Effect of Weed Removal Time On Corn Yield As Affected by Nitrogen Source and Rate.

Two of the greatest factors, following genetics, impacting production and yield in agronomic crops are fertility and weed management.  The uptake efficiency of nitrogen is dependent upon many factors including tillage system, soil type, crop, weeds, and the amount and type of nitrogen fertilizer applied.  The relationship and interaction between crops and weeds is important, and determining how North Carolina corn production may be impacted by different fertilizers could improve nitrogen use efficiency and overall corn yields.  Field studies were conducted in 2011 at the Upper Coastal Plains Research Station near Rocky Mount, NC and at the Central Crops Research Station in Clayton, NC.  Treatment factors included N source, N rate and weed removal time with a factorial treatment arrangement.  The N sources included urea ammonium nitrate, chicken litter, and sulfur coated urea with rates of 0, 27.22, 54.43, and 81.65 kg N/A.  Weed removal times were at 0 (weed free), 7.62, and 15.24 cm heights.  Significant location, nitrogen source, and weed removal height effects were observed for corn yield. When weeds were allowed to remain in the field with corn, the weeds were able to compete with the corn for nitrogen over a greater time period therefore reducing corn yield potential which showed the importance of the critical period of weed removal.  The interaction between location and source of nitrogen is due to the difference in soil types at the research stations with Clayton having a lighter, sandier soil which is better known for leaching and Rocky Mount having a heavier soil with greater clay content.  The increased corn yield corresponding with an increase in applied nitrogen is expected, as nitrogen is an essential nutrient in corn production and is partially due to the increase in Nitrogen Uptake Efficiency with greater nitrogen rates applied.