Weigh up the options before manuring legumes
Research from the New South Wales Department of Primary Industries (DPI) has found that in 2013 and 2014 brown manuring had no clear yield advantage in the following wheat crop over harvesting pulses for grain. However, brown manuring still remains a useful tool to combat herbicide-resistant weeds.
The benefits of having a pulse crop phase – most notably the fixation of nitrogen – in a farming system are widely known. The team from the NSW DPI, with funding from the GRDC, is trying to determine the role brown manure has in a farming system and how long residual effects of pulses can last in following crops.
Three cropping sequences are under investigation at Wagga Wagga, NSW. The first year of each started with pulses in 2012, 2013 and 2014, and was then followed by two wheat crops to measure residual effects on wheat yield and protein. In the first year of these sequences, six different pulses were compared over three sowing times, then brown manured or harvested for grain. All experiments were conducted largely under weed-free conditions.
NSW DPI pulse research agronomist Dr Eric Armstrong says in all sequences, brown manuring was timed to anthesis of black oats.
One of the key findings to come out of these cropping sequences was that there were no significant differences between wheat yields following any of the legume treatments either brown manured or harvested in either 2013 or 2014. Yields in both years were close to 3.5 tonnes per hectare across all treatments. Some frosting and a dry finish were experienced in both years.
“The message is simple,” Dr Armstrong says. “Under these conditions in southern NSW, growers will maximise their rotation gross margin by taking their pulse crops through to harvest and selling the grain.
”The main rotation effect from the trial was seen in wheat protein (Table 1). Dr Armstrong says after a pulse crop, wheat grain proteins were up to 10 per cent higher compared with wheat after wheat, significantly improving grain quality and returns.
“There was also strong evidence that manuring pulses compared with those harvested for grain leads to a further increase in grain protein of between 1 and 1.5 per cent, but this is unlikely to negate the opportunity cost of manuring the previous crop for yield and protein gains alone,” he says.
Dr Armstrong says there were still some benefits evident in the system for a second wheat crop after pulses, demonstrating longer-term benefits. He says protein levels of the second wheat crop were about 0.5 per cent higher following manured pulse crops compared with following harvested pulse crops.
“This suggests all pulse crops in southern NSW are likely to have similar flow-on benefits to the following wheat crops in most situations, provided they are well managed,” he says. “Therefore, growers should choose the pulse that best fits their farming system – the one easiest to grow and most profitable to market.
“From these studies and previous work, brown manuring in southern NSW fits best when herbicide-resistant weeds are the major driver. The moisture conservation and residual nitrogen for the following crop is an added bonus. It is important for growers to remember that legumes grown under strong competition from weeds are unlikely to fix much, if any, nitrogen,” Dr Armstrong says.
|2013 crop||Variety||2014 wheat protein % at 11% moisture|
|Field peas||Morgan PSE 23||10.79||11.91|
|Field peas||PBA Hayman||11.52||11.99|
|Field peas||PBA Percy||11.24||12.16|
Dr Eric Armstrong
02 6938 1814
GRDC Project Code DAV00113