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Cover crops are used by many farmers, but very few know how much nitrogen (N) or dry matter they are getting from their cover crops. There are some methods in the literature for estimating cover crop contributions. We are evaluating these methods in on-farm WSARE-funded trials in the Northern Willamette Valley to find the most practical and accurate method for use on farms. The vast majority of research in this area has been done with single species cover crops. Since farmers in Oregon often use cover crop mixtures, we are evaluating these methods on mixtures chosen by the farmer collaborators. The three methods described below provide different approaches you can use to evaluate N and dry matter contributions from your cover crops. At the end of the project we will report how they worked for us.
OSU’s publication Using Cover Crops in Oregon, publication EM 8704 available through the Extension Service Publication and Media Catalog, describes how to measure the fresh weight of a cover crop to get estimates of N-contribution. This method is based on years of research with single species cover crops in the Willamette Valley. The % N in several legume species was tested and conversion factors where developed to simplify estimates the N contribution of a cover crop based on fresh weight of the cover crop. To use this method, cut the leaves and stems from representative 16 ft2 sections in your field. This should be done when the canopy is dry but not wilting. Weigh the fresh cover crop and multiply by the conversion factor for your species (table 1) to estimate total N, they recommend dividing the answer by 2 to estimate the lbs N/acre that will be available to the subsequent crop. One challenge using this method is that cover crop canopies are often wet during the spring. The method relies on rough estimates of %dry matter and %N in cover crops that can vary under different moisture regimes and at different growth stages.
|Cover Crop||N Factor|
|Austrian winter pea||8|
|Fava bell bean||
|Hairy or lana vetch||9|
|Kenland red clover||10|
Table 1. N factor for various legumes (EM 8704)
Marianne Sarrantonio’s Northeast Cover Crop Handbook (1994) describes an entirely different approach to estimating cover crop N and dry matter contributions based on canopy height and % ground cover. This method uses look up tables found in the book that we have not reprinted here. To measure % ground cover one needs a strong piece of cord about 27’ long. Every 6” for 24 ½’ draw a thin band around the string with a permanent marker (making 50 bands). Tie each end of the string to a stake and stretch the string tightly across the cover crop. Then walk next to the string and look straight down to count the number of points directly above or below any part of a cover crop plant. Repeat this once in an area and add the two numbers together to get the estimate of % ground cover, and record an estimate of average canopy height. This procedure should be repeated in at least 3-5 representative parts of the field. Next, use the look up tables published in the Northeast Cover Crop Handbook (pp. 31-34) to find an estimate of the dry matter contribution. Finally, use the table on pg. 41 of the book to estimate the %N in the dry matter to estimate total N contribution. Remember to divide this value by 2 to estimate plant available N.
A third method, also described in the Northeast Cover Crop Handbook uses laboratory forage analysis for total %N and % dry matter analysis. If the lab only reports results as % crude protein, divide this value by 6.25 to estimate total %N. In our project we are cutting the cover crop from representative 4ft2 quadrants in the cover crop stand. Be sure to take at least 3-5 samples from a field. Record the fresh weight of the 4ft2 sample, remove a representative subset of the sample and record the fresh weight. Immediately send the samples to the laboratory for analysis. The following formulas will help you convert the lab results into estimates of lbs dry matter/acre and total N/acre contributed by the cover crop.
• Total lbs dry matter/A = 4ft2 quadrant fresh weight x % dry matter x 10890
• Total lbs N/A = Total lbs dry matter/A x %N
• Estimated plant available N = (Total lbs N/A) / 2
The final method we are using in the WSARE trials involves separating each species from the 4ft2 quadrant to test them separately. This will allow us to get more accurate estimates of the proportion of each plant in the mixture. We will compare the results of the three simpler methods to this more labor intensive method to find the most accurate and practical method for estimating cover crop N and dry matter contribution from multi-species cover crops on farms. In the meantime, you can choose the method that best suits your situation. Be aware that all these methods can only provide estimates of cover crop N and dry matter contributions, but they are likely to be more accurate than guesswork.
In this free introduction course, you will learn what exactly is "urban agriculture," along with essential definitions and concepts to help you get started on this exciting journey!
Throughout this intro course, you will explore some of the scholarly literature in the field of urban agriculture and investigate and record the basic requirements of your single chosen crop.
By the end, you will have a good understanding of urban agriculture and will know if you would like to continue in the series.
This course is part of ourOnline Urban Agriculture Program. Other courses in the series include:
You can take this course by ...Read full story.
This 3-video presentation revisits a live workshop by Susan Schoenian. Learn about SIPM-Sustainable Integrated Parasite Management in Goats and Sheep. Speaker: Susan Schoenian, Sheep and Goat Specialist at the University of Maryland's Western Maryland Research & Education Center. She represents the American Consortium for Small Ruminant Parasite Control.
Gastrointestinal parasites of sheep and goats are becoming increasingly resistant to currently available commercial de-wormers. Parasite loads not only reduce performance, but can lead to animal death. When sold, infected animals may spread parasites to other pastures. Learn more sustainable methods at this presentation.
Access these three webinar presentations at the reduced price of $25. The links are listed on your registration confirmation. After you have watched the three presentations, contact Maud ...Read full story.
In this Urban Agriculture Systems online course you'll learn the foundational concepts needed to establish a productive growing space, especially within the confines of an urban environment. In this course, we will work through a number of aspects of site planning and management. You'll do a quick examination of your sites soil, practice fertility adjustment and balancing, and consider how your project fits within its social environment.
After completing this course, you'll be able to:
OSU Dry Farming Project
2020 Virtual Field Tour Series
Save the Dates
Mark your calendars! The 2020 Dry Farm Project field tours will be held on Wednesday mornings at 10:00AM in August and September. There will be nine field tours featuring different elements of the five core projects listed below. View more information and a final schedule once posted.
The Dry Farming Project began in 2013 with case studies of farms in Western Oregon and Northern California (coordinated by Community Alliance with Family Farmers) that dry farm a variety of fruit and vegetable crops. These case studies revealed a suite of management practices that support crop production without supplemental irrigation including: careful timing of tillage, early planting, cultivation or surface ...Read full story.
Enjoy an informative and entertaining look at historic and present-day techniques for extending your garden produce throughout the winter months. We will discuss plans for creating a root cellar, ideas for recycling spaces and containers, and specific conditions for various produce. Resource handouts will be provided, and there will be time for Q & A. Via ZOOM!
Presenter: Brief bio:
Tresa has lived in various climates and remote locations where the use of root cellars determined her quality of life after the autumn harvest and before the productivity of gardens in spring. From Glacier Bay, Alaska, a remote island on the Oregon coast to central Oregon high desert and 10,000-foot elevation in Colorado, she has practiced techniques gleaned from ...Read full story.
In 1980 Jack Gray and Mary Jo Wade started Winter Green Farm just 20 miles west of Eugene, five years later Wali and Jabrila Via joined them and in 2009 long-time employees Chris Overbaugh and Shannon Shipp-Overbaugh a...
Manure and bedding collects rapidly on most livestock farms, especially in the winter. Instead of pitching the waste out the back of the barn, consider turning the materials into a valuable, usable product. Compost. If an active compos...
As summer approaches and the soil dries, forage plants become dormant. Some years in drier areas of Oregon dormancy may begin in the late spring. If you have irrigation rights, your pastures can provide supplemental nutrition even duri...
Gophers are useful animals in the wild as they aerate the soil, eat insects and mix surface soil layers, but they are a nuisance on the farm when conflict surfaces between the farmer and the gopher over land use. Their economic impact...