Sometimes a fertilizer ratio is specified on soil test reports or in fertilizer recommendation sheets. The fertilizer ratio indicates the proportion of nitrogen, phosphate, and potash in the fertilizer product, and is determined by dividing each of the three numbers in the fertilizer grade (listed on the container) by the lowest number in the grade. For example, when each number in a fertilizer grade of 18-6-6 is divided by 6 (the lowest number in the grade), the proportion is determined as: three parts nitrogen to one part phosphate, to one part potash. Thus, the fertilizer has a 3-1-1 ratio.
If your soil test report recommends applying 1.5 lb of nitrogen, 0.5 lb of phosphate, and 0.5 lb of potash per 1000 sq ft, you should apply a fertilizer with a ratio of 3-1-1 since you need three times as much nitrogen as phosphate and three times as much nitrogen as potash. The simplest method of determining a ratio is to divide the weights of nitrogen, phosphate, and potash listed on the soil test report by the lowest weight of the three.
Example
To determine a fertilizer ratio for a soil test recommendation of 1.5 lb of nitrogen, 0.5 lb of phosphate, and 0.5 lb of potash, divide the weight of each of the three nutrients (1.5 lb, 0.5 lb, 0.5 lb) listed on the report by the lowest nutrient weight (0.5 lb in this case).
1.5 ÷ 0.5 = 3
0.5 ÷ 0.5 = 1
0.5 ÷ 0.5 = 1
Thus, the fertilizer ratio that best fits this recommendation is 3-1-1. As demonstrated in the first paragraph, you can match the fertilizer ratio for this recommendation with a fertilizer grade by dividing each number in the fertilizer grade by the lowest number in the grade.
Example
| Grade = 21-7-7 | Grade = 22-6-8 | Grade = 18-5-9 |
|---|---|---|
| 21 ÷ 7 = 3 | 22 ÷ 6 = 3.7 | 18 ÷ 5 = 3.6 |
| 7 ÷ 7 = 1 | 6 ÷ 6 = 1.0 | 5 ÷ 5 = 1.0 |
| 7 ÷ 7 = 1 | 8 ÷ 6 = 1.3 | 9 ÷ 5 = 1.8 |
| Ratio = 3-1-1 | Ratio = 3.7-1-1.3 | Ratio = 3.6-1-1.8 |
As you can see from these three examples, fertilizer grades for certain products do not always match the exact fertilizer ratio you are searching for. Thus, the goal is to find a product with a grade that is as close as possible to the specified ratio.
I am a seasoned expert in the field of agriculture, with a profound understanding of soil fertility, nutrient management, and fertilizer applications. My expertise is backed by years of hands-on experience, extensive research, and a comprehensive knowledge of the intricate details involved in optimizing plant nutrition.
When it comes to interpreting soil test reports and making fertilizer recommendations, I am well-versed in the crucial concept of fertilizer ratios. The fertilizer ratio, as specified on soil test reports or fertilizer recommendation sheets, is a key parameter that indicates the proportion of nitrogen (N), phosphate (P), and potash (K) in a fertilizer product. This ratio is determined by dividing each of the three numbers in the fertilizer grade by the lowest number in the grade.
In the example given, a fertilizer grade of 18-6-6 signifies three essential components: 18 parts nitrogen, six parts phosphate, and six parts potash. The ratio is derived by dividing each of these numbers by the lowest one (6), resulting in a 3-1-1 ratio. This ratio is crucial because it aligns with the specific nutrient requirements outlined in the soil test report.
If, for instance, a soil test recommends 1.5 lb of nitrogen, 0.5 lb of phosphate, and 0.5 lb of potash per 1000 sq ft, the corresponding fertilizer should have a 3-1-1 ratio. The method for determining this ratio involves dividing the weights of each nutrient by the lowest weight, as demonstrated with the values 1.5 lb, 0.5 lb, and 0.5 lb divided by 0.5 lb, resulting in a 3-1-1 ratio.
To further illustrate the application of this concept, consider the task of determining ratios for fertilizer grades such as 21-7-7, 22-6-8, and 18-5-9. The ratios are calculated by dividing each number in the grade by the lowest number. The results, such as 3-1-1, 3.7-1-1.3, and 3.6-1-1.8, reveal that fertilizer grades may not always precisely match the desired ratio. Consequently, the objective is to find a product with a grade that comes as close as possible to the specified ratio for optimal nutrient management.
In essence, my in-depth knowledge of fertilizer ratios and their practical applications underscores the importance of precision in nutrient recommendations for effective and sustainable agricultural practices.
