In my previous On Pasture article I discussed taking a pasture inventory on a bi-weekly basis and using that information to help us make better grazing management and forage utilization decisions. The next step in the process is creating a grazing wedge. A grazing wedge is a simple visual depiction of what you have available for grazing in all of your pastures. Once the data is entered into the spreadsheet, it can be sorted from highest to lowest available stockdays/acre (SDA) creating ‘the grazing wedge’.
Here is an example grazing wedge with available stockdays/acre on the y-axis and paddock ID on the x-axis.
It shows we have a range in forage availability from 80 SDA to -5 SDA. The -5 designation says this paddock was grazed too short and will need additional recovery time. You can also see we have paddocks at various stages of recovery.
Let’s look at what else a grazing wedge can tell us. The following wedge was from May 5.
I use three critical inventory levels in making grazing management decisions. The first is the ‘begin grazing’ threshold and is shown as a green line. This is the minimum amount of forage I want in a pasture before I begin grazing. For irrigated or high natural rainfall pastures, I use 30 stockdays/acre.
We are typically out on pasture around May 5-10 on this ranch, but this year we had a very slow spring. The inventory taken on May 5 told me we were still several days and maybe even a couple weeks from being ready to graze.
By May 19 most paddocks were at the ‘begin grazing’ threshold as shown in the grazing wedge below. In an irrigated or high natural rainfall situation, I like to have about 15-20% of the paddocks at the target level before we begin grazing. It now may be safe to begin grazing without having to worry about running out of grass by getting out too early. However, the relatively flat slope of the bars says growth rate is still slow.
The next line on the graph is the ‘optimum grazing’ level and is shown in blue. This is the amount of forage I would like to have available in every paddock as I come to it, once the grazing season is in full swing. My target is 75 stockdays/acre or about one ton of forage to be removed by the grazing herd as they come through the paddock. We’re generally looking at a 50-60% utilization rate on irrigated pastures so we should have about two tons of forage standing in the field when the stock come in.
By June 7 we have a few pastures above the target level for optimum grazing. I’ve added the black diagonal line to the chart now. This line runs from the target level on the Y-axis to 0 on the far end of the X-axis. We use this line to monitor our recovery rate. In a perfect world, each bar would exactly touch the reference line.
The recovery line tells me the paddocks I’m coming up to for the next several days are a going to be optimum and both the cows and grazier will be happy. However, from Paddock 11 on down they are all going to be a little on the short side if I don’t start allowing for more recovery time. I know I need to adjust my management by giving the herd a little smaller area each time I move them (usually daily in our operation) over the next week or so and try to leave a little more residual so they recover more quickly.
By July 6 we see most of the paddock bars are near the target recovery line.
This is the type of management information you can generate using regular pasture inventories and building a grazing wedge for each two-week period. Without this information, our management is usually reactionary to whatever is going on in the pastures as we see it today. With these planning tools you can be proactive in your management and create the forage availability scenario you desire.