Potato producers face two predominant challenges when they pursue organic farming: disease and nutrient management. Both factors are limited by regulations that on the one hand prohibit the use of chemical fertilizers, especially nitrogen and, on the other hand, most synthetic pesticides. Late blight, caused by Phytophthora infestans is commonly thought to be the factor which limits yield the most

According to the USDA’s certified organic survey summary, organic potato production is on the rise in the U.S., with certified organic potato production acreage more than doubling from 8,000 to 17,000 acres between 2008 and 2016, and organic potato sales increasing fivefold, from USD30m to USD150m over the same time period.

Organic potato cultivation requires a whole system perspective, with particular focus on rotation design. Producing organic potatoes relies strongly on indirect, preventive and long-term strategic measures for both plant nutrition and plant protection, according to specialists.

Nutrient Management

Research conducted by the University of Kassel (Germany), shows that in organic farming, nutrient availability in spring and early summer is one of the hardest challenges to overcome, also being one of the principal yield limiting factors. Plant nutrition, therefore, relies on carefully designed rotations including, ideally, 25% or more legumes in the alternation and the addition of organic fertilizers, such as solid and liquid animal manures, green manures (uprooted or sown crop parts left to wither on a field so that they serve as a mulch and soil amendment) and composts.

With the exception of liquid manure, these fertilizers are usually delivered over an extended period of time (slow release type) and highly dependent on the soil moisture and temperature for mineralization processes that make the nutrients available to the plants.

“In potato production, rotations, cover and green manure crops and animal manure are typically used to manage nutrients. Unfortunately, there are strong interactions between the type and timing of nutrient application and several pests and diseases, especially wire-worms and black scurf (caused by Rhizoctonia solani),” explain researchers from Kassel. “While wire-worms are often a problem if the potatoes follow in the rotation after several years of pasture or grass-clover, R. solani is favored by high amounts of raw organic materials from manure or possibly also grass-clover pre-crops under suboptimal climatic conditions,” the researchers add.  Disregarding the negative effects, the Kassel experts found  remarkably positive effects of the use of straw mulch. This is because  straw mulch applications reduced potato virus Y infestation, while at the end of the potato season the straw reduced nitrogen leaching.

You can read the rest of this article in the Autumn Issue of Potato Business Digital magazine, which you can access by clicking here.