Foliar Application of Protein Hydrolysates on Baby-Leaf Spinach Grown at Different N Levels

Surpluses of N are associated with environmental and health problems. To optimise N use and reduce nitrate accumulation in leafy species like spinach, the application of biostimulants is suggested. An experiment in controlled conditions (growth chamber/soilless) evaluated baby-spinach responses to two protein hydrolysates (PHs) from plant (legume, Trainer(R)) and animal (meat, Isabion(R)) sources, combined with three N rates: 2 (N2, deficient), 8 (N8, sub-optimal), and 14 (N14, optimal) mM of N. Biometrical and morphological traits of shoots and roots as well as the physio-metabolic (gas exchange, N assimilation, and NUtE), physical, mineral, and antioxidant profiles of leaves were assessed. The legume-PH boosts growth and yield only at the highest N conditions, while there was no effect at lower N rates. The legume-PH modulates root architecture and chlorophylls has positive responses only at optimal N availability, such as an increase in N uptake, leaf expansion, and photosynthetic activity at the canopy level. The PHs do not improve NUtE, leaf colour, consistency, cations, or antioxidants. Neither do PHs have any effect on reducing nitrate accumulation. Legume-PH improves N assimilation only at optimal N availability, while meat-PH does not, reaching the highest nitrate value at the highest N rate (2677 mg kg(-1) fw), even if this value is under the EC limits for fresh spinach.

Automated summary

This study investigated the effects of protein hydrolysates from different sources on the growth and nutritional characteristics of spinach at different nitrogen levels. The results showed that protein hydrolysates from plant sources only had a promoting effect at the highest nitrogen level, while protein hydrolysates from animal sources not only had no promoting effect, but also led to nitrate accumulation.