Many agricultural regions worldwide cultivate only one crop per year, resulting in long fallow periods with low soil cover and without vegetation (Pinto et al., 2017). This condition causes low resource use efficiency, potential water and wind erosion, and negative carbon (C) balances, contributing to reduced soil organic matter contents (Caviglia and Andrade, 2010; Caviglia et al., 2013; Andrade et al., 2017). The decrease in organic matter levels affects nutrient supply to crops through mineralization (Carciochi et al., 2018; Reussi Calvo et al., 2018; Sainz Rozas et al., 2019). Moreover, the absence of permanent crops limits nutrient recycling in most agroecosystems. For instance, water excesses during winter fallows lead to nutrient losses from the soil through leaching (Gabriel et al., 2013; Frasier et al., 2017), particularly for soil mobile nutrients such as nitrogen (N) (as NO₃ ^-) and sulfur (S) (as SO₄ ^-2). Additionally, erosion and runoff, promoted by the lack of soil coverage, can increase losses of low-mobile nutrients such as phosphorus (P) (De Baets et al., 2011). To mitigate nutrient losses, farmers have adopted the practice of planting crops that grow between two cash crops, reducing or eliminating fallow periods (Thorup-Kristensen et al., 2003; Rinnofner et al., 2008). These crops are known as “cover crops”, “green bridge crops”, or “catch crops” (CCs), and are not grazed (unlike forage crops), incorporated into the soil (unlike green manures), or harvested (unlike cash crops) (Thorup-Kristensen et al., 2003; Rinnofner et al., 2008; Sievers and Cook, 2018; Crespo et al., 2022; Seitz et al., 2022).

The term “CCs” is commonly used because these crops accumulate nutrients in their biomass and subsequently release them through the decomposition of their residues (Valkama et al., 2015; Kang et al., 2018). In this way, CCs play a pivotal role in nutrient recycling, diminishing nutrient losses during fallow periods and supplying nutrients to the succeeding cash crop in the sequence. This role holds various environmental and economic implications. For instance, CCs have the potential to reduce the need for N fertilizers, thereby lowering greenhouse gas emissions and mitigating eutrophication from N leaching and P runoff (Abdalla et al., 2019; Alvarez et al., 2022). Additionally, CCs could lessen dependence on external inputs such as fertilizers, thereby reducing production costs. Consequently, CCs contribute to enhancing nutrient use efficiency and establishing sustainable agroecosystems over time, helping to close nutrient cycles (Restovich et al., 2012; Daryanto et al., 2018).

The quantity and timing of nutrients supplied from CCs residues to the succeeding cash crop depend on factors such as the species, the accumulated biomass, and the C:nutrient ratio of the decomposing residue (Restovich et al., 2012; Sievers and Cook, 2018). Nevertheless, CCs may also reduce nutrient availability through immobilization, adversely affecting the nutrition of the following crop (Jahanzad et al., 2016; Sievers and Cook, 2018; Otte et al., 2019; Carciochi et al., 2021a). Besides that, CCs incorporate C into the soil, leading to an increase in soil organic C content (Duval et al., 2016; Jian et al., 2020). If the CC is a legume, it could incorporate N by biological fixation and allow for a reduction in the N fertilizer rate in the main crop. Furthermore, CCs help control weeds, improve soil structure, and diminish soil erosion and evaporation (Schipanski et al., 2014; Rimski-Korsakov et al., 2015). Conversely, some reported negative effects of CCs include reductions in cash crop productivity, often linked to the consumptive water use of CCs, particularly in semiarid environments (Blanco-Canqui et al., 2015), or the occasional increase in greenhouse gas emissions following their termination (Basche et al., 2014).

The Argentinean Pampas region covers ca. 60 Mha and accounts for 90% of the country’s grain production (Lavado and Taboada, 2009; SAGyP, 2023). Commercial arable agriculture based on nutrient extraction has been used for decades generating negative nutrient balances and soil degradation, which were magnified by the widespread cropping of soybean (Glycine max. (L.) Merr.) (Lavado and Taboada, 2009; Wyngaard et al., 2022). In the last 20 years, winter CCs have been slowly adopted by farmers as a possible tool for improving soil quality (Rimski-Korsakov et al., 2015; Alvarez et al., 2017). Currently, a survey conducted by the SAGyP (2023) indicates a 318% increase in the area with CCs (from 110,000 ha to 350,000 ha) in the Pampas region from 2019 to 2022. This makes the Argentinean Pampas an appropriate area to analyze the potential impact of CCs on nutrient cycling and C balance in agroecosystems.

All the benefits provided by CCs to the agroecosystems are known as “ecosystem services”. So far, the existing information about CCs in the Argentinean Pampas has been summarized by Alvarez et al. (2017) and Rimski-Korsakov et al. (2015), who focused on their effect on some ecosystem services, such as improvements in chemical and physical soil properties, crop yields, and water availability after their termination. However, no study has yet summarized CCs characteristics (i.e., dry matter and nutrient accumulation, and quality of the residues) and the possible effect on nutrient (N, S, and P) availability for the succeeding crop and C contribution to the soil. This is crucial for fine-tuning fertilizer rates, which enhances economic profits and minimizes environmental externalities, and for understanding the CCs ability to supply C while maintaining or improving the soil C balance. Therefore, for the CCs species mainly used in the Argentinean Pampas, we aim to i) synthesize characteristics of the CCs such as aboveground dry matter accumulation, nutrient (N, S, and P) concentration and accumulation, and C:nutrient ratio, ii) explore factors defining the mentioned characteristics, and iii) discuss their implications on the ecosystem services provided to the agroecosystems.

Previous studies summarized the effect of CCs on soil water availability, soil erosion control, soil physical and chemical properties, and weed suppression, among others (Schipanski et al., 2014; Rimski-Korsakov et al., 2015; Alvarez et al., 2017; Daryanto et al., 2018; Blanco-Canqui and Ruis, 2020). To the best of our knowledge, this is one of the first investigations that synthesizes and analyzes a large dataset containing 98 site-years, allowing us to i) explore the variability on C, N, S, and P accumulation and the C:nutrient ratio in the aboveground dry matter of different CCs species, ii) identify factors explaining these variables, and iii) associate them with ecosystem services. Our study showed that grasses presented the highest biomass and C accumulation, as well as higher C:nutrient ratios. In contrast, vetch accumulated high amounts of nutrients with low C:nutrient ratios, while mixtures presented intermediate conditions between their monocultures (i.e., grasses and vetch). This is highly relevant to select the appropriate CCs species based on the desired ecosystem service and to encourage the inclusion of CCs in cropping systems with negative nutrient balances and soil degradation, such as those in the Argentinean Pampas region (Lavado and Taboada, 2009).

The C:nutrient ratio of CCs residues plays a significant role in the mineralization-immobilization turnover. In this context, C:N ratios below 20 to 25:1 (Sievers and Cook, 2018), and C:P and C:S ratios below 200:1 (Eriksen et al., 2004; Halvin et al., 2005) suggest net nutrient mineralization. Hence, it is important to consider these thresholds to predict the impact of CCs on nutrient availability and the duration of soil coverage. When C:nutrient ratios suggest mineralization, net nutrient contributions to the following crop are expected, as well as a rapid decline in soil coverage over time. Conversely, in cases of immobilization, microorganisms take up nutrients from the soil to decompose the residues, thereby diminishing nutrient availability for the subsequent crop, and soil coverage is extended for a long period (Eriksen, 2008; Murungu et al., 2011; Sievers and Cook, 2018).

The overall high aboveground dry matter and C accumulation and high C:nutrient ratio in grasses indicate that they would be an appropriate option when the goal of CCs is to enhance C sequestration and maintain or even improve soil organic C stocks (Schipanski et al., 2014; Daryanto et al., 2018). In this context, after five years of using CC, Duval et al. (2016) reported greater increments in soil organic C concentration with grasses (wheat and oat) than with vetch, being the C changes in the topsoil associated with the quantity of C input. Although grasses were not the CC group with the highest nutrient accumulation, the significant amount of nutrient uptake suggests that they could prevent N and S losses, mainly through leaching, and in the case of P, through runoff (Eriksen et al., 2004; De Baets et al., 2011; Restovich et al., 2012; Gabriel et al., 2013). Moreover, the high C:nutrient ratio suggests very slow residue decomposition, leading to prolonged soil surface coverage (Eriksen, 2008; Murungu et al., 2011). Therefore, grasses would also be a suitable option for i) protecting the soil surface, reducing soil losses through water and wind erosion (De Baets et al., 2011; Vincent-Caboud et al., 2019); ii) promoting weed suppression during the CC and cash crop growing seasons (Finney et al., 2017; Vincent-Caboud et al., 2019), and iii) reducing water losses through evaporation after their termination (Restovich et al., 2012; Alfonso et al., 2020). However, it should be highlighted that the high C:nutrient ratios would cause nutrients immobilization, increasing the fertilizer rates required to satisfy the succeeding cash crop demand (Eriksen et al., 2004; Lupwayi et al., 2007; Murungu et al., 2011; Carciochi et al., 2021b).

Vetch presented the highest nutrient accumulation, indicating its key role in reducing nutrient losses during fallow periods and the associated environmental externalities (Gabriel et al., 2013; Frasier et al., 2017). Nitrogen losses by N₂O emissions and NO₃ ^- leaching have been questioned when analyzing the whole sequence vetch-cash crop. Meta-analyses conducted for the northern hemisphere indicate that legume CCs increase N₂O emissions compared to other species (Basche et al., 2014; Muhammad et al., 2019). However, studies conducted in the Argentinean Pampas showed no significant differences in N₂O emissions with or without CCs, including vetch (Vangeli et al., 2022; Petrasek et al., 2023). Regarding NO₃ ^- leaching, lower NO₃ ^–N content in soil was reported after vetch and other CCs, compared with a fallow condition, suggesting lower potential N losses through this mechanism (Restovich et al., 2012; Frasier et al., 2017). In addition, as 60% of the N in vetch comes from biological N fixation (Enrico et al., 2020), it is noteworthy that substantial N inputs to the systems are expected (IQR = 47.4 to 86.3 kg N ha^-1). The highest nutrient accumulation, along with the lowest C:nutrient ratio, suggests that vetch could rapidly release significant amounts of N, P, and S that would be available to the succeeding crop in the sequence (Eriksen, 2008; Murungu et al., 2011; Sievers and Cook, 2018; Vincent-Caboud et al., 2019). However, the observed variability in nutrients accumulation indicated that they should be quantified in each growing condition and, in combination with the nutrient requirement of the crops, adjust the nutrient rates to apply via organic or inorganic fertilizer, in order to achieve the sustainability of the agroecosystem.

As expected, mixtures containing grasses and vetch presented intermediate CCs characteristics between the respective monocultures, which agreed with previous studies (Restovich et al., 2012; Ketterings et al., 2015; Thapa et al., 2018). Therefore, mixtures could provide the different ecosystem services mentioned in a balanced way (Finney et al., 2016; Frasier et al., 2017; Vincent-Caboud et al., 2019). Especially in this CC group, the definition of their nutrient characteristics is crucial to predict the role of mixtures in the agroecosystems. For example, mixtures with low biomass accumulation, and thus low C:nutrient ratios, act as a nutrient source for the succeeding crop in the sequence, while high biomass and its associated high C:nutrient ratios, will cause nutrient immobilization and a prolonged protection of the soil surface because of their lower rate of decomposition (Eriksen et al., 2004; Lupwayi et al., 2007; Finney et al., 2016; Vincent-Caboud et al., 2019). Notably, nutrient-related traits are not only determined by biomass accumulation but also by the proportion of each species in the mixture (Hayden et al., 2014; Poffenbarger et al., 2015). Unfortunately, the available information was insufficient to include this variable in our analysis. However, we are aware that the proportion of each species should be considered to predict the behavior of mixtures (i.e., whether they are more similar to vetch or grasses) associated with the discussed ecosystem services.

As determined by Thapa et al. (2018), our observations indicate that biomass accumulation defines the magnitude of the ecosystem service provided by each CC group. In agreement with previous studies (Ketterings et al., 2015; Mirsky et al., 2017; Thapa et al., 2018), we detected factors such as the termination date, CC cycle duration, and precipitation during the CC growing season that determined the CC biomass accumulation. The location of the analyzed sites weakly explained CCs biomass accumulation, but detailed studies on CCs spatial variability are encouraged to be conducted. Contemplating the mentioned factors affecting biomass accumulation is a key point as they will influence nutrient concentrations, accumulations, and C:nutrient ratios, impacting the ecosystem services discussed. It should be highlighted that this study did not assess the C and nutrient accumulation in the roots of CCs which are known to significantly impact on the C and nutrients input to the system (Couëdel et al., 2018; Villarino et al., 2021), which deserves to be analyzed in future studies. It is worth noting that a high aboveground dry matter accumulation would not always be desirable. For example, we observed that C:nutrient ratios in grasses and mixtures increased as the dry matter accumulation also did, which would cause nutrient immobilization (Lupwayi et al., 2007; Vincent-Caboud et al., 2019). Additionally, long CCs cycle durations and late termination dates might reduce water availability for the succeeding cash crop, severely diminishing grain yield in semi-arid areas or in years with low precipitation (Meyer et al., 2019).

This synthesis-analysis offers a comprehensive understanding of nutrient and C characteristics of different CCs species grown in the Argentinean Pampas region, surpassing previous studies conducted in specific site-years. Grasses, except for ryegrass, accumulated high biomass and C, whereas vetch accumulated the highest nutrient content with the lowest C:nutrient ratios, and mixtures presented balanced characteristics. Our findings highlight the importance of selecting CCs species based on the intended ecosystem service. The information provided in this study is useful for predicting nutrient contributions from CCs to the succeeding crop and estimating the potential input of C to agroecosystems. Additional information on species such as ryegrass, cruciferous, and legumes other than vetch is limited, emphasizing the need to generate more data on these CCs.

The original contributions presented in the study are included in the article/ Supplementary Material , further inquiries can be directed to the corresponding authors.

FC and WC organized the database, performed the statistical analyses, and wrote the manuscript. All authors contributed to the article and approved the submitted version.