The African SoilCares scanner app generates a fertilizer advice based upon measured macronutrients and crop specific needs. A full scanner report comprises six parts, these are: (1) General information, (2) Soil status, (3) Actual nutrient need, (4) Soil correction plan, (5) Suitable crop types and (6) Disclaimer. In this article we explain each part of the report.
1. General information
This section provides basic information on the generated report. It includes the sample number, creation date, field name, field size, measured soil texture, crop name and selected target yield.
1.1 Target Yield
The target yield shows the yield in kg of a crop that the farmer would like to achieve. Additionally the target yield also influences the amount of lime, organic material and fertilizer that will be recommended.
If no target yield is entered by the user or if the target yield is unrealistically low/high a default target yield will automatically be calculated by our recommendation system. The default values are determined by a certain percentage of the maximum attainable fresh weight yield of each crop. If the entered values are between a potential fresh weight yield of 15% and 125% for a specific crop, this is considered to be a realistic target yield. If the values are below 15% or exceeding 125% of the potential fresh weight yield for the specific crop will be set to 20% of the harvestable yield which is used as default value for the produced report.
2. Soil status
The SoilCares scanner measures six soil parameters on which the fertilizer recommendations are based. These parameters include pH (water), Organic carbon, Total Nitrogen, Total Phosphorus, Exchangeable Potassium and Cation Exchange Capacity. The thresholds are classified into three categories: high, adequate and low. The threshold values are provided based on international literature and local experts. The thresholds for NPK are crop specific, hence the measured levels of high, adequate and low may differ between different crops on the same measured soil.
3. Actual nutrient need
The actual nutrient need shows the entire amount of nutrient needed to maintain sufficient soil fertility and provide nutrients for crop growth. This section is shown in the PDF report that can be downloaded from the app. It is not shown within the app itself.
- a) Nitrogen (N): is one of the most important nutrients required by crops. Following the nutrient balance approach, we estimate the crop N requirement as the difference between attainable crop N uptake and the soils’ capacity to supply or fix N. We employ the mono-component model of Janssen (1984) to estimate how much N mineralizes during the crop growing season. Briefly, the N crop requirement is estimated based on the crop N uptake, soil N supply, N mineralization (manure/compost) and available N. Additionally we also correct our results according to nutrient losses due to leaching. This applies especially for N but also for P and K.
- b) Phosphorus (P): Phosphorus recommendation also follows the nutrient balance approach, combining crop nutrient requirements with the actual soil soil analysis results. For the NPK App, P Total is used for the assessment of the actual nutrient status and to determine a suitable fertilizer advice.
- c) Potassium (K): K is also a key nutrient required in large amounts by crops. The application of K aims to maintain the level of K reserves in the soil for optimum crop yield. For our recommendations K-exchangeable is used to assess the soil nutrient status and associated optimum fertilizer dose.
- e) Lime requirement: Our lime recommendation is based on the pH value of the soil. The pH is measured in water. The lime requirement is based on a top soil layer of 10 cm and is expressed in kg agricultural lime. Liming is only required when the soil pH is lower than the optimum pH required by the crop. Assuming that the optimum pH for most common crops lies around a pH value of 4.9, we divided the lime recommendations into three classes: (1) where pH value is < 4.9, (2) pH ranging between 4.9 and 6.4, (3) pH > 6.4. The lime advice is based on the neutralizing value of liming materials. It is important to note that even if the pH is adequate, it is still recommended to apply a certain amount of lime as maintenance to correct for annual soil acidification.
- d) Compost requirement: Compost is required to balance the decomposition of the Soil Organic Matter (SOM) in the soil. The recommendations for Organic matter are based on the Organic Carbon measurements of Scanner. If the Carbon is below the optimum level of 17% of the recommended compost the natural decomposition is counterbalanced and organic carbon is added to increase the organic matter on the long term. In general, our compost requirement is divided into 3 classes: (1) when organic carbon is < 17, (2) organic carbon ranging between 17 and 50, (3) when organic carbon is > 50. Due to the scarcity of organic matter resource in Africa, the recommended compost dose is maximized to 3 tons per ha. Additionally possible nutrient inputs via compost are not accounted for in the fertilizer recommendations.
4. Soil correction plan
The soil correction plan shows a detailed fertilizer management advice that is based on the actual nutrient need.
This section provides insights on possible alternatives of fertilizer applications to achieve the desired crop yield and to maintain an adequate soil fertility level. These are coupled with agronomic practices undertaken at different stages of the growing season. Application timings are therefore depending on the crop choice and vary from 2 to 6 applications. The recommendations are based on the results of the soil sample analysis and the nutrient requirement of the selected crops. Possible recommendations are calculated and presented in three options: the best option, first alternative and second alternative. The best option consists of a combination of fertilizers that match the macro- and micronutrient requirement as good as possible. The first and second alternative advice does not consider the micronutrient requirement but rather advises basic fertilizer products that are available anywhere (In the current Scanner advice only macronutrients are measured and considered for the recommendations). We provide the fertilizer combinations based on the fertilizer products available in the region. The list of fertilizers can be adjusted to region specific availability. If there are any additional changes that need to be made, please contact our support service.
5. Suitable crop types
In this section, we provide a list of suitable crops to grow on analyzed soil based on the pH results. Green smileys are used to indicate crop suitability and red smileys indicate difficulty for growing certain crops without any soil amendment.
Example for the pH range of each crop class:
Potatoes low < 4.7 high > 7.2
Beans low < 4.8 high > 7.5
Grains low < 4.8 high > 7.5
Vegetables low < 5.1 high > 7.5
The disclaimer contains the legal rights information on the sample presented and analyzed.