Estimating pasture forage mass for pasture-based dairies

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Pasture-based dairy production in the United States relies on the ability of the dairy producer to estimate pasture production and animal dry matter intake. Pasture is the primary source of forage for organic dairies, and the National Organic Program livestock production regulations require a minimum of 30% dry matter intake from pasture for 120 days grazing per animal. Pasture availability and utilization is key to describe nutrient balance on pasture. Estimating forage mass from pasture may be difficult because pre- and post-grazing measurements must be recorded. The standard method to measure pasture forage mass is to clip the forage from the pasture, dry the forage sample, and weigh the dried forage to determine dry matter. However, this method requires an immense amount of effort and time to collect forage samples, and many dairy producers are not willing to collect this information for daily pasture management.

Precision pasture-based technology has been used for many years in New Zealand; however, these technologies have yet to gain wide acceptance among United States pasture-based dairy producers. Two popular devices to accurately measure pasture forage mass are the electronic rising plate meter and the rapid pasture meter.

The electronic rising plate measures the amount of forage mass in paddocks. Briefly, the pole of the rising plate meter is pushed vertically through the sward until it touches the ground, and the weight of the plate compresses the pasture vegetation. An electronic counter records the compressed forage height in 5 mm increments and instantly displays the results. Pasture management software is used to evaluate the readings from the rising plate meter from different paddocks.

The rising plate meter correlates the compressed forage sward height to the forage mass below the plate, and therefore, a calibration equation is needed to convert the pasture readings to dry matter yield. Different calibration equations are required for different pasture species and different seasons, hence many dairy producers have not utilized this technology because of the effort required to update the rising plate meter calibrations on a continual basis.

New technology is available from New Zealand (C-Dax pasture meter, C-Dax Ltd., Palmerson North, New Zealand) that uses GPS software to map pastures and a high speed program to take multiple measurements per second of pre- and post-grazing areas. The pasture meter can be mounted on an all-terrain vehicle or farm vehicle and has the potential to provide fast and accurate measurements of pasture forage mass.

The rapid pasture meter uses light and optical sensors to record 200 pasture height measurements per second and averages those readings to represent a data point on a map of the paddock. FarmKeeper software aids with GPS mapping of paddocks and pastures, and recording and analyzing the pasture measurements. The rapid pasture meter must use a calibration equation to accurately measure the forage in a pasture.

Accurate estimation of pasture forage mass is essential for pasture-based dairy farms in the United States and around the world. Electronic rising plate meters and rapid pasture meters have been developed and evaluated in New Zealand and have shown similar dry matter accuracies from pasture forage mass. Grazing dairy producers in the United States have these technologies available to them to more accurately determine pasture forage mass, and thus improve the profitability of their dairy operation.

These technologies will be discussed at the Organic Dairy Day on Tuesday, August 13, 2013 at the West Central Research and Outreach Center in Morris, MN. For more information on the Organic Dairy Day program, please contact Brad Heins at hein0106@umn.edu or 320-589-1711.


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