1. The document discusses learnings from surveys on input use in Nigeria and Tanzania, finding herbicide and fertilizer most common in Nigeria but rare for cassava in Tanzania. 2. It outlines the principles of a fertilizer recommendation tool, including determining attainable yield based on weather data, estimating indigenous and fertilizer nutrient supply, nutrient uptake, converting uptake to yield, and optimizing recommendations based on costs and return on investment. 3. It describes how the tool determines water-limited yield using the LINTUL modeling framework based on precipitation, solar, and soil data, and specifies crop and soil parameters used in the model for cassava.

1. Learnings from the RC and baseline survey
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Nigeria: use of herbicides very common. Farmers using fertilizer are almost always farmers using herbicide.
Tanzania: use of inputs in cassava is very rare, but not so in other crops (e.g. fertilizer in maize, pesticides
in cash crops like cashew, cotton,…)

2. Principles of the Fertilizer Recommendation Tool
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1. Determine the attainable yield (water-limited) yield (based on meteo data) - LINTUL
2. Estimate the indigenous nutrient supply of the soil (based on soil data)
+ add the nutrient supply from fertilizer – QUEFTS(1)
3. Estimate the nutrient uptake – QUEFTS(2)
4. Convert uptake into yield – QUEFTS(3)
5. Optimize nutrient supply based on cost of available fertilizers and RoI
6. Package the recommendations in a smartphone app for field use
The FR-DST is developed based on following steps and principles:

3. Determining water-limited yield
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Water-limited yield is calculated using the LINTUL modelling framework:
LINTUL (Light Interception and Utilization) determines growth and root biomass accumulation
and uses following data:
• Daily precipitation from CHIRPs – UCSB (ftp://ftp.chg.ucsb.edu/pub/org/chg/products/CHIRPS-2.0/)
• Solar data from TRMM – NASA (https://power.larc.nasa.gov/cgi-bin/agro.cgi)
• Soil parameters (bd, orgC, FC, WP, WSP, pH,…) from ISRIC (ftp://ftp.soilgrids.org/data/recent/)
LINTUL
LINTUL has recently been modified & calibrated for cassava.
ACAI uses default parametrization based on literature.
Crop parameters: e.g., Light Use Efficiency = 1.4 g DM MJ-1 IPAR
(Veldkamp, 1985); Light Extinction coefficient; Storage root bulking
initiation (40-45 days for TME419); Root growth rate,…
Soil parameters: Field capacity, wilting point and saturation based on
pedotransfer functions, maximum rooting depth,…