Did irrigation wheat beat the heat in 2015?

The ARC-Grain Crops Institute’s recently published 2015 National Irrigation Wheat Cultivar Evaluation trial results suggest a considerable number of cultivars produced profitable yields, despite high temperatures.

The 2015 National Irrigation Wheat Cultivar Evaluation Programme was conducted with 23 entries from the major seed companies of South Africa, namely Sensako, Pannar as well as from the Agricultural Research Council’s (ARC’s) Small Grain Institute.

In 2015, South Africa experienced its worst drought in 30 years due to the El Niño effect. A combination of low rainfall and incessant heat led to the drying up of many farm dams in KwaZulu-Natal, the Free State, Mpumalanga and Limpopo.
Temperatures were higher than normal during the entire wheat growing period, especially in the warmer northern regions and KwaZulu-Natal.

Many irrigation wheat farmers did not have enough water to meet the high rate of evaporation. Figure 1 shows temperature data from Groblersdal, indicating that temperatures were at least 3°C higher than normal from June to October.

Grain yields
Heat stress can have significant effects on the grain yield of wheat. It causes premature leaf senescence, tiller abortion, a reduction in the number of seeds/ear, reduced duration of grain fill and reduced grain size. Scientific data suggests a 3% to 5% (±190kg/ha) reduction in grain yield of wheat can occur for every 1°C increase in average temperature above 15°C.

Despite the heat and drought, a considerable number of cultivars still produced profitable yields. These results once again highlighted the importance of good cultivar choice for successful irrigation wheat production in South Africa, as well as the importance of cultivar evaluation.

The cultivar evaluation trials were carried out in the cooler central irrigation areas, the warmer northern irrigation areas, KwaZulu-Natal and the Highveld. The results of the 2015 cultivar trials under irrigation were presented to the National Wheat Cultivar Adaptation workgroup on 11 February 2016. The report was accepted and new recommendations for the 2016 season were finalised.

In the following section, yields of early planted irrigation cultivars in the different areas are presented. Four-year average yields for the cultivars are also provided to give an indication of the yield stability.

Cultivar evaluation results

Cooler central irrigation areas: The average yield for the first plantings in the cooler central irrigation areas in 2015 was 9,11t/ ha. PAN 3400 (9,90t/ha), SST  8125 (9,74t/ha), SST 806 (9,70t/ ha) and SST 835 (9,56t/ ha) produced the highest yields (Table 1). Average hectolitre (hl) mass was good in 2015 at 82,52 kg/hl. All cultivars had a hectolitre mass above 77kg/ hl.

Grain protein content was also acceptable at 12,61%. Falling number values were high, with an average of 341 seconds. Four-year average grain yields indicate that SST 806 produced the highest yield (9,48t/ha), followed by SST 835 (9,47t/ha), PAN 3400 (9,45t/ha), PAN 3497 (9,41t/ha) and SST 884 (9,40  t/ha) (Figure 2). It should be noted that the yields of these five cultivars were not significantly different from each other.

Warmer northern irrigation areas
The average yield for the first plantings in 2015 was 7,99t/ ha. The combined analysis showed that SST 895 (8,63t/ha), SST 884 (8,59t/ha), PAN 3400 (8,52t/ ha) and SST 875 (8,48t/ha) had the highest yields (Table 2). 

It should be noted that the yields of these first four cultivars did not differ significantly from each other. Average hectolitre mass was 80,84kg/ hl, and grain protein content was 11,71%. Falling number values were an average of 352 seconds. The four-year average grain yields indicated that SST 806 (8,27t/ ha) produced the highest yield, followed by SST 895 (8,21t/ha) and SST  884 (8,12t/ha) (Figure 3).

Highveld irrigation areas
The average yield of the Highveld areas was 8,55t/ha. The combined analysis indicated that PAN  3497 (9,51t/ha), SST 8134 (9,26 t/ha), SST 884 (9,03t/ha) and PAN 3623 (9,02t/ ha) had the highest yields (Table 3). The hectolitre mass was acceptable for all cultivars, with an average of 83,39kg/hl. Average grain protein content
was also acceptable in 2015 at 11,60%.

Falling number values were generally high, with an average of 315 seconds. The three-year average grain yields indicate that PAN 3497 (8,85t/ ha) produced the highest yield, followed by SST 875 (8,62t/ha) and SST 835 (8,58t/ha) (Figure 4).

KwaZulu-Natal irrigation areas
KwaZulu-Natal was the region worst-affected by the heat and drought in 2015. The average yield was low at 5,42t/ha.
However, the combined analysis showed that Renoster (6,18t/ ha), SST 8135 (6,13t/ ha), SST 884 (6,01t/ ha) and SST 8134 (6,00t/ha) had the highest yields (Table 4).

The yields of these cultivars were not significantly different from each other. The four-year average grain yields indicated that SST 806 (7,49t/ha) produced the highest yield, followed by SST 835 (7,43t/ha) and Krokodil (7,30t/ha) (Figure 5). Average hectolitre mass for 2015 was 81,60kg/hl. Grain protein content was very high during 2015 at 14,57%. Falling number values were generally high, with an average of 308 seconds.

More detailed information on the performance of irrigation wheat cultivars, including data on the one-year performance as well as the long-term data for all the production regions and different planting times, is available in the Production Guidelines published by the ARC-Small Grain Institute.

The research was made possible through funding by the Winter Cereal Trust and the Agricultural Research Council.
Report compiled by Dr Ernest Dube, Willem Kilian, Ben van Rensburg, Manus van der Merwe, Dawie du Plessis, Elsa van der Merwe and Hesta Hatting.

For more information contact the ARC-Small Grain Institute on 058 307 3400.