Corn Steep Liquor application on pepper plants (Capsicum annum L.) stimulates growth under nitrogen-deficient growing conditions

•Corn Steep Liquor contains metabolites that protect plants from environmental stresses.•Under nitrogen-limited conditions, the use of Corn Steep Liquor improves plant growth.•Corn Steep Liquor via root application improves plant growth more than foliar application. Excessive nitrogen fertilization in crops is causing serious environmental problems related to eutrophication of natural resources such as seas, aquifers, coastal lagoons like the Mar Menor (Spain), etc. Therefore, there is a need to design agronomic strategies that allow plants to be grown below their nutritional requirements, primarily nitrogen. One of these strategies is the use of biostimulants products made from botanical extracts, as they contain active compounds that stimulate certain metabolic processes in plants favoring nitrogen absorption and assimilation. In this experiment, foliar and root application of Corn Steep Liquor (CSL) extract was evaluated at four stages of pepper plant (Capsicum annuum L.) cultivation under different amounts of nitrogen, ranging from 100 % to 25% N. At the end of the experiment parameters of vegetative growth, nitrate, ammonium, total nitrogen concentration in the leaves, amino acid concentration, soluble proteins, and the enzymatic activities of glutamine synthetase and nitrate reductase were measured. The results showed that plants reduced their vegetative growth as nitrogen concentration in the nutrient solution decreased. However, this reduction was less pronounced in plants treated with exogenous CSL in the leaves, improving the efficient use of nitrogen (NUtE and NUE in particular) by increasing nitrogen assimilation (NR and GS enzymatic activities) and the concentration of amino acids and proteins.