Dry matter estimation and potassium fertilization of intensively managed soft red winter wheat

Dry matter production must be predicted to utilize nitrogen recommendation models for winter wheat at growth stage 30. Four methods of dry matter estimation were evaluated for their ability to predict dry matter production. The pasture probe, height, and rising plate methods did not have adequate prediction ability. The drop plate method predicted dry matter with an r² of prediction of 0.82 for all sites combined. The predictive ability for an individual site was lower. The combined model on an individual site caused a wide range of errors. Consequently, the four methods are not recommended for estimating dry matter. The changes in percent nitrogen and dry matter near growth stage 30 were measured. Dry matter increased significantly, but percent nitrogen did not vary significantly. The number of clipped samples necessary to estimate the dry matter for the five ha field studied was four samples. The number of samples needed for larger fields will depend on the variability of the dry matter in the field and on the variation inherent to the sampling technique.

Adequate potassium nutrition is required for high yields of winter wheat. Current soil test levels were evaluated and found to adequately describe the crop’s need for potassium. The influence of preplant and growth stage 25 applied potassium on yield and lodging was evaluated. On the medium to high potassium test soils used, the timing of the application did not affect yields or lodging. Ethephon reduced lodging better than potassium.