# Increased Grain Amino Acid Content in Rice with Earthworm Castings
## 3 Results and Discussion  
Total amino acid content in rice grains was significantly influenced by both the level of earthworm castings and cultivar (Table 1). There was no significant interaction effect between the level of earthworm castings and cultivar on total amino acid content in the grain of rice. Averaged across the four cultivars, total amino acid content in the grain was 8% higher under EC17 than under EC0. Huanghuazhan had the highest total amino acid content in grains, more than 10% higher than that of the other three cultivars. N is a principal constitute element of amino acids. It is generally considered that amino acid content is positively linearly related to N content in the rice grain [8]. Some findings of this study are consistent with those of previous studies: Huanghuazhan, the cultivar with highest grain amino acid content, also had higher grain N content than the other three cultivars (Table 1). However, unexpectedly, no significant difference was recorded in the grain N content between the EC17 and EC0 treatments. Thus, increasing the grain N content was not the mechanism for the positive impact of applying earthworm castings on amino acid content in rice grains. Our study also showed that the EC17 treatment had a significantly higher ratio of amino acid to N than EC0 (Table 1). This result suggests that the increased grain amino acid content in rice induced by applying earthworm castings might be mostly attributable to the improved efficiency of converting N to amino acid. This could be further supported and informed by that the linear regression between grain amino acid and N contents was different under EC17 and EC0 (Figure 1). These results suggest that further investigations are required to determine the effects of earthworm castings on the metabolism of amino acid in rice grains. \begin{table}
\begin{tabular}{c c c c c} \hline
**Earthworm** & **Cultivar** & **Total Amino Acid** & **Total N** & **Ratio of Amino** \\
**Castings** & **Cultivar** & **(mg g\({}^{-1}\))** & **(mg g\({}^{-1}\))** & **Acid to N** \\ \hline EC0 & Huanghuazhan & 67.8 (3.52) & 15.3 (0.28) & 4.44 (0.232) \\  & Liangyoupejiu & 60.8 (2.40) & 13.8 (0.05) & 4.42 (0.179) \\  & Longliangyou 97 & 56.7 (3.63) & 13.4 (0.22) & 4.22 (0.288) \\  & Xiangliangyou 396 & 58.8 (3.40) & 13.7 (0.07) & 4.30 (0.250) \\  & Mean & 61.0 (1.82) & 14.1 (0.20) & 4.35 (0.110) \\ EC17 & Huanghuazhan & 73.0 (3.61) & 15.3 (0.07) & 4.78 (0.218) \\  & Liangyoupejiu & 62.9 (2.49) & 13.6 (0.09) & 4.63 (0.198) \\  & Longliangyou 97 & 64.4 (1.67) & 13.5 (0.01) & 4.79 (0.125) \\  & Xiangliangyou 396 & 62.0 (2.62) & 13.2 (0.11) & 4.71 (0.183) \\  & Mean & 65.6 (1.65) & 13.9 (0.22) & 4.73 (0.084) \\ \hline \multicolumn{5}{c}{Analysis of variance (\(F\)-value)} \\ \hline Earthworm castings & 4.65 \({}^{\star}\) & 2.20 ns & 6.29 \({}^{\star}\) \\ Cultivar & 5.03 \({}^{\star\star}\) & 70.44 \({}^{\star\star}\) & 0.11 ns \\ Earthworm castings \(\times\) Cultivar & 0.34 ns & 1.36 ns & 0.24 ns \\ \hline \multicolumn{5}{c}{EC0 and EC17 represent 0 and 17 kg earthworm castings m\({}^{-2}\), respectively; Values in parentheses are SE (\(n=4\)): \({}^{\star}\), significance at the 0.05 probability level; \({}^{\star\star}\), significance at 0.01 probability level; ns, non-significance at the 0.05 probability level.} \\ \end{tabular}
\end{table} 
Table 1: Effects of earthworm casting application on total amino acid and nitrogen (N) content and on ratio of amino acid to N in grains of four rice cultivars. Figure 1: Linear regression between total amino acid and N contents in grains of four rice cultivars under two levels of earthworm castings. EC0 and EC17 represent 0 and 17 kg earthworm castings m\({}^{-2}\), respectively. Each data point is the mean for one cultivar under one level of earthworm castings. Error bars are SE (\(n=4\)). Application of earthworm castings can affect plant metabolism including protein synthetic activity [16; 17].