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Can I credit nitrogen for unharvested sugar beets and fallow fields?

unharvested sugar beets Minnesota nitrogen

By: Dan Kaiser and John Lamb, Extension nutrient management specialists

The 2019 growing season was extremely challenging with late plantings across Minnesota and some fields which went unharvested. While crops like corn can still be harvested this spring, others such as sugar beet cannot. Other situations such as fallowed fields also raise questions regarding nitrogen crediting for this year’s crop. Here are a few things to consider for some non-traditional questions which come up following difficult growing seasons.

How do I handle my unharvested sugar beet acres?

Two questions always arise when it comes to unharvested beets. First, how do I manage tillage in fields with unharvested sugar beet? Sugar beet roots can present challenges when it comes to fall tillage operations. The best option is to first remove the foliage and then leave the field un-tilled in the fall, as the root will start to decompose over the winter. A single pass with a soil finisher in the spring prior to planting is usually sufficient to prepare the soil, as sugar beet roots will work up more easily in the spring after they have softened and started to break down. It is best to wait and not rush tillage in the fall and recognize that results may vary from field to field based on conditions.

The second question is, should I credit any nitrogen from unharvested sugar beet? While we do suggest crediting sugar beet tops based on their greenness in the Red River Valley, sugar beets left in the field do not provide any potential nitrogen credit to the following crop. In fact, an additional 20 lbs. of N may be required if a crop like corn or wheat follows sugar beet. It is more likely that N will be tied up as the root decomposes, so adding additional N to a crop requiring N fertilizer application is warranted. In addition to N, corn following sugar beet may be at risk of fallow syndrome, requiring a low rate of “pop up” phosphorus and zinc starter fertilizer.

In comparison, research in Minnesota where soybean was not harvested showed no N credit to the following corn crop. While I have not heard of many, if any, unharvested soybean acres, do not expect an N credit or penalty from soybean and keep planned N application rates the same.

Can I expect a credit from fallowed acres?

The current fertilizer guidelines for corn production in Minnesota suggest that as much as a 75 lb. N credit could be expected under fallow conditions. If a credit is used, the credit taken from the suggested N application rates for corn following corn. Using the current guidelines, the amount of N needed for corn following a fallow year would range from 90 to 120 lbs. of N per acre depending on the N price/crop value ratio, which is roughly in line with the suggestions for corn following soybean. When crediting N from a previous crop, it is important to always take a credit from the corn following corn nitrogen guidelines and not the corn following soybean guidelines.

Collecting a two foot soil nitrate test is an option for growers to look at potential N credits or N carried over from the 2019 growing season. However, remember that the pre-plant nitrate test is only valid in situations where fertilizer or manure were not applied in fall 2019. For those interested, guidelines for how to use the test are included in the current corn fertilizer guidelines.

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