On-Farm Trials Demonstrate The Unpredictability Of Soybean Response To Starter Fertilizer

Being able to predict when starter fertilizers will increase soybean yields would enable producers to make better fertilizer management decisions.

Starter fertilizers (2x2 and in-furrow) have produced mixed results in SMaRT (Soybean Management and Research Technology) on-farm trials. In-furrow fertilizer increased soybean yields in two of 11 trials and decreased yields at one location. Starter fertilizer placed in a 2x2 band increased soybean yields in one of three trials and decreased yields at one of the sites. This article will focus on the three trials that showed a yield increase from starter fertilizer to identify any commonalities that might help predict when starter fertilizer will increase soybean yields.

Table 1. Effect of starter fertilizer on soybean yields at the three SMaRT locations showing a positive response to starter fertilizer.

The information presented in Table 2 shows the analysis, application rate and application method for the fertilizers applied at the three responsive sites. This information shows that yield increases can be obtained from both fluid and dry fertilizers and in-furrow and 2x2 placement methods. Soybeans are more sensitive to salt injury than corn so in-furrow fertilizer use on soybeans requires extra caution. Michigan State University Extension recommends the 2x2 placement method as it provides a greater level of crop safety.

2. Fertilizer analysis, application rate and fertilizer placement method for the three SmaRT locations showing a positive response to starter fertilizer.

The potential for a positive yield response from starter fertilizer is predicted to increase when phosphorus (P) and potassium (K) soil test levels are below the critical levels for these nutrients and when planting into cool, wet soils. The soil test P and K levels for each of the responsive sites are listed in Table 3. All P and K soil test levels were above the critical levels except the Allegan location where the K level was below the critical level of 97 ppm. So, existing P and K soil test levels were not good predictors of the starter fertilizer yield response at these sites.

Three factors generally lead to lower soil temperatures: 1) early planting dates; 2) no-tillage or high residue cover; and 3) fine-textured soils. This information is provided in Table 3. None of the fields were planted early, two of the fields were tilled and had low residue cover and none of the sites had fine-textured soils. Again, there were no consistent factors that could be identified to explain the positive yield response from starter fertilizer at these sites.
 
Table 3. Planting dates, tillage and soil test information for the three SMaRT locations showing a positive response to starter fertilizer.

*CEC stands for cation exchange capacity

Unfortunately, there doesn’t appear to be any common factors that can be identified from these locations for predicting when starter fertilizer will increase soybean yields. However, these sites do not disprove or refute the general consensus that a positive response to starter fertilizer is more likely when P and K soil test levels are below the critical levels and when planting into cool, wet soil conditions.

Source : msu.edu