What causes high replicate variance in my soil nutrient data?

[PaulM]

I’m trying to interpret the results from my soil nutrient analysis, but the variance in my replicates is higher than I expected. I’m not sure if this is due to my sampling method or an issue with the assay’s precision, and it’s making me question the validity of the entire dataset.

[Charles_A]

I had a similar issue last year. I found the repeatability got better after I started mixing all subsamples from a single site really well before splitting for analysis.

[Olivia.B]

In my experience a high coefficient of variation across replicates often points to the lab instrument or prep drift. We kept an extra blank and a calibration check and saw one day the CV drop a bit.

[Jeffrey_C]

Could it be the actual soil heterogeneity you are sampling from I chased measurement error once and realized maybe the soil changes a few meters apart matter more than the tech?

[MatthewT]

I tried increasing reps per site from 3 to 6 and used random subsampling the variance reduced but not eliminated.

[John.L]

I once checked field moisture at collection time and it reminded me how timing can throw off results then I circled back to the same point and felt stuck again.

[Benjamin92]

Honestly I am not sure if the dataset is salvageable yet maybe rerun a subset with tighter SOP and log everything.