The use of biostimulants is becoming a useful tool for increasing crop productivity while enhancing nutritional quality. However, new studies are necessary to confirm that the joint application of different types of biostimulants, together with bioactive compounds, is effective and not harmful to plants. This study examined the impact of applying the biostimulant Green Leaves, comprising Macrocystis algae extract and containing a mixture of amino acids, corn steep liquor extract, calcium, and the bioactive compound glycine betaine. The effect of applying two different doses (3 and 5 mL L⁻¹) of this biostimulant was evaluated on lettuce plants, and growth and quality parameters were analyzed along with photosynthetic efficiency, nutritional status, and nutrient efficiency parameters. The application of Green Leaves improved plant weight (25%) and leaf area and enhanced the photosynthetic rate, the accumulation of soluble sugars and proteins, and the agronomic efficiency of all essential nutrients. The 3 mL L⁻¹ dose improved the nutritional quality of lettuce plants, improving the concentration of phenolic compounds and ascorbate and the antioxidant capacity and reducing NO₃⁻ accumulation. The 5 mL L⁻¹ dose improved the absorption of most nutrients, especially N, which reduced the need for fertilizers, thus reducing costs and environmental impact. In short, the Green Leaves product has been identified as a useful product for obtaining higher yield and better quality.

The industrial washing of corn grain during its milling generates a residue known as “corn steep liquor (CSL)”. This residue is rich in amino acids, carbohydrates, vitamins, and mineral nutrients that can stimulate the vegetative growth when applied to plants. However, the mode of action of this product is not yet known. This work involved the foliar and root application to pepper plants, at a dose of 5 mL L⁻¹, of two CSL products (CSL-H and CSL-B), which differ in the way they have been stabilized. In both cases, the size of the plants was increased, root application being more efficient than foliar. According to the studies carried out, this was because the CSL products increased the synthesis of hormones related to cell division and elongation, the net assimilation rate of CO₂, and the concentrations of the amino acids alanine, proline, and tryptophan. In addition, root application of CSL-H also increased the concentrations of arginine, isoleucine, leucine, and cysteine. These data suggest that the mode of action of these products is related to regulation, synthesis of hormones, and the stimulation of carbon and nitrogen metabolism, the CSL-H treatment being the one that produced the most changes in the amino acids analyzed.

Biostimulants are substances or microorganisms that are applied to plants, soil, or seeds, to improve the growth, development, performance, and quality of crops. Their application is mainly directed towards improving the resistance of crops against abiotic and biotic stresses. These compounds are formulated from a great variety of compounds: humic substances, complex organic materials (sewage sludge extracts, composts, and manure), chemical elements (Al, Co, Na, Se, and Si), inorganic salts including phosphite, seaweed extracts (brown, red, and green), amino acids, etc. As of today, it has been observed that corn steep liquor (CSL), which is obtained from the industrial process of corn transformation, may be a good ingredient for the formulation of biostimulant products. CSL contains a large amount of different chemical compounds with biological activity for the plants and soil. The use of CSL industrial waste, previously formulated, could have a direct or indirect effect on the physiological processes and metabolic routes of plants related to the adaptation to abiotic and biotic stresses, as their compounds are part of these metabolic pathways, act as elicitor compounds, and/or have their own biological activity in the plants. There is evidence that the application of CSL could protect plants from specific abiotic and biotic stresses, such as an excess of light or temperature, nutritional limitations, salinity, drought, or pathogens. In addition, it can improve the growth of the plant when these are grown in hydroponic systems, and can improve the health of soils. The present article is focused on describing the most relevant scientific aspects of CSL when used as an ingredient to formulate biostimulants for agriculture. It will discuss its chemical composition, the analytical techniques utilized to elucidate and quantify its compounds, its uses in agriculture, and mode of action in the plants.

Salinity, caused by irrigation with water containing high salt concentrations, excessive fertilization, or the loss of leaching capacity in some soils, is a serious problem on a global scale. Its incidence leads to osmotic and specific effects, as well as an imbalance in nutrient uptake that hinders the growth of most crops. Biostimulants can improve salt tolerance by reducing the uptake and accumulation of toxic ions. Corn steep liquor (CSL) is a byproduct of corn cleaning and maceration. This study investigates whether CSL application induces adaptive responses in pepper (Capsicum annuum L.) plants cultivated under saline conditions. Four treatments were carried out with pepper plants in a culture chamber: irrigation with Hoagland nutrient solution; irrigation with 100 mM NaCl in the Hoagland nutrient solution; irrigation with 100 mM NaCl in the Hoagland nutrient solution and the foliar application of CSL at 5 mL L⁻¹ every 7 days; and irrigation with 100 mM NaCl in the Hoagland nutrient solution and root application of CSL at 5 mL L⁻¹ every 7 days. The beneficial effect of CSL in reducing the phytotoxicity of salt stress was found to be due to an improvement in the photosynthetic efficiency and a reduction in the generation of reactive oxygen species. Thus, the increase in MDA concentration due to saline treatment is less when applying CSL, which is 3.5 times less when it is performed via the foliar route and 4.6 times if the treatment is on the root. The results show that CSL application increased the aerial biomass and leaf area under saline conditions through physiological mechanisms that varied depending on the application method.

Use of biostimulants for stimulating plant growth and mitigating the negative impacts of biotic and abiotic stresses is a promising strategy to achieve higher crop yields. Fungicides such as azoxystrobin are used to control several pests and fungal diseases in plants but at the cost of altering various physiological processes; thereby, leading to reduced crop yields. The efficiency of the compound RAZORMIN^® as a biostimulant product while taking into account its role in plant growth stimulation and fungicide azoxystrobin stress mitigation was evaluated in this study. The efficacy of RAZORMIN^® was assessed considering its impact on the stimulation of growth-related physiological processes and stress mitigation mechanism, e.g., reactive oxygen species (ROS) detoxification. Application of RAZORMIN^® significantly increased plant growth by improving fresh weight, photosynthetic efficiency, net photosynthesis rate, gas exchange, nitrogen (N) metabolism (with increases in soluble amino acids, foliar N concentration, and N use efficiency), growth hormone concentrations (mainly gibberellins and cytokinins), nutritional status of plants (producing a greater accumulation of phosphorus, potassium, calcium, magnesium, sulfur, zinc, molybdenum, iron, and boron), and sugars concentration. Furthermore, the application of RAZORMIN^® on plants under fungicide azoxystrobin stress demonstrated its anti-stress and protective role by stimulating the antioxidant defense system and improving photosynthetic efficiency.

Sunburn is an important issue affecting the yield of many crops, mainly in arid and semi-arid regions. Excessive solar radiation and high temperatures can reduce growth and cause leaf chlorosis, oxidative stress, and photosynthesis impairment. It is thus necessary to develop agricultural techniques to protect plants in a cost-effective and reproducible manner. A potential method is through the spray of protective compounds based on particulate films, such as those based on kaolin. The objective of this study is to evaluate the effects of spraying the protective product Archer^® Eclipse, created by Atlántica Agrícola S.A. (Alicante, Spain), on sunburn damage in a sensitive species such as the cucumber plants (Cucumis sativus L.). To evaluate the effects of sunburn on the plants, parameters related to biomass, leaf temperature, photosynthesis, and oxidative stress were analysed. Plants sprayed with Archer^® Eclipse showed fewer sunburn symptoms and obtained 43% more shoot biomass than those that were not treated. In addition, plants sprayed with Archer^® Eclipse showed 3 °C lower leaf temperatures, higher photosynthesis performance, 88% more water use efficiency, and 21% more chlorophyll concentration. Finally, plants treated with Archer^® Eclipse presented 6% less accumulations of carotenoids and 67% less total phenols, but lower oxidative stress indicators. In conclusion, this study confirms the efficiency of Archer^® Eclipse in protecting a sensitive vegetable plant such as the cucumber from sunburn-inducing conditions.