PO 24. Recognize how the following affect plant tissue analysis results.

Multiple factors influence the analysis of plant tissues and the recommendations made from those analyses.  Crop species and growth stage affect the age and area of plant to be sampled, as well as the critical value, sufficiency range, and toxic value for the nutrients being examined.

The plant parts sampled should be healthy to obtain an accurate, meaningful result.  The plant part should not be covered in soil or dust, mechanically injured, damaged by insects, or diseased.  Furthermore, attention should be paid to the particular test(s) being done, as the relationship between plant analysis and response varies with the parts sampled.

Crop stress level can impact nutrient concentrations.  Sampling should be done on plants that are not under moisture or temperature stress, as they can develop unusual concentrations of minerals, which can be misleading.

Nutrient concentrations vary throughout the day, so the timing of sampling is important.  Unless specified otherwise by a particular test instruction, early morning sampling is preferred, to avoid aberrations due to moisture and temperature stress that may result at other times of the day.

Proper sample handling assists in providing accurate, meaningful results.  Samples should be cleaned to remove surface contamination.  Washing should be quick to avoid the leaching of nutrients like P and Ca.  Kits are usually available, which include instructions that tell you what portion of the plant to sample, how many plants to sample, the age of the plants, etc.  They may also include tips on how to dry, store, and ship the samples.