Performing regular soil analysis is an essential element of plant nutrition management. Soil analysis is also used as a tool for diagnosing the state and trend of soil fertility development over time. It is used to measure soil nutrients that are expected to become available to plants. However, soil analysis does not determine the total amount of nutrients in the soil. Measuring total nutrient content is not an important indicator for plant growth, as only a small fraction of the nutrient is available to plants. The roots absorb nutrients available for absorption, both positively and negatively charged ions from the soil (Table 1).
Soil analysis results (See Figure 1) can be classified into 3 categories:
This classification of soil analysis and subdivision into “yes,” “no,” and “possible” categories aids in understanding the limits and benefits when making recommendations for nutrient application.
Figure 1. Significance of soil analysis with likely crop response to yield to nutrient addition. Increased yields due to nutrient additions are possible with low soil assay values and unlikely with high soil assay values.
There are different methodology for fertilizing the soil and different recommendations based on the same soil analysis. For example, one methodology makes recommendations for nutrient application only when economic benefits from increased yields are likely. In contrast, another practice for applying nutrients is to maintain soil fertility. Therefore, fertilization is carried out by the introduction of nutrients carried out by the crop. Nutrients are applied even if the soil has sufficient levels of these nutrients.
The concentration of nutrients depends on the depth of the fertile soil layer, which affects the results of soil analysis. To determine the correct sampling depth, you need to think about the purpose of soil analysis. To estimate the need for fertilizers before planting, a soil sample is taken at a depth where most of the root system will be located, this depth is usually 15 to 30 cm.
Surface samples at a depth of 3 - 7 cm are sometimes used to estimate the fertilizer requirement for perennial crops, where fertilizers are applied to the soil surface many times. Diagnosing problems in gardens may require sampling at various depths.