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Residual Dry Matter (RDM) Monitoring Photo Guide
John M. Harper UCCE Livestock & Natural Resources Advisor
Mendocino & Lake Counties
Adapted from Wildlands Solutions Field Guide Series
Residual Dry Matter • Amount of old plant material left on the
ground at the beginning of a new growing season
• Previous season’s use • Health or condition of annual rangelands
Methods of Estimating RDM • Direct clipping & weighing
– 0.96 square ft circle (13.25 inside diameter) – Include stems, seed stalks & litter – Weigh the RDM collected with gram scale – Multiply by 100 to obtain pounds per acre – Example: 9.3 grams X 100 = 930 lbs/acre RDM
Methods of Estimating RDM • Comparative yield
– 1 square foot rectangle – Rank 1-5 visually – Clip & weigh to validate
• Photo standards or guides
Monitoring RDM • When to monitor
– Same time of year – End of use period – Prior to fall rains in late September or October
• Key areas – Be representative – Be within a single ecological site – Be capable of responding to management actions
Monitoring RDM • Utilization mapping
– Rangeland use pattern mapping
– Consolidate RDM classes into 3 or 4
– Identify areas that meet management objectives and those that don’t
Photo Guides • Six reference classes of RDM
– > 1000 lbs per acre – 750-1000 lbs per acre – 500-750 lbs per acre – 250-500 lbs per acre – >125 lbs per acre
• Visual reference points – Robel pole 1 1/8 inch diameter with 1 inch markings – Colored golf balls 1 ½ inch diameter – Close photo – 5 ft high and 10 ft distance from pole – General photo – 5 ft high and 20 ft from pole
RDM exceeds 1000 lbs/acre • Considerable grazing
use • Seed stalks maybe
heavily used • Ground cover complete • Robel pole covered to
height of 2-4+ inches • Golf balls barely visible
at 10 ft • Golf balls seldom visible
at 20 ft
RDM between 750 & 1000 lbs/acre • Clear evidence of
grazing • Seed stalks heavily used
or trampled • Considerable ground
cover left • Some bare soil apparent • Robel pole covered to a
height of 1-2+ inches • Golf balls partially
visible at 10 ft • Golf balls may be barely
visible at 20 ft
RDM between 500 & 750 lbs/acre • Extensive grazing use • Residual vegetation
patchy with some less than 1 inch and others 3-5 inches tall
• Some bare soil apparent • Robel pole partially
covered at a height of 1-2 inches
• Golf balls clearly visible at 10 ft
• Golf balls mostly visible at 20 ft
RDM between 250 & 500 lbs/acre • Extensive grazing use • Standing seed stalks
scarce some as litter • Ground cover sparse &
clumpy • Large areas uniformly
grazed to 1 inch scattered areas of 3-5 inches
• Some bare soil readily apparent
• Robel pole is fully visible • Golf balls clearly visible at
10 ft & mostly at 20 ft
RDM between 125 & 250 lbs/acre • Extreme grazing use • Residual vegetation
scarce with most grazed to 1 inch and only scattered areas of 3-5 inches
• Standing seed stalks rare some stalks and seed heads as litter
• Bare soil obvious • Robel pole fully visible • Golf balls clearly visible
at both distances
RDM less than 125 lbs/acre • Total use a.k.a. “nuked”
or “hammered” • No standing seed stalks
remain • Some seed stalks occur as
litter • Most areas grazed to less
than 1 inch • Considerable bare soil
readily apparent • Golf balls clearly visible at
greater than 20 ft
North Coast RDM • Adjust for precipitation,
soils and slope – Greater than 40 inches – Increase for highly erosive
soils – 750 lbs/acre – 10% slope – 1000 lbs/acre – 10 to 25%
slope – 1250 lbs/acre – 25 to 40%
slope – 1250 + lbs/acre - >40%
slope