Soil analysis helps us to learn about our soils and to know what nutrients to use on crops
A soil analysis can be very extensive and include many parameters. Sometimes, it might seem that we need to know everything, but each analysis has a cost. It is thus important to have clarity on what parameters to analyze and with what frequency.
In order to ensure a reliable, representative result for a field, samples need to be properly taken. It is important not to mix zones that have different textures, since doing so would provoke changes in other soil parameters. It is likewise important not to mix soils from fields that have different management regimes. In other words, a field frequently fertilized with slurry should not be mixed with another one that uses mineral fertilizer; neither should a plowed field be mixed with one that employs direct seeding.
Even if the soil is more or less homogenous within a single field or group of fields, there is a certain degree of variability. It is therefore important to gather samples from more than one point of the field or group of fields. As a minimum, sub-samples should be obtained from 3 different points of each field. In large fields it is advisable to take approximately one sample per 2.5 acres. These points need to be well distributed and include the field’s center, edges, areas with slopes, etc.
Soil gathered from all points must be carefully mixed. Then, based on that mixture, it is necessary to choose a final sample weighing approximately one pound. The remaining soil can be discarded.
Sampling depth is also important. In general, it is advisable to take the sample at a depth of between 0 and 16 inches, which is where the plant develops its roots. In very deep soils that can be easily penetrated by plant roots, it is a good idea to take the sample at a depth of 24 or 28 inches.
What Soil Parameters Should We Analyze?
- Soil Texture
Texture indicates the proportion of particles of different sizes present in the soil. We often speak in terms of gross soils, fine soils, soils with a large clay content, etc. At a technical-scientific level, textures are divided into four major groups, depending upon their proportion of clay, silt, and sand. The categories are: clay soils, sandy soils, silty soils, and loamy soils (that is, soils where the proportions of clay, sand, and soil are approximately equal). Soils can also fall between two categories, for example, sandy-loam soils.
- Soil pH: Stability is Key
pH is a chemical parameter indicating whether a substance is acidic or basic. The scale of results runs from 0 to 14. pH 7 soils are neutral. If the pH is higher than 7, the soil is basic; if it is lower than 7, the soil is acidic. The closer the pH gets to 0, the more acidic it becomes, and the closer it gets to 14, the more basic. pH affects the availability of nutrients as well as crop growth. Soils with an extreme pH are not fertile, since there are no nutrients available for the plants.
- Organic Matter: Key for Fertile Soil
Organic matter is key for fertile, productive soil. The soil’s organic matter consists of the organic compounds it contains. Roughly speaking, soil color can help to indicate whether organic matter content is high, since dark soils tend to have more organic matter. Organic matter has an influence on a wide range of soil properties and increases biological activity. It helps make soil nutrients available for the plant, keeps the soil pH stable, and reduces the risk of erosion.
Several different actions can be taken to increase or decrease organic matter in the soil. It is thus worthwhile to analyze organic content periodically. These analyses are especially recommended if an action is taken to increase organic matter in the soil, such as the utilization of manure or direct seeding.
- Electrical Conductivity: Know the Salinity of Your Soils
Crops do not grow correctly in saline soils. In fact, in highly saline areas, it is necessary to frequently engage in localized irrigation for fruit-producing plants in order to wash salts away from the root zone. Soils can become saline due to water with too many dissolved salts and/or due to a lack of good drainage. This occurs above all in irrigated fields of arid zones. It is therefore important to incorporate a washing factor when calculating irrigation. In non-irrigated zones a single measurement of conductivity may suffice. In irrigated zones, this parameter might vary, on account of which it is a good idea to conduct a periodic analysis.
- Phosphorus: The Key to Growth
Phosphorus is one of the macronutrients crops need in order to grow correctly. Depending upon soil moisture, soil temperature, and crop root type, the crop might uptake more or less phosphorus from the soil. This makes it complex to interpret a phosphorus analysis. Interpretation tables vary, depending upon the zones and crops in question. Phosphorus has low mobility in soil.
- Potassium: For Quality Production
Potassium is another macronutrient necessary for correct crop development. Potassium is modified by several agricultural techniques, such as: mineral and/or organic fertilization, soil management, removal of plant residues that are rich in potassium, etc. Nonetheless, potassium is an element with low mobility in soil.
Potassium is a major factor for final product quality. In this regard, not only are potassium shortages relevant, but also potassium excesses. When a tree receives sufficient potassium, sugar levels in the fruit increase, but an excess of potassium leads to rotting of the fruit. In cereals potassium increases lignification and produces a higher quality straw.
- Nitrogen: Maximizing Yield
Nitrogen is the leading macronutrient. Nitrogen in the soil is found in many different forms. Some are accessible for crops while others are not. Nitric nitrogen is the nitrogen fraction that can be directly uptaken by plants. Ammoniacal nitrogen can also be uptaken by plants, provided that it is first transformed into nitric nitrogen. These two nitrogen fractions are the ones that are analyzed in a nitrogen soil analysis. In general, the ammoniacal part is very small, for which reason an analysis of nitric nitrogen tends to be sufficient. With that, one can go ahead with fertilization planning.
Nitrogen content of the soil is highly variable both in space and in time. Rain, soil management, fertilization, and the handling of residues, among other factors, directly affect the soil’s nitric nitrogen content. As such, levels after a rainy winter could be radically different from those of the immediately preceding autumn. It is thus recommended to conduct at least one soil analysis per year. This analysis can be made prior to planting or at the end of winter. If it is done prior to planting, it is possible to calculate the available nitrogen at the end of winter, if one knows certain parameters, such as: crop needs, fertilization applied, temperature, and precipitation, etc. Conducting the analysis at the end of winter ensures a contribution of nutrients to cover crop needs, even if the underlying fertilization was made “blindly.”
At AGQ Labs we have a modern Soil Factory Lab capable of analyzing more than 300 samples a day, utilizing state-of-the-art technology and a totally automated analysis process. We also have a remarkable team of agronomists trained to interpret the data resulting from the analytics, translating all that information into a correct management of any crop.
Feel free to contact our Agronomy department.