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Pre-harvest Sprouting and Falling Numbers (09/11/14)

Many reports indicate that the 2014 small grain yields will be some of the largest ever.

Pre-harvest Sprouting and Falling Numbers

Many reports indicate that the 2014 small grain plsc.ransom.instrumentyields will be some of the largest ever. Moderate temperatures and adequate rainfall coupled with improved management practices and varieties have enable these record or near record yields. Unfortunately, much of the crop remains in the field awaiting harvest. The recent rains have delayed harvest further and have increased worries about low test weight, pre-harvest sprouting and low falling numbers. High test weight in wheat is usually associated with high flour yield and sound kernels, therefore the milling industry prefers grain with high test weight and low test weight grain fetches a lower price at the elevator. Repeated wetting and drying of matured grain causes the seed coat to loosen and the kernel surface to wrinkle, causing a reduction in test weight. All varieties are susceptible to test weight loss when weathered. However, those varieties with the highest non-weathered test wet are likely to maintain a relatively higher test weight when weathered than other varieties. Durum is generally thought to be more susceptible to this type of weathering than bread wheat.

Grain that sprouts before harvest is heavily discounted at the elevator because of its limited utility in the traditional milling and baking applications. Pre-harvest sprouting occurs when the mature kernels are repeatedly wetted or when they are exposed to a prolonged wet period. Generally upon reaching physiological maturity, seeds are dormant for a short period to ensure that the embryo does not begin to grow until the seed dries enough to further prevent germination. This period of after-ripening dormancy can vary between varieties, so some varieties are more susceptible to sprouting than others. Sprout damage can be visible if the process is far enough along at harvest that the radicle and coleoptile emerge from the effected seed. Sprouted kernels are counted during the grain grading process and result in dockage.

Even if no visible spouting can be see, the grain may still be subject to heavy discounts or rejection at the elevator if the physiological processes of germination have proceeded sufficiently to impact the quality of the endosperm. One of the first enzymes activated during germination is alpha amylase, which breaks down the kernel’s endosperm into the chemicals needed for the growth and development of the nascent seedling. Unfortunately, the degraded starch in seeds with high alpha amylase activity is of very poor quality for baking. Grain with this type of damage can be identified with the falling numbers test. This test measures the rate at which a plunger descends through a slurry of flour and water in a test tube. The slurry made with flour degraded by alpha amylase will be less viscous so the plunger will descend more rapidly than in a slurry made with flour from sound kernels. A falling number greater than 350 indicates very low alpha amylase activity. Falling numbers between 200-300 seconds indicate that some level of sprouting has occurred. Falling numbers less than 150 indicate that the grain was highly sprouted and is not likely to be usable for bread-making applications.

At this point in the season there is little that one can do to manage the weathering and sprouting damage that might occur in fields that have not yet been harvested. Selecting varieties that that are more resistant to weathering may be a strategy for future years if differences are noted in the varieties grown this year. Since pre-harvest sprouting has not been a widespread problem for several years, we have limited data available on varietal differences for this trait in published university sources.

Joel Ransom

Extension Agronomist for Cereal Crops

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