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It seems that each growing season in Minnesota is different and this year is no exception. Cool, dry weather followed by a cool, wet soil environment has created some very unique field situations. As always, there have been some problems. There are also some lessons to be learned from various attempts to discover a solution to these problems. Some of these are described in the paragraphs that follow.

Go Deep When Looking For Nitrogen

The excessive rainfall had everybody thinking about nitrogen losses. Nearly everyone agreed that there was a high probability of some loss. As always, there is no way to predict losses from either leaching or denitrification. Judging by the light green to yellow color in many fields, the applied N was either lost or moved below the active root zone.

There’s a natural, logical inclination to collect soil samples and analyze for nitrate-nitrogen in an effort to determine if some applied nitrogen has been lost. This diagnostic tool can help if soil samples are collected to a depth of 24 inches. Research has shown that substantial amounts of nitrate-nitrogen can collect at depths of 12 to 24 inches. So, a sample taken from a depth of 0 to 6 inches and analyzed for nitrate-nitrogen provides little useful information. Yes, it is difficult to collect accurate soil samples when soils derived from glacial till are very wet. However, the soil from 12 to 24 inches is really needed before we can make any intelligent decision regarding the addition of supplemental fertilizer nitrogen.

It would be nice if it were possible to predict the amount of nitrate-nitrogen to a depth of 24 inches from a 0 to 6 inch soil samples. Several research projects have focused on developing this type of relationship. None have been successful.

Cold Soils Plus Wet Soils Plus Fallow Syndrome Equals Stunted Corn

Many corn fields throughout central Minnesota were stunted in mid-June and the purple color was dominant. Many of these fields followed a sugarbeet crop in 2003. Fortunately, there was a dramatic change in two weeks as temperatures increased and soils dried. There may or may not be a reduction in yield in the 2004 corn yield.

In the future, risk of yield loss in these situations can be reduced or eliminated by using phosphate fertilizer in a band for corn planting. The location of the band is not crucial. This band can be in direct contact with the seed, very close to the seed at planting or below and to the side of the seed. A rate of 15 to 20 lb. phosphate per acre is appropriate if soil test levels are in the medium or high range. Otherwise, use the rate suggested for banded applications.

Broadcast applications of phosphate fertilizer are not effective in overcoming this problem. Those who had lost soybeans in 2004 because of standing water should make plans to band phosphate fertilizer for corn in 2005.

Used Correctly, Plant Analysis Is A Good Diagnostic Tool

When looking at stunted, off-color plants, it’s logical to think about plant analysis as a diagnostic tool to get some answers. This is especially true when a deficiency or shortage of two nutrients (nitrogen and sulfur, for example) occurs at the same time.

Let’s suppose that two corn plants are being compared. One is tall and dark green; the other is short and light green. Both are analyzed for nitrogen. The concentration or percentage of nitrogen is lower in the tall, green plant. What happened? Was there a mix-up in sample identification?

The situation just described is a consequence of “plant dilution”. The nitrogen absorbed by the taller plant is diluted by the other plant components. As a result, the concentration or percentage of nitrogen may be lower than the concentration in the stunted plant with less growth. This "plant dilution" effect can be confusing.

Collection of additional plant samples will help to avoid some of the confusion. In addition to the plants that are showing clear symptoms of the abnormal growth, collect samples that show marginal symptoms and compare the analysis. In many situations, more useful plant analysis information will be obtained by analyzing the marginally different plants.

Plant tissue submitted for analysis should be accompanied by a soil sample. The interpretation of the soil test may, in itself, may provide a reasonable explanation for a cause of a problem.

Interpretation of the results of plant analysis is less complicated if there are standards of sufficiency, deficiency, or excess that can be used for a comparison. These standards do not exist for all growth stages of all crops.

There have been situations where an interpretation of plant analysis produced a wrong answer. It can happen. Caution in the interpretation of the results of plant analysis is advised. If possible and practical, have results of both soil and plant analysis available when troubleshooting a problem.

Certainly, the growing season is not over yet, there’s more to be seen and learned.