Features of layerage formation in the oil radish agrophytocenosis under conditions of the Right-bank Forest-steppe of Ukraine

Abstract

 Changes in the modern view of the field structure as a complex multilevel agrophytocenosis cause the search for effective mechanisms that take into consideration this factor for the fulfillment of the productivity of a certain genotype, since under such features each layer has an inherent level of individual characteristics that are realized precisely in the elements of individual productivity. Despite the significance of the study of the agrophytocenosis layerage, this criterion for oil radish is not studied enough, which proves both the novelty and practical value of our research. The purpose of the research was to conduct a complex assessment of the oil radish agrophytocenosis by the layerage criterion and to establish the mechanism of formation of this criterion taking into consideration the change in the technological approaches to its construction. Methodology of research. The research was conducted during 2013-2017 under conditions of the experimental field of Vinnytsia National Agrarian University on the soils that are typical for the right-bank Forest-Steppe. Methodologically, the mechanism of layerage formation in the oil radish agrophytocenosis was studied considering technological factors such as the row-spacing (two values of 15 and 30 cm) and seeding rates (in the ratio of 4.0, 3.0, 2.0 and 1.0 million germinating seeds per hectare under 15 cm row-spacing, and 2.0, 1.5, 1.0 and 0.5 million germinating seeds per hectare under 30 cm row-spacing, respectively) against the background of four variants of mineral nutrition (non-fertilized background, N30P30K30, N60P60K60,  N90P90K90). Zhuravka variety was used as a genotype that is widely distributed in the
research area. Approved techniques for researching cross-pollinated crops were used. Layerage assessment included determination of the integral vitality coefficient (IVC), morphometric characteristics of different plant idiotypes with the involvement of statistical estimates of the magnitude of the values (R), coefficient of variation (v), Fisher's (F) criterion, and the others. Research results. It has been established that the vitality structure of the agrophytocenosis in the form of the integrated vitality coefficient (IVC) has significant differences and different levels of cenosis stress depending on the technological parameters of sowing and fertilization. It has been proved that the increase in the seeding rates for oil radish affected the intensity of all individual plant characteristics in relation to their mean value for all research variants. This is indicated by the high-inverse relationship between IVC and the seeding-rate within the variants (r = -0.822 – -0.917 (under P ≤ 0.01) depending on the phenophase. It should also be noted that in the variants sown by a drill method with the seeding rates of 1.0 – 4.0 million germinating seeds per hectar, the vitality coefficient was higher in the initial stages of vegetation in the phase of the rosette of 0.687 – 1.039. In the process of plant growth and development, it decreased to a minimum of 0.517 – 0.946 in the flowering phase. In the wide-row variants, the reduction of the vitality coefficient was observed in the phase of the green pod. According to the results obtained, the peak of the coenotic stress of the oil radish agrophytocenoses having ordinary drilled rows is achievable in the flowering phase, and in the wide-row schemes it is shifted to the phase of the green pod. The study of the combination of the seeding rates and sowing method shows that the highest coenotic stress was noted in the variant of drill sowing under the seeding rate of 4.0 million germinating seed per hectar on the background of N90P90K90 based on the lowest levels of the vitality coefficient compared to other variants studied. Mineral fertilizers weaken a biological stress between plants in the cenosis. However, according to our estimates, this effect will be positive only before reaching a certain value of gradation of fertilization rates. Under the appropriate level of narrow plant spacing, an additional nutrition of more than 60 kg of reactant per ha for
the oil radish, on the contrary, enhances competition in agrophytocenoses as a result of the more intensive differentiation of the plant stand into different layers and stimulation of the most competitive plants, and due to the general improvement of growth processes of all components, including segetal. Thus, under the total growth of phytomass per unit of area, additional nutrition only enhances the process of interspecific antagonism and provides a clear stratification in the vertical crop profile into essentially different plant idiotypes, as evidenced by the decrease in IVC on the background of fertilization with N90P90K90 in thevariants of 4.0 million of germinating seeds per hectar. Peculiarities of the vitality strategy of agrophytocenosis in the system of the studied factors as well as the results of such typification of plant idiotypes and their determination into three layers in the vertical projection of the sowing are determined. According to the morphometric gradation of plants within the layers, the highest variation of the indicators was observed in the plants of the upper layer, which is defined as the dominant vitality strategy of these plants and a less coenical stress of their development due to the highly competitive rates of their growth in agrophytocenosis, starting from the initial stages of vegetation. On the contrary, as for morphological indicators of plants of the middle layer, the variation coefficient is lower compared to all three groups, which we explain by the coenotic predominance of plants of this layer in the sowing. The mechanism of the layerage formation and intensity in the oil radish cenosis on the background of different backgrounds of mineral nutrition is developed, on the basis of which the factor of layerage is selected as a criterion for an adequate estimation of the positive effect of the supplementary mineral nutrition. In addition, the analysis of the effect of hydrothermal vegetation conditions on the intensity and morphological variability of the ideotypic structure of the oil radish agrophytocenosis has been carried out. Conclusions. The existence of intensive layerage (plant idiotypes) of the oil radish agrophytocenosis has been proved. Increase in the seeding rate leads to formation of a higher percentage of plants of the lower layer that are smaller in height, stem diameter, leaf area and weight characteristics with a tendency to lower
vitality coefficient and reduced vitality strategy. Reduction of the seeding rate contributes to the expansion in variation of plant morphological indicators and formation of the upper layer of plants. Unfavourable weather conditions aggravate layerage formation of the sowing during plant growth of the lower layer idiotype. Mineral fertilizers perform a layer-regulating function but only under adequate combination of the fertilization rate and density of the agrophytocenosis.