International Fertilizers promotional photograph. Roscoe Burtchell farm, Fort Fairfield. Yield: 160 twelve-peck barrels per acre.

Common fertilizers are rated as having certain variable percentages of nitrogen (N) phosphorous (P) and potassium (K). The percentages appear as a series of three numbers as, for example, 3-10-15.

When applying fertilizer it is not simply a matter of, "the more the better." Too much fertilizer can damage plants. When selecting a fertilizer, the farmer must consider the condition of the soil, the expected growing conditions, and the needs of the crop. While yields are affected by the proper application of fertilizer, they are also affected by the particular variety of a crop that has been planted, growing conditions, soil, and the skill of the farmer. The limited data provided with these International Fertilizers photographs gives information about only one of the many factors that affect crop yield and quality.