for Researchers

Tissue analysis is conducted at various growth stages to determine elemental content of a particular plant part for one or more macro or micro nutrients. Sampling and sample preparation are an important part of the overall process. Leftover material from tests can be returned if requested.

Sample Collection

Plant, forage and grain sample collection will vary depending on the experiment being conducted. Please label all samples and completely fill out the sample information sheets to ensure efficient lab analysis and processing. Please contact the KSU Soil Testing Lab if you need any additional information or suggestions on plant, forage, and grain sample collection.


Available Testing

Sulfuric Acid Hydrogen Peroxide Digestion

  1. Prepared plant material (0.2500g) is weighed into a 50mL Kimax digestion tube.
  2. In a fume hood, 2mL of concentrated sulfuric acid is added to the tube, then 1mL 30% peroxide.
  3. After the oxidation reaction has subsided, the tube is placed on a digestion block at 285°C for 20 minutes.
  4. The tube is then cooled to room temperature and another 1mL of peroxide is added before returning to the digestion block.
  5. This is repeated until the acid in the tube is colorless.
  6. After cooling, the sample is diluted to 50mL with ddH20 and mixed by inverting the tube twice.

Analysis for Nitrogen is on AlpkemRFA. Analysis for Phosphorus and Potassium is on ICP.

Salicylic-Sulfuric Acid Digestion
  1. Prepared plant material (0.2500g) is weighed into a 75mL Techator digestion tube.
  2. Boiling chips and 10mL of the Salicylic-sulfuric acid mixture is added.
  3. After 2 hours, 0.6g of sodium thiosulfate is added and each tube mixed on a Vortex mixer.
  4. Samples stand overnight.
  5. The tubes are placed in a cold Techator digestion block in a fume hood and the temperature is set at 200°C.
  6. After 1 hour, the temperature is increased to 385°C for 1 hour, and then samples are removed from the block and allowed to cool.
  7. One catalyst tablet (SST-Auto from Alfie Packers) is added to each and the tubes are returned to the hot block for 3.5 hours.
  8. After cooling, samples are diluted to 75mL using ddH2O and mixed by inverting the tube 3 times.

Analysis for Nitrogen is on AlpkemRFA and Phosphorus is by ICP.

Nitric-Perchloric Acid Digestion
  1. Prepared plant material (0.2500g) is weighed into a 50 mL Kimax digestion tube.
  2. Boiling chips and 5mL of Nitric acid is added in a fume hood.
  3. Tubes are covered with saran wrap overnight.
  4. 5mL of Perchloric acid is added to predigested plant material and tubes are placed on a cold Techator digestion block.
  5. Heat is set at 200°C and digests are heated for 3 hours or until white fumes appear and the acid is clear (and colorless when cooled to room temperature).
  6. Tubes are diluted to 25mL or 50mL with ddH2O and mixed by inverting twice.

    Analysis for B, Ca2+, Mg2+, K+, Cu+, Fe3+, Mn2+, Zn+, and SO 4 2- is by ICP Spectrometry using Nitric-Perchloric digested plant material.
Total Carbon & Nitrogen

A LECO TruSpec CN combustion analyzer reports total levels (inorganic and organic) of C and N on a weight percent basis. An 0.15g sample of prepared tissue is normally used.


Grain protein is converted from total N (combustion) values by multiplying by 5.7 (wheat) or by 6.25 (other grains). Protein in other plant tissue is converted by multiplying N by 6.25.

Soil Testing Laboratory

K-State Research and Extension
2308 Throckmorton PSC
1712 Claflin Road
Manhattan, KS 66506-5503

Ph: +1-785-532-7897

Lab Hours: 

Mon-Fri 8am-5pm