Too much N, too much of a good thing on sunflower

Too much nitrogen can actually decrease the oil concentration in sunflower seeds, which decreases the quality of the crop, according to researchers in Argentina.  |  Soil Science Society of America photo

Sunflower value is based on oil and protein concentrations in the seeds. These elements set the price of the crop for end users, such as animal pellets and protein powders.

Modern varieties of sunflower can produce more oil and protein, but they require more nitrogen to do so. However, research from Argentina shows that too much nitrogen actually lowers the protein and oil content in sunflowers, thus lowering the value.

Balancing nitrogen in sunflower production has become a major goal for Argentine scientist Nahuel Reussi Calvo.

He said too much nitrogen can decrease the quality of seeds.

Calvo said to grow quality sunflowers with a high nutritional value, farmers must ensure the crop has access to nutrients, one of the most important being nitrogen.

Recently in Agronomy Journal, a publication of the American Society of Agronomy, the researcher suggested that farmers will do better with a balanced nutritional approach.

His work has been targeting the best rate of nitrogen fertilizer that will grow high-quality sunflowers but minimize the economic and environmental costs of applying fertilizer. With near record-high prices for urea, producer margins on the crop can be greatly affected.

Traditionally, scientists measure nitrogen available for sunflowers by taking soil samples before planting. However, the target nitrogen levels for these tests are not up-to-date to match the needs of modern sunflowers. Like so many crops, the baseline data for fertilizer recommendations does not reflect today’s agronomics.

Consequently, researchers set out to determine if there are better ways to determine how much nitrogen sunflowers need.

First, Calvo and the research team used the traditional soil sample analysis method combined with another soil sample analysis. The extra soil sample helps determine the amount of nitrogen provided in the soil when organic matter naturally breaks down.

The next method took place during the growing season. The team used sensors to measure leaf greenness at different growth stages. This is a test that’s proven successful for measuring nitrogen content in crops like wheat, barley, corn and potatoes.

After harvest, they measured grain nitrogen concentration in sunflower seeds for the third method. This is a useful tool for predicting the nutritional value of crops like corn, wheat, rice and cotton.

Researchers determined the three new methods for measuring nitrogen for sunflowers were better than the traditional soil sample analysis method. Leaf greenness sensors were a promising tool for monitoring nitrogen during the growing season. The grain nitrogen concentration in seeds successfully diagnosed nitrogen deficiencies.

The next steps in this research will be to repeat the study on farms with different soil types, management practices, and levels of other nutrients like phosphorus and sulfur.

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