PHOTO: MATT MCINTOSH
PHOTO:VERITAS
NUTRIENT MANAGEMENT ▶▶▶
This indicates what Fraser calls ‘luxury uptake’, where the plants absorbed more nutrients than they could actually use. “The plants were basically just being greedy. It wasn’t translat- ing to yield at all,” she says.
It was also observed that bacteria in the P-starved systems were doing a lot more work to make what P was present available to the crop in question. According to Fraser, bacteria and fungi evolved to find P when they need it, and make up for deficiencies. Enzymic activity, she says, was therefore a lot higher in the soils where P is not abundantly applied.
“It’s fairly widespread in bacteria to turn on a gene that produces enzymes that alter phos- phorus more effectively when needed,” she says. “Basically the bacteria become lazy when they are in an environment with a lot of bioavailable phosphorus.”
Same yield possible with less P Fraser says these revelations indicate less can sometimes be more when it comes to apply- ing P. Limiting inputs can promote natural nu- trient processes within the field, while saving farmers money and reducing the risk of P loading in waterways – something which is of particular concern for farmers in the Great Lakes region. Those interested in reducing the amount of P they apply, says Fraser, can try test strips to determine any yield differences. Following 4R nutrient stewardship and preci- sion nutrient application strategies also makes a significant difference. “You don’t always need a blanket application,” she says, adding that alternative nutrient amendments in or- ganic and conventional systems – such as re- cycled waste products – should continue to be investigated.
2. Accounting for differences b etween sites In the 2016-2017 crop year, Aaron Breimer, general manager for Veritas Farm Manage- ment – a drone tech and data-service compa- ny based in Ontario – headed a project analys- ing strip-till strategies which producers could use to mitigate off-target phosphorus move- ment, while maintaining or increasing produc- tivity and profitability. This involved looking for
NEED TO KNOW:
▶ Crops will absorb more P than required, given nutrient over- abundance. ▶ Greater-than-necessary absorption of P does not translate to higher yield. ▶ Microbes that make P bioavailable for crops become less effective in high-P environments.
both yield increases and the potential to reduce fertiliser applications through more accurate placement.
Breimer says smart-grid soil analysis tech- niques were used to divide tillage test plots into zones of expected yield, with fertiliser ap- plied variably based on the yield potential of each zone. Plant tissue samples were taken to see how much phosphorus was being ab- sorbed by the crops, while samples of crop res- idue and the soil itself revealed how much of the nutrient was water extractable (a runoff risk). Yield and yield related data were also re- corded. “We don’t believe that a field is uni- form from one end to the other. There’s consid- erable variability. We also believe there’s variability in soil texture levels as you go across the field,” says Breimer. “What we were doing is going back and sampling the same area time and time again.”
Higher fertility soils Breimer says no positive or negative differenc-
es in crop productivity were observed between strip tillage and other approaches (minimum- till and no-till). Regarding the potential for applying less P per acre, he says their data indi- cated that farmers working with very fertile conditions might be able to successfully re- duce input amounts without corresponding reductions in yields. However, he and his col- leagues did not find an economic or agronom- ic justification for doing so. If some areas are fertile, he says, the fertiliser savings there could be transferred to lower-fertility areas. “Traditionally the thinking is if you have phos- phorus levels above 35 parts per million, you probably don’t need to apply a lot. But, if you talk to a farmer or a certified agronomist, they might say you need a little,” he says.
Nutrient absorption in strip-till The data also showed that crops planted in strip-till rows absorbed phosphorus at a higher rate early in the season – but that gain didn’t last. “By the time we got to maturity, the levels had basically levelled out. Strip-till seemed to give it a little extra kick in the spring,” says Bre- imer. Additionally, increases in water-soluble phosphorus in soil and crop residues were only significant in plots with very high phosphorus levels. Even in plots with very low levels of available phosphorus – the only places where sulphur deficiencies also appeared to be an is- sue – no system indicated statistically different crop residue levels.
Aaron Breimer of Veritas Farm Management: “We need to do a better job of soil sampling.”
“Each site was so unique […] The biggest dif- ference was not between different treatments but between different sites,” says Breimer. He adds that useful insights into each test area were found, but those insights became lost once all test data was compiled in aggregate. While he says more research sites and seasons are needed to draw concrete conclusions, Bre- imer believes strip-tillage is a good compro-
▶ FUTURE FARMING |22 May 2020 53
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