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Effects of plant density on the yield of field pea and faba bean varieties across southern and central NSW—preliminary findings

EL Armstrong1, PW Matthews2, NA Fettell3, DJ Holding4, LG Gaynor1, CJ Lisle1 and BR Cullis1

1NSW Department of Primary Industries, Agricultural Research Institute, Wagga Wagga, NSW 2650
2NSW Department of Primary Industries, Agricultural Research and Advisory Station, Temora, NSW 2666
3NSW Department of Primary Industries, Agricultural Research and Advisory Station, Condobolin, NSW 2877
4AnDi Communications, previously NSW Department of Primary Industries, Agricultural Research Institute, Wagga Wagga, NSW 2650

Abstract

Plant density is a major determinant of crop yield, and is particularly important in large-seeded species such as field pea and faba bean, where the logistics and cost of sowing large quantities of seed become a significant issue compared to cereals. This paper presents preliminary findings of investigations into plant density of field pea and faba bean across southern NSW from 1996 to 2007. Trials were conducted annually and conditions varied from highly favourable through to severe drought. The initial analysis was based on 37 field pea and 25 faba bean trials that included commercial varieties and advanced breeding lines. Up to six target densities were sown in each trial. Established rather than targeted plant density was used assess yield response and this varied from 10 to 80 plants/m2.

The preliminary analysis looked at the overall data set for each species and highlighted large variability in yield response to plant density across sites and seasons. However, faba bean and field pea showed different average yield responses to plant density. Faba bean was more responsive and average yield increased up to the highest density, whereas yields of field pea plateaued above 40-45 plants/m2. These differences were observed in high and low yielding environments. Further analysis is planned to determine optimum plant density for each species. This will involve grouping the data (eg by plant type, site yield, flowering time, sowing time, seasonal rainfall) to better predict yield response to changing crop plant density.

Key words

Seed rate, plant population, grain legumes

Introduction

Plant density is a major determinant of field pea and faba bean yield (Adisarwanto and Knight 1997; Carter 1996; Marcellos and Constable 1986; Matthews et al. 2001, McMurray 2004, McRae et al. 2008). It can affect early ground cover (Jettner et al. 1998b), competitive ability with weeds (Lemerle et al. 2004, Lemerle et al. 2006), soil surface evaporation, light interception (Jettner et al. 1998b), lodging and the development of an optimum number of fruiting sites in a crop canopy to maximise grain yield (Jettner et al 1998a and b). Optimum plant density will vary depending on crop or variety (differences in vigour, height and branching), time of sowing and the nature of the season (Anderson et al. 2004).

Field pea plants vary in leaf type (conventional and semi-leafless) and plant architecture (ranging from short erect to tall scrambling), and it is likely these plant types respond differently to plant density. Faba bean is a relatively new crop to southern and central NSW showing enormous potential, however its large seed-size means crops require much higher seeding rates compared to wheat (140 kg/ha and 60 kg/ha respectively). The need for high seeding rates and the large seed size is also an issue with seeding equipment designed primarily for sowing cereals. It is therefore crucial to be able to confidently recommend optimum plant density for new varieties to avoid the risk of growers sowing at below optimum plant populations, resulting in poorly performing crops. A series of trials, similar to the field peas, was conducted for faba bean across southern and central NSW.

Method

Field pea

Between 1996 and 2007 a series of 37 field pea trials, each including up to six key commercial or advanced breeding lines was sown. The experiments use a range of sowing rates to produce up to six targeted plant populations, which ranged from 10 to 80 plants/m2. The 2006 trials failed due to severe drought. The varieties were changed as new lines were released and old varieties outclassed. The varieties were chosen to represent the key field pea types—tall scrambling; mid-height, erect semi-leafless; and short, erect, semi-leafless.

Faba bean

A series of 25 faba bean trials, each including up to six key commercial or advanced breeding lines sown at up to six targeted plant populations were conducted between 1996 and 2007. The varieties were changed as new varieties were released and old ones were outclassed. The varieties were chosen to represent three seed-size classes—small; medium; and large.

Trial location

The trials were conducted across a range of locations and seasons to represent a range of environments from low rainfall, short season to high rainfall, long season. Sites over the 12 seasons included the dryland sites of Gilgandra, Condobolin, Parkes, Yenda, Lockhart, Temora, Ardlethan, Thuddungra, and Wagga Wagga, and the irrigated sites of Coleambally and Griffith.

Analysis

Raw data only is used in this paper to enable presentation of preliminary findings before a more detailed analysis using ASREML (a mixed model analysis program – see Gilmour et al. 2002, Verbyla et al. 1999) is completed. Data is expressed as deviations from the site mean yield to enable realistic comparisons between site-years that vary significantly in yield. For further clarity, trials are grouped into low (<1.5 t/ha), medium (1.5-2.5 t/ha) and high (>2.5 t/ha) yielding sites. Loess smoothing curves are used to depict lines that best fit the response of yield to increasing plant density for each crop. Plant densities were measured at establishment for all trials.

Results

Preliminary investigation of the complete set of data for both field pea and faba bean is presented below (Figure 1) and highlights the enormous variability in the relationship between yield and plant density in pulse crops. Not surprising, deviations from the mean are much lower at low yielding sites (<1.5 t/ha), and this is most evident in field pea.

The raw data suggests faba bean (Figure 1a) is more responsive than field pea to increasing plant populations over all yield levels and continued to respond over the full range of plant densities used. The largest increase in yield occurred up to about 30 plants/m2, after which the yield response to increasing plant populations declined The response to plant density tended to be less in the low yielding environments (< 1.5 t/ha) compared to the higher yielding environments. In field pea, yield tended to increase up to about 40-45 plants/m2 but unlike faba bean there is a clear yield plateau above this plant population (Figure 1b). A more detailed statistical analysis is currently underway, including:

  • Individual variety yield responses
  • Grouping data on site mean yield to identify similar location responses over a range of yield levels.
  • Grouping of similar plant types (eg tall vs short)
  • Grouping varieties based on flowering time and maturity.
  • Grouping trials by geographical or environmental zones
  • Grouping sites on sowing time (early, mid or late compared to recommended sowing time)

Discussion

The objective is to determine the economic optimum target plant density for each crop species and new variety as it is released, and to identify and group varieties with similar responses. This data suggests there is a wider range of densities that will result in optimum yield of both field pea and faba bean than previously thought. Within this ‘safe’ range of targeted densities, particularly at the lower end, other management practices become far more important and can have a bigger impact on the outcome:

  • soil type, and its suitability to that crop;
  • seed bed conditions and soil moisture;
  • correct adjustment of seeding equipment, including sowing depth and soil coverage;
  • seed fungicide dressings;
  • sowing date;
  • presence or absence of weeds; and
  • seasonal rainfall.

Figure 1. Yield deviation from site mean of low (<1.5 t/ha), medium (1.5-2.5 t/ha) and high (>2.5 t/ha) yielding sites for a) faba beans and b) field peas sown at a range of plant densities at numerous sites across southern and central NSW from 1996 to 2007.

Acknowledgements

The authors would like to acknowledge the team of NSW Department of Primary Industries staff responsible for managing this series of trials over the 11 seasons: Peter Shephard, Vince Van Der Rijt and Ian Menz, Wagga Wagga, Richard McCallum and Jim Presley, Condobolin and the Crop Evaluation Unit staff based at Wagga Wagga, Temora, Young and Condobolin.

References

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Anderson WK, Sharma DL, Shackley BJ and D’Antuono MF (2004) Rainfall, sowing time, soil type and cultivar influence optimum plant population for wheat in Western Australia. Australian Journal of Agricultural Research 55, 921-930.

Carter JM (1996). Faba beans need higher seeding rates in high rainfall areas. Proceedings of the 8th Australian Agronomy Conference, Toowoomba. Australian Society of Agronomy.

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Jettner R, Loss SP, Siddique KHM and Martin, LD (1998b). Responses of faba bean (Vicia faba L.) to sowing rate in south-western Australia. II. Canopy development, radiation absorption and dry matter partitioning. Australian Journal of Agricultural Research 49, 999-1008.

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Marcellos H and Constable GA (1986). Effects of plant density and sowing date on grain yield of faba beans (Vicia faba L.) in northern New South Wales. Australian Journal of Experimental Agriculture 26, 493-496.

Matthews PW, Carpenter DJ, Smith A and Fettell N (2001). Faba bean seeding rates for central and southern NSW. Proceedings of the 10th Australian Agronomy Conference, Hobart. Australian Society of Agronomy.

McMurray L (2004). Plant density impacts Kaspa field pea’s grain yield. Australian Farm Journal Feb 2004. pp 45-46.

McRae FJ, McCaffery DW and Matthews PW (2008). 2008 Winter Crop Variety Sowing Guide. NSW Department of Primary Industries, pp 74-85.

Gilmour AR, Cullis BR, Welham SJ and Thompson R (2002). ASReml Reference Manual 2nd edition, Release 1.0. NSW Agriculture Biometrical Bulletin 3. Orange, NSW 2800, Australia: NSW Agriculture.

Verbyla AP, Cullis BR, Kenward MG and Welham SJ (1999). The analysis of designed experiments and longitudinal data using smoothing splines (with discussion). Applied Statistics 48, 269–312.

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