For information . . . on fertilizer price swings, see Comparing world fertilizer prices in this week's CropWatch. Also see Nutrient Management for Agronomic Crops in Nebraska, (EC155).

Credit residual soil nitrate-N. Collect soil samples to at least a 3- to 4-foot depth for corn and sugar beets. 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.

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 over time). With Western Sugar implementing quality contracts in 2007, producers will definitely want to deep sample for residual nitrate and set realistic sugar beet production goals.

Credit nitrogen from previous crop residue or legume crops. Soil tests will not show these credits as the residue or nodules must break down during the growing season. Use less nitrogen for corn after sugar beet, alfalfa and dry bean. The nitrogen credit for alfalfa ranges from 80 to 150 lbs per acre (see Fertilizer Suggestions For Corn, G174). UNL research shows that the average nitrogen rate required to maximize corn yield following sugar beets is only 90 to 100 lbs nitrogen per acre. The nitrogen credit for corn following dry bean is about 25 lbs/ac. Because most producers fertilize dry beans with nitrogen to improve yield, sampling for residual nitrate is suggested on bean ground that will go to sugar beets (quality considerations) or corn (total nitrogen cost).

Credit 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, however. Nitorgen availability varies with organic sources because nitrogen must be converted from organic to usable inorganic forms. The crop should be monitored mid-summer to see if additional inorganic nitrogen may be required to reach yield expectations. More information can be found at http://cropwatch.unl.edu/focusnitrogen.htm or http://soilfertility.unl.edu.

Credit nitrogen released from soil organic matter. This is considered in the UNL algorithm for corn when you have soil test results.

Improve nitrogen use efficiency with timing of application. Split applications or multiple applications if you are using center pivots generally improves nitrogen use efficiency.

Know your soil P, K and Zn levels. Potassium levels in most western Nebraska soils are more than sufficient for optimum crop performance. Many fields have high phosphorus levels because of a sugar beet history and the likelihood of an economic response to phosphorus fertilizer is low. Soil samples for the 0- to 8-inch depth should be analyzed for pH, organic matter, P, K and zinc, then follow UNL suggested application rates. Nutrient placement can be important in efficient use. Recovery of P and Zn during the year of application is greater with band applications than with broadcast application. Band application can be done at planting (standard 2-by2-inch band beside the seed) or can be done with strip or zone tillage (shank) equipment if the phosphorus is placed about 4 to 5 inches below the surface under the seed. Application rates for phosphorus 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 (more than 230 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 to evaluate whether 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 with 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 for unbiased information from University of Nebraska-Lincoln Extension educators and specialists.

Gary Hergert
Extension Soils Specialist
Panhandle REC

Copyright 2006 by the University of Nebraska Board of Regents. All rights reserved.

Published by University of Nebraska-Lincoln Extension in the Institute of Agriculture and Natural Resources Cooperating with the counties and the U.S. Department of Agriculture.

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