Iowa Admin. Code r. 21-49.4
Additional plant food nutrients, besides nitrogen, phosphorus and potassium, when mentioned in any form or manner, shall be registered and shall be guaranteed. Guarantees shall be made on the elemental basis. The minimum percentages which will be accepted for registration are as follows:
| Element | Percent |
| Calcium (Ca) | 1.00 |
| Magnesium (Mg) | 0.50 |
| Sulfur (S) | 1.00 |
| Boron (B) | 0.02 |
| Chlorine (CI) | 0.10 |
| Cobalt (Co) | 0.0005 |
| Copper (Cu) | 0.05 |
| Iron (Fe) | 0.10 |
| Manganese (Mn) | 0.05 |
| Molybdenum (Mo) | 0.0005 |
| Sodium (Na) | 0.10 |
| Zinc (Zn) | 0.05 |
Guarantees or claims for the above-listed additional plant nutrients are the only ones which will be accepted. Proposed labels and directions for use shall be furnished with the application for registration. Any of the above-listed elements which are guaranteed shall appear in the order listed, immediately following guarantees for nitrogen, phosphorus and potassium. A warning statement is required on the label for any product which contains 0.03 or more boron in a water-soluble form or 0.001 percent or more of molybdenum. The statement shall carry the word "WARNING" in letters large enough to be conspicuous; it shall state the crops for which the bulk dry animal nutrient may be used and it shall state that use of the bulk dry animal nutrient on any other than those reCornmended may result in serious injury to the crops.
Iowa Admin. Code r. 21-49.4