Are you getting the most out of your manure?

Sunday, December 4, 2011

Knowing what is in it and using it where it will give the most benefit are
keys to maximizing your manure's value

by KEITH REID

If livestock are part of your farming operation, their manure is something you will need to deal with. For some, manure is no more than a byproduct that is expensive and time-consuming to get rid of. Properly managed, however, manure can be a valuable source of nutrients for the crops on your farm. The difference is due primarily to your attitude, but also to the supply of manure relative to the needs of your crops.

There is a range of livestock intensity across farms in Ontario. At the low end of the spectrum, livestock graze on unimproved pasture with no purchased feed or fertilizer, so every kilogram of meat or milk leaving the farm is an export of nutrients. Soil fertility levels and productivity will continually decline in this situation.

At the other end of the spectrum are farms depending almost exclusively on purchased feed and where the manure is all returned to a small land base. Since crops cannot possibly use all the nutrients provided by excessive manure rates, soil fertility rises to extreme levels and the risk of nutrient runoff rises proportionately. If these farms are not to become "pollution hot spots," the only options are to reduce the number of animals, increase the land base to utilize the manure, or export the manure to other farms where it would provide a benefit. 

The ideal situation is to be somewhere in the middle, where nutrients exported from the farm in meat, milk or crops are balanced by those coming onto the farm as feed or fertilizer. You can figure out where your own nutrient balance lies with some fairly simple math, if you have the records of purchased feed and fertilizer.  The kilograms of nutrients in purchased feed are equal to the tonnes of feed multiplied by the per cent of each nutrient, times 10 (since each per cent represents 10 kilograms per tonne).

The math is the same for fertilizer, except that the amount of phosphorus pentoxide (P2O5) needs to be divided by 2.29 to give the amount of phosphorus (P), and the amount of potassium oxide (K2O) needs to be divided by 1.2 to give the amount of potassium (K). Adding these together determines the amount of nutrients imported to your farm each year.

The same calculations can be done for products that are sold off the farm to determine the amount of nutrient export. Comparing the imports and exports will help you to see if your farm is close to being in balance or is a long way off on either the deficient or excessive side of the line.

Assuming you are not one of the few farmers with excess nutrients, you can probably get more out of the manure you have. This will help to reduce fertilizer costs and increase crop yields, both of which add to your bottom line.

The first step in maximizing the manure's value is to use the manure in the fields where it will give the greatest benefit. If all of the fields have similar soil test results, this means that the crops that need the most fertilizer (probably corn) will use most of the manure nutrients.

The situation changes if there are big differences in soil test results. In this case, the value of the P and K in the manure for a low-testing field could be greater than the value of the nitrogen (N) for a crop grown in a field with high soil tests, where the P and K in manure would not increase crop yields. 

The second step is to know what is in the manure. You can do this by sampling manure ahead of time, but it is difficult to get a representative sample from a large pile or pit. It is much more efficient to plan your manure applications based on "book values" for N and P, targeting a rate to provide about three-quarters of the N requirement of the crop, then collect samples as the storage is emptied for analysis. At the same time, keep track of the rate of manure actually applied to the field, then record the weather conditions at the time of application and the length of time before the manure was incorporated.

When the analytical results of the manure come back, you will have all the information you need to calculate the amount of nutrients actually applied to each field that are available to the crop. Fertilizer can be applied to meet any shortfall from crop requirements.

Although your fertilizer expense will not be eliminated, you will spend less than you would have without optimizing the manure nutrients, while reducing the risk of applying excess nutrients where they could be lost to the environment. BF

Keith Reid is Manager (Eastern Canada), Soil Nutrient and GHG Management,
Agriculture and Agri-Food Canada, Guelph.