Drs. Robert Mullen, Mark Sulc, and Maurice Watson, School of Environmental and Natural Resources, OARDCDairy Nutrition Specialist, The Ohio State University
Fertilization of cool season grasses with either organic manure or inorganic, commercial fertilizer should be done to optimize the production system and meet your goals as a producer. The goal of this article is to provide some information on fertility management of cool season grasses.
Soil testing to determine soil nutrient status is the best way to quantify the amount of phosphorus (P) and potassium (K) you need to supply as a manager. With the cost of these inputs rising over the past few years, routine soil sampling should be utilized. Soil testing should be conducted the same way as we recommend for row crop production. Collect 15 to 25 random soil cores to a depth of 8 inches, make a composite sample, and submit it to a soil testing laboratory for analysis. Recommendations for fertilizer P and K based upon soil test levels are available online in the Ohio Agronomy Guide in the Forage Production chapter (http://ohioline.osu.edu/b472/0008.html).
Ideally, P and K should be applied and incorporated prior to seeding based on the recommendation. A small amount of nitrogen (N) should also be supplied prior to planting, whether as commercial fertilizer or as manure to promote good stand establishment. The amount of N needed is around 30 lb/ acre. If you are supplying manure for N, remember that you are also supplying P and K, so make certain to quantify the amounts you are supplying. Knowing the amount of nutrients you are providing will ensure that they are not at a level that will limit production. Additional information on nutrient content of various manures can be found at: http://ohioline.osu.edu/b604/b604_15.html. Manure applied should be adequately incorporated into the soil, and seeding should not be done immediately after manure application. Seeding just after manure application (especially at high rates) can inhibit seed germination. Avoid gross over-application of both N and K (which includes manure), as they can lead to forage nutrient balance issues, especially early in the spring. Quick growth and excessive K uptake can decrease plant uptake of magnesium (Mg). Ruminant animals being fed this Mg deficient plant material can develop grass tetany. Dry cows being fed a forage high in K can develop milk fever.
Maintaining an optimum soil pH for the grass you are growing is also important for stand longevity. Different grasses require different pH levels, so know where you need to be with soil pH. If soil pH is too low (acidic), lime can be applied to adjust soil pH to the optimum level. Ideally, lime should be applied well before seeding (preferably 6 months), but if you need to make an adjustment, make the application whenever possible. Make certain that the lime is adequately incorporated into the soil so that it can neutralize soil acidity as fast as possible.
Fertilizing established stands
Soil test information is the best guide for making fertilizer decisions on established stands. The recommendations for established stands are the same as they are for pre-establishment. When soil nutrient levels are above optimum, the timing of P and K application is not critical; it can be done anytime during the growing season. When soil test levels are below the optimum, split applications is the best way to supply needed nutrients. The recommended split is after the first cutting in the spring and after the final cutting in fall. This is especially true for K due to grass tetany and milk fever concerns. Care should be taken when utilizing manure as the nutrient source in the spring. Remember, manure not only supplies N, but it also supplies K, so applying manure to get the desired N response can lead to high K levels, which can represent risk to animals. In addition, avoid smothering the grass with an excessive manure application.
Nitrogen application should also be split to ensure that N is available throughout the growing season. The current recommendation is that N be supplied at a rate to match yield potential and that the total N budget be split between N applied prior to green-up and after each cutting. Forty percent of the total budget should be applied prior to green-up in the spring and 30% of the budget should be applied after each cutting. Nitrogen recommendations for cool season grasses can be found in the Ohio Agronomy Guide in the Forage Production chapter (http://ohioline.osu.edu/b472/0008.html).