Effects of Se and K-humate on nitrogen concentrations
The N concentration in the soil varied in availability and total content in oat straw and seeds after the foliar application of Se and K-humate. Se alone increased the availability of N in the soil in the following order: Se3 > Se2 > Se1 > control. Thus, Se was found to increase the available N-soil in an application-rate-dependent manner (Table 2). The availability of N-soil after Se application was improved via the simultaneous application of K-humate with the same rate-dependence as observed with Se alone. Comparable results were found using the sum of means for analysis. The insignificant difference found between the sum of means for control and treatment at an Se concentration of 12 × 10−3 mM Se may reflect the relatively low concentration of Se used.
The total N-straw content increased as a result of an increased content of N-plant (Table 2). Differences were found to be insignificant between Se concentrations of 12 × 10−3 mM, 63 × 10−3 mM, and controls. Likewise, the simultaneous application of K-humate showed insignificant differences between Se concentrations of 63 × 10−3 mM and 88 × 10−3 mM. Insignificant differences were noted between the control and Se concentration of 12 × 10−3 mM and the Se concentration of 63 × 10−3 and 88 × 10−3 mM using the sum of means. The total N-seeds content increased for application rates of 12 × 10−3–88 × 10−3 mM, and the simultaneous application of K-humate augmented this increase. The application rate dependency of the effects of Se and K-humate application was identical to that observed in N-soil and N-straw. No significant differences among Se and K-humate applications were observed. An insignificant difference was observed among the sum of means for Se and K-humate applications at concentrations of 63 × 10−3 and 88 × 10−3 mM.
The application of Se caused proportional increases in N-soil, N-straw, and N-seeds, and the simultaneous application of K-humate improved this effect. Previously, the application of Se resulted in an increase in the accumulation of NPK which altered N and K distribution. However, the distribution of P was not affected19. Furthermore, the application of Se ultimately resulted in an increase in the accumulation of N, calcium (Ca), K, and Mn20. A significant increase in concentrations of N and S in the rice grain plants grown under N-limiting conditions was also observed while the Ca that have been treated with Se regardless of N supply21. Thus, a synergistic interaction between Se and N in total grain proteins was reported21.
Effects of Se and K-humate on P
The effect of applications of different Se concentrations without K-humate on the available P-soil showed a reduction in the following order: Se3 > Se2 > Se1 > control (Table 3). Thus, the foliar application rate of Se caused a rate-dependent increase in the available P-soil. Simultaneous application of K-humate further increased P-soil availability. A rate dependency similar to Se alone was also observed with simultaneous Se and K-humate application. A similar result was observed using the sum of means for data analysis. Significant differences were observed among all treatments.
Foliar application of Se increased total P-straw. An insignificant difference was found between the control and Se concentrations of 12 × 10−3 and 63 × 10−3 mM, which was similar to findings observed after the application of K-humate. Moreover, insignificant differences were observed between the applications of Se and Se + K-humate. An insignificant effect was found between control and Se concentrations of (12 × 10−3 and 63 × 10−3 mM), and K-humate application using the sum of means.
The application of Se having concentrations ranging from 12 × 10−3 to 88 × 10−3 mM resulted in increased P-seeds and the addition of K-humate augmented this effect (Table 3). The effect of Se and K-humate applications showed a decrease in the following order: Se3 > Se2 > Se1 > control. Insignificant differences between values were observed when Se was applied without K-humate at concentrations of 12 × 10−3 and 63 × 10−3 mM, and for the sum of means for Se and K-humate applications at concentrations of 12 × 10−3 and 63 × 10−3 mM. Thus, the application rate of Se caused a proportional increase in P-soil, P-straw, and P-seeds. Furthermore, the simultaneous application of K-humate augmented this effect.
Consistently, concentrations of P and Ca increased in response to the application of selenite-Se (Na2SeO3⋅5H2O) to maize seedlings22, and the application of Se led to an increase in the accumulation of NPK, with alteration of N and K distribution. However, the distribution of P was not influenced19.
Effects of the foliar application of Se and K-humate on K
Different application rates of Se without humate increased K-soil and this effect showed a decrease in the following order: Se3 > Se2 > Se1 = control (Table 4). Again, the foliar application rate of Se causes a proportional increase, in this case, in K-soil. The application of K-humate with Se augmented this effect. A similar rate dependency was also observed with simultaneous application and when the sum of means was used. An insignificant difference was observed between the sum of means for controls and Se concentrations of 12 × 10−3 mM.
The foliar application of Se led to a slight increase in the total K-straw content (Table 4). An insignificant change was observed for Se concentrations from 12 × 10−3 to 88 × 10−3 mM, and similar results were found with the additional application of K-humate.
The application of Se at concentrations from 12 × 10−3 to 88 × 10−3 mM resulted in a slight increase in K-seeds, and the additional application of K-humate only slightly increased the accumulation of K (Table 4). An insignificant difference was observed between Se alone and with K-humate. Similar findings were noted when the sum of means was used for analysis. Se application rates thus produce a proportional increase in K-soil but not in K-straw or K-seeds. Comparable data were noted after K-humate addition. Concentrations of K previously decreased in response to selenite-Se (Na2SeO3⋅5H2O) application to maize seedlings; however, magnesium (Mg) concentrations did not change22. Moreover, the application of Se led to the accumulation of NPK and altered N and K distribution without affecting the P distribution19. Consistently, the application of Se ultimately resulted in increasing K accumulation20.
Effects of Se and K-humate application on oat growth
Application of Se improved the yield, which was assessed as kg × 10−3/feddan (Table 5). Higher concentrations of Se produced a higher yield of oat. The effect of Se showed a reduction in the following order: Se3 > Se2 > Se1 > control. The simultaneous application of K-humate increased the yield only slightly, resulting in insignificant differences. Similar findings were also observed when the sum of means was used. In contrast, seed production was not significantly affected, and plant length (m × 10–2) did not show a significant response. In contrast, Se application to potato plants enhanced tuber yield, plant growth, and quality compared with controls. Moreover, Se application along with different N additions ultimately increased potato productivity compared with Se or N alone23. Similarly, the grain yield increased when Se was applied; this application was significant at low levels24.
Effects of Se and K-humate applications on OMS (%) and non-enzymatic antioxidants and total phenols in oat plants
The total OMS content increased with increasing Se concentrations, perhaps due to stimulation of root growth or microbial biomass. This effect showed a decrease in the following order: Se3 > Se2 > Se1 > control. The addition of K-humate by foliar application significantly augmented the OMS content (%) (Table 6). Application of Se also increased the non-enzymatic antioxidant content; however, the increases were insignificant at Se concentrations of 12 × 10−3 and 63 × 10−3 mM. The highest values for non-enzymatic antioxidants were observed at Se concentrations of 88 × 10−3 mM. The application of K-humate along with Se did not significantly augment the effects observed after the application of Se alone. Analyses using the sum of means were completely consistent with these findings.
Se positively enhanced the total phenol content with effects decreasing in the following order: Se3 > Se2 > Se1 > control. Furthermore, this effect was significantly amplified with the simultaneous application of K-humate. Analysis using the sum of means gave comparable results. Se enhances the ability of plants to cope with stress by stimulating plant cell antioxidant capacity though the upregulating of antioxidant enzymes, such as CAT, SOD, and GSH-Px. Se also increases the synthesis of PCs, GSH, proline, ascorbate, alkaloids, flavonoids, and carotenoids. Se may also induce the spontaneous dismutation of the superoxide radical into H2O2. Elevated antioxidant capacity can reduce lipid peroxidation by lowering ROS accumulation under metal-induced oxidative stress conditions25. Application of Se using foliar spray also induced an increase in the concentration of rosmarinic acid20.
Effects of Se and K-humate applications on Se content
After the application of Se, Se-soil concentrations increased. The effects of Se concentrations decreased in the following order: Se3 > Se2 > Se1 > control. The additional application of K-humate significantly amplified these effects (Table 7). The treatment of K-humate that increased Se content in the soil may be owing to experimental errors, however, increasing Se content in either straw or seeds may be owing to the increased stimulating movement from soil to different parts of the plant. Se-straw content increased with increasing the Se foliar application; this effect decreased in the following order: Se3 > Se2 > Se1 > control. The simultaneous application of K-humate augmented the effects observed after the application of Se alone. Total Se concentration also increased Se-seeds like Se-straw for Se alone, Se with K-humate, and using the sum of means for analysis.
Effects of Se and K-humate application on Cr content
The highest concentrations of Cr were observed in control plants followed by Se2 > Se3 > Se1. In response to Se application, the Cr-straw content decreased (Table 8). The difference between Se2 and Se3 was insignificant. K-humate addition induced a notable increase in Cr-straw in the following order: control > Se3 > Se2 > Se1. This may be owing to the increased stimulating movement of Cr from soil to different parts of the plant. Results obtained from Se treatments varied depending on the presence of K-humate. Cr-seeds decreased in the following order: Se2 > Se3 > Se2 > control. The addition of K-humate increased the Cr-seed content compared with Se alone; however, the difference between Se2 and Se3 was insignificant. Analysis using the sum of means did not produce significant differences.
Effects of Se and K-humate applications on Fe content
Variable effects were produced using different application rates of Se on Fe-straw, and this effect was observed in the following order: Se3 > Se1 > control > Se2 (Table 9). Differences were insignificant among control, Se1, and Se2. K-humate caused concentrations of Fe-straw to significantly increase in the following order: control > Se3 > Se2 > Se1. Differences between control and Se3 as well as Se1 and Se2 were insignificant. Analysis using the sum of means was similar. Neither Se nor Se with K-humate applications produced significant changes in Fe-seeds. Analysis using the sum of means was similar. Low concentration of Se application may enhance plant productivity and encourage phytoremediation by improving plant tolerance to stress and enhancing photosynthesis25. Further, a significant increase was observed in concentrations of Fe and S in rice grain grown in N-limiting conditions while Ca that have been treated with Se regardless of N supply21.
Effects of Se and K-humate application on Mn content
Application of Se reduced the Mn-straw content, and this effect was observed in the following order: control > Se2 > Se1 > Se3. No significant difference was found between control and Se1 (Table 10). In contrast, K-humate addition further reduced Mn-straw concentrations in the following order: control > Se1 > Se3 > Se2. The control and Se1 were not significantly different when using the sum of means for analysis. Likewise, no significant difference was seen between Se1 and Se3. Accumulation of Mn in seeds varied among treatments in the following order: control > Se2 > Se3 > Se1. K-humate addition altered this order to be in the following order: control > Se2 > Se1 > Se3. No significant differences were observed between Se2 and Se3 when the sum of means for analysis was used. Previously, the application of Se increased the concentrations of Mg and molybdenum in grains grown in 16 and 24 mM N compared with N-limited plants21.
Effect of Se and K-humate applications on Zn content in oat plants
Application of Se2—the middle concentration of Se—resulted in highest accumulation in Zn-straw, and this effect was observed in the following order: Se2 > Se1 > control > Se3 (Table 11). The application of K-humate with Se resulted in some insignificant variations compared with the application of Se alone. Control, Se1, and Se3 were insignificantly different when the sum of means was used for the analysis. Concentrations of Zn in seeds were reduced after Se application. K-humate with Se foliar application altered the concentration of Zn in seeds with impacts in the following order: control > Se3 > Se1 > Se2. The difference between Se1 and Se3 was insignificant. Additionally, insignificant differences in Zn concentrations after application of Se1, Se2, and Se3 were found when the sum of means was used for analysis. Low concentrations of Se possibly enhance plant productivity and phytoremediation capacity by improving the ability of plants to tolerate stress and enhancing photosynthesis25.
Effects of Se and K-humate application on Cu content
Increasing concentrations of Se from 12 × 10−3 to 88 × 10−3 mM increased the concentration of Cu-seed, and this effect was observed in the following order: Se1 > control > Se2 > Se3 as it shown in Table 12. Application of Se with K-humate showed significant changes in the Cu-straw content in the following order: Se1 > Se2 > control > Se3. No significant differences were observed using the sum of means for analyses. In contrast, the foliar application of Se resulted in increases in Cu-seed at concentrations of Se1 and Se3; however, at 63 × 10−3 mM (Se2), a reduction in Cu-seed was observed. K-humate with Se simultaneously resulted in increased Cu-seed content with impacts decreasing in the following order: Se3 > Se1 > control > Se2. The sum of means analysis showed no significant variation between control and Se2. Previously, the application of Se led to a decrease in the concentrations of Cu in grains grown in 16 and 24 mm N compared with N-limited plants21.
Source: Ecology - nature.com
