The effect of vermicompost-derived humic substances on nutrient status and yield of organic potato in field conditions

Many commercial products containing humic substances (HS) are currently used in commercial crop production worldwide as innovative means for plant nutrition and growth promotion. However, still little work has been done on science based application of HS for vegetable production in soil and climate conditions of temperate zone, especially under organic growth conditions. The aim of the present study was to evaluate the effect of pre-plant (seed-tuber treatment) and foliar application of commercially-produced vermicompost-derived HS preparation on nutrient (N, P, K, Ca, Mg, S, Fe, Mn, Zn, Cu, Mo, B) status and yield of potato in organic farming system. The field experiments were carried out in Stende State Cereals Breeding Institute, Latvia, during the vegetation season of 2012. In general, the effect was highly variable between the nutrients studied, and dependent on timing as well as application methods. The HS induced increases in P and decreases in K and N uptake did not change the optimal till high macronutrient status of potato crop. While positive aspects of different HS application methods were found for Cu, pre-plant and foliar HS tested was hardly effective to prevent micronutrient Zn and B deficiencies. Moreover, HS induced decreases in Zn and Mn concentrations significantly declined nutrient status of potato. Obtained data revealed that pre-plant HS treatment induced a small positive effect on potato yield (109% of control), while no response was stated for foliar application method. Consequently, the results from the present experiments confirmed only limited benefit from HS application in organic field conditions.