I have been getting problems following dry matter determination for grass samples as I obtained more than 95% DM content in fresh grass, which is very odd. The practice is to dry the sample before grinding and only then the dried sample is send for proximate analyses.
Based on FAO - Quality Assurance for Feed Analysis Laboratories (2011), samples need to be ground, but it does not mention whether we have to dry the moisture out first or not in case of wet samples.
Furthermore, dry matter test for silage is suggested to be done at 60 celcius for 24 hours.
I would like to know is this applicable to fresh grass (moisture more than 15%)? And if it's partially dried (DM >85%), do I need to dry it again before grinding? In addition to that, should I continue to dry wet samples first before proceeding to the DM test?
Anyone with experience in testing dry matter in grasses/forages/fodder, please help. Thank you very much.
To get the DM you need to weigh fresh, dry out all the moisture 60C for 24h and re weight. Then express the dry weight over the wet weight as a %.
Depending on size and how wet the samples are, you may need to dry for longer than 24 hours at 60 degrees Celsius. You may need to cool the samples down in a desiccator to avoid error.
Yes agreed - probably up to 48h for grass silages etc. And cool in desiccator
The sample you send it for proximate analysis is partial Dry sample thus you need to corrected the results obtined as partial dry mater and for DM% in the original sample(Fresh sample ) = ((Partial DM Sample %/100 )× (DM% in Partial Sample/100). × 100.
the dry mater test for silage at 60 celcius for 24 hours depend on the sample size and
may be need more time up to 48h and this you decide it when you found your sample is still wet low than 85% DM and could not ground it.
please note you must turned up and down the sample with good separation in Aluminium tray during the partial DM and make sure not accumulated .
Note heat method may be underestimate DM, alternatively you can estimate DM in silage by Toluene distillation Method.
I hope it would useful for your research
good luck
📷Le pourcentage de la matière sèche (MS) est déterminé selon la méthode de l’Association of Official Analytical Chemist (AOAC, 1990). 0,5g d’échantillon est introduit dans un creuset en porcelaine préalablement pesé (P1) et dans une étuve à 103 oC pendant
une nuit. A la sortie, le creuset est introduit dans un dessiccateur, puis pesé de nouveau (P2) et la matière sèche (MS) est obtenue à partir de la formule suivante: ((P2-P1)/m)*100
Nur Athirah Mohd Azhar
You can dry your samples at 72 oC for 72 hours then re weight and grinding samples as soon as possible for analysis.
Best wishes.
All the precedents suggestions are useful. If you want to determine MS only, the temperature is 105°C. This sample is only for DM test and not be use for other determinations. For nitrogen detrmination we use fres samples.
Best wishes
Dry matter of the grass samples: not necessary to grind the sample. you can make it into small pieces and dry it till there is no further decrease in the weight while drying. grinding itself will reduce the moisture content. DM is always measured from the fresh sample.
For silage the Drying temperature is less as at beyond this the VFA may be affected.
You may dry at 60 Celsius until a constant weight is achieved. This is preferable because of variation in the moisture content (MC) of the silage. If it is very high in moisture, 24 hours will not be okay. Whatever the MC is, drying to a constant is much safer, and gives accurate a more accurate result.
For silage dry matter estimation 60 degree C for h may not be sufficient. Again silage condition and the source of silage also determine the moisture content. The basic principle of DM estimation is to dry till we will get a constant weight for 2 consucative days.
Regards
DM determination for any solid sample can be dine at 105 degrees Celsius but the dried sample will not be appropriate for further analyses. Samples high in moisture content are usually dried at lower temperatures but for longer periods, this will ensure that only the moisture us removed in the process of drying.
Many factors affect the time it takes for a sample to be fully dried, this includes the weight/size of sample, area surface of sample during drying and the amount of moisture.
To ensure sample is completely devoid of moisture, the sample should be dried to a constant weight with substantial interval between readings.
I hope this helps. All the best
Helen
There is an angle that should be considered aside from all the useful suggestions above. As fed DM is different and separate from the DM% earlier described so far. The underlining fact is that both depends on attaintment of constant weights. The answers so far needed to also be structured to reflect that moisture determination must follow standard procedure and the heated material heated till the constant weight is attained, cooled in a dessicator prior to the taking of the post dried weight
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