Scott BJ, Martin P and Riethmuller GP (2013)
This monograph reviews the claimed advantages and disadvantages of wide rows and, in Australia, quantifies the effects of widening rows on yields in wheat, barley, canola and lupins. General conclusions have been drawn.
Farmers have adopted wider rows (>18 cm) to improve the passage of sowing machinery through stubble. The direct effect of wide rows on yield often has been either minimised or overlooked in adopting the practice while the other advantages of wide rows have been emphasised. Frequently identified advantages of wide rows, beyond stubble clearance, include reduced fuel consumption, with fewer ground-engaging components, and increased speed of the sowing operation. Other claims about the advantages of wide row spacing, including improved harvestability, seed size, grain quality and higher yield appear to be, in reality, limited and inconsistent.
Crops sown in wide rows are considered less competitive with weeds and at increased risk of seedling damage from close fertiliser placement. In addition, crops sown in wide rows have reduced plant populations compared with those sown in narrower rows, even when fertiliser and seed are placed separately.
Historically, square planting arrangements with cereals have higher yields compared with rectangular patterns. On this basis widening rows, and hence moving to a more rectangular pattern, could be predicted to reduce grain yield of cereals. Data from 89 experiments on wheat, available across Australia, were examined for preparation of this monograph. The yield change (kilograms per hectare per centimetre of row space widening) was related to estimated yield at 18 cm row spacing (a common spacing in earlier Australian agriculture). The rate of yield loss (kg/ha/cm) with row widening increased as yield in 18 cm rows increased, although there was considerable variability between experiments.
Generally, at yields below 700 kg/ha, widening row spacing beyond 18 cm increased estimated grain yield. For example, at yields of 500 kg/ha, doubling the row space to
36 cm increased yield to 520 kg/ha. However, at yields of 2000 kg/ha, widening rows to 36 cm reduced yield to 1860 kg/ha, and at 4000 kg/ha yield was reduced to 3640 kg/ha with 36 cm row spacing.
Although only 18 experiments were identified for barley, the rate of change of yield with changes in row spacing was similar to wheat. This suggests wheat and barley are similar in their reaction to row space changes. At yields of <1100 kg/ha at 18 cm row spacing, widening rows increased barley yield.
Canola yield declined as row spacing increased, and the rate of decline was greater as yield with 18 cm rows increased in Western Australia (14 experiments), and central and southern NSW (13 experiments). The rate of decline was not significantly different between the two states, and was not different from the relationship obtained for wheat.
Data were assembled on lupins from WA (29 experiments) and NSW (10 experiments). In WA lupin grain yield related to row spacing was not always linear. A two-phase linear approach, limiting the range of data to more closely approximate linearity, addressed this issue. In the row spacing range of 18-30 cm minimum, and 42-60 cm maximum, lupin yield increased more frequently with increased row spacing in WA. This result contrasted with that of wheat and canola in the same State. Data from NSW indicated lupin yields generally decreased as row spacing widened, but there was insufficient data to fit a linear function. In WA when rows were widened further, from beyond the range 42-50 cm minimum to 84-100 cm maximum, yield reduced with wider row spacings.
A number of studies have examined changes in agronomic practices (for example, weed control, sowing time, cultivar and fertiliser management) and their effect on yield under wider rows. It was implicit from the present study that any agronomic practice that lowered grain yield in 18 cm rows was likely to also lower the rate of yield loss (kg/ha/cm) as row spacing increased. The agronomic practices that commonly produced the highest yield at 18 cm rows also produced the highest yield at 36 cm rows. The suggestion is that yield at 18 cm row spacing has a dominant influence on yield at wider row spacing, and differences in the rate of reduction of yield between practices are smaller in their effect on yield at wide rows. Retention of stubble compared with removal, did not directly affect the loss of yield with increased row spacing. Any effects on yield loss with wider rows were indirect and were through changes in grain yield at 18 cm induced by stubble management.
The most appropriate action to maximise grain yield at wide rows seemed to be sound agronomic practice and cultivar selection. This approach generally produced the highest yield irrespective of row spacing. 'Paired or ribbon row' sowing appeared to offer some scope in mitigating the loss of grain yield as row space increased.
From the point of view of adopting conservation farming techniques, increasing row spacing is an 'enabling' change, which makes sowing through stubble achievable. The benefits in stubble handling are greatest with high stubble loads. High stubble loads are more frequent in higher rainfall areas with higher grain yields; the conditions where reductions in grain yields from wide rows are likely to be greatest. Long term data from Wagga Wagga (high rainfall wheatbelt NSW: average yield 3440 kg/ha), Condobolin (low rainfall NSW: 1840 kg/ha) and Merredin (low rainfall WA: 2230 kg/ha) were used to estimate the losses in grain yield from wide row spacings.
The loss of yield at Wagga Wagga for row spacings of 30 cm and 36 cm would be 200 kg/ha and 300 kg/ha. The loss of yield resulted from row widening, but needs to be compared with any cost savings or advantages associated with wider rows.
Results from this review suggest farmers regularly managing high stubble loads at sowing avoid increasing row spacings where possible. If there are no other palatable options to manage stubble at sowing, farmers are advised to keep row spacings as narrow as possible while still permitting unimpeded sowing through stubble.