History and Global Perspective of Soil Sampling and Analysis.

Soil testing and the commercial fertilizer industry became significant parts of North American agriculture at nearly the same time. Most soil test methods in use today are based on publications dated in the 1940s or 1950s, a time when fertilizer use was about 11% of current consumption. As fertilizer use grew, so did the need for science-based guidance of its management and most Land Grant universities initiated service laboratories to meet the need. The practice was encouraged not only by universities but also by the fertilizer industry as it was soon evident that soil testing was an excellent means of convincing farmers to fertilize. With time, the private sector realized that soil testing could be a profitable industry in itself and commercial laboratories gradually became the dominant supplier of the service to farmers and their advisers.

Soil sampling has always been a challenge and widely recognized as the greatest source of error in the soil testing process. The advent of variable rate fertilizer application technology forced changes in soil sampling protocols and greatly expanded study of how to better characterize within field variability. Controversies arose around numerous practices including size of grids, grid vs cell sampling, zone vs grid sampling, the role of soil classification maps, number of cores to composite, etc. Some controversies remain unresolved with the market place finding room for diverse practices. Soil sampling has a history of comfortable beliefs based on soil testing being a robust practice. Those beliefs may not always agree with reality.  

Outside North America the role of soil testing today varies markedly from plant-based approaches for assessing regional nutrient needs where soil testing is only a research tool to cases where government run soil testing surveys have been performed periodically to guide nutrient use.