Potato Review

www.potatoreview.com POTATO REVIEW JANUARY/FEBRUARY 2021 15 COVER CROPPING the rhizosphere of brassicas facilitate glucosinolate hydrolysis. Oil radish can be ailed or grazed o by sheep ahead of potato planting in March/ April and do not require incorporation, which provides a long window for low doses of isothiocyanates to interact with PCN, reducing viability. Maximum e cacy for PCN reduction in this window has been found to be lower at between c.10–30%. A preliminary consideration that needs to be taken into account is the species and variety of biofumigant used. More information is needed, as there is currently no impartial database of the biocidal isothiocyanate or clubroot pro le of a plethora of commercial varieties marketed as biofumigants. It is known that preference should be given to those that produce high quantities of glucosinolates such as sinigrin, gluconasturtiin and glucotropaeolin. Making the wrong choice of cover crop can increase population density of plant parasitic nematodes. Pratylenchus nematodes in particular can build rapidly when green manures are applied, unless one is used with proven biofumigant properties. A well-documented nematode-fungus disease complex is the interaction between Pratylenchus spp. and VerticilliumWilt (Verticillium dahlia) resulting in Potato Early Dying that causes signi cant reduction in tuber size and yield. Soil structure For many growers, one of the reasons to grow cover crops – sometimes known as green manures - is to help build soil organic matter. In healthy soils, relatively low nitrogen levels limit microbes’ ability to utilise carbon compounds, so they excrete them as polymers which act as a kind of ‘glue’ - creating a porous, interconnected structure in the soil. Over time this increases the volume and connectivity of pore structures, improving the supply of oxygen to micro-organisms, connecting water and nutrient pools to plant roots. A highly cultivated soil is likely to have reduce aggregate structure, which means the soils disperse readily and can take many months to recover from any punishment they receive. With regular amendments of soil organic matter there is a more extensive network of pores which allow for greater circulation of air, nutrients and retention of water. Furthermore, the carbon within aggregates is protected from oxidation. Increased fresh organic matter with green manures can increase soil borne rhizoctonia solani. is emphasises the importance of thinking through what you are trying to achieve. If you are looking to improve soil structure, additions of amendments such as FYM or cover crops are good, but you have to consider other potential unintended consequences. Cash crops may benefit from nutrient capture When best practice is used to get the most from cover crops, they act as cost-saving sinks, retaining nitrogen and phosphate in the eld which would otherwise be lost via leaching or soil erosion over winter. In terms of phosphate, the roots of buckwheat exude substances which help to solubilise phosphate that may otherwise be unavailable and have also been found to have a high storage capacity for inorganic phosphate. erefore, when buckwheat is incorporated into the soil it decays quickly, making phosphate, and other nutrients, more available to the succeeding crop. Creating the foundations for harvests to come Cover cropping does demand a di erent way of thinking, but we are seeing greater uptake among our members alongside a regenerative and sustainable approach to all management practices. Potatoes are particularly intrusive to the soil but adopting a whole systems approach and savvy cropping can maximise nancial returns, as well as creating the foundation for harvests to come. “Potatoes are particularly intrusive to the soil but adopting a whole systems approach and savvy cropping can maximise financial returns.”