What is soil sampling

Soil sampling has been a regular practice in agricultural production systems for obtaining relevant data that will help the producers and the experts in the decision-making process.  Soil analysis - for the purpose of implementing various agricultural operations and processes (tilling, fertilizing, pH adjustment, sowing, crop rotation, etc.) is an important tool to precisely (qualitatively and quantitatively) generate meaningful information and used as decision support for executing the above-mentioned practices.

Soil sampling is a process that consists of several stages:

1st stage: Create a soil sample plan

Carefully choosing soil sampling points is one of the crucial things to be able to obtain a realistic set of data that will correspond to the real situation on the agricultural field that is a subject of sampling.  One of the best and most accurate ways of making such a plan is to use soil sampling software and use the following types of sampling:

Grid sampling

The development of site-specific crop nutritional programs based on global positioning systems (GPS), used for the purpose of implementing variable-rate fertilization (VRF), demands that soil sampling be organized into a systematic grid pattern, i.e., a network of intersecting parallel lines.

A plant nutritional map, based on a grid sample, is a valuable resource for precision plant nutrition. The density of the samples needs to be suitable and tailor-made for every area to provide enough accuracy for the creation of relevant soil maps.

Site-specific management zone sampling

This type needs additional layers of data from more precisely defined zones provided by yield maps, orthophoto, and topography. When these sets of data are combined in the soil sampling software it creates a perfect soil sampling tool that will certainly generate points that are going to accurately present the true situation in the field. These additional sources provide information showing where soil sampling can help to interpret variability even more precisely. 

2nd stage: Taking samples

With the help of the predefined GPS points, the samples can be taken manually (with a hand-held soil sampler) or automatically (automatic soil sampler mounted on a vehicle). Samples must be collected at the proper depths to ensure accurate measurements of nutrients. Samples should also be taken in a manner that minimizes contamination. If the sample analyzed is not truly representative, then the result of the soil’s chemical analysis will likely generate values per soil parameter that do not accurately describe the property of the zone, and hence the field, that is the subject of the analysis. 

3rd stage: Sample analysis and data integration interpretation

The samples need to be analyzed and the several most common methods are spectroscopy, titration, and handheld sensors. Information from the soil samples is later integrated into a decision-making software or interpreted by an expert. Both ways will generate a report that is easily readable by the producer or the manager.

Knowledge of the interrelations of soils with the natural conditions on a field site is essential to plan and perform farming activities that avoid damaging the structure and fertility of the soil.  This credible layer of data can be the foundation of several important aspects that will improve crop production management and respectfully bring more profit for the producers, both by a potential increase of the yield or cutting costs. Soil sampling is the first step in many agricultural operations, which include implementation of site-specific management (variable-rate fertilizing), soil remediation, drainage systems, crop rotation and many other crucial agro-technological operations.

A sampling of an agricultural plot can be very beneficial in several aspects. They can be improved time management throughout the production season, tailor-made prescription map for variable rate fertilizing, cost reduction from accurate fertilizer application (depending on nutrient availability) and improve the overall sustainability of the arable soil by lowering the potential risks from intensive agricultural production. All the above-mentioned positive implementations of soil sampling are tools for potential yield increasing, achieving crop uniformity and improvement of crop and soil health.