How does SoilCares calculate the nutrient need and fertilzier requirements?

If you have a LIAB or a Scanner the selection of the recommended fertilizer uses the same rules for both devices, the only difference is that for the Scanner fertilizer only containing macronutrients are advised and for the LIAB the recommendations will also include micronutrients.

In general the fertilizer recommendations provided by SoilCares are using the soil properties, characteristics of the soil and crop nutrient need to determine the amount of fertilizer recommended in the reports.

In general the nutrient recommendation scheme determines the crop nutrient uptake needed for optimal or desired crop yield. Which is followed by a fertilizer recommendation, which recommends the fertilizer application rate to meet the crop nutrient uptake.

In the fertilizer recommendations the nutrient chemical form of the fertilizer, the effect of fertilizer application method and root nutrient uptake efficiency is taken into account.

Therefore Soilcares follows the with its nutrient recommendations the mass balance approach.

• Application rate A (kg/ha/acre) equals the estimated crop nutrient uptake, when soil nutrient status is adequate
• Application rate A is increased with Y (both in kg/ha/acre) when nutrient status is (very) low and
• Application rate A is reduced with X (both in kg/ha/acre) when status is (very) hight.

At a low status, the maximum yield cannot achieved by only compensating for crop nutrient uptake. Then A+Y nutrients (kg/ha/acre) need to be applied in order to increase the soil nutrient status and crop yield. At a high soil nutrient status, a small application rate (A-X, kg/ha/acre) is sufficient for maximal yield. A, X and Y are all crop, soil and region dependent.

Figure 1 & 2 : Visualization of the balance approach (Figure 1) and the classification method: for each class a different level of nutrient application rate is recommended : (Class 1 = low, Class II = adequate, Class III = high) application rate decreases when soil nutrient status increases (Figure 2).

More specifically, the rules and conditions that SoilCares has automated, follow two equations to calculate the nutrient and fertilizer application rate.

Nutrient application rate = Attainable crop yield x Crop Nutrient Content + Soil Nutrient Status Correction + Crop Sensitivity Correction.

Fertilizer Application Rate * (100/fertilizer nutrient content) / (fertilizer use efficiency/100)

Explanation of the factors:

• Attainable crop yield (kg/ha/acre) is predefined or set by the customer
• Crop nutrient content equals the content at optimal yield level and is based on literature data
• Soil status correction is maximal for the lowest nutrient class and minimal (0/kg/ha/acre) for the adequate and higher soil class.
• Crop nutrient recommendations depend on attainable crop yield but also on the nutrient sensitivity. Crops are classified in nutrient sensitivity groups – typically low, medium and high. Crops with deep rooting system are generally less sensitive compared to crops with a shallow rooting system.
• Nutrient content of fertilizer is variable between and within fertilizer types.
• Fertilizer use efficiency depends on the chemical form of the nutrient in the fertilizer and then adjusted depending on the application method.

The aim of the SoilCares recommendation is to bring the Farmer’s soil nutrient level to an adequate level and add the quantity of nutrients required to grow the desired crop and obtain the targeted yield.

6 detailed steps of how SoilCares is providing fertilizer recommendations are described below:

1. Evaluation of the soil fertility status

The LIAB and the Scanner first respectively determine the specific soil properties of the farmer’s field regarding their respective Marco and Micro nutrients.

2. Classification into soil fertility classes

Based on either country or partner specific Soil and Crop Thresholds the status of the nutrients is determined according to currently 2 classes: low, adequate or high.

Example:

Determination of Soil nutrient requirements

Depending on the Soil fertility class in the 2. Step the global Soil Correction Table will establish the quantities in kg/ha of nutrients needed to reach an “adequate” soil fertility level.

The table above gives a simplified example about how the soil nutrient requirements are estimated based on the analyzed soil class.

If the Phosphorus level of the sample tested is Low, then 35 extra kilograms of Phosphorus need to be applied per hectare/acre to reach an “adequate” level.

*Nitrogen values are depending on N-uptake, supply and mineralization and therefore are calculated case specifically as followed: N uptake-soil N supply- N mineralization= N-requirement.

Determinations of Crop nutrient requirement

Once the quantities of nutrients required to obtain an adequate soil level are defined, the crop nutrient requirements will be determined.

Specific Crop uptake ratios are determined per country/partner.

1. Calculation of the Total nutrient requirement

Once both Soil Nutrient requirements (SNR) and Crop nutrient requirements (CNR) have been determined then the system calculates the Total nutrient requirement (TNR).

• If the soil is poor in nutrients: SNR + CNR = TNR

Example: If the soil level of Phosphorus is low, 35kg/ha need to be applied to bring it to an adequate level, and 1.15 kg/t/ha need to be applied for the banana uptake.

• If the soil is rich in nutrients: CNR – SNR = TNR

Example: If the soil level of Phosphorus is high, the soil has extra phosphorus available for the banana uptake. The extra phosphorus -35kg/ha need to be deducted from the 1.15 kg/t/ha banana nutrient requirement.

• If the soil quality requires no additional nutrients, then only the crop nutrient requirements are considered: CNR + 0 = TNR

Example: The soil requires no extra nutrients to reach an adequate level. Therefore, only the 1.15kg/t/ha of phosphorus need to be applied for the banana uptake.

6. Correction for Soil nutrient losses after application.

When fertilisers are applied, only a certain percentage stays available for crop uptake, the rest is lost due to erosion, rainfall, leaching, volatilization… The system therefore applies an extra recovery fraction of nutrients depending on how the fertiliser is applied (plant-hole row and broad and non-planthole. A SoilCares Fertiliser Recovery Table has been developed per nutrient providing the percentage of loss that needs to be added to the Total Nutrient Requirement.

From the Total Nutrient Requirement of Phosphorus plant hole broad applied, 50% will be lost due to external factors. Therefore the system will automatically add an extra 50% of phosphorus to the total amount.

Conversion into Fertiliser recommendations.

Once the total of the soil and crop nutrient requirements after losses has been determined, it is changed into fertilizer recommendations.

Are taken into consideration:

• Fertiliser combinations might consist of one to three fertiliser products being available in the region (no combination of multinutrient fertiliser allowed).
• Nitrogen and phosphorus requirement are met for 100%. (Overfertilisation or deficiency situations are not allowed).
• Requirements for other nutrients are met as much as possible; deviations between fertiliser requirement and dose are minimized. When micronutrients are required (only available for the LIAB), multinutrient fertiliser containing those micronutrients are preferred over fertiliser without these nutrients.
• Ureum based nitrogen fertiliser are preferred on non-acidic soils (ph<6) and not recommend for acidic soils in order to prevent further acidification.
• Fertiliser application is considering local application time and quantity rates.
• The number of fertiliser is minimized. As a consequence, a combination of one multinutrient and one straight fertiliser is preferred over a combination of three straight fertiliser, given an equal deviation between required and recommended amount of nutrients.

Note: The Scanner will consider only NPK, PH and Organic matter needs whereas the Lab-in-a-box will look at both Macro and Micro nutrient requirements.

List of extra features of the SoilCares fertiliser module:

• To adapt the fertilizer quantities recommended to smallholder farmers and their available resources, the system will automatically recommend 20% of the highest potential/attainable yield set in the system by a linear equation, this is also the case when:
  • no target yield was entered and the field size is </= 1 hectare
  • an unreasonable low target yield was entered
• The system will automatically recalculate the target yields when these are considered unreasonable:
  • To 70% of the highest potential/attainable yield set in the system for large scale farmers
  • To 20% of the highest potential/attainable yield set in the system for smallholder farmer
• All the tables are filled in with Generic data put together and provide a default option by SoilCares, but all tables can be customized according to the customer’s needs.