Dairy Excel: Remember to fertilize hay fields, too

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Bring on the warm spring rains, the hot summer breezes and the beautiful smell of a recently cut alfalfa hay field.

Guess what? Believe it or not, I am tired of winter already.

Push the pencil. Winter brings time to either push snow or push the pencil. Hopefully many alfalfa or grass hay producers will have time to do a little pencil pushing.

Forage producers in northeastern Ohio probably had a good hay harvest year, if they were able to cut early, cut often, and lucky enough to find those few hot drying days we had in 2003.

Many were not so lucky. Moderate to high forage yields are necessary in forage systems to cover overhead costs.

Profit. To maintain profitability, forage managers need to ensure that fertilization practices allow adequate yield without wasting money on unneeded fertilizer.

We need to answer the question, “How much fertilizer do I need?”

Usually the potential forage yield from a field is determined by the available water holding capacity of the soil in the field.

The actual forage yield from a field will be determined by the crop grown, weather, soil fertility; fertilizers applied, and harvest management.

Ratios. Remember that the fertilizer ratio needed for grass-legume hay where no N is needed is 100 pounds of 0-12-45 per ton of hay removed.

This same ratio should be used for N-fertilized grass hay with the addition of 50-60 pounds of N per acre per cut.

Soil samples. The accuracy of a fertilizer recommendation depends on how well the soil sample on which the recommendation was based represents the area on which the recommendation will be used.

The physical and chemical characteristics of soil in an area can vary considerably from place to place because of natural factors and the management to which the area has been subjected.

Natural variation arises from soil-forming processes (such as mineral weathering and erosion) that lead to accumulations or losses of nutrients at different sites

Management. Management factors might include tillage and fertilization practices, crop selection and past manure rates.

It may be necessary to take many samples from a given area (at random or in a systematic manner) to assess its fertility accurately.

When soil test phosphorus (P) is less than 50 pounds per acre, yields can be expected to be below potential.

As soil test levels drop below 40, yields drop off rapidly.

Above or below. When soil test phosphorus is above 50, no P fertilizer is needed to maintain production for short periods of time.

However, if no phosphorus is applied, the crops removing phosphorus will reduce soil phosphorus, resulting in reduced yields as the soil test decreases below the critical value.

Forage crops remove 12 pounds of phosphorus per ton of dry forage removed from the field.

Many soil test results are reported in pounds per acre, but some are reported in parts per million with would be a number one-half of the pounds per acre.

(Example: 50 pounds per acre on a soil test would be equal to 25 ppm for a soil test in parts per million.)

Potassium. When soil test potassium (K) is less than 120, yields can be expected to be below potential.

As soil test levels drop below 120 yields may drop off rapidly.

When soil test potassium is above 120, no potassium fertilizer is needed to maintain production for short periods of time.

However, if no potassium is applied the crop removing potassium will reduce soil potassium, resulting in reduced crop yields as the soil test decreases below the critical value.

Forage crops remove 45 pounds of potassium per ton of dry forage removed from the field.

Supplement. Supplemental P and K fertilizers are needed to replace fertility removed in harvested crops and to increase plant nutrients in soils low in fertility.

When the soil test is maintained in the medium to high range, supplemental nutrients only need to be applied at the removal rate in order to maintain yields near the maximum.

However, when soil test phosphorus drops into the low range higher rates of supplement are needed since part of the phosphorus is held by the soil and is less available to plants.

How much? On soils testing low in phosphorus, supplemental phosphorus at up to 4 times the removal rate may be needed to obtain maximum yield.

Crops grown on soils testing medium to high in potassium will produce their maximum yield when potassium is supplemented at the crop removal rate.

Crops grown on soils testing low in potassium only need supplemental potassium at the crop removal rate, since soils in our region do not hold potassium in forms not readily available to plants.

Determined by yield. Growers need to remember that fertilizer needs are determined by forage yield.

A ton of hay removes 12 pounds of phosphorus per ton and 45 pounds of potassium per ton – a 5 ton annual yield will need 58 pounds of actual phosphorus and 225 pounds of actual potash replaced.

Different crops require different soil pH levels for optimum performance; alfalfa should have a pH of 6.5 to 6.8.

The topsoil in fields with acid subsoils (most common in eastern Ohio) should be maintained at a higher pH to minimize chances for nutrient deficiencies associated with acid soil conditions.

(The author is an agricultural extension agent in Stark and Summit counties. Questions or comments can be sent in care of Farm and Dairy, P.O. Box 38, Salem, OH 44460.)

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