Soybean, cotton, and maize are essential crops in tropical agriculture due to their economic significance, agronomic adaptability, and contribution to sustainable farming systems (Momesso et al., 2022). Soybean serves as a primary protein and oil source, cotton thrives in warm climates with high drought tolerance, and maize is vital for food security and crop rotation (Viveiros et al., 2024). Foliar application of nutrients and biostimulants enhances crop performance by improving nutrient assimilation, particularly under restricted root absorption (Moreira et al., 2022). The integration of foliar spraying with nutrients, biostimulants, and other agrochemicals in these crops has been shown to enhance physiological responses, mitigate stress-induced yield losses, and improve overall crop productivity (Rodrigues et al., 2021a). Given their extensive cultivation and contribution to global agricultural output, optimizing foliar application strategies supports sustainable intensification, ensuring greater resilience and efficiency in tropical agroecosystems (Momesso et al., 2019).

Weeds compete with crops both nutritionally and physically (Priess et al., 2020). Herbicides are the easy-to-apply and cost-effective form of weeds control (Tataridas et al., 2022; Ofosu et al., 2023), its improper use can cause environmental contamination and toxicity to humans and non-target plants (Mehdizadeh et al., 2021; Van Bruggen et al., 2021). Moreover, the repeated use of or reliance on herbicides with a single mode of action can lead to the selection of resistant weed species, which are more difficult to control and require the use of higher doses or alternative herbicides, worsening environmental and health risks (Gupta, 2018; Song et al., 2020). The use of herbicides is further complicated by the potential for drift, which is influenced by wind speed, temperature, and relative humidity (Langaro et al., 2017). If adjacent crops are not tolerant to the applied herbicide, contact with the product due to drift may result in phytotoxic stress (Hand et al., 2021).

Carfentrazone-ethyl is a contact herbicide that inhibits protoporphyrinogen oxidase (PPOX), an enzyme responsible for converting protoporphyrinogen IX into the chlorophyll precursor protoporphyrin IX in the chloroplast (Sherman et al., 1991; Bertucci et al., 2019). Its inhibition leads to the accumulation of protoporphyrinogen IX, which diffuses into the cytoplasm and undergoes nonenzymatic oxidation to protoporphyrin IX, disrupting cellular function (Dayan et al., 1997). In the presence of light, cytoplasmic protoporphyrin IX forms singlet oxygen (¹O₂), initiating the process of lipid peroxidation (Moretti et al., 2021). Within two days of carfentrazone-ethyl exposure, protein and lipid oxidation lead to the loss of chlorophyll and carotenoids, as well as membrane rupture. The most affected lipids are phospholipids, which form the lipid bilayer of cellular membranes, particularly in chloroplasts, where photosynthesis takes place. Among the oxidized proteins, key components of the photosynthetic apparatus are affected, including proteins from the photosystem II complex (Farooq et al., 2013, 2019). Contact herbicides such as carfentrazone-ethyl applied to weeds that have emerged before soybean, maize and cotton crops planting or applied in a targeted manner after crops emergence. This latter usage raises the possibility of phytotoxicity induction due to drift (Li et al., 2022; Sahu et al., 2023).

Phytotoxicity can increase the crops production of reactive oxygen species (ROS), such as superoxide anion (O₂ ^-), hydrogen peroxide (H₂O₂), hydroxyl radical (OH^-), and ¹O₂ (Farmer and Mueller, 2013). ROS production is a normal part of plant development, but excess ROS production under stress conditions disrupts the redox balance that regulates the plant’s defense system, leading to oxidative stress (Farooq et al., 2019; Silva et al., 2020). The defense system of plants includes both enzymes, such as superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX), and non-enzymatic molecules, including ascorbic acid, vitamin E, flavonoids, proline, and glutathione (Davar et al., 2013). All of these molecules require the presence of nutrients that directly participate in plant metabolism and membrane integrity (Adrees et al., 2015).

Nitrogen (N) and phosphorus (P) are essential macronutrients that support plant growth, metabolism, and stress tolerance by contributing to energy transfer, photosynthesis, and protein synthesis. Their availability is critical under stress conditions, as they activate the antioxidant defense system to mitigate oxidative damage from ROS (Moreira et al., 2016, 2017, 2018). Plants with an adequate nutrient supply tend to have greater stress tolerance (Marschner, 2012). Although crops can obtain nutrients from soil, that may be a necessary supplement during periods of high nutrient demand (Fernández and Brown, 2013). Foliar application provides a faster response than soil application because nutrients taken up by leaves directly enter metabolic processes (Oliveira et al., 2022). The foliar application of nutrients to plants in the vegetative stage can help protect the photosynthetic system and activate plant antioxidant defense systems, thereby reducing symptoms of stress (Reid et al., 1997; Taiz et al., 2017). However, nutrient absorption and, consequently, the efficiency of foliar application vary according to the nutrient, plant, environment, and the specific product applied (Fernández and Brown, 2013).

The objective of this study was to evaluate the efficacy of foliar application of soluble monoammonium phosphate (MAP) in mitigating herbicide-induced oxidative stress in soybean, maize, and cotton crops. Specifically, we evaluated the effects of MAP supplementation on physiological and biochemical parameters such as chlorophyll content, photosynthetic enzyme activity, antioxidant metabolism, and oxidative stress indicators to determine whether this practice can enhance crops productivity by reducing the phytotoxic effects of the herbicide carfentrazone-ethyl.

Crop productivity and grain and fiber quality are the outcomes of primary plant processes that regulate the rates of absorption, assimilation and distribution of nutrients and biomass (Rogeri et al., 2017; Saleem et al., 2023). Some of the factors that influence these processes are controllable, such as phytotechnical management and fertilization (Crusciol et al., 2022). Traditional soil fertilization serves a clear and specific purpose: to supplement the quantity and quality of nutrients provided by the soil for plant growth. Similarly, foliar fertilization must have well-defined objectives, guided by technical and/or economic considerations, such as mitigating oxidative stress (Fernández and Brown, 2013).

Oxidative stress reduces the photosynthetic rate, leading to an increase in Ci (Moretti et al., 2021). The low availability of CO₂ caused by stomatal closure may reduce the ability of photosystem II to maintain an adequate balance between electron transport, carbonmetabolism, and ATP and NADPH consumption (Hermans et al., 2004). Elevated Ci blocks electron transport and interrupts ATP and NADPH production, leaving the plant unable to assimilate available CO₂ for conversion into energy products (Bari et al., 2020).

In the present study, the induction of oxidative stress by herbicide application displaced the entire stocks of N and P in the leaves of the crops toward the recovery of the affected photosynthetic processes. P participates in chlorophyll production in the form of ATP, and N is found in the pyrrolic rings of chlorophylls, in which a central magnesium atom is linked to four N atoms (Fiedor et al., 2008). Failure to supplement P and N after phytotoxicity induction can negatively affect nucleic acid synthesis and the cell membrane and directly reduce chlorophyll content (Ahmad et al., 2021; Hand et al., 2021). Chlorophyll is responsible for capturing light energy and initiating photosynthetic activity, carbon metabolism, and antioxidant enzyme activity (Khan et al., 2023; Zhou et al., 2023). The herbicide carfentrazone-ethyl inhibits PPOX, an enzyme in the pathway for the synthesis of chlorophyll a. Inhibiting PPOX not only reduces chlorophyll levels but also increases ROS formation due to the reaction of protoporphyrinogen IX accumulated in the cytoplasm with light (Sánchez-Moreiras et al., 2020). Our results demonstrate that foliar fertilization with MAP can restore chlorophyll production after oxidative stress.

Foliar fertilization with MAP increased gas exchange parameters, which are linked to carbon fixation activity, and the production of sucrose. Sucrose is the main sugar for transport in many plants, and its production is favored by the increased availability of Pi (inorganic phosphate) provided via foliar MAP application (Pelá et al., 2019). Greater Pi availability increases energy capacity and facilitates the movement of triose molecules from the cytoplasm to the cytosol, initiating sucrose synthesis. Conversely, the absence of P supplementation favors starch production in chloroplasts (Maheshwari et al., 2021). These effects of foliar MAP fertilization are part of a chain linked to the recovery of chlorophyll levels.

Throughout the photosynthetic process, CO₂ plays the role of substrate. It diffuses into plant cells through the stomata; thus, plants with higher stomatal conductance have a greater capacity to balance CO₂ uptake with water loss through transpiration (Taiz et al., 2017). Our results were obtained during a period following P and N supplementation. To obtain a better understanding of the effects of foliar fertilization with N and P on gas exchange and photosynthetic processes, studies throughout the entire crop cycle are needed.

Foliar MAP fertilization of soybean, maize, and cotton to attenuate phytotoxicity caused by the herbicide carfentrazone-ethyl increased A, gs, and WUE and consequently reduced E. In addition, Ci decreased, and A/Ci increased. These effects reflect an increase in the rate of carbon assimilation by RuBisCO, an enzyme present in all photosynthetic organisms (Kubien et al., 2008). Foliar fertilization with MAP increased RuBisCO activity by providing N and P, which are components of RuBisCO and chlorophyll (Xu et al., 2012; Guo et al., 2016). Increasing the production of photosynthetic components promotes the accumulation of organic compounds, which act in cellular osmotic adjustment and contribute to photosynthetic efficiency (Xu et al., 2012). Collectively, our effects illustrate the benefits of foliar MAP application for improving photosynthetic efficiency and optimizing water use and gas exchange processes in crops.

The herbicide carfentrazone-ethyl does not directly interrupt photosynthetic processes. However, direct contact between the plant and the herbicide interrupts chlorophyll production and increases the accumulation of compounds that lead to the formation of singlet oxygen (Holmes et al., 2022; Li et al., 2022). The resulting lipid peroxidation and membrane disruption negatively affect photosynthesis, respiration, and electron transport (Sahu et al., 2023). Nutrients play crucial roles in photosynthetic processes; for example, P is involved in electron transport, and N is involved in chloroplast formation and protein synthesis, activates enzymes, and contributes to plant biomass production (Moreira et al., 2014, 2018; Rodrigues et al., 2021b). Thus, foliar fertilization with these nutrients under conditions of oxidative stress provides a resource for the recovery of plants affected by phytotoxicity (Hudina and Stampar, 2001; Zanao et al., 2020). Supplementation of plants with N under stress conditions increases nitrate-N absorption, nitrate reductase activity, and antioxidant defense mechanisms, reducing pigment photooxidation in chloroplasts and consequently in leaves (Kang et al., 2023). Oxidative stress may reduce the P content of the plant, limiting the growth of its root system (Ahmad et al., 2018). Foliar supplementation with P restores root growth and increases water and nutrient absorption, strengthening the plant’s defense system. Additionally, P supplementation increases nitrate reductase activity, leading to greater nitrate assimilation under stress conditions (Ahmad et al., 2021; Viveiros et al., 2024).

In the present study, phytotoxicity induction reduced the activity of antioxidant enzymes in all three crops, and foliar supplementation with P and N restored high levels of enzyme activity. To assess the effects of phytotoxicity induction on lipid peroxidation, the leaf concentrations of MDA and H₂O₂ were evaluated. MDA is commonly used as an indicator of oxidative stress and is formed from the oxidation of polyunsaturated fatty acids (Rodrigues et al., 2021b; Viveiros et al., 2024). H₂O₂ is derived from the reduction of O₂ ^- by SOD and is neutralized in two steps by CAT (Gill and Tuteja, 2010). Phytotoxicity induction increased the leaf contents of both MDA and H₂O₂, and these increases were reversed by foliar MAP application, consistent with the changes in SOD activity (Niu et al., 2021). SOD is the first line of defense against oxidative stress, and the increases in SOD activity in the treatments containing foliar MAP indicate that MAP application improved the plant’s ability to combat ROS (Almeselmani et al., 2006; Gong et al., 2020). These results highlight the positive impact of MAP application on boosting antioxidative enzymatic activity and mitigating oxidative stress.

Proline is a nitrogenous compound that contributes to the recovery of plant growth and combatting phytotoxicity (Torello and Rice, 1986; Rodrigues et al., 2021a). Surprisingly, herbicide application without foliar MAP fertilization did not significantly alter proline concentrations compared with the treatments with MAP application, in contrast to the effects of phytotoxicity induction on other indicators of oxidative stress. In summary, foliar MAP fertilization provides P and N in direct contact with the leaf, which improves photosynthetic efficiency, reduces ROS formation, and mitigates the effects of oxidative stress on plants (Fernández and Brown, 2013; Rodrigues et al., 2021b).

This study evaluated the ability of foliar fertilization with soluble MAP (containing N and P) to mitigate oxidative stress induced by the herbicide carfentrazone-ethyl in soybean, maize, and cotton. Foliar supplementation with MAP alleviated symptoms of phytotoxicity, regardless of the timing of MAP application. However, yields were highest when soluble MAP was applied in a total of four phenological stages. Phosphorus and N enhance plant defense and cellular recovery under stress by supporting energy transfer, protein synthesis, and antioxidant activation, ultimately improving resilience and productivity.