Tomato growth, nutrient dynamics and yield in response to a fermented grass-based liquid fertilizer in peat-based substrate
University of Latvia, Faculty of Medicine and Life Sciences, Institute of Biology,
4, O. Vaciesa street, Riga, LV−1004, Latvia
*Correspondence: andis.karlsons@lu.lv
Abstract:
Sustainable horticultural production increasingly relies on renewable nutrient sources in order to reduce the use of conventional mineral fertilizers. Fermented grass biomass can be used to produce liquid fertilizers suitable for greenhouse tomato cultivation; however, their effects on nutrient availability and crop performance in peat-based substrates are still insufficiently understood. The aim of this study was to evaluate the effects of a grass-derived liquid fertilizer, applied at increasing rates, in comparison with conventional mineral fertilization on plant growth, nutrient dynamics and yield of tomato (Solanum lycopersicum L., cv. ‘Betalux’). The experiment included a conventional mineral fertilization control and four liquid fertilizer treatments (T1–T4). Nutrient concentrations in the substrate and plant leaves were monitored throughout the growing season, together with yield parameters and the SPAD chlorophyll index. Conventional fertilization resulted in the highest total yield (1545.6 g plant⁻¹), fruit number (40 fruits plant⁻¹) and a stable nutrient status. Among the liquid fertilizer treatments, T3 performed best, producing 1,224.4 g plant⁻¹ and 35.3 fruits plant⁻¹, corresponding to a 21% yield reduction compared with the mineral control, while mean fruit weight was only moderately lower. Lower application rates (T1 and T2) resulted in progressive depletion of nitrogen, phosphorus, calcium, magnesium, iron and boron in plant tissues and led to 25–27% lower yields. In contrast, excessive application of liquid fertilizer (T4) caused substrate acidification and elevated electrical conductivity, resulting in salt accumulation, impaired nutrient uptake and the lowest yield (798.1 g plant⁻¹), despite producing the largest fruits (42.85 ± 2.06 g). Molybdenum uptake was strongly influenced by substrate pH rather than by total Mo content, whereas zinc, copper and manganese concentrations remained relatively stable. Overall, the results indicate that grass-derived liquid fertilizers can support tomato nutrition in peat-based systems only within a limited application range. Careful dose management or partial supplementation is required to avoid nutrient deficiencies at low application rates and salinity-induced yield losses at excessive rates.
Key words:
greenhouse cultivation, nutrient uptake, organic fertilization, SPAD index, tomato yield