MAIZE INTERCROPPING AND NITROGEN FERTILIZATION AIMING GRAIN YIELD AND IMPLEMENT A NO-TILL SYSTEM

DOI: https://doi.org/10.18512/rbms2021v20e1225 MAIZE INTERCROPPING AND NITROGEN FERTILIZATION AIMING GRAIN YIELD AND IMPLEMENT A NO-TILL SYSTEM Abstract – Intercropping grain crops with cover crops is a sustainable cultivation strategy that is useful for ensuring straw production for the no-tillage system (NTS) implementation and supply of nutrients, especially N, for successive crops. The aim of this study was to evaluate the influence of maize (Zea mays L.) cropping systems (CSs), when grown alone or intercropped with sunn hemp and ruzigrass, in combination with N fertilization in topdressing, on the maize agronomic performance and straw accumulation with NTS implementation. The experiment was conducted during the 2017/2018 season with a randomized block design in a split-plot scheme with four replications. The plots comprised maize alone, intercropped with sunn hemp (Crotalaria spectabilis), or intercropped with ruzigrass (Urochloa ruziziensis). The subplots were under four N rates: 0, 70, 140, and 210 kg ha-1. The intercropping systems promoted greater N accumulation and straw production and did not reduce grain yield (GY). The addition of N fertilizers increased leaf nitrogen content (LNC) and GY. Intercropping reduced maize LNC; however, higher N fertilizer application in topdressing mitigated this effect. The intercropping of maize with cover crops is a viable and sustainable alternative for agriculture, as maize GY is not affected, and there is a greater straw production and N accumulation. Therefore, NTS implementation will help in increasing N supply in successive crops.


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The no-tillage system (NTS) involves cultivating plants with minimal soil disturbance, keeping the straw on the surface, implementing crop rotation in the area, and maintaining live roots in the soil. Therefore, it seeks to reduce the cost of production, increase the yield and quality of the harvested product, and preserve and recover natural resources.
The choice of cover crop is an important factor in the implemention of the NTS. Crops in the rotation scheme must permanently maintain the minimum amount of straw on the soil surface (Aidar et al., 2007). Furthermore, the decomposition of this straw can help improve the availability of nutrients such as N for the production system (Gitti et al., 2012).
Grasses represented by Urochloa spp. (Amaral et al., 2016) and legumes, such as sunn hemp (Teodoro et al., 2011), are widely used in the formation of straw in the NTS. However, the exclusive cultivation of cover crops is not attractive to rural producers who seek income from agricultural products. Thus, a way to ensure both straw production and economic return is through the practice of intercropping, with simultaneous cultivation of these plants and grain-producing crops (Kappes & Zancanaro, 2015).
Maize (Zea mays L.) is a highly economically important crop worldwide, because it is used as food, fodder, and a raw material in ethanol production. The crop is cultivated in all regions of the Brazilian territory, generating high grain yields (GYs). In the 2017/2018 harvest season, 16.61 million ha of land was under maize cultivation, with an average yield of 4.9 t ha -1 , taking into account the two annual harvests (Conab, 2018). Additionally, because of its C4 metabolism, high photosynthetic efficiency, and rapid initial growth, maize is one of the main agricultural crops recommended for the intercropping system, presenting a competitive advantage in relation to cover crops grown in intercropping (Oliveira et al., 2010;Kappes & Zancanaro, 2015).
In the case of maize intercropping with Urochloa spp., called the Santa Fé System (Kluthcouski et al., 2000), long-term improvements in the soil physical quality and straw maintenance on the surface are also promoted because of the high C/N ratio of plant residues (Amaral et al., 2016).
When sunn hemp is intercropped with maize, called the Santa Brígida System (Oliveira et al., 2010), there is a greater release of nutrients through the rapid decomposition of crop residues, which have a lower C/N ratio (Maluf et al., 2015).
Moreover, sunn hemp is associated with microorganisms with the ability to biologically fix N, inserting high amounts of nutrients into the production system through mineralization and/or exudation of organic acids through its roots. This can provide nutrients for crops in succession or even in intercropping, enabling the reduction of mineral N fertilization. This aids in cost and pollution management because of the high consumption of fossil fuels for the manufacturing of N fertilizers (Souza et al., 2011). The use of maize cropping systems (CSs) intercropped with cover crops can be a strategy for high maize and straw yields, with lower N fertilization.
Therefore, the study of these interactions is important in economic and environmental areas. Thus, the aim of this study was to evaluate the influence of maize (Zea mays L.) cropping systems (CSs), when grown alone or intercropped with sunn hemp and ruzigrass, in combination with N fertilization in topdressing, on the maize agronomic performance and straw accumulation with NTS implementation.

Material and Methods
The experiment was conducted at the of Urochloa ruziziensis seeds (Kluthcouski et al., 2000). Then, through a seeder-fertilizer, the maize was sown on the seeds of cover crops, using the hybrid DOW 2B810 PW, cycle of approximately 4 140 days, with spacing interrows of 0.45 m, obtaining a population of 66,000 plants ha -1 .
Pest control was carried out with the seeds industrial treatment with: Tiamethoxan 350 g L -1 , for control of caterpillar-elasm, greenbellied stink bug and maize leafhopper in the initial period of crop development. At 29 days after emergence, Thiamethoxan 141 g L -1 + Lambda-cyhalothrin 106 g L -1 were applied to control caterpillars, and Imidacloprid 250 g L -1 + bifenthrin 50 g L -1 to control leafhoppers of the maize.
Chemical weed management was carried out in the maize alone system using the herbicide  (Carmo et al., 2000).
During harvest, the thousand-grain mass (TKM) (g) was determined by randomly collecting and weighing four samples of 1000 maize grains. Maize GY (t ha -1 ) was obtained after the crop attained physiological maturity by manually harvesting the ears of the useful area in each subplot, and mechanically tracing them. The grains were weighed, and the yield was estimated in t ha -1 . The samples were then placed in an oven at 105 °C until a constant mass was obtained to remove all the moisture from the grains; 13% moisture was considered the standard value adopted for maize. Accordingly, the TKM and GY were corrected to 13% moisture content.
The agronomic efficiency (kg kg -1 ) was determined according to the method described by and extrapolation of the quantity obtained (t ha -1 ), determining yield. Thereafter, the material was ground and the N content (g kg -1 ) was determined using the semi-micro Kjeldahl method (Carmo et al., 2000). N accumulation (kg ha -1 ) was determined based on N content and straw yield.
Data were subjected to analysis of variance using the F test ( p ≤ 0.05 ) and, when necessary, the means were compared using the Tukey test ( p ≤ 0.05). Checking significant effects for N rates and interaction between cropping systems and N rate, they were evaluated by means of polynomial regression analysis. Statistical analyzes were performed using the AgroEstat software (Barbosa & Maldonado Júnior, 2015).

Results and Discussion
The cropping systems (CSs) of maize grown alone, intercropped with ruzigrass, and intercropped with sunn hemp did not influence leaf nitrogen contente (LNC), thousand-grain mass (TKM), or maize grain yield (GY) ( Latosol (Oxisol) in the summer season in a region with rainfall distribution and volume similar to that of the present study, a decrease in GY for maize intercropped with ruzigrass (8.9 t ha -1 ) and legumes (8.8 t ha -1 ) compared to maize alone (9.8 t ha -1 ) over two agricultural years.
These differences between results found in the literature, in relation to maize GY, may be related to crop management and edaphoclimatic factors, as mentioned above. The present study and the study by Gonçalves et al. (2016) were carried out in eutrophic soils (V>50%) with high natural fertility, and maize intercropping did not reduce maize GY, whereas the study by Arf et al. (2018a) (Figure 1).
Regarding N topdressing, it was observed that the increase in N rates increased the nutrient content of maize leaves, thousand-grain mass (TKM), and GY (Table 1). For every 10 kg ha -1 of N supplied as fertilizer, there was an increase of approximately 0.40 g kg -1 in the LNC, 0.90 g in the TKM, and 51.7 kg ha -1 in the GY (Figure 2).

Several studies have indicated an increase in GY
with the supply of topdressing N for maize crops (Silva et al., 2010;Gonçalves et al., 2016), which is attributed to the importance of nutrients in the metabolic functions, growth, and production of plants.
The LNC was within the range considered adequate (27-35 g kg -1 ) for maize (Cantarella et al., 1997), across the CSs and N fertilizer treatments (Table 1)    With regard to straw, only the CS influenced the yield, content, and accumulation of N ( Figure 5A). There was a lower value in the straw yield from maize grown alone, which was justified by the higher number of plants in the intercropping systems compared to the sole crop. This result was also verified by Arf et al. (2018b), who compared the straw yield of maize grown in intercropping with sunn hemp, pigeon pea, jack bean, or ruzigrass in relation to maize grown alone. The presence of sunn hemp and ruzigrass increased straw yield by 38% and 41%, respectively. The minimum amount of straw necessary for soil cover in the no-till system (NTS) in the Cerrado biome is 7.0 to 8.0 t ha -1 , well-distributed for full soil cover (Aidar et al., 2007). The intercropping systems of maize with sunn hemp and with ruzigrass, with straw yield values close to 10 t ha -1 , proved to be advantageous for implementing a quality NTS.
Thus, in addition to not interfering with GY, the insertion of cover crops intercropped with maize promotes greater straw production, helping to control nematodes (Leandro & Asmus, 2015) and weeds (Lamego et al., 2015), and providing a high amount of nutrients for crops grown in succession (Silva et al., 2010), factors that favor a more conservative and sustainable agriculture.
As for the N content, the straw in the intercropping system of maize with sunn hemp was superior compared to that of the others, with values of 11.45 g kg -1 for maize alone, 10.86 g kg -1 for maize intercropped with ruzigrass, and 13.39 g kg -1 in maize intercropped with sunn hemp ( Figure   5B). This result was due to the large amount of kg ha -1 ), due to the high straw yield ( Figure 5C).   Grain yield of the maize hybrid DOW 2B810 PW was not negatively affected when the was cultivated intercropped with ruzigrass (U. ruziziensis) or sunn hemp (C. spectabilis).
The increase in N fertilization in topdressing increased leaf Nitrogen content and maize grain yield, with an increase of 51.7 kg ha -1 in grain yield for every 10 kg ha -1 of N applied.
The intercropping of maize with ruzigrass and sunn hemp promoted greater straw yield and N accumulation, enabling the implementation of a quality no-tillage system.