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Legume Cover Crops Provide Nitrogen and Soil Benefits
- 1. Legume Cover Crops in an Organic System Julie Grossman Department of Soil Science North Carolina State University
- 3. Primary sources of N in organic systems Soil Nitrogen Legumes Animal manures
- 4. National Organic Program What it means… National Organic Program (NOP): Soil Requirement Management in Organic reduced-tillage encouraged No- or Systems 205.203(a) Select and implement tillage and cultivation practices that maintain or improve the physical, chemical, and biological condition of soil and minimize soil erosion. • . 205.203(b): Manage crop nutrients and soil fertility Application of organic residues through rotations, cover crops, and the application • Section encouraged: cover crops, composts, and of plant and animal materials manures 205.203(c) and (d): Manage plant and animal Need to build, or at least maintain soil materials to maintain or improve soil organic matter organic matter. content in a manner that does not contribute to contamination of crops, soil, or water by plant Certain inputs prohibited. Limit over- nutrients, pathogenic organisms, heavy metals, or application of nutrients. residues of prohibited substances. NOP,
- 5. Cover crop (n): A crop planted between periods of regular crop production to provide other benefits besides food production . Legume cover crops contribute up to 300 kg N ha-1 yr-1 depending on species, climate, management, and soil properties (Ledgard, 2001; Tonitto et al., 2006) Soil organic matter increases result from regular use of legume cover crops in rotation (Marriot and Wander, 2006; Wander et al., 2007)
- 6. Is the main purpose to add N, or Is erosion control in fall or to scavenge nutrients? spring a primary objective? Do you want the cover crop to provide Are root large amounts of residue to build soil diseases or carbon? plant parasitic nematodes a problem? Does the soil have a compaction Is weed suppression your main goal? problem? Will the climate and water holding capacties of your soil What species is best for influence water your climate (i.e. winter?) uptake by cover crop and ‗steal‘ water from main crop?
- 7. Providing fixed-N through winter annual legume cover crops N2 Crop residue Mineral Nitrogen Biological Nitrogen Fixation Decomposition
- 8. Decomposition and N release from legumes is a microbially-controlled process Available N decomposition Partially Microbes Humus Legume residue decomposed themselves • Nitrogen accumulation and release in legumes controlled by: • Rate of biological nitrogen fixation • Growth stage at which terminated • Residue biochemistry • Association with decomposing microorganisms • Climatic conditions; temperature and moisture
- 10. Slight Fall Cover Cover crop growth & Crop dormancy Spring kill Planting growth Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sept Crop Harvest Planting Rotation With Winter Annual Leguminous Cover Crops
- 11. Austrian Winter Pea, Hairy Vetch: AU Early Cover Whistler and Variety (Auburn Univ), winter unstated hardy Early Cover (NY), AU Hairy Vetch, Purple Merit Prosperity, USDA Subterranian clover, Denmark White Lupin, TifBlue78 Crimson Clover:AU Robin, AU Sunrise,Tibbee, Dixie Berseem clover, Bigbee http://aggie-horticulture.tamu.edu/extension/Texascrops/foragelegumes/index.html, NCAT
- 12. Winter Annual Cover Crops Cover crop Slight fall growth; Strong spring growth Cover crop kill dormancy planted Crop planting October April – May Aug-Sept Legumes Grasses Austrian Winter Pea Annual cereals: rye, wheat, buckwheat, oats Crimson Clover Hairy Vetch Subterranean Clover
- 13. Austrian Winter Pea Also called Field Peas Grown as summer crop in northern regions Succulent stems break down easily and are a quick source of available N Peas do not make a good organic mulch for weed control Susceptible to Sclerotinia crown rot Range of Austrian Winter Pea
- 14. Hairy Vetch Winter hardy, so is popular in northern regions Often contributes up to 100 lb N acre-1 to the following crop Breeding has developed early- maturing varieties: Early Cover Purple Prosperity Purple Bounty
- 15. Crimson Clover Historically thought to be one of the best cover crops for the Southeast Not winter hardy Named varieties developed at Auburn University Sunrise Tibbee Robin Dixie The ―crimson clover zone‖—east of the Mississippi, from southern Pennsylvania and southern Illinois south
- 16. Summer Annual Cover Crops Cover crop Summer Cover crop planting growth kill October April – May Aug-Sept Legumes Grasses Cowpeas Sorghum sudangrass Berseem clover Velvetbean (Mucuna)
- 17. Cowpea Native to Africa and do well in hot climates Many different cowpea varieties exist, including some intended for food (blackeyed peas, southern peas, crowder peas, etc), as well as later maturing types like Iron-Clay Rapidly form dense cover that can shade out weeds quickly
- 18. Velvetbean Mucuna pruriens The plant is an annual, climbing shrub with long vines that can reach over 15 m in length. When the plant is young, it is almost completely covered with fuzzy hairs Native to Southeast Asia, does well in warm moist climates Popular in southern U.S. from 1875-1960 Some evidence from Auburn university shows velvetbean may have nematacidal properties
- 19. Biennial and Perennial Cover Crops Grown throughout year October April – May Aug-Sept Legumes Alfalfa Red clover White clover Yellow/sweet clover
- 20. UC Davis cover crop database; a great resource! http://sarep.ucdavis.edu/ccrop/search_ccrop.html#crops
- 21. Legume N Value? 4 E q u iva le n t N P ric e ($ /lb N ) E q u iv a le n t N P ric e 3 C rim s o n c lo v e r U AN 30% 2 1 0 0 50 100 150 200 250 L e g u m e P ro d u c tivity (lb N /a c )
- 22. Legume N Value? 4 E q u iva le n t N P ric e ($ /lb N ) E q u iv a le n t N P ric e 3 C rim s o n c lo v e r U AN 30% 2 1 0 0 50 100 150 200 250 L e g u m e P ro d u c tivity (lb N /a c )
- 23. How do I know how much N is in my cover crop? 1. Determine the biomass produced. 2. Determine the nutrient levels in that biomass. 3. Predict how quickly the biomass will decompose, releasing nutrients for cash crops. 4. Calculate whether additional nutrients are required for the desired crop yields.
- 24. First step: determine your biomass 3ft 1. Find a yardstick or metal frame of known dimensions. 3ft 9 ft2 2. In several areas of your field, clip the plants at ground level You have sampled two 3x3 ft within the known area. regions of your field. The dried 3. Dry the samples in an oven at samples together weigh 2.5 lbs. about 140°F for 24 to 48 hours How much biomass per acre do until they are crunchy dry you have? 4. Calculate: ANSWER: 6,050 LB ACRE ___________________________ Area sampled: 3x3 = 9 ft2 * 2 = (18 ft2 ) 2.5 lbs * 43,560 sq ft = 6050 18 1 acre
- 25. Cover crop residue left after rolling with the crimper controls weeds and contributes N to corn
- 26. Another way to determine biomass (but not as accurate!) 1. Use height and density of You have a hairy vetch cover crop the cover crop to that is 18 inches tall and has determine biomass 100% coverage. How much biomass do you have? ANSWER: 3,800 lbs 2. At 100% ground cover and ____________________________ 6 inch height, most First 6 inches = 2000 lbs legumes contain 2000 lbs / Additional 12 inches = (150 lbs)(12 inches) = 1800 acre of dry matter 1800 + 2000 = 3,800 lbs! Less than 100% cover? Multiply by 3. For each additional inch, the percent cover you have. 60% add 150 lbs cover? (3800 lbs) (.60) = 2,280 lbs (Adapted from Sarrantonio, 1998)
- 27. Second step: determine the nutrients in your biomass • Use tissue tests or If your hairy vetch cover estimate %N in cover crop in the last example crop (3,800 lbs of biomass) • Multiply the dry biomass has 4% N at kill, how yield times the much N are you applying percentage of nitrogen. to your field? ANSWER: 152 lbs of N _____________________ (3,800 lbs/acre)(.04) = 152 lbs of N
- 28. How much N is in my cover crop? Which cover crop? Examples How much N? Legumes Hairy vetch, crimson 3-4% at flowering clover, Austrian winter 2.5-3% at seed-set pea Non-legume grasses Rye, sudex 2-3% at flowering 1.5-2.5% at seed-set Other non-legumes Brassicas, buckwheat Similar to slightly below grasses
- 30. Roots are the unknown zone of N contribution! Impressive Austrian winter pea root system!
- 31. Third step: How much N will be made available to my crop? To conservatively estimate how If your hairy vetch is incorporated much N is made available to your in the soil in early may in a normal crop over the entire growing spring, how much N will be season, multiply legume biomass available to your crop? nitrogen: _______________________ by 0.50 if the cover crop residue (152 lbs of N)(.50) = will be incorporated by 0.40 if the residue will be left on the soil surface. 76 lbs of N!
- 32. Tillage in organic systems Cover crop termination using a disk Cultivation for weed control Challenges: • Erosion • Depletion of organic matter • Energy costs
- 33. Levels of microbially-available carbon (Aka, microbe food!) in organic and conventional soils are different When organic management is combined with elimination of Organic no-tillage tillage, the result is more carbon that microbes can use for growth and development, and thus more nutrient release! No cover crop Organic w/ tillage Conventional no-tillage Conventional tillage
- 34. Systems with reduced tillage and high cover crop use have greater microbial activity 1. Microbial biomass carbon 2. Microbial biomass nitrogen Organic no-tillage Organic no-tillage Organic w/ tillage Organic w/ tillage Conventional Conventional Microbial biomass carbon (1) and nitrogen (2) across multiple sampling dates. Data are analyzed across treatments within each sampling date. Larsen, 2012
- 35. Cover crops can be terminated by a roller crimper Weed control can be impressive Large water-filled drum with chevron-shaped blades No, not this kind of crimper! Roller on front, planter on back
- 36. Total legume N contributed to rolled systems can be high Legume Biomass N (Kg ha-1) 250.0 Hairy Vetch 200.0 Crimson Clover Austrian Winter Pea 150.0 Kg ha-1 100.0 50.0 0.0 aue aum ear mel vet aur* aus* dix* tib big hub den* tif whi pea * Designates 1 year of data only Parr et al., Agronomy Journal, 2011
- 37. Termination time using a roller impacts legume N biomass in Hairy Vetch (Vicia villosa) late 250 mid early 200 Biomass N (Kg ha-1) 150 100 Unsuccessful termination causes Mid April competition with cash crop Late April 50 Mid May 0 "Early Cover" "Merit" "WinterHardy "Purple Early Cover" Prosperity" Cultivar
- 38. N is lower in overly-mature cover crops Crimson Clover Hairy Vetch Mulch Mulch
- 39. Nitrogen Release Rate from Vicia villosa using different termination approaches
- 40. What to grow, why to grow it and how to grow it! SARE publication; FREE!
- 41. The good stuff! http://grossman.soil.ncsu.edu
- 42. And we couldn‘t get it done without the students ….. Thanks! Projects supported by the Fulbright, Natural Resources Conservation Service Conservation Innovation Grant, and USDA Organic Transitions Programs.
Editor's Notes
- My main goal for the next 40 minutes is to help you understand the range of research conducted by my lab which, as its broad goal, explores the ways in which we can better manage plant-soil-microbe relationships in order to develop sustainable food production systems. Specifically we have been exploring how legumes can be a critical piece of both organic and conventional farming systems, and describe some of the work my group and I do to try to answer timely research questions to help farmers use legume cover crops to their maximum potential.
- Congress passed the Organic Foods Production Act of 1990 in order to establish national standards for how organic foods are produced. This legislation requires that all except the smallest organic growers have to be certified by a State or private agency accredited under national standards. USDA implemented this legislation on October 21, 2002. Soil fertility management practices in organic systems include those that increase or promote 1) soil organic matter, 2) biological activity and 3) nutrient availability.
- Legume cover cropos are often used in rotation with cash crops to meet some of the goals set forward in organic agricultureA cover crop is…Benefits arising from cover crop use include Such contributions can result in corn yields that meet (Drinkwater et al., 2000; Utomo et al., 1990) or exceed (Gallagher et al., 2003) HBN-fertilized corn.
- While a cover crop can be a legume or a non-legume, one of the primary ways that organic growers bring N to their crop plants is through the process of biological nitrogen fixation mediated through legume cover crops. Biological Nitrogen Fixation: plant-bacteria relationship through which plants can use atmospheric N otherwise unavailable to themMaize picture from free clip art: http://plants.phillipmartin.info/plants_corn_plant.htm
- Even if legume- based N fertility reliably meets crop N needs, large N losses from these systems would be environmentally problematic. increased storage of N within the soil OM fractioncan leave a pool of N vulnerable to loss if N is mineralized in excess of crop needs (Baggs et al., 2000; Rosecrance et al., 2000; Crews and Peoples, 2005).
- A wide range of legume possibilities exist that could be terminated using the roller crimper
- Cover crops are typically planted between rotations of income-producing crops, but they can also be planted at the same time.
- The Austrian winter pea is a low growing vine annual legume. It is sometimes called a black pea or field pea. It has a hollow, slender, succulent stem that is 2-4 feet long. The Austrian winter pea pods have 3-5 round dark seeds that are commonly mottled with purple or brown spots. The foliage is pale green and the flowers are purple, pink or reddish. Peas prefer well-limed, well-drained clay or heavy loam soils, near-neutral pH or above and moderate fertility. They also do well on loamy sands in North Carolina. Field peas usually are drilled 1 to 3 inches deep to ensure contact with moist soil and good anchoring for plants.If you broadcast peas, incorporation will greatly improve stands, as seed left exposed on the surface generally does not germinate well. Longvined plants that are shallow-seeded at low seeding rates tend to fall over (lodge), lay against the soil and rot.
- ith its rapid, robust growth, crimson clover provides early spring nitrogen for full-season crops. Rapid fall growth, or summer growth in cool areas, also makes it a top choice for short-rotation niches as a weed suppressing green manure. Seed six to eight weeks before the average date of first frost at 15 to 18 lb./A drilled, 22 to 30 lb./A broadcast. As with other winter legumes, the ideal date varies with elevation. In North Carolina, for example, the recommended seeding dates are three weeks later along the coast than in the mountains.Don’t plant too early or crimson clover will go to seed in the fall and not regrow in spring until the soil warms up enough to germinate seeds.
- Cover crops are typically planted between rotations of income-producing crops, but they can also be planted at the same time.
- Cover crops are typically planted between rotations of income-producing crops, but they can also be planted at the same time.
- We began by addressing the question of appropriate timing of legume kill using the roller/crimper by killing each of the 14 legume populations at 3 different kill dates: mid-April, late-April, and mid-May. Biomass was taken from each plot after rolling and N quantified.
- If the stand has less than 100 percent ground coverage, multiply the total weight by the percentage of ground covered, represented as a decimal number (the percentage divided by 100). If the percentage of ground covered in the example above is 60 percent, then the weight of the dry matter is: 3,800 X 0.60 (60/100) = 2,280 pounds of dry biomass (Adapted from Sarrantonio, 1998)
- Determining the ratio of carbon to nitrogen (C:N) in the cover crop biomass is the most common way to estimate how quickly biomass N will be mineralized and released for use by cash crops. As a general rule, cover crop residues with C:N ratios lower than 25:1 will release N quickly. In the southeastern U. S., legume cover crops, such as hairy vetch and crimson clover, killed immediately before corn planting generally have C:N ratios of 10:1 to 20:1 (Ranells and Wagger, 1997). Residues with C:N ratios greater than 25:1, such as cereal rye and wheat, decompose more slowly and their N is more slowly released.
- One common management tool used in organic agriculture is that of tillage, which is used for both weed control as you can see here in the first slide, and for cover crop termination. This causes challenges such as erosion, organic matter depletion and increase in energy costs as more fuel is used for the increased number of operations.One of the major goals of organic agriculture is to reduce tillage, but you can see how this would be difficult
- Reducing tillage also helps us achieve one of the other goals set forth by the national organic program – that of increasing soil biological activity.Research conducted by Erika Larsen in our lab supports the idea that systems that reduce tillage in combination with increased carbon-rich inputs, such as are found in organically managed systems, can result in increased pools of microbial carbon and nitrogen.When comparing microbial biomass across long term organic and conventional systems each with a tillage and no-tillage component, we can see the increases reuslting when organic management is combinned with the elimination of tillage. Additional research conducted by Erika also show increases in additional labile C and N pools, such as particulate organic matter in these same treatments, serving as a slowly-available nutrient source for cash crops. However, due to weed control issues, yields in these no-till organic systems can be extremely low, a chalenge other researchers are grappling with.
- An alternative method for cover crop termination with which our lab has been playing around with is known as a roller crimper….Oh wait! Not THAT kind of crimper! Lets try that again…
- In Mary Parr’s masters research we investigated the total N contributions from a wide range of legume species and varieties and found that some species, such as hairy vetch, provided up to 100% of the N requirments of corn, whereas others fell a bit below the crop’s N requirements.Corn normally requires 134-179 kg ha-1 (120-160 lbs N acre yr )kg/ha × 0.89 = lbs/acre Vetch delivered 150 – 180 lb N acreBigbee:Hubam: sweet cloverDenmark: SubterranianclovrTif = LupinAll biomass data for mid-May except those denoted by * where the optimum date was late April
- I mentioned earlier that we have some decisions that can be made in timing of termination. So what happens when we kill the cover crops at various points using the roller crimper? Well, logically the longer we let the cover crop grow in the field the more N that accumulates in the legume tissue. Early termination at a point when it may be more reasonable for corn planting, such as in early to mid april, isn’t an option due to insufficient termination of the cover.
- We have also found that when corn is planted into legume residue that was not killed until seed had almost set, that we sometimes observed N deficiency symptoms in the corn, an observation corroborated by the soil N data. In summary, we have learned that when using the roller crimper timing is everything and may not fit all systems in terms of optimizing both N delivery, competition with a cash crop and weed control.
- After looking at the N-dynamics under rolled legumes, we realized that there may be differences in the way that legume species release available N when using different termination approaches in the spring. Matt Brown is exploring this research question using time series of both traditional soil N extractions as well as PRS plant root simulator probes to measure flux of available N under decomposing mulches. He is comparing rolled systems to those that are flail mowed and left on the soil surface, and those that are mowed and incorporated into the soil using tillage (here seen as ‘till’), with the hypothesis that the incorporated residues may release N at a faster rate. Here you see the prs probe data for hairy vetch residues. The data supports our hypothesis that incorporated residues do release N at a higher rate, especially within the first few weeks after termination. For more on Matt’s findings stay tuned for his defense seminar this fall!