Hi,

You need first to ensure that your sample is representative of the population you are analysing

If you sample is complex, then divide it into separate parts for example the leafy part together, the stem and root as three separates. Record the fresh weight of each separate

Reduce the sample fractions by cutting into smaller parts for drying in an oven at 70oC to constant mass.  Record the fresh weight sample before drying and the oven dry weight in the cold after drying. Calculate the % dry matter for each fraction, from which the total dry matter can be calculated.

Grind each separate on their own and analysed them separately for NPK using recommended test methods. From the result you will be able to calculate the NPK of the whole plant sample of the population.

Good  luck

To prepare plant samples for laboratory analyses, you should dry them at 60°C maximum, the grind finely (

Hi,

Dry the whole sample in an oven with forced air at 40 °C. Samples would have to lose more or less a 90% of weight. Mill them as fine as possible. To analyze, mix and get a representative weight  of them.

I'l agrre with my colleagues coments. But is important that sampling of individuals be hazardous, if it is a culture plant, number each one and make an alleatory selecction. 

I'l agree with Lilia Rabeharisoa.

Good question and valuable answers, indeed the first and foremost thing to be ensure is the proper sampling and sample preparation. Rest a number of methods are available to analyze the NPK content.

One of the related question is that whether plants have available form of nutrients or in what form does the plant material possess the nutrients. If for instance i prepare a compost from the leaves litter and wish to compare the nutrient pool in initial substrate and the final compost, what methodology need to be followed. Does the initial substrate (leaves litter) too have the available nutrients as the final compost? If yes how i can estimate?

PS: since discussion is going on in the related topic i too put my question. Sorry for any interruption.

I am adding with 1st answer, if there there is any grain/fruit you can also another  separate for fruit/grain. Nonetheless, if you have soil sample for NPK, It will be helpful for interpreting NPK of Plant sample. Thanks

I am agree with Lilia Rabeharisoa

in addition to the previous precise answers, pay attention to know how to clean your samples, according to your plant type,  and avoid pollution during dessication and grinding.

good work

Plant samples collected were oven dried at 70 degree Celsius till a constant weight was obtained. A portion of these dried samples were ground (< 0.2mm) for the determination of NPK.

Hi, sorry for interrupting. I just want to know why many standard method for drying plant material must use 70 degree celsius? Does anyone know the reason behind it? Thank you.

After harvesting the samples you can separate the plant parts (viz. leaves, stem, flower, fruits,and roots etc) and kept it  for drying in an oven at 70 C till constant weight. The separated samples were grind it for  analysis of N, P and K by suitable methods. You can estimate N, P and K by using an Autoanalyzer.

Why 70 C? It does not have to be 70 C; you will find drying temperatures from 60 to 80 C in the literature. What is important is obtaining a constant weight without degrading the sample.

A range of temperatures can be used for drying plant material although temperatures over 90°C are not recommended. We prefer a higher temperature (60-80°C) to cause an instant cessation of plant metabolism. Tests in our research group indicate that these temperatures do not cause a significant loss of plant N. This is also supported by many other published works for example: Maryland, 1968, Agron. J. 60, 658-9; Sharkey 1970 Grass Forage Sci. 25, 289-294; Ramsumair et al., 2014.Trop Agric. 91,179-86; Cone et al., 1996. J Ag Sci. 126, 7-14).

After harvesting you should divide your plants in to three portions like stem,leaves and roots.After that wash the roots with tapwater and measure the fresh weight of all three samples. Shift your sample to oven for drying  at 70 C till constant weight. Then measure the desire attributes .

I agree with Karuppiah Karunaichamy

Wonderful topic at hand, Does the drying temperature differ from crop to crop? between oven drying and room temperature air-drying which one is more convenient or recommendable? any further detailed preparation procedures in steps for cereals crop such Maize, Pearl Millet, Sorghum, and Cowpea?