Information about the Kentucky State University Cooperative Extension Program 2021

Dr. Leigh Whittinghill, Assistant Professor of Urban Agriculture

This worksheet is designed to help you calculate how much fertilizer you will need to grow your selected crops. This will first help you determine the nutrient recommendations for your crops, adjusted to the scale you will be planting. Then you will calculate how much fertilizer of your choosing you will need to apply to meet that recommendation. Finally, you will determine how much total fertilizer you will need to purchase for the growing season. Using appropriate crop nutrient recommendations and planning your fertilizer applications to match those recommendations is important for two reasons. First, when you over apply nutrients to your farm or garden, you are paying for nutrients that do not influence your final yield, which affects your overall farm or garden budget. Second, nutrients not used by the crops are often leached out of the field. These nutrients often end up in ground or surface waters and affect their quality. Nitrogen and phosphorus, in particular, contribute to a process called eutrophication. Excess nitrogen and phosphorus contribute to algae growth in surface waters, which is unsightly and can affect recreation directly, especially if the algae blooms include toxic species. Worse, when the algae dies, the bacteria that break it down use up the oxygen in the water. When oxygen levels get too low, or hypoxic, it can cause fish and invertebrates to die, giving those areas the name “dead zones.” Agriculture is one of the largest contributors of nutrients that lead to eutrophication and hypoxia. The Gulf of Mexico dead zone is one of the world’s largest dead zones and reached a record size of 8,776 square miles in 2017.

Using appropriate crop nutrient recommendations and planning your fertilizer applications to match those recommendations is important for two reasons. First, when you over apply nutrients to your farm or garden, you are paying for nutrients that do not influence your final yield, which affects your overall farm or garden budget. Second, nutrients not used by the crops are often leached out of the field. These nutrients often end up in ground or surface waters and affect their quality. Nitrogen and phosphorus, in particular, contribute to a process called eutrophication. Excess nitrogen and phosphorus contribute to algae growth in surface waters, which is unsightly and can affect recreation directly, especially if the algae blooms include toxic species. Worse, when the algae dies, the bacteria that break it down use up the oxygen in the water. When oxygen levels get too low, or hypoxic, it can cause fish and invertebrates to die, giving those areas the name “dead zones.” Agriculture is one of the largest contributors of nutrients that lead to eutrophication and hypoxia. The Gulf of Mexico dead zone is one of the world’s largest dead zones and reached a record size of 8,776 square miles in 2017.

The following instructions will help you gather the information you need to calculate your fertilizer needs. Before getting started, make sure to have your planting calendar and planting plan on hand, and have access to a soil test that was submitted in the last three years. If you need help developing a planting calendar, check out our fact sheet Developing a Crop Planting Calendar (KYSU-CEP-FAC-0078), available at: https://www.kysu.edu/documents/school-of-agriculture-communities-and-the-environment/planting_calendar_with_tables_accessible_031021.pdf.