ENVIRONMENTAL IMPACT ON CANOLA YIELD AND OIL

Graham Walton¹, Ping Si² and Bill Bowden¹

1. Agriculture Western Australia, Locked Bag 4, Bentley WA 6893

e-mails, gwalton@agric.wa.gov.au, bbowden@agric.wa.gov.au

2. Faculty of Agriculture, University of Western Australia, Nedlands WA 6907

ABSTRACT

The production of canola (Bassica napus) in Western Australia has grown rapidly, with 560,000 tonnes produced in 1998, at an average of 1.2 t/ha and 42% oil. A significant portion of this total had less than 40% oil content. The crop is winter sown with the post-anthesis ripening phase coinciding with rapidly rising atmospheric temperature and declining rainfall, environmental conditions affecting yield and oil content. To ensure that the industry is sustainable, the growers need a decision-aid to choose the most suitable variety and sowing date in any geographical region for producing a canola crop with a minimum of 42% oil.

A series of field experiments were conducted at 5 locations in Western Australia in 1997 to examine the effects of sowing date, and variety on canola yield and oil. Both variety and location had significant effects on yield and oil. Post-anthesis duration was positively correlated with seed yield and oil content.

The post-anthesis duration was significantly correlated with the post-anthesis rainfall (r = 80 **) and was negatively correlated with the mean daily temperature during seed development (r = - 0.62**). For the environmental conditions encountered in these field trials, post-anthesis rainfall accounted for the highest variation in yield and oil.

It is possible to use the correlation between oil content, post-anthesis rainfall and post antheis duration as a predictive tool for the canola industry to determine the best sowing date in Western Australia for crops to achieve a specified level of oil.

KEYWORDS

Varieties, location, anthesis, rainfall, temperature.

INTRODUCTION

The canola industry in Western Australia produced 560,000 tonnes in 1998, of which approximately 10% had seed with less than 40% oil. In previous years up to 28% of production has been of a similar low level of oil. Low oil appears to be a result of environmental influence such as drought. We need to understand the factors influencing the level of oil in canola seed and provide guidelines to growers enabling them tomaximise oil content.

There are four factors with major impact on the level of oil found in canola crops in W.A., they are:-

varieties, soil moisture and temperature, during the crops’ reproductive stage. These factors can be controlled to a large extent by selecting the appropriate variety and time of sowing in any region.

The new canola varieties have higher levels of oil and protein than the older varieties, the triazine tolerant canola varieties have less oil than the susceptible varieties. Inducing drought at different growth stages of canola, has shown that stress after flowering severely reduced yield and oil content. Comparing well watered plants with droughted plants, Jensen et al (1996) found oil content fell from 43.2% to 39.9%, while Mailer and Cornish (1987) found oil content fell from 36.9% to 31.4%. However, unless irrigation is an option, the grower has little control over the onset of drought except to sow early in an attempt to avoid moisture stress. High temperatures during the post-anthesis seed development in canola reduces oil content. The relationship between percent oil and the daily mean temperature averaged over this period vary from 1.2% oil loss for each 1 ⁰ C rise (Canvin 1965) to 1.5% oil per 1 ⁰ C (Ryan 1979; Hocking and Stapper 1993).

Field experiments at five locations were conducted in 1997 to examine the effects of time of sowing and variety on canola crop phenology, seed yield and oil content.

MATERIAL AND METHODS

The field experiments had five varieties sown at four different times at Mullewa, Wongan Hills, Merredin, Newdegate and Mount Barker. The varieties were Monty, Hyola 42, Karoo, Oscar and Drum. The cultivars were sown at 6 kg seed per hectare, with adequate fertilizer and management for weed and pest control. Each treatment had three replications. The dates of flowering, when 50% of the plants in the plot had first flower and dates of harvest were recorded. Rainfall and temperature was recorded at meteorological weather stations near the sites. The duration of plant growth from seeding to flowering (anthesis) and from flowering to harvest were calculated. The total rainfall that fell and the calculated daily mean temperature in the post-anthesis period were calculated. The rainfall and daily mean temperature for each month is given in Table 1. The yield was recorded at harvest and seed analysed for oil with NMR equipment. The oil is equated to seed with 8.5% moisture.

Table 1. The rainfall (mm) recorded and the calculated daily mean temperature (^o C) for each month at the five locations in Western Australia, 1997

	Mullewa		Wongan Hills		Merredin		Newdegate		Mt Barker
	Rainfall	Temp.	Rainfall	Temp.	Rainfall	Temp.	Rainfall	Temp.	Rainfall	Temp.
Jan	0.8	29		28	0.0		0.2	24	9.8	21
Feb	26.2	28	36.8	28	44.2	26	24.4	25	40.8	17
Mar	0.0	24	1.6	23	4.4	22	12.2	20	21.5	17
Apr	84.8	22	19.4	19	28.6	20	20.6	16	18.3	17
May	21.4	16	33.4	15	36.0	14	30.4	13	51.2	13
June	26.6	14	22.4	13	24.0	13	28.4	11	55.2	11
July	59.8	12	51.2	10	47.2	10	52.6	8	74.2	10
August	52.8	12	67.2	11	50.8	11	24.4	9	89.0	9
Sept	25.8	14	45.0	14	31.8	13	53.0	11	68.3	11
Oct	13.2	17	18.2	18	9.8	17	29.0	14	30.2	13
Nov	0.0	21	11.8	20	8.6	19	9.4	16	18.8	11
Dec	0.0	26	0.4	27	0.4	24	2.2	21	8.0	19

Total	311.4		307.4		285.8		286.8		485.1

RESULTS

Effects of location and variety

The geographic location had a significant effect on both yield and oil (tables 2 and 3). Mount Barker had the highest yield (1.74 t/ha) and oil (44.7%). Merredin had the lowest yield (0.59 t/ha) and oil (39.1%). Varieties had a significant effect on yield and oil (table 2), with the early maturing Monty and Hyola 42 varieties outperforming the mid-maturing Oscar, Karoo and Drum. The early maturing varieties had longer duration between flowering and maturity (table 3).

Table 2. Seed yield (kg/ha) and oil content (%) at 8.5% moisture of varietal means over a number of sowing dates at locations in Western Australia.

Location

Monty

Hyola 42

Oscar

Drum

Karoo

Grouse

Pinnacle

Dunkeld

Mean

Mullewa

Yield

1620

1501

1016

804

1220

1198

Oil

43.5

42.0

40.8

38.3

39.8

40.9

Wongan Hills

Yield

1408

1312

904

603

985

1015

Oil

41.4

40.3

39.1

37.6

38.8

39.4

Merredin

Yield

759

780

527

361

574

603

Oil

41.8

40.6

39.2

37.0

37.4

39.2

Newdegate

Yield

1468

1723

1568

1200

1354

1430

Oil

40.7

41.1

39.5

37.1

37.4

39.1

Mt Barker

Yield

1881

1836

1420

2038

1430

1849

1742

Oil

45.0

43.9

42.9

46.2

43.8

46.4

44.7

Mean

Yield

1314

1440

1170

742

1111

2038

1430

1849

Oil

41.8

40.5

37.5

39.3

46.2

43.8

46.4

Table 3. The duration between flowering and maturity (days) of varietal means over locations (excluding Mt Barker) in four times of sowing in Western Australia.

Variety	Sowing time 1	Sowing time 2	Sowing time 3	Sowing time 4
Monty	83	79	68	63
Hyola 42	82	72	62	54
Oscar	73	68	62	58
Drum	73	70	62	58
Karoo	70	70	61	60

Effects of early sowing

There were significant differences in the effect time of sowing had on yield and oil. Early sowing always gave high yield and oil, regardless of the location or variety (Table 4). This effect was more dramatic in low, than in high rainfall locations. A two week earlier sowing between early and mid May at Mullewa increased yield by 110 kg/ha and oil content by 2.2%. At Mount barker, a three week earlier sowing in May increased oil content by 1.6%. The reduction in post anthesis duration with later sowing times was the same for each variety. The non triazine tolerant (TT) varieties outperformed the TT varieties Karoo, Drum and Pinnacle. The order of varieties for oil content does not change from location to location.

Table 4. Yield (kg/ha) and oil content (%) for the times of sowing over the means of locations and varieties.

	Sowing time 1	Sowing time 2	Sowing time 3	Sowing time 4
Yield	1578	1520	1216	652
Oil	42.9	41.0	40.2	39.2

Effect of plant development

Both yield and oil content correlated with the post-anthesis duration of plant growth (r = 0.53, 0.65 respectively). There was no correlation with pre-anthesis duration (r = 0.13).

Effect of environment

Both yield and oil content correlated with post-anthesis rainfall (figures 1 and 2) and was negatively correlated with post-anthesis temperature (figures 3 and 4). Higher rainfall and cooler temperatures during seed development gave higher yield and oil content. Oil content increased by an average over all varieties and locations 0.86% for each 1 ^o C fall in daily mean temperature and by 0.06% for each 1 mm rain during seed development. Post-anthesis duration was significantly correlated with post-anthesis rainfall (r = 0.80**) and was negatively correlated with daily mean temperature during seed development (r = 0.62**).

Figures 1 to 4. Correlations of yield and oil content with post-anthesis rainfall and post-anthesis temperature of a number of varieties grown at 5 locations in Western Australia.

CONCLUSIONS

The significant effects of location, variety and time of sowing on yield and oil content can be explained through the significant correlation with post-anthesis plant growth duration. There was a trend for yield and oil to increase in locations having higher rainfall and cooler temperatures after flowering.. Mount Barker gave the highest yields and oil, followed by Newdegate (yield) and Mullewa (oil content). Merredin produced the least yield and oil. The early maturity varieties gave the highest yields and oil. The earliest sowings always outperformed the later sowings at all locations.

Early sowing, early flowering and locations with long growing season, all provide extended duration of plant development after flowering. For early sowing and maturity, this post-anthesis duration increases with early flowering. In Western Australia, the growing season finishes by November/December with a rapid fall in rainfall and increase in daily mean temperature. The advance in flowering date allows seed development to occur in higher rainfall and cool temperatures, both factors correlated with yield and oil content.

It is postulated that a simple model for estimating oil content and yield can be developed using the strong correlations found between oil content (or yield) and post-anthesis rainfall. Utilizing the meteorological records at various regions/locations to calculate the post-anthesis duration that corresponds to the necessary rainfall, then extrapolate the required date of sowing from phenological development for the variety.

REFERENCES

Canvin, D.T., (1965). The effect of temperature on the oil content and fatty acid composition of the oils from several oil seed crops. Canadian Journal. of Botany. 43, 62-69.

Hocking, Peter and Stapper, Maarten, (1993). Effects of sowing time and nitrogen fertilizer rate on growth, yield and nitrogen accumulation of canola, mustard and wheat. Proceedings 9^th Australian Research Assembly on Brassicas, Wagga Wagga., New South Wales, 1993, 33-44.

Jensen, C.R., Mogensen, V. O., Mortensen, G., Fieldsend, J.K., Milford, G.F.I., Andersen, M.N. and Thage. J.H., (1996). Seed glucosinolate, oil and protein contents of field grown rape (Brassica napus) affected by soil drying and evaporative demand. Field Crop Research. 47, 93-105.

Mailer, R.J. and Cornish, P.S. (1987). Effects of water stress on glucosinolate and oil concentrations in the seed of rape (Brassica napus L.) and turnip rape (B. rapa L. var. silvestris [Lam] Briggs). Australian. Journal Experimental Agriculture 27, 707-11.

Ryan, S.A., (1979). Genetic and environmental variation in the protein content of rapeseed meal. Thesis for Doctor of Philosophy, University of W.A.