Anthropogenic climate change has triggered significant modifications in Earth’s climate patterns by modifying temperature and precipitation patterns (Bhatti et al., 2024). With predictions indicating a worsening trend in the next years (IPCC, 2019). All these alterations in climate have profound impacts on agriculture and livestock, particularly impacting countries heavily dependent on agriculture for economic gains (Guo et al., 2022). Therefore, implementing strategies to mitigate climate change and foster resilient cultivation practices becomes paramount for safeguarding future food security.

The agricultural sector constitutes a substantial source of greenhouse gas (GHG) emissions. In this sector, GHG mainly originates from changes in land use, ruminant metabolism, and nitrogen fertilization (Ma et al., 2024). In the broader framework of global initiatives aimed at mitigating greenhouse gas emissions, the adoption of cultivation practices designed to mitigate these emissions assumes critical importance. Within this spectrum of mitigation strategies, an integrated crop-livestock system emerges as a particularly promising agricultural approach (Delandmeter et al., 2024). These systems possess the potential to not only reduce fertilizer consumption but also improve the carbon sink capacity of crops, increase plant resilience against abiotic stresses (Han et al., 2024; Silveira et al., 2024), and improve productivity and soil fertility by promoting greater nutrient cycling, when compared to monoculture systems (Farias et al., 2020; Muniz et al., 2021; Vendramini et al., 2023; Silva et al., 2024b).

Integrated crop-livestock systems involve the integrated execution of agricultural and livestock activities, either in rotation, succession, or consortium, within the same area but at different times (Nunes et al., 2021). In the last decades, attention has been directed toward assessing the impact of integrated systems on soil characteristics and productivity (Lima et al., 2023). These systems have proven effective in pasture recovery (Santos et al., 2023; Damian et al., 2023) and improvements in soil health (Silva et al., 2024b). Soil health is the soil’s capacity to function as a vital ecosystem that supports biological productivity, preserves environmental quality, and enhances the well-being of plants and animals (Barbosa et al., 2023; Serafim et al., 2023; Carvalho et al., 2024). Consequently, with improvements in soil health, the productivity of crops grown in succession, such as soybean, has shown significant increases. Brito et al. (2023) observed a 21% increase in soybean grain yield when grown in an integrated system, after maize was intercropped with forage, when compared to growing after maize in monoculture. Silva et al. (2024c), on the other hand, found that integrated systems improve soil fertility, which increased the cumulative grain yield of soybeans by 15%.

Although the benefits of integrated systems on productivity have been well-established in the scientific literature, there remains a notable gap in understanding the physiological advantages experienced by plants in such cultivation systems and few physiological mechanisms responsible for enhancing plant growth under integrated systems are known. Evidence indicates that plants may experience higher soil moisture levels during the growing season and drought periods because crop residues cover the soil (Silva et al., 2024a) and protect the soil from solar radiation. Therefore, plants growing under these conditions can maintain an elevated stomatal conductance, transpiration flux, nutrient absorption, and photosynthesis. Moreover, the additional availability of nutrients in the soil resulting from the decay of plant residues may result in higher absorption of these nutrients, presumably increasing chlorophyll biosynthesis, photosynthesis, and biomass accumulation. Due to the higher photosynthesis and decay of crop residues, soil carbon stocks increase under crop-livestock systems, increasing overall soil metabolism (Carvalho et al., 2024; Silva et al., 2024b). Improvements in soil microbial conditions are also possible, even in the short term, in no-till systems, when compared to conventional cultivation (Mirzavand et al., 2022).

Many different strategies can be used to conduct a successfully integrated system. While the production of plant residues resulting from production from double cropping (e.g., maize + forage) for soybean no-till system is well established (Costa et al., 2020; Dias et al., 2020; Santos et al., 2021; Coelho et al., 2023; Silva et al., 2024c), there is a lack of information regarding the production of plant residues from triple cropping (e.g., maize + forage + legume), particularly when utilizing legumes in the system. Therefore, the ecosystem services for the soil-plant system, such as plant nutrition (Jensen et al., 2020; Gut et al., 2022), soil conservation (Kebede, 2021; Silva et al., 2022; Witcombe et al., 2023), soil microbial (Mirzavand et al., 2022), soil health (Yan et al., 2023), and maximization of productivity, quality, and profitability (Pereira et al., 2023; Souza et al., 2023) resulting from an integrated triple cropping system remains scarce in the literature.

Our study aimed to compare the conventional soybean cultivation method (soybean grown without plant residues on the soil from the previous crop) with alternative regimes in which soybeans are grown over soil residues from monoculture or a prior triple consortium of maize, three cultivars of Panicum maximum (Zuri, Tamani, and Quênia guinea grass), and Pigeon pea (Cajanus cajan cv. BRS Mandarim), and how these systems affect soil cover biomass production, initial nutrient concentration in plant residues, soil respiration and microclimate, as well as soybean growth, physiology and productivity. We hypothesize that soil cover crop residues would have a higher nutrient concentration. Growing soybean on these plant residues would result in increased photosynthetic rates, chlorophyll index, aboveground biomass production, soil respiration, and grain yield compared to conventional soybean cultivation method. Furthermore, residues from a triple intercropping system would lead to improved soil microclimatic conditions, higher photosynthetic rates of soybean, and increased aboveground biomass productivity, as well as a higher soybean grain yield, compared to monoculture residues.

Our integration strategies resulted in different dry masses of plant residues for soil cover ( Figure 4 ). Those integration strategies incorporating Zuri guinea grass were particularly effective in generating the highest of soil cover residues quantities. Interestingly, the biomass production remained similar whether Zuri guinea grass guinea grass was cultivated in monoculture or consortium with maize + Pigeon pea, with an increase of 50,6% in relation to the biomass of maize and increase 44,9% in relation to the soil cover biomass of Pigeon pea in monoculture, that presented the lowest soil cover biomass production among all integration strategies. Intermediate soil cover biomass productions were observed for treatments involving Tamani guinea grass guinea grass and Quênia guinea grass guinea grass, both in monoculture and when intercropped with maize and Pigeon pea.

The concentration of nutrients within the biomass generated by each integration strategy varied based on the composition of the biomass ( Figure 5 ). Pigeon pea in monoculture showed the highest concentrations of N and P, with increases of 59.2% and 51.1%, respectively, compared to maize monoculture, which had the lowest concentrations. On the other hand, the intercropped systems and monoculture cultivars of Panicum maximum and Pigeon pea showed increases of 44.3% and 42.3% in N and P concentrations, respectively, compared to maize monoculture ( Figures 5A, C ). For the concentration of K ( Figure 5E ) and S ( Figure 5F ), it was observed that cultivars of Panicum maximum and Pigeon pea in monocultures and intercropped systems had similar concentrations, with average increases of 54.4% and 38.8% in K and S concentrations, respectively, compared to maize monoculture, which had the lowest concentrations ( Figures 5E, F ).

Were observed that the soil surface temperature was, on average, 10°C higher (p<0.05) in plots without soil cover residues compared to those with crop residues covering the soil ( Figure 6A ). However, no differences were observed in the soil surface temperature among different integration strategies ( Figure 6A ). This same pattern was observed in the soil temperature measured at a depth of 5 cm ( Figure 6B ). Soil moisture was lower (p<0.05) in plots where soybeans were cultivated without soil cover compared to other treatments, except for Quênia guinea grass in monoculture ( Figure 6C ). Soil respiration (R_soil ) was not changed by treatments ( Figure 7 ).

Leaf gas exchange measurements revealed that net photosynthesis rate (A) was influenced by the treatments ( Figure 8A ). Net photosynthesis rate was lower (p<0.05) in soybean plants cultivated without soil cover compared to maize monoculture, Zuri guinea grass monoculture, Maize + Tamani guinea grass guinea grass + Pigeon pea, and Maize + Zuri guinea grass guinea grass + Pigeon pea ( Figure 8A ). However, stomatal conductance (g_s ) and transpiration rate (E) were not affected by the treatments ( Figures 8B, C ).

The highest concentration of leaf chlorophyll in soybean plants was observed in the treatment containing Zuri guinea grass residue in monoculture, while the lowest chlorophyll index was observed in soybean plants cultivated without soil cover ( Figure 9 ). All integration strategies showed higher values of leaf chlorophyll when compared to soybean plants cultivated without soil cover.

Our integration strategies influenced plant height ( Figure 10A ). Soybean plants grown without soil cover exhibited the lowest height, while the tallest soybean plants were observed in the treatments: Tamani guinea grass guinea grass monoculture, Zuri guinea grass guinea grass monoculture, Maize + Tamani guinea grass guinea grass + Pigeon pea, and Maize + Quênia guinea grass + Pigeon pea ( Figure 10A ). The highest aboveground biomass productions of soybean plants were observed in the triple intercropping treatments, followed by Tamani guinea grass, Quênia, Zuri guinea grass guinea grass, and Pigeon pea in monoculture, which exhibited similar biomass levels. The lowest aboveground biomass production of soybeans was observed in plants cultivated without soil cover ( Figure 10B ). Cropping systems also influenced grain yield ( Figure 10C ). Systems including tropical forages (monoculture or triple consortium) showed increases in grain yield of 21.0% and 36.8% compared to monoculture maize and the conventional system (without soil cover biomass), which presented the lowest grain yield.

Study aimed to compare the conventional soybean cultivation method with alternative regimes wherein soybean is grown over plant residues from prior tropical forage cultivation, either combined or not with maize or Pigeon pea plants. main hypothesis was corroborated since, the benefits of integrated systems on the physiology of soybean plants were detected. Furthermore, higher biomass production and nutrient concentration was observed when soybean was cultivated over crop residues originating from triple consortium through integration, which combined maize, a C4 grass, and a legume. In the following paragraphs, we discuss the potential implications of our results for more sustainable soybean cultivation.

Were observed variations in the production of plant residues by the different integrated crop-livestock regimes ( Figure 4 ). The higher biomass production of Zuri guinea grass in both monoculture and intercropping is presumably related to its morphological characteristics, such as tall stature, rapid growth, high stem production (support structures), high dry matter yield, and vigorous regrowth during the off-season, leading to high production of plant residues (Silva et al., 2023a). On the other hand, Quênia guinea grass and Tamani guinea grass are grasses with intermediate and low statures, respectively (Tesk et al., 2020), explaining the intermediate biomass production results for soil cover ( Figure 4 ).

It is important to note that the dry mass production of plant residues from the triple intercropping of maize + Tamani guinea grass + Pigeon pea was 14.5% higher than the monoculture of Tamani guinea grass, and for the triple intercropping with Zuri guinea grass and Quênia guinea grass, the production was similar to monocultures ( Figure 4 ). The use of tropical forages (either as monocultures or in consortium) as cover crops is beneficial because, even under conditions of low or absent rainfall during off-season period ( Figure 2 ), these forages show regrowth and adequate residue production for the no-tillage of soybean (Silva et al., 2024b). However, the presence of legumes in the system brings additional benefits such as increased carbon stocks in the soil (Han et al., 2024), biological nitrogen fixation (Jensen et al., 2020), organic matter input (Silva et al., 2022; Yan et al., 2023), improving physiological indices (Nasar et al., 2020) and increasing crop yields (Pereira et al., 2023).

The lower production of plant residues produced by maize in monoculture ( Figure 4 ) is explained by the low quantity of residue left after harvest and by the early decomposition process that these residues undergo, as they remained in the field since harvest for ensilage (in May). On the other hand, Pigeon pea, due to lower precipitation ( Figure 2 ), exhibited less regrowth, emitting fewer leaves (Ceballos et al., 2018), resulting in lower production of plant residues ( Figure 4 ). Another important factor observed was that plant residues from maize and Pigeon pea monoculture did not provide adequate soil coverage (Dias et al., 2020; Santos et al., 2020), compared to systems with the presence of Panicum genus. These results demonstrate how integrated systems have the potential to increase the production of soil cover biomass, contributing to nutrient cycling (Oliveira et al., 2019), showing that the interspecific interactions in the triple intercropping are driven by plant-plant complementarity and cooperation rather than competition (Justes et al., 2021). Furthermore, the inclusion of Pigeon pea in the system presumably resulted in greater nitrogen input into the soil-plant system due to biological fixation and a gradual release of nutrients due to residue mineralization (Laroca et al., 2018), contributing to increased productivity of subsequent crops (Santos et al., 2020).

Panicum cultivars have been showing positive results in intercropping systems (Leal et al., 2023; Lima et al., 2023; Silva et al., 2023b, 2024c), providing soil improvements through decomposition, mineralization, and nutrient recycling. Additionally, the presence of Pigeon pea in the system contributes to increased soil nitrogen stocks through biological nitrogen fixation (Silva et al., 2022). Therefore, triple intercropping in the same area can be an important tool to combine the advantages of individually cultivated species (Pereira Filho et al., 2019). The higher concentrations of N and P obtained in the Pigeon pea residues cultivated in monoculture ( Figure 5 ) are presumably associated with symbiotic association with bacteria from the Rhizobium genus, which facilitate N acquisition through biological fixation (Silva et al., 2020). As for the concentration of P, Wang and Lambers (2020) reported that cover crops, such as legumes, can mobilize labile P from the soil through mechanisms associated with the root system, rhizosphere pH, release of organic acids, phosphatase activity, and incorporate it into their biomass.

The biomass residues resulting from maize in monoculture showed lower concentrations of N, P, K, and S, due to the lower biomass production and consequently nutrient cycling. These results are consistent with studies conducted by Dias et al. (2020); Muniz et al. (2021), and Silva et al. (2023b), which compared integrated systems with the soybean/maize succession system. Tropical forage crops in monoculture or intercropped are efficient in reducing K losses through leaching (Silva et al., 2023b; Volf et al., 2023), being one of the most extracted nutrients by forage crops. Through their deep root system, they absorb K from the deeper soil layers, accumulate it in their biomass, and upon desiccation, release it on the surface, benefiting the succeeding crop (Costa et al., 2021). It is important to highlight that in soybean cultivated on the residues of different cropping systems, potassium fertilization was not applied, aiming to take advantage of the cycling of this nutrient. Silva et al. (2023b) observed that tropical forages used as soil cover crops can supply the amount of K required by the soybean crop, eliminating the need for mineral potassium fertilization.

The availability of S is influenced by the organic matter content present in the soil (Kumar et al., 2022), and integrated systems like those investigated in our research can be considered a highly efficient way to increase soil organic matter (Silva et al., 2023b), mainly due to the presence of Pigeon pea, as legume residues contain significant amounts of nitrogen that enhance carbon stabilization in organic matter (Silva et al., 2022). Therefore, the nutrient concentration per unit area in the integrated systems in our study is a good indicator of the performance of tropical forage crops as cover crops and the ecosystem services provided, reducing nutrient losses through leaching and/or runoff, maintaining soil moisture, and increasing nutrient cycling for the succeeding crop (Couedel et al., 2023).

Results showed that irrespective of the integrated crop-livestock system used (whether soil crop residues originated from a monoculture or a combination of three species), both the soil surface temperature and the temperature at a depth of 5 cm were lower when compared to conventional soybean cultivation. In some cases, this temperature difference exceeded 10°C compared to the conventional method. This difference was also observed in soil moisture, which was higher in all integrated systems, irrespective of the integration strategy used. Demonstrating the potential of cover crops to contribute to more favorable conditions (lower temperature and higher soil moisture) for the development of soybean plants, even in situations where rainfall distribution is inadequate ( Figure 2 ). These results are widely supported by other studies and are related to increased shading and soil protection due to the presence of vegetation cover (Akhtar et al., 2019; Farias et al., 2020; Wang et al., 2021; Silva et al., 2024a).

Contrary to our expectation, soil respiration was not increased under an integrated system, since soil respiration is positively correlated with soil moisture and soil organic matter content but is often higher in warmer soils (Oliveira et al., 2020). This multifactorial interaction between edaphoclimatic conditions resulted in a similar carbon flux rate from soil to the atmosphere between integrated systems and conventional soybean cultivation, suggesting no additional carbon flux from soil to the atmosphere under integrated systems. Additionally, the higher deposition of organic matter under an integrated crop-livestock system on the soil promotes greater soil roughness, facilitating water flow between soil particles and maintaining soil moisture for longer periods (Akhtar et al., 2019). Some studies suggest that increased moisture in integrated systems protects plants against drought episodes, as the soil remains moist for longer, allowing stomata to remain open for extended periods, leading to greater carbon fixation and nutrient absorption compared to plants in traditional cultivation systems (Silva et al., 2024a).

Higher photosynthetic rates may be achieved when stomatal conductance (a measure of stomata openness) is higher (Kusumi et al., 2012). In the present study, no significant increase in stomatal conductance or transpiration rate of plants grown in integrated systems was observed, do not corroborate our main hypothesis. Thus, the photosynthetic gains observed in Figure 8 are not related to a higher stomatal opening but rather to other metabolic factors.

Although stomatal conductance and transpiration rate were not altered in the present study, a significant increase in net photosynthesis rate was observed in some specific integrated systems. This increase is presumably related to the higher availability of nutrients originating from the degradation of plant residues ( Figure 5 ). When released, these nutrients are absorbed by plants and become part of the chemical composition of various plant molecules. For example, N is often positively correlated with photosynthesis rates due to its high concentration in the enzyme Rubisco, the most abundant enzyme in plants and responsible for carbon fixation in the Calvin-Benson cycle (Nasar et al., 2020; Liu et al., 2023). P, in turn, is associated with photosynthesis because it is involved in the transfer and storage of energy, the synthesis of nucleotide molecules, and the functioning of various intermediate molecules in pathways related to photosynthesis (Dang et al., 2023). S is part of the composition of proteins, vitamins, and important enzymatic cofactors in photosynthesis; for example, ferredoxin acts as an electron carrier in the light reactions of photosynthesis (Taiz et al., 2017). K participates in the enzymatic activation of photosynthesis enzymes, in addition to activating photosystem II and being important in the process of carbohydrate transport (Johnson et al., 2022). All these nutrients were released in large quantities by the integrated systems, cumulatively impacting photosynthetic rates positively.

The greater availability of nutrients allows plants to invest resources in a more efficient photosynthetic apparatus (Silva et al., 2023b). This hypothesis was corroborated by the data presented in Figure 9 , in which the leaf chlorophyll index was significantly higher in plants that grew in integrated systems, regardless of the type (in monoculture or combination). This presumably led to greater energy absorption, associated with a more efficient photosystem, higher electron transport rate, and energy dissipation. Several studies have found a positive correlation between both photosynthesis rate and chlorophyll index and photosynthesis and the concentration of N, P, K, and S (Singh et al., 2019; Latifinia and Eisvand, 2022; Silva et al., 2024b). These correlations were also observed in multivariate analyses in Figure 11 .

Both the benefits of soil improvement and the benefits brought about in plant physiology and biochemistry by integration systems resulted in taller and more productive plants (Laroca et al., 2018; Lima et al., 2023; Vendramini et al., 2023). Were observed that soybean plants under the integrated systems had a greater height compared to those that grew under conventional cultivation conditions. While height did not show any response pattern among different types of integration (composed of a monoculture or three species), productivity showed a clear pattern.

The production of aboveground biomass was higher in triple integration systems, reaching values of approximately 15,000 kg ha^-1, followed by monoculture integration systems, except maize. The lowest aboveground biomass productions were observed in the conventional soybean treatment. A possible explanation for the greater production of aboveground biomass of soybean in the triple intercropping is that this system combined the multiple benefits of individually grown crops, promoting less variation in soil temperature and preserving humidity (Muniz et al., 2021), favoring the best use of nutrients accumulated in the plants residue biomass (Kebede, 2021), throughout the soybean development cycle (Silva et al., 2024c), positively influencing growth and development of soybean plants.

The forage and triple intercropping monoculture systems showed greater potential for increasing soybean productivity, with increases of 21.0% and 36.8% compared to soybean grown in maize biomass and soil without cover residue, respectively. These results are associated with the importance of cover crops for increasing grain productivity, indicating a clear advantage of triple integration systems over conventional systems (Pariz et al., 2020; Kumari et al., 2023; Pereira et al., 2023).

It is worth noting that the benefits of integration systems are not only associated with improvements in soil climatic parameters or soil nutrition. The chemical diversity of compounds derived from the degradation of organic matter is of utmost importance for soil health and its microbiota growth (Serafim et al., 2023).

Studies show that greater species diversity in the integration system leads to higher productivity, as corroborated in the present study (Laroca et al., 2018; Pereira et al., 2023; Silva et al., 2024c). Additionally, according to compound diversity, the soil C pool can be favored, as well as the enzymatic activity of many important enzymes. Han et al. (2024), evaluating the consortium of maize and legumes (forage peanuts), observed an increase in the content of organic C and N in the soil compared to maize grown in monoculture. Carvalho et al. (2024) reported that a long-term crop-livestock integration system favors an increase in C levels in the soil. This greater chemical and allelochemical diversity also causes better weed and disease control, in addition to improving soil structure and water retention (Silva et al., 2020; Linhares et al., 2020; Silva et al., 2021).

The data presented in this study demonstrated that integrated systems, with the presence of grasses and legumes, can improve soil microclimate conditions and nutrient availability, enhancing soybean physiology through increased net photosynthesis rate and leaf chlorophyll index, resulting in greater plant height, aboveground biomass production, and soybean yield.

The results indicate that cultivars of Panicum maximum (Zuri, Tamani, and Quenia guinea grasses) and pigeon pea can be recommended for intercropping with maize, contributing to the sustainability of agricultural production. Furthermore, the findings are based on short-term results, and further investigation is strongly recommended regarding integrated systems with triple intercropping of maize with grasses and legumes and their effects on soil microclimate, nutrient availability, physiology, and long-term soybean productivity.