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|