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Effects Of Grazing On Wheat Grain Yield And Quality ...

Effects of grazing on wheat grain yield and quality in Western Australia

Shahajahan Miyan and Samantha Clune

Centre for Cropping Systems, Department of Agriculture and Food , Northam, WA 6401.Email: smiyan@agric.wa.gov.au

Abstract

A field trial was conducted at Southern Brook, Western Australia in 2007 comparing a long season wheat (EGA Wedgetail) with a spring wheat cultivar (Yitpi) on a clay loam soil with pH 4.7 (CaCl₂) following three years of pasture. The main aim of the trial was to compare the effect of grazing pressure (stocking rate) on the grain yield and quality of the two wheat cultivars after grazing. Plots were ripped after summer rain and sown at 110 kg/ha on the 17^th of May, 2007. The grazing pressure treatments were ungrazed, low pressure (20 DSE/ha) and high pressure (40 DSE/ha) in a randomised block design. Yitpi consistently produced more biomass than the EGA Wedgetail under each grazing regime. Food on offer (FOO) was maintained under the low grazing regime but uneven grazing resulted in variation in plant maturity for grain production. Sheep condition score improved over the grazing period. By the end of the grazing period there was a significant difference in condition score and sheep live weight between the high and low grazing pressures. There was a significant decrease in grain yield due to high grazing pressure for both wheat cultivars.

Key Words

winter wheat, dual purpose wheat, stocking rate, grazing pressure, grazing wheat

Introduction

The autumn/winter feed gap is a common problem faced by farmers in mixed farming systems (Anon. 2005). Dry matter is generally limited after the break of season when pasture plants regenerate after a dry summer through to winter when cold temperatures restrict plant growth. Supplementary feeding is often required to make up for this period of low animal production (Anon. 2005).

Dual purpose premium wheats (e.g. EGA Wedgetail and Wylah) are winter type wheats with APW grain quality in WA which can be used for grazing in late autumn and early winter, as well as for producing premium grade grain at harvest (Amjad et al. 2006). The dual purpose wheats have the potential to benefit both livestock and crop production through:

• spreading the sowing window and possibly climatic impacts (e.g. frost, drought, waterlogging);

• providing grazing in the late autumn and early winter;

• recovering post-grazing to produce equal or higher grain yield of potentially premium quality.

In this environment, there was little information available to compare the effects of grazing pressure on the performance of dual purpose wheat with other commercial wheats commonly grown. This study was undertaken to evaluate the effect of grazing pressures on the grain yield and quality of a dual purpose wheat cultivar compared to a spring wheat cultivar, and to assess the benefit of grazing on sheep live weight and condition score in this environment.

Methods

A field trial was conducted at Southern Brook (100 km NE Perth) in 2007 comparing a dual purpose wheat (EGA Wedgetail) with a spring wheat (Yitpi) cultivar in a clay loam soil, following three years of pasture. Plots were ripped after summer rain and sown at 110 kg/ha on the 17^th of May, 2007. Urea was applied at 50 kg/ha on 27^th of June 2007. No opportunity to sow earlier occurred due to lack of rain in April and in early May. The experiment comprised 18 plots with ungrazed (0 DSE/ha)¹, low grazing pressure (20 DSE/ha) and high grazing pressure (40 DSE/ha) treatments in a randomised block design. The trial was grazed with Merino sheep (ewes) from 17^th of July to 7^th of August 2007. The plots were 50 m wide and 100 m long.

Soil samples were collected from the trial location prior to seeding. The samples were taken from 0-10 cm depth for standard soil chemical analysis (Table 1). Plant numbers were counted at 10 locations (1 m length over two adjacent rows). Plant biomass, conditional score and sheep live weight were recorded. The whole of each trial plot was harvested with a header and a sub-sample was taken for grain quality analysis. Grain yield (t/ha), and grain protein (% by near infrared reflectance calibrated against the standard Kjeldahl test), hectolitre weight (kg/hl), screenings (% <2 mm), and 1000 grain weight (g) were measured on all plots. Analysis of variance was carried out using Genstat for Windows 10^th edition.

Table1. Soil test results of the experimental site at Southern Brook, 2007

Soil Type	Top Soil pH (CaCl₂)	Org. C (%)	P (mg/kg)	K (mg/kg)	Electrical conductivity (mS/m)	NO₃-N (mg/kg)
Clay loam	4.7	1.22	45	351	0.123	29

Results

The ideal time of sowing for a dual purpose wheat would be late April or early May. However, in the months of March and April, the trial site received only 24 mm rainfall. The growing season (April-October) rainfall was 230 mm (average growing season rainfall is 366 mm).

Figure 1. Average weekly food on offer (FOO) at Southern Brook, 2007

Effect on plant biomass and flowering dates at Southern Brook

More biomass (P<0.05) was available on Yitpi than EGA Wedgetail under each grazing regime (Figure 1). Food on offer (FOO) was maintained under the low grazing regime but uneven grazing resulted in variation in plant maturity. Biomass levels were least on the high grazing pressure treatment (P<0.05) but grazing was more even and resulted in delayed but even plant maturity. Compared to no grazing, low grazing pressure delayed the flowering by 6-10 days and by 14-18 days under high grazing pressures (Table 2). A similar trend was also reported by Amjad et al. (2006). The delays in flowering date due to grazing were related to removal of main stems and their replacement by later tillers. This resulted in a large decline in grain yield, particularly with EGA Wedgetail (Table 3). In general the delay in flowering diminishes the risk of frost, but increases the likelihood of moisture stress during grain filling period.

Table 2. Flowering dates of two wheat cultivars at Southern Brook

Treatment	Yitpi	EGA Wedgetail
Ungrazed	22-September	30-September
Low grazing pressure	30- September	07-October
High grazing pressure	09 -October	17-October

Figure 2. Average condition score of sheep at Southern Brook in 2007

Figure 3. Average live weight (kg) of sheep at Southern Brook in 2007

Effect on sheep live weight and condition score at Southern Brook

Condition score improved over the grazing period (Figure 2). There was no difference in condition score between the cultivars at each grazing regime but under high grazing pressure there was significantly less improvement (P<0.05) in condition score compared to the low grazing pressure which is consistent with the available biomass produced.

Sheep live weight improved over the grazing period (Figure 3). Under both cultivars at low grazing pressure, live weight continued to increase cumulatively. However, under the high grazing pressure live weight began to decline significantly (p <0.05) in the last part of the grazing period. This reflected the decline in biomass production (Figure 1).

Grain yield and quality

Results from this trial showed that there was significant reduction (p<0.05) in grain yield due to the grazing pressure. However, there was no difference between low and ungrazed treatments in grain yield after grazing. The mean of all the high grazing pressure treatments yielded an average of 0.77 t/ha compared to the ungrazed wheats of 2.01 t/ha (62% less) (Table 3). Dual purpose wheat EGA Wedgetail produced significantly less (P<0.05) grain yield compared to commercial wheat Yitpi whether grazed or not. The screening %, however, was significantly lower for the dual purpose wheat. At both the low and high grazing pressure Yitpi had a significantly lower protein than EGA Wedgetail, possibly due to its higher grain yield. At low grazing pressure there was no significant difference in grain protein from the ungrazed treatment for both cultivars but at high grazing pressure grain protein significantly increased. Apart from the obvious inverse relation between protein and yield, the low protein overall was possibly related to insufficient N fertilizer at sowing and differences in soil moisture and temperature during grain filling. Screening % (never above the acceptable limit for delivery into milling grades) and protein increased with grazing for both cultivars.

Table 3. Effect of grazing on grain yield and quality of wheat at Southern Brook in 2007

Grain yield (t/ha)

Cultivar	Ungrazed	Low grazing pressure	High grazing pressure
EGA Wedgetail	1.57	1.57	0.46
Yitpi	2.45	1.79	1.08
l.s.d. (P=0.05)		0.58

Grain protein (%)

Cultivar	Ungrazed	Low grazing pressure	High grazing pressure
EGA Wedgetail	9.1	9.4	10.6
Yitpi	8.3	8.3	9.9
l.s.d. (P=0.05)		0.9

Hectolitre weight (kg/kl)

Cultivar	Ungrazed	Low grazing pressure	High grazing pressure
EGA Wedgetail	82	82	83
Yitpi	83	84	84
l.s.d. (P=0.05)		1

Screening (%)

Cultivar	Ungrazed	Low grazing pressure	High grazing pressure
EGA Wedgetail	0.5	0.9	1.9
Yitpi	0.9	1.2	2.5
l.s.d. (P=0.05)		0.9

Conclusion

The trial results indicate that spring wheat (such as Yitpi) is potentially better suited for both biomass and grain yield compared to dual purpose winter type (EGA Wedgetail) in this environment. Further testing of long season wheat types, especially when sown in March or April if possible, is required for a more complete assessment of the dual purpose grain and grazing system. However, the benefits from grazing wheat on livestock weight gain, especially at the stocking rate of 20 DSE/ha, were clear in this experiment even though the seasonal rainfall was below average for the location. This result warrants economic evaluation over a wider range of seasons and locations.

Acknowledgements

We are grateful to Barbara Sage and Tenielle Martin for their technical and field assistance. We thank the farmer Allen Lawrence for providing land for the field trial. Helpful suggestions on the manuscript were received from David Kessell. This project is supported by Grain and Graze Avon Project. Grain and Graze is cooperatively funded by Grains Research and Development Corporation, Meat and Livestock Australia, Australian Wool Innovation and Land and Water Australia.

References

Amjad M, Sharma DL, Curtis B and Anderson WK. (2006) Dual purpose long season winter wheats to improve productivity in Western Australia. In the Proceedings of 13^th Agronomy Conference, 10-14 September, 2006, Perth, Western Australia.

Anon. (2005) Research priority: addressing rotations for mixed farming systems, Murrumbidgee Grain & Graze research trials, grazing wheat agronomy.

¹Stocking rate measurement is expressed as (DSE/ha) = Dry Sheep Equivalent = 45 kg non-pregnant sheep

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