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

Abstract

English: Canola serves as a very favorable crop to produce oil world wide. Canola production in South Africa is mainly restricted to the Western Cape Province under winter rainfall conditions. The Protein Research Foundation propagated the production expansion to the central part of South Africa. The semi arid area (Central part of South Africa) is characterized by variable and unreliable summer rainfall. Irrigation is therefore vital for sustainable production of a winter crop like canola. The aim of this study was to establish the crop's plasticity ability, water use, water use efficiency and transpiration coefficient under a range of water application and plant density treatments combinations for the central South Africa. An experiment with a line source sprinkler irrigation system was conducted near Bloemfontein 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. These water applications were combined with the following planting densities: PD25 = 25plants m², PD50 = 50 plants m², PD75 = 75 plants m², PD100 = 100 plants m², PD125 = 125 plants m². Seeds (558 - 4653 kg ha-¹) and biomass (1983 - 6733 kg ha-¹) yields induced by the treatments proved that canola has a high plasticity. This is because over the full range of water application treatments optimized yields were realized at only one plant density though different for seed (25 plant m-² ) and biomass (75 plants m-²) yields. Compensation of 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 water application (W1) to 421 mm with 363 mm water application (W5) but was not influenced by plant density at all. Water use efficiency confirmed the optimum plant density for fodder production is 75 plants m-² and for seed production is 25-² plants m-². The water use efficiency 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 2.26 was 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 of plant density on the two components of evapotranspiration. A transpiration coefficient of 0.0045 was calculated for canola when planted for fodder at an optimum plant density of 75 plants m-² under moderate (W3) to full (W5) irrigation.

Afrikaans: Kanola word wêreldwyd gereken as een van die mees belowendste gewasse vir oliesaadproduksie. Die gewas word hoofsaaklik in die Wes-Kaap Provinsie verbou en die Proteiennavorsingstigting is van mening dat dit moontlik ook in die sentrale dele van Suid-Afrika verbou kan word. Die klimaat van die sentrale deel word as halfdroog beskou en word gekarakteriseer deur wisselvallige en onbetroubare somerreënval en baie lae winterreën wat besproeiing noodsaak vir die verbouing van wintergewasse soos kanola. Die doel van die studie was om die plastisiteitsvermoë, waterverbruik, waterverbruiksdoeltreffenheid transpirasie koëffisiënt van kanola in die sentrale deel van plantdigheidsbehandelingskombinasies te ondersoek. 'n Veldeksperiment met kanola as toetsgewas is onder 'n lynbronsprinkelaarbesproeiingstelsel naby Bloemfontein in die Vrystaat uitgevoer. Die waterbehandelings, uitsluitende die 57 mm reën, het bestaan uit: Wl = 118 mm, W2 = 176 mm, W3 = 238 mm, W4 = 274 mm en W5 = 363 mm. Hierdie water behandelings is met die volgende plantdigthede gekombineer: PD25 = 25 plante m², PD50 = 50 plante m², PD75 = 75 plante m², PDIOO = 100 plante m-², PD125 = 125 plante m-². Saad- (558 - 4653 kg ha-¹) en biomassaopbrengste (1983 - 6733 kg ha¹) wat deur die behandelings geskep is, het bewys dat kanola oor 'n hoë plastisiteitvermoë beskik. 'n Verdere bewys daarvan lS die feit dat oor die volle reeks van watertoedieningsbehandelings optimum opbrengste by slegs een plantestand verkry is, alhoewel dit vir saad (25 plante m-²) en biomassa (75 plante m") verskil het. Kompensasie in opbrengste by die lae plantdigthede is veroorsaak deur meer sytakke wat aanleiding gegee het tot meer peule per plant. Totale evapotranspirasie (ET) het linieër (r² = 0.97) van 245 mm met 118 mm watertoediening (Wl) na 421 mm met 363 mm watertoediening (W5) toegeneem. Plantdigthede het egter me die totale ET beïnvloed me. Die waterverbruiksdoeltreffendheid bevestig dat die optimum plantdigtheid vir voerproduksie 75 plante m-² en vir saadproduksie 25 plante m-² is. Die waterverbruiksdoeltreffendheid by die twee plantdigthede was onderskeidelik 12.9 kg ha-¹ mm-¹ en 9.6 kg ha¹ mm¹. Die β koëffisiënt van kanola was konstant (2.26) oor die vol tot matige beperkende besproeiingsbehandelings (W5-W3), maar nie vir die lae besproeiingpeile nie (W2 - Wl). Die β koëffisiënt is gebruik om die evapotranspirasie van W3 - W5 behandelings in evaporasie (56%) en transpirasie (44%) te skei. Vanweë die veranderlikheid van die β koëffisiënt by die lae besproeiingspeile was dit nie moontlik om die skeiding in evapotranspirasie vir die behandelings te bereken nie. 'n Transpirasiekoëffisiënt van 0.0045 is vir kanola onder voerproduksie by 'n optimum plantdigtheid van 75 plante m-². by matige (W3) tot volbesproeiingspeile (W5) verkry.