Starter Fertilizer In Soybeans

 

The use of starter fertilizer, while very common in corn production, is not a routine practice for many soybean producers. While the limited use of starter fertilizer in soybeans may be due, in part, to equipment limitations, it is instead most likely the result of mixed yield responses realized by the practice and the high sensitivity of soybean germination when placing fertilizers in the seed furrow. University testing has shown small yield increases from the application of starter fertilizers are possible but not consistent.

 

Starter fertilizer is typically a relatively small amount of plant nutrients placed near the seed during the planting operation. Actual placement can vary, including in the furrow, below the seed, to the side of the seed, or below and to the side of the seed (2” below and 2” to the side or ‘2x2 placement’ is common). The objective is to place a concentrated band of plant nutrients in an area where young roots can easily reach them and promote early seedling development. In soybean production, most starter fertilizers contain a mixture of nitrogen (N) and Phosphorus (P). Potassium (K) is not a limiting factor in most South Dakota soils.

 

The mixed response of soybeans to starter fertilizer may be attributed to several factors:

 

 

In general, only small amounts of fertilizer should be placed in contact with the seed. The soluble salts in fertilizers may cause seedling injury due to plasmolysis, desiccation, or toxicity. Symptoms are commonly referred to as fertilizer burn. One must consider soil texture, soil moisture, row spacing, and fertilizer type when determining the maximum rate that can be applied with the seed at planting. Table 1 shows maximum in-furrow starter fertilizer rates for a fine-medium textured, dry (conditions in 2015) soil where soybeans are planted in 30” rows. Allowable stand loss is 15% in this example. More detailed calculations for soybeans and other crops can be examined using an online tool.

 

Table 1. Maximum fertilizer rate to be applied in-furrow with soybean seed.* 

 

 

Many planters are equipped to apply fertilizer in-furrow with the seed. However, any time fertilizer can be placed away from the seed, the risk of stand reduction and potential yield loss due to fertilizer burn diminishes. Broadcast or banding applications may require an extra trip across the field but can help solve the problem of fertilizer burn. University research has shown that soybean yield response to banded and broadcast fertilizers has consistently been the same in the upper Midwest. Evidently, soybean roots have the ability to efficiently extract P from the soil regardless of placement method. A phosphorus placement study in South Dakota showed minimal differences in grain yield between banding and broadcasting application methods (Figure 1). University research has also shown that soybeans will also respond to extra P applied prior to corn in the previous year in a corn-soybean rotation.

 

 

 

It is important to remember that response to starter fertilizer may occur independent of soil fertility levels. Cool temperatures in early spring may lead to a variety of short-term nutrient deficiencies due to factors such as reduced mineralization rates, less diffusion of immobile nutrients, and slow plant uptake. Starter fertilizers may stimulate early growth in these conditions and result in an overall healthier plant that may be able to better compete with future stressors such as weed, insect, or disease pressure.