Effectiveness of a soy protein hydrolysate on lettuce growth and quality

Background/Introduction

In recent decades, the scientific community, in collaboration with private companies, has proposed some technological innovations to improve the quality of agricultural products and make agriculture more sustainable, leading to a significant reduction in the use of fertilizers. Among these, biostimulants represent a promising innovation in agriculture. Protein hydrolysates are a category of biostimulants obtained through the hydrolysis of protein-rich biomass. Enzymatic hydrolysis, which is based on the use of proteases, is a viable alternative to chemical hydrolysis because it can be performed under mild conditions, avoiding side reactions without decreasing the nutritional value of the protein source.

Goals

The objective of this work is to examine the effects of two soy protein hydrolysates, namely SPH A and SPH B, on lettuce (Lactuca sativa, var. Batavia Canasta green) under no stress and in conditions of reduced NPK nutrition, in terms of both yield and other parameters.

Methodology

Lettuce plants were grown in an experimental greenhouse, under monitored conditions (25 ± 3 °C, 16 h photoperiod). The first group of plants (thesis 1, standard fertilization, 5 replicates) received complete fertilization (100% N). In the second group, mineral fertilization was reduced to 50% N (thesis 2, reduced fertilization, 5 replicates); the third and fourth groups of plants with 50% N fertilization received SPH A and SPH B, respectively. The nutrients used for fertilization were as follows: Ca(NO₃)₂, NH₄NO₃, K₃PO₄ and K₂SO₄. Destructive analyses were performed, such as total fresh biomass, chlorophylls a+b and carotenoids, the phenol index and anthocyanin, nitrate content, and total and reducing sugars.

Results

Significant differences between the control and stress plants were observed in lettuce yield. Moreover, yields obtained after treatments with SPH A and SPH B were slightly higher (+14% and +17%, respectively) with respect to the stress conditions. The results obtained for chlorophyll a+b, carotenoids and total sugar were not statistically significant. However, plants grown under optimal fertilization conditions showed the highest nitrate levels, while stress resulted in a significant drop regardless of whether treatment A or B was applied.

Conclusions

These results confirm that biostimulants cannot fully replace fertilizers but could be helpful in decreasing the quantity of mineral nutrition or aiding in nutrient deficiency. However, to achieve this goal, a thorough investigation is necessary in order to define not only the NPK uptake for each cultivar but also the application time and dose of protein hydrolysate for each crop and the environmental conditions.