The New Agriculture Network's on-line newsletter with seasonal advice for field crop and vegetable growers interested in organic agriculture.
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Soil organic matter in a continuous corn cropping systemLowell Gentry and Sieglinde Snapp
Crop and Soil Sciences, Kellogg Biological Station
Soil organic matter (SOM) plays a critical role in fertility, water holding capacity, aggregate stability, tilth, and overall soil quality. It has been estimated that 50 percent of the SOM of most soils was lost in the first 100 years after the agricultural conversion of prairies and savannahs. A major goal of the USDA/NRCS has been to decrease soil erosion through practices such as reduced tillage, contour farming, grassed waterways, and buffer strips. These techniques have been instrumental in saving billions of tons of topsoil and have helped conserve SOM levels across the United States, especially on vulnerable lands.
Surprisingly, results from a long term rotation experiment initiated in 1993 at the Kellogg Biological Station (KBS) indicate that SOM has not increased under a continuous corn cropping system during the past 15 years, but rather has increased for a four-year rotation of corn-corn-soybean-wheat (see Figure 1).
| Figure 1. Soil organic matter levels in a continuous corn cropping system versus a four-year rotation during the past 15 years. |
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In 1993, this sandy loam soil had 1.5 percent organic matter. After 15 years, SOM has remained the same for the continuous corn cropping system; however, there is a significant increase in SOM due to crop rotation; and a trend for increased SOM for soil receiving cover crop inputs.
Here we explore several possible explanations for this observation: A) microorganisms in low organic matter soils (1.5 percent SOM) may be carbon limited and have a greater propensity to degrade corn residues; B) diversity and quality of biomass inputs may contribute to carbon sequestration; C); greater living cover exists in the rotation (especially when using cover crops) compared with continuous corn (see Figure 2); and D) corn grown in northern latitudes becomes source limited and partition more dry matter to grain.
| Figure 2. Months of continuous living cover during a four-year period. |
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In regard to explanation C, a corn crop only has living roots in the soil for about five months per year, or 20 months over a four-year period. A corn-corn-soybean-wheat rotation has living cover for about 33 months, and adding cover crops such as interseeding crimson clover into corn and frost-seeding red clover into wheat provides living roots for a total of 40 months. We believe that continuous living cover likely plays a role in building SOM over time.
In regard to explanation D, source limitations (sunlight) lead to a physiological response of corn where more kernels are set than can be filled, and in an attempt to fill those kernels the plant is forced to cannabolize dry matter from the leaves and stalks to make grain. In 2006, the continuous corn plots at KBS produced 159 bu/A of corn with 135 lbs of N/A. The harvest index of this crop, which is the ratio of the amount of grain divided by the entire above ground plant biomass, was 59 percent (many working agricultural models use a value of 50 percent for harvest index). A high harvest index directly reflects the increased partitioning of dry matter from the leaves and stalks to the grain. Therefore due to light limitations in northern states, continuous corn cropping systems return less stover than is generally expected and this may be part of the reason why SOM has not increased in the continuous corn plots over the past 15 years.
Today, with the high price of organic corn, there may be some temptation to grow second year corn. However, we need to remember the benefits of crop rotation, such as improved soil fertility, reduced soil erosion, breaking pest cycles (weed, disease, and insect problem), and spreading the workload. These results from the Living Field Laboratory demonstrate the need for long-term research studies to quantify the accumulative benefits of both crop rotation and the use of cover crops on SOM. For more information about our long-term research site, go to the Living Field Laboratory at: www.kbs.msu.edu/faculty/snapp/LFL.php
Abram J. Bicksler and John B. Masiunas
University of Illinois
Canada thistle (Cirsium arvense) is a vigorous, perennial weed that spreads by a fibrous root system or wind blown seed. Canada thistle is considered a noxious weed and has become a common problem of sustainable and organic farms. What makes Canada thistle such a problem weed? It can rapidly spread, forms dense patches, suppresses growth of crops, and is poorly controlled using standard approaches. Tillage can cut the roots into small pieces, spreading patches; tillage equipment can also carry root pieces to new sites. Mowing must start at thistle flowering and be repeated numerous times. Common winter annual cover crops (i.e. cereal rye, hairy vetch, wheat) are not present during the most susceptible growth stages of Canada thistle.
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What are the key factors to controlling Canada thistle? It is a long-day plant; flowering and seed production starts in July through August. Shoots must be killed to prevent seed production. Emerging Canada thistle seedlings will not survive shading from other plants. Grow competitive crops that rapidly close canopy. Thistle plants store sugars and other carbohydrates in their roots. The stored carbohydrates allow thistles to overwinter and emerge in the spring or after disturbance. Established Canada thistle is best controlled after emergence at the beginning of flowering, when root carbohydrate reserves are lowest. Depletion of these reserves will reduce the thistles’ fitness and ability to re-grow from roots.
| Our research combined tillage, summer annual cover crops, and mowing to control Canada thistle. Sudangrass alone or combined with cowpea (70:30 sudangrass:cowpea) produced 13 to 14 Mt/ha of biomass. Sudangrass alone or combined with cowpea caused a 96 percent reduction in thistle density in the first growing season. One year after planting sudangrass, thistle numbers were still below 10 percent of the beginning densities. Neither buckwheat nor a summer fallow adequately suppressed Canada thistle. Mowing is less important for reducing thistle fitness and survival compared to the Sudangrass cover crop. We recommend disking thistle-infested areas several times during the spring to eliminate emerged thistle, prevent flowering, cut roots into small pieces, and create a uniform seed-bed for sudangrass. In early June, drill a sterile sudangrass hybrid such as “Special Effort” at 55 lbs/acre into the freshly prepared seedbed. The thick sudangrass canopy can shade out Canada thistle. Sudangrass may be mowed when 4 to 6 feet height to manage cover crop growth and prevent flowering of surviving Canada thistle. Use a flail mower to create a surface mulch and encourage sudangrass regrowth and tillering. In late fall or early spring, incorporate the sudangrass residue into the soil and plant a competitive crop. Use cultivation, hand-removal, or spot treatment with herbicides or flaming to control any remaining Canada thistle. |
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Abram Bicksler, John Masiunas, and Dan Anderson
University of Illinois
Canada thistle, also called creeping thistle, California thistle, and field thistle, Cirsium arvense, is a vigorous, competitive perennial weed that can establish from seed or wide-ranging, deep creeping roots. It is native to Europe, parts of North Africa, and the Middle East, and was introduced to North America in the early 17th century and has spread extensively. Canada thistle is a problem throughout the Midwestern United States on organic, sustainable and conventional farms. Cirsium species are troublesome weeds in organic cropping systems of northern Europe.
Distinguishing Canada thistle from other thistles.
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| Canada thistle seedheads. | Mature plant with purple flowers. | Canada thistle rosettes soon after emergence. |
Canada thistle can be distinguished from other thistles by three characteristics: 1) creeping horizontal lateral roots, 2) dense clonal growth, and 3) small dioecious (contain both male and female parts) flower heads (Nuzzo, 1997). Moreover, Canada thistle can be differentiated from other Cirsium and Cardus species by the following traits: 1) small dioecious flower heads <1 inch high; and 2) stems not conspicuously spiny-winged. Up to four varieties of Canada thistle have been recognized across the world, based predominantly upon their leaf morphology and pubescence. Canada thistle may change morphology in response to environmental conditions, and various ecotypes may respond differently to management practices.
Limitations to Canada thistle spread
Canada thistle is the most frequently declared noxious thistle in this country. Canada thistle requires a day-length of at least 14 to 16 hours for flowering to be induced, depending on ecotype. Canada thistle can survive winter temperatures of -17o F but is limited in its southerly distribution in the United States because it is less successful in hot, dry climates. It is generally a serious weed problem in areas receiving 18 to 36 inches of rainfall a year and it thrives on deep, productive well-aerated soils that do not become too warm. Optimum growth occurs at daytime temperatures of 77o F and nighttime temperatures of 59o F in soils with high nitrogen.
Thistle flowering and seed production
Thistles flower from July to September and sometimes into October. Seeds become viable within 8-10 days after flower opening, and an individual plant may produce from 5,000 to 40,000 seeds a year. There are conflicting reports about the number of days after flowering that a plant can be cut and still produce viable seed. Viable seed may be produced if the plant is cut down 4 days after flowering, 7 to 9 days after flowering, or 10 to 11 days after flowering. A small proportion of seeds (0.2 percent) can disperse one-half mile or more from the parent plant; thus, Canada thistle is difficult to prevent even if you are using best management practices. Canada thistle seeds float and are easily spread by flooding or in irrigation water from surface sources. Viable seeds can also be dispersed in manure. Canada thistle seeds germinate best in the top one-third inch of soil at temperatures averaging from 68o to 86o F. Approximately 60 to 90 percent of seeds germinate within one year; however, some seeds can remain dormant in the soil for up to 20 years. The deeper the seed is buried, the longer the viability.
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| Canada thistle seed (enlarged) and seedling. | |
Seedlings
Seedlings are sensitive to competition for light and are unlikely to survive in competition with established plants. Once established, however, Canada thistle spread is primarily vegetative in both agricultural fields and in natural communities. Within 8 to 10 weeks of emergence, seedlings develop a taproot and spreading lateral roots that can penetrate to over 2 feet after 6 months. The horizontal spreading lateral roots can grow up to 25 feet in one season, but most patches spread at the rate of 3 to 7 feet per year. At the base of these spreading lateral roots, adventitious buds develop, rendering the plants able to regenerate if hoed or cultivated.
Roots and vegetative reproduction
Edges of shoots can pinpoint the spread of the patch, because roots do not spread far beyond aboveground shoots. Most regeneration occurs from roots within or just below the plough layer. Most root buds are produced in the center of the Canada thistle patch, and each foot of root can average 4 to 8 root buds. The greatest Canada thistle shoot density corresponds to regions with the most underlying root biomass and adventitious root buds. The densities of adventitious root buds are three to five times greater in late summer than in spring. Cultivation stimulates the growth of horizontal roots, which increases the number of new vertical shoots borne by the chopped horizontal runners. Root fragments smaller than 1 inch in length may not re-grow, whereas root fragments 2 to 3 inches long readily regenerate shoots. Adventitious root buds are inhibited when the main shoot is present. If the main shoot is removed by tillage or mowing new shoots can emerge rapidly. In outdoor boxes, a single C. arvense plant was able to produce 26 emerged adventitious shoots, 154 adventitious root buds, and 360 feet of roots after just 18 weeks of growth. Even in systems that use herbicides, such as glyphosate, dose-response and time-course experiments have shown that the herbicide is more likely to reduce root bud numbers and secondary shoot re-growth potential than overall root biomass, still rendering Canada thistle able to regenerate.
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| Two-year root growth of Canada thistle from an original one-foot length of root (from Merrill Ross. Control Practices for Canada Thistle). | |
Control strategies should aim to deplete carbohydrate reserves. Carbohydrate reserves are stored in roots rather than in shoot bases or root buds, and that these reserves can range from as low as 3 percent of root fresh weight in spring to as high as 26 percent of root fresh weight in the fall. Canada thistle carbohydrate reserves were lowest from May through August, increased in the fall, and then began decreasing in April. In growth chamber experiments, carbohydrate movements to and from the roots correspond to environmental conditions typical of fall and early spring. Moreover, environmental cues seem to supersede growth stage control of carbohydrate movement. Development of root buds is highest in the autumn when short days and moderate temperatures dominate, and root bud elongation is greatest with the long days and high temperatures of summer.
In addition to regeneration from root buds, Canada thistle shoots can grow from lateral buds at internodes on stem segments. These shoot pieces then survive if partially buried in the soil. This capacity to regenerate from root and stem fragments is particularly troublesome, as cultivation has been used for Canada thistle control.
Canada thistle impact on crops.
Canada thistle causes extensive crop yield losses through competition, and perhaps, allelopathy (release of inhibitory chemicals). The prickly mature foliage increases harvest difficulty and deters livestock from grazing. A density of 2 Canada thistle shoots per 1 ft2 caused yield losses of 34 percent in barley, 26 percent in canola, 36 percent in winter wheat, and 48 percent in alfalfa grown for seed. In addition to deterring livestock grazing and competing with crops, Canada thistles’ shoots, roots, and leaf litter can reduce shoot and root growth of other plants through allelopathy.
Canada thistle and other perennial weeds are very difficult to control once established, so any management strategy must also prevent their introduction and spread. Canada thistle spreads as a contaminant in crop seed, hay and packing material. Additionally, it can be spread in soil attached to vehicles and farm equipment. Thus, using clean seed, hay, and packing material and cleaning equipment are important for preventing Canada thistle from being introduced or from spreading once on a farm.
There are a few key places in the Canada thistle life cycle that are most susceptible to management. Thistle seedlings are very sensitive to competition for light and cannot survive in dense competitive stands of established plants. Canada thistle seedlings were very sensitive to plant stand density, light, soil aeration, and soil moisture conditions. The seedling to rosette and the rosette to flowering transitions, when root food reserves are at a minimum, are particularly important times for reducing Canada thistle populations. During July to October, carbohydrate reserves accumulate in thistle roots while from May to July the carbohydrate reserves are at their lowest. The lowest root carbohydrate reserves in Canada thistle occur just before flowering. If insect (such as stem-mining weevil) feeding on Canada thistle shoots occurs just before flowering, levels of carbohydrates in the root system tend to be reduced. Moreover, if shoots are tilled between the 7-10 leaf stages (for plants originating from 5 cm and 20 cm root fragments, respectively), minimum re-growth is observed. Drought stress on Canada thistle also increases the efficacy of mechanical control. Several years of drought can reduce perennial root biomass and decrease adventitious bud production, limiting adventitious shoot production.
In conclusion, you should focus on maximizing early spring rosette and seedling mortality. Reducing seed production and inhibiting the survival of newly shed seeds is also important, but persistence of seeds that are already in the soil seed bank has little effect on population growth because of the importance of vegetative propagation in Canada thistle patch growth.
Selected Sources
Bond, W. and R. Turner. 2006. The biology and non-chemical control of creeping thistle (Cirsium arvense). HDRA online publication: www.organicweeds.org.uk
Doll, J. D. 1997. Controlling Canada thistle. University of Wisconsin-Madison: North Central Regional Extension Publication. No. 218.
Donald, W. W. 1994. The biology of Canada thistle (Cirsium arvense). Rev. Weed Sci. 6:77-101.
Doyle, S., M. Morgan, and S. K. McDonald. 2005. Organic noxious weed management. Canada thistle, Cirsium arvense Family Asteraceeae. www.cepep.colostate.edu/factsheets/CanadaThistle.pdf
Graglia, E. and B. Melander. 2005. Mechanical control of Cirsium arvense in organic farming. 13th European Weed Research Society, #4600. http://orgprints.org/4600/01/4600.pdf
Graglia, E., B. Melander, and R. K. Jensen. 2006. Mechanical and cultural strategies to control Cirsium arvense in organic arable cropping systems. Weed Res. 46:304-312.
Gustavsson, A-M. D. 1997. Growth and regenerative capacity of plants of Cirsium arvense. Weed Res. 37:229-236.
Haderlie, L. C., S. Dewey, and D. Kidder. 1987. Canada thistle biology and control. University of Idaho Cooperative Extension Service: Bulletin No. 666.
[HDRA] Henry Doubleday Research Association. 2006. Creeping Thistle Management Strategies in Organic Systems. Available:www.organicweeds.org.uk.
Hogdson, J. M. 1968. The nature, ecology, and control of Canada thistle. U.S. Department of Agriculture Technical Bulletin: 1386.McAllister, R. S. and L. C. Haderlie. 1985. Seasonal variations in Canada thistle (Cirsium arvense) root bud growth and root carbohydrate reserves. Weed Sci. 33:44-49.
Nuzzo, V. 1997. Element Stewardship Abstract for Cirsium arvense. The Nature Conservancy. Arlington, VA.Sullivan, P. 2004. Thistle control alternatives. ATTRA NCAT www.attra.ncat.org/attra-pub/PDF/thistlecontrol.pdf
Vicki Morrone, MSU CS Mott Group for Sustainable Food
Mark your calendars: on September 18 there will be an Equipment Day for vegetable farmers featuring demonstrations that may help streamline many steps of small-scale vegetable production including:
- Soil management
- Irrigating
- Mulching
- Weeding
- Transplanting
- Cooling for transport
- Bed formation
- FSA and Credit Union representatives
The event will take place September 18 from 9:00AM to 4:00PM at the Southwest Michigan Research Center (SWMREC), 1791 Hillandale Road, Benton Harbor, Michigan, 49022.
Cost is $25 per person before September 12 and $30 per person after this date. A box lunch is included.
Trade booths are available for $50 until September 12 and $75 after this date, including walk-ins. Price includes registrations for two people, a table and two chairs.
Register online (www.MichiganOrganic.msu.edu) or by mail (303 Natural Resources, East Lansing, Michigan, 48824), make checks payable to Michigan State University.
Questions contact: Vicki Morrone, (517) 353-3542. This program is sponsored by the USDA Farm Service Agency and the CS Mott Group for Sustainable Food Systems at Michigan State University.
Take a break from your own labors on this last holiday of the summer and visit Whethem Organic Farm. Learn about organic food and farming, why local production is important, and how you can find all kinds of locally grown food. If you have questions about how organic food is produced, the techniques and materials used, this is your chance to get answers. Information will also be available on their Community Supported Agriculture (CSA).
The tour will be held on Monday, Sept. 1 (Labor Day) from 11 AM to 3 PM at Whetham Organic Farm in Flushing, Mich. Walking tours of the farm begin at noon and 2 PM. This is a perfect time to show the kids where food comes from and give them a chance to dig a few potatoes or carrots. Fresh produce will be available to purchase.
There is no charge for this event, but please let them know you are coming by leaving a message at 810-867-4435.
Directions: 11230 W. Mt Morris Rd in Flushing Township. Approximately 7 miles west of I-75 (exit 126); 10 miles north of I-69 (exit 123) to Mt Morris Rd, then 1 ½ miles east; 4 miles south of M-57 on M-13 to Mt Morris Rd, then 1 ½ miles east.
Shari Hawley, Southern Sustainable Agriculture Working Group
2009 Practical Tools and Solutions for Sustaining Family Farms Conference January 21-24, 2009, Chattanooga, Tennessee.
Southern Sustainable Agriculture Working Group’s (Southern SAWG) 18th annual conference will be held January 21-24, 2009 at the Chattanooga Convention Center in Chattanooga, Tennessee and will headquarter at the adjacent Marriott Hotel.
Pre-conference events begin on Wednesday and include one-and-a-half day intensive short courses as well as several half-day field trips and mini courses. Then on Friday and Saturday, the general conference will offer eight tracks of highly essential conference sessions, a trade show, silent auction, video show, Taste of Tennessee dinner and more.
The general conference offers sustainable production and direct marketing information for horticultural and livestock producers, enterprise management lessons, farm policy education, community food systems development training and the opportunity to have a nice, long chat with peers from across the South.
The conference schedule will be available in October at www.ssawg.org or call 678-494-0696 to request a brochure. See you in Chattanooga at the EVER-PRACTICAL Southern SAWG conference!
Illinois
Northern Illinois, Kane County – David Campbell of Lily Lake Organic Farm
August has been our driest month so far this growing season although we still continue to receive generous rainfalls. We received 2.5 inches in one day last week. Aside from that, we’ve had many cool, dry days, along with heavy morning dews. Both corn and soybeans are looking good, but are behind in maturity.
We will be caught up with hay harvest tomorrow. We are weeding soybean fields presently. Weed pressure is very light this year in my bean fields despite all of the rain, although later than normal planting dates have most likely diminished weed populations. I will be spreading gypsum later this week on all of my oats/clover and hay ground that will be planted to winter wheat.
I am planning to moldboard plow, following right behind with my disk and drag in my oats/clover fields and most of my hay fields early in September. This will be in preparation for winter wheat planting scheduled to take place around the end of September.
West Central Illinois, Fulton County – Anne Patterson of Living Earth Farm
It continues to be quite cool for August. The last few nights have been in the mid 50s with highs in the low 80s. We’ve had 0.4 inches of rain since August 13, with a total of 0.6 inches for August. It is cool, dry and sunny and seems more like September than August.
The August greens such as spinach, carrots, lettuces, tatsoi, mizuna, kale, white turnips and arugula need water to get germinated, so I have had to use sprinklers. Because it is a fairly small area that has been planted, I have not set up any drip tape system.
I am looking beyond summer crops and now concentrating on fall/early winter crops. Although I have harvested more than enough tomatoes per week for my e-customers and one farmer’s market, many of the vines are struggling due to wilt and the length of my tomato season will be shortened. The markets in central Illinois are selling tomatoes at rock bottom prices many at below $2/lb., including heirlooms.
I am mowing old beds, tilling and planting winter soil builder seed, which is 40 percent bell beans, 25 percent field peas, 25 percent common vetch and 10 percent cayuse oats on some beds and cold soil builder of 85 percent hairy vetch and 15 percent cereal rye on remaining areas.
I am harvesting cucumbers, tomatoes, tomatillos, okra, ground cherries, black berries, potatoes, peppers, cantaloupe, melon, chard, beets, basil, parsley, eggplant, and summer squash for e-customers and farmers market.We had our “Country Sprouts” educational hands-on morning on August 12 with 25 first through third graders and four chaperones attending. These were summer camp kids from the local YMCA of Canton.
We had a fruit and vegetable treasure hunt, planted some transplants, made salsa and painted gourd houses from gourds I had grown last season. The kids were really into this event. Asking lots of questions and eating things right out of the field at times. The event was run by my intern and part-time employee. They did a great job!
During the next two weeks I will continue to do all the things regarding harvesting and marketing with minimal outside help. Farmer’s market goes through September 24 and e-customers to October 8. All remaining fall crops are being grown for a restaurant using primarily local produce. My original hope was to go through October 29 for e-customers, but due to severe crop loss I will end season a little earlier. I plan to get all beds cleared and into a winter cover crop (see above seed mixes I use).
I have decided to keep outside employee use to a minimum of 18 hours per week through the remainder of the season. I’ll continue to keep new fall and winter crops watered. I will weed bramble patch and mulch for winter. I still want to build some new raised beds and I am considering buying a used hoophouse not far from my farm.
Minnesota
Western Minnesota, Lac qui Parle County – Carmen Fernholz
I finished up small grain harvest last week with the flax crop. All of the small grains including winter wheat, oats and barley were average to a little above average in yield. I am currently doing primary fall tillage in some of these fields in preparation for winter wheat and winter barley seeding, which I hope to complete by September 10. I will be trying some companion seeding trials with clover and alfalfa to see if I can get a good enough take on these legumes to allow them to survive through the winter.
Third cutting of alfalfa was completed several weeks back. Corn crop is still seeing the results of the severe wind storm of July 31 and there is not much hope for a good crop. Soybeans, however, do look good and I think we are over the peak infestation of aphids. I had a phenomenally high number of Asian beetles in my fields which did not spare me some yield damage from the aphids, but did succeed in lessening the impact for most of the infestation period. I am looking at some new treatments for next season that we will be doing some trials on at the Lamberton research station.
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