Yield and quality responses of Ivory Russet and Russet Burbank potatoes to P rate, banded P application, soil fumigation, and mycorrhizal inoculation in high-P soils.
Start Date: 2020
Principal Investigators: Carl Rosen, James Crants, and Matt McNearney
Organization: University of Minnesota
Potato yield responses to phosphorus (P) fertilizer rare often positive even in soils with high soil-test P concentrations. For example, in soils with Bray P concentrations over 50 ppm, when yields of 400 cwt·ac-1 or higher are desired, the University of Minnesota Extension recommended rate of P fertilization is 75 lbs·ac-1 P2O5, and it is noted that responses in acidic, irrigated soils have been observed at application rates as high as 150 lbs·ac-1 P2O5.
Positive potato yield responses to differences in P rate even in high-P soils and at high application rates suggest that potato plants are not efficient at taking up soil P. Potatoes have relatively shallow root systems, rarely extending much below two feet into the soil, limiting the volume of soil from which they are able to acquire P. In addition, potatoes tend not to form extensive mycorrhizal associations, especially following fumigation, limiting how thoroughly they exploit P resources in the soil within the range of their root systems.
Both root system extent and success in forming mycorrhizal associations may be greatly affected by potato plant genetics. Different cultivars may therefore show different yield responses to P rate. In a P response study conducted at the Sand Plain Research Farm in Becker, MN, in 2019, the Ivory Russet showed a positive yield response at application rates between 125 and 250 lbs·ac-1 P2O5 in soil where Bray P concentration ranged from 64 to 78 ppm. In a separate study in the same facility in the same year, Russet Burbank showed no yield response to P rate at rates of 0 or 80 lbs·ac-1 P2O5 in soil with 28 to 31 ppm Bray P. As a determinate cultivar, Ivory Russet may have a less extensive root system than indeterminate Russet Burbank, and there may also be differences between the two cultivars in terms of their efficiency at forming mycorrhizal associations.
If mycorrhizal associations affect P use efficiency, it is plausible that soil fumigation, which is frequently used to control soil-borne pathogens, including fungal pathogens such as Verticillium, has a negative effect on potato P use efficiency. If so, this negative effect may be partially or fully compensated for by applying mycorrhizal products to potato fields at planting. Alternatively, if potato P uptake is limited more by the extensiveness of potato root systems than by their effectiveness at absorbing P within range of their root and mycorrhizal networks, P uptake efficiency might be improved by placing P closer to the plants through banded application.
Finally, it is possible that Bray P alone is not the best indicator of potato P response in acid soils. Research in Eastern Canada has found that the P saturation index (PSI), the ratio of Melich-3 extractable P to Melich-3 extractable aluminum (Al), may be a better predictor.
The objectives of this study were to evaluate how potato yield responses to P rate are affected by (1) cultivar, (2) soil fumigation with metam sodium, (3) applying a mycorrhizal product at planting, and (4) banded versus broadcast application of P fertilizer, and (5) to evaluate PSI, Bray P, and Mehlich-3 P as predictors of potato yield response to P.