Ground Cover Supplement : GC Supplement - Tactical cereal agronomy
Agronomy outweighs genetics in sorghum yield GRDC-funded research is refining agronomy packages for sorghum in the northern region, where it remains the main summer crop By Loretta Serafin and Guy McMullen WHILE SORGHUM IS reliably grown in the medium-to-high-rainfall zone of the northern region, crop modelling suggests yields could be falling short of their potential. To address this, research funded by the GRDC and the New South Wales Department of Primary Industries (DPI), with support from Pacific Seeds, is examining the impact of plant population, row configuration, nutrition and hybrid selection on grain yield. As part of the research a dryland and irrigated sorghum trial was established at Breeza on the NSW Liverpool Plains in 2013-14. The trial included the following treatments: ¢ two sowing times: 'ideal' (end of October) and late (mid December); ¢ two row configurations: 90 centimetres solid (two rows per plot) and twin row (four rows with pairs of two rows 7.5cm apart); ¢ three sorghum hybrids: MR-Buster (as a commercial benchmark) and two recently released hybrids, MR-Scorpio and 85G33; ¢ three plant populations: 50,000, 75,000 and 100,000 plants per hectare; ¢ three nitrogen (N) application rates: 0, 100 and 200 kilograms N/ha applied as urea at sowing; and ¢ three phosphorus application rates: 0, 10 and 20kg phosphorus/ha applied as triple superphosphate at sowing. SOWING TIME Sowing in the ideal window generated higher yields in both the irrigated and the dryland trials. On average, the ideal sowing yielded 0.25 tonnes/ha more than the later sowing at the dryland site and 0.35t/ha more in the irrigated trial. Yield differences due to hybrid selection were small, with much larger yield differences resulting from varying row spacing, sowing time and plant density. ROW CONFIGURATION In the dryland trial, the 90cm row spacing yielded more than the twin row configuration at all three plant populations and across both sowing times. In the irrigated trial the twin row spacing sown at the earlier ideal time yielded the same as the 90cm row spacing regardless of sowing time or plant population. However, twin row spacing sown at the later sowing time yielded less at all three populations. PLANT POPULATION In the irrigated trial, yields increased as plant population increased from 50,000 to 75,000 plants/ha and then reached a plateau. In the dryland trial there was a significant increase in yield with the ideal planting time as plant population increased from 50,000 to 75,000 plants/ha (3.01 versus 4.10t/ha). However, there was no difference in yield between the 75,000 and 100,000 plants/ha treatments (4.1 and 4.17t/ha). There was no significant response to varying population in the late sowing treatment (average yield 3.3t/ha). NITROGEN RESPONSE There was a significant response to nitrogen in the dryland trials, with yield increasing in the plots sown at the ideal sowing time as nitrogen rate increased. An additional 0.76t/ha yield was generated from applying 100kg N/ha compared with the nil fertiliser treatment and a further 1.05t/ ha generated with the application of an additional 100kg N/ha in the 200kg N/ha. As such, there was close to a 2t/ha response from the application of 200kg N/ha. The response to nitrogen was less in the later sown treatment, with no difference between the 100 and 200kg N/ha treatments. However, the 200kg N/ha treatment yielded 0.85t/ha more than the nil nitrogen treatment. Applying 200kg N/ha to crops sown at the ideal time in the irrigated trial boosted yield by 2.9t/ha compared with the nil nitrogen treatment and by 2.3t/ha compared with the 100kg N/ha treatment. The response to nitrogen was similar in the late-sown irrigated treatments; however, there was no significant difference between the 100 and 200kg N/ha treatments, which were 2.0 and 2.3t/ha higher yielding than the nil nitrogen treatment. PHOSPHORUS RESPONSE In the irrigated trials the response to phosphorus was almost identical regardless of sowing time and was only significant when it was coupled with the application of nitrogen. The response to phosphorus in the dryland trials was not clear. Yields were higher in response to phosphorus in the late-sown crops than in crops sown at the ideal time. LOW-TO-MEDIUM-RAINFALL AREAS Trials across the low-to-medium- rainfall zone of the northern growing region show that the genetic potential of sorghum hybrids is rarely the limiting factor for sorghum yield in this area. Current recommendations for optimising yield of sorghum in the low-to-medium-rainfall zone are to: ¢ plant a hybrid with at least a moderate level of tillering as early as possible; ¢ select a single-skip or super- wide configuration; and ¢ establish an even population of between 30,000 to 50,000 plants per hectare. A series of 12 dryland trials were carried out over five years between 2010 and 2015 at sites west of the Newell Highway, NSW: Mungindi, Morialta Junction, Rowena, Tulloona, Gurley, Garah, Bellata, Ashley and Bullarah. SOWING TIME Seven of the 12 trials were planted in the early planting window between September and October and five in the late planting window of January. Average yields from the seven early- planting trials ranged from 4.53 to 0.74t/ha. Yields from the five late-planting trials ranged from 4.30 to 1.59t/ha. While it is not possible to draw firm conclusions on the best planting time for this region, the early-planted sorghum yielded more and has a better fit within the region's farming system than late-planted sorghum.
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