DO CROTALARIA PLANT HEIGHT AND MAIZE INTER- ROW SPACING AFFECT INTERCROPPED MAIZE YIELD?

Intercropping with Crotalaria species may reduce maize yield; thus, evaluations must understand and explain competition in an intercropped system. The aim was to evaluate the effects of Crotalaria species and inter-row maize spacing on the growth and yield of intercropped maize. A randomized block design in a split-plot scheme was used. Plots comprised maize inter-row spacings of 0.45 and 0.90 m. Subplots consisted of four cropping systems: maize monoculture and three systems of maize intercropped with C. juncea, C. spectabilis, and C. ochroleuca. Plant heights of maize and Crotalaria species throughout the cycle, maize yield, and Crotalaria dry mass were evaluated. The critical plant height of Crotalaria that reduced maize yield ranged from 0.32 to 0.75 m, that is, the more advanced the maize cycle, the greater the critical plant height of Crotalaria. Intercropping with C. juncea was the only one that reduced maize yield (21%) compared to its monoculture, and inter-row maize spacing did not affect the variables. These results were due to the greater plant height (more than 100% higher) and final dry mass (more than 80% higher) of C. juncea compared to the other Crotalaria species, promoting competition with maize for water, light, and nutrients. The choice of Crotalaria species is essential for management in maize intercropped systems, associating the ecosystem benefits of the intercropping without reducing the cereal yield.


2
Intercropping has been considered the fourth green revolution worldwide and can be a highly sustainable cropping system (Martin-Guay et al., 2018). Compared to monoculture, the benefits of intercropping are numerous, mainly including higher biomass production per area, soil protection against erosion, carbon sequestration, and nutrient cycling, in addition to the possibility of associating more than one economic activity in the same area and reducing the use of mineral fertilizers (Zhang & Li, 2003;Oliveira et al., 2010;Martin-Guay et al., 2018;Mingotte et al., 2020Mingotte et al., , 2021. Furthermore, intercropping consists in the production of the main species, considered to be of direct economic interest, and forage or green manure species, promoting economic and ecosystem benefits (Oliveira et al., 2010;Cambaúva et al., 2019;Borghi et al., 2013).
Due to its tall stature, high competitive ability, and C4 photosynthetic cycle, maize is the species of economic interest most used worldwide in intercropped systems (Zhang & Li, 2003;Oliveira et al., 2010). These characteristics give maize high plasticity and suitability to be used in intercropped systems. However, in specific managements and intercropping configurations, the secondary species used can reduce maize yield (Arf et al., 2018;Mingotte et al., 2021). This fact may interfere with the use of this system by producers. Thus, studies are needed to evaluate the effects of the growth of cover crops on maize yield growth to assist in the recommendation of more specific management.
Crotalaria spp. stand among the most used cover crops in intercropping with maize (Arf et al., 2018;Trevisan et al., 2021). This intercropping system is called the Santa Brígida system (Oliveira et al., 2010). It can be considered one of the most sustainable in agriculture since it associates with the cultivation of grass and legumes, integrating into the same area the benefits of cultivating these two types of plants (Liu et al., 2017;Cambaúva et al., 2019). There are several species within the genus Crotalaria, with plants ranging from short stature (<1.5 m) to tall stature (>2.5 m), which causes differences in the requirement and absorption of water, light, and nutrients (Allen et al., 1998;Barbosa et al., 2020;Silva et al., 2020). Through competition for these factors, these differences can interfere with the yield of intercropped maize, so the species most suitable for this cropping system should be evaluated.
In addition to the species, other factors may interfere with the success of the maize intercropped system especially the inter-row spacing used in the cereal crop (Borghi & Crusciol, 2007;Borghi et al., 2013). Since maize is sensitive to competition for light, water, and nutrients (Mao et al., 2012;Deienno et al., 2021;Trevisan et al., 2021), the use of smaller interrow spacings can be an alternative to suppress the growth of intercropped plants, reducing competition with the cereal (Borghi & Crusciol, 2007;Borghi et al., 2013). Thus, studies involving these factors are necessary to promote recommendations for more specific management assisting producers and technicians in adopting The objective was to evaluate the effects of Crotalaria species and inter-row spacing on the growth and yield of intercropped maize.

Material and Methods
The experiment was conducted in the   The calculations for fertilization were performed according to the recommendations suggested by Cantarella et al. (1997). For sowing fertilization, the dose used was 250 kg ha -1 of the formulation 8-28-16 applied to the sowing furrow.

Results and Discussion
There were differences in plant height among the Crotalaria species throughout the cycle (Table 1). In all periods evaluated, Inter-row spacing and the interaction between the studied factors did not interfere in the final dry mass of Crotalaria.
In general, the heights of maize plants showed no differences as a function of the cropping systems throughout the cycle ( Regarding maize yield, only the intercropping of maize + C. juncea differed from the others, generating a mean yield 22.5% lower than the means of the others. As observed for the height of Crotalaria species, the quadratic model was the one that best represented the variation in the height of maize plants over time (Figure 4). In addition, regression analysis confirmed similarity in maize height over time in all cropping systems.
The correlation between the height of     Means followed by the same lowercase letter in the column do not differ from each other by Tukey test at 5% probability level; *, ** significant at 5 and 1% probability levels, respectively and ns -not significant by F test. cm every ten days in the maize cycle.
The competition for water, light, and nutrients reduced maize yield due to the increase in the height of Crotalaria plants, and this effect was independent of the inter-row spacing used.
The variation in maize yield as a function of   shading conditions compared to the complete sun management factor was dependent on the shading period. Gou et al. (2017) demonstrated that the intercropping of maize and wheat reduces the radiation use efficiency of maize, affecting its biomass accumulation. Zhai et al. (2018) highlight that maize is one of the most sensitive cultivated plants to intra-and interspecific competition, indicating that competition for light with maize is harmful to its yield. In Intercropping maize with tall plants can reduce the availability of water and nutrients for this cereal, given the increased demand for to that discussed for water, according to which taller plants have a higher nutritional demand than shorter plants ( Barbosa et al., 2020). In addition, competition for nutrients is also more severe when a synchronism occurs in the cycle of intercropped crops.
When evaluating the effect of sowing times of Crotalaria intercropped with maize, Gitti et al. (2012) verified that the intercropping of maize with C. juncea sown simultaneously with the cereal, as in the present study, reduced maize yield by up to 38%, a pattern similar to that observed here. The authors also verified that the sowing of C. juncea from the maize phenological stage V4 led to yields similar to those obtained with maize monoculture. This result is because the later sowing of Crotalaria breaks the synchronism for resources throughout the cycle of the two species, promoting the dominance of maize over Crotalaria. Silva et al. (2020) verified that intercropped systems of maize with Urochloa ruziziensis reduced soil water availability by more than 10% compared to maize monoculture, especially in the grain filling stage of maize, limiting its access to readily available water. This finding was also observed by Mao et al. (2012), who evaluated the intercropping of maize with pea. When evaluating the temporal variation of soil moisture in systems of maize monoculture and intercropping with C. spectabilis, Trevisan et al. (2021) observed that soil moisture was lower in the intercropped system at certain stages.
Regarding nutrients, Sapucay et al. (2020) observed that maize intercropped systems require more nitrogen fertilization to achieve yield levels similar to those obtained in the monoculture system.

In intercropped systems with grasses, such as
Brachiaria species, maize has greater competition for nutrients than its intercropping with legumes (Freitas et al., 2015;Sapucay et al., 2020;Deienno et al., 2021). However, even with legumes, such as Crotalaria species, the competition of maize for nutrients has been verified. Deienno et al. (2021) observed that the leaf N content of maize in the intercropping with C. spectabilis was reduced compared to maize monoculture, especially at topdressing N doses of up to 70 kg ha -1 . According to the authors, this reduction in leaf N content demonstrates the competition of maize with Crotalaria for nutrients. However, this was not enough to reduce the yield of intercropped maize because the leaf N content was within the range considered adequate, which is between 27 and 35 g kg -1 (Cantarella et al., 1997).
When comparing the NPK absorption rate of Crotalaria species, Barbosa et al. (2020) observed that the maximum accumulation of N, P,  inte-rrow spacing did not reduce the growth of Crotalaria (Table 1), which may be due to