Dietary Phosphorus and Water Quality

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Phosphorus (P) is a very important mineral for both cows and their rumen microbes.  It is involved in almost all metabolic reactions so being deficient can be very detrimental.  However, it is also a very important element in almost all metabolic reactions in plants.  Therefore, as cows eat plants and plant materials they are getting enough P to meet their requirements.  Grains tend to be higher in P compared with forages, and byproducts (distiller’s grains, corn gluten feed, and wheat midds) tend to be the highest.  Because it is so prevalent in plants supplemental P is almost never needed.  

What is the big deal about P?  The issue with P is that, like animals and plants on land, algae also need P to grow.   When too much P gets into waterways either through manure contamination or soil erosion algae grows uncontrollably.  Too much algae in the water blocks out the light killing aquatic plants, which serve as habitat and food supply of higher level organisms.  When this algae bloom finally dies the decomposition of the algae draws oxygen out of the water making it impossible for fish and other aquatic organisms (fish, shellfish, etc.) to survive.  

So how much is too much?  Like the level of any nutrient, the level of P required for the cow depends on her milk production and how available the P in the feed is.  However, in most cases a P concentration of 0.35% to 0.38% of ration dry matter will be enough to meet the needs of the cow.  In the “Reducing Dietary Phosphorus in the Dairy Herd” publication by Zhiguo Wu and Virginia Ishler with Penn State University there is a nice example of how overfeeding P in the ration contributes to higher levels in the manure.  For a cow milking 75 lbs and eating 50 lbs of dry matter, a dietary P content of 0.35% of ration dry matter will result in 1.9 lbs/ton of P in the manure where as a dietary P content of 0.48% of ration dry matter will result in 2.9 lbs/ton of P in the manure.  Because P fed above the level that the cow needs will just be excreted going from a recommended P level of 0.35% to a high level of 0.48% results in the significant increase in manure P levels.  

Higher manure P means that there may be limitations as to where that manure can be spread.  Another calculation from this publication shows that when a cow is fed a 0.48% P diet compared with a 0.38% P diet an additional 12.2 pounds of manure P is excreted over a 305 day lactation.  This higher P diet would require an additional 0.31 acres to spread the manure on compared with the low P diet.  If additional land was not available P would be applied at 14.5 lbs/acre in excess of what the crop could remove and would result in an increase in the soil P test over time. 

Although many have reduced the level of P in their rations, there are still a few that throw in a little extra for good measure.  This is not only bad for the environment, but it is also represents an unnecessary cost.  Deficiency issues are not seen until you get around 0.3% P, and a dietary level of 0.3% P is hard to create using normal feedstuffs.  Therefore, concerns about loss of milk production or reproductive performance due too little P are unwarranted.  

Phosphorus, has, and will continue to, receive a lot of attention, but the positive side is that it is something that can be easily controlled at the farm level.

Feed Management

Feed Management is an excellent program that all dairy farmers should be taking advantage of.  It is a Natural Resources Conservation Service program that is available nationwide, but is receiving a great deal of attention in Pennsylvania.  When farmers apply for this program they can receive $2,000/group per for the first year, $1,500/group per for the second year, and $1,100/group for the third year of the contract.  A group can be the high producing cows, low producing cows, heifer groups, etc.  Farmers can apply for up to five groups on their farm so that can be a good amount of money.  There has been $1 million set aside in Pennsylvania to cover new plan applications so there is plenty of funding available for anyone who is interested.   The payments are to cover the cost of having a feed management plan written by a certified plan writer and the quarterly follow-up that the plan writer needs to do.  In Pennsylvania, the plan writers are trained by Penn State Cooperative Extension and state extension specialists.  The goal of a feed management program is to reduce nitrogen and/or phosphorus excretion by the cows through ration alterations and/or feed management changes on the farm.  These plans are very flexible and tailored to every individual farm, and are designed to be things that the farmer is capable and willing to implement on the farm.  If you are interested in learning more about this program contact your local NRCS office.

Winter Manure Spreading; a Necessary Evil

Winter spreading of manure is not something that is popular with many environmental folks.  This has recently come to a head in Iowa where they are allowing producers to spread manure in the winter for five more years with approval by the state.  However, a local advocacy group, that has been fighting this ruling, is vowing to take note of every bit of manure spread and report any problems.  

The winter months, when the ground is frozen, are the months that see the most manure runoff because the manure and it's nutrients do not have an opportunity to be incorporated into the soil.  Therefore, they sit on top of the soil until the ground thaws.  Therefore, any sudden precipitation or snow melt can lead to manure runoff into local waterways. 

In Pennsylvania, winter manure spreading is still allowed, but with certain regulations.  For example, the maximum that can be spread is 5,000 gallons of liquid manure or 20 tons of dry manure per acre or applied to the phosphorus removal rate of the coming year's crop.  There needs to be 40% crop residue, a growing cover crop, or pasture for manure to be spread on any field.  There may be other rules that apply once the new Manure Manual regulations come out this spring, and the EPA is still working with Pennsylvania to try to eliminate winter spreading all together.

Although many do not like winter manure spreading, including many farmers, building enough storage to last through the entire winter is very costly.  For example, an average concrete storage big enough for four months of storage on a 100 lactating cow dairy can cost around $50,000.  With milk prices and feed costs the way they are finding that kind of money is difficult.  There are cost-share programs available to alleviate the installation costs, but even coming up with the money to cost share is challenging for many small dairies.  

This is a very difficult issue with no good solutions, but for now responsibly spreading manure any time of year is a must.