Ask the Agronomist by Rainbow Plant Food: Part 2

With harvest well underway in many parts of the country, our agronomists at Rainbow Plant Food took time to answer some of the questions we have received from farmers this year. From sweet potatoes to corn and soybeans, we’re discussing Rainbow fertilizer grades and which Rainbow fertilizer may be right for you.

Question: What’s the difference between Rainbow, Super Rainbow and International?

Answer: Rainbow International is formulated to give an even distribution of N, P and K. It is a reliable, cost-effective alternative to physically mixed materials. Granules of this product contain a standard amount of nitrogen, phosphorus, potassium and sulfur – the four essential ingredients for above-average yields.

Rainbow provides complete nutritional benefits to meet your crops’ needs. This formulation includes the same four basic minerals as our International product (N, P, K and S) and adds other nutrients such as boron, manganese and zinc. This product is perfect for just about every crop, including cotton, corn, tobacco, soybeans and more.

Super Rainbow offers you optimal nutritional benefits through additional nutrients such as magnesium, sulfur and calcium to facilitate exceptional yields and higher grades. This product line also includes additional micronutrients including copper, iron and boron – all of which act as catalysts to activate enzyme systems and maximize plant health and crop quality. 

No matter what your crops and soil require, there’s a Rainbow fertilizer for you. Get in touch with your local rep to find the perfect formulation for your crops.

Q: I want to grow sweet potatoes. What fertilizer do you recommend?

A: You requested some information about Rainbow fertilizer as a nutrient source for Sweet Potatoes. Of the three major nutrients (NPK), potassium plays the largest role in a full and healthy crop. Boron is also important for sweet potatoes because it prevents blistering disorder.

There are two grades of Rainbow Plant Food produced specifically for sweet potatoes – Super Rainbow 6-3-18 and Rainbow 8-4-24. The nutrients in both options exist in a highly available water-soluble sulfate form, so action is quick on roots for your sweet potatoes.

Learn more about Rainbow Plant Food for sweet potatoes in this write up.

Q: What is a good Rainbow mix for corn and soybeans, and how much should be applied?

A: Corn and soybean plants need 13 different plant nutrients to grow to the right size and yield potential. Practically all soils in the coastal plain are deficient in sulfur, manganese and boron, so unless a good available secondary NS micronutrient source is supplied in your fertilizer, your crop may suffer.

We recommend Rainbow 5-15-30 for both corn and soybeans. The nutrient breakdown in this formulation is as follows:

For applications rates, we recommend the following:

  • Irrigated Corn: 500 lbs of 5-15-30 Rainbow per acre
  • Dryland Corn: 400 lbs of 5-15-30 Rainbow per acre
  • Soybeans: 200 lbs of 5-15-30 Rainbow per acre


Have a question of your own you would like to have answered? Visit our Ask The Agronomist page or tweet your question to us @Rainbow_Plant