Nitrogen (N) is a major input into the cropping system and fundamental decisions are made in-season on fertiliser management. The question remains, how much N do we have available to crops after an exceptional 2016 season?
N decision making in 2016 were in stark comparison to the decisions made in 2015 and BCG research officer Sebastian Ie explained that inter-season variability and its effect on N supply and demand, make this a continued challenge.
“Seasonal conditions, like temperature and rainfall, have a strong effect on both crop N uptake and the soil processes that lead to N being either stored in the soil or lost to the environment,”
Understanding how much N is in the soil will enable growers to more efficiently allocate the right product, at the right rate and right time to match crop demand.
By taking into consideration the amount of N removed in grain at harvest, and subtracting that from the amount of N available at pre-sowing soil tests, applied N and an estimate of mineralisation, growers are able to get a rough estimate of N available.
Mr Ie clarified that “many growers use paddock history as a guide to determine available N at the start of a season, which will assist in determining N inputs, but this can become inaccurate under extreme or unusual conditions.”
BCG trials in 2016 at Kalkee found that this method overestimated the amount of N available after a hayed off crop, and soil sampling provided a more accurate gauge of paddock N status.
While 2016 experience was a vastly different set of circumstances the principle could be the same.
At the recent GRDC Research Update in Rupanyup, Rob Norton (International Plant Nutrition Institute) suggested that seasonal conditions in 2016 may have caused higher levels of mineralisation, leaching, and denitrification. Consequently, undertaking soil sampling may be the best method to assess nutrient supply for 2017.
Members can access the results from the 2016 Kalkee trial here, “Saving N for a rainy day: N management after a dry finish”.
BCG will again be conducting soil sampling in 2017. For more information follow the link to the soil sampling flyer 2017, or complete your expression of interest online or by phoning the BCG office on 03 5492 2787.
