Cropping

Vital to monitor nutrients after harvest

By Country News

Growers altering their farming systems are changing the balance of soils, according to a recent analysis of nutrient removal.

Incitec Pivot Fertilisers agronomist Lee Menhenett co-ordinated a program of grain and leaf tissue testing from 27 commercial crops in the Mallee and Riverine Plains over summer.

The program found switching from a grain harvest to a hay cut could increase potassium removal, with about three times as much potassium removed from a tonne of wheat hay than from a tonne of grain in the tested crops.

Mr Menhenett said if the straw was taken after harvesting wheat or barley grains, potassium removal could double from the paddock.

“Given that most growers are not applying potassium in their fertiliser programs, there is a need to at least monitor potassium availability where hay or straw cutting is happening more often.”

He said growers could monitor the availability of potassium to crops by leaf tissue testing during crop growth or soil testing.

“Another nutrient not often applied in fertilisers and being removed in considerable amounts from grain harvests is copper.”

Based on the grain testing, 20 to 30 g/ha of copper is potentially being removed annually from grain crops.

Mr Menhenett suggested growers consider applying copper fertiliser in test strips, to assess the response to the micronutrient in crops.

“The overall theme from the results was the high level of variation in nutrient removal between and within crop types,” he said.

“One key point to note is that grain growers who are using a phosphorus replacement strategy based on a rule of thumb removal rate are at risk of over-estimating or under-estimating their phosphorus requirements by a fair margin, because the variation in removal is actually quite high.”

Depending on the yield, the overall phosphorus removal per hectare was between six and 13 kg/ha.

Mr Menhenett said growers who will use a nutrient replacement strategy to guide phosphorus decisions should arrange their own grain testing from areas of known and stable yields.

He said monitoring removal from grain and hay cuts can be arranged through the Nutrient Advantage laboratory.