4R Nutrient Stewardship is fundamentally based on the diagnosis of soil fertility, writes Fernando Garcia, International Plant Nutrition Institute. This is because soil sampling is commonly the first and critical step in identifying the soil fertility status of any field or management zone.
To add perspective, while sampling a 30-ha field, the 0 to 20 cm layer weighs between 72 to 84 million kg, but we are only collecting 0.5 to 1.0 kg for lab analysis. To be successful, our soil sample must be representative of over 100 million times the amount of soil in the field. Avoiding errors during sampling does much to improve the final result achieved by the lab.
Basic recommended soil sampling procedures include:
- Separate samples for each distinct management areas
- Get 15 to 20 cores per sample
- Adjust sampling when banding fertilizers
- Sample to proper depth(s)
- Adjust time of sampling
- Handle the sample properly. Mix well and take a sub-sample for the lab
- Use clean equipment
- Avoid contamination
- Clearly identify each sample