The effect of different concentrations of fish-protein hydrolysate liquid on growth and yield of spinach is discussed here. The results of the plant growth parameters are depicted in Table 2. The fresh shoot weight was found to be the highest in T
3 (216.50 g/plant) followed by T
2 (197.95 g/plant) and both the treatments were significant differences from each other. Fan et. al. also reported 1.6 times increase in shoot weight of spinach as the effect of the application of an extract of brown macroalga (
Ascophyllum nodosum)
(Fan et al., 2013). Although T
4 (168.35 g/plant) and T
5 (156.78 g/plant) performed better than the control, they were not significantly different from each other. The lowest fresh shoot weight was observed in control, T
1 (154.00 g/plant).
The fresh root weight was found to be significantly highest in the treatment T
3 (24.18 g/plant) that were followed by T
2 (21.13 g/plant). Similar positive effects of the application of protein hydrolysates on root development were noted in tomatoes
(Colla et al., 2014). There was a significant difference between the shoot weight in T3 (216.50g/plant) and T2 (197.95 g/plant) being highest in T
3 (216.50 g/plant) with a 2ml dose. It is also observed from the study that there was no significant difference in the root weight with the treatments T
1 (18.75 g/plant) and T
4 (16.53 g/plant). The lowest fresh root weight was observed in the treatment of T
5 (15.00 g/plant).
The highest total fresh weight was observed T
3 (240.68 g/plant) followed by T
2 (218.88 g/plant). There was a significant difference in the sample with treatments T
1 (172.75 g/plant), T
4 (184.88 g/plant) and T
5 (171.78 g/plant). The lowest total fresh weight was recorded in the treatment of T
5 (15.00 g/plant).
The above observations signify that treatment T
3 performed superior over all other treatments. According to one of the reports, the maximum benefits were reported at very low dosages
(Ertani et al., 2014). The study also reveals that plant growth parameters increasing with the concentration from 0.5 ml dosage to 2.0 ml and then further increase in the concentration decreases the plant growth parameters. In some parameters, it was observed that the highest dosage (10.0 ml dosage) underperformed as compared to control and it might have had a deleterious effect on the plant.
Effect on shoot weight (yield)
The average fresh shoot weight of the control group was 154g. When the control was compared with treatment groups (Fig 1) in all the cases there is a positive effect of the application of FPH on spinach yield except the highest dose of 10 ml per lit per plant. Dose proportionality, i.e. increase in the yield with an increase in the dose, was observed in the case of 0.5 ml and 2.0 ml doses. When the dose was enhanced from 2.0 ml to 5.0 ml, rather than increase, the decrease in the yield was observed, however, the yield (168.35 g) was more than the yield observed in the control-set. Recently many studies have reported the increase in yield with the use of organic inputs. One of such interesting study noted enhancement of yield and grain quality of winter wheat with applications of amino acid-based biostimulants
(Popko et al., 2018). Another study showed an increase in the yield of greenhouse spinach by the application of plant and seaweed-based biostimulants
(Rouphael et al., 2018). Also, protein hydrolysate-based biostimulant boosted the yield and nitrogen use efficiency in greenhouse spinach
(Carillo et al., 2019). The increases in growth, leaf mineral composition, yield and fruit quality were reported in two greenhouse tomato cultivars as a result of foliar applications of legume-derived protein hydrolysate
(Rouphael et al., 2017). In our study, a further increase in the dose to 10 ml resulted in bringing down the yield (156.78g) almost equal to the control group (154.00g). Thus, in the case of a 10 ml dose, the effect of the application of biostimulant FPH was not visible when compared to the control yield. Overall, it is concluded from these results that higher doses of 5 ml and 10 ml do not result in the dose-proportional increase in yield. The optimal dose at which the highest yield was obtained is 2 ml per lit. The percent increase in the yield (shoot weight) was calculated taking the yield of the control group (154.00g) as a base. The formula used to calculate the percent increase in the yield was: Percent increase in yield with specific dose = [(Yield obtained with respective dose - Yield obtained in the control set)/ Yield obtained in the control set] *100. The percent increase has been tabulated in the Table 3. It was observed that the application of 0.5 ml dose resulted in 28.4% and in the case of 2 ml dose the yield increased to the tune of 40.6%. This increase in yield of 40.6% was the highest among all concentrations tested. In the case of a 5.0 ml dose, the percent increase in yield observed was 9.3%. This implies that when the dose was increased 2.5 times from 2ml to 5 ml, it did not result in increase in yield but contrarily resulted in drop in the yield. When compared to 2 ml dose, the yield obtained from 5 ml dose was about 77% less. In the case of the highest dose of 10 ml the yield obtained was almost similar to what was observed for the control. There was no significant increase in the yield. It can be concluded from the yields obtained from the two higher doses of 5 ml and 10 ml that use of optimal quantity of FPH is very crucial to obtain desired results. The excess use of FPH results in an adverse effect on growth. This can be further looked into details when we correlate the growth of roots with different doses (Fig 3).
Effect on the root growth and correlation with yield
Healthy roots are very important for the healthy growth of the plants. There are several reports available highlighting the role of protein hydrolysate in enhancing shoot and root biomass and productivity
(Lisiecka et al., 2011; Paradiković et al., 2011; Colla et al., 2014; Nardi et al., 2016; Ertani et al., 2018). In this study, we uprooted the plants very carefully so that roots will not be cut or lost during the uprooting process. Then separated roots (Fig 5) from the shoot and noted down the weight and depth (length, not reported here) of the fresh-roots. The weights of the fresh-roots ranged from 15g to 24.18g (Fig 2). In the control group, a fresh-root weight of 18.75g was observed and it increased in the case of application of 0.5ml and 2.0 ml dose respectively to 21.13g and 24.18g. However, the doses of 5 ml and 10 ml did not impact the growth of roots positively. In both cases of 5 ml and 10 ml resulted in a slight decrease in the fresh-root weights respectively to 16.53g and 15.00gm compared to the control group (18.75 g). To correlate the effect of root growth on the overall yield of spinach. The percent change in root weight with respect to control using a formula similar to that used for calculating percent change in yield was calculated.
To correlate root weight and yield, Fig 3 depicted both the percent change in root weight and yield. This correlation (Fig 3) revealed that the highest percent increase in the yield (2.0ml dose; 40.6% increase) was observed where the root-weight was highest (24.18g). Also, an increase of 28.4% yield in the case of 0.5 ml dose was associated with a 12.7% increase in root-weight as compared to control. Furthermore, this study of correlating root growth with yield revealed that one of the reasons for the decrease in yield with the increase of the doses to 5 ml and 10 ml was because of the adverse effect of these higher doses on the root growth. In both cases of 5 ml and 10 ml root weights observed, respectively 16.53g and 15.00 g, were less than the root weight of control (18.75g). When viewed as a percent change in root weights, 5.0 ml and 10 ml dose exhibited respectively 11.9% and 20% lower weights with respect to control. Despite the lowering of root weight, the dose of 5.0 ml was able to maintain an increase in the yield to the tune of 9.3%. However, in the case of the highest dose,10 ml, the beneficial effect of FPH was not observed on the yield and the adverse effect on root growth was further profound. Similar phytotoxic and growth retarding effects were also reported in the case of repeated application of animal-derived protein hydrolysate (
Cerdán et al., 2009;
Lisiecka et al., 2011). Additionally, leaf chlorosis in basil was observed by foliar spray of animal-derived protein-hydrolysate at several trials carried out at the University of Tuscia-Italy
(Colla et al., 2014). This reveals that optimal dose is important to attain full benefits of the application of biostimulants. The excessive dose may lead to retarded growth of roots and thus will not benefit plants for maintaining healthy growth. Visual observations in the research also revealed that the leaf size of the plants in 0.5 ml and 2 ml dose were bigger than that of the other doses.