How to estimate the pasture forage mass in the field

Home grown pasture is a key contributor to livestock feed in most farms.  An accurate assessment of feed availability from the pasture at any particular point in time is an important requirement for feed planning and budgeting.  Regular assessment of quantity of pasture allows early identification of forage surplus or deficit and this enables farmers to develop accurate feed budgets, plan feed requirements and make better overall grazing management decisions.

There are a number of forage assessment techniques available to farmers but the easiest is through the measurement of pasture height.  There is a strong correlation between pasture height and pasture forage mass.

The simplest way to measure forage height is by use of a ruler. Placing the end of the ruler on the ground while holding the ruler vertically, estimate the average height of the upper leaves of the pasture. Record the pasture height from different points in the field.  Calculate the average height of the pasture from 15 to 30 or more points depending on the size of the field.

The next step is to evaluate the pasture density.  Do this in relative terms, whether the pasture is thin, average or thick. Using the average pasture height and estimated density look up the estimated forage mass on the calibrated table.  Find the row corresponding to the average pasture height and the column corresponding to the estimated density. The number in that cell is the estimated forage mass in kilograms of dry matter per acre.

General calibrations for pasture forage density and forage mass at different mean heights as measured by a ruler

Ruler height (Inches Forage mass(Kg)
  Thin Average Thick
3 373 470 694
4 483 607 901
5 585 733 1096
6 681 850 1279
7 770 956 1450
8 851 1053 1609
9 923 1139 1756
10 992 1215 1891
11 1051 1281 2014
12 1104 1337 2125
13 1150 1383 2224
14 1188 1419 2311
15 1219 1444 2385
16 1243 1460 2449
17 1261 1465 2499
18 1270 1470 2538



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