The relationship between root biomass and productivity of spring oilseed rape (Brassica napus L.) as influenced by crop density and fertilization.

A field experiment was conducted from 2008 to 2010 at the Experimental Station of the Lithuanian University of Agriculture (currently – Aleksandras Stulginskis University) on a Calc(ar)i-Endohypogleyic Luvisol (LVg-n-wcc). The objective of this study was to establish the relationship between root biomass and productivity of spring oilseed rape (Brassica napus L.) as influenced by crop density and fertilization level. Treatments of the experiment: factor A – fertilization: 1) without fertilizers, 2) with fertilizers (N 134 P 64 K 94 ); factor B – crop density: 1) 2 kg ha -1 (50.1–100 plants m -2 ), 2) 4 kg ha -1 (100.1–150 plants m -2 ), 3) 6 kg ha -1 (150.1–200 plants m -2 ), 4) 8 kg ha -1 (200.1– 250 plants m -2 ), 5) 10 kg ha -1 (250.1–300 plants m -2 ), 6) 12 kg ha -1 (300.1–350 plants m -2 ), 7) 14 kg ha -1 (350.1–400 plants m -2 ), 8) 16 kg ha -1 (400.1–450 plants m -2 ). It was established that without fertilizers, the highest root dry biomass (2.48 t ha -1 ) of spring oilseed rape at the 0–10 cm soil layer was formed at a plant density of 150.1–200 plants m -2 , while in the crop with fertilizers at a plant density of 100.1–150 plants m -2 (2.64 t ha -1 ). Plant root biomass in the 0–10 cm soil layer at a very high crop density (400–450 plants m -2 ) with and without fertilizers was significantly (P < 0.05) lower (by 35.0% to 37.9% and by 32.2% to 40.9%, respectively) as compared with those densities, where root biomass was the highest. In the treatment without fertilizers parabolic statistically significant (P < 0.05) relationships were established between rape crop density and root dry biomass at the 0–10 and 10–20 cm soil layers. Mineral fertilization, compared with no fertilization, significantly (P < 0.05) increased (by 34.7% to 44.6%) spring rape root biomass at the 0–10 cm soil layer and did not have any significant effect on root biomass at the 10–20 cm soil layer. Parabolic and statistically significant (P < 0.01) relationships exist between the above-ground dry biomass of oilseed rape and plant density. In the crop without fertilizers, the highest spring rape seed yield (2.31–2.38 t ha -1 ) was obtained at a crop density of 250.1–350 plants m -2 and in the crop with fertilizers – at a crop density of 100.1–200 plants m -2 (3.28–3.32 t ha -1 ). A trend of spring oilseed yield decrease with increasing crop density at investigated levels of fertilization was established. Mineral fertilization, compared with no fertilization, at all spring rape plant densities significantly (P < 0.05) (from 30.3% to 81.4%) increased rape seed yield. In the crop without fertilizers, spring rape seed yield significantly depended on the crop density (r 2 = 0.90, P < 0.05) and the above-ground dry biomass of rape at the flowering stage (r 2 = 0.67, P < 0.05). In the crop with fertilizers, rape seed yield was significantly influenced by the crop density (r 2 = 0.66, P < 0.05) and dry biomass of rape roots in the 0–10 cm soil layer at the flowering stage (r 2 = 0.86, P < 0.01).

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