Chlorophyll fluorescence induction method in assessing the efficiency of pre-sowing agro-technological construction of the oilseed radish (Raphanus sativus L. var. oleiformis Pers.) agrocenosis
Chlorophyll fluorescence induction (CFI) is a measure of photosynthetic performance and is widely used by plant physiologists and ecophysiologists. The basic principle of CFI analysis is relatively straightforward. The specified method of analysis during 2015–2020 was applied to assess the optimality of selection of technological sowing parameters such as sowing rate (estimated interval 0.5–4.0 million germinable seeds ha-1 ), row width (15–30 cm), presowing fertilizer (N0–90P0–90K0–90) for three varieties of oilseed radish. The widely tested basic indicators of the CFI curve (F0, Fpl, Fm, Fst) were used, as well as possible indices and ratios calculated on their basis in accordance with the CFI analysis methodology. For the first time, the species characteristics of oilseed radish were investigated by the nature of the CFI curve in relation to spring rape, white mustard, and spring mustard on the 1.5 germinable seeds ha-1 (30 cm row width, N0P0K0) variant. It was established by the stress sensitivity category of the PSII photosystem that a reliable possibility of using the CFI method for identification studied technological options for sowing. The share of the influence of the technological factor of the sowing method (in %) on the formation of indicators F0, Fpl, Fm, Fst in the dispersion scheme of the experiment was consistently 19.3, 8.4, 19.5, 6.3. The influence of the seeding rate factor on the results of F0, Fpl, Fm, Fst was (in %) 26.6, 9.5, 42.3, 9.3 and the influence of the fertilizer factor was 13.5, 16.4, 5.7, 12.7, respectively. The formation of the specified basic indicators of the CFI curve in the resulting interaction of the technological parameters of sowing depended on the hydrothermal conditions of the vegetation of oilseed radish with the share of influence of 20.1, 40.2, 28.1, 30.0, respectively. It was determined that the decrease in the indicator of the hydrothermal coefficient (in the ratio of the increase in the sum of average daily temperatures to the decrease in the amount of precipitation) ensures the following dynamics of changes in the main and derivative indicators of CFI: a decrease Fpl 1.3%, Fm 11.8%, ER 8.7%, Lwp 15.9%, RFd 25.3%, Kprp 21.9%, Kfd 17.7% and growth F0 5.1%, Fst 7.3%, Que 40.4%, Kef 24.0%, Vt 71.3%. The comparison during the study period of options 4.0 and 0.5 million germinable seeds ha-1 determined an averaged decrease in F0 and Fst indicators by 29.5% and 29.1% while increasing Fpl and Fm by 2.2% and 38.5%. According to the determined level of CFI indicators for various technological schemes of sowing, an expedient option was recommended, which ensures the highest efficiency of the PSII photosystem of oilseed radish in the range of 1.0–2.0 germinable seeds ha-1 with a fertilization rate of N30–60P30–60K30–60 for row sowing and 1.5 germinable seeds ha-1 with a fertilization rate of N60–90P60–90K60–90 for wide-row sowing.