Which statement about GDD usage is true?

• A. To measure soil fertility.
• B. To predict plant development stages and timing of events like flowering and harvest.
• C. To determine rainfall patterns.
• D. To calculate market prices.

Answer: (B)

Growing degree days measure heat accumulation to predict when a plant will reach specific development stages. Plants need a certain amount of warmth to progress from one stage to the next, so by adding up daily heat units above a base temperature, you can estimate when flowering, fruiting, or harvest will occur. This makes GDD a practical tool for timing field activities like planting, irrigation, fertilization, pest management, and especially scheduling harvest.

In practice, you calculate a daily heat unit value from the day's average temperature above a base temperature, then accumulate those values over time. When the total reaches a known threshold for a crop stage, you expect that stage to occur around that time. That’s why the statement about GDD usage being to predict plant development stages and timing of events like flowering and harvest is the best fit.

GDD isn’t used to measure soil fertility, determine rainfall patterns, or calculate market prices, which are addressed by soil testing, climate data, and economic factors, respectively.