Dear Sameeha,

Using dried and preserved plant samples that are almost a year old for macronutrient analysis may not be ideal, as the nutrients in pieces may have degraded over time. Macronutrients, such as nitrogen, phosphorus, and potassium, are essential for plant growth and development. Their levels can change over time due to various factors, such as exposure to light, temperature, and humidity.

The preservation method used for the samples can also affect the nutrient content. Drying and grinding samples can help to preserve the pieces and maintain their nutrient content, but it is still possible that some nutrients may have leached out over time.

It's worth noting that the best practice for plant macronutrient analysis is to use fresh samples, which are collected and analyzed as quickly as possible. However, suppose dried-preserved samples are the only option. In that case, it's recommended to consult with the lab to check their capabilities on the analysis of old samples and also to compare the results with fresh samples.

I hope this explanation was helpful,

Edgar M Cambaza