**5. Conclusions**

(C1) The analysis of random vibrations on any of the MCLS complex cultivator's variants is an opportunity and an obligation that must be mentioned in the work methodology that uses this equipment for research. The experiments carried out with the MCLS variants were also its first research applications. The literature shows that this is the most realistic way of approaching work processes in agriculture, having indisputable advantages over mathematical modelling and simulation. Among the most essential advantages is eliminating some assumptions that are often overly simplistic, lacking real motivation, and, above all, rarely verified, at least in the validation process. Moreover, simulation and mathematical modelling must validate their results experimentally; otherwise, they remain only scientific ballast.

(C2) The main results with immediate applications of random vibrations are the improvement of noise and vibration, the determination of dangerous demands for the elements of the structure, the determination of some limit values necessary for the choice of the material of some parts and sub-assemblies in the design, the estimation of the lifetime of the required elements in the regime of accumulation of fatigue, the identification of design or work regime deficiencies, and procedures for improving the quality of soil processing.

(C3) The presented results underline the deficiencies that must be resolved to increase the grower's performance. The recommendations refer to the control of the horizontalisation of the structure during work (with consequences for increasing the quality of soil processing relative to the working depth), the possibilities of ballasting the structure for better control of the working depth, limiting the operating speed, and the requirement of soil processing on some lands with satisfactory flatness.

(C4) A vital conclusion drawn from the results obtained is that to avoid malfunctions or damage due to premature fatigue, it is recommended that the "weakest" design elements, the ones that give way first, be among the cheapest or be simple, easy-to-replace, and cheap elements inserted into the subassemblies that will fail first in the event of an overload. We refer in particular to the fact that it is not rational to take into account the maximum loading for the structure (experimentally recorded). However, it is good to impose provisions for introducing safety elements. Thus, important and expensive subassemblies and parts will be protected. In the design of the 1960s and 1970s, for example, there were safety screws on ploughs that, by giving way first, protected the working bodies, their supports, and the load-bearing structure. Later, the abandonment of some of these safety elements produced the failure of load-bearing structures, for example.

(C5) Since we failed to validate the intuitive assumption that the working organs in the first line behind the tractor would be the most intensively requested, neither in these investigations nor in those described in [41], we deduce that, at least in the experimental conditions, the distribution of the maximum load is random over the twelve working bodies. An important consequence of this finding is that we cannot schedule a rotation of the working bodies on the load-bearing structure positions to equalise the wear and use the full working capacity of all working bodies. Moreover, a statistically higher load was observed for the working body in the last line of organs in the load-bearing structure. First, only the result of the statistical analysis was validated based on the analysis of the images taken during the experiments. It is shown that certain aspects must be fixed in the operation of this machine, which will improve the quality of the work.

(C6) The results of the experimental research agree with those in the literature, presenting significant randomness and revealing average values of the efforts at the level of working bodies expected from a theoretical point of view. The experiments present an original character through a large number of measurement points, the study of the distribution of their results, and the investigation of the links between these measurements.

Obviously, in such a complex problem as soil processing, there will always be future work directions. In the case of the problem whose research is described in this article, there are many open problems, among which are mentioned: the dependence of the descriptive and inferential statistical characteristics on the work speed; the estimation of the soil processing problem with these work organs on all the work variants of the MCLS; solving the problems already listed for all the categories of working bodies that can be mounted on the load-bearing structure of the MCLS; and the study of the processing speed limit depending on the quality of the work performed. All these problems, which do not cover even half of the ways to continue the studies, should be carried out on several types of soil at different humidity levels, aiming, if not to optimise, at least to improve agricultural soil processing. Another interesting problem is the selection of a minimum number of measurements of the soil characteristics that can be used to fix the starting parameters of the soil processing. Among these measurements, we mention humidity, resistance to penetration, plant residue amount or density, and soil resistance's quantified characteristics (apart from resistance to penetration).

Before choosing a way to continue, evaluating the possible benefits of each possibility of continuing the research is required. The evaluation creates the conditions for an optimal choice of development paths, considering the material and human resources, especially the enormous costs of experimental research, which in the end necessarily also includes the theoretical one.

**Author Contributions:** Conceptualisation, P.C.,N.C. and V.M.; methodology, P.C.,N.C. and V.M.; software, P.C. and C.P.; validation, P.C., N.C., C.P., R.S., C.M.-I., O.-D.C. and E.-A.L.; formal analysis, P.C.,N.C., R.S., N.-V.V., C.M.-I. and E.-A.L.; investigation, P.C., N.C., C.P., V.M., N.-V.V., N.U., M.M., C.M.-I. and O.-D.C.; resources, P.C., R.S., N.-V.V., N.U. and M.M.; data curation, P.C, C.P., V.M., O.-D.C. and E.-A.L.; writing—original draft preparation, P.C. and N.C.; writing—review and editing, P.C., V.M. and N.U.; visualisation, N.U., O.-D.C. and E.-A.L.; supervision, P.C., V.M., N.-V.V., N.U. and M.M.; project administration, P.C., V.M., R.S. and C.M.-I.; funding acquisition, V.M., N.-V.V., N.U. and M.M. All authors have read and agreed to the published version of the manuscript.

**Funding:** The APC was funded by the National University of Science and Technology Politehnica Bucharest, Romania, within the PubArt Program.

**Institutional Review Board Statement:** Not applicable.

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