Studies of the availability of soil phosphorus (P) and potassium (K) in organic farming systems, and of plant adaptations to low P- and K-availability
TLDR Organic farms need to supplement phosphorus and potassium to maintain soil health and crop yields.
In organic farming systems, nutrient purchase restrictions often led to negative nutrient budgets, particularly in low animal density areas, as observed in five organic dairy farms in Southern Norway. These farms experienced a decrease in ammonium-acetate lactate (AL) soluble phosphorus (P) over time, necessitating future P supplementation. Although potassium (K) levels did not show a similar decrease, many areas had low K concentrations, indicating a need for K supplementation as well. The use of plant material as mulch increased vegetable and grain yields, but only 15-20% of the nutrients in the mulch were recovered by crops, with significant nitrogen losses. Plant adaptations to low P, such as changes in root traits, were studied, but these adaptations were deemed of limited practical significance in Nordic agricultural soils. The study highlighted the importance of developing nutrient supplies that meet organic standards and the need for organic farmers to minimize nutrient losses.