Agroecology AECL 1000
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This 6 page Class Notes was uploaded by Nathanael Schmeler on Tuesday October 27, 2015. The Class Notes belongs to AECL 1000 at University of Wyoming taught by Staff in Fall. Since its upload, it has received 26 views. For similar materials see /class/230318/aecl-1000-university-of-wyoming in Agriculture Education at University of Wyoming.
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Date Created: 10/27/15
Leena Horton Writer Meghan Reedy Programmer Kali Bonnell Researcher AECL 1000 November 14 2007 Ohl What to grow what to grow what to Growl When you hear the words arid and semi arid fifty inches of water a year of precipitation does not come to mind Those regions typically receive that precipitation which is hard to believe While that sounds like a great deal of water when you consider evaporation and transpiration ratios the significance begins to diminish and fifty inches quickly disappears So what is a farmer to do They cannot control the weather but they can control what they plant In those regions with a high evapotranspiration ratio the ideal answer is cover cropping While numerous plants function as cover crops these regions require something a little more and that is why legumes are the cover crop of choice The benefit of cover cropping is substantial and when that cover crop happens to be a legune the result is even better Yet when planning to cover crop your farm it is important to know the average precipitation values type of soil you are working with and what affect the cover crop is having on your soil In the western United States 80 receives less than 500 mm roughly 15 inches of annual precipitation In Africa 50 of the area has similar precipitation Australia approximately 70 Mexico 75 and South America differs between 65 and 75 on an average annual basis Holechek 2004 The remaining percentages still fall well within the 50 inches of precipitation with exceptions in areas near the equator These percentages demonstrate just how prevalent of a problem the lack of precipitation is Additionally climate models predict that average temperatures will increase Consequently the increase in temperature will affect the evapotranspiration ratio primarily the evaporation making the need for water efficient farming even more important Ragab 2002 Cover cropping is a relatively new addition to traditional agriculture but is quickly becoming standard practice The two methods of cover cropping include the planting of a crop during what would normally be a fallow year or intercropping planting a cover crop right alongside the desired crop Both methods help to contain provide an increase in organic matter when the cover crop is a legume the quality of that organic matter increases due to the additional nitrogen which results in a lower carbon nitrogen CzN ratio Because of the lower C N ratio microbial decomposition is more rapid which may result in a decrease in overall organic matter mass Gleissman 2007 Dominant soil orders within arid regions are Aridisols or Entisols depending on their maturity as determined by the accumulation of organic matter Aridisols are the more mature with a very shallow layer of organic matter while Entisols are still in the parent material stage Brady 2002 Some arid regions can have Mollisols however the presence of a mollisol suggests that there is sufficient precipitation to create a mollic epipedon that has a high accumulation of organic material The fact that the dominant soil orders lack organic matter makes it important to have a management plan that provides a large amount of organic matter In the arid regions the amount of precipitation is not conducive to dense vegetation and the unavailability of nutrients provided by organic matter makes it even more difficult to grow a crop The roots quickly extract those nutrients that are available thus rapidly depleting them Brady 2002 This makes the use of legumes as cover crop doubly beneficial as they not only provide organic matter but are also nitrogen fixers which is one of the nutrients most limiting in arid regions Cover crops in general increase primary production for subsequent crops due to the addition of nutrients organic matter and reduced water loss With legumes the increase in primary production generates additional organic carbon The nitrogen fixing microbes found in conjunction with legumes use the carbon as an energy source Tonitto 2006L A common practice for legumes is to grow them as a winter cover crop this of course is climate dependent The subsequent crops after winter cover cropping by a legume have on average an increased yield and require less fertilizer herbicide and pesticide application Sainju 2003 Popular legume cover crops include hairy vetch Vicia villosa crimson clover Trifolium incarnatum bellbean Vicia faba red clover Trifolium pretense sweet clover Melilotus officinalis field pea Pisum sativum and alfalfa Medicago sativa Tonitto 2006 Gleissman 2007 and Sainju 2003 The majority of these legumes provide not only substantial organic matter and nitrogen but they also serve as a foliage crop or pasture One legume that is quickly growing popularity is the medic species Medicago in Australia Australian farmers learned quite by accident the benefits of using medic as a cover crop during what would have normally been their fallow year Medic once considered a pest species provides a high quality livestock forage and is self regenerating As a legume it also puts nitrogen back into the soil for subsequent crops to use Farmers now use the ley system crop rotation pattern of pasture medic crop pasture medic This rotation improves soil quality and water use efficiency Groose 1999 The genus Medicago predominantly found in Mediterranean climates is uncommon in the arid and semi arid regions As a result the United States does not consider it as one of the popular legumes for cover cropping Currently researchers are trying to manipulate the genetic make up of medic so that it can be implemented in our higher elevation climes The scarcity of precipitation quality of soil and general nutrient deficiency predominantly found in arid and semi arid regions demands a detailed management program for farming Implementation of legume cover crops into the management program is easily done and the rewards are well worth it Literature Review Brady Nyle C and Ray R Weil The Nature and Properties of Soils Thirteenth Edition Upper Saddle River New Jersey Pearson Prentice Hall 2002 pp 58 88 91 98 100 103 104 233 236 Gleissman Stephen R Agroecology The Ecology of Sustainable Food Systems Boca Ragon Fl Taylor amp Francis Group 2007 pp 108 109 208 211225 Groose Robin W Lamb chops amp rolls on 12 inches of rain Casper Star Tribune 22 Aug 1999 Haan RL et al Evaluation of Annual Medicago for Upper Midwest agroecosystems Journal of Agronomy amp Crop Science 188 2002 417 425 Holechek Jerry L et al Range t Prin ipl and Practices Fifth Edition Upper Saddle River New Jersey Pearson Prentice Hall 2004 pp 51 55 Qi A et al Modelling the effects of Temperature on the rates of seedling emergence and leaf appearance in Legume cover crops Exploring Agriculture 35 1999327 344 Ragab R and Christel Prudhomme Climate Change and Water Resources management in Arid and Semi arid Regions Prospective and challenges for the 21 Century Biosystems engineering 811 2002 3 34 Sainju Upendra M Wayne F Whitehead and Bharat P Singh Agricultural Management Practices to Sustain Crop Yields and Improve Soil and Environmental Qualities The Scientif World Journal 3 2003 768 789 Tonitto C et al Replacing bare fallows with cover crops in fertilizer intensive cropping systems A meta analysis of crop yield and N dynamics Agriculture Ecosystems amp Environment 112 2006 58 72
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