NDSU Crop and Pest Report
Soils


ISSUE 7  June 13, 2002

 

FERTILIZER AND HEAVY RAINFALL

Light steady rainfall is desirable for moving fertilizer, especially urea, into the soil if applied to the soil surface. However, heavy downpours which result in surface water runoff would also be expected to move a large portion of the urea off the field and into waterways. In fields where ponding occurs, the fertilizer which was dissolved during the rain will remain dissolved until the water evaporates and will tend to concentrate near the last places where water stands. It is not possible to estimate losses from runoff immediately after fertilizer application, however, they should be considered substantial. Fertilizer injected into the soil, such as with an ammonia side-dress application, are only at risk if the soil actually moves. Fertilizer which was cultivated into the soil will also only be at risk if the soil moves.

 

NITROGEN STATUS OF SOIL COVERED WITH WATER

Areas of fields in the eastern 50 miles of North Dakota which have been covered with water due to heavy rains are in danger not only of crop damage or loss, but loss of nitrogen fertilizer due to denitrification. Denitrification is a bacteria mediated process which occurs during low oxygen conditions such as flooding. In warm soils, as we now have, losses of 50% in 24 hours is common. The nitrogen must be nitrate for the denitrification conversion of nitrate to nitrogen gases to occur. Nitrogen applied last fall is most at risk, but any nitrogen which was applied earlier than two weeks before the rains is largely at risk as well, since a large portion of that later applied ammonium fertilizer has also been converted to nitrate between application and the rain.

If crops survive being covered with water, they will appear yellow for a time simply because of the stress being flooded causes. However, if the crop do not restore their green color in about 10 days, supplemental nitrogen may be needed to help make a decent crop. Tissue tests or soil samples can confirm N status. Nitrogen deficiency symptoms will appear first on lower leaves. Newer leaves will be more green.

 

GROWING DEGREE DAYS- 1961-1990 AVERAGE COMPARED WITH 2002

Growing degree days are lower this year than the 30 year average. Although the temperatures during the rest of the season may make up some difference, there is some concern that longer season row crops may need a wider frost-free window in the fall if summer degree days are just normal. Corn GDD’s are from normal to 20% lower than the long-term mean, figuring that crop emergence was May 10. If the crop did not emerge until later, these GDD’s cannot be factored into its estimated maturity.

Location

Wheat (32o)
April 20 - June 11

Corn (50o)
May 10 - June 11

30 year
Est. mean

2002

30 year
Est. mean

2002

Bowbells

1086

860

325

283

Bowman

1122

996

361

354

Carrington

1165

928

336

329

Crary

1124

891

341

309

Dickinson

1095

939

330

312

Fargo

1256

1072

387

393

Grand Forks

1188

977

365

355

Hettinger

1140

955

337

332

Jamestown

1222

974

374

341

Langdon

1080

837

324

273

Mandan

1205

996

361

354

Minot

1173

923

341

309

Wishek

1101

972

328

334

Williston

1222

963

369

323

Dave Franzen
NDSU Extension Soil Specialist
(701) 231-8884
dfranzen@ndsuext.nodak.edu


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