**5. Conclusions**

The results of the study showed that the e ffect of biostimulators and foliar fertilizers was closely related to weather conditions, and so it was not possible to clearly indicate whether there was a positive effect from the treatments on pea seed yield in each year. Adob Zn IDHA was the only fertilizer that stimulated yields, especially under average moisture conditions and less so in drought conditions in two of three years of the study. Among tested biostimulants and fertilizers, a repeatable in years increase of the yield in both, dry and wet years, was obtained after the application of Adob Zn IDHA foliar fertilizer. In addition, this fertilizer stimulated vegetative development of the plants, i.e., plant height in the average year and plant dry mass in the wetter year.

Similarly, in regard to the enzymatic parameters tested, it cannot be clearly determined which biostimulator treatments was best for pea cultivation and improved soil biochemical activity. A significant relationship between the e ffect of applied biostimulators and the development phase of the plant, as well as the year of the study was indicated. Depending on the year, the positive effect of Bolero Mo application on dehydrogenase, acid phosphatase and catalase activity, and Adob B application on alkaline phosphatase activity was noted. The BNF level was best influenced by the Titanit biostimulator, but it should be noted that all the treatments used in this study were found to stimulate this parameter.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2073-4395/10/10/1558/s1, Table S1: Effects of experimental treatments on DHA; three-way ANOVA results, Table S2: Effects of experimental treatments on PAC; three-way ANOVA results, Table S3: E ffects of experimental treatments on PAL; three-way ANOVA results, Table S4: E ffects of experimental treatments on CAT; three-way ANOVA results, Table S5: E ffects of experimental treatments on BIF; three-way ANOVA results, Table S6: E ffects of experimental treatments on Y; two-way ANOVA results, Table S7: E ffects of experimental treatments on M; two-way ANOVA results, Table S8: Effects of experimental treatments on TSW; two-way ANOVA results, Table S9: E ffects of experimental treatments on SSPW; ANOVA results, Table S10: E ffects of experimental treatments on H; two-way ANOVA results, Table S11: E ffects of experimental treatments on SW/P; two-way ANOVA results, Table S12: E ffects of experimental treatments on CCI; two-way ANOVA results, Table S13: E ffects of experimental treatments on Fv/Fm; two-way ANOVA results, Table S14: E ffects of experimental treatments on PDM; two-way ANOVA results, Table S15: Effects of experimental treatments on LAI; two-way ANOVA results, Table S16: Effects of experimental treatments on BNF; two-way ANOVA results.

**Author Contributions:** H.S., A.N., K.R., K.P., A.F. and A.W.-M. conceived and designed the experiments; H.S., A.N., K.R., K.P., A.F., A.W.-M., and L.D. performed the field experiments and analyzed the data; A.B. carried out the statistical analysis; H.S., A.N., wrote the paper; H.S., A.N., K.R. revised the manuscript. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by Polish Ministry of Agriculture and Rural Development project number HOR 3.3/2011–2015 And The APC was funded by Ministry of Science and Higher Education programme Project No. 005/RID/2018/19.

**Acknowledgments:** This study was made possible by a gran<sup>t</sup> from the Polish Ministry of Agriculture and Rural Development, Project: Improving domestic sources of plant protein, their production, trading and use in animal feed, project No. HOR 3.3/2011–2015 and within the framework of Ministry of Science and Higher Education programme as 'Regional Initiative Excellence' in years 2019–2022, Project No. 005/RID/2018/19.

**Conflicts of Interest:** The authors declare no conflict of interest.
