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Cover Crop Nitrogen Scavenging Credit Calculator for Merced Rye
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Directions: This calculator was developed by Eric Brennan (USDA-ARS, Salinas, CA) to determine the cover crop nitrogen scavenging credit based on cover crop shoot height and Feekes growth stage values entered in the yellow boxes below. To use the calculator you'll need to first download a copy to your Google drive. The calculator works for cover crops that are planted in rows (spaced 6 to 8 inches apart) and broadcast assuming the cover crop plant density is at least 10 plants per square foot. As height and Feekes values are changed you can see how this affects the cover crop's estimated biomass, Carbon to Nitrogen ratio (C:N), percent nitrogen, shoot nitrogen uptake and the cover crop nitrogen credit. Based on the Ag. Order 4.0 regulation, to recieve a credit a cover crop must (1) be grown for 90 days over the winter period (October to April) (2) have at least 4500 lbs per acre of oven-dry shoot biomass, and (3) have a C:N of 20:1 or more. For example, for Merced rye to meet these requirements it must have a minumum height of 30.5 inches and a minimum Feekes growth stage is 9; this combination will give a nitrogen scavenging credit of 95 lbs/acre). The calculator will determine nitrogen uptake even if the 3 requirement have not yet been met. (For more details, hover your mouse over cells below with a black traingle in the upper right corner). This video (Cover crop nitrogen credits for farms in California’s central coast, Ag Order 4.0, https://youtu.be/BTRKk7Zd1so) provides more information on the different types of cover crop nitrogen scavenging credits available to growers in the Ag. Order 4.0 regulation. 9/4/2024 IMPORTANT UPDATE, Based on a recent analysis, the Feekes growth stage required to meet the C:N ratio of 20:1 will likely need to be modified in the calculator to account for differences in C:N ratio changes due to cover crop planting date. Stay tuned. Thanks for your patience on this. Questions/comments: email eric.brennan@usda.gov
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Height in Inches (click triangle in the green box below to choose a shoot height between 10 to 75 inches)
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33
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Feekes growth stage # (click triangle in the yellow box below to choose a growth stage based onTable 1 on right).
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10.1Heading begins, 1st awns of head are just visible
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Cover Crop Shoot Biomass (lb/acre oven-dry shoots)
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5,004
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Cover crop Shoot C:N (20 = 20:1 or 20 carbon to 1 nitrogen, etc.)
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29:1
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Cover Crop Shoot Nitrogen Percentage
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1.4
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Cover Crop Shoot Nitrogen uptake (lbs/acre, usually not more than 200 )
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69
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Cover Crop Nitrogen Scavenging Credit (lbs/acre, usually not more than 200)
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67
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