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