Sally A. Flis, Ph.D. – Feed and Crop Support Specialist, Dairy One

The calendar says the first day of spring is Sunday, March 20th, only a few short weeks away. The weather feels like spring every two or three days and in some places maple syrup is boiling and fields are getting plowed. If you are a grazer you are getting anxious about getting pastures ready for the season and when the first day of grazing will come. Well, here are a few things to think about when you are staring out the window at your pastures over the coming weeks:

Soil Testing – When is the last time you sampled?

Regular soil testing will help you manage the nutrients that both your growing pasture and your animals are seeing. Soil pH is one of the most important measures on a soil test. When soil pH is less than 6.0 the availability of nitrogen, phosphorus, potassium, sulfur, calcium, and magnesium decreases and the availability of micronutrients that can cause toxicity increase. The ideal range for nutrient availability is 6.2 to 7.5. Above 7.5 nutrient availability decreases. Soil pH can be increased with the addition of liming materials. In a pasture situation, where soil is not being disturbed, lime should be applied when the pasture is at its shortest to get the best soil contact.

In standard soil tests phosphorus, potassium, calcium, magnesium, sodium, aluminum, zinc, sulfur, manganese, iron, copper, and boron can be measured. Nutrient application recommendations are based on the extraction used and the production expectations of the pasture. Keeping records of grazing time, stocking rate, yield of mowings, and any nutrient applications will give you the most accurate recommendations for additional nutrient applications. Nutrients to meet pasture production needs can be supplied from animal wastes or commercial fertilizers.

Pasture Testing

Using forage testing and soil testing together will give you the most accurate nutrient recommendations. Plant mineral concentrations are directly related to soil mineral concentrations. Last spring a soil and forage sample were submitted from the same pasture (Table 1). A medium soil test range for P has a recommendation for 20 lbs/ac of P2O5 to meet crop needs. The forage test for the pasture has a result for P at the high end of the typical range, indicating that soil and nutrient applications are meeting plant needs. High soil test K has a recommendation for 0 lbs/ac of K2O from fertilizer and the forage test for the pasture is also at the high end of the typical tissue range indicating that the plant is meeting the K needs from the soil and nutrient applications.

ItemPasture (MMG), % DMTypical Pasture Test Range (MMG)Soil, PPM (Morgan Analysis)Soil Test Range
Phosphorus (P)0.400.2 – 0.46 %7Medium
Potassium (K)3.101.4 – 3.46 %134High

 

Forage testing will also let you evaluate nitrogen use and needs. Nitrogen is not measured on soil tests due to the dynamic behavior of it in the soil. Soil health tests can provide a measure of the potential for the soil organic matter to provide N. Forage testing will provide crude protein. Crude protein is a measure of the total N in the tissue multiplied by 6.25 and is directly related to the amount of N taken up by the plant. Crude protein concentration in the plant can be influenced by soil N coming from the breakdown of organic matter by soil microbes and N applied from animal manures or commercial fertilizers.

Finally, forage testing is also useful to determine if you are meeting the needs of your animals. A pasture forage test will provide you with crude protein, fiber, sugar, and mineral concentrations. Crude protein and fiber concentrations are influenced by stage of maturity of the sample. As maturity of the pasture increases, fiber concentrations increase and protein concentrations decrease. Increased fiber concentrations are related to decreased intake and energy from the pasture. Timing of grazing or harvest is a management tool to adjust fiber and crude protein concentrations.