Rye cover crops slow asparagus emergence

While rye-cover crops in asparagus have disadvantages, they really proved worthwhile this spring.

The use of rye cover crop in asparagus has become wide spread in the main growing areas of Michigan’s Oceana County, but isn’t as common in secondary growing areas. Admittedly, rye cover crops have some costs and problems. At the industry standard of two to three bushels of seed per acre, rye cover can be expensive in some years. Many growers opt to grow their own seed for just this reason. Unless you are equipped to broadcast the rye during your last fungicide application in late August, it requires an additional trip across the field at the end of the fern-growing season. It can also be contaminated with some problem weeds, especially hairy vetch, which seems to get worse the farther seed gets from certified.

Rye cover crops can sometimes be difficult to kill in cool springs, occasionally requiring the application of a post-emergent grass killer if the glyphosate applied before asparagus emergence doesn’t work as hoped. Also, in dry years growing rye cover crops can draw moisture away from the crop. Worst, perhaps, is that once all of the asparagus has emerged in the spring, the insulating blanket of dead, chopped rye can make fields more likely to frost, because it reduces the re-radiation of heat from the soil.

But for all of these problems, years like 2012 point out the great advantage of a rye cover crop. The insulating effect of the growing rye tends to prevent the soil from warming prematurely, thereby delaying the emergence of asparagus spears in the spring. That effect has been particularly valuable this spring, when unseasonably warm March temperatures caused asparagus in fields without rye cover to emerge early, resulting in a lot more freeze damage and loss. While variability in weather patterns make this characteristic difficult to quantify scientifically, grower experience, especially this year, bare out the value of rye cover in slowing crop emergence.

Added to this advantage are the other important effects that rye cover crops bring to asparagus production. In the fall, rye cover crops can soak up excess nutrients and protect soil from erosion as the asparagus fern senesces. If established in late August, rye can also provide some suppression of germination and growth of problematic weeds including marestail. In the spring, a good rye cover crop, even once it has been killed and chopped, is a great way to prevent wind erosion and the resulting sandblasting of spears during harvest. It also reduces the splashing of sand up on to the spear during heavy rain, resulting in cleaner spears for the whole spear processing and fresh market industries.

While the killed, chopped rye disintegrates quickly (there is usually no sign of residue by the end of harvest season), it is one way to add at least a little organic matter to a production system, which takes out more than it puts back in to the soil. If you have resisted using rye cover crops in asparagus in the past, consider giving the idea further consideration at the end of this growing season.

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