1. K-State home
  2. »Agronomy
  3. »Services
  4. »K-State Soil Testing Lab
  5. »Researcher Services
  6. »Plant, Forage, & Grain

Department of Agronomy

Plant, Forage & Grain Analysis

Analytical Scale

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.

Decontamination to remove foreign substances may be necessary, particularly if the tissue is covered with dust or spray materials that contain elements included in the analysis. Oven drying (55-65 C) and sample size reduction (grinding) prepares the sample for laboratory analysis.

Available Testing

Sulfuric Acid Hydrogen Peroxide Digestion

Prepared plant material (0.2500g) is weighed into a 50 ml Kimax digestion tube. In a fume hood, 2ml of concentrated sulfuric acid is added to the tube, then 1ml 30% peroxide. After oxidation reaction has subsided, the tube is placed on a digestion block at 3000C for 20 minutes. Tube is then cooled to room temperature and another 1 ml of peroxide is added before returning to the digestion block. This is repeated until the acid in the tube is clear and colorless.  After cooling, the sample is diluted to 50 ml with ddH20 and mixed by inverting the tube twice.

Analysis for Potassium (K + ) is by Flame Atomic Absorption using sulfuric acid/hydrogen peroxide digested plant material.

Salicylic-Sulfuric Acid Digestion

Prepared plant material (0.2500g) is weighed into a 75ml Techator digestion tube. Boiling chips and 10 ml of the Salicylic-sulfuric acid mixture is added. After 2 hours, 0.6 grams of sodium thiosulfate is added and each tube mixed on a Vortex mixer.  Samples stand overnight.  Tubes are placed in a cold Techator digestion block in a fume hood with a fume capture system attached and the temperature is set at 2000C.

After 1 hour, the temperature is increased to 3850C for 1 hour them samples are removed from the block and allowed to cool. 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.  After cooling, samples are diluted to 75ml using ddH2O and mixed by inverting the tube 3 times.

Nitric-Perchloric Acid Digestion

Prepared plant material (0.2500g) is weighed into a 50 ml Kimax digestion tube. Boiling chips and 5 ml of Nitric acid is added in a fume hood.  Tubes are covered with saran wrap overnight.  5ml of Perchloric acid is added to predigested plant material and tubes are placed on a cold Techator digestion block. Heat is set at 2000C and digests are heated for 2.5 to 3 hours or until white fumes appear and the acid is clear (and colorless when cooled to room temperature).  Tubes are diluted to 25 or 50 ml with ddH2O and mixed by inverting twice.

Analysis for Ca 2 + , Mg 2+ , K + , Cu + , Fe 3+ , Mn 2+ , Zn + , SO 4 2- is by Flame Atomic Absorption or ICP Spectrometry using Nitric-Perchloric digested plant material.

Nitrogen & Phosphorus

Digested plant material from either a sulfuric acid/hydrogen peroxide digest or a Salicylic-Sulfuric digest is analyzed simultaneously using the Technicon AAII auto analyzer with the colorimetric Industrial Method 334-74W/B using separate channels.

Total Carbon & Nitrogen

A LECO CN 2000 combustion analyzer reports total levels (inorganic and organic) of C and N on a weight percent basis. A 0.15-g 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.



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 so lab analysis and processing can occur efficiently.

Please contact the KSU Soil Testing Lab if you need any additional information or suggestions on plant, forage and grain sample collection.

Contact Us

Soil Testing Laboratory
Email the Lab

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

Ph: +1-785-532-7897
Fx: +1-785-532-7412