By Susanne von Rosenberg, UC Master Gardener of Napa County
This is the time of year when we start to prepare our soil beds for spring planting. Because Napa County has large rural areas and many households keep backyard chickens, many of us have access to free manure. Used properly, manure can be an excellent soil amendment and organic fertilizer, increasing soil fertility and tilth. But how do you make sure that you are using it properly and what concerns should you have?
Animal manures typically contain the poop and urine of animals, as well as bedding material, and often undigested or partially digested food that has passed through the animals' digestive tract. They may also contain feathers or hair. Risks associated with using animal manure include food-borne illness, excess nitrogen “burning” plants, high salt levels, herbicide residues and excess carbon.
To prevent food-borne illness, use only manures from herbivores. Do not use manure from pigs, dogs or cats; they may carry parasites that can infect humans. Even manure from herbivores (including cows, horses, goats, chickens and rabbits) can be contaminated with E. coli, Salmonella and Campylobacter bacteria, and Giardia or Cryptosporidium protozoa.
Many commercially available manures are pasteurized to kill soil-borne pathogens. If you have a source of raw manure, it's best to compost it before using. Your compost pile should reach a temperature of at least 140°F for several weeks, and you need to turn the pile several times to make sure all of the manure has composted.
Another benefit of composting manure is that it stabilizes the nutrients, enabling a long, slow release. Aging manure is not the same as composting it. Aging manure creates conditions that cause pathogens to decrease over time due to changes in moisture, temperature and nutrient availability. But pathogens are not actively killed by aging. Aging keeps them from reproducing, so populations slowly decline.
If you do want to use uncomposted manure in food gardens, then you should turn it into the soil at least 120 days before you plant crops that grow in or near the soil (such as root vegetables, but also plants such as strawberries) and 90 days before you plant trellised crops such as tomatoes or pole beans. Even if you've composted the manure, it's best to wait 90 days after you add it to the soil to plant food crops in that bed.
Of course, you can always use uncomposted manure in flower beds as long as you don't plan to eat the flowers. Be extra careful in washing vegetables from any garden beds containing uncomposted manure. People who are more susceptible to food-borne illness (including pregnant women, small children and people with compromised immune systems) should not eat uncooked vegetables from these areas.
Most manures are relatively low in available nitrogen. As with most organic fertilizers, the nitrogen in manure typically requires bacterial action to make the nitrogen available to plants. Uncomposted chicken manure is an exception. It can contain excess nitrogen (high ammonia levels) that can “burn” plants, causing leaf tips or entire leaves to dry out and die. In extreme cases excess ammonia can kill your plants. Overapplying chemical fertilizer can have the same result. Composting reduces the ammonia content so it will no longer burn plants.
On the other hand, if your manure contains a lot of bedding material, you may end up with too much carbon. The ideal ratio of carbon to nitrogen is about 30 to 1. If your composted manure exceeds this ratio, it may immobilize nitrogen in the soil and deprive nitrogen-loving plants (most annuals) of the nitrogen they need. However, high-carbon composted manure would still make a great mulch.
Finally, manures can be contaminated with herbicides such as those used on lawns, turfgrass, pasture and hay crops. Herbicide residues can remain active for a long time, even after passing through an animal's digestive system and, in some cases, even after manure is composted. These residues can cause poor germination and kill seedlings or cause new leaves to become twisted and malformed. Sensitive plants include most vegetable crops and grapes.
The residues do eventually break down and lose activity over time, particularly as they are exposed to microbes, heat and moisture. If you're getting manure from someone else, ask if the animals are eating hay or pasture treated with herbicides. If you're using manure from your own animals, avoid feeding them hay from herbicide-treated fields and avoid using herbicides on their pasture. If you purchase manure, try to get assurance that it contains no herbicide residue.
Be aware that some manures, especially cow or steer manure, can be high in salts. If you have used cow or steer manure, rotate it with other sources to give the salts a chance to leach out of the soil over time.
Napa Library Talks: First Thursday of each month. Register to get Zoom link. Thursday, February 4: Soil is the Solution: Healing the Earth One Yard at a Time.
Got Garden Questions? Contact our Help Desk. The team is working remotely so please submit your questions through our diagnosis form, sending any photos to mastergardeners@countyofnapa.org or leave a detailed message at 707- 253-4143. A Master Gardener will get back to you by phone or email.
For more information visit http://napamg.ucanr.edu or find us on Facebook or Instagram, UC Master Gardeners of Napa County.
- Author: Cheryl A Potts
I love pouring over seed catalogs and gardening magazines. I greatly enjoy picking my sweet peas and harvesting my chard and lettuce. I relish writing about gardens and sitting at our Master Gardener's table at the Vacaville Farmers Market on a sunny Saturday morning, talking with home gardeners about their plant problems and chatting with fellow Master Gardeners.
What I do not love has been trying to learn the technical side of gardening--the chemistry, the science of what makes it work. I got as far as biology in high school, but became turned off to science at the dissection of that poor frog.
However, as an adult Master Gardener, it is time I looked reality in the eye, planted my feet firmly on my nutrient-poor soil, and learn some science.
I have decided to to start with nitrogen. Why? Because it is the first number listed on fertilizer labels, and I really want to understand what that means.
Researching nitrogen, I discovered it is the 5th most common element in the universe and makes up 78% of the earth's atmosphere. Bringing it down to more useful information for a gardener, nitrogen is an essential nutrient that is a naturally an inert gas which needs to be "fixed"or drawn out of the air and converted to a form usable to a plant. Simply stated, plants without sufficient nitrogen display poor or stopped growth and/or pale green or yellowing leaves due to the fact that they are not able to make sufficient chlorophyll. Therefore, photosynthesis cannot occur.
One can recognize nitrogen deficiency by noticing spindly stems, the pale or yellowing of leaves, especially of the most mature ones, and wilting of sufficiently watered plants, even if the weather is not overly warm. It is good to know which plants are most commonly are effected by nitrogen deficiency so as to keep an eye out. These are fruit trees, vegetable plants, and broad leafed evergreens.
The good news is that gardeners can manage the nitrogen content of their soil several ways. One method is adding organic materials by actually planting crops in the fall or very early spring that fix nitrogen. These would be legumes used as a cover crop, including alfalfa, clover, hairy vetch, or peas, as these plants actually work the bacteria in the soil to absorb nitrogen from the air and place it in the tiny root nodules. This is called "nitrogen fixation". These plants, when mature, are to be chopped up and dug into the soil.
Another material to get nitrogen into the soil is manure from grass eating animals. Let the manure age at least 6 months before using to prevent burning of your plants. Poultry manure is also a good source, but let it air out for 4 months before using. Bone meal is a fast acting fertilize, but can also burn plants. Mix with water or dig it lightly into the soil. Crab meal, feather meal, alfalfa meal, soybean and cottonseed meal are all also recommend. Just be very sure to do a little research, know what your plant needs, and follow directions exactly.
So what does all this have to do with that first number on the fertilizer bag? There are always three numbers, and those numbers simply tell you what the percentage is of each of the three main nutrients found inside the box. The first number is for nitrogen, represented in chemistry by a capital "N". The second number is for phosphorus, represented by a "P", and the third number, represented by a "K" , tells you the percentage of potassium. So if you are wanting a deep green lawn or lush, green kale, you would use a product with a high first number.
So what would be the reasoning for looking for a higher second or third number? To find out, read my blog next month as I explore phosphorus. Meanwhile, work on memorizing N-P-K along with me, and you will be a tad closer to being a real science type.
- Author: Trina Wood
For home gardeners, spring is a busy time of year and there’s never a tomato with more flavor than one grown to full ripeness on the vine. But there are also many safety precautions to follow to prevent contamination of fruits and vegetables with pathogens that cause serious food-borne illnesses.
Michele Jay-Russell, a veterinarian and research microbiologist at the Western Institute for Food Safety and Security (WIFSS) and program manager of the Western Center for Food Safety (WCFS), recently co-authored a study that highlights the need to be aware of the hazards associated with using raw animal manure to fertilize home gardens. (Read full article here.)
The basis for the study began in July of 2010 when a shire mare from a rural Northern California farm was brought to the William R. Pritchard Veterinary Medical Teaching Hospital for treatment of colic. Following protocol, the veterinarians on call screened the horse for Salmonella to avoid infecting other horses during hospitalization. She tested positive and after successful treatment for colic, went home. Her owners then notified the veterinarians that some of their other draft horses were sick as well — all 8 were tested and 6 came back positive for the same Salmonella Oranienburg strain, including the mare that still had the infection.
Jay-Russell heard about the case from her colleague John Madigan, professor of medicine and epidemiology at the school. The farm’s owners invited Jay-Russell and Madigan to the farm to see if they could uncover the source of the Salmonella infection. They sampled water from horse troughs, manure storage piles, wild turkey feces and soil from the family’s edible home garden where raw horse manure had been used as fertilizer. Each of those locations had a percentage of positive samples over the sampling period from August 2010 to March 2011.
“We showed the owners how to continue collecting samples and provided them with a FedEx number to ship them to UC Davis,” Jay-Russell said. “During that whole time, the garden soil kept coming back positive, which showed that this strain of Salmonella could persist for months.”
While the researchers couldn’t be completely certain about the original source of Salmonella on the farm, they suspect that a recent surge in the wild turkey population on the property introduced the bacteria to the horses by pooping in the horse corrals and in the water troughs. They speculated that the wild turkeys brought the Salmonella onto the property, although they couldn’t rule out the possibility that the birds were exposed on the farm or to other potential sources of Salmonella.
“What is clearer is that the raw horse manure applied as fertilizer was the most likely source of garden soil contamination,” Jay-Russell explained. “We suspect that the damp climate in Mendocino County may have contributed to the longevity of this bacterium in the soil long after the owners stopped applying the horse manure to the garden. Fortunately, the owners didn’t get sick, but our investigation showed the potential for widespread dissemination of Salmonella in a farm environment following equine infection.”
To promote safe gardening practices, Jay-Russell has teamed with Trevor Suslow, a Cooperative Extension food safety specialist in the Department of Plant Sciences, to speak to groups of small farmers around the state about best practices. They also use a brochure in English and Spanish, “Food Safety Tips for Your Edible Home Garden,” that includes information about safe uses of animal manure and ways to minimize animal fecal contamination.
“It’s good to let people know about the risks and to correct misinformation about ways to treat the compost pile before using it in the garden,” Jay-Russell said. “The biggest take home message from this experience is to be very careful about using manure from sick horses — and to be cautious about offers of free manure — you don’t know what’s in there. Commercial compost should be bought from a reputable source.”
She urges gardeners to take a class and learn how to compost correctly and safely. Each county in California has UC Cooperative Extension advisors and many have Master Gardener programs offering information on food safety.
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