Possibilities to influence on the reduction of generative organs in winter oilseed rape (Brassica napus L.)

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1 Tom XXI Rośliny Oleiste 2 Perla Kuchtová, Jan Vašák, Ivana Hyklová, Petr Baranyk Czech University of Agriculture, Prague Possibilities to influence on the reduction of generative organs in winter oilseed rape (Brassica napus L.) Możliwości wpływania na redukcję organów generatywnych u rzepaku ozimego Možnosti ovlivnění redukce generativních orgánů řepky ozimé (Brassica napus L.) Słowa kluczowe: Key words: rzepak ozimy, liczba łuszczyn, organy generatywne, azot, termin siewu, nawożenie, dekapitacja, defoliacja winter rapeseed, pods number, generative organs, nitrogen, time of sowing, stand thickness, decapitation, defoliation Článek obsahuje zpracování výsledků tříletého pozorování tvorby a redukce generativních orgánů ozimé řepky. Jedná se o studium vlivu termínu výsevu, hustoty porostu, hnojení dusíkem, a zásahů do celistvosti rostliny. Redukce generativních orgánů se zvyšuje s růstem hustoty porostu a při poklesu dávek dusíku. Opožděné výsevy tvoří nejméně generativních orgánů. Dekapitace a defoliace rostlin počátkem kvetení významně zvyšují redukci již vytvořených generativních orgánů v porovnání s kontrolou. Przedstawiono trzyletnie wyniki obserwacji nad przebiegiem tworzenia i redukcji liczby organów generatywnych na rzepaku ozimym. Badano wpływ terminu siewu, zagęszczenia roślin, nawożenia azotem i ingerencji w postać rośliny. Redukcja liczby organów generatywnych zwiększała się ze wzrostem zagęszczenia roślin i z obniżaniem nawożenia azotem. Przy opóźnionych siewach rośliny wytwarzały najmniej organów generatywnych. Dekapitacja i defoliacja roślin na początku kwitnienia istotnie zwiększały w porównaniu z kontrolą redukcję już wytworzonych organów generatywnych. The contribution includes results of three year observation concerning creation and reduction of generative organs of winter oilseed rape. Sowing time, stand density, nitrogen nutrition and intervention into the integrity of plants are subjects of the study. Reduction of generative organs were increasing with increase of stand density and with the decrease of nitrogen doses. Late sowing created the least number of generative organs. Decapitation and defoliation of plants at the beginning of flowering substantially increased the reduction of already created generative organs in comparison with the check plants.

2 726 Perla Kuchtová... Introduction The yield potential of the rape plant is proportional to its size in the flowering period and a function of the dry matter accumulation during the grow stadium before flowering (Mendham et al. 1981, Tommey and Evans 1993). The main yield component is the number of pods per square unit (Mendham et al. 1984). The yield of seeds is also in correlation with the number of pods per square unit (Grosse et al. 1992). The development of the yield is strongly influenced by the environment. Single components of the yield vary in accordance to the sensibility and compensation capability of varieties in the competing relations. Plants exposed to higher temperatures during the prolongation period did not achieved this yield, apparently as a result of competition between flowers grown on lower branches (Tommey, Evans 1992). According to Diepenbrock and Dessler in Diepenbrock (1995) the high degree of plasticity of the yield structure of rape by the influence of the year can be explained by the variability of losses of branches, buds, flowers and pods after the end of flowering. Vasak et al. in 1997 name as yield components of winter rape the number of plants per square meter, number of pods per plant, number of branches per plant, number of seeds in a pod and WTS (weight of 1 seeds). Vasak 1997 states, that the theoretical yield capability exceeds 9 tons per hectare. The average of 3 5 buds and approximately 2 seeds per pod are created per plant. Due to the introduction of new hybrid varieties of rape, the value 5 tons of rape seeds per hectare can be considered as a realistic achievable yield at present time. Fabry et all. (1992) states, that the influence of the genotype, which determines the level of elements of the yield, is often superimposed by the influence or the year, further by ecological conditions and by the agronomic technology. Those relations have mutual influence and furthermore they are strongly modified by competitive relations as well as by the organization of the plantation. Material and methods On the experimental station Cerveny Ujezd of the Czech Agricultural University in Prague we have observed the influence of the time of sowing, stand density, doses nitrogen, decapitation or defoliation of plants on the reduction of generative organs (see overview of studies).

3 Possibilities to influence on the reduction Overwiev: studies of creation of generative organs Study Badania Date of sowing Data siewu Stand density [plants/m 2 ] Gęstość [rośliny/m 2 ] Nitrogen fertilization Nawożenie azotowe [kg/ha] Plants decapitation Dekapitacja roślin Plants defoliation Defoliacja roślin early wczesny: Variant Wariant agro-technical optymalny: late późny: D 1 1 term 1 termin: Def 1 1 term 1 termin: D 2 2 term 2 termin: Def 2 2 term 2 termin: Cerveny Ujezd is situated on the attitude of 45 m over the sea level, the average yearly temperature is 7,6 C, they yearly total of precipitation is 549 mm, the soil is deep, clay brown earth with good reserves of nutrition. The tests were tended in accordance with standard procedures used for experiments in the field of the rape production system. Forecrop: winter wheat Variety: Lirajet Sowing: Nitrogen fertilization: spring regeneration 7 kg N/ha ammonium saltpeter with Ca (LAV) prolongation 5 kg N/ha LAV budding 3 kg N/ha LAV Sum 15 kg N/ha LAV Herbicides: before sowing Butisan Star 2,5 l/ha on forecrop Gallant,6 l/ha Insecticides: 3rd decade of March Nurelle,6 l/ha (Ceutorrhynchus) (as per signalization) 1st decade of April Nurelle,6 l/ha (Meligethes) 3rd decade of April Nurelle,6 l/ha end of April Decis,3 l/ha Lot area: 1 m 2, 4 repetitions During the spring regeneration period we have thinned out lots to 6 plants per m 2. In studies of stand thickness we have not achieved the required thickness (especially in case of very dense plantations), in spite of stepped sowing. We had to adapt the original plan. Later were those lots thinned out to 1, 4, 8 and 11 plants/m 2. In studies of the influence of fertilization with N we have subdivided doses of nitrogen to three doses according to agronomic technology.

4 728 Perla Kuchtová... In the study of integrity disturbance we have made interventions in the plant integrity before the beginning of determinations ( ) and at second determination ( ). Beginning with the stadium of yellow bud up to begin of the green maturity (6 determinations) on the same plants (5 plants 1 strong, 1 weak and 3 average) generative organs were counted in weekly intervals. Approximately 3 days after the end of florescence, ten days before the mechanized harvest, plants were harvested manually and the final number of generative organs pods was determined. Results Large interventions in the integrity of the vegetation (1 plants/m 2, delayed sowings) as well as interventions in the integrity of a plant (decapitation, defoliation) stimulate the creation of pods on secondary inflorescence and shift the maximum of their number to later periods (diagrams 1 5). The form of changes (increases and following decreases) of the sum of pods as well as shifts of maximum of number of those organs as function of sowing delay, decrease of stand density, increases of N doses and changes of plant integrity by decapitation a defoliation can be seen on diagrams 6 1. Tables No 1 4 state the sum of pods for particular determinations only. They were designed with the aim to valuate the increase respectively the decrease of pods between the particular determinations and in the period between the achieved maximum and the harvest. In the second determination, the highest increase of pods (43%) on the main inflorescence is shown by the third time of sowing, (see table 1), T1 and T2 show a comparable increase of 1% and 12%. On secondary inflorescence has T1 the highest increase (65%) in comparison to T3 (33%), T2 shows a decrease of 7%. Later are increases and decreases on main inflorescence stabilized around values 1% to +9%. T2 registers on secondary branches between the 2nd and the 3rd determination an increase of 25% and T3 increases the number of pods by 148%. For the 5th determination is for all variants significant a strong decrease by 21%, 19% a 17% on main inflorescence and by 59%, 33% and 31% on secondary inflorescence decreasing for T1, T2 and T3. Important is the difference in the reduction on main florescence 35%, 44% a 42%, and on secondary inflorescence 82%, 85% and 9% for T1, T2 and T3 between the 5th and 6th determination. Concerning reductions between maximum and the harvest values are not very differentiated, 54% (T1), 55% (T2) and 52% (T3) for main inflorescence and 95% (T1), 91% (T2) and 93% (T3) for secondary inflorescence.

5 Possibilities to influence on the reduction Table 1 Influence of sowing dates on the total number of pods on one plant Wpływ terminów siewu na liczbę organów generatywnych na jednej roślinie Červený Újezd. Mean: Date of sowing Termin siewu Main inflorescence Główny kwiatostan Early 342,6 378,47 341,87 338,6 266,73 173,93 Wczesny A,1,1,1,21,35 B,54 Agrotechnical 265,4 296,47 286,7 291,4 236,87 132,73 A,12,4,2,19,44 Optymalny B,55 Late 142,47 23,47 22,87 218,87 181,6 16,13 Późny A,43,9,1,17,42 B,52 Secondary inflorescences Boczne kwiatostany Early 118,13 195, 139,67 13,7 53,2 9,53 Wczesny A,65,28,7,59,82 B,95 Agrotechnical 17,33 99,73 125, 11,8 74,7 11,7 A,7,25,11,33,85 Optymalny B,91 Late 36,73 48,73 12,8 143,6 98,53 9,4 Późny A,33 1,48,19,31,9 B,93 Main and secondary inflorescences Wszystkie kwiatostany Early 46,73 573,47 481,53 468,67 319,93 183,47 Wczesny A,24,16,3,32,43 B,68 Agrotechnical 372,73 396,2 411,7 42,2 31,93 143,8 A,6,4,2,23,54 Optymalny B,65 Late 179,2 252,2 341,67 362,47 28,13 115,53 Późny A,41,35,6,23,59 B,68 A Increase or decrease of pods number between following observations Przyrost lub spadek liczby łuszczyn pomiędzy kolejnymi obserwacjami B Reduction ratio of pods between the peak value and at the harvest Stosunek redukcji liczby łuszczyn pomiędzy wartością maksymalną i przy zbiorze

6 73 Perla Kuchtová... Table 2 Influence of stand density on the total number of pods on one plant Wpływ zagęszczenia siewu na liczbę łuszczyn na jednej roślinie Stand density Zagęszczenie roślin Main inflorescence Główny kwiatostan 1 32,53 456,33 51,8 479,27 45,33 34,73 [plants/m 2 ] A,51,12,6,6,24 B, , 285,7 297,33 272,67 26, 185,73 [plants/m 2 ] A,15,4,8,5,29 B, ,8 269,33 27,2 235,73 217,47 123,4 [plants/m 2 ] A,23,,13,8,43 B, ,27 232,13 225,27 197,13 162,8 15,33 [plants/m 2 ] A,26,3,12,17,35 B,55 Secondary inflorescences Boczne kwiatostany 1 186,7 585,8 62,33 626,4 68,7 289,87 [plants/m 2 ] A 2,15,3,4,9,57 B, ,13 174,6 198,93 24,27 181,47 43,4 [plants/m 2 ] A,73,14,3,11,76 B, ,73 19,8 94,67 77,8 4,73 2, [plants/m 2 ] A,62,14,18,48,95 B, ,53 91,87 91,93 8,93 45,93 4,73 [plants/m 2 ] A,6,,12,43,9 B,95 Main and secondary inflorescences Wszystkie kwiatostany 1 488,6 142, ,13 115,67 113,4 63,6 [plants/m 2 ] A 1,13,7,1,2,44 B, ,13 459,67 496,27 476,93 441,47 229,13 [plants/m 2 ] A,32,8,4,7,48 B, ,53 379,13 364,87 313,53 258,2 125,4 [plants/m 2 ] A,32,4,14,18,51 B, ,8 324, 317,2 278,7 28,73 11,7 [plants/m 2 ] A,34,2,12,25,47 B,66 A, B as in table 1 jak w tabeli 1

7 Possibilities to influence on the reduction Influence of nitrogen fertilization on the total number of pods on one plant Wpływ nawożenia azotem na liczbę łuszczyn na jednej roślinie Nitrogen fertilization Nawożenie azotem Table Main inflorescence Główny kwiatostan 75 kg/ha 15kg/ha 225 kg/ha 3 kg/ha 23,87 225,67 187,13 181,7 138,67 87,47 A,11,17,3,23,37 B,61 246,6 298,33 298,13 279,6 236,6 155,6 A,21,,6,15,34 B,48 257,87 342,73 317,8 35,87 255,93 153,33 A,33,7,4,16,4 B,55 223,6 37,73 287,2 269,8 219,13 135,7 A,38,7,6,19,38 B,56 236, 39,67 312,13 3,67 252, 157,6 A,31,1,4,16,37 B,5 Secondary inflorescences Boczne kwiatostany 75 kg/ha 15kg/ha 225 kg/ha 3 kg/ha 43,93 59,67 43,6 44,13 18,67 1,8 A,36,27,1,58,9 B,97 92,53 149, 143,53 116,87 6,4 5,93 A,61,4,19,48,9 B,96 89,47 155,27 153,67 129,6 65,33 8,33 A,74,1,16,5,87 B,95 91,93 135,7 117,53 85,33 29,27 3,4 A,47,13,27,66,88 B,97 1,8 187,33 22,73 194,73 11,6 11,6 A,86,8,4,48,89 B,94 A, B as in table 1 jak w tabeli 1

8 732 Perla Kuchtová... Main and secondary inflorescences Wszystkie kwiatostany 75 kg/ha 15kg/ha 225 kg/ha 3 kg/ha table 3 follow ciąg dalszy tabeli 3 247,8 285,33 23,73 225,2 157,33 89,27 A,15,19,2,3,43 B,69 339,13 447,33 441,67 396,47 297, 161,53 A,32,1,1,25,46 B,64 347,33 498, 471,47 435,47 321,27 161,67 A,43,5,8,26,5 B,68 315,53 442,8 44,73 355,13 248,4 138,47 A,4,9,12,3,44 B,69 336,8 497, 514,87 495,4 353,6 169,2 A,48,4,4,29,52 B,66 Table 4 Influence of plant decapitation (D) and plant defoliation (Def) on the total number of pods on one plant Wpływ dekapitacji roślin (D) i defoliacji roślin (Def) na liczbę łuszczyn na jednej roślinie Variants Warianty Main inflorescence Główny kwiatostan D 1* 148,3 211,2 192,5 199,3 162, 14,2 A,42,9,4,19,36 B,51 D 2** 93, 29,7 211,3 215,5 2,8 117,5 A 1,25,1,2,7,41 B,44 Def 1* 25,1 34,8 232,4 22,1 165,7 79,2 A,49,24,5,25,52 B,74 Def 2** 14,4 282,6 263,1 233,9 187,4 84, A 1,71,7,11,2,55 B,7 Check 27,5 364,6 344,9 33,1 279,2 172,7 Kontrola A B

9 Possibilities to influence on the reduction Secondary inflorescences Boczne kwiatostany D 1* D 2** Def 1* Def 2** table 4 follow ciąg dalszy tabeli 4 78,9 124,7 159,5 18,8 88,6 23,5 A,58,28,13,51,73 B,87 5,1 137,8 245,3 311,4 225,8 3, A 1,75,78,27,27,87 B,9 83,1 1,9 12,5 8,6 5,4 1,1 A,21,2,21,93,8 B,99 33,8 122,4 11,3 87,8 25, 1,4 A 2,62,1,2,72,94 B,99 Check 97,7 181,7 217, 184,1 93,5 12,5 Kontrola A,86,19,15,49,87 B,94 Main and secondary inflorescences Wszystkie kwiatostany D 1* 227,2 335,9 352, 38,1 25,6 127,7 A,48,5,8,34,49 B,66 D 2** 143,1 347,5 456,6 526,9 426,6 147,5 A 1,43,31,15,19,65 B,72 Def 1* 288,2 45,7 334,9 3,7 171,1 8,3 A,41,17,1,43,53 B,8 Def 2** 138,2 45, 373,4 321,7 212,4 85,4 A 1,93,8,14,34,6 B,79 Check 368,2 546,3 561,9 514,2 372,7 185,2 Kontrola A,48,3,8,28,5 B,67 A, B as in table 1 jak w tabeli 1 * decapitation or defoliation date termin dekapitacji lub defoliacji ** decapitation or defoliation date termin dekapitacji lub defoliacji

10 734 Perla Kuchtová wczesny MI wczesny AI optymalny MI optymalny AI późny MI późny AI Graph 1. Influence of sowing dates on the total number of pods on one plant Wpływ terminów siewu, na liczbę łuszczyn na jednej roślinie MI main inflorescence kwiatostan główny, AI secondary inflorescences kwiatostany boczne MI 1 AI 4 MI 4 AI 8 MI 8 AI 11 MI 11 AI Graph 2. Influence of stand density on the total number of pods on one plant Wpływ zagęszczenia roślin na liczbę łuszczyn na jednej roślinie

11 Possibilities to influence on the reduction MI AI 75 MI 75 AI 15 MI 15 AI 225 MI 225 AI 3 MI 3 AI Graph 3. Influence of N fertilization on the total number of pods on one plant Wpływ nawożenia azotem na liczbę łuszczyn na jednej roślinie D1 MI D1 AI D2 MI D2 AI Def1 MI Def1 AI Def2 MI Def2 AI Check plants MI Check plants AI Graph 4. Influence of decapitation (D) and defoliation (Def) on the total number of pods on one plant Wpływ dekapitacji (D) i defoliacji (Def) na liczbę łuszczyn na jednej roślinie

12 736 Perla Kuchtová y = 26,37x ,44x + 385,8 R 2 =, y = -33,486x ,29x - 35,96 R 2 =,9469 y = 24,599x ,93x + 25,83 R 2 =,971 wczesny optymalny późny Graph 5. Influence of sowing dates on the total number of pods on one plant main and secondary inflorescences Wpływ terminów siewu, na liczbę łuszczyn na jednej roślinie suma dla wszystkich kwiatostanów y = 2,615x ,49x + 158,59 R2 =, y = 97,352x2 + 79,1x 86,933 R2 =,9162 y = 34,64x ,34x + 157,56 R2 =,9577 y = 22,969x ,79x + 196,21 R 2 =,9747 Graph 6. Influence of stand density on the total number of pods on one plant main and secondary inflorescences Wpływ zagęszczenia roślin na liczbę łuszczyn na jednej roślinie suma dla wszystkich kwiatostanów suma dla wszystkich kwiatostanów

13 Possibilities to influence on the reduction y = 42,173x ,42x + 129,63 R 2 =,996 y = 33,964x ,5x + 24,99 R 2 =,971 y = 26,83x ,21x + 225,88 R 2 =,9475 y = 1,376x ,856x + 227,32 75 R 2 =, y = 28,456x ,64x + 22,2 R =, Graph 7. Influence of N fertilization on the total number of pods on one plant main and secondary inflorescences Wpływ nawożenia azotem na liczbę łuszczyn na jednej roślinie suma dla wszystkich kwiatostanów 6 y = 43,864x ,66x + 163,7 R2 =, y = 31,79x ,83x + 61,38 R 2 =,9647 y = 58,127x ,3x 234,11 R 2 =,9681 D1 D Check plants wzorzec Graph 8. Influence of decapitation on the total number of pods on one plant main and secondary inflorescences Wpływ dekapitacji na liczbę łuszczyn na jednej roślinie suma dla wszystkich kwiatostanów

14 738 Perla Kuchtová y = 22,798x2 + 18,8x + 228,45 R2 =,9298 y = 43,864x ,66x + 163,7 R 2 =,9847 Def1 Def2 1 5 y = 4,711x ,45x 34,6 R2 =,863 Check plants wzorzec Graph 9. Influence of defoliation on the total number of pods on one plant main and secondary inflorescences Wpływ defoliacji na liczbę łuszczyn na jednej roślinie suma dla wszystkich kwiatostanów In stand density (table No 2) the highest increase can be seen on main inflorescence of the most thin stand density (1 plants), namely 51%, than ascending for 4, 8 a 11: 15%, 23% and 26% between the 1rst and second determination (table No 2). Afterwards changes are not so dramatic up to the 6th determination, which means a decrease by 24%, 38%, 43% a 35% of pods for 1, 4, 8 and 11 plants. Relatively high is the decrease in case of 11 plants/m 2 between the 4th and the 5th determination: 17%. Concerning secondary inflorescence, the lowest decrease has the density 1 plants/m 2 57% followed by 76% (4 plants), 95% (8 plants) and 9% (11 plants). The decrease between the maximum and the harvest on main inflorescence reaches the highest value for the density 11 (55%), followed by 8 (54%), 4 (38%) and 1 plants/m 2 (33%). In case of secondary inflorescence the highest decrease is reached by the density 8 (98%), followed by 11 with 95% and 4 with 78%. The thinnest variant has on secondary branches the lowest decrease (51%). The variant, which was not fertilized by nitrogen shows in the second term an increase of pods on main inflorescence by 11%, 75 kg N by 21%, 15 kg N by 33%, 225 kg N by 38% and 3 kg by 31%. In case of not fertilized On secondary inflorescence was the increase for not fertilized variant by 36%, in case

15 Possibilities to influence on the reduction of 75 kg N 61%, in case of 15 kg N 74%, in case 225 kg N 47% and in case of 3 kg N 86%. Changes of number of pods are not significant in the following determinations, up to 5th determination on main branches and up to 4th determination on secondary branches, where a high decrease could be seen in case of variants 75, 15 a 225 kg N by 19%, 16% and 27% respectively. On main inflorescence has the highest decrease at fifth determination at the not fertilized variant:: 23%. Whereas the decrease on the main inflorescence start approximately by 37% ( a 3 kg N/ha between the 6th and the 5th determination, decreases in secondary inflorescence are traditionally the highest from 87% (15 kg N) up to 9% (, 75 kg N). Between the maximum and the harvest, the highest decrease on main inflorescence has the variant, which was not fertilized (61%) and the lowest fertilized variant 15 kg N (55%). The decrease on secondary inflorescence is practically even, from 94% for 3 kg N up to 97% for not fertilized and fertilized by 225 kg N. The removing of the terminal (decapitation) on main inflorescence at the first determination (D 1 means decapitation ) has shown an increase of pods at the 2nd determination by 42%, defoliation at the same period (Def 1 defoliation ) by 49% with a following decrease (3. determination) by 24%. The decapitation at the second determination (D ) has registered basically a constant number of pods up to the harvest with a minimum decrease at the harvest (in comparison to remaining variants) at the 5th determination 7%. The highest decrease between the 5th and the 6th determination was shown by both variants of defoliation, namely 52% (Def 1) and 55% (Def 2 defoliation )). Those variants had the higher decrease in the period between the maximum and the harvest 74% and 7% (Def 1 a Def 2). On secondary branches D 1 manifested itself by increase of pods by 58% (2nd determination), 28% (3rd determination) a 13% (4th determination) with a following decrease of 51% (5th determination) and 73% (harvest). D 2 has shown an increase of 78% (3rd determination) and 27% (4th determination) with a decrease by 27% (4th determination) and 87% in the harvest. Def 1 has shown an increase at the 3rd determination by 21% with the same decrease at the 4th determination and 93% decrease at the fifth determination, at the harvest was the decrease 8%. Def 2 has shown only a decrease by 1%, 2%, 72% and 94% at the 3rd, 4th and 5th determination as well as at the harvest. The check has shown an decrease of 15% on main inflorescence before the harvest and 38% at the harvest. On secondary inflorescence was the decrease higher, starting by the 4th determination (when D 1 and D 2 still have shown a increase), 15%. At the 5th determination was the decrease 49% and at the harvest 87%. The lowest decrease between the maximum and the harvest had D 2 (44%), D 1 (51%) and the check. The highest reduction was observed by Def 1, namely 74% in comparison to 7% in case of Def 2.

16 74 Perla Kuchtová... Discussion and conclusions It is obvious, that an earlier sowing gives plants enough time for storing of reserve substances thus enabling them to create a higher number of pods. The relations the higher the number of created pods the higher the reduction, is valid here. In spite of the higher reduction we harvest more pods from earlier established plantations than in the case of the later sowing. Early sowings give a higher guarantee of yield. We have found out, that the very low stand thickness has perfectly modified the structure of the plant as well as the structure of yield distribution of pods. In spite of large compensating capacities of such flexible plant as rape, it is not suitable to grow plantations with stand density lower than 4 plants/m 2. It is sufficient to calculate the harvested pods per square unit, put in the conservative WTS value and the number of approximately 2 seeds per pod and we find out, that starting by 1 plants per m 2 we cannot expect an extraordinary yield. Nitrogen is an intensifying factor. Our result seems to confirm, that in case of good soils the fertilization 15 kg N/ha can be sufficient for the needs of rape and the fertilization with higher doses could be ineffective. Besides, the creation of yield is always a resultant of many factors. Very important combination is made up of our study of stand density, time of sowing and fertilization, but the selection of a efficient soil and necessary inputs oriented towards the protection of plants against diseases and parasites cannot be disregarded. Only when all those conditions are met, success in rape production can be expected. An intervention into the plant integrity by terminal removal (decapitation) and defoliation is substantial. By such interventions a damage of plantation by climatic excesses as e.g. hailstorm can be simulated to a certain grade. We have found out, that plants in the period shortly before inflorescence react to decapitation more sensitively than in a later stadium. Plants in this sensitive stage suffer mostly by the damage respectively by the removal of leafs surface. Rape can quite well compensate the loss of the terminal. Side branches are not marked as much as the main branches, concerning the creation of pods, but the result is obvious in advance no yield is created on the secondary branches. Conclusions The reduction of the number of pods starts with the creation of first pods. All we can do for yield we have to do during the establishing of the plantation (time of sowing, density) and than in the period of the spring regeneration up to prolongation of stem (nutrition, protection). Afterwards is rape very sensitive to any mechanical damage, because it loses its capability to compensate the reduction

17 Possibilities to influence on the reduction of a certain yield element. Nevertheless there is a period suitable for the limitation of reduction of pods already created, mainly because of the lack of assimilates. This period is first ten days of flowering. References Diepenbrock W., Becker H.C Physiological Potentials for Yield Improvement of Annual Oil and Protein Crops, Blackwell Wissenschafts-Verlag Berlin-Vienna, Fábry A. a kol Olejniny. Ministerstvo zemědělství ČR, 419. Grosse F., Léon J., Diepenbrock W Ertragsbildung und Ertragstruktur bei Winterraps (Brassica napus L.). I. Genotypische Variabilität. J. Agronomy & Crop Science, 169: Mendham N.J., Scott R.K The limiting effect of plant size at inflorescence initiation on subsequent growth and yield of oilseed rape (Brassica napus). Journal of Agricultural science, Cambridge, 84: Tommey A.M., Evans E.J Analysis of post-flowering compensatory growth in winter oilseed rape (Brassica napus), Journal of Agricultural Science, Cambridge, 118: Vašák J., Fábry A., Zukalová H., Morbacher J., Baranyk P. a kol Systém výroby řepky. Česká pěstitelská technologie ozimé řepky pro roky Svaz pěstitelů a zpracovatelů olejnin, Praha.