Effects of Effective Microorganisms Combined With Organic and Inorganic Fertilizers on the Mineral Composition and Biochemical Quality of Onion (Allium cepa L.) and Spinach (Spinacia oleracea L.)

Abstract

Background and objectives: Effective microorganisms (EM) are promoted as a way of improving the efficiency of organic nutrient sources, but their effect on the nutritional quality of vegetables under different organic–inorganic fertilizer regimes is not well established. We tested the hypothesis that the response to EM depends on fertilizer source and rate, and compared fertilizer combinations, with and without EM, for their effects on the mineral composition and biochemical quality of onion (Allium cepa L.) and spinach (Spinacia oleracea L.).

Methods: Five pot-culture trials were conducted at Gomal University, Dera Ismail Khan, Pakistan, in 2009-10 and 2010-11, each as a completely randomized design with a split-plot arrangement (EM, applied or not, as the main factor; fertilizer treatment as the sub-factor) and three replications. The untreated control (T0) received no EM and was shared by both EM levels, so the EM effect and the EM × fertilizer interaction were tested on the fertilized treatments only. Trial I compared sole organic manure or NPK; Trials II–V combined organic manure at 100% or 50% of the recommended dose with NPK at 100% or 50%, using farmyard manure, pressmud, compost and poultry manure. Macronutrients (Na, Ca, Mg, N, P, K), micronutrients (Zn, Fe, Cu, Cr, Mn, Ni), dietary fiber, vitamin C, and crude protein (total N × 6.25) were determined in spinach leaves and onion bulbs, and data were analysed by ANOVA with LSD comparisons at p < 0.05.

Results: Fertilizer treatment affected (LSD, p < 0.05) the mineral composition and biochemical quality of onion and spinach, whereas the EM effect and EM × fertilizer interaction varied among traits and trials and are interpreted as trends. Pressmud generally gave the highest concentrations of minerals, dietary fiber, vitamin C, and crude protein, and EM generally increased them further, although the EM benefit varied among trials and traits. In spinach (Trial I, 2010-11), pressmud with EM increased N, P and K by up to 70, 29 and 23% and dietary fiber, vitamin C and crude protein by up to 71, 65 and 60%, respectively, over the untreated control. Relative increases in onion were larger (crude protein almost eleven-fold) because baseline values in unfertilized bulbs were very low. Farmyard manure, compost and poultry manure gave smaller improvements.

Conclusions: Pressmud combined with NPK and EM warrants further evaluation as a strategy for improving the nutritional quality of spinach and onion. These data do not by themselves establish synergy between EM and fertilizer or any saving of fertilizer. Increases in sodium, chromium and nickel concentrations are not necessarily nutritional benefits and require food-safety assessment. Even on a dry-weight basis, onion Cr and Ni concentrations were well below the FAO/WHO guideline values commonly cited for vegetables (2.3 and 5.0 mg kg⁻¹), whereas the dietary significance of the higher sodium requires fresh-weight, portion-based assessment.

Limitations: The results come from pot experiments with a single soil at one location and need validation under field conditions; microbial activity, soil properties, yield, and economics were not assessed. ANOVA summary statistics are not reported.