How To Choose The Right Starter Fertilizer For Your Soil

Most vegetable growers understand the importance of soil fertilizers and are applying them. But some may not realize the importance of applying starter fertilizers when the weather is wet and cold.

“Spring is an ideal time to consider applying a starter fertilizer with all your plantings,” said Mosbah Kushad, University of Illinois professor in the Department of Crop Sciences.

A starter fertilizer is a small quantity of either soluble or granular fertilizers that contains mainly nitrogen and phosphorus, and in some cases, potassium and other micronutrients, as well. Phosphorus is very important because of its poor mobility in the soil, making it difficult for the roots of young seedlings to get the necessary amount for root growth unless soil analysis indicates that the soil is high in phosphorus.

Kushad said there are many soil fertilizers to choose from, but growers should make their decision based on a soil test.

“Generally a high-quality starter fertilizer that contains at least nitrogen and phosphorus will be helpful,” he said. “A standard starter fertilizer is 8-32-16 or 10-52-8, but any water-soluble fertilizer that is high in phosphorus will be satisfactory.”

In soils with high phosphorus (more than 15 ppm), ammonium nitrate is a good starter fertilizer. However, in soils with high pH and low phosphorus, ammonium sulfate maybe a better choice, Kushad said.

If soil tests show less than 10 ppm of phosphorus, a starter fertilizer containing two to three times more phosphorus than nitrogen, such as mono- or diammonium phosphate, will be a better choice, he said. Growers can also add micronutrients, such as boron, manganese, and iron with the starter fertilizers if soil analysis indicates deficiency.

Once a soil fertilizer is selected, it’s important to read and apply the recommended amounts by the manufacturer to obtain the best results.

“The rate of starter fertilizer to apply will depend on the soil analysis and the crop,” he said. “For example, in sweet corn, if the soil test shows low phosphorus levels of less than 10 ppm, then apply about 40 to 50 pounds per acre along with about 10 to 20 pounds of nitrogen. Apply the fertilizer banded in a furrow about 3 inches away from the seeds and about 3 inches below the seed depth. In other words, if you planted the seeds 3 inches deep, then place the starter fertilizer 6 inches deep. If soil tests show more than 15 ppm, then growers should reduce the amount of phosphorus to 10 to 20 pounds.”

In peppers, if the soil test is less than 10 ppm, broadcast 80 to 90 pounds phosphorus before transplanting and then apply 30 to 40 pounds of either ammonium phosphate or another form of starter fertilizer in furrows below the transplants. Nitrogen levels in the starter fertilizer should be somewhere around 10 to 15 pounds for both chili and sweet peppers.

Watermelons and cantaloupes will also respond to a starter fertilizer, depending on soil analysis. A 50- to 60-pound per-acre rate of phosphorus, along with 10 pounds of nitrogen may be applied if the soil analysis shows less than 10 ppm phosphorus. Make sure to band the fertilizer and to provide adequate soil moisture at or soon after the fertilizer application, he added.

“Soil nutrient levels exceeding crop needs can be as harmful as deficient soils,” Kushad cautioned. “Very high phosphorus levels (above about 310 pounds of P205 per acre or 140 pounds of phosphorus per acre) in the soil may lead to iron and zinc deficiencies. Serious nutrient imbalances can also occur in soils high in potassium, magnesium or calcium.”

For these reasons, Kushad highly recommends soil nutrient analysis at least every two years in order to help establish rates of starter and regular fertilizers needed for good growth and best yield.

For more information on vegetable and fruit production, read the Illinois Fruit and Vegetable News online at http://www.ipm.uiuc.edu/ifvn/index.html.

Source: Jennifer Shike, College of Agricultural, Consumer and Environmental Sciences, Media Communications Specialist, University of Illinois; [email protected].