## 2 Materials and Methods  
To verify that the spectroradiometer gets dispersed consistently, 65 soil samples were collected from Radhapuram area between 8.15 and 8.44 latitudes and between 77.64 and 77.82 longitudes, as illustrated in Figure 1. The 65 data points were divided into 45 training samples (shown as red dots in Figure 1) and 20 testing samples for model development (shown as black dots in Figure 1). Semi-micro Kjeldahl method was utilized to detect accurate organic carbon (AOC) and real nitrogen (AN) [12; 13; 14]. The real phosphorus and potassium contents were determined using an ultraviolet spectrophotometer, UV-2600 (made by RRSC, ISRO, Bangalore, India). Table 1 displays spectroradiometer results for selected soil samples, calculated using techniques in Appendix A. Samples from farmers' field were collected in coordination with Department of Agriculture using a Global Positioning System (GPS) receiver to collect geo-referenced soil samples in various locations. The collected samples were sent to the Soil Science Laboratory of CWRDM and were processed, air dried, and sieved using 2 mm sieve for further analysis. The collected soil samples were analysed for following parameters using pH, electrical conductivity (EC), organic carbon (OC), phosphorus (P), potassium (K), sulphur (S), calcium (Ca), and magnesium (Mg) using standard procedures as given in Table A1. In addition, a model was developed to estimate the levels of nitrogen, organic carbon, phosphorus, and potassium. Figure 2 depicts the detailed flow chart of the model. The technique of our planned work is detailed in the sections that follow. In addition, chemical characteristics and descriptive statistics of the 65 soil samples were computed and studied. Table 2 provides statistics of soil nutrient content samples. The AOC, AN, AP, and AK content of soil varies from 0.150 g kg\({}^{-1}\) to 0.874 g kg\({}^{-1}\), 112 g kg\({}^{-1}\) to 257.6 g kg\({}^{-1}\), 10.248 g kg\({}^{-1}\) to 71.332 g kg\({}^{-1}\), and 127.568 g kg\({}^{-1}\) to 1313.242 g kg\({}^{-1}\), with mean values of 0.443, 190.22, 24.954, and 437. The coefficients of variation (CV percent) of AOC, AN, AP, and AK all fluctuated significantly [15]. According to our study area, the 65 soil samples were reasonable in terms of the diversity of soil chemical nutrients (AOC, AP, and AK). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Sample Code** & **OC** & **N** & **P** & **K** \\ \hline RP-10A & 0.150754 & 112 & 18.3904 & 272.272 \\ \hline RP-10B & 0.150754 & 134.4 & 17.808 & 296.24 \\ \hline RP-11A & 0.633166 & 224 & 51.9904 & 491.568 \\ \hline RP-11B & 0.271357 & 168 & 43.1312 & 230.272 \\ \hline RP-12A & 0.512563 & 179.2 & 21.4816 & 650.944 \\ \hline RP-12B & 0.512563 & 179.2 & 18.48 & 463.344 \\ \hline RP-13A & 0.572864 & 156.8 & 71.3328 & 484.176 \\ \hline RP-13B & 0.211055 & 134.4 & 37.6992 & 169.344 \\ \hline RP-14A & 0.663317 & 235.2 & 28.1456 & 498.288 \\ \hline RP-14B & 0.603015 & 235.2 & 27.3168 & 475.888 \\ \hline RP-15A & 0.331658 & 224 & 25.424 & 478.352 \\ \hline RP-15B & 0.693467 & 224 & 36.0304 & 276.864 \\ \hline RP-16A & 0.422111 & 156.8 & 17.36 & 474.32 \\ \hline RP-16B & 0.723618 & 179.2 & 22.3664 & 520.24 \\ \hline RP-17A & 0.874372 & 224 & 24.3264 & 793.408 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Some soil samples of spectroradiometer data in Radhapuram, Tirunelveli District.