Other data collection
In addition to taking these readings, quality samples are collected from paddocks to monitor any changes over time or with management changes. These are processed at a feed testing centre in Shepparton using NIR technology and the ‘Dairy One’ method for estimation of metabolisable energy (ME). There are numerous ways of testing forage quality and different methods may return slightly different figures.
Records of grazing rotations, irrigations, diet, herd numbers and production are also kept. Working around an operating farm, we cannot always get measurements the day before, after or on the day of grazing. As a result, we have to make some assumptions around growth rate based on this “calendar of events” we put together.
Having collated all this information, financial analysis is undertaken at the end of the season.
After testing the various technologies available to measure these forage types, it was decided that an Automated Pasture Reader (APR) would be used to collect information needed to estimate the mass (kgDM/ha) and growth rates of selected paddocks.
How the APR works:
As you move across the paddock, the reader takes consecutive measurements of the distance between its sensor and the top of the pasture (equating to multiple “pings” per second). From these measurements, the reader generates an average height, which is used to calculate a figure for overall dry matter per hectare.
Like all measurement devices, accuracy is dependent on the robustness of device's calculation of forage mass. There is only one calculation programmed into the APR to convert height to dry matter. This is problematic for a number of reasons:
The dry matter content of plants varies between forage types, varieties and seasons
Plant structure varies between forage types and season
In lucerne, for example, leaf to stem ratio changes during a regrowth period.
The density and composition of pasture will change seasonally (e.g. clover disappears in Summer, lucerne and paspalum thin out in Autumn)
Calibrating the APR:
To accommodate these flucations, the APR must be ground-truthed by taking cuttings from the focal paddocks. A series of cuttings, each of a set size, are taken once a fortnight. To account for any variability across the bays, the cuts are taken from a range of areas. They are then dried and weighed to produce a dataset used to plot kg DM/ha against height.
It is common for these curves to look different across the seasons and forage types. Figure 1, for example, shows the monthly equations (dry matter relative to height) derived for Lucerne on the Stewart’s farm, and Figure 2 shows the monthly questions derived for the perennial ryegrass pasture on the Humphris' for Summer 2015-16.
On the Humphris farm, different forage types will be monitored throughout the year to understand how each of these contributes to the overall system. For details see here.
As part of the Accelerating Change project, Murray Dairy and DEDJTR have teamed up to gather and interpret data around the mangement and performance of different forage types - perennial pasture, annual ryegrasses, fescue, lucerne and sorghum - as well as the impact of irrigation scheduling on the project's two partner farms.
On the Stewart farm consecutive perennial pasture and lucerne paddocks will be irrigated at different intervals -- (I) once per grazing and (II) three times every 2 grazings -- to test whether intervals can be stretched out to reduce water usage without compromising plant growth, yield and/or quality. One pasture paddock will be dried off for comparison. See here for details.