Soils are the source of thirteen of the sixteen essential plant nutrients and can be viewed as suppliers of nutrients to plants. Plants absorb available nutrients, which can be replenished by adding fertilizers.
To achieve good yield and quality, nutrient balance has to be maintained. Nutrient imbalance may result in deficiencies, toxicities or interference of one nutrient with the absorption of others.
This may result in stress to the crop, causing a decrease in quality and/or yields. Soil analysis is an important tool for evaluating or avoiding problems of nutrients balance.
Why is soil analysis important?
You can roughly estimate just how much fertilizers you need to apply according to general growing recommendations for your crop. But is it too much, or maybe too little? This is where soil analysis comes in.
Soil analysis eliminates at least one unknown from the “equation”: when adding nutrients to the soil, knowing the starting point is a very valuable piece of information.
Here are the basics of how to make sense of soil analysis reports .
1. Take the soil sample correctly
Taking the sample correctly is the number one step for any reliable soil analysis result. The soil sampling should be well planned and preformed. For example, the sample site should be far from roads, fences, tree groups, piles of fertilizers and manure or any other object that can locally affect the soil properties and content.
The sample should represent the entire field as closely as possible. If the field is not uniform, and consists of different areas with different properties, each area should be sampled . Compiling results from completely different areas and averaging them into one report , will obviously give us a very misleading result.
2. Consider all growing conditions
Keep in mind that there are many factors that affect the plant growth. The soil analysis will not supply answers to poor or inadequate conditions, such as critically low or high temperatures, inadequate drainage, wrong application of fertilizers, accumulation of salts, plant diseases, pests damage, competition with weeds etc.
Assuming you took samples correctly and you acknowledge the many factors that may affect you crop, how do you proceed to interpret the numbers in the soil analysis lab reports ?
3. What do the numbers in the report stand for?
Soils usually contain much higher amounts of nutrients than what we see in the reports , because lab results describe only the available nutrients to plant. To estimate the amounts of nutrients which are actually available to plants, different testing methods were developed. Some of these methods give empirical values or measures.
4. Don’t look only at the numbers in the report
It’s true, lab reports can be confusing: different labs use different testing methods, resulting in different results for the same sample ! They may even use the same methods, but express the results in different units.
To correlate the numbers in the soil analysis report with crop response to added nutrients, numerous field experiments are required. The reason is that the same numbers may lead to different recommendations in different soils, different areas and under different conditions. The numbers in the report , coupled by the description of the nutrient content in the soil, can indicate if the predicted crop response to fertilizers will be favorable or not.
5. Choose the right lab
Good labs , with good experience, use their regional database to give a description of each nutrient (indicating if its level is too high , too low or adequate) and even fertilization recommendations.
Don’t take these recommendation as “instructions”. Remember that no one knows your crop better than you do. You are the best judge of your crop needs and specific conditions.
6. Use your experience
The soil analysis report , together with your close familiarity with your crop and field conditions, give you the starting-point to tackle the next question: how much fertilizers to apply?
First thing to remember is that different crops remove from the soil different amounts of nutrients. So knowing your crop needs is essential. Next is your crop target yield. Generally speaking, higher fertilization level gives higher yields, but only up to a certain point. Beyond that, adding fertilizers will not increase yields and may even reduce them as a result of salts accumulation in the root zone.
Bottom line is that soil analysis lab reports give us a good starting point for making better fertilization-management decisions. They should be put in context and their interpretation should be adjusted to the individual crop behavior and specific field conditions.