Identifying whether a crop has been fertilized using organic or synthetic fertilizer involves a combination of testing and observation:

1.Soil and Plant Testing:
-Chemical Analysis: Lab tests can detect specific chemicals associated with synthetic fertilizers, such as nitrates, phosphates, and potassium in higher concentrations than typically found in organic soils.
-Isotope Analysis: Stable isotope ratios of nitrogen (δ15N) differ between organic and synthetic fertilizers. Organic fertilizers often show a more varied isotope signature due to their natural sources.

2.Residue Testing:
-Pesticide Residue: Synthetic fertilizers may contain residues of chemicals not present in organic fertilizers.
-Heavy Metals: Synthetic fertilizers can sometimes leave trace amounts of heavy metals, which can be detected through soil tests.

3.Observation and Documentation:
-Certification Records: Organic certification bodies maintain records of inputs used on certified farms.
– Farm Practices: Visual inspection and interviews with farmers about their fertilization practices can provide insights. Organic farms often use compost, manure, and cover crops, while synthetic fertilizer use is characterized by packaged granular or liquid fertilizers.

4. Microbial Activity:
–Soil Health Indicators: Organic fertilizers typically enhance microbial activity and soil organic matter, leading to improved soil structure and biodiversity. Soil testing for microbial biomass and diversity can provide clues.

Combining these methods can help determine whether a crop has been fertilized using organic or synthetic fertilizers.