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Fertilizing grass hay crops with manure


May 27, 2008
By Doug Beegle

As grass hay harvest gets underway, farmers need to be thinking about fertilizing those stands with nitrogen (N). Manure is an excellent choice for these grass hay fields, especially with current high fertilizer prices.

As grass hay harvest gets underway, farmers need to be thinking about fertilizing those stands with nitrogen (N).

The most efficient way to fertilize these grass hay stands is to split apply nitrogen based on the expected yield of the next growth. The actual rate should be 50 lb N/ton of expected hay yield.

Fertilizer should be applied as soon after cutting as practical and manure is an excellent choice for these grass hay fields, especially with current high fertilizer prices.

Grass hay has a high demand for all manure nutrients so it will make good use of manure nutrients. Be aware that if manure is used as the sole source of nitrogen for a grass hay crop, excess phosphorous and potassium will likely be applied over time.

Follow regular soil testing to monitor for excesses of these nutrients. Grass hay fields are a much better choice for manure than legume based hay fields because they need the nitrogen, where as the legumes do not need the nitrogen.

Applying manure between cuttings also provides another window to spread manure. This is typically manure that, if not spread on these hay fields, would be stored and spread in the fall when manure nutrient use efficiency is generally very low. Applying to these hay fields can thus dramatically increase the economic return from manure nutrients compared to late fall applications of the same manure for next year’s crops.

Farmers need to be careful not to apply too much manure that they smother the hay. They also need to apply as soon after harvest as practical to reduce potential injury to the regrowth and watch soil conditions so that they do not cause compaction by driving heavy manure spreaders on wet soils in these hay fields.

Liquid manure is probably best on hay fields because there is less chance of smothering and producers are less likely to gather up remnants of the manure in the next hay harvest. farmers should estimate the amount of nitrogen that will be available from the manure application to make sure it is adequate for optimum production. Depending on the rate applied, supplemental fertilizer nitrogen may be needed also.

The availability of manure nitrogen applied between hay cuttings will range from around 50 percent, if it gets significant rain within a day of application, to only 20 percent if there is no rain for a week.

For example, using book values, applying 5000 gal/A of dairy manure and getting it rained in right away will supply adequate nitrogen for most second cuttings of grass hay (5000 gal/A x 28 lb N/1000 gal x 0.5 = 70 lb avail. N). However, if 5000 gal/A is applied anticipating rain and it does not rain, the farmer may only get 28 lb available N/A (5000 gal/A x 28 lb N/1000 gal x 0.2 = 28 lb avail. N), which means an additional 42 lb N/A, probably as fertilizer, will be required to meet the crop needs for optimum production in this situation.

The bottom line is that with good management, this 5000 gal/A manure application to a grass hay field could be worth as much as $150/A in fertilizer nutrient value.

Doug Beegle is a soil fertility specialist with the Penn State Crop Management Extension Group.
From the May 13 issue of Field Crop News.


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