Starter fertilizer boost depends on soil tests

As planting season begins, farmers often question if starter fertilizer is providing yield and economic benefits.

Starter fertilizer is defined as fertilizer applied with the specific purpose of helping the plants acquire more nutrients early in the season. This is in addition to the fertilizer used in the nutrient management program that is based on deficiency correction/sufficiency approaches.

There are two main reasons to use a starter. The best reason is when soil tests indicate the field is deficient in one or more nutrients, and these nutrients are relatively easy to apply with the planter.

The other main reason is if the field to be planted is covered with more than 70% residue and you expect the soil to be cool and wet.

Back when most growers cultivated, starter made the young corn plants taller and greener quicker, which allowed cultivation to occur earlier in the season and resulted in better weed control.

Also, phosphorus applied with the planter helps the plants mature earlier which can result in drier corn.

If starter is going to be placed near the seed, be sure the dose will not hurt germination and stand establishment.

But if the soil test levels for the starter nutrients are greater than the critical value for these nutrients, starter will probably not help yields, especially on fine-textured soils. Spending time loading the starter material and making sure all the equipment is working may take valuable time during planting.

Corn research

From 1995 to 2019, farmers working with the Nebraska On-Farm Research Network conducted 35 studies looking at starter fertilizer on corn.

Some were in the same field for a number of years, others moved around. Various starter materials were evaluated, and not all studies reported soil test P levels.

Eighteen of the studies compared a 10-34-0 starter fertilizer in the range of 4-6 gallons per acre to a no-starter check. Soil P levels were between 4 and 35 ppm, but not all studies reported the specific P extractants used.

• For soils with P soil tests at or below 10 ppm there was an average yield increase of 14.3 bu./acre due to the starter (four sites).
• For soils with P soil tests of 10-20 ppm there was an average increase of 2.6 bu./acre (five sites).
• For soils with P soil tests of 20-35 ppm, there was an average increase of 0.3 bu./acre (nine sites).

When all the data were combined, regardless of soil test values, there was an average increase of 4 bu./acre.

This analysis disregards statistical analysis. Of the 18 studies, only five had statistically significant differences. Of these five, the average yield increase was 12 bu./acre and the average soil test P level was 9 ppm.

Soybean research

A similar analysis of the soybean on-farm research found six starter studies between 1992 and 2015, with only three sites reporting soil test P, all of which were greater than 17 ppm.