• Credit residual soil nitrate-N. Collect soil samples to at least a 3- to 4-foot depth. Suggested sampling increments are 0 to 8 inches, 8 to 24 inches and 24 to 48 inches. Residual nitrate-N is used as efficiently as fertilizer nitrogen. If the field has a history of manure application, nitrate-N can be substantial. For more information see NebGuide G1740, Guidelines for Soil Sampling, at www.ianrpubs.unl.edu/sendIt/g1740.pdf) or EC154, Soil Sampling for Precision Agriculture, at www.ianrpubs.unl.edu/sendIt/ec154.pdf.
• Set realistic yield goals. Expected yield is THE major factor in determining the nitrogen rate for corn. UNL suggests using a proven five-year average corn yield plus 5% (to account for hybrid and management improvements).
• Credit N from previous crop residue or legume crops. Soil tests will not show legume or crop residue credits as the residue or nodules must break down during the growing season. Use less nitrogen for corn after soybean, sugar beet, alfalfa and dry bean in your rotation. The nitrogen credit for alfalfa ranges from 80 to 150 lbs/ac (see NebGuide G174, Fertilizer Suggestions for Corn, at www.ianrpubs.unl.edu/sendIt/g174.pdf ).
• Value and use manure sources properly. Manure is an excellent nutrient source for nitrogen, phosphorus and micronutrients (zinc and iron). It often produces higher yields than inorganic fertilizer alone. Manure and compost should be tested for nutrient content. The old “ball park” figure of 10 lb nitrogen and 5 lb phosphate per ton can be inaccurate for today’s manure produced with corn by-products. Nitrogen availability in manure varies because nitrogen must be converted from organic to usable inorganic forms. The crop should be monitored mid-summer to see if additional inorganic N may be required to reach yield expectations. More information can be found on UNL’s Soil Fertility Web site at soilfertility.unl.edu or in previous issues of CropWatch
• A spreadsheet to calculate the value of manure can be found on the UNL Comprehensive Nutrient Management Planning Web site at http://cnmp.unl.edu/NebraskaManureValueCalculator1.33.xls.
• Soil organic matter. Nitrogen release from organic matter is considered in the UNL algorithm for corn when you have soil test results. (give web site spreadsheet URL).
• Improve nitrogen use efficiency with timing of application. Split applications or multiple applications if you are using center pivots generally improve nitrogen use efficiency.
• Know your soil P, K and Zn levels. Soil sample the 0- to 8-inch depth for these nutrients and follow UNL suggested application rates. Nutrient placement can be important and affect efficient use. Band application can be done at planting (standard 2-by-2 inch band beside the seed) or can be done with strip or zone tillage (shank) equipment if the phosphorus is placed about 2 to 3 inches below seed depth. Phosphorus application rates can be reduced by 50% with banding as compared to broadcast application.
• Not all fertilizer recommendations are the same. University of Nebraska–Lincoln fertilizer recommendations tend to be lower than those suggested by many commercial labs. UNL suggestions are based on research and on-farm verification. They are generally the most economical rates, even for high yield (>250 bu/ac) situations.
• Consider replicated strip trials to determine the effect of lower or higher rates on yield. Use yield maps or aerial photos to determine the yield variability across fields and evaluate if fertilizer application should be on a management zone or variable rate basis. Fine-tuning fertilizer use needs to be an on-going process.
• Comparison shop. Look at different products and do some “fertilizer arithmetic” to compare the actual cost per pound of nutrients, especially mixed grade fertilizers. Work with a reputable dealer who can provide accurate estimates, timely delivery and well-maintained equipment. Remember, service after the sale is also important. Also look to unbiased information from Extension educators and specialists. Following these suggestions can help keep crop production profitable in 2008.

Gary W. Hergert
Extension Soils Specialist
Panhandle REC, Scottsbluff

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