Spectrum Analytic Inc
1087 Jamison Rd
Washington Court House, OH 43160
(800) 321-1562
1087 Jamison Rd
Washington Court House, OH 43160
(800) 321-1562
Knowledge is key to using your analytic results to their fullest. The Spectrum Agronomic Library provides you with useful information that will help you to better understand the complex science of agronomy. Our agronomists will be continually adding original and reprinted articles, so check the library regularly for new information.
On March 1, 2015, Spectrum Analytic activated the Penn State fertility recommendations for soil samples sent to Spectrum Analytic. We did this because we had many customers from Pennsylvania requesting the Penn State recommendations for use in Nutrient Management plans. Keep in mind these are Penn State recommendations, so you need to contact agronomists at Penn State if you have questions about how they were derived.
The system is set up so that crops are in the 40,000 series followed by the Penn State crop code system. For example: Corn for Grain (No-till) in Penn State crop code 1044, in the Spectrum Analytic system the crop code will be 41044. We did this to minimize conflict of numbers between the Penn State crop code system and the crop codes that Spectrum Analytic already has in place for our present recommendation system. If you would like a complete list of the Penn State crop codes you can go to our website, click on crop codes and do an alphabetical listing of the crops, from here you can highlight and copy the crops you want and paste the list into a word document or spreadsheet for future use.
We have tried to duplicate as closely as possible the nitrogen, phosphorus, potassium and magnesium recommendations from Penn State. The lime recommendations as well as micronutrient recommendations default to the Spectrum Analytic system. Keep in mind that the optimum ranges for soil pH, phosphorus (P) and potassium (K) are from Penn State. The Spectrum Analytic recommendation system sets the target pH in the middle of the optimum range for our crops, while the target pH for Penn State agronomic crops is the pH level at the lowest end of the optimum range. For vegetable crops, the Opt pH also defines target pH for lime recommendations. The lower limit of the Optimum range on the graph is 0.5 pH units less than the Opt pH. The High pH sets upper limit of Optimum range (7.0 for all veg crops). Where Opt pH is 7.0 the optimum range for the graph is 6.5 to 7.0. Where Opt pH is 6.5, the optimum range is 6.0 to 7.0.
The Spectrum Analytic system does not have Penn State comments for each crop as listed on the recommendations from Penn State. However you can reference all the comments for Penn State by going to their website and looking up the specific crop. http://agsci.psu.edu/aasl/soil-testing/soil-fertility-testing/handbooks
The chart below is used by Penn State for nitrogen credit (lb N/A) from previous legume crops
| Corn Yield Goal (bushel/acre) or Corn Silage Yield Goal (tons/acre) | |||||
|---|---|---|---|---|---|
| Legume & percent stand | 100 bu/17 tons | 130 bu/21 tons | 160 bu/25 tons | 190 bu/29 tons | 220 bu/33 tons |
| Alfalfa, clover, trefoil <25% stand | 40 | 40 | 40 | 80 | 120 |
| Alfalfa, clover, trefoil 25-50% stand | 60 | 80 | 80 | 120 | 160 |
| Alfalfa, clover, trefoil >50% stand | 80 | 110 | 120 | 130 | 200 |
| Soybeans | 30 | 40 | 50 | 70 | 90 |
The PSNT is a soil test for nitrate-nitrogen (NO3-N) developed for use at the 4 to 6 leaf stage of corn to help in making more accurate N fertilizer recommendations at sidedressing time. The test, designed by Dr. Fred Magdoff at the University of Vermont, was initially developed to help in estimating the amount of N available where manure or other organic wastes have been applied, or corn is grown in rotation with a forage legume. The PSNT was initially developed to identify fields that would not be expected to respond to additional N. The test uses the NO3-N content of the top foot of soil as an estimate of the amount of N available to the crop. Research in a number of states has confirmed that this test can be useful in managing N on corn. Work in Massachusetts, California and Florida has also shown the PSNT to be useful for some vegetable crops. By far, the major use of PSNT is in the production of field corn, which is the focus of this paper.
As the PSNT has been adopted by agriculture, there has been a great demand to make calibrated N recommendations based on the test results. In other words, agronomists have been asked to make N recommendations that are adjusted for, or inversely proportional to the amount of residual NO3-N found in the soil. Given that the original purpose of the PSNT was simply to identify soils that were non-responsive to N, we may be asking a lot of this test by using it to accurately calibrate soil N status levels or N recommendations. However, some progress in this area has occurred. There is agreement on the general range of soil NO3-N that is considered critical for adequate corn growth without additional N applications. This range is from 21 to 30 ppm NO3-N in the top 12 inches of the soil when the corn is in the 4 to 6 leaf stage. Many Universities consider the critical NO3-N value to be 25 ppm.
There is less agreement on how much supplemental N to recommend when the PSNT result is between zero and the critical level. In other words, how do we calibrate N recommendations to PSNT results? Most of us understand that agronomists often disagree on fertilizer recommendations, and the PSNT is no exception. There is some research that supports higher N recommendations when the PSNT result is low and lower recommendations when the result is closer to the critical level. However, many factors of weather, soil conditions, corn hybrid, crop management, and others may change crop response to a particular PSNT level. It is not within the scope of this paper to thoroughly discuss all of the factors that can influence the reliability of N recommendations based on PSNT results. However, like all soil testing, the PSNT should be used as a guide, not a guarantee. Neither the PSNT result nor the N recommendation should be over-simplified to a simple recipe. The PSNT is simply one part of the complicated process of crop management.
Another occasional point of confusion occurs when we try to reconcile the ppm of NO3-N with the amount of N required by a corn crop, or the amount of N applied prior to taking the PSNT sample. The PSNT result is an “index” of available N, not a calculation factor. You should not try to perform calculations to reconcile the amount of N applied or crop uptake with PSNT results, because they will not likely “add up”. We must keep in mind that a crop typically utilizes N from below the 12 inch sampling depth; it will receive N from mineralizing soil organic matter; it may lose access to N due to denitrification or leaching later in the season; or other factors may change the N available to the crop, either before or after the PSNT is taken.