# Reuse of Spent Coffee Grounds: Alternative Applications, Challenges, and Prospects--A Review
## 3 Fertilizer from SCGs
Future research should focus on determining the long-term impact of SCGs on soil and plants to clearly establish whether the lettuce is safe for human consumption. SCGs contribute to the carotenoid and chlorophyll content of Lactuca sativa lettuce. In the study by [PERSON] et al. (2012), SCGs were used as a soil amendment in the range of 0 to 20%. The lutein content in lettuce increased by 90%, \(\beta\)-carotene by 72%, and chlorophylls by 61%. The pigment content increased in proportion to the quantity of SCGs added to the medium. The plant contained lower amounts of organic nitrogen compared to conventionally grown lettuces. This may indicate that it was under nutrient stress or the compounds in the SCGs had a toxic effect and led to signaling stress in the plant. Small quantities of SCGs (up to 10%) are beneficial to plants and are increasingly important in agriculture. Therefore, further research on the effects of bioactive compounds in SCGs on plant growth is important [23]. SCGs show potential for use in agriculture but present significant challenges. Although pigment levels increase, the reduced nutritional quality of lettuce raises major concerns. This study indicates that adding more than 10% SCGs is detrimental to plants, highlighting the need for precise SCG application rates that positively affect crops. Additionally, the focus was on the short-term effects of SCGs, leaving long-term impacts, such as toxin accumulation in soil and changes in soil microbiota, unknown. Future research should address these issues to provide viable solutions. Table 2 presents the parameters of using SCGs as a fertilizer. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Plant** & **Form of Coffee** & **Parameters** & **Results** & **References** \\ \hline \multirow{4}{*}{-} & SCGs mixed in a 9:1 ratio with collagen, rice starch, and food-grade gelatin & SCGs dried at 105 °C with the addition of biomass ash (oak wood) & Collagen, gelatin—strong inhibition of nutrient and organic matter release. & [20] \\  & 0, 2.5, 5, and 10\% addition to peat & SCGs air-dried, stored at refrigeration temperature & & \\  & & & & \\ \hline \multirow{4}{*}{Lettuce} & 1, 2, 2.5, 5, 7.5, 10, 12.5, and 15\% addition to soil & SCGs dried at room temperature, homogenized, stored at 5 °C & & \\  & & & & \\ \hline \multirow{4}{*}{Lettuce} & 2.5, 5, 10, 15, and 20\% addition to soil & Fresh SCGs homogenized & & \\  & & & & \\ \cline{1-1}  & 5, 10, 25, and 50\% mixed with another fertilizer, and 0.5 g, 1 g, and 25 g applied as a surface fertilizer & & & \\ \hline \multirow{4}{*}{Wheat} & 5, 10, 25, and 50\% mixed with another fertilizer, and 0.5 g, 1 g, and 25 g applied as a surface fertilizer & & & \\  & & & & \\ \cline{1-1}  & & & & \\ \cline{1-1}  & & & & \\ \cline{1-1}  & & & & \\ \hline \multirow{4}{*}{Lettuce, carrot, and spinach} & 5, 10, 25, and 50\% mixed with another fertilizer, and 0.5 g, 1 g, and 25 g applied as a surface fertilizer & & & \\ \cline{1-1}  & & & & \\ \cline{1-1}  & & & & \\ \cline{1-1}  & & & & \\ \cline{1-1}  & & & & \\ \cline{1-1}  & & & & \\ \hline \multirow{4}{*}{Lettuce, carrot, and spinach} & 5, 10, 25, and 50\% mixed with another fertilizer, and 0.5 g, 1 g, and 25 g applied as a surface fertilizer & & & \\ \cline{1-1}  & & & & \\ \cline{1-1}  & & & & \\ \cline{1-1}  & & & & \\ \cline{1-1}  & & & & \\ \cline{1-1}  & & & & \\ \hline \multirow{4}{*}{Wheat} & 5, 10, 25, and 50\% mixed with another fertilizer, and 0.5 g, 1 g, and 25 g applied as a surface fertilizer & & & \\ \cline{1-1}  & & & & \\ \cline{1-1}  & & & & \\ \cline{1-1}  & & & & \\ \cline{1-1}  & & & & \\ \cline{1-1}  & & & & \\ \hline \multirow{4}{*}{Lettuce, carrot, and spinach} & \multirow{4}{*}{-} & SCGs stored in containers with air circulation and 0.5 g, 1 g, and 25 g applied with water (to & \\ \cline{1-1}  & & & & \\ \cline{1-1}  & & & & \\ \cline{1-1}  & & & & \\ \cline{1-1}  & & & & \\ \cline{1-1}  & & & & \\ \cline{1-1}  & & & & \\ \hline \end{tabular}
\end{table} 
Table 2: Parameters for SCGs as fertilizer.