Soil Temperatures for Germination

County Agent News

Dan Folske

May 3, 2010

Soil Temperatures for Germination

            The minimum soil temperatures for germination of various crops or groups of crops is 40 degrees for spring wheat, durum, barley, canola, mustard, safflower, field peas and lentils; 45 degrees for oats, chickpeas, and sunflowers; 48 degrees for flax, and 50 degrees for corn, soybeans and dry beans.  Optimal soil temperatures for germination and emergence are about 5 to 10 degrees warmer.

            When seeding into soils at or near the minimum germination temperature for the crop, consider the use of basic seed treatment products.  Seed planted into cooler soil will take longer to germinate and emerge, which means that it will have greater exposure to soil pathogens. If the soil is wet, this will also favor the activity of many soil-borne pathogens.  Seed treatment will help provide protection against these pathogens, which can reduce stands due to seed rots and seedling blights.  It will also help protect the seed or seedling if we run into adverse conditions following seeding which further delays emergence, such as a cool, wet spell or a late spring snow storm.

            Most seed treatment products are registered for on-farm use, either for drill box application or to be applied in a mist or slurry with an auger treater. For information on current seed treatment products registered on all crops in North Dakota, check the 2010 North Dakota Field Crop fungicide Guide (Extension Circular PP-622) available at the Extension office or http://www.ag.ndsu.nodak.edu/extplantpath/ .  Always read the label carefully and follow the label directions for application procedures, rates, and specific diseases controlled.

            Producers are reminded that information on soil temperatures can be obtained from the North Dakota Agricultural Weather Network (NDAWN) station.  Current soil temperatures under bare ground can be obtained by calling the weather station at 243-6325, be sure to press * at end of message.  Additional information on soil temperatures such as the average daily soil temperatures and soil temperatures under turf can be obtained at the NDAWN website which is http://ndawn.ndsu.nodak.edu.  Remember soil reference temperatures are taken at approximately 9 AM, not in the middle of the warmest part of the afternoon.

Reducing Risk On Surface Applied Urea

            While urea is best managed by covering with soil soon after application to eliminate the potential for any significant nitrogen loss due to volatilization, there are situations where producers may have to rely on surface applications.  Some examples would be direct seeding or no-till with no capability of side-banding or mid-row banding and nitrogen needs which exceed what can safely be placed with the seed or top dressing winter wheat.

            Ammonia volatilization is basically loss of nitrogen to the air and a number of environmental and soil related factors interact together to affect this process.   Most research shows that losses are enhanced by high soil pH, warm temperatures, and damp soil surfaces or light rains sufficient to moisten the soil surface but insufficient to move the urea below the soil surface.  Tillage systems which leave the crop residue on the soil surface can also increase volatilization losses of urea because the urease enzyme, which is responsible for the hydrolysis of urea and volatilization loss, is more concentrated and active in crop residues than it is in bare soil.

            The best scenario for surface applied urea to prevent volatilization loss would be to have rainfall of at least one-half inch within 24 hours of application.  The least desirable scenario for surface applied urea would be application to heavy residue when the soil surface and residue is wet followed by warm, windy conditions.   Due to all the interacting factors, it is impossible to predict exactly how much nitrogen could be lost, however, nitrogen losses under these conditions could easily be in the range of 10 to 20 percent if it remains on the surface for 4 to 7 days before a significant rain and could possibly be as high as 50 percent.  Recent research conducted in Montana documented ammonia losses that have ranged from as low as 3 percent of the application rate to as high as 40 percent and averaged 24 percent even when applied under relatively cool condition in early spring or late fall.  To minimize nitrogen loss, try to apply urea when the soil surface and residue are dry, and then hope that things remain relatively dry until a significant rainfall occurs.

            Another option to limit the potential loss of nitrogen with broadcast urea applications would be to have the urea treated with a urease inhibitor that is commercially available under the trade name of Agrotain.  Agrotain will add to the cost of the fertility program but will keep urea stable on the surface and provide protection against volatilization for about two weeks, allowing more time for adequate rainfall to incorporate the urea before any significant nitrogen loss occurs.  Agrotain treatments were included in the Montana studies and reduced the nitrogen loss from 40 percent to 18 percent in the highest nitrogen loss scenario and from 24 percent to 9 percent on average.  The Agrotain treatment didn’t totally eliminate nitrogen loss due to volatilization, but reduced it by around 60 percent, which would more than pay for the cost of treatment.