from this Session: Nitrogen Management
Wednesday, November 3, 2010
Long Beach Convention Center, Exhibit Hall BC, Lower Level

Nathan Mueller and Dorivar Ruiz Diaz, Kansas State University, Manhattan, KS
Management of winter annual weeds (WAWs) is a concern to many no-till producers.  The objectives of this study were to examine how various dates to control WAWs may affect soil N, water, and corn response under no-till conditions.  Field research was conducted in 2010 at seven sites in Kansas on rainfed no-till corn-soybean systems. Timing of WAW control had four treatments; fall, early pre-plant (2-4 weeks prior to planting), pre-emergences (within 1 week of planting), and post-emergences (V2). Corn planting dates were 12 to 20 April 2010.  The second factor, nitrogen, had five treatments: 0, 13, 27, 53, 107 kg N ha-1.  Locations were selected based on previous history of a high density of WAWs.  Two sites were excluded from this analysis due to loss of treatment timings of WAWs in relation to planting dates.  N uptake by WAWs ranged 9 to 25 kg N ha-1 with a C:N ratio of 16 to 30 if left until maturity in early to mid May in 2010.  Soil nitrate-N in early June was not significantly affected by timing of control.  However, early corn growth (V5-V8) was significantly increased by early pre-plant control over pre-emergence control of WAWs.  Early growth was significantly increased with fall and early pre-plant control over post-emergence control.  Early growth of corn was significantly increased by added nitrogen, but there was no significant increase with the addition of more than 13 kg N ha-1 over the control.  Gravimetric water content averaged from 0-90 cm, taken in early June when corn was V5-V8, was slightly lower with the fall and early pre-plant compared to post-emergence control. This suggests any water use by WAWs can be alleviated when early season rainfall is above average, as was in 2010.  Chlorophyll meter readings at R1-R2 with post-emergence control were significantly lower than with early pre-plant control suggesting N uptake by WAWs could significantly impact reproductive growth stages if controlled after corn emergence. In 2010, early pre-plant burndown of WAWs appears to maximize early growth and N uptake in no-till corn.  Additional responses and variables are still being assessed.