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It's Time to Top-dress Winter Pasture

Posted Feb. 1, 2005

As I write this article, we have just entered the new year. Looking back on the weather of fall 2004, it was different, just like in every other year. We started winter pasture planting season in August with ample moisture. Those who were ready planted on time and got excellent stands of winter pasture. Worms and hoppers were not a big problem since they had plenty of other green to eat in most areas. Then, in September, when it should have rained, it didn't. October and November were again wet, and it's raining today. Because of this, many wheat fields have either received no nitrogen (N) for the year or have lost some from leaching.

February is typically the time when top-dress applications of N are made to small grains for graze out or for grain harvest. Research by the Noble Research Institute has repeatedly shown that about 140 pounds actual N is optimal for small grains for forage only. Nitrogen application timing fall, spring or split doesn't affect total production, only production timing.

So, how do you know how much N to apply in February? The first question you should ask is "Do I need to?" Do you have growing cattle that can efficiently utilize high-quality forage? If so, how much N has already been applied? That number subtracted from 140 is a good place to start calculating.

If you have 10 days, you can do some testing. Take a soil sample from 0 to 6 inches and 6 to 12 inches and have it analyzed for nitrate nitrogen. Then a soil and crop specialist can recommend the needed amount of N based on your production goals. Another test that can be done is a forage analysis for crude protein. Crude protein is expected to be in the high teens or higher. If it's less than that, more N may be needed.

Color can be used as a rudimentary indicator. Dark green, healthy plants may not need any more N while pale yellow plants probably do. You can also look for dark green growthy spots where there is a cow pie. This would indicate a need for more fertilizer.

If you have a couple of weeks and the initiative, you could apply some check strips of, say, 60 pounds of actual N across the middle of the field in an "X" pattern in early February. If you can't tell the difference between these strips and the rest of the field within about three weeks, you probably don't need more N. If you see a big difference between these strips and the rest of the field, you probably do need N. This method is even better when done in the fall. That gives you the whole fall/winter season to gauge your N status compared to an "N rich" strip.

Some new technology that is available is the Green Seeker system. This system uses infrared optical sensing and computer calculations to determine the optimum N top-dress rate, on the go, during application. If your fertilizer dealer does not own one of these rigs, you can use the same technology with a hand-held unit and computer Web site to determine an N rate for your field. More information on this technology is available at nue.okstate.edu.

I know fertilizer prices are extremely high. Remember that phosphorus, potassium and pH must also be adequate to get the most out of your nitrogen fertilizer dollar.