Effect of water application and plant density on canola (Brassica napus L.) in the Free State

[摘要] English: Canola serves as a very favorable crop to produce oil world wide. Canola production inSouth Africa is mainly restricted to the Western Cape Province under winter rainfallconditions. The Protein Research Foundation propagated the production expansion to thecentral part of South Africa. The semi arid area (Central part of South Africa) ischaracterized by variable and unreliable summer rainfall. Irrigation is therefore vital forsustainable production of a winter crop like canola. The aim of this study was to establishthe crop's plasticity ability, water use, water use efficiency and transpiration coefficientunder a range of water application and plant density treatments combinations for thecentral South Africa.An experiment with a line source sprinkler irrigation system was conducted nearBloemfontein in the Free State Province. Water applications, excluding 57 mm rain were:WI = 118 mm, W2 = 176 mm, W3 = 238 mm, W4 = 274 mm and W5 = 363 mm. Thesewater applications were combined with the following planting densities: PD25 = 25plantsm², PD50 = 50 plants m², PD75 = 75 plants m², PD100 = 100 plants m², PD125 = 125plants m².Seeds (558 - 4653 kg ha-¹) and biomass (1983 - 6733 kg ha-¹) yields induced by thetreatments proved that canola has a high plasticity. This is because over the full range ofwater application treatments optimized yields were realized at only one plant densitythough different for seed (25 plant m-²) and biomass (75 plants m-²) yields. Compensationof yields at lower plant densities resulted from branches and hence pods per plant.Total evapotranspiration increased linear (r² = 0.97) from 245 mm with 118 mm waterapplication (W1) to 421 mm with 363 mm water application (W5) but was not influencedby plant density at all. Water use efficiency confirmed the optimum plant density forfodder production is 75 plants m-²and for seed production is 25-² plants m-². The water useefficiency at these two plant densities were 12.9 kg ha-¹ mm-¹ and 9.6 kg ha-¹ mm-¹,respectively. The β coefficient of canola was constant (2.26) for the full to moderate irrigation regimes(W5 - W3), but not for the low irrigation regimes (W2 - Wl). The β coefficient of 2.26was used to separate the evapotranspiration of the W3 - W5 treatments into evaporation(56%) and transpiration (44%). This method was not suitable to establish the influence ofplant density on the two components of evapotranspiration. A transpiration coefficient of0.0045 was calculated for canola when planted for fodder at an optimum plant density of75 plants m-² under moderate (W3) to full (W5) irrigation.

[发布机构] University of the Free State