Managing N Loss With Cover Crops and N Tests

By Sarah Young Livestock Editor
Thursday, October 16, 2008 7:53 AM CDT

No producer wants to experience nitrogen loss, especially when nitrogen prices are at historically high prices. A producer’s overall goal is to maximize yield while minimizing total input costs.

Producers need to find out how to gain higher nitrogen recovery by crops while reducing overall risk of nitrogen loss.

“Unfortunately not all those factors that affect nitrogen loss are under our control,” said Nancy Drummey, Discovery Farms outreach educator at a recent field day held at Koepke Farms in Oconomowoc.

Nitrogen is usually applied at the “optimum nitrogen” rate, but what exactly is that rate? Will it solve the nitrogen loss problem by only applying the optimum rate? Drummey says the calculation is confusing because it is tied closely to soil type and the soils ability to hold onto nitrogen.

“We have to go beyond rates,” she said.

Most nitrogen is lost as nitrate and usually in the top three feet of soil. Those higher amounts are found on corn on corn acres, and fields with long manure history.

Cover crops

Barren soils make it easy for nitrogen to escape. Using quick establishing cover crops help to save and hang onto nitrogen in the soil.

Nitrate reduction increases with the overall growth and biomass of the cover crop.

In Kentucky, the use of rye as a cover crop resulted in a 94 percent reduction in nitrate. However, in Minnesota, only a 13 percent reduction was found, and Drummey attributes the low number to frozen tile.

She added that Wisconsin numbers would be higher because most tile lines don’t freeze solid, and last winter at the Koepke Farm, lines were running all day long, every day.

In research conducted at the Arlington Research Station, soil nitrate left in soil after the application of 40 tons per acre of dairy manure was reduced by almost 50 percent when using a cover crop versus no cover crop.

Winter rye, oats, triticale and even barely are suggested cover crops following corn silage harvest. Following small grains or vegetable crops, Drummey suggests winter rye, oats, clover and vetch.

Vegetable crops give the most time for cover crops to become established, but they are becoming more popular after legumes and corn silage.

There are some limitations when it comes to cover crops.

With cover crops, there is a short window of opportunity to get the crop planted and established well enough to make a difference. The additional planting and removing time and labor costs n need to be compared with the cost of saving the nitrogen. In the spring, cover crops can draw down available moisture if not removed quickly and early in the planting season.

Nitrogen test options

Once the corn crop is established, Drummey suggests a pre-sidedress nitrogen test to determine nitrogen loss to gauge nitrogen rates before sidedressing. The test is generally conducted four weeks after planting between planting and V6 growth stage.

Another useful test for growers is the End of Season Stalk Test. Inexpensive, the test measures nitrogen as insufficient, adequate, or excessive. This gives growers insight into their current nitrogen program, and can be used to aid in the following year’s application.

“It gives us a good idea if you’re in the ballpark,” Drummey said.

Application timing

Most nitrogen is taken up by corn at the V6 stage, five to six weeks after planting. The longer the nitrogen sits in the barren soil, the greater the opportunity for loss, said Drummey. Use soil type to help determine optimum application timing.

* Medium to fine well-drained soils: The optimum application should be completed in the pre-plant timeframe in the spring. Fall and sidedress applications are not recommended.

* Medium to fine poorly drained soils: Optimum application would be sidedressing, but generally okay to use pre-plant application. Fall applications are not recommended.

* Coarse soils: Optimum applications would be sidedressing, and fall and pre-plant applications are highly discouraged.

All nitrogen application and timing need to be heavily managed to reap the highest benefits. It is possible not all farms and fields in your operation will require the same nitrogen application time or rates.

“You really need to think of each field independently,” she said.

Comments »

Comment on this story

Comments will be approved within 48 hours

Name:

Email: (optional)

Comments:

Image Verification: (Case sensitive)