Dear Makid,

do not dry and extract DOC from fresh soil as suggested by Jones, D.L., Willett, V.B., 2006. Experimental evaluation of methods to quantify dissolved organic nitrogen (DON) and dissolved organic carbon (DOC) in soil. Soil Biol. Biochem. 38, 991–999. https://doi.org/10.1016/j.soilbio.2005.08.012.

For total carbon measurements (e.g. element analyzer) soils are usually dried at 40°C until constant weight. For soil water determination soils are heated up to 105 or even 110°C.

Best

Nils

110 degree celsius

I think if you want to analyse dissolved organic matter in soil then the best temperature for oven drying of soil is 60 degree Celsius.

Dear Makid,

do not dry and extract DOC from fresh soil as suggested by Jones, D.L., Willett, V.B., 2006. Experimental evaluation of methods to quantify dissolved organic nitrogen (DON) and dissolved organic carbon (DOC) in soil. Soil Biol. Biochem. 38, 991–999. https://doi.org/10.1016/j.soilbio.2005.08.012.

For total carbon measurements (e.g. element analyzer) soils are usually dried at 40°C until constant weight. For soil water determination soils are heated up to 105 or even 110°C.

Best

Nils

I agree with Nils: Do not dry at all, but use fresh soil with its natural water content for extraction.

drying may destroy the DOC. so i also agree with Nils sir.

Do not oven dry at 105 -110 oC except for soil water determination.Air drying at room temprature is normal for DOC

Adewale is correct. Any heating may change the nature of the soil organic matter status. Air drying is natural (soils frequently air dry in nature) and causes the least change in SOM while it stops most microbial processes. Usually, air dry soil contains about 1-3% H20 depending mainly on soil texture and organic matter content. If you want to correct your analyses for water content, you can then dry a subsample of the soil sample at 105 C to determine the hygroscopic water content of the air dry soil. This is common practice for most common and routine soil analyses.

You are to determine the dissolved organic matter, then why will you need to go for soil drying on an oven. Drying the soils on oven may cause the loss of the organic matter even at low temperature (about 60 C). Air dried samples are sufficient to provide the dissolved organic matter. Also, follow the procedure suggested by Dr. Nils. I agree with the suggestions given by Dr. Larry.

Best regards,

SD

I recommend Sovan's answer

Best Regards

Hello all,

Is it manadotry to air dried (oven) soil samples for elemental analysis on recommended temperture for example 40-65 oC? Is it not sufficient If we dry on room temperature until constant weight? Should we oven dry before sieving or we can dry after sieving too? Thank you.

Dear Abhishek,

You don't need to oven dry the soil samples for any elemental analysis. Drying in shed in room temperature to constant weight is sufficient for any analysis. Drying followed by sieving is recommended.

With Regards,

SD

Best temperature for oven drying of soil is 60 degree Celsius.

I agree with Sovan. For just general elemental analysis air drying is adequate. In fact most analytical methods are done on air-dried soils. Air-dried soils may have about 1-3% water, this variation is very minor when conducting normal chemical analysis. The soils are in the same state. Once the soils are air dried, they may be crushed and then sieved to some standard particle size (usually 1-2 mm) and homogenized (well mixed) before analysis. Crushing is recommended to reduce the particle (actually aggregate) size before sieving. If uncrushed soil is sieved then segregation of soil separates may occur which might bias the analyses because the smaller particles may contain more clay and the larger particles contain more sand. Each of these fractions has a different capacity to hold nutrients and so, this might cause a bias in analysis.

Look, I don't want to be arrogant or rude, but I am working more than 28 years in soil sampling, soil analyzing and interpretation of achieved results related to vegetation cover. The question is, what kind of analyses you're doing after drying of soil. You mentioned you're anaylsing the quantity of dissolved organic matter. So, you're doing all the analyses in soil solution. If yes, than you MUST have air dried soil samples. So, I completely agree with all the colleagues who adviced you to avoiud using the oven in drying of soil samples for analysing of dissolved organic matter.

Only air drying is sufficient for dissolved organic matter analysis. Organic content is significantly reduced during oven drying process over 60 degree C temperature.