The Impacts of Nitrogen and Potassium Fertilization on Rice Lodging.

‘CL151’ has become a popular rice cultivar because of its high yield potential; however, lodging is problematic.  Combinations of N, K, and fungicide applications were evaluated to develop practices that potentially minimize lodging.  Field studies were conducted on Sharkey clay (Chromic Epiaquerts) and Dundee silt loam (Typic Endoaqualfs) soils.  Treatments consisted of a factorial combination of N rate, K rate and fungicide timing.  Nitrogen and K rates were 112 and 224 kg N ha^-1 and 67 and 134 kg K₂O ha^-1.  Azoxistrobin was applied at the rate of 0.2 kg ha^-1 at either panicle differentiation (PD) or boot.  Grain yield, lodging percent, nor lodging severity were affected by interactions for either soil type.  For the Dundee silt loam, 112 kg N ha^-1 averaged over K rate and fungicide timing resulted in 5% less grain yield compared to 224 kg N ha^-1.  However, 53% of the plots that received 224 kg N ha^-1 lodged whereas no lodging occurred when 112 kg N ha^-1 was applied.  The severity of lodging at 224 kg N ha^-1 rated 4 on a scale of 1-5 where 1 = erect and 5 = flat on ground.  For the Sharkey clay soil, results were similar; however, the yield loss when 112 kg N ha^-1 was applied was 15%.  Lodging occurred on and average of 10% of the individual plots and the severity rated 2 when 224 kg N ha^-1 was applied.  A fungicide application at PD or Boot increased rice grain yield by 6% compared to none being applied.  In summary, N rate is the largest determining factor in managing CL151 for lodging.  Up to 95% of the maximum yield potential (Ymax) can be achieved with N while minimizing lodging; however, lodging is expected when N fertilization exceeds 95% of Ymax.