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Home  > Question of the Week

Question of the Week

Permalink What can you tell me about nitrate accumulation in leafy greens during the winter months?

Answer: Nitrate accumulation is minimized by varietal selection, fertilizer management, and timing of harvest. Nitrate concentration in vegetables typically increases with rate of nitrogen fertilization. Generally, it is best to avoid fertilizing with both pre-plant and broadcasting fertilizer, especially those with high amounts of soluble nitrogen. A more stable nitrogen source, such as compost, is recommended.

Washington State University has produced a PowerPoint presentation on this topic, titled "Leafy Greens as a Winter Crop in Washington State." It is available at The take-away message from this presentation is that the amount of accumulation varies from each variety but, in general, Asian greens tend to have more nitrate accumulation. We suggest looking at the varieties list and grow the ones that demonstrate lower accumulations. For example, Mizuna and Pac Choy had high accumulations, while arugula had very low accumulations.

Before you plant next winter, consider getting a soil test to determine the soil nitrogen level. Also, the longer the greens are in the ground, the lower the accumulation, so you should wait at least 11-12 weeks before harvesting.

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Permalink What can you tell me about preventing and controlling thistles in forage crops?

Answer: Weeds are signs that something is happening in the field that may weaken grasses and decrease productivity. As long as a grass stand is maintained intact through proper management, the grass community will thrive. However, when some kind of disturbance occurs, the grasses often have a hard time bouncing back without weed populations becoming established. Why does this happen? Weeds take advantage of a niche left open by grasses as they disappear. But why can’t a grass plant take that niche just as easily as a weed? The reason is that weeds have evolved to be very competitive for nutrients and have adapted to soil conditions that most grasses have not. If a soil is disturbed through compaction (the destruction of soil structure due to animal impact or machinery), or if it has become infertile due to intensive cropping and harvesting of nutrients, weed species will find a comfortable home. This is nature’s way of correcting imbalances, because deep-rooted weeds can scavenge non-available nutrients, translocate them to their leaves and stems, and return them to the soil when they die. This is, in effect, a way of soil building in degraded soils. After the soil has become porous due to the rooting of weeds, and nutrients have been returned to the soil, natural grassland plant succession can take over and the grasses will begin to return.

Preventing Thistles in Forage Crops

The presence of weeds in an established forage crop or pasture is usually a sign of a management problem. Fertility, proper planting procedure, and harvest management are the most effective ways to maintain dense, productive pastures. Ensure adequate soil fertility and optimum pH with nitrogen-fixing legumes and applications of lime as per soil test. When establishing new pastures, ensure that you use weed-free seed on a well prepared seedbed, or use a no-till drill at the appropriate time. Also, be sure to practice good harvest management, whether grazing or haying, by leaving enough forage standing after harvest to allow for regrowth. It is especially important to rest pasture plants after grazing to allow full regrowth, thereby ensuring plant health and productivity.

Consider the following for establishing a weed-free forage crop:

• Control weeds prior to planting with successive tillage. This allows weeds to germinate, which can be killed by the next tillage. Some growers use a broad spectrum herbicide to control weeds prior to planting.
• Apply lime and fertilizers according to soil test, and incorporate with tillage.
• Prepare a good seedbed, with no large soil clumps.
• Select weed-free certified seed.
• Plant with a drill, or broadcast at a higher seeding rate and drag the field with a harrow to obtain seed to soil contact. Good seed to soil contact ensures good germination and seedling growth.
• If weeds occur in the stand, mow them high. Grasses have their growing points at the base of the plant prior to flowering, and weeds like thistles have their growing points higher on the plants. Mowing creates an environment that favors grass growth over weed growth, given proper fertility management.

Controlling Thistles in Forages

If thistles become established in a forage stand, they can be controlled through mowing, grubbing the individual plants (for small infestations), or using an herbicide. Broad-spectrum herbicides like Roundup kill all plants, not only the target species. The same goes with low-toxicity herbicides like citric and acetic acids. If these tools are used, spot treatment will provide the best results.

The frequency of mowing for the control of thistles depends on rainfall. A single summer mowing is usually beneficial after flowering but before the seeds set. However, additional clippings will be required if later summer rain results in significant lush weed regrowth. Mowing after flowering but before seed set will reduce weed seed production and decrease the amount of weed seeds in the soil for the following year. Perennial weeds, like thistles or dock, should be mowed successively throughout the grazing season to starve the plant and reduce seed production. Note that many plants, like thistles, will continue to set flowers after they have been mown, and will usually set them closer to the ground after mowing. To compensate for this, mow perennial weeds high to clip flowers to minimize seed production and prevent the plant from setting subsequent flowers low to the ground.

For more information, see the ATTRA publication Thistle Control Alternatives, available at This publication focuses on the cultural, biological, organic, and least-toxic methods available for their control.

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Permalink What resources are available to help me conduct an energy self-audit of my farm?

Answer: Understanding the energy required and consumed by your farm is the first step in planning how to reduce energy consumption, invest in more energy-efficient equipment, and select renewable energy equipment. There are a number of energy analysis tools which will help you audit your own farm and buildings.

The Farm Assessment Toolkit will help you assess your farm’s energy efficiency as well as identify areas for improvement and suggestions for energy-efficient equipment. Each assessment will take about 10 to 20 minutes to complete. The assessments collect general information about your operation to help determine if you may be able to save energy. At the end of each assessment, you will get a report with your responses and any appropriate energy tips. After completing an assessment, you can print out the report and use it to guide decisions you make to improve the energy efficiency of your operation.

You may also wish to use is the Energy Tools available from NRCS, available at These tools allow you to assess improvements that can be made to things like lighting, a greenhouse, and ventilation. They also explain the basics of things like solar water pumping.

More farm energy calculators are available on the ATTRA website at

Finally, you might be interested in Farm Energy Calculators: Evaluations and Recommendations. This 2009 report by the National Center for Appropriate Technology evaluates over 30 farm energy decision-making tools, including comments from farmer-reviewers, and includes a dozen recommendations for making these tools more useful. The report is available at

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Permalink What can you tell me about processing sunflower seeds on-farm for poultry and pigs?

Answer: Sunflowers seeds have three basic components—the hull, the oil, and the seed body. The hull is very high in cellulose and other fibrous components and is largely indigestible for pigs and poultry. If the hulls of sunflowers can be removed prior to feeding to pigs and poultry, the sunflower seeds will be a much better source of energy and protein. However, removing the hulls can be difficult. You might want to review the Rodale Press’s plans for a simple sunflower seed huller and oil press, which is available online at

The oil in sunflower seeds is an excellent source of energy for pigs and poultry. It is also commonly extracted and processed into biodiesel. On-farm oil extraction is rarely 100% complete, so even if you choose to first process sunflowers for biodiesel, the remaining material can be a good source of energy for pigs and poultry.

The seed body itself is rich in amino acids (the building blocks for proteins) as well as some energy that is available for pigs and poultry. As the crude fiber content increases, the energy value of the feedstuff decreases. Interestingly, the crude protein content (and more importantly the amount of lysine and methionine) is highest for a product that has both hulls and oil removed. This makes sense when you consider that neither hulls nor the oil contains amino acids that are available to either pigs or chickens.

Because the oil in sunflower seeds is mostly unsaturated you should limit the amount of sunflower seeds and oil fed to finishing pigs. Generally 10% sunflower seed (no hulls, but full oil) is considered “safe” to feed to pigs for the last couple of months. Feeding more vegetable oil may result in softer, oily pork fat, which may be better for your arteries, but is generally considered undesirable by consumers of pork. The soft fat issues seen in pigs when fed very high levels of vegetable oil is not as well established in poultry but may also be an issue.

In summary, the quality of sunflowers as a feed for pigs and poultry is directly related to the removal of the hulls. If you can remove most of the hulls you have an excellent source of energy and protein for your animals. If removing the hulls is not really possible, ground sunflower seeds will not really harm the animals, but they will require more feed per pound of gain due to the lower energy value of the feedstuff. General feeding guidelines for pigs and poultry are as follows:

Seeds and oil, hulls removed
Young pigs: maximum of 15% of diet
Finishing pigs: maximum of 10% of diet
Breeding stock: maximum of 25% of diet
Poultry: maximum of 20% of diet

If most of the oil is removed, these inclusion levels can be increased slightly without negatively impacting fat quality of the finished animal. If hulls are not removed, these inclusion levels should be decreased in order to support typical rate of growth and feed efficiency.

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