Beet doesn’t need heaps of fertiliser

This is the finding of the second of a three-year project run by MPI’s Sustainable Farming Fund (SFF) on fodder beet agronomic solutions. 

The project is aimed at informing farmers about fertiliser responses and helping them increase profitability by minimising costs and maximising yields. 

Ravensdown agronomist Chris Lowe did trial work in South Canterbury on Haden and Julie Batty’s farm – one of seven sites. 

“We found that the high rates of N applied in the past are not necessary,” Lowe says. “Statistically we saw no difference between treatments above 100kg N/ha, so there is a potential for cost saving by farmers.”

Although a difference was seen on most sites between the control (no N applied) and the lowest rates applied (100kg N/ha in year one and 50kg N/ha in year two), the results were similar in year two -- no effect on yield above 100kg N/ha.  

The first season of the trial looked at crop agronomy, performance and fertiliser response. In year two it looked at the consistency of plant response to fertiliser rates on different soil types.

In year two, soil tests were taken before and after the study and fertiliser was applied at 50kg N/ha increments up to 300kg N/ha. Orari had the lowest total available N because of its shallow stony soils, making it the most likely to show a response from application. However, there was no yield increase recorded: fertiliser rates were higher than 100kg N/ha. 

Nitrogen concentration in the leaf increased from 0.77% (4.8% crude protein [CP]) in the control plot to 1.49% (9.3% CP) for the 300kg N/ha treatment. Total N uptake also increased from 208kg/ha for the control to 433kg/ha for the 300kg N/ha application.

 “Obviously the higher application rates increase the N concentration in the plant but this leads to environmental implications. It may be better in protein content for animals but you have the spinoff of high N in the urine.”

The highest CP level in the current experiment of 9.3% is lower than the 12% needed for animal maintenance in winter.

Lowe says a key components of N management is understanding how much is readily available in the soil.

“The key is to measure N beforehand so you know how much N is actually in the soil. If you can measure what is in the soil then you can manage what you put on,” he says.

“It is also vital to understand that N applications are to drive canopy growth to achieve canopy closure at the longest day, so early N is critical. After Christmas it is to maintain canopy and green leaf retention, so attention should turn to disease control.”

Average yields for the Orari crop were down from 33 tonnes DM/ha in year one to 29.2t DM/ha in year two, which Lowe suspects is a result of the beet western yellow virus. He says the yellow leaf that occurs with the disease is sometimes misinterpreted as K or magnesium (Mg) deficiency.

“I know of companies that have recommended 300-400kg K/ha – crazy amounts. We regularly tissue test our crops and rarely see Mg or K deficiencies.” 

He says farmers should question these recommendations, particularly as the trial sites have not shown a consistent yield response to K across a range soil types over both years. 

The final year of the SFF trial will look to expand these findings to paddock scale and and to foliar disease control.