As University of Arkansas professor of animal science Shane Gadberry points out, the availability has increased in recent years of byproducts high in nitrogen that can be fed to dairy cows. “Grains and most byproduct feeds are also fairly high in phosphorus and forages are high in potassium,” Gadberry told Ozarks Farm & Neighbor. “Cumulatively, as these nutrients are concentrated in manure, the manure becomes a valuable source of N, P and K for local land application.”
However, this also means when manure is used to fertilize forage crops, the nutrients being placed on the ground can differ in proportion to what’s being taken up from the plant. For instance, on a dry matter basis, bermudagrass takes up 37 pounds of nitrogen, 12 pounds of phosphate (P2O5) and 42 pounds of potash (K2O) for every ton harvested. The proportion of phosphorus in the manure is greater than the proportion of phosphorus in the plant compared to nitrogen and potassium, and Gadberry said, “This can result in an accumulation of soil phosphorus with continuous application over time, since manure is often applied based on plant nitrogen needs in mind.”
This means, whether manure or commercial fertilizer is being used, a soil test report and yield expectations based on soil type and rainfall patterns are important for fertilization. Areas under nutrient management plans may restrict the amount of manure use based on soil test phosphorus index values. It’s also important to apply fertilizers at times that are appropriate to stimulate growth of desired plants, while minimizing chances of nutrient losses.
Tony Rickard, University of Missouri Extension dairy specialist and program director for Barry County and the southwest region, said there’s also a difference in the nutritional composition of manure from dry versus lactating cows. A 1,400 pound lactating cow, Rickard told OFN, will put out about 2.4 cubic feet of manure a day, compared to 1.82 cubic feet for a dry cow. The composition of both will be about 88 percent water; whereas the lactating cow will produce about 0.82 pounds of nitrogen a day, 0.42 pounds of phosphate, and 0.48 pounds of potash, the dry cow’s manure will yield about a half a pound of nitrogen per cow per day, about 0.2 pounds of phosphate and about 0.4 pounds of potash.
Research in Texas found supplemental inorganic phosphorus applied to bermudagrass did not benefit yield, but supplemental inorganic nitrogen at 50 pound/acre per cutting did. Rickard said, “In our pasture based dairy systems, what we’re finding is if we don’t have clovers in the field, which we do recommend, then we are going to need to do some nitrogen supplementation on the pastures.” On the other hand, “The phosphorus and the potash values are such that once we get soil tests up to where they belong, then we don’t need to be spreading either P or K onto those pastures.”
Dairy producers in this region use their own manure; they don’t sell it. “We have mainly smaller dairies,” Rickard explained.” “They’re either collecting manure at the parlor, and they may do it as a liquid system where they’ll use a honey wagon to haul it out, or they’ll use a manure spreader. They’re utilizing it for either crop ground or for possibly pastures, and there’s really not much manure to do that with in order to have a source to sell.” Even bigger operators with 300-500 cows need the nutrients in their manure for their own pastures.”
