Minnesota crop producers working for the extra yield have frequently considered the use of foliar application of fertilizer for both crops. Is this practice important? Does it pay? These are two of the frequently asked questions.

The concept of foliar fertilization has been researched for several years. Several projects focused on this management practice during the mid-1970’s. More recently, there has been an intensive evaluation of in-season application of fertilizer – N for soybean production. Results of some of the research trials conducted in Minnesota are summarized in the tables that follow.

Application of fluid fertilizer containing N, P2O5, K2O, and S was evaluated for corn production at the Southern Research and Outreach Center at Waseca. This mixture was applied 1, 2, or 3 times from mid-August through early September. Nutrients applied with each time of application were 25.3, 12.5, 6.3, and 1.0 lb of N, P2O5, K2O and S respectively. The results are listed in Table 1. All treatments received full N at 150 lb./acre as 82-0-0. In addition, there was a broadcast application of 60 lb. P2O5 and 100 lb. K2O per acre.

Table 1. Corn yield as affected by foliar application of N, P2O5, K2O and S.

The application times were selected so that the fluid fertilizer would be applied during grain fill. The results of this study showed that foliar application of fertilizer had no positive effect on corn yield.

Following a report of a positive response of foliar application for a soybean crop, trials were conducted at three locations to evaluate the potential use of this management practice for soybean production in Minnesota. The fertilizer was applied during pod fill. The results are summarized in Table 2. There were two varieties at each location. Results were consistent with both varieties. Values in Table 2 are averages for the two varieties.

Table 2. Influence of foliar application of fertilizer on soybean yield.

These results show that foliar fertilization is not a management practice that will increase soybean yield. Other universities throughout the Corn Belt conducted similar studies. The results were similar. Foliar fertilization had no effect on soybean yield.

There is a risk to foliar fertilization. The N could cause burning of the foliage and reduce yield. The yields summarized in Table 3 illustrate this risk. The N was applied as liquid urea to supply 75 lb. N per acre.

Table 3. The effect of application of fertilizer N (urea) on soybean yield.

Treatment	Yield
	(bu/a)
control (no N)	45.1
liquid urea (early bloom)	42.4
liquid urea (late bloom)	37.6

In this study, the yield reduction from the late application of urea was caused by foliage burn.

Studies with in-season application of fertilizer N have been more extensive. In these trials conducted throughout Minnesota at 15 sites, there was a positive response to N at one site.

While the foliar application of fertilizer may seem like a logical management practice, this method of fertilizer application has not increased yield of corn and soybean in Minnesota. This practice is not recommended.