Tuesday, June 7, 2011

Questions about Nitrogen and Corn?

For some, planting this season is just wrapping up with the final fields of beans being planted. For others things are in full swing. If you are like old Hank Kimball here in the office, things are getting piecemealed in one plot at a time. One of the big questions floating around is, “How much nitrogen do I include in a sidedress application for corn that is planted late?” There is not a simple answer to that question.

Let’s start with where our nitrogen recommendations come from. N (lb/A) = -27 + (1.36* Yield Goal) – N Credit. Simple right? Total pounds of nitrogen to apply equals 1.36 times your yield goal, minus 27, minus any nitrogen credits. The two big questions arise around yield goal and nitrogen credits. Do we need to decrease our yield goal, and do we need to adjust for any nitrogen credits?

There have been many recent teleconferences, late night email exchanges, and phone calls made to our State Corn Specialist, Dr. Peter Thomison, and to Purdue’s own Dr. Bob Nielsen. Both agree that yield loss from late planting depends on what happens later in the season. Will we see ideal rainfall and optimal temperatures or will it turn off hot and dry for the rest of the summer? In recent years with late planted corn yields were as high as 8 % above average to as low as 20 % below average. In most research studies corn planted mid-May faced a 10 % yield loss which increased to 20 % if corn was planted early June. So bringing that yield goal down some may be warranted. It all depends on the weather!

Nitrogen credits are a hot topic, mostly in the form of cover crops and manure. Manure, if you could get any out and incorporated this spring, applied at a rate based on a soil test and manure analysis is fairly easy to account for. The question arises when it was applied last summer after wheat. Will any nitrogen be available?

Cover crops can provide some nitrogen, whether fixed by bacteria in the roots of leguminous cover crops or taken up by a rye cover crop. This nitrogen can be quite finicky in its release and timing. Nitrogen release from residue is a biological process, so environment plays a major role. This is further complicated by the cover crops growing season. To fix nitrogen the Rhizobia bacteria found in a legumes root nodules need an optimal habitat and time. Typically a full growing season is needed to generate a significant amount of nitrogen. However, without bacteria fixing nitrogen, a legume will act like any other crop and take up available nitrogen from the soil.

So how big is the nitrogen credit from manure or a cover crop? An accurate way to determine what is available before a sidedress application of nitrogen is made is to take a pre-sidedress nitrogen test (PSNT). Pulling 10 to 20 cores per field depending on field size, 12 inches deep, combining into a single sample, air drying, and submitting to a testing lab can help you know what nitrogen is available. Once the results come back you can consult with your fertilizer company or local Extension office to determine how much nitrogen to apply in a sidedress. The tests need to be taken as close to the time of nitrogen application as possible. It is recommended to contact your testing lab ahead of time to determine the turnaround time on the samples.

Determining an optimal rate of nitrogen for corn is complicated enough without late planting. But if we wanted a simple job we wouldn’t be in agriculture. A little extra time spent in a corn field that received manure or had a cover crop last season may pay dividends! If you have a surplus of manure in a pit that needs to be emptied, consider sidedressing your corn with it! Just ask Putnam County AgNR Educator Glen Arnold! It can work.

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