A closer look at the fertilizer bag

Paige Burns CED, Horticulture agent

Micronutrient deficiencies can be hard to identify. Iron deficiency closely resembles Round up chemical damage.

Photo courtesy of haifa-group.com

ROCKINGHAM — Most people are aware that plants need to be fertilized in order to grow well. How much do you know about the fertilizer you’re using?

Plants require 17 essential nutrients for proper growth, with 9 macronutrients and 8micronutrients. Bags of fertilizer are labeled with the percentage of nitrogen, phosphorus, and potash (also known as N-P-K) of that particular formulation. So a bag of 10-10-10 is 10% nitrogen, 10% phosphorus, and 10% potash (or potassium). 8-0-24 is eight percent nitrogen, zero phosphorus, and 24% potash. You get the picture.

NPK are considered macronutrients for plants; other macronutrients include carbon, hydrogen, oxygen, sulfur, magnesium, and calcium.

Carbon, hydrogen and oxygen are provided by the environment (air and water); magnesium and calcium are readily available as long as the soil is properly limed to the correct pH, as both are components of liming material (if dolomitic lime is used). Sulfur is usually available from the atmosphere, although since air pollution has been reduced over the years, sulfur deficiencies are more common than they once were.

What is often forgotten in fertility considerations are the micronutrients. Micronutrients include iron, boron, manganese, nickel, zinc, copper, chlorine and molybdenum.

Micronutrients, as the name suggests, are needed only in very, very small amounts by the plant. Research in plant dry matter showed manganese at a level 1000 times less than nitrogen. The amount of manganese is 1000 times more than the uber micronutrient, molybdenum. Though needed in minute amounts, micros are still essential for plant health. Signs of deficiency may be subtle, and often mistaken for disease or environmental issues.

One commonly deficient micronutrient in sandy soils is boron. This nutrient is essential for pollen germination and seed and cell wall formation. Without sufficient boron, pollination may be poor, fruit misshapen, and developing leaves malformed. A common sign of boron deficiency is a hollow center in the core of a broccoli stem. Boron is pretty important if you’re trying growing vegetables.

In some regions, micronutrients are supplied through the soil and supplementation is less important. Unfortunately, sandy soil is a very poor source of micronutrients. Other potential sources include organic matter and organic fertilizers, such as compost and animal manures.

Not only is compost and animal manure a source of micronutrients, those materials provide attachment points for all nutrients which sand alone does not have (water is also held by organic matter much better than sand alone).

Correct soil pH is also critical to create an environment conducive to nutrient availability. Our natural soil pH is around 4.5-4.8 (sometimes even lower, in the 3s), and most vegetables need 6.0-6.4. At low soil pH, nutrients are unavailable to the plant or lost through leaching, especially boron and molybdenum.

Micronutrients can be purchased like any fertilizer, and applied to soil or, with some formulations, as a spray for direct foliar application (this is frequently done with boron and even calcium, which is not a micronutrient, but frequently deficient in fruit). Because micronutrients are need in such small amounts, foliar sprays can be an effective way to get micronutrients into plants. If buying bagged fertilizer, check the label to see if micronutrients are included – they are generally found in the small print.

When tobacco was a more common crop in the area, it was easier to find fertilizer with micronutrients because it was needed to grow good tobacco. Rainbow brand fertilizer is one that typically contains micronutrients in its formulations.

Nowadays, fewer people understand the value of paying the higher price for fertilizer with the needed micros, but they are essential in order to grow a quality crop.