The inhibitory potential of green manure return on the germination and seedling growth of Eleusine indica L

Abstract

Trifolium repens L. (white clover) and Lolium perenne L. (ryegrass) are green manures widely used in conservation tillage systems worldwide. Eleusine indica L. (goosegrass) is a globally recognized noxious weed. Herein, we investigated the effects of aqueous extracts, decomposed liquids, and different straw-to-soil ratios on the germination and growth of goosegrass. The results showed that high concentrations (≥ 30%) of aqueous extracts or decomposed liquids of both green manures significantly inhibited germination-related parameters of goosegrass. The strongest inhibitory effect was observed for the 7-day decomposition treatment, and white clover's inhibitory effect was greater than ryegrass's. A pot experiment showed that non-photochemical quenching, catalase, and peroxidase activity levels of goosegrass leaves were significantly increased. At the same time, the net photosynthetic rate significantly decreased. Seedling growth was inhibited when the straw-to-soil ratio was greater than 3:100. The ryegrass treatments inhibited goosegrass seedlings more than the white clover treatments. This study demonstrated the inhibitory potential of white clover and ryegrass straw return on seed germination and seedling growth of goosegrass. The study has also helped to identify weed-resistant substances in these green manures so that their weed-control properties can be used more effectively and herbicide usage can be reduced.

Keywords: antioxidant enzyme activity; decomposition; green manure; photosynthetic parameters; seed viability; weed controlling.

Figure 1

The flowchart of the experimental process (WC, white clover; RG, ryegrass; AE, aqueous extract; DL: decomposed liquid).

Figure 2

Effects of the AE concentration of green manure species on goosegrass seed germination (A–D, n = 5), plant height (E, n = 10), and fresh weight (F, n = 3). Data are presented as mean ± SD. Different capital letters indicate significant differences between green manure species by the same concentration (P<0.05). Lowercase letters indicate significant differences among extract concentrations by the same green manures (P ≤ 0.05). S: green manures species; C: concentration; *: P ≤ 0.05; **: P ≤ 0.01; ***: P ≤ 0.001; NS: no significant difference.

Figure 3

Effects of the DL concentration of green manure species on goosegrass seed germination (A–D, n = 5), plant height (E, n = 10), and fresh weight (F, n = 3). Data are presented as mean ± SD. Different capital letters indicate significant differences among decomposition days by the same green manure and concentration (P<0.05). Lowercase letters indicate significant differences among extract concentrations by the same green manures and decomposition days (P<0.05). T: decomposition duration; C: concentration; *: P ≤ 0.05; **: P ≤ 0.01; ***: P ≤ 0.001; NS: no significant difference.

Figure 4

RI accumulated the value of green manure extracts on goosegrass. RI, response index; WC, white clover; RG, ryegrass; AE, aqueous extract; DL, decomposed liquid. The adjacent columns from left to right in the same treatment represent concentrations of 2%, 5%, 30%, and 80% respectively.

Figure 5

Effect of different ratios on goosegrass seedling growth (A) and the SPAD value (B, n = 5). Data are presented as mean ± SD. Different lowercase letters indicate significant differences among ratios by the same green manure (P ≤ 0.05). *, **, and *** above the column and the line indicate significant differences between WC and RG by the same ratio at the levels of P ≤ 0.05, P ≤ 0.01, and P ≤ 0.001, respectively. NS: no significant difference. S: green manure species. R: straw-to-soil ratio.

Figure 6

Effect of different ratios on goosegrass photosynthetic parameters (A–D, n = 5). Data are presented as mean ± SD. Different lowercase letters indicate significant differences among ratios by the same green manure (P ≤ 0.05). *, **, and *** above the column and the line indicate significant differences between WC and RG by the same ratio P ≤ 0.05, P ≤ 0.01, and P ≤ 0.001, respectively. NS: no significant difference. S: green manure species. R: straw-to-soil ratio.

Figure 7

Effect of different ratios on the fluorescence parameters of goosegrass seedlings (A–D, n = 5). Data are presented as mean ± SD. Different lowercase letters indicate significant differences between ratios by the same green manure (P ≤ 0.05). *, **, and *** above the column and the line indicate significant differences between WC and RG by the same ratio at P ≤ 0.05, P ≤ 0.01, and P ≤ 0.001, respectively. NS: no significant difference. S: green manure species. R: straw-to-soil ratio.

Figure 8

Effects of different ratios on antioxidant enzyme activities (A, B), soluble protein, and MDA content (C, D) of goosegrass seedlings. Data are presented as mean ± SD. Different lowercase letters indicate significant differences between ratios by the same green manure (P< 0.05). *, **, and *** above the column and the line indicate significant differences between WC and RG by the same ratio at P< 0.05, P< 0.01, and P< 0.001, respectively. NS: no significant difference. S: green manure species. R: straw-to-soil ratio.

Figure 9

(A) Relationship between different parameters of goosegrass seedlings. The red ellipse represents a negative relationship among parameters, and the blue represents a positive relationship among parameters. The stronger the correlation is, the smaller the ellipse is. The numbers represent the correlation coefficients calculated using the Spearman method. ns: no significant difference, * P ≤ 0.05, ** P ≤ 0.01, *** P ≤ 0.001. (Ba) The results of multiple comparisons on the eigenvalues of PC1 for different treatments (P ≤ 0.05). (Bb) The variance contributions of the 16 parameters in the straw returning experiment to PC1 and PC2. (Bc) Principal component analysis (PCA) of different treatments among goosegrass seedlings. (Bd) The results of multiple comparisons on the eigenvalues of PC2 for different treatments (P ≤ 0.05).