Starter fertilizer for corn

A few weeks ago, I did an informal email survey of crop consultants mainly from NE South Dakota. I asked the group what percent of their producers used starter fertilizers, liquid or dry and how applied. A starter is usually defined as the placement of small quantities of nutrients in a concentrated zone in close proximity to the point of seed placement at the time of planting. The consultants responded that most (60 – 100%) of their clients did use starters, almost all used liquids as the source and most applied directly with the seed. The results surprised me somewhat in the number of producers using starters.

I also summarized 71 starter studies that SDSU has done on corn from the past 25 years. The results suggest reasons why producers are using starters. The studies indicate the response we see from starters is usually from the phosphorus (P) fertilizer component. Additional nutrients such as potassium, sulfur or zinc are also applied if soil tests warrant a need. Except for very coarse soils in some years, the applied nitrogen (N) in a starter is not that valuable, especially if some preplant N was applied.

Two-thirds of the summarized starter studies had an early growth response from the starter but only 20% of the sites had a significant yield response to the starter fertilizer. The frequency of a yield response was higher with lower P tests. However, even under very high Olsen P tests (greater than 16 ppm but less than 30 ppm); a few significant economical yield responses were seen by adding a starter. This type of response would be considered a ‘true’ starter response as P soil tests are very high and responses to broadcast P would not be expected.

In general, the rate of starter only needs to supply about 15-20 lbs of P2O5/a which is about 5 gal/a of 10-34-0. If soil P tests are low, additional P above that which is applied with the starter will be needed so soil P tests don’t drop further. However, if medium or higher tests exist, starters can often be used to supply all the P that is needed for the yield goal selected.

Yield responses from starters, especially at higher P soil tests, occur in those planting seasons where we have some stress. The stress is often cool soil conditions, but can include dry soil conditions or compaction issues. These conditions often limit root growth, P movement and early plant P uptake which is especially important for corn. Therefore a concentrated band of P near the seed can improve early P uptake, corn growth and development. If stress conditions persist into late spring, the P starter is more likely to provide a yield increase above normal broadcast P applications.