Potato Review

30 POTATO REVIEW NOVEMBER/DECEMBER 2020 BIOSTIMULANTS uptake of resources and whether they are subsequently used to develop a better or longer- lasting canopy. If this does not happen, you are unlikely to see a change in yield,” Mark said. Another reason the crop may not be achieving its yield potential is nutrient availability. One of the minerals prone to becoming locked up in the soil is phosphate (P), which can often be present in the soil, but unavailable for uptake because of its tendency to bind with other elements. “Trials have explored whether the application of two biostimulants stimulating mycorrhizal growth were able to increase P uptake,” said Mark. “We found that while both products increased the amount of P in the foliage and tubers, there was no increase in yield.” Calcium (Ca) is another such mineral which can become bound to other elements. Key to cell structure, it is important for tuber quality, also impacting on skin nish and by building thicker skin, helping prevent bruising and invasion by pests. Mark and his team have tested di erent biostimulants which reportedly improve uptake of Ca into the plant. While not producing statistically signi cant results on yield or quality, leaves (but not always tubers) were found to have elevated concentrations of Ca, he notes. Another way in which biostimulants can work is by boosting carbohydrate production in the plant. Colleagues of Mark, Dr Marc Allison and Dr James Fowler, ran trials in 1996 and 1997 to assess the e ects of applying the biostimulant Fulcrum. In order to thoroughly test the product, which reportedly boosts carbohydrate assimilation by the leaf, in one experiment they tested 16 replicates of the product vs the control in the eld. However, they found no signi cant e ects of Fulcrum on canopy coverage, yield, dry matter concentration or size distribution. “Judicious selection of two or three digs in each treatment could produce an apparent increase or decrease in yield. is highlights the need for a well-designed, adequately replicated testing protocol, as limited samples may lead to unreliable and unrealistic results,” said Mark. Bigger rooting, smaller canopies Some biostimulants change the partitioning of biomass in the plant, by stimulating growth to favour one organ over another, explained Mark, adding that the overall biomass of the plant often remains the same. e e cacy of such biostimulants was tested in glasshouse experiments undertaken by Cambridge University Farm. e results showed that a seaweed extract containing cytokinin hormones altered partitioning and resulted in a 19% increase in root mass. However, despite the bigger root mass, the canopy in the seaweed treatment was slightly smaller. As the potato plant is reliant on canopy size to optimise photosynthesis and converting it to dry matter, this could have been a contributory reason for the lack of di erence in yield compared with the control. Optimising radiation use e ciency is another method which may have potential to improve yield, and Mark reports that researchers at the former Scottish Crop Research Institute observed increases in photosynthetic rates following application of one biostimulant. However, the e ects were very temporary and no impact on nal yield was observed. While many of the biostimulants tested in the NIAB CUF trials over the past 30 years had product claims, there have been no signi cant e ects on tuber yield or size distribution to date. “We have also not observed any changes in skin blemishing, rotting, internal defects or fry colour,” said Mark. Furthermore, results of high-yielding (> 100 t/ha), multiple-year trials performed by Mark Pavek’s group at Washington State University on 26 ‘non-traditional production additives’ over 2016-2019 and presented to CUPGRA members on a visit, showed that although there were almost the same number of negative and positive results compared with the control, there was no statistically signi cant e ect of any product on marketable yield (Figure 1). “If crops are stressed, biostimulants may have a small e ect, but it may often be undetectable or di cult to measure,” said Mark. “If crops are stressed, biostimulants may have a small e ect, but it may often be undetectable.” The key driver of potato yield is the expansion and longevity of the green canopy. Partitioning of biomass can mean bigger rooting systems (but smaller canopies). Image by Alexey Hulsov.