The relationship between existing or expected prices to costs of production should carry more weight than just making marketing decisions at the expected seasonal price extremes. The USDA has spreadsheets of national and major terminal prices that are available at the web site which provides ERS data sets. Most state's Agricultural Statistics offices have paper or spreadsheet history of monthly average prices for the state and sometimes by state crop producing region. Seasonals are regular occurring patterns that are related to the calendar year, and are usually closely related to the seasonal nature of crop production and harvesting. Cycles are somewhat regularly occurring patterns that could span minutes or many, many years.
Seasonal patterns are one special type of cycle.
Trends are longer term, one directional changes such as a long-term uptrend in prices caused by inflation. This could help setting price time goals. For More Details Ferris, John N. Agricultural Price and Commodity Market Analysis . W. C. B. McGraw -Hill. Ferris John N. Seasonal Cash Price Patterns for Selling Decisions on Corn Soybeans and Wheat .