Możliwości wpływania na redukcję organów generatywnych u rzepaku ozimego.

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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: rzepak ozimy, liczba łuszczyn, organy generatywne, azot, termin siewu, nawożenie, dekapitacja, defoliacja

Key words: 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, na-wożenia azotem i ingerencji w postać rośliny. Redukcja liczby organów generatywnych zwięk-szała się ze wzrostem zagęszczenia roślin i z ob-niżaniem 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 wytwo-rzonych 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.

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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 1000 seeds). Vasak 1997 states, that the theoretical yield capability exceeds 9 tons per hectare. The average of 300–500 buds and approximately 20 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).

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Overwiev: studies of creation of generative organs

Study — Badania Variant — Wariant

Date of sowing Data siewu early — wczesny: 20.8. – 24.8. agro-technical — optymalny: 30.8. – 4.9. late — późny: 9.9. – 11.9. Stand density [plants/m2]

Gęstość [rośliny/m2]

10 40 80 110

Nitrogen fertilization Nawożenie azotowe [kg/ha]

0 75 150 225 300 Plants decapitation Dekapitacja roślin D 1 — 1 term — 1 termin: 26.4. – 29.4. D 2 — 2 term— 2 termin: 3.5. – 6.5. Plants defoliation Defoliacja roślin

Def 1 — 1 term— 1 termin: 26.4. – 29.4.

Def 2 — 2 term— 2 termin: 3.5. – 6.5.

Cerveny Ujezd is situated on the attitude of 405 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: 28.8. – 4.9.

Nitrogen fertilization: spring regeneration 70 kg N/ha — ammonium saltpeter

with Ca (LAV)

prolongation 50 kg N/ha — LAV

budding 30 kg N/ha — LAV

Sum 150 kg N/ha — LAV

Herbicides: before sowing Butisan Star 2,5 l/ha on forecrop Gallant 0,6 l/ha

Insecticides: 3rd decade of March Nurelle 0,6 l/ha (Ceutorrhynchus) (as per signalization) 1st decade of April Nurelle 0,6 l/ha (Meligethes)

3rd decade of April Nurelle 0,6 l/ha end of April Decis — 0,3 l/ha

Lot area: 10 m2, 4 repetitions

During the spring regeneration period we have thinned out lots to 60 plants per m2. 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 10, 40, 80 and 110 plants/m2. In studies of the influence of fertilization with N we have subdivided doses of nitrogen to three doses according to agronomic technology.

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In the study of integrity disturbance we have made interventions in the plant integrity before the beginning of determinations (26.4. – 29.4.) and at second determination (3.5. – 6.5.).

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 30 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 (10 plants/m2, 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 6–10.

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 shownby the third t i m e o f s o w i n g , (see table 1), T1 and T2 show a comparable increase of 10% 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 –10% 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 90% 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.

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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: 1997–1998–1999

1997 5.05.97 12.05.97 19.05.97 26.05.97 4.06.97 5.07.97 1998 29.04.98 6.05.98 14.05.98 22.05.98 28.05.98 30.06.98 Date of sowing Termin siewu _{1999 26.04.99 3.05.99 10.05.99 17.05.99 24.05.99 2.07.99} Main inflorescence — Główny kwiatostan

342,60 378,47 341,87 338,60 266,73 173,93 A 0,10 –0,10 –0,01 –0,21 –0,35 Early Wczesny B –0,54 265,40 296,47 286,07 291,40 236,87 132,73 A 0,12 –0,04 0,02 –0,19 –0,44 Agro-technical Optymalny B –0,55 142,47 203,47 220,87 218,87 181,60 106,13 A 0,43 0,09 –0,01 –0,17 –0,42 Late Późny B –0,52

Secondary inflorescences — Boczne kwiatostany

118,13 195,00 139,67 130,07 53,20 9,53 A 0,65 –0,28 –0,07 –0,59 –0,82 Early Wczesny B –0,95 107,33 99,73 125,00 110,80 74,07 11,07 A –0,07 0,25 –0,11 –0,33 –0,85 Agro-technical Optymalny B –0,91 36,73 48,73 120,80 143,60 98,53 9,40 A 0,33 1,48 0,19 –0,31 –0,90 Late Późny B –0,93

Main and secondary inflorescences — Wszystkie kwiatostany

460,73 573,47 481,53 468,67 319,93 183,47 A 0,24 –0,16 –0,03 –0,32 –0,43 Early Wczesny B –0,68 372,73 396,20 411,07 402,20 310,93 143,80 A 0,06 0,04 –0,02 –0,23 –0,54 Agro-technical Optymalny B –0,65 179,20 252,20 341,67 362,47 280,13 115,53 A 0,41 0,35 0,06 –0,23 –0,59 Late Późny B –0,68

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

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Table 2 Influence of stand density on the total number of pods on one plant

Wpływ zagęszczenia siewu na liczbę łuszczyn na jednej roślinie

1997 5.05.97 12.05.97 19.05.97 26.05.97 4.06.97 5.07.97 1998 29.04.98 6.05.98 14.05.98 22.05.98 28.05.98 30.06.98 Stand density

Zagęszczenie

roślin 1999 26.04.99 3.05.99 10.05.99 17.05.99 24.05.99 2.07.99 Main inflorescence — Główny kwiatostan

302,53 456,33 510,80 479,27 450,33 340,73 A 0,51 0,12 –0,06 –0,06 –0,24 10 [plants/m2] B –0,33 247,00 285,07 297,33 272,67 260,00 185,73 A 0,15 0,04 –0,08 –0,05 –0,29 40 [plants/m2] B –0,38 219,80 269,33 270,20 235,73 217,47 123,40 A 0,23 0,00 –0,13 –0,08 –0,43 80 [plants/m2] B –0,54 184,27 232,13 225,27 197,13 162,80 105,33 A 0,26 –0,03 –0,12 –0,17 –0,35 110 [plants/m2] B –0,55

186,07 585,80 602,33 626,40 680,07 289,87 A 2,15 0,03 0,04 0,09 –0,57 10 [plants/m2] B –0,51 101,13 174,60 198,93 204,27 181,47 43,40 A 0,73 0,14 0,03 –0,11 –0,76 40 [plants/m2] B –0,78 67,73 109,80 94,67 77,80 40,73 2,00 A 0,62 –0,14 –0,18 –0,48 –0,95 80 [plants/m2] B –0,98 57,53 91,87 91,93 80,93 45,93 4,73 A 0,60 0,00 –0,12 –0,43 –0,90 110 [plants/m2] B –0,95

488,60 1042,13 1113,13 1105,67 1130,40 630,60 A 1,13 0,07 –0,01 0,02 –0,44 10 [plants/m2] B –0,39 348,13 459,67 496,27 476,93 441,47 229,13 A 0,32 0,08 –0,04 –0,07 –0,48 40 [plants/m2] B –0,54 287,53 379,13 364,87 313,53 258,20 125,40 A 0,32 –0,04 –0,14 –0,18 –0,51 80 [plants/m2] B –0,67 241,80 324,00 317,20 278,07 208,73 110,07 A 0,34 –0,02 –0,12 –0,25 –0,47 110 [plants/m2] B –0,66

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Table 3 Influence of nitrogen fertilization on the total number of pods on one plant

Wpływ nawożenia azotem na liczbę łuszczyn na jednej roślinie

1997 5.05.97 12.05.97 19.05.97 26.05.97 4.06.97 5.07.97 1998 29.04.98 6.05.98 14.05.98 22.05.98 28.05.98 30.06.98 Nitrogen fertilization Nawożenie azotem 1999 26.04.99 3.05.99 10.05.99 17.05.99 24.05.99 2.07.99 Main inflorescence — Główny kwiatostan

203,87 225,67 187,13 181,07 138,67 87,47 A 0,11 –0,17 –0,03 –0,23 –0,37 0 B –0,61 246,60 298,33 298,13 279,60 236,60 155,60 A 0,21 0,00 –0,06 –0,15 –0,34 75 kg/ha B –0,48 257,87 342,73 317,80 305,87 255,93 153,33 A 0,33 –0,07 –0,04 –0,16 –0,40 150kg/ha B –0,55 223,60 307,73 287,20 269,80 219,13 135,07 A 0,38 –0,07 –0,06 –0,19 –0,38 225 kg/ha B –0,56 236,00 309,67 312,13 300,67 252,00 157,60 A 0,31 0,01 –0,04 –0,16 –0,37 300 kg/ha B –0,50

43,93 59,67 43,60 44,13 18,67 1,80 A 0,36 –0,27 0,01 –0,58 –0,90 0 B –0,97 92,53 149,00 143,53 116,87 60,40 5,93 A 0,61 –0,04 –0,19 –0,48 –0,90 75 kg/ha B –0,96 89,47 155,27 153,67 129,60 65,33 8,33 A 0,74 –0,01 –0,16 –0,50 –0,87 150kg/ha B –0,95 91,93 135,07 117,53 85,33 29,27 3,40 A 0,47 –0,13 –0,27 –0,66 –0,88 225 kg/ha B –0,97 100,80 187,33 202,73 194,73 101,60 11,60 A 0,86 0,08 –0,04 –0,48 –0,89 300 kg/ha B –0,94

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table 3 — follow —ciąg dalszy tabeli 3 Main and secondary inflorescences — Wszystkie kwiatostany

247,80 285,33 230,73 225,20 157,33 89,27 A 0,15 –0,19 –0,02 –0,30 –0,43 0 B –0,69 339,13 447,33 441,67 396,47 297,00 161,53 A 0,32 –0,01 –0,10 –0,25 –0,46 75 kg/ha B –0,64 347,33 498,00 471,47 435,47 321,27 161,67 A 0,43 –0,05 –0,08 –0,26 –0,50 150kg/ha B –0,68 315,53 442,80 404,73 355,13 248,40 138,47 A 0,40 –0,09 –0,12 –0,30 –0,44 225 kg/ha B –0,69 336,80 497,00 514,87 495,40 353,60 169,20 A 0,48 0,04 –0,04 –0,29 –0,52 300 kg/ha B –0,66 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 1997 5.05.97 12.05.97 19.05.97 26.05.97 4.06.97 5.07.97 1998 29.04.98 6.05.98 14.05.98 22.05.98 28.05.98 30.06.98 Variants Warianty 1999 26.04.99 3.05.99 10.05.99 17.05.99 24.05.99 2.07.99 Main inflorescence — Główny kwiatostan

148,30 211,20 192,50 199,30 162,00 104,20 A 0,42 –0,09 0,04 –0,19 –0,36 D 1* B –0,51 93,00 209,70 211,30 215,50 200,80 117,50 A 1,25 0,01 0,02 –0,07 –0,41 D 2** B –0,44 205,10 304,80 232,40 220,10 165,70 79,20 A 0,49 –0,24 –0,05 –0,25 –0,52 Def 1* B –0,74 104,40 282,60 263,10 233,90 187,40 84,00 A 1,71 –0,07 –0,11 –0,20 –0,55 Def 2** B –0,70 270,50 364,60 344,90 330,10 279,20 172,70 A Check Kontrola B

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table 4 — follow —ciąg dalszy tabeli 4 Secondary inflorescences — Boczne kwiatostany

78,90 124,70 159,50 180,80 88,60 23,50 A 0,58 0,28 0,13 –0,51 –0,73 D 1* B –0,87 50,10 137,80 245,30 311,40 225,80 30,00 A 1,75 0,78 0,27 –0,27 –0,87 D 2** B –0,90 83,10 100,90 102,50 80,60 5,40 1,10 A 0,21 0,02 –0,21 –0,93 –0,80 Def 1* B –0,99 33,80 122,40 110,30 87,80 25,00 1,40 A 2,62 –0,10 –0,20 –0,72 –0,94 Def 2** B –0,99 97,70 181,70 217,00 184,10 93,50 12,50 A 0,86 0,19 –0,15 –0,49 –0,87 Check Kontrola B –0,94

227,20 335,90 352,00 380,10 250,60 127,70 A 0,48 0,05 0,08 –0,34 –0,49 D 1* B –0,66 143,10 347,50 456,60 526,90 426,60 147,50 A 1,43 0,31 0,15 –0,19 –0,65 D 2** B –0,72 288,20 405,70 334,90 300,70 171,10 80,30 A 0,41 –0,17 –0,10 –0,43 –0,53 Def 1* B –0,80 138,20 405,00 373,40 321,70 212,40 85,40 A 1,93 –0,08 –0,14 –0,34 –0,60 Def 2** B –0,79 368,20 546,30 561,90 514,20 372,70 185,20 A 0,48 0,03 –0,08 –0,28 –0,50 Check Kontrola B –0,67

A, B — as in table 1 — jak w tabeli 1

* — decapitation or defoliation date — termin dekapitacji lub defoliacji — 26.04. – 29.04 ** — decapitation or defoliation date — termin dekapitacji lub defoliacji — 3.05. – 6.05

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0 50 100 150 200 250 300 350 400 1 2 3 4 5 6 wczesny MI wczesny AI optymalny MI optymalny AI późny MI późny AI Liczba łuszczyn — Number of pods

Data of determination — Termin obserwacji

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

0 100 200 300 400 500 600 700 800 1 2 10 MI 10 AI 40 MI 40 AI 80 MI 80 AI 110 MI 110 AI 3 4 5 6

Liczba

łuszczyn —

Number of pods

Graph 2. Influence of stand density on the total number of pods on one plant Wpływ zagęszczenia roślin na liczbę łuszczyn na jednej roślinie

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0 50 100 150 200 250 300 350 400 1 2 3 4 5 6 0 MI 0 AI 75 MI 75 AI 150 MI 150 AI 225 MI 225 AI 300 MI 300 AI Liczba łuszczyn — Number of pods

Graph 3. Influence of N fertilization on the total number of pods on one plant — Wpływ nawożenia azotem na liczbę łuszczyn na jednej roślinie

0 50 100 150 200 250 300 350 400 1 2 3 4 5 6 D1 MI D1 AI D2 MI D2 AI Def1 MI Def1 AI Def2 MI Def2 AI Check plants MI Check plants AI Liczba łuszczyn — Number of pods

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

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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 = –26,307x2 + 122,44x + 385,08 R2 = 0,9518 y = –24,599x2 + 131,93x + 250,83 R2 = 0,971 y = -33,486x2 + 228,29x - 35,96 R2 = 0,9469 0 100 200 300 400 500 1 2 3 4 5 6 wczesny optymalny późny Liczba łuszczyn — Number of pods

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

y = –97,352x2 + 709,1x – 86,933 R2 = 0,9162 y = –34,064x2 + 219,34x + 157,56 R2 = 0,9577 y = –22,969x2 + 125,79x + 196,21 R2 = 0,9747 y = –20,615x2 + 114,49x + 158,59 R2 = 0,9801 0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1 2 3 4 5 6 10 40 80 110

Liczba

łuszczyn —

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y = –42,173x2 + 258,42x + 129,63 R2 = 0,9906 y = –33,964x2 + 195,05x + 204,99 R2 = 0,971 y = –28,456x2 + 159,64x + 220,02 R2 = 0,9857 y = –26,083x2 + 139,21x + 225,88 R2 = 0,9475 y = –10,376x2 + 38,856x + 227,32 R2 = 0,9588 0 50 100 150 200 250 300 350 400 450 500 550 1 2 3 4 5 6 0 75 150 225 300

Liczba

łuszczyn —

Number of pods

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 y = –43,864x2 + 264,66x + 163,7 R2 = 0,9847 y = –58,127x2 + 416,3x – 234,11 R2 = 0,9681 y = –31,079x2 + 196,83x + 61,38 R2 = 0,9647 0 100 200 300 400 500 600 1 2 3 4 5 6 D1 D2 Check plants wzorzec Liczba łuszczyn — Number of pods

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

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y = –43,864x2 + 264,66x + 163,7 R2 = 0,9847 y = –40,711x2 + 259,45x – 34,6 R2 = 0,8603 y = –22,798x2 + 108,8x + 228,45 R2 = 0,9298 0 50 100 150 200 250 300 350 400 450 500 550 600 1 2 3 4 5 6 Def1 Def2 Check plants wzorzec Liczba łuszczyn — Number of pods

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 s t a n d d e n s i ty (table No 2) the highest increase can be seen on main inflorescence of the most thin stand density (10 plants), namely 51%, than ascending for 40, 80 a 110: 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 10, 40, 80 and 110 plants. Relatively high is the decrease in case of 110 plants/m2 between the 4th and the 5th determination: 17%. Concerning secondary inflorescence, the lowest decrease has the density 10 plants/m2 — 57% followed by 76% (40 plants), 95% (80 plants) and 90% (110 plants). The decrease between the maximum and the harvest on main inflorescence reaches the highest value for the density 110 (55%), followed by 80 (54%), 40 (38%) and 10 plants/m2 (33%). In case of secondary inflorescence the highest decrease is reached by the density 80 (98%), followed by 110 with 95% and 40 with 78%. The thinnest variant has on secondary branches the lowest decrease (51%).

The variant, which was not fertilized by n it r o g e n shows in the second term an increase of pods on main inflorescence by 11%, 75 kg N by 21%, 150 kg N by 33%, 225 kg N by 38% and 300 kg by 31%. In case of not fertilized On secondary inflorescence was the increase for not fertilized variant by 36%, in case

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of 75 kg N 61%, in case of 150 kg N 74%, in case 225 kg N 47% and in case of 300 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, 150 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% (0 a 300 kg N/habetween the 6th and the 5th determination, decreases in secondary inflorescence are traditionally the highest — from 87% (150 kg N) up to 90% (0, 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 150 kg N (55%). The decrease on secondary inflorescence is practically even, from 94% for 300 kg N up to 97% for not fertilized and fertilized by 225 kg N.

The removing of the terminal (d e c a p it a t io n ) on main inflorescence at the first determination (D 1 means decapitation 26.4. – 29.4.) has shown an increase of pods at the 2nd determination by 42%, d e f o l ia ti o n at the same period (Def 1 — defoliation 26.4. – 29.4.) by 49% with a following decrease (3. determination) by 24%. The decapitation at the second determination (D 2 — 3.5. – 6.5.) 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 3.5. – 6.5.)). Those variants had the higher decrease in the period between the maximum and the harvest 74% and 70% (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 80%. Def 2 has shown only a decrease by 10%, 20%, 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 70% in case of Def 2.

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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 40 plants/m2. It is sufficient to calculate the harvested pods per square unit, put in the conservative WTS value and the number of approximately 20 seeds per pod and we find out, that starting by 10 plants per m2 we cannot expect an extraordinary yield.

Nitrogen is an intensifying factor. Our result seems to confirm, that in case of good soils the fertilization 150 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

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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. 1995. Physiological Potentials for Yield Improvement of Annual Oil and Protein Crops, Blackwell Wissenschafts-Verlag Berlin-Vienna, 21-89.

Fábry A. a kol. 1992. Olejniny. Ministerstvo zemědělství ČR, 419.

Grosse F., Léon J., Diepenbrock W. 1992. Ertragsbildung und Ertragstruktur bei Winterraps (Brassica napus L.). I. Genotypische Variabilität. J. Agronomy & Crop Science, 169: 70-93.

Mendham N.J., Scott R.K. 1975. 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: 487-502.

Tommey A.M., Evans E.J. 1992. Analysis of post-flowering compensatory growth in winter oilseed rape (Brassica napus), Journal of Agricultural Science, Cambridge, 118: 301-308.

Vašák J., Fábry A., Zukalová H., Morbacher J., Baranyk P. a kol. 1997. Systém výroby řepky. Česká pěstitelská technologie ozimé řepky pro roky 1997-1999. Svaz pěstitelů a zpracovatelů olejnin, Praha.