# Intra-Plot Variable N Fertilization in Winter Wheat through Machine Learning and Farmer Knowledge
## 2 Materials and Methods  
### Field Sites  
This study was conducted using data from 14 rainfed wheat fields of Araba /Alava (northern Spain), belonging to two farmers. Farmer 1 had 13 plots and a yield monitor, while farmer 2 did not have a yield monitor and wanted an N fertilization map for use at one of his plots. The average size of the plots analyzed was 4.3 ha. The 12.2 ha Torres plot is the biggest while the smallest is Apelarri F with 2.1 ha (Table 1). The extension covered in this study was 60.4 ha (Figure 1). All plots were sown at a seed rate of 230 kg ha\({}^{-1}\) between 19 and 25 November 2018 (Table 1). The same fertilization scheme was applied for all plots of Farmer 1. The basal application of fertilizer was 53 kg N ha\({}^{-1}\), 36 kg P ha\({}^{-1}\), and 102 kg K ha\({}^{-1}\) and was applied on 30 December 2018. The second and third N topdressing fertilizer applications were made on 26 February 2019 and 25 March 2019. Calcium ammonium nitrate (CAN), which has a nitrogen concentration of 27%, was used for this purpose. The CAN fertilizer dose applied was 220 and 210 kg ha\({}^{-1}\). The total N rate was 169 kg N ha\({}^{-1}\). The yield information obtained from a yield monitor from the 13 plots of the 2018-2019 cropping season was used. In the 2019-2020 cropping season, the plot of farmer 2 was sown at a seed rate of 230 kg ha\({}^{-1}\) and basal fertilization consisted of 412 kg ha\({}^{-1}\) of 15-13-13 (N-P\({}_{2}\)O\({}_{5}\)-K\({}_{2}\)O). Normally, a herbicide treatment is carried out approximately in GS31 and a fungicide treatment about 15 days later.  
The average elevation of the plots ranged between 480 and 560 m above sea level. Annual rainfall is usually around 750 mm. Summers are mild, with an average temperature in the months of July and August of 20 \({}^{\circ}\)C due to the influence of cold ocean currents, while December, January, and February are milder (6 \({}^{\circ}\)C) than in other climates in similar latitudes. According to [PERSON] [22], the region is classified as having a \"warm-summer Mediterranean climate\" (Csb). The soils in this study have carbonates with an alkaline pH, normally between 8 and 8.5. Regarding texture, the predominant fraction is generally silt. In the case of the implementation plot, the texture was silty loam. The rotation normally includes wheat, 1 or 2 years of barley, and a non-cereal crop. This crop can be an oilseed, protein, or forage crop. In the irrigated plots, the rotation is whe  
\begin{table}
\begin{tabular}{l l l l l} \hline \hline
**Plot** & **Yield (t ha\({}^{-1}\))** & **Area (ha)** & **S2 Pixels within Plot** & **Elevation (m)** \\ \hline Alto & 8.6 & 5.1 & 426 & 502 \\ Apelarri & 8.2 & 2.6 & 207 & 505 \\ Apelarri F & 7.8 & 2.1 & 185 & 508 \\ Babea & 6.7 & 3.8 & 323 & 521 \\ Baratua & 5.6 & 2.7 & 217 & 511 \\ Foronda & 6.4 & 3.2 & 254 & 513 \\ Iruleku & 7.4 & 4.1 & 346 & 534 \\ Kukura & 6.3 & 5.0 & 417 & 508 \\ Menor & 5.2 & 4.6 & 358 & 538 \\ Ollavarre & 4.6 & 4.3 & 353 & 554 \\ Otata & 6.3 & 3.0 & 246 & 541 \\ Parque & 4.7 & 5.2 & 413 & 531 \\ Prado & 7.1 & 2.5 & 208 & 501 \\ Torres & & 12.2 & 916 & 511 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Average plot yield, area, number of Sentinel-2 pixels, and elevation.  
an extensive irrigated crop: potato, sugar beet, green beans, or corn. In the best soils, the alternative is wheat-irrigated crop.