Did you know that when you ship 1,000 lbs of milk from your pastured cows, you are sending off 6 lbs of nitrogen, and 2 lbs each of phosphorus, potassium and calcium? A thousand lbs of beef includes 27 lbs of N, 8 lbs of P, 2 lbs of K, and 13 lbs of Ca. How are you going to return that to pasture? A better question: how much of it should you return, since the cows are returning a fair amount themselves.
With good grazing management, 60-96% of the nutrients in grazed forage are returned directly to pasture in manure and urine. If the herd is making full use of the pasture and not spending all their time in the shade, on a high spot, or next to the water, they might be spreading their manure and urine fairly evenly.
The return means the nutrients go back on pasture, but that doesn’t always solve the problem. For example, nitrogen is our most limiting mineral nutrient in pastures. For a dairy cow producing 60 lbs of milk per day, 180 lbs of N are returned over a 200-day grazing season. Of that, only about 25% or 45 lbs of N are available for plant uptake, and the rest is in forms that are not accessible. Legumes may provide more N, especially if legumes make up 25-50% of the total forage present.
But since you know some of the nutrients are coming off, how much can and should you return? If you’re giving the herd supplemental feed such as grain or a TMR (total mixed ration), you might be returning enough.
To get the straight scoop of what is already there, the key is soil testing. Soil testing will help make sure the pasture provides enough nutrients for the legumes and the forages. The first and most important thing you should find out is the soil pH. If your pasture soil’s pH is too low, lime or wood ash will help. The pH should be your primary goal, and then if soil test results show that phosphorus and potassium are below optimum levels, you should try to add those nutrients in amendments.
Keeping your pasture soils at optimum levels for production can help you concentrate on nutrient return, or making sure the grazing allows for ideal and even distribution around the pasture. Moving the herd frequently, using movable water troughs and salt blocks are some ways to help you make sure the herd does their part. More to come on that!
Check out our article on soil testing! We’ve got tips to make it work for you, and fun, to boot.