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Article

Interspecific Competition as Affected by Nitrogen Application in Sweet Corn–Soybean Intercropping System

by
Xia Yu
1,†,
Shihao Xiao
1,†,
Tingxian Yan
2,
Zhongping Chen
3,
Quan Zhou
1,
Yuzhuo Pan
1,
Wenting Yang
1,* and
Meijuan Lu
1,4,*
1
Key Laboratory of Crop Physiology, Ecology and Genetic Breeding, Jiangxi Agricultural University, Nanchang 330045, China
2
Institute of Crop Sciences, Jiangxi Academy of Agricultural Sciences, Nanchang 330200, China
3
Agricultural Technology Extension Center of Jiangxi Province, Nanchang 330046, China
4
College of Territorial Resources and Environment, Jiangxi Agricultural University, Nanchang 330045, China
*
Authors to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Agronomy 2023, 13(9), 2268; https://doi.org/10.3390/agronomy13092268
Submission received: 29 July 2023 / Revised: 18 August 2023 / Accepted: 23 August 2023 / Published: 29 August 2023
(This article belongs to the Section Innovative Cropping Systems)
Browse Figures
Versions Notes

Abstract

:
Corn (Zea mays L.)–soybean (Glycine max (L.) Merr.) intercropping is one of the main traditional intercropping systems used. We hypothesized that sweet corn–soybean intercropping with reduced nitrogen application could improve the crops’ fresh grain yield and nitrogen acquisition. We clarified whether sweet corn intercropped with soybean has the advantages of improved crop yield and carbon and nitrogen accumulation and assessed interspecific competition in the intercropping systems. A four-year (2017–2020) field experiment was conducted with three nitrogen application levels (0, 150, and 300 kg∙ha−1) and three planting patterns (monocropped sweet corn, monocropped soybean, sweet corn–soybean intercropping) at Jiangxi Agricultural University, Nanchang, China. The LER (land equivalent ratio), AG (aggressivity), and CR (competitive ratio) were calculated using the fresh grain yield and nitrogen and carbon accumulation of sweet corn and soybean. The LER values were greater than 1.0 in most of the intercropped patterns, except for the value based on the crops’ fresh grain yield without nitrogen application in 2020. Sweet corn had greater values of CR and AG than soybean in the intercropping system. Compared with common nitrogen application (300 kg∙ha−1), reduced nitrogen application (150 kg∙ha−1) did not significantly reduce the LER or the average CR and AG values. Under reduced nitrogen application, the values of LER, CR, and AG, based on the crops’ fresh grain yield and nitrogen acquisition, were not significantly different between the four years. In conclusion, based on the LER, CR, and AG, sweet corn–soybean intercropping had the advantage of crop yield and nitrogen acquisition, and sweet corn was the superior competitor. Sweet corn–soybean intercropping with nitrogen application (150 kg N ha−1) showed good inter-annual stability of crop productivity and competitiveness of the sweet corn.

1. Introduction

With the increasing global population and demand for grain, improving crop productivity to ensure food security has become a major challenge with limited arable land [1]. N fertilizer is applied to increase crop yields [2]; however, the overuse of N fertilizer contributes substantially to regional soil acidification [3], and affects crop yield and quality [2]. Excessive NO3−-N accumulation in deep soil is a significant potential threat to the safety of underwater ecosystems [4]. When corn N uptake reaches a plateau, potential N losses result from applications that exceed the recommended rates [5]. Reasonable nitrogen rates in the cropping system may make it possible to maintain a high crop yield and reduce the negative impact of nitrogen on the environment [6,7].
Intercropping, a traditional and widespread practice, has high resource use efficiency and is a high-productivity cropping system [8,9]. Many scientists have identified intercropping systems, especially cereal–legume intercropping systems, that have the potential to increase crop yields [10,11,12]; increase crop nutrient absorption [13,14]; improve soil fertility and microbial communities [15,16,17]; promote pest, disease, and weed control [9,18,19]; and reduce the use of chemical fertilizers and pesticides [20,21]. Corn–soybean intercropping is one of the main cereal–legume intercropping systems used, and it is distributed throughout most of the world [22], including Africa [23], America [24], Asia [25], Australia [26], and Europe [27]. The effects of the intercropping system on crop yields, land use efficiency, and nitrogen fertilizer use on grain or silage corn in corn–soybean intercropping systems have been reported [22,28,29,30]; however, studies on the intercropping of sweet corn and soybean are limited [31,32,33].
Sweet corn is a variety of corn with a high sugar content and high nutritional value for humans [34]. The demand for sweet corn has increased greatly around the world, especially in the USA [35,36]. With the limited land available, intercropping may be a feasible way to meet the demand for sweet corn. Sweet corn has a shorter growth period than grain corn, and rational nitrogen reduction could achieve targeted sweet corn yields while minimizing NO3-N leaching [37]. We hypothesized that sweet corn–soybean intercropping with reduced nitrogen application could improve the crops’ fresh grain yield and nitrogen acquisition. To address the above issues, the objectives of this study were to determine whether sweet corn intercropped with soybean has the advantages of improving the crops’ fresh grain yield and carbon and nitrogen accumulation compared with sweet corn monoculture, and to assess interspecific competition in the intercropping systems.

2. Materials and Methods

2.1. Site Description

Field experiments were conducted from 2017 to 2020 at the Agricultural New and High-Technology Station of Jiangxi Agricultural University (28°46′ N, 115°55′ E), Nanchang, China, where a subtropical monsoon climate prevails with an annual average total solar radiation of 101.76 kcal cm−2, and the frost-free period is 272 days. The soil of the experimental field is Ferralsols soil, with a pH of 4.53 (1:5 1 mol/L KCl), 24.63 g kg−1 of organic matter, 183.23 mg kg−1 of available nitrogen, 23.83 mg kg−1 of Olsen phosphorus (P), and 102.03 mg kg−1 of potassium (K) in the cultivated soil (20 cm). The monthly rainfall and mean temperature data were collected from the Jiangxi Meteorological Service in Nanchang (Figure 1).

2.2. Experimental Design and Crop Management

The four-year field experiments were laid out as a two-factor randomized complete block design with three replicates. The two factors were the cropping system and nitrogen rate. The cropping systems included monocropped sweet corn (MC), monocropped soybean (MS), and sweet corn–soybean intercropping (CS); the nitrogen rates had three levels, 0 kg ha−1 as a control (N0), 300 kg ha−1 as the conventional nitrogen application level (N2), and 150 kg ha−1 as a reduced nitrogen application rate (N1) (Table 1).
The field plot was 5.5 × 4.8 m, and a 0.5 m wide border separated the adjacent plots. Monocropped sweet corn was planted in wide and narrow rows, at 70 cm between the two center rows, with 40 cm row spacing between the two outer rows (Figure 2). The planting distance of sweet corn in the same row was 30 cm. The row of monocropped soybean had a row spacing of 30 cm, and the planting distance in the same row was 20 cm. In sweet corn–soybean intercropping, the rows of sweet corn, soybean, and sweet corn–soybean were all at 40 cm, and the planting distances of sweet corn and soybean in the same row were 25 and 20 cm, respectively (Figure 2). In CS, there were eight rows of sweet corn and six rows of soybean. In MC and MS, there were 10 rows of sweet corn or 18 rows of soybean in each plot, respectively.
The sweet corn cultivar ‘Ganketian 6’ was used, a semi-compact sweet corn variety. The time from sowing to the milky maturity period is about 90 days. The soybean cultivar was ‘Taiwan 292’, an early maturing variety; it takes about 65 days from sowing to harvest the fresh pods. According to the actual weather situation each year, the seeding and harvest times are shown in Table 2. Before planting, basal fertilization included 0, 30, and 60 kg N ha−1 as urea for N0, N1, and N2, respectively, 40.5 kg K2O ha−1 as potassium chloride, and 45 kg P2O5 ha−1 as calcium superphosphate. The first topdressing at the V6 stage of sweet corn included 0, 45, and 90 kg N ha−1 as urea for N0, N1, and N2, respectively, and 40.5 kg K2O ha−1 as potassium chloride. The second topdressing at the V14 stage of sweet corn included 0, 75, and 150 kg N ha−1 as urea for N0, N1, and N2, respectively, and 54 kg K2O ha−1 as potassium chloride. All of the nitrogen fertilizer was only applied to sweet corn; soybean did not have nitrogen fertilizer applications, both in the monoculture and intercropping systems. The fertilizer application was the same every year from 2017 to 2020 (Table 3). Emamectin benzoate was used to control corn borer (Ostrinia furnacalis) and fall armyworm (Spodoptera frugiperda (Smith)). No herbicide was applied in the experiments.

2.3. Sampling and Measurements

Plant samples were collected at crop harvest. The soybean fresh pod yields were measured by collecting all soybean pods in five plants randomly from the middle rows in the MS and CS. The sweet corn fresh ear yields were measured from ten ears randomly selected from four center rows in the mono- and intercropped plots. In order to determine the total plant biomass, two sweet corn and two soybean plants were randomly sampled from each plot in the middle rows at the harvest time. The sweet corn ears and shoots and the soybean pods and shoots were packed separately. All of the plant samples were dried in an oven at 105 °C for 30 min, and then dried at 80 °C to a constant weight; then, the dry weight was recorded. Each dry sample was ground (to <0.15 mm) in a ball mill for testing its nitrogen and carbon content. The nitrogen contents of the plant samples were determined via the standard macro-Kjeldahl procedure using a Kjeltec TM 2300 analyzer unit (Foss Tecator AB, Hoganas, Sweden), and the carbon concentration was determined via the K2Cr2O7–H2SO4 oxidation method [38].

2.4. Evaluation of Intercropping Systems Performance

2.4.1. Land Equivalent Ratio (LER)

The LER is the relative land area required by a monocropping system to produce the same yield achieved via an intercropping system [39]. The LER for a sweet corn–soybean intercropping system is the sum of the two partial LER values for sweet corn (LERC) and soybean (LERS):
L E R C = Y i e l d I C Y i e l d M C
L E R S = Y i e l d I S Y i e l d M S
L E R = L E R C + L E R S
YieldIC refers to the fresh ear yield of sweet corn in the CS treatment; YieldMC refers to the fresh ear yield of sweet corn in the MC treatment in the present study; YieldIS refers to the fresh pod yield of soybean in the CS; and YieldMS refers to the fresh pod yield of soybean in the MS in the present study. An LER value higher than 1.0 indicates an advantage from intercropping system.

2.4.2. Competitive Ratio (CR)

The CR is another index that is often used to measure the interspecific competition between crop species in an intercropping system [40]. It is expressed as follows:
CR = Yield IC / ( Yield MC × A C ) Yield IS / ( Yield MS × A S )
where CR is the competitive ratio of sweet corn relative to soybean; YieldIC and YieldIS are the fresh ear or pod yields or nitrogen and carbon accumulation per unit area of sweet corn and soybean in the intercropping system, respectively; and YieldMC and YieldMS are the yields per nitrogen and carbon accumulation unit area of sweet corn and soybean in the monoculture system, respectively. AC and AS are the proportions of the area occupied by sweet corn and soybean in the intercropping relative to the monocropping system, respectively; Ac was 0.57 and As was 0.43 in the present study. When CR is larger than 1.0, this indicates that the competitive ability of sweet corn is higher than soybean at the co-growth stage in the sweet corn–soybean intercropping system.

2.4.3. Aggressivity (AG)

The interspecies competition of the sweet corn intercropping with soybeans was quantified as follows [39]:
AG = Yield IC Yield MC × A C − Yield IS Yield MS × A S
where AG is the aggressivity of sweet corn relative to soybean. The Ac and As values are the proportions of sweet corn to intercrop soybean; Ac was 0.57 and As was 0.43 in the present study. The YieldIC, YieldIS, YieldMC, and YieldMS are the same as those in Section 2.4.2. When a sweet corn value of AG is higher than 0, this indicates the competitiveness of sweet corn is greater than that of soybean in the sweet corn–soybean intercropping system.

2.5. Statistical Analysis

Analysis of variance (ANOVA) was performed for the LER, AG, and CR based on crop yield, nitrogen acquisition, and carbon accumulation in the four-year field experiments using the statistical software SPSS 25.0 (IBM Corp. in Armonk, NY, USA) [41]. Differences between the treatments were tested with Duncan’s multiple range test at the 0.05 significance level.

3. Results

3.1. Land Equivalent Ratio (LER) of Sweet Corn–Soybean Intercropping System

Compared with N0, nitrogen application (N1 and N2) significantly increased the LERS based on crop fresh grain yield and carbon accumulation in 2020, but significantly decreased the LERS based on nitrogen absorption and carbon accumulation in 2017. Compared with the N2, reducing the nitrogen application (N1) did not decrease the LERS in any of the four years. Meanwhile, the cropping system and nitrogen application did not significantly affect the LERB during the four years (Table 4).
The LER values were greater than 1.0 for most of the intercropped treatments, except the LER value based on the crop yield from the N0 treatment in the fourth year (2020). These results indicated that land use efficiency of the sweet corn–soybean intercropping system was greater than the monocropping systems. Compared with N0, nitrogen application (N1, N2) decreased the LER values based on the accumulation of nitrogen and carbon in 2017. However, there was no difference among nitrogen rates from 2018 to 2020. Compared with N2, reducing the nitrogen application (N1) did not significantly reduce the LER values in any year.
Different years had obvious effects on the LER values in the N0 treatment. Compared with the LERS in 2017, the values based on crop accumulation of nitrogen and carbon were significantly lower in 2018–2020, and the values based on crop fresh grain yields were significantly lower in 2019 and 2020. The LERB had no significant difference among the four years. Compared with the LER in 2017, the values based on the crop accumulation of nitrogen and carbon were significantly lower in 2019 and 2020. The LER based on the crop fresh grain yield had a declining trend from 2018 to 2020, especially the LER value under N0 that was less than 1.0 in 2020.
Nitrogen application (N1 and N2) benefited crop yield and nitrogen acquisition stability in the present research. In the N1 and N2 treatments, compared to the LER in 2017, the values based on crop yield and nitrogen acquisition did not significantly decrease or increase in 2018–2020. The significant difference was only found in the LERS and LER based on crop carbon accumulations from N1; the LERS and LER values in 2017 were obviously decreased compared to those in 2018.

3.2. Competition Indices of Sweet Corn–Soybean Intercropping System

The CR values of sweet corn to soybean were all greater than 1.0 (Figure 3A), indicating that sweet corn was a superior competitor in the sweet corn–soybean intercropping system. Based on fresh crop grain yield, compared with the CR from the N0 treatment, the CR from N2 increased significantly in 2020; the CR values from N1 and N2 had a decreasing trend in 2017 and 2018.
Based on crop nitrogen acquisition, compared with CR from N0, the CR value from N1 and N2 decreased significantly in 2017, and that from N2 in 2018, but there were no obvious differences in 2019 and 2020 (Figure 3B). Based on the crop carbon accumulation (Figure 3C), compared with CR from N0, the CR value from N2 decreased significantly in 2017, but that from N1 increased significantly in 2018, up to 23.3%. The average of the CR values was not different among the nitrogen rates (N0, N1, and N2) in any year.
The years obviously influenced the CR values in the same intercropping pattern. Based on the crop yield and nitrogen acquisition, compared with CR from N0 in 2017, the CR values decreased significantly in 2018–2020. However, the CR values from the N1 and N2 had no significant difference. Based on crop nitrogen acquisition, compared with the CR from N0 in 2018, the values in 2019 and 2020 were reduced significantly. Compared with the CR from N2 in 2017, the CR values in 2018 and 2020 were reduced significantly. Based on crop carbon accumulation, compared with the CR from N2 in 2017, the CR values in 2018 and 2019 were reduced significantly. All of the CR values from N1 had no difference among the four years. This indicates that sweet corn in the intercropping system from N1 had a good inter-year stable competitiveness.
Based on the fresh crop grain yield and nitrogen and carbon accumulation (Figure 4), all of the AG values were greater than 0, which indicated that sweet corn was a superior competitor in the sweet corn–soybean intercropping system. Based on crop yield (Figure 4A), compared with the AG from N0, the AG from N1 and N2 had a declining trend in 2017 and 2018, but they increased significantly in 2020. Based on the crop nitrogen acquisition (Figure 4B), compared with the AG from N0, the values from N1 and N2 decreased significantly in 2017, and the value from N2 decreased significantly in 2018. Based on the crop carbon accumulation (Figure 4C), compared with the AG from N0, the values from N1 and N2 significantly reduced in 2017, and the value from N1 also significantly reduced in 2020, but the AG value from N1 increased significantly in 2018. From the four-year average analysis, nitrogen application significantly reduced the aggressivity of sweet corn based on crop nitrogen acquisition, but it did not significantly affect the aggressivity of sweet corn based on the crop yield and carbon accumulation.
Based on the crop yield, compared with the AG value from N0 in 2017, the values were significantly reduced in 2019 and 2020. However, the AG values from N1 and N2 had no significant difference during the four years. Based on crop nitrogen acquisition, compared with the AG value from N0 in 2017, the values decreased significantly in 2018–2020. Compared with the AG value from N2 in 2017, the value significantly decreased in 2018. However, the AG values from N1 had no significant difference during the four years. Based on the crop carbon accumulation, compared with the AG value from N0 in 2017, the values were significantly reduced in 2018–2020. Compared with the AG value from N1 in 2017, the value increased significantly in 2018, but it decreased significantly in 2019.

4. Discussion

The present results showed the LER values were greater than 1.0 for most of the intercropped treatments, except the value based on crop grain yield from N0 at 2020. The maize–alfalfa intercropping system with or without nitrogen fertilizer application significantly improved the yield, biomass dry matter, and plant–soil nutrient contents compared with mono-cropped maize [15]. Intercropping without nitrogen application had the most obvious advantage over the others with nitrogen fertilizer in 2017 (the first year). This may be because the soil nutrition was high in the first year, and the nitrogen acquisition by sweet corn may mainly have been from soil since the soil indigenous N content or fixed N2 were principal contributors to crop N uptake, more than the crop residues or fertilizer combined [42]. However, the LER values from N0 continued to decrease with increasing cultivation year; the value in 2020 was significantly lower than that in 2017. With the cultivation year continuing, there may be inadequate nitrogen for the sweet corn due to the lack of exogenous nitrogen and the continuous consumption of soil nitrogen without nitrogen fertilizer application, resulting in a significant decrease in the accumulation of carbon and nitrogen in 2020. A 47-year field experiment indicated that the total soil nitrogen declined without nitrogen application [43]. Furthermore, two-year field experiments indicated that the yield and growth characteristics of corn were highly dependent on the rate and timing of the applied N [44]. Therefore, nitrogen input is a key factor to maintain high crop productivity, even though intercropping could increase crop yields.
All of the LER values were greater than 1.0 from N application in the four years of field experiments (Table 4), which indicated that the sweet corn–soybean intercropping system had great production stability. These results were similar to previous studies [22,30]. Interspecific competition could be alleviated by increasing the N application rate. The advantages of cereal–legume intercropping systems could be attributed to the significant complementarity in the utilization of resources, such as the use of different sources of nitrogen, namely, fixation of atmospheric nitrogen by legumes and utilization of mineral fertilizer by cereals, together with the utilization of environmental resources at different times during the different growth periods of the crop species [45]. The application of nitrogen fertilizer maintains a continuous and stable production and the production advantages of the intercropping system. Is it that the more nitrogen fertilizer is applied, the better the crop production advantage? Obviously, it is not. Our current results showed that, compared with conventional nitrogen application (N2), reduced nitrogen application (N1) did not significantly reduce the LER based on yields in sweet corn–soybean intercropping. In other words, greater nitrogen application could not promote increased yields of sweet corn and soybean. 15N tracer studies showed that the N mineralized from SOM typically provides >50% the N assimilated by maize over a growing season, despite large N fertilizer applications [46,47]. Hammad et al. [48] found that compared with farmers’ habitual fertilization (300 kg ha−1), a 16.7% reduction in nitrogen fertilizer (250 kg ha−1) did not reduce maize yields in semi-arid areas. Meanwhile, a 240 kg N ha−1 application weakened the excellence of maize–soybean relay strip intercropping [49]; a maize–soybean relay intercropping system with 180 kg N ha−1 is a sustainable and environmentally friendly cropping system [50]. A meta-analysis indicated that the LER decreased with the rate of N fertilizer at low temporal niche differentiations [51]. Moreover, high nitrogen fertilizer could inhibit biological nitrogen fixation in legumes [52]. Therefore, the sweet corn–soybean intercropping system had low input, low risk, high output, and stable crop yields. It provided a feasible solution to reducing nitrogen fertilization in an intensive agriculture.
The results showed that the competition ratios (CR) based on crop yield and carbon and nitrogen accumulation were both greater than 1.0, and the aggressivity (AG) was greater than 0, indicating that sweet corn had a competitive advantage in the sweet corn–soybean intercropping system. This may be because corn has a high capacity for intercepting photosynthetically active radiation (PAR) [53]. In the present study, sweet corn and soybeans were sown at the same time, and they had long co-growth time. The planting distance of the sweet corn was smaller in intercropping than in monocropping, which may have decreased the radiation intercepted by soybeans, and limited the growth of soybeans [54]. Previous studies had shown that corn was the dominant species in corn–legume intercropping systems [45,55].
In the present study, nitrogen fertilizer application inhibited the competitive ratio and aggressivity of sweet corn based on crop yield and nitrogen acquisition in 2017, but it had a certain promotional effect in 2019 and 2020. This may be due to the high soil nitrogen in the first year (2017), and the application of nitrogen may cause the crop to undergo “luxury absorption” of nitrogen under the effect of interspecific interaction, which inhibited the competitive advantage of sweet corn. High N availability in the soil would reduce the competitive ability of legume species in cereal–legume intercropping systems [56]; legumes increase crop production with low inputs [57]. Another important reason was that the competition ratio and aggressivity of sweet corn in all of the intercropping systems decreased in 2019-2020 compared to that in 2017. Especially in the treatments without nitrogen application, the competition ratio and aggressivity of sweet corn reached a significant decrease, but there were no significant reductions in the treatments with nitrogen application. In another words, nitrogen application improved the competition ratio and aggressivity of sweet corn in the continued planting system.
Interspecies competition and compensation largely depend on N availability. Rational nitrogen managements could alleviate the interspecific competition, enhancing the advantage of the intercropping system [58]. The present study found that compared with N2 (300 kg ha−1), N1 (150 kg ha−1) did not significantly reduce the competitiveness of sweet corn, but resulted in better inter-annual stability. A similar result was reported in a sugarcane–soybean intercropping system [59].

5. Conclusions

The present study demonstrates that a sweet corn–soybean intercropping system improved the land use efficiency and nitrogen acquisition compared with a sweet corn monoculture. Sweet corn was the dominant crop through the AG and CR indices in the sweet corn–soybean intercropping system. Sweet corn–soybean intercropping with nitrogen application (150 kg N ha−1) showed good inter-annual stability regarding crop productivity and competitiveness of the sweet corn. Sweet corn intercropped with soybean with 150 kg N ha−1 applied before planting at the V6 and V14 growth stages of sweet corn is a good practice in terms of land use efficiency and nitrogen fertilizer application.

Author Contributions

X.Y. and S.X. conducted the experiment and wrote the manuscript; W.Y. and M.L. designed the experiment and developed scientific questions and objectives; Q.Z. and T.Y. carried out the revising; T.Y., Z.C. and Q.Z. helped with experiment design, management, and provided data analyses; Z.C. and Y.P. performed the experiment and data analyses, together with the first author. All authors contributed to developing the manuscript by providing comments. All authors have read and agreed to the published version of the manuscript.

Funding

This study was financed by the National Natural Science Foundation of China (Grant No. 31901125 and 31360108).

Data Availability Statement

The datasets used during the current study are available from the corresponding author on reasonable request.

Acknowledgments

We would like to thank Long Changzhi, Zhu Shuwei, Jin Li, Zhang Kaige, Li Wenwen, Xu Gang, and Cai Rushen very much for helping us to manage sweet corn and soybean cultivation and sample collection for the four years of field experiments. We would also like to thank Marisol Berti of North Dakota State University for English checking, and the anonymous reviewers for their valuable comments.

Conflicts of Interest

The authors declare no conflict of interest.

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Agronomy 13 02268 g001
Figure 1. Monthly rainfall and mean temperature during 2017–2020 in Nanchang.
Figure 1. Monthly rainfall and mean temperature during 2017–2020 in Nanchang.
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Figure 2. Field arrangement of different cropping systems. Note: MC, monocropped sweet corn; MS, monocropped soybean; CS, sweet corn–soybean intercropping.
Figure 2. Field arrangement of different cropping systems. Note: MC, monocropped sweet corn; MS, monocropped soybean; CS, sweet corn–soybean intercropping.
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Agronomy 13 02268 g003aAgronomy 13 02268 g003b
Figure 3. Competitive ratios (CRs) of sweet corn relative to soybean in sweet corn–soybean intercropping systems based on fresh grain yield (A), crop nitrogen acquisition (B), and carbon accumulation (C). Note: CS means sweet corn–soybean intercropping; N0, N1, and N2 mean the nitrogen rates are 0 kg∙ha−1, 150 kg∙ha−1, and 300 kg∙ha−1, respectively. Following different small letters in the same year and capital letters in the same treatment within 2017–2020 are significant at the 5% level.
Figure 3. Competitive ratios (CRs) of sweet corn relative to soybean in sweet corn–soybean intercropping systems based on fresh grain yield (A), crop nitrogen acquisition (B), and carbon accumulation (C). Note: CS means sweet corn–soybean intercropping; N0, N1, and N2 mean the nitrogen rates are 0 kg∙ha−1, 150 kg∙ha−1, and 300 kg∙ha−1, respectively. Following different small letters in the same year and capital letters in the same treatment within 2017–2020 are significant at the 5% level.
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Figure 4. Aggressivity (AG) indices of sweet corn relative to soybean in sweet corn–soybean intercropping systems based on fresh grain yield (A), crop nitrogen acquisition (B), and carbon accumulation (C). Note: CS means sweet corn–soybean intercropping; N0, N1, and N2 mean the nitrogen rates are 0 kg∙ha−1, 150 kg∙ha−1, and 300 kg∙ha−1, respectively. Following different small letters in the same year and capital letters in the same treatment within 2017–2020 are significant at the 5% level.
Figure 4. Aggressivity (AG) indices of sweet corn relative to soybean in sweet corn–soybean intercropping systems based on fresh grain yield (A), crop nitrogen acquisition (B), and carbon accumulation (C). Note: CS means sweet corn–soybean intercropping; N0, N1, and N2 mean the nitrogen rates are 0 kg∙ha−1, 150 kg∙ha−1, and 300 kg∙ha−1, respectively. Following different small letters in the same year and capital letters in the same treatment within 2017–2020 are significant at the 5% level.
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Table 1. Field experiment design of sweet corn–soybean intercropping.
Table 1. Field experiment design of sweet corn–soybean intercropping.
Cropping SystemsNitrogen Rates (kg∙ha−1)Cropping Patterns
MCN00Monocropped sweet corn
MCN1150Monocropped sweet corn
MCN2300Monocropped sweet corn
MB0Monocropped soybean
CSN00Sweet corn–soybean intercropping
CSN1150Sweet corn–soybean intercropping
CSN2300Sweet corn–soybean intercropping
Table 2. Timing of each operation for sweet corn and soybean in the 2017–2020 cropping seasons.
Table 2. Timing of each operation for sweet corn and soybean in the 2017–2020 cropping seasons.
Operation2017201820192020
Sweet CornSoybeanSweet CornSoybeanSweet CornSoybeanSweet CornSoybean
Seeding 3 April 8 April 24 March 24 March 7 April 7 April 17 April 17 April
Harvesting 14 July 20 June 4 July 17 June 01 July 23 June 12 July 27 June
Table 3. Fertilizer application dates in the 2017–2020 cropping seasons.
Table 3. Fertilizer application dates in the 2017–2020 cropping seasons.
Operation2017201820192020
Basal fertilizer3 April 24 March 7 April 17 April
First topdressing4 May 12 May 27 May 16 May
Second topdressing29 May 3 June 14 June 27 May
Table 4. Land equivalent ratios (LER) in sweet corn–soybean intercropping systems.
Table 4. Land equivalent ratios (LER) in sweet corn–soybean intercropping systems.
TreatmentsLERSLERBLER
201720182019202020172018201920202017201820192020
Crop yield
CSN01.25 Aa1.14 Aa0.79 ABa0.55 Bb0.33 Aa0.44 Aa0.34 Aa0.37 Aa1.58 Aa1.58 Aa1.13 Aa0.92 Aa
CSN10.84 Aa0.90 Aa0.83 Aa0.82 Aa0.33 Aa0.39 Aa0.32 Aa0.39 Aa1.17 Aa1.29 Aa1.15 Aa1.21 Aa
CSN20.88 Aa0.82 Aa0.77 Aa0.97 Aa0.41 Aa0.39 Aa0.36 Aa0.28 Aa1.29 Aa1.21 Aa1.14 Aa1.24 Aa
Nitrogen acquisition
CSN01.63 Aa1.08 Ba0.71 Ca0.80 BCa0.37 Aa0.42 Aa0.40 Aa0.40 Aa2.00 Aa1.50 Ba1.11 Ba1.20 Ba
CSN10.81 Ab0.94 Aab0.66 Aa0.87 Aa0.31 Aa0.45 Aa0.42 Aa0.33 Aa1.12 Ab1.39 Aa1.08 Aa1.21 Aa
CSN20.81 ABb0.65 Bb0.79 ABa0.99 Aa0.33 Aa0.46 Aa0.4 Aa0.36 Aa1.14 Ab1.11 Aa1.19 Aa1.35 Aa
Carbon accumulation
CSN01.30 Aa0.94 Bab0.74 Ba0.65 Bb0.35 Aa0.46 Aa0.41 Aa0.36 Aa1.65 Aa1.40 ABab1.15 Ba1.01 Ba
CSN10.85 Bb1.16 Aa0.70 Ba0.94 ABa0.31 Aa0.42 Aa0.37 Aa0.33 Aa1.15 Bb1.58 Aa1.06 Ba1.27 ABa
CSN20.71 ABb0.65 Bb0.78 ABa0.91 Aa0.33 Aa0.35 Aa0.41 Aa0.35 Aa1.04 Ab1.00 Ab1.19 Aa1.26 Aa
Note: LERS and LERB mean partial land equivalent ratio of sweet corn and soybean, respectively. CS means sweet corn–soybean intercropping; N0, N1, and N2 mean the nitrogen rates are 0 kg∙ha−1, 150 kg∙ha−1, and 300 kg∙ha−1, respectively. Following different small letters in a column in crop yield, nitrogen acquisition and carbon accumulation and capital letters in a row within 2017–2020 are significant at a 5% significance level.
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Yu, X.; Xiao, S.; Yan, T.; Chen, Z.; Zhou, Q.; Pan, Y.; Yang, W.; Lu, M. Interspecific Competition as Affected by Nitrogen Application in Sweet Corn–Soybean Intercropping System. Agronomy 2023, 13, 2268. https://doi.org/10.3390/agronomy13092268

AMA Style

Yu X, Xiao S, Yan T, Chen Z, Zhou Q, Pan Y, Yang W, Lu M. Interspecific Competition as Affected by Nitrogen Application in Sweet Corn–Soybean Intercropping System. Agronomy. 2023; 13(9):2268. https://doi.org/10.3390/agronomy13092268

Chicago/Turabian Style

Yu, Xia, Shihao Xiao, Tingxian Yan, Zhongping Chen, Quan Zhou, Yuzhuo Pan, Wenting Yang, and Meijuan Lu. 2023. "Interspecific Competition as Affected by Nitrogen Application in Sweet Corn–Soybean Intercropping System" Agronomy 13, no. 9: 2268. https://doi.org/10.3390/agronomy13092268

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