NEW results from a barley crop in a long-running fertiliser experiment on Queensland’s Darling Downs are highlighting the value of taking a systems approach to crop nutrition.
Incitec Pivot Fertilisers subtropical systems agronomist, Bede O’Mara, said a review of the results showed the pros and cons of different strategies in a dry winter.
“It’s the dirt, not the ‘fert’, which is making a difference at this site – the cumulative effect of running the cropping system in balance,” he said.
Mr O’Mara identified the nutrition combination closest to balance after more than 30 years of summer and winter crops in this experiment as 80 kilograms/hectare of nitrogen and 10 kg/ha of phosphorus.
“But every year is different, and we are never going to know what the season has in store for us,” he said.
“In the long run at this site, the highest yielding results from 13 winter cereal crops under all fallow lengths have been achieved when using 120kg/ha of nitrogen and 20kg/ha of phosphorus.”
In 2017, coming after a mungbean crop, with low starting soil moisture and only 153 millimetres of growing season rainfall, this combination still provided the best yields in the Scope CL barley trial at 1.9 tonnes/ha.
However, it produced only slightly more grain than the crop grown with the least inputs, 40kg/ha of nitrogen and 5kg/ha of phosphorus, which yielded 1.8t/ha.
Mr O’Mara said the barley yields were limited by moisture, not nutrition in 2017.
“If we had received more rain, even just an average season, the crops grown with many of the higher fertiliser rates and where there was better soil fertility would have had the potential to yield much higher,” he said.
Historically, barley has produced up to 3.6t/ha at the site.
He said gross returns net of fertiliser cost for the 120kg/ha of nitrogen and 20kg/ha of phosphorus treatment in last year’s barley were solid at $379/ha.
Mr O’Mara calculated net returns from the trial based on fertiliser prices at the time of planting in June last year ($2.71/kg of phosphorus and $1.02/kg of nitrogen) and $290/t on-farm for F2 barley.
Growing the crop with less inputs (40kg/ha of nitrogen and 5kg/ha of phosphorus) improved gross returns net of fertiliser cost to $466/ha.
“You could say reducing rates last year would have worked well, but we only know that in hindsight,” he said.
“To make that call at the start of the season means limiting yields and returns in average or above average seasons.
“Using 40kg/ha of nitrogen would also have left little to no nitrogen in the soil tank for the following season.”
By comparison, he said the 80kg/ha of nitrogen and 120kg/ha of nitrogen treatments left positive nutrient balances of 40 and 80kg/ha of nitrogen respectively, given the lower yielding, dry season.
This ‘left over’ nitrogen will contribute to the 2018 crop, which is likely to be chickpeas.
Long term results
Incitec Pivot Fertilisers’ long-term nutrition trial was established in 1985 on ‘Colonsay’ on the Darling Downs in Queensland.
More than 30 crops have been grown in the experiment, including five barley crops and six wheat crops, a range of summer crops, pulses and cotton.
In each crop, four nitrogen rates (0, 40, 80 and 120kg/ha) and four phosphorus rates (0, 5, 10 and 20kg/ha) are used, with Mr O’Mara measuring the responses for each rate of nitrogen and phosphorus alone and in combination.
“All the better barley yields last year were achieved where nitrogen was used in combination with phosphorus,” he said.
“This is something we’ve seen consistently in this long-term experiment.”
But it’s more than just each crop’s fertiliser application being compared.
After more than 30 years with the same treatments in the same plots there are stark differences in cumulative soil fertility between plots.
For example, in deep N soil tests conducted in March this year, there was 76kg/ha of nitrate nitrogen in the 0-90cm soil profile at the nil nitrogen rate and 646 kg/ha of nitrate nitrogen where 120kg/ha of nitrogen had been used in every crop.
While this is a very high level of nutrient, the bulk of it is at the 30-60cm depth where it will be available to the coming crops.
“This is not something you see on-farm because using a very high fertiliser rate like this, higher than district practice, in every crop consistently for 33 years is not something growers would do,” he said.
Tillage regime comparison
Mr O’Mara said responses to different tillage operations were also beginning to be seen in the long-term nutrition experiment.
He singled out the deep phosphorus (deep P) treatment, where 20kg/ha of phosphorus was applied at 22cm depth in December 2013 and June 2015 and compared with deep ripping and zero till treatments.
“Deep P is starting to show its value in improving fertiliser responses,” he said.
“Last year, the deep P treatment showed significantly higher grain yields at all nitrogen rates compared with deep ripping and zero till treatments.
“This is consistent with findings from the Central Downs Grower Group which has seen better responses to deep P in drier seasons.
“There also appears to be some multi-nutrient interactions with the different tillage treatments which we will be concentrating on in coming crops, along with an ENTEC comparison to assess its suitability for protecting applied nitrogen and improving nitrogen use efficiency in broadacre cropping systems.”
For growers ready to sow this year’s cereals, he said it was important to ensure enough fertiliser was applied to cover the expected crop removal based on a realistic yield expectation.
Mr O’Mara encouraged growers to monitor responses from a systems perspective.
“Consider putting in some high nitrogen or even nil nitrogen strips in your upcoming crops to test whether your overall nitrogen rate is adequate, as well as using grain tests to measure nutrient removal and regular soil testing,” he said.
Source: Incitec Pivot Fertilisers
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