# Cotton Yield Estimate Using Sentinel-2 Data and an Ecosystem Model over the Southern US
## 3 Results
### The GPP-Lint Yield Relationship for Upland Cotton  
As shown in Figure 5, BEPS-simulated GPP strongly correlated with cotton lint yield from the NASS statistics for the 17 counties (\(R^{2}=0.85\)). This suggests that cotton GPP from simulation can be used as a reliable proxy for cotton yield. It is noteworthy to mention that Equations (3) and (4) have no intercepts, while the regression equation in Figure 5 has an intercept. If the intercept is forced to zero in Figure 5, the slope is 0.61 and the \(R^{2}\) is 0.67. A similar intercept was also observed when cotton biomass was used to explain the variation in seed cotton as shown in [PERSON] (2017). This small intercept suggests that there may be systematic uncertainty in the GPP simulation or that the correlation between GPP and cotton yield is nonlinear when both GPP and cotton yield are small. For example, the cotton \(\mathrm{V_{cmax}}\) was fixed to 120 \(\mathrm{\SIUnitSymbolMicro m^{-2}\cdot s^{-1}}\) in our simulations as, currently, there is no such information available for each pixel from the satellite. As shown in Table 2, the cotton lint yield in tile 17 RKA (GA) was lower than the full-season cotton yield in MS. Cotton needs enough heat to grow. With respect to cotton grown in a double-crop system following wheat, the length of fruiting period and adequate temperature accumulation for both maturation are reduced, thereby lowering the lint yield potential. [PERSON] et al. (2017) found that, for cotton after wheat in a double-cropping system, the lint yield is generally low depending on the plant dates (lint yield range: 750-944 kg/ha). As shown in the 2012 Georgia cotton production guide ([[http://www.ugacotton.com/vault/productionguide/2012](http://www.ugacotton.com/vault/productionguide/2012) CottonProductionGuide.pdf]([http://www.ugacotton.com/vault/productionguide/2012](http://www.ugacotton.com/vault/productionguide/2012) CottonProductionGuide.pdf)), the cotton yield in a double-cropping system can have a yield reduction of up to 30% due to the limited growing season, when compared to full-season cotton planted in early May. In Arkansas, the yield potential decreases by 2% every day if cotton is planted past May 20 ([[https://www.uaex.edu/publications/PDF/FSA-2163.pdf](https://www.uaex.edu/publications/PDF/FSA-2163.pdf)]([https://www.uaex.edu/publications/PDF/FSA-2163.pdf](https://www.uaex.edu/publications/PDF/FSA-2163.pdf))). This suggests the importance of capturing planting date for cotton yield estimation, while our GPP simulation explained such variation in cotton growing season. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**County** & **FIPS** & **Area (ha)** & **Production (kg)** & **Lint Yield (kg/ha)** & **GPP (BEPS)** \\ \hline TX (145 KB) & & & & & \\ Lynn & 48,305 & 120,522 & 79,922,356 & 663 & 715 \\ Garza & 48,169 & 16,593 & 12,322,983 & 743 & 752 \\ Dawson & 48,115 & 105,198 & 69,978,487 & 665 & 805 \\ Borden & 48,033 & 23,329 & 12,449,007 & 534 & 630 \\ \hline MS (15 SYT) & & & & & \\ Coahoma & 28,027 & 36,881 & 42,187,930 & 1144 & 1722 \\ Quintman & 28,119 & 10,192 & 11,590,623 & 1137 & 1985 \\ Tallahatchie & 28,135 & 17,839 & 23,602,659 & 1323 & 2116 \\ Sunflower & 28,133 & 8379 & 10,650,446 & 1271 & 1891 \\ Leflore & 28,083 & 17,748 & 21,326,898 & 1202 & 2200 \\ Carroll & 28,015 & 8859 & 10,161,688 & 1147 & 2118 \\ \hline GA (17 RKQ) & & & & & \\ Worth & 13,321 & 22,541 & 21,292,891 & 945 & 1532 \\ Tift & 13,277 & 9227 & 8,268,221 & 896 & 1409 \\ Colquitt & 13,071 & 19,223 & 20,181,571 & 1050 & 1536 \\ Cook & 13,075 & 7244 & 5,267,657 & 727 & 1364 \\ Berrien & 13,019 & 11,088 & 9,001,692 & 812 & 1451 \\ Thomas & 13,275 & 12,505 & 10,779,804 & 862 & 1552 \\ Brooks & 13,027 & 15,459 & 14,291,575 & 924 & 1529 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The statistics of cotton area, production, and yield from the National Agricultural Statistics Service (NASS) and the Boreal Ecosystems Productivity Simulator (BEPS) in 2017 for the three Sentinel-2 tiles.