Page 1 Page 2 Page 3 Page 4 Page 5 Page 6 Page 7 Page 8 Page 9 Page 10 Page 11 Page 12 Page 13 Page 14 Page 15 Page 16 Page 17 Page 18 Page 19 Page 20 Page 21 Page 22 Page 23 Page 24 Page 25 Page 26 Page 27 Page 28 Page 29 Page 30 Page 31 Page 32 Page 33 Page 34 Page 35 Page 36 Page 37 Page 38 Page 39 Page 40 Page 41 Page 4222 IREC Farmers' Newsletter No. 196 — Summer 2016 Total dry matter averaged across all varieties and targeted plant densities was significantly higher on the 30 and 60 cm row spacings than the 90 cm row spacing, at 10.0, 10.4 and 8.5 t/ha respectively. This in part explains how the narrower row spacing was higher yielding than the 90 cm row spacing. In general terms, grain yield was correlated with total dry matter production. Targeted plant density results The actual plant densities achieved for the 25 and 40 plants/m2 density targets were an average of 21 and 31 plants/m2, respectively. Across all varieties and row spacings, the 40 plants/m2 targeted plant density was significantly higher yielding than the 25 plants/m2, at 3.9 and 3.4 t/ ha respectively. There was a significant interaction between targeted plant density and row spacing (Figure 3). At the higher targeted plant density (40 plants/ m2), the narrower row spacing (30 cm) yielded higher than the wider row spacings (60 and 90 cm) for all three varieties. However, at the lower targeted plant density (25 plants/m2) there was no statistical effect of row spacing on grain yield for Bidgee and Djakal varieties, with the only exception being N005A-80 at 90 cm row spacing. From this data, it is apparent that plant density has a greater influence over grain yield than row spacing. Summary This experiment demonstrated that under overhead irrigation on a relatively flat layout, soybean grain yields above 4.5 t/ha were achievable. Variety selection, row spacing and targeted plant density were all key agronomic factors for achieving high yields under this irrigation method and paddock layout. In summary, based on this experiment, for soybeans grown under overhead irrigation: • Djakal and N005A-80 varieties yielded higher than Bidgee •  30 cm row spacing was found to be the optimum row spacing especially at higher targeted plant densities •  optimum plant density, especially at narrow row spacing was 30 plants/m2 — maintaining a population at or above this level was critical to maximising yield potential. Acknowledgements This experiment was part of the Southern NSW Soybean Agronomy Project (DAN00192, 2014–18), which is jointly funded by GRDC and NSW DPI. Technical assistance was provided by John Dando and Paul Morris. Further information Mathew Dunn Soybean Agronomist T: 02 6951 2747 E: [email protected] Figure 3. Soybean grain yield for row spacing x targeted plant density interaction averaged across varieties Variety selection, row spacing and targeted plant density were key agronomic factors for achieving high yields when using overhead irrigation. 3.63 4.47 3.51 3.74 3.09 3.48 0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00 4.50 5.00 25 40 25 40 25 40 30 60 90 Yield (t/ha) Row spacing (30, 60, 90 cm) x sowing density (25, 40 plants/m2) l.s.d.(P=0.05) = 0.44 t/ha Soybean grain yields above 4.5 t/ha were achieved under overhead irrigation on a relatively flat layout in the Finley experiment. Row spacing (30, 60, 90 cm) x sowing density (25, 40 plants/m2 ) Yield (t/ha) l.s.d.(P=0.05) = 0.44 t/ha