Integrated evaluation of rape readiness for overwintering

Abstract

Rape (Brassica napus L.) overwintering has been studied in Lithuania and elsewhere; however, data have been analysed separately without inetgration into a common evaluation system. In this work the chosen integrated evaluation method enabled us to make complex evaluation of rape readiness for overwintering in crops of different density. A comprehensive evaluation of rape readiness for overwintering in crops of different density was performed using experimental data of the years 2000–2002. The variances of the individual indicators were subdivided into scales of nine points, and means were assigned to these points. The resulting evaluation points (EP) were marked in a network diagram with the radius scaled from 1 to 9. Evaluation threshold (ET = 5 evaluation points) was also marked, indicating the border between positive and negative assessment. This method thus allows at one sight a distinct, reproducible illustration and evaluation of different indicators characterizing readiness for overwintering. Additionally, interactions between indicators and areas demarcated by the evaluation points of all indications are visualized in the network diagram. An integrated evaluation index (IEI), consisting of the average of evaluation points, its standard deviation and standard deviation of the average of the evaluation points below the ET, was calculated to make generalized data assessments. Comprehensive evaluation using 21 indicators of rape readiness for overwintering in crops of different density showed that importance of these indicators varied. Better plant readiness for overwintering in a crop of the lowest density was determined by high values of assessment of terminal bud height, root collar diameter and nutrient accumulation in the terminal bud compared with a more dense crop. The suitability of the integrated evaluation method in such cases highlights the establishment of very strong and significant correlation (r = 0.98, p≤0.01) between the number of plants that survived the winter and the average evaluation points of readiness for overwintering. The areas determined by values of all indicators, according to different crop densities and calculated integrated evaluation indices, showed that rape readiness for overwintering in a crop with a density of < 20 plants m−2 (IEI = 6.37–1.69–1.15) and with a density of 20.1–40 plants m−2 (IEI = 5.67–1.28–1.02) was better than the average one; in a crop with a density of 40.1–60 plants m−2 (IEI = 4.97–0.85–0.53) was equal to the average one; and in a crop with a density of 60.1–80 plants m−2 (IEI = 3.62–1.23–0.79) and with a density of 80.1–100 plants m−2 (IEI = 3.10–1.76–0.67) was worse than the average one. Very strong and significant correlation was established between the number of plants that survived winter and average of evaluation points of indicators determining rape overwintering.