Soil testing offers the measure of the availability of nutrients to crops, and plant analysis indicates the removal of nutrients from the soil. In soil and plant analysis, the higher and lower critical limits have a significant relation to the agricultural development of a nation. At lower production, the lower critical limit is useful. Soil testing is multipurpose:
1. Grouping soils into different classes based on the levels of nutrients to suggest fertilizer practices
2. Predicting the chances of getting profitable responses
3. Evaluating the soil productivity
4. Determining specific soil conditions like alkali
Soil Testing is a Program that is Divided into Four Phases
• Collecting soil samples
• Extraction and determining the available nutrients
• Calibrating the interpreting the analytical results
• Making fertilizer recommendations
The soil testing program depends on the operative precision in all four stages.
Basic Principles of Soil Testing Recommendations
To prepare the fertilizer recommendation norms for each class of soil test values, it is crucial to prepare crop response curves. This could be prepared by a specific situation, or it might be the average of the experiments where the climate, soil and operator varied.
The interpretation of soil testing involves economics because it is used to create fertilizer recommendations for an economic goal which is usually for the maximum profit per acre/hectare of land. This also involves the cost of fertilizer and the price of the produce. From the response curve, it is possible to calculate the amount of fertilizers and the maximum profit per acre/hectare.
If there is no crop response curve, the fertilizer required for maximum yield will be evaluated with maximum field experiments. The soil with maximum soil test values and the soil that has no fertilizer response should also be included. This will help determine the fertilizer needed for maximum yield at different fertility indexes. This will present a linear relationship. The curve might be used as the baseline for a recommendation of fertilizer at different soil test values or fertility index. The thumb rule is that two-thirds of the amount needed for maximum yield is the maximum economic rate.
Along with the soil test values, the most economical rate of the fertilizer will depend on multiple other factors whose interpretation will depend on personal judgements.
Factors Involved in Soil Test Fertilizer Recommendation
- Initial fertility status of the soil
- Additional produce and the price of the additional produce
- Cost of the fertilizer
- Farm management quality
- Possible risks involved
- Productive potential of the land
- Availability of the fertilizer
- Crops that will be grown
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- To choose the fertilizer, consider the soil characteristics and the crops to be grown.
- For the methods of fertilizer application, consider the soil characteristics and other factors like crops and types of fertilizers.
- For the time of fertilizer application, consider the soil texture.
To get accurate fertilizer recommendations and get the highest efficiency, you shall need the following:
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- Good soil samples and well-based soil sample information
- Soil test calibration relationships that reflect both profit response and crop response
With increasing awareness of fertilizer effects on environmental quality, soil tests can be used to determine whether the fertilizer should be applied or not.
One of the most important factors for soil test fertilizer recommendation is giving proper credit to the nutrient sources. These include legumes, manure, and irrigation water. The cost to collect and analyze water samples for nitrate or manure samples for nutrient content has increased little while the value of nutrients has increased substantially. Unless the retail fertilizer prices drop to match the recent downturn in grain prices, you cannot ignore the benefits of accurate soil testing. It is crucial to have the best information based on careful soil testing before investing in fertilizers. Make sure to take into account all the available nutrient sources.
Another crucial element of soil test fertilizer recommendation is the accurate interpretation of the soil test results. Different soil testing labs will have different fertilizer recommendations based on philosophies like deficiency correction, maintenance, or maintenance plus build-up. Therefore, the soil test result interpretations and recommendations differ among other soil test labs.
Soil Test Crop Response and Targeted Yield Concept
Because of the adoption of multiple cropping and the introduction of high-yielding varieties of principal crops, the soils are depleted of nutrients quickly. Therefore, crop production has become highly fertilizer-oriented.
Since the cost of fertilizers is high, it is necessary to use fertilizers sensibly. Any soil test method intended for use in advisory work must be correlated with actual crop response obtained under field conditions. The success of fertilizer recommendations will depend on the accuracy of the calibrations obtained this way. Modern approaches to fertility evaluation are primarily focused on increasing fertilizer use efficiency.
Individualized soil testing and fertilizer recommendations use the site and grower-specific information instead of laboratory-generated recommendations based on assumptions and generalizations. The following factors are considered:
Soil Test Calibration Relevancy – It is crucial to think about how appropriate the calibration used in the standard recommendation for the field is. Are there unusual soil types? Different climates, crop variety, cropping history and field variability are some of the factors that can cause differences.
Yield Potential – The yield potential determines the economic value of each percentage change in the relative yield, which might influence the calibration curve.
Fertilizer placement – The band placement often reduces the lost yield. The sub-optimal soil test levels are built to optimum levels since the short-term recovery of the applied fertilizer by crop plants is improved. Some recommendation systems reduce the rate of recommended fertilizer when banding is used compared to broadcast. However, the rate studies have shown that the optimum rate when banding is sometimes greater than or equal to the broadcast rate. Balancing the recommendations to ensure every nutrient is used efficiently is crucial.