Grains Research and Development Corporation (GRDC)

In-crop nitrogen key to summer sorghum yields


With the summer cropping season on our doorstep, growers are weighing up their planting options against the market, seasonal conditions and gross margin calculations.

For many the summer cropping rotation will include sorghum and maximising crop yield and profitability will be a key driver of all pre-plant and in-crop agronomic decisions.

Recent research funded by the GRDC, Queensland Alliance for Agriculture and Food Innovation (QAFFI), Department of Agriculture, Fisheries and Forestry Queensland (DAFF) and NSW Department of Primary Industries (NSW DPI) and presented by Matthew Gardner, NSW DPI Research Agronomist, Tamworth, has highlighted the importance of managing crop nitrogen (N) nutrition to yield estimations and grain protein targets.

The research took in data from 12 sites across the northern region during 2012-2013 to determine the agronomic and economic responses of grain sorghum to varying levels of N nutrition.

A N response curve was developed from the sites and it was found that 90 per cent relative yield was achieved when starting soil N was approximately 110 kg N/ha. Therefore, sites where starting soil N was less than 70kg N/hectare were all responsive to N application. Even at sites where starting soil N exceeded 110 kg N/ha protein responses to N application were still observed.

It was concluded that sorghum growers can significantly boost yield and therefore profitability through targeting a grain protein level of between nine and ten percent.

Protein levels in grain sorghum aren’t always closely monitored by growers simply because there is no payment structure for protein.

However, this research suggests protein levels could provide important information on crop performance and enable growers to maximise yield potential and profitability.

Protein levels in sorghum are closely linked to yield - that is, if protein levels are below a certain level, yield will be affected. 
If yield doesn’t reach expectations, this raises a couple of key questions such as whether the crop was deficient in N and if it wasn’t, whether there was a relationship to how that particular variety utilises N.

Nitrogen and water continue to be major limiting factors in crop yield potential yet the greatest economic returns are achieved when grain yield is maximised, highlighting the critical relationship between yield and profitability.

Careful management of crop N application can ensure that growers maximise their return on investment.

The research found that where nitrogen application resulted in yield increases, the return on N investment was $2-$5 for every $1 spent.

Profit margins suggest sorghum may be as profitable in its own right in western growing regions if slightly more yield can be achieved to make up for a lower price.

N represents a large input cost within the gross margin for sorghum, however, the lack of protein premiums mean that luxurious N applications directly reduce profitability.

 At the end of the day, it is a balancing act to ensure that the management of N nutrition in-crop optimises protein levels, yield and financial returns.

Caption: GRDC Northern Region Panellist Loretta Serafin, Leader Northern Dryland Cropping Systems, NSW Department of Primary Industries

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