Managing resources and risk for 8 tonne cereal crops

Brendan Griffiths¹, Linda Bailey³, Chris Guppy¹, Nilatha Hulugalle², Craig Birchall¹

1. University of New England
2. NSW Department of Primary Industries
3. Griffiths Agriculture, Goondiwindi

Take home messages

Outline of the project

The principal focus of the project was to investigate agronomic factors that would limit the capacity of irrigated wheat to achieve high yields in Northern NSW and Southern Queensland as the majority of previous research occurred under southern conditions. This paper will broadly outline the agronomic impact of: 1) Crop establishment (methods, spacing and planting rate), 2) Nitrogen management (rate and timing) and 3) plant growth regulators on grain yield. Future papers will provide more detail on the plant physiology underlying these yield responses. Furthermore, all of the experiments conducted in this project were sown immediately following irrigated cotton.

Crop establishment

One of the key questions being raised was; “What were the appropriate methods of establishment including planting rates and row configurations for the northern environment”? Southern irrigated wheat research suggested planting rates of 80 seedlings/m² and row spacing <18cm were appropriate for the Southern irrigated cropping region to avoid lodging. However, work by Stapper 2007a, suggested slightly wider configurations (up to 25cm) was possible without yield penalty but this response may have been variety dependent.

The appropriate methods of crop establishment were also under question for the north and our initial survey showed commercial methods of establishment varied from using fixed tyne, broadacre planting equipment to precision planting equipment with a specific row crop application and even aerial sowing. Not surprisingly, anecdotal feedback from the field suggested results were extremely variable. Therefore a pilot study was conducted investigating several of the methods of establishing irrigated wheat and their effectiveness in achieving adequate and uniform plant stands.

The experiment was sown into dry soil, prepared into level 2 m beds and irrigated via flood furrow, with a seed rate of 180 seeds/m planted (Table 1). Treatments 2 and 4 represent the standard commercial sowing equipment used by wheat producers in the region. Treatment 1 was spread on top of the soil surface to replicate aerial sowing as is common practice. Emergence was 20-30% better than standard tyne or disc practices when a purpose made precision planter was used, and 300% better than broadcast seed (Table 1).

Based on the results of the experiment in Table 1, it was decided further investigations relating to the appropriate row spacing and planting rates would be conducted and that the tyne machine would be the appropriate standard.

Table 1: Mean emergence and yield, of four planting methods in the Macintyre Valley, 2008, wheat cv EGA Bellaroi.

Means followed by same letter do not significantly differ (P=0.05, LSD)

ns – not significant

Seedling emergence

Tyne sowing produced consistent emergence near 80% irrespective of the planting rate and row spacing when sown dry and then flood furrow irrigated on 2 m beds (Table 2). No yield benefit was gained through increased plant population, irrespective of row spacing (Table 2).

Table 2: Emergence trial 2011, ACRI Narrabri, (within row spacing trial) wheat cv Hyperno.

Means followed by same letter do not significantly differ (P=0.05, LSD)

Row spacing

Yield data was also collected from several of the row spacing experiments conducted in consecutive years at ACRI, at Narrabri, Northern NSW (Table 3). In both instances, 180 kg/ha of applied nitrogen was targeted, and approximately 150 plants/m² were established. Total plant available water in 2010 was 603mm, including 268mm effective rainfall, and 524mm including 140mm effective rainfall in 2011. There was no significant yield decrease at row spacings even as wide as 45 cm (4 rows across a 2 m flat bed). This contrasts with southern farming systems where wide rows are used to reduce lodging risk, but may decrease yield when greater than 18 cm (Poole 2004; 2006; Stapper 2007b).

Table 3: Row spacing experiments 2010, 2011, ACRI Narrabri, wheat cv. Hyperno.

Means followed by same letter do not significantly differ (P=0.10, LSD)
ns – not significant

Nitrogen rates and timing

Nitrogen has possibly been the most widely researched topic in the production of cereal crops worldwide. Work from the southern Australian irrigated wheat growing regions suggest that nitrogen rates of 140 kg/ha (Lacy 2007) are required to achieve maximum yields, and should be applied in split applications. Key to the utilisation of high amounts of soil applied nitrogen is minimising the risk of crop lodging which was identified in the Southern Australia irrigated wheat research as the single largest limitation in high yielding irrigated wheats. Crucial to achieving high yielding irrigated wheat is to ascertain the appropriate amount of nitrogen that may be applied in order to achieve optimum yields and design an agronomic system that minimises crop lodging risk in order to capitalise on high N rates.

In contrast to the split application recommendation in southern regions, split or delayed application of nitrogen decreased yield by 5-15% (Table 4).  The experiment was configured in 30 cm row spacing, with approximately 150/m² seedlings emerged, planted into 2m flat beds and irrigated via flood furrow. Background amounts of soil nitrate were less than 30 kg/ha in the top 90 cm of soil. All nitrogen applied in this experiment was as Green Urea^tm. Furthermore, yield increased a further 16% when applied nitrogen was doubled to 354 kg/ha N. This trend is consistent with other experiments conducted with this project and with work conducted by Hulugalle (2005) where yield responses were seen up to very high levels of applied nitrogen, in the absence of lodging. Lodging was observed in the highest applied N treatment only and would not have been yield limiting as it was <15%. Total plant available water was 524mm, including 140mm effective rainfall .These amounts of nitrogen are well in excess of the nitrogen rates anecdotally anticipated would be appropriate for the northern wheat growing regions, prior to the commencement of this project.

There are many agronomic tools that may be employed in the management of the risk of lodging when high levels of soil nitrogen are included in the growing system. It is also apparent from our research that there is a strong relationship between irrigation timing and volume, and soil nitrogen levels, in crop physiological behaviour and ultimately crop lodging. These relationships will be discussed in detail in future publications from this project.

Table 4: Nitrogen rate and timing experiment 2011 ACRI Narrabri, wheat cv Hyperno.

Means followed by same letter do not significantly differ (P=0.05, LSD)

Use of plant growth regulators

One tool that may be used to minimise crop lodging and maximise yield, particularly in high nitrogen situations, are plant growth regulators. A combination of two PGR’s increased yield by 16% when applied at Z31 (Table 5). This experiment was configured with 30 cm row spacing sown into a 2 m flat bed. Approximately 150 seedlings emerged and the site was irrigated via flood furrow. 180 kg/ha N was applied at sowing and the site had less than 30 kg/ha residual soil nitrate/ 90 cm soil.  Despite the fact that no lodging was observed in this experiment, a significant positive effect on yield was achieved using the products in this experiment when applied at the booting stage of crop growth. This trend has been consistent through several experiments conducted using these products and mixtures. 

Table 5: Comparison of plant growth regulators, timing, rate, and mixtures, ACRI Narrabri, 2011, wheat cv EGA Gregory.

Means followed by same letter do not significantly differ (P=0.05, LSD)
Mean comparisons performed only when AOV Treatment P(F) is significant at mean comparison OSL.

Conclusion

It has become apparent throughout the course of this project that there are various behavioural characteristics of irrigated wheat peculiar to the northern growing regions of Northern NSW and Southern Qld. Preliminary findings of the project showed methods of establishment used commercially in the north produced highly variable seedling emergence results. Our project has also shown that seedling emergence may be made more consistent when appropriate methods of establishment are utilised. Row spacings appeared to have minimal impacts on crop yields up to around 8 t/ha. Nitrogen rates in excess of 300 kg/ha were required to achieve yields in excess of 9 t/ha. Also showing significant promise is the usefulness of plant growth regulators in the northern irrigated wheat system in achieving crop yield increases, and further investigations in this area will need to be conducted.

References

Hulugalle N R (2005) Recovering leached N by sowing wheat after Irrigated cotton in a vertosol. Journal of Sustainable Agriculture, Vol 27(2), The Haworth Press.

Lacy J (2007) Positioning 8 tonne wheat in the farm (Grains Research and Development Corporation: Griffith).

Poole N (2004) Canopy management in cereals - Why? In 'Hi-Grain Update'. (Grains Research and Development Corporation Research Update: Griffith).

Poole N (2006) A 2005 review of canopy management trials from southern Australia - Would the same concepts work in northern NSW? '. (Grains Research and Development Corporation Research Update: Bellata).

Stapper M (2007a) Factors to achieving highest possible wheat yield. In 'Research Updates'. (Grains Research and Development Corporation: Griffith).

Stapper M (2007b) High-yielding irrigated wheat crop management. Grains Research and Development Corporation, Canberra.

Contact details

Brendan Griffiths
Ph: 0427 715 990
Email: griffb@bigpond.com

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