By Blake Jackson
Grid sampling, where fields are divided into smaller sections and soil samples are collected from each, offers detailed insights into soil variability that might otherwise go unnoticed. This approach is increasingly used on farms with variable rate application technology, allowing for more precise nutrient management.
Research from Cornell CALS’ Nutrient Management Spear Program (NMSP) has shown that detailed soil information helps farmers make informed fertilizer decisions, including lime, phosphorus, and potassium applications, reducing unnecessary costs and maximizing productivity. Despite these benefits, questions remain about the best way to use grid sampling for phosphorus (P) management.
The New York Phosphorus Index (P-Index) 2.0 evaluates soil test P values to guide P applications, balancing crop needs with environmental protection. Typically, one P-Index score is assigned per field, but the precision ag team at NMSP studied soil data from 20 corn fields across six New York farms to explore grid-level application. They assessed 0.5, 1.0, and 2.5-acre grids across four P-loss risk categories: low, medium, high, and very high.
“Grid sampling for P management was most useful in fields with soil test P levels between 40 and 100 lbs P per acre," Manuel Marcaida III, NMSP data analyst and lead author said.
"For fields with uniformly low or excessively high soil test P levels, taking a field composite sample provided adequate information for nutrient management planning.”
For variable fields, a 2.5-acre grid size captured meaningful variability without incurring the higher costs of finer sampling.
These results suggest that farmers and advisors can optimize soil sampling to identify P-loss zones, improve nutrient efficiency, and reduce environmental impact.
Marcaida added, “Soil grid maps show you the lay of the land - literally - so you can decide whether a single P-Index score is appropriate for the whole field, or if you’d rather break the field into P management zones to maximize nutrient efficiency and minimize environmental impact.”
Photo Credit: gettyimages-casarsaguru
Categories: New York, Crops, Education