Harvest Practices « Seed Production

Thomas G. Chastain

The Willamette Valley does not expect much rain during harvest of grass seed crops. The production practices for grass seed crops in the region have evolved to take advantage of the dry conditions that are prevalent during harvest. But when rain falls during the harvest season, questions arise regarding the effects of this late precipitation on seed yield and quality of grass seed crops.

Seed Field — Aerial view of windrow harvested Willamette Valley grass seed field.

For grass seed crops that are at the pre-harvest stage during precipitation events, rain is usually not a problem and even after the crop is cut, the worst consequence is that the crop will take more time to dry down to reach combine seed moisture in the swath. However, if the delay in drying is too long, grass blades can grow up and through the swath making combining operations difficult. Tall fescue seems to be particularly problematic with regard to post-swathing leaf growth. When grass blades grow back up through the swath, some farmers recut the swath to facilitate combine harvesting but some seed losses can be expected in this operation due to shattering. If the crop is swathed onto wet soil and remains there for an extended period, there can be some losses in yield and quality as a result of the action of fungi and other pests.

The potential for damage to seed crop yield and quality is dependent on the intensity and duration of rainfall. Excessive rain after the grass seed crop is swathed can be a problem, especially in July and early August (for later maturing crops). First, the action of the falling rain in some circumstances can be sufficient to cause shatter losses of seed in the swath. Secondly, if rain is persistent and is accompanied by high humidity, then seed can sprout, thereby reducing the quality and marketability of the seed. These late season high rainfall events are not very common and that is why the seed industry has few artificial drying facilities in the region. Pre-harvest sprouting of grass seed was observed in the Willamette Valley in 1983 and again in 1993. Light rainfall after swathing of the crop is not generally a problem.

Thomas G. Chastain

In order to maximize harvest efficiency and seed yield, using the appropriate timing for harvest is essential. Seed moisture content is the most reliable indicator of seed maturity and harvest timing in grass seed crops.

Since pollination and seed maturation are not uniform processes in grass seed crops, a range of seed maturity can be found in a single field. Harvesting within the correct range of seed moisture contents will maximize seed yield and minimize losses of seed during harvest. Seed moisture content is also an important factor in the storage of harvested seed. High seed moisture content reduces longevity of seed in storage and reduces seed quality.

To optimize the timing to swath grass seed crops and to maximize the quantity of seed harvested, seed growers must balance cutting late-maturing seeds too early with cutting early-maturing seeds too late. Cutting too early at high seed moisture content shortens the seed fill period leading to immature seed and reduced seed size or weight. Cutting too late at low seed moisture content can reduce yield as a result of seed shattering losses.

The table below shows the seed moisture content range recommended for swathing of grass seed crops:

Crop	Recommended seed moisture for swathing (%)	Moisture loss per day (%)
Annual ryegrass	43-48	2.0-3.0
Orchardgrass	42-46	1.0
Tall Fescue (forage)	40-43	2.5-3.0
Tall Fescue (turf)	35-45	2.5-3.0
Perennial ryegrass	35-43	3.0
Chewings fescue	30	5.0
Creeping red fescue	25-35	4.0
Kentucky bluegrass	24-28	3.0-4.0

Illustrated instructions on how to conduct a seed moisture test in grass seed crops and guidelines for seed moisture contents for best harvest efficiency can be found in OSU’s publication EM 9012. Here’s a link to the publication:

Using Seed Moisture as a Harvest Management Tool

A video showing step by step instructions on collecting seed and methods to test moisture content of seed is linked below:

Seed moisture and harvest video

Thomas G. Chastain

Grass seed harvest has begun here in the Willamette Valley. In order to maximize harvest efficiency and seed yield, using the appropriate timing for harvest is essential. Seed moisture content has been found to be the most reliable indicator of seed maturity and harvest timing in grass seed crops.

Crop fields are generally not uniform and the harvested yield can vary across the field. Perennial ryegrass seed production fields are also not very uniform but some farmers use yield monitors on their combines to estimate seed yield and the spatial variability in seed yield across their fields.

This variability can be mapped for the fields where yield monitors are used and these maps can serve as the basis for making crop management decisions. But the reliability of these yield monitor-based estimates was not known for perennial ryegrass seed crops.

A recent paper by co-authored by extension agronomist in seed production Bill Young and others at OSU finds that there is considerable variability in seed yield in an otherwise uniform perennial ryegrass seed field and that a yield monitor can reliably capture this variability in seed yield.

Click on the link below to go to the article:

Reliability of Yield Mapping System for Estimating Perennial Ryegrass Seed Yield

Thomas G. Chastain

This spring has seen alternating very dry and warm periods and cool, wet periods in the Willamette Valley. While the effect of these varying conditions on seed yield remains to be determined, grass seed harvest will soon be under way. To maximize harvest efficiency, identifying the best timing for harvest is essential. Seed moisture content has been found to be the most reliable indicator of seed maturity and harvest timing in grass seed crops.

Range of maturity in perennial ryegrass spikes taken from one field (Tom Silberstein photo)

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Seed Production

Category Archives: Harvest Practices

Rain during grass seed harvest

Seed moisture and harvest timing in grass seed crops

Harvest timing in grass seed crops

Seed moisture content: a guide to harvest timing in grass seed crops

Yield mapping in perennial ryegrass seed crops

Harvest timing in grass seed crops by seed moisture content

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