It certainly doesn't look like it at the moment, but spring is just about here. It seems like it has been quite a while since I've seen grass; not just green grass, but any grass. I imagine the cows laying around, chewing cud with their eyes shut in quiet slumber and daydreaming about some new green fresh forage.
I was asked recently when you should take soil fertility samples on pastures. The real answer to that question is usually six months prior to asking. If we know we are going to be reseeding some pasture in the spring, then we should be collecting the soil samples the previous September or October. I prefer to collect them in early September. If you want to see trends, it is best to pull those samples at the same time frame each time.
Just like an annual field crop, your forage crop needs to be fertilized and managed. It is extremely difficult to maintain a stand of quality forages that will produce nutritious feed when some elements are low. Everyone has tried it, but you soon see that by "getting by" with lower levels of nutrients, especially phosphorus and potassium, you are just that, "getting by" but with lower yields, lower quality forages, and lower carrying capacities.
A soil test is usually a good place to start. Samples should be taken that match up similar soils and management. If a field is used for hay, then it should be tested separately from a field that is only grazed. After you get the results from the tests, you can then get a better handle on where the fields are fertility wise and amend as needed. Macro nutrients such as calcium, magnesium, nitrogen, phosphorus, potassium, sodium, and sulfur are generally needed in larger amounts depending on where you are located and materials used over time. Calcium certainly plays an important part with soil pH and thus availability of most other nutrients, which is why I usually say, "lime first" if needed or if in doubt, lime. Fertilizer can be commercial or from animal manure. When using animal wastes, you need to get a good sample of that material and test it for nutrient content and then apply it according to a soil test just like commercial fertilizer.
Apply lime in the fall after you get your soil tests back. This gives the lime time to start breaking down and becoming available. Ag lime is not an instant fix, it takes some time. Some nutrients, such as phosphorus, are easily tied up as the pH drops. If your soil test comes back with a pH below 6.0, it might be wise to apply lime to correct the pH first, then go back and resample six months down the road for phosphorus. This is increasingly true as pH continues to fall below 5.8. An extra soil test of total phosphorus can give you an idea of the total amount present. This is not a typical test and is an added expense. The difference gives you a better idea of how much is tied up due to the pH level. There is often a fair amount of phosphorus present, especially in lower soil profiles. It is just not in soluble form. Ideally, most nutrients are most available when the pH is close to 7.0.
The next topic today is residual forages or the amount of stem and leaf left behind after the last grazing of the previous year's growth. Yes, there should be something left! Pastures with more residue will have more start up energy in the spring. That dry residue matches up well with the new growth to help provide some dry matter with all that rich, new, watery, green growth. This makes it easier to be utilized more efficiently by the cows or whatever is grazing it. Fields with the most residue might be the best to graze first and ideally, that is not the same field each year. These same fields also make nice places to calf.
Fields that were grazed down tight last fall before they went dormant, will be slower to respond in the spring. They are more likely to have weed pressure or increased amounts of short tolerant species such as bluegrass or native white clover because of reduced energy reserves and being less competitive. Fields that were grazed down fairly tight last fall (2 inches for most tall cool season grasses) after they went dormant, will be more competitive in the spring and respond accordingly. The first scenario is the better one for frost-seeding clovers into because the clover seedlings will have a better chance of survival with the reduced competition.
With winter still dragging on a bit, you still have some time to frost seed some clover onto the field. I usually recommend slightly higher seeding rates for frost seeding than for conventional seeding. White clovers can be seeded at 1-1.5 lbs. per acre, remembering that it is a lot smaller seed than red clover and will be around longer. It is very easy to get too much clover seed on. White clover is especially small in size. You can mix the seed in with fertilizer or some pelletized lime. Red clover should be seeded at 6-8 lbs. per acre; birdsfoot trefoil at 5 lbs. per acre and common lespedeza with hulled seed at 10 lbs. per acre. All legumes should be inoculated with the appropriate inoculants for that species to insure proper bacteria, good germination, and growth. Coated seed, when available can solve lots of problems including seed size, the inoculants, and can even help the pH for the seedling.
I'll end today with a comment on cover. Cover is very important. I've said that at least once before. As the pastures start greening back up just like the cows are dreaming of, it is very important to not start grazing too quickly. The plant will first start to rebuild its solar panel. Photosynthesis is needed to build back new roots and reserves. The more photosynthesis occurring per acre, the more carbon there is and more potential for increasing soil organic matter. Photosynthesis needs leaf surface area, so that solar panel to move forward. When leaf is removed too early by grazing, the solar panels capability is greatly diminished. We also do not want any bare soil. We want all of the energy from the sun to be captured by that green solar panel. We do not want that energy wasted on heating up bare soil which can increase oxidation of carbon, we want it converted to energy in plants.
Keep on grazing!