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Quantifying safflower development using environmental parameters

Nick Wachsmann1, Rob Norton1 and David Jochinke2

1 Joint Centre for Crop Innovation, The University of Melbourne, Horsham, Vic 3401. www.jcci.unimelb.edu.au
Email nwachsma@bigpond.com, rnorton@unimelb.edu.au
2 A.V. Jochinke & Co, RMB 4621, Horsham, Vic 3401. www.jochinke.com.au Email david@jochinke.com.au

Abstract

Using data from experiments sown between July and October in 2000 and 2001 in the Victorian Wimmera
(n = 18), thermal and photothermal time accumulation and linear regression with temperature and daylength were tested as predictors of development for the safflower (Carthamus tinctorius) cultivar Sironaria. In paired experiments sown in nearby paddocks, safflower flowered about one week earlier where conditions limited water use between sowing and flowering to <350 mm. A photothermal requirement of 6806°Cd6h6 on drier sites and 6191°Cd5h8 on wetter sites predicted flowering dates with a RMSD of 1.5 d in the experimental data set, 4.8 d in an independent data set (n=6) and 2.7 d when both data sets were combined.

Key Words

Phenology, modelling, water availability

Introduction

Safflower (Carthamus tinctorius) is an oilseed crop recognised for having deep roots, a long growing season and a higher water requirement than other crops usually grown in the wheat belt of southern Australia. Safflower can be used to de-water wet soil profiles and manage salinity, but yields are low under drier conditions. Understanding crop development can help explain adaptation to different environments and sowing times. Development in safflower is generally considered to be controlled by temperature and daylength, although the relative importance of these parameters is thought to vary between cultivars.

Methods

An experimental data set (n=18) on the safflower cultivar Sironaria sown at 17 kg/ha was compiled from a series of agronomic experiments in the Victorian Wimmera. Sowing times ranged from mid-winter to mid-spring in both 2000 and 2001. Flowering was recorded when 50% of terminal capitula had opened. Soil water contents were estimated gravimetrically to 2 m depth and an infrared thermometer was used to measure canopy temperatures. Climate data were obtained from on-site data loggers or nearby Bureau of Meteorology (BOM) stations. The utility of temperature and daylength to predict safflower development was tested using thermal and photothermal time accumulation, and linear regression with mean daily temperature (Tm) and daylength (Tm + Lm) as predictors (Summerfield and Roberts 1987). Base (threshold) units for the thermal (Tb) and photothermal time (TbLb) models were selected on the lowest CV% between observations when durations were calculated above a base unit range of 0 to 12°C and 0 to 12 h. The subscript to Tb or Lb refers to the base temperature (Tb) or daylength (Lb) used in the models. Predicted flowering dates are the mean thermal or photothermal duration of all experimental observations. For the regression models, development rate was expressed as a reciprocal of the calendar duration of a phenophase. All models were subsequently tested with an independent data set (n=6), including a 16.5 h daylength treatment (Stuchbery and Drum 1988; Stuchbery 1999; S Knights, pers. comm.; M McCallum, pers. comm.). Climate data for these observations were provided by these researchers or the BOM. The capacity of each model to predict safflower development was compared using the root mean square deviation (RMSD) between the observed and predicted duration between sowing and flowering.

Results and Discussion

Depending on the experimental site and sowing time, safflower commenced flowering between early December and mid-January. Mean daily temperatures and daylengths between sowing and flowering ranged from 12.7 to 18.8°C and 12.2 to 14.1 h, respectively. In identically designed and managed experiments in nearby paddocks, safflower flowered 8 d earlier where conditions limited the mean total water use (TWU) between sowing and flowering to 340 mm, compared to 446 mm on the wetter site. Given that stem elongation commenced at a similar time at both sites, this result indicates that safflower development can be affected by water availability. Average daytime canopy temperatures around the time of flowering were 6°C warmer at the drier site, suggesting reduced transpiration and the more rapid accumulation of thermal time.

These data were subsequently partitioned according to whether TWU between sowing and flowering exceeded 350 mm. When water availability was taken into account, all four models predicted the duration between sowing and flowering in the experimental data set with a RMSD of <3.7 d (Table 1). Photothermal time accumulation produced the best results with a requirement of 6806°Cd6h6 on drier sites and 6191°Cd5h8 on wetter sites predicting flowering dates with a RMSD of 1.5 d in the experimental data set, 4.8 d in an independent data set (n=6) and 2.7 d when both data sets were combined (Figure 1). Base units for the thermal and photothermal time models were inconsistent on sites with different amounts of available water. This may be due to confounding as mean daily temperatures are highly correlated with daylength in southern Australia. Regression with mean daily temperature performed poorly in the independent data set, largely because it overestimated the flowering date of a 16.5 h daylength treatment by 15 d. Daylength therefore needs to be considered when modelling the development of the safflower cultivar Sironaria.

Table 1. Thermal, photothermal and regression values used to predict the flowering date of safflower and the RMSD between observed and predicted flowering dates when these values were applied to the experimental, independent and all data within wetter and drier sites. DR = 1/days between sowing and flowering.

Model

Water use

Thermal, photothermal and regression values obtained from the experimental data set

Exp. data
RMSD

Ind. data
RMSD

All data
RMSD

Thermal time

<350 mm

680 °Cd8

2.2 d

4.5 d

3.0 d

 

>350mm

612 °Cd9

Photothermal time

<350 mm

6806 °Cd6h6

1.5 d

4.8 d

2.7 d

 

>350mm

6191 °C d5h8

Regression (Tm)

<350 mm

DR=-0.00989+0.00134Tm(r2=0.99)

3.7 d

8.5 d

5.3 d

 

>350mm

DR=-0.01370+0.00157Tm(r2=0.97)

Regression (Tm+Lm)

<350 mm

DR=-0.01162+0.00128Tm+0.00019Lm (r2=0.99)

2.5 d

5.0 d

3.6 d

 

>350mm

DR=-0.01787+0.00114Tm+0.00077Lm (r2=0.98)

Figure 1. Relationship between the observed and predicted duration between sowing and flowering for safflower when calculated using a photothermal duration of 6806°Cd6h6 on drier sites and 6191°Cd6h6 on wetter sites.

Conclusion

Temperature and daylength can be used to predict safflower development, but differences in water availability need to be considered. Of the four models tested, photothermal time accumulation was superior for the sowing times and climate encompassed by these observations. Data from other latitudes or controlled environment studies are needed to explore interactions between daylength and temperature so that the model can be refined for other situations.

References

Stuchbery, J (1989). Safflower variety comparison – Dooen and St Helen Plains. In, Summary of Research Results 1989. Dooen Experimental Centre, Department of Agriculture, Victoria, pp. 147-151.

Stuchbery, J and Drum, M (1988). Safflower variety comparison – Dooen and Green Lake. In, Summary of Research Results 1988. Dooen Experimental Centre, Department of Agriculture, Victoria, pp. 115-117.

Summerfield RJ and Roberts EH (1987). Effects of illuminance on flowering in long- and short-day grain legumes: a reappraisal and unifying model. In Manipulation of Flowering. Ed JG Atherton. Butterworths, London.

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