Molasses-based waste water irrigation: a friend or foe for carrot (Daucus carota L.) growth, yield and nutritional quality

Abstract

Management of molasses-based wastewater generated in yeast and sugar industries is a major environmental concern due to its high chemical oxygen demand and other recalcitrant substances. Several strategies have been used to reduce the inland discharge of wastewater but the results are not satisfactory due to high operating cost. However, reuse of molasses-based wastewater irrigation in agriculture has been a major interest nowadays to reduce the freshwater consumption. Thus, it is crucial to monitor the impacts of molasses-based waste water irrigation on growth, metabolism, yield and nutritional quality of crops for safer consumer's health. In present study, carrot seeds of a local cultivar (T-29) were germinated on filter paper in Petri dishes under controlled conditions. The germinated seeds were then transplanted into pots and irrigated with three different treatments normal water (T0), diluted molasses-based wastewater (T1), and untreated molasses-based wastewater (T2), in six replicates. Results revealed that carrot irrigated with untreated molasses-based waste water had exhibited significant reductions in growth, yield, physiology, metabolism, and nutritional contents. Additionally, accumulation of Cd and Pb contents in carrot roots irrigated with untreated molasses-based waste water exceed the permissible limits suggested by WHO and their consumption may cause health risks. While, diluted molasses-based waste water irrigation positively enhanced the growth, yield of carrot plants without affecting the nutritional quality. This strategy is cost effective, appeared as most appropriate alternative mean to reduce the freshwater consumption in water deficit regions of the world.

Keywords: Carrot cultivation; Waste water remediation; Water scarcity.

Fig. 1

Classified filled barplots (a) seed germination (%), (b), seedling emergence (%), (c) leaf length (cm), (d) number of leaves per plant, (e) plant fresh biomass, (f) plant dry biomass, (g) root length (cm), (h) root diameter (mm²), and (i) root weight (g) carrot cultivar T-29. The three irrigation treatments from T₀ to T₂ represented by different color filled violins. One-way ANOVA calculated significant differences, followed by LSD test based lettering are also presented, where same letter did not vary significantly. Each barplot is presenting mean value and error bar represents standard error of six replicates

Fig. 2

Classified filled barplots (a) total soluble sugars, (b) reducing sugars, (c) non-reducing sugars, (d) total soluble proteins, and (e) total free amino acids in leaves of carrot cultivar T-29. The three irrigation treatments from T₀ to T₂ represented by different color filled violins. One-way ANOVA calculated significant differences, followed by LSD test based lettering are also presented, where same letter did not vary significantly. Each barplot is presenting mean value and error bar represents standard error of six replicates

Fig. 3

Classified filled barplots of activity of stress responsive enzymes (a) POX, (b) PAL, (c) SOD, (d) CAT, (e) nitrate reductase, (f) nitrite reductase in leaves of carrot cultivar T-29. The three irrigation treatments from T₀ to T₂ represented by different color filled violins. One-way ANOVA calculated significant differences, followed by LSD test based lettering are also presented, where same letter did not vary significantly. Each barplot is presenting mean value and error bar represents standard error of six replicates

Fig. 4

Classified filled barplots of physical parameters of carrot juice (a) volume, (b) viscosity, (c) torque, (d) pH, (e) TSS: total soluble solids, (f) dietary fibers. The three irrigation treatments from T₀ to T₂ represented by different color filled violins. One-way ANOVA calculated significant differences, followed by LSD test based lettering are also presented, where same letter did not vary significantly. Each barplot is presenting mean value and error bar represents standard error of six replicates

Fig. 5

Classified filled violin plots (a) moisture content, (b) crude proteins, (c) crude fat, (d) crude carbohydrates, (e) crude fibers, (f) total ash contents in leaves of carrot cultivar T-29. The three irrigation treatments from T₀ to T₂ represented by different color filled violins. Each violin is delimited 25th and 75th percentile and mean of 5 to 7 seedlings from six replicates represented by dots. One way ANOVA calculated significant differences among the treatment represented with *** (P < 0.0001), ** (P < 0.001), * (P < 0.05), and ns: non-significant (P > 0.05) notations

Fig. 6

Pearson’s correlation coefficients among 49 pairs of response variables of carrot cultivar treated with different irrigation treatments

Fig. 7

Biplot of principal components analysis of 3 irrigation treatments and 49 response variables of carrot cultivar T-29

Fig. 8

Cluster based heatmap of three irrigation treatments and 49 response variables of carrot cultivar (T-29)