Maize-soybean Relay Intercropping Research Articles

Relay strip intercropping of soybeans and maize achieves high net ecosystem economic benefits by boosting land output and alleviating greenhouse gas emissions.

Cereal-legume intercropping provides a solution for achieving global food security, but the mechanism of greenhouse gas emissions and net ecosystem economic benefits of maize-soybean relay intercropping are poorly understood. Hence, we conducted a two-factor experiment to investigate the effects of cropping systems, containing maize-soybean relay intercropping (IMS), monoculture maize (M) and monoculture soybean (S), as well as three nitrogen levels at 0 (N0), 180 (N1), 240 (N2) kg N ha-1 on crop grain yield, greenhouse gas emissions, soil carbon stock and net ecosystem economic benefit (NEEB). The average grain yield of IMS (7.7 t ha-1) increased by 28.5% and 242.4% compared with M (6.0 t ha-1) and S (2.2 t ha-1). The land equivalent ratio (LER) of IMS was 2.0, which was mainly contributed by maize (partial LER: 1.2) rather than soybean (partial LER: 0.8). Although the total grain yield of IMS remarkably enhanced by 43.6% and 45.5% in N1 and N2 contrast in N0, the LER was 37.5% and 38.6% lower in N1 and N2 than in N0. The net global warming potential (GWP) of maize and soybean was 11.6% and 1.8% lower in IMS than in the corresponding monoculture, which resulted from a decline in GWP and enhanced soil organic carbon stock rate. Moreover, NEEB was 133.5% higher in IMS (14 032.0 Chinese yuan per year) than in M, mainly resulting from an increase in total economic gains and a decline in GWP cost. A more robust response in yield gain rather than total costs to N inputs of IMS led to 46.8% and 48.3% higher NEEB in N1 and N2 than in N0. Maize-soybean relay intercropping with 180 kg N ha-1 application can obtain yield advantages without raising environmental costs, which provides an approach to achieving sustainable agricultural production. © 2024 Society of Chemical Industry.

Effects of N levels on land productivity and N2O emissions in maize-soybean relay intercropping.

Relay intercropping of maize and soybean can improve land productivity. However, the mechanism behind N2O emissions in this practice remains unclear. A two-factor randomized block field trial was conducted to reveal the mechanism of N2O emissions in a full additive maize-soybean relay intercropping. Factor A was three cropping systems - that is, monoculture maize (Zea mays L.), monoculture soybean (Glycine max L. Merr.) and maize-soybean relay intercropping. Factor B was different N supply, containing no N, reduced N and conventional N. Differences in N2O emissions, soil properties, rhizosphere bacterial communities and yield advantage were evaluated. The land equivalent ratio was 1.55-2.44, and the cumulative N2O emission ( ) was notably lower by 60.2% in intercropping than in monoculture, respectively. Reduced N declined without penalty on the yield advantages. The relay intercropping shifted soil properties - for example, soil organic matter, total N, and protease activity - and improved the soil microorganism community - for example, Proteobacteria and Acidobacteria. Intercropping reduced by directly suppressing nirS- and amoA-regulated N2O generation during soil N cycling, or nirS- and amoA-mediated soil properties shifted to reduce indirectly. Reduced N directly reduced by decreasing soil N content and reducing soil microorganism activities to alleviate N2O produced in soil N cycling. Conducting a full additive maize-soybean relay intercropping with reduced nitrogen supply provides a way to alleviate N2O emissions without the penalty on the yield advantage by changing rhizosphere bacterial communities and soil N cycling. © 2024 Society of Chemical Industry.

Maize-legume intercropping achieves yield advantages by improving leaf functions and dry matter partition

Intercropping can obtain yield advantages, but the mechanism of yield advantages of maize-legume intercropping is still unclear. Then, we explored the effects of cropping systems and N input on yield advantages in a two-year experiment. Cropping systems included monoculture maize (Zea mays L.) (MM), monoculture soybean (Glycine max L. Merr.) (MS), monoculture peanut (Arachis hypogaea L.) (MP), maize-soybean substitutive relay intercropping (IMS), and maize-peanut substitutive strip intercropping (IMP). N input included without N (N0) and N addition (N1). Results showed that maize’s leaf area index was 31.0% and 34.6% higher in IMS and IMP than in MM. The specific leaf weight and chlorophyll a (chl a) of maize were notably higher by 8.0% and 18.8% in IMS, 3.1%, and 18.6% in IMP compared with MM. Finally, N addition resulted in a higher thousand kernels weight of maize in IMS and IMP than that in MM. More dry matter accumulated and partitioned to the grain, maize's averaged partial land equivalent ratio and the net effect were 0.76 and 2.75 t ha−1 in IMS, 0.78 and 2.83 t ha−1 in IMP. The leaf area index and specific leaf weight of intercropped soybean were 16.8% and 26% higher than MS. Although soybean suffers from shade during coexistence, recovered growth strengthens leaf functional traits and increases dry matter accumulation. The averaged partial land equivalent ratio and the net effect of intercropped soybean were 0.76 and 0.47 t ha−1. The leaf area index and specific leaf weight of peanuts in IMP were 69.1% and 14.4% lower than in the MP. The chlorophyll a and chlorophyll b of peanut in MP were 17.0% and 24.4% higher than in IMP. A less dry matter was partitioned to the grain for intercropped peanut. The averaged pLER and NE of intercropped peanuts were 0.26 and -0.55 t ha−1. In conclusion, the strengthened leaf functional traits promote dry matter accumulation, maize-soybean relay intercropping obtained a win–win yield advantage, and maize-peanut strip intercropping achieved a trade-off yield advantage.

Effect of row spacing under maize-soybean relay intercropping system on yield, competition, and economic returns

Interrow spacing of intercrop species directly affects yield and competition indices such as land equivalent ratio of intercropping. The objectives of this research were to analyze (i) the maize and soybean yields under different spatial arrangements in maize-soybean relay strip intercropping (MSR) and (ii) the interspecies competition to provide a basis for optimization of rowspacing in MSR. The field trial was conducted in 2011 and 2012 at the Research Farm of the Sichuan Agricultural University in Ya'an to determine the impacts of various interrow planting distances on yield and competition indices in cereal (maize crop)-legume (soybean crop) relay strip intercropping. Three planting arrangements were utilized based on the distance between maize-maize, maize-soybean, and soybean-soybean as (T1) 50, 40, and 70 cm, (T2) 50, 50, and 50 cm, and (T3) 50, 60, and 30 cm, respectively, and comparison was made with the sole maize (SM) and sole soybean (SSB). Experimental results revealed that grain yield of maize crop was improved with enhancing row spaces between maize and soybean, while "low-high-low" trend was observed for soybean yield in T$_{1}$, T$_{2}$, and T3, respectively, in both years. Competitive ratio, aggressivity, and relative crowding coefficient were consistently greater for maize than soybean in all treatments. The highest LER (1.67) was reported in T$_{2}$ treatment, which was 9% and 4% higher than in T$_{1}$ and T$_{3}$, respectively. Higher LER explains that both crops are facilitating each other in a positive way and increase the average net income of T$_{2}$ as compared to T$_{1}$ and T$_{3}$. Enhancing distance between maize-soybean rows with reducing distance between soybean rows put pressure on soybean due to intraspecific competition. Combined results of competitive indices and economic analysis showed that intercrops performed at their maximum in treatment T$_{2}$. Therefore, the maximum intercropping advantages can be achieved by changing the row spacing, which determines the competitive relationship and productivity of MSR.

Effects of nutrient uptake and utilization on yield of maize-legume strip intercropping system

<p id="C2">To clarify the difference of nutrient uptake and utilization to yield advantage between maize-soybean relay intercropping and maize-peanut intercropping, we conducted a field experiment for two consecutive years. The results were obtained by comparing nitrogen (N), phosphorous (P), and potassium (K) absorption efficiency and utilization in the intercropping with sole cropping. The results showed that land equivalent ratio (LER) of maize-soybean relay intercropping was 1.16-1.72, which had the advantage of intercropping yield, but the LER of maize-peanut intercropping was 0.89-1.13, which had no obvious yield disadvantage. In maize-soybean relay intercropping system, the amount of N, P, and K uptake was higher than that of the corresponding sole cropping by 32.60%-54.22%, 27.35%-34.64, and 17.74%-24.42%, respectively, but the N utilization efficiency was lower by 21.99%-42.07%. The contributions of the N, P, and K uptake efficiencies to LER were 0.34-0.62, 0.31-0.46, and 0.22-0.32, and the utilization efficiencies contributions were -0.11 to -0.35, -0.03 to -0.31, and -0.11 to 0.22, respectively. In maize-peanut intercropping system, the amount of N, P, and K uptake was higher than that of the corresponding sole cropping by -7.86% to 31.58%, 23.09%-46.52%, and 1.60%-55.48%, respectively, and the N utilization efficiency was higher by 7.55-26.60. The contributions of the N, P and K uptake efficiencies to LER were 0-0.22, 0.05-0.27, and -0.11-0.32, respectively, and the utilization efficiencies contributions were -0.25-0.19, -0.32-0.11, and -0.47-0.32, respectively. In conclusion, yield advantage of maize-soybean relay intercropping was mainly from enhanced nutrient uptake efficiency, but there was no obvious yield advantage in maize-peanut intercropping mainly due to relatively less contribution of nutrient uptake to yield advantage.

Spatiotemporal shading regulates anthocyanin, proanthocyanidin, and sucrose accumulation in black soybean seeds

AbstractThe accumulation of soybean seed constituents such as anthocyanin, proanthocyanidin (PA), and sucrose is affected by various environmental stresses. Considerable information is available on the effects of different environmental stresses; however, the effect of shade at various development stages on the accumulation of the various seed constituents remains elusive. We investigated the effect of shade application on anthocyanin, PA, and sucrose contents at different seed development stages of two black soybean [Glycine max (L.) Merr.] varieties. This study comprised two separate trials: maize–soybean relay intercropping (IC) and soybean monoculture. The shade treatments in the soybean monoculture trial comprised shade applications at whole growth stage, at vegetative stage (SV), and at reproductive stage (SR) and a no‐shade control. Anthocyanin, PA, and sucrose contents were analyzed from seeds obtained at development stages of full‐size seed (R6), physiological maturity (R7), full maturity, 95% mature pods on the plant (R8), and natural air dry (AD). Genotype, shade, and planting season and their interactions had a strong influence on anthocyanin, PA, and sucrose accumulation in soybean seeds at the different seed development stages. Among all the shade treatments, relay IC recorded the highest anthocyanin contents in 2017 (1.88 mg g−1) and 2018 (1.76 mg g−1) in AD seeds. In addition, the application of shade increased PA, and maximum PA (27.14 mg g−1) was obtained in the SV treatment at R6 stage. The overall best sucrose contents (6.14 mg g−1 in 2017 and 7.04 mg g−1 in 2018) were obtained in soybean seeds harvested at R8 under SV treatment.

Optimum leaf defoliation: A new agronomic approach for increasing nutrient uptake and land equivalent ratio of maize soybean relay intercropping system

Upper canopy leaves of maize decrease the light-transmittance at middle-strata-leaves of maize and soybean canopy in maize-soybean relay-intercropping systems (MS). This affects the uptake of nutrients and distribution patterns in various plant organs of intercrop species in MS. Judicious defoliation of maize plants in MS could help to alleviate this problem and improve nutrient uptake and intercrop yields. In a two-year field experiment with MS, including the measurements of biomass production, nutrients uptake, and distribution at the organ level, and grain yields of intercrop species, maize plants were subjected to four-leaf defoliation treatments to improve the light-transmittance of maize and soybean plants. Defoliation of the topmost two-leaves (T2), four-leaves (T4), six-leaves (T6) was compared to no defoliation (T0).Compared to T0, treatment T2 improved the uptake of nitrogen (N), phosphorus (P), and potassium (K) in each plant part of maize by 23, 12, and 11% (grain), 22, 19, and 13% (straw), and 28, 14, and 18% (root), respectively. Defoliation also enhanced the uptake of N, P, and K in each plant part of soybean by 5, 5, and 10% (grain), 10, 17, and 13% (straw), and 14, 11, and 11% (root), respectively. The improved nutrient uptake in T2 increased the total biomass and its distribution in the root, straw, and grain of soybean and maize by 15 and 13%, and 21 and 15%, 20 and 14%, 7 and 10%, respectively compared to T0. On average, over two years, under T2, relay-cropped maize obtained 107% of the sole-yield, and relay-cropped soybean obtained 65% of the sole-yield. The T2 defoliation treatment also achieved the highest land equivalent ratio of 1.69 and 1.77, with a net profit of 1301.6 $ ha−1 and 1293.4 $ ha−1 in 2017 and 2018, respectively.Following the optimum defoliation treatment of maize in maize-soybean intercrops, i.e., defoliation of the topmost two-leaves, the nutrient uptake can be increased, and the nutrient partitioning over plant organs be better balanced. Optimum defoliation, therefore, enhances the productivity of maize-soybean intercropping systems.

Maize leaf-removal: A new agronomic approach to increase dry matter, flower number and seed-yield of soybean in maize soybean relay intercropping system

Shading conditions adversely affect flower-number and pod-number of soybeans under maize-soybean relay-intercropping (MSR). Here we reveal that leaf-removal from maize-canopy improves the photosynthetically active radiation (PAR) transmittance and dry-matter production (DMP) of soybean (especially during the co-growth phase), and compensates the maize seed-yield loss by considerably increasing soybean seed-yield. In a two-year experiment with MSR, maize-plants were subjected to different leaf-removal treatments to increase the PAR-transmittance of soybean; removal of the topmost two-leaves (R2), four-leaves (R4), six-leaves (R6), with no-removal of leaves (R0). Leaf-removal treatments improved the PAR-transmittance, photosynthetic-rate, and morphological-characteristics of soybean under MSR. At 90 days after sowing, the dry-matter of pods, and seeds was increased by 25%, and 32%, respectively under R6 than R0. Importantly, enhanced PAR-transmittance and DMP under R6 enabled soybean to initiate a greater number of flowers 182.2 plant−1 compared to 142.7 plant−1 under R0, and it also decreased the flower-abscission (by 13%, from 54.9% under R0 to 47.6% under R6). These positive responses increased the pod-number by 49% and seed-number by 28% under R6 than R0. Overall, under R6, relay-intercropped soybean produced 78% of sole-soybean seed-yield, and relay-intercropped maize produced 81% of sole-maize seed-yield and achieved the land equivalent ratio of 1.59.

Effects of maize-soybean relay intercropping on crop nutrient uptake and soil bacterial community

Maize-soybean relay intercropping is an effective approach to improve the crop yield and nutrient use efficiency, which is widely practiced by farmers in southwest of China. To elucidate the characteristics of different planting patterns on crop nutrient uptake, soil chemical properties, and soil bacteria community in maize-soybean relay intercropping systems, we conducted a field experiment in 2015–2016 with single factor treatments, including monoculture maize (MM), monoculture soybean (MS), maize-soybean relay intercropping (IMS), and fallow (CK). The results showed that the N uptake of maize grain increased in IMS compared with MM. Compared with MS, the yield and uptake of N, P, and K of soybean grain were increased by 25.5, 24.4, 9.6, and 22.4% in IMS, respectively, while the N and K uptakes in soybean straw were decreased in IMS. The soil total nitrogen, available phosphorus, and soil organic matter contents were significantly higher in IMS than those of the corresponding monocultures and CK. Moreover, the soil protease, soil urease, and soil nitrate reductase activities in IMS were higher than those of the corresponding monocultures and CK. The phyla Proteobacteria, Acidobacteria, Chloroflexi, and Actinobacteria dominated in all treatments. Shannon's index in IMS was higher than that of the corresponding monocultures and CK. The phylum Proteobacteria proportion was positively correlated with maize soil organic matter and soybean soil total nitrogen content, respectively. These results indicated that the belowground interactions increased the crop nutrient (N and P) uptake and soil bacterial community diversity, both of which contributed to improved soil nutrient management for legume-cereal relay intercropping systems.

Relay-intercropping soybean with maize maintains soil fertility and increases nitrogen recovery efficiency by reducing nitrogen input

Optimized nitrogen (N) management can increase N-use efficiency in intercropping systems. Legume-nonlegume intercropping systems can reduce N input by exploiting biological N fixation by legumes. Measurement of N utilization can help in dissecting the mechanisms underlying N uptake and utilization in legume-nonlegume intercropping systems. An experiment was performed with three planting patterns: monoculture maize (MM), monoculture soybean (SS), and maize-soybean relay intercropping (IMS), and three N application levels: zero N (NN), reduced N (RN), and conventional N (CN) to investigate crop N uptake and utilization characteristics. N recovery efficiency and 15N recovery rate of crops were higher under RN than under CN, and those under RN were higher under intercropping than under the corresponding monocultures. Compared with MM, IMS showed a lower soil N-dependent rate (SNDR) in 2012. However, the SNDR of MM rapidly declined from 86.8% in 2012 to 49.4% in 2014, whereas that of IMS declined slowly from 75.4% in 2012 to 69.4% in 2014. The interspecific N competition rate (NCRms) was higher under RN than under CN, and increased yearly. Soybean nodule dry weight and nitrogenase activities were respectively 34.2% and 12.5% higher under intercropping than in monoculture at the beginning seed stage. The amount (Ndfa) and ratio (%Ndfa) of soybean N2 fixation were significantly greater under IS than under SS. In conclusion, N fertilizer was more efficiently used under RN than under CN; in particular, the relay intercropping system promoted N fertilizer utilization in comparison with the corresponding monocultures. An intercropping system helps to maintain soil fertility because interspecific N competition promotes biological N fixation by soybean by reducing N input. Thus, a maize-soybean relay intercropping system with reduced N application is sustainable and environmentally friendly.

Narrow-wide row planting pattern improves the light environment and seed yields of intercrop species in relay intercropping system.

Different planting patterns affect the light interception of intercrops under intercropping conditions. Here we revealed that narrow-wide-row relay-intercropping improves the light interception across maize leaves in wide rows (60cm) and narrow rows (40cm), accelerated the biomass production of intercrop-species and compensated the slight maize yield loss by considerably increasing the soybean yield. In a two-year experiment, maize was planted with soybean in different planting patterns (1M1S, 50:50cm and 2M2S, 40:60cm) of relay-intercropping, both planting patterns were compared with sole cropping of maize (M) and soybean (S). As compared to M and 1M1S, 2M2S increased the total light interception of maize leaves in wide rows (WR) by 27% and 23%, 20% and 10%, 16% and 9% which in turn significantly enhanced the photosynthetic rate of WR maize leaves by 7% and 5%, 12% and 9%, and 19% and 4%, at tasseling, grain-filling and maturity stage of maize, respectively. Similarly, the light transmittance at soybean canopy increased by 218%, 160% and 172% at V2, V5 and R1 stage in 2M2S compared with 1M1S. The improved light environment at soybean canopy in 2M2S considerably enhanced the mean biomass accumulation, and allocation to stem and leaves of soybean by 168%, and 131% and 207%, respectively, while it decreased the mean biomass accumulation, and distribution to stem, leaves and seed of maize by 4%, and 4%, 6% and 5%, respectively than 1M1S. Compared to 1M1S, 2M2S also increased the CR values of soybean (by 157%) but decreased the CR values of maize (by 61%). Overall, under 2M2S, relay-cropped maize and soybean produced 94% and 69% of the sole cropping yield, and the 2M2S achieved LER of 1.7 with net income of 1387.7 US $ ha-1 in 2016 and 1434.4 US $ ha-1 in 2017. Our findings implied that selection of optimum planting pattern (2M2S) may increase the light interception and influence the light distribution between maize and soybean rows under relay-intercropping conditions which will significantly increase the intercrops productivity. Therefore, more attention should be paid to the light environment when considering the sustainability of maize-soybean relay-intercropping via appropriate planting pattern selection.

Yield advantage and nitrogen fate in an additive maize-soybean relay intercropping system

Sustainable agricultural development is urgently required to satisfy future food demands while decreasing environmental costs. Intercropping can increase per-unit farmland productivity through a resource-efficient utilization. However, the fate of N in intercropping systems remains unclear. To study the yield advantages and the fate of N in additive maize–soybean relay intercropping (IMS) systems, we quantified crop yield, soil N transformation abilities, soil bacterial abundances, and the fate of 15N. This study was conducted using three planting patterns, namely, monoculture maize (Zea mays L.) (MM), monoculture soybean (Glycine max L. Merr.) (MS), and IMS, and two N application rates, specifically, no N and applied N (N1, 45 and 135 kg N ha−1 for MS and MM, correspondingly; and N for the IMS, which was the sum of the monocultures). Results showed that a higher per-unit farmland productivity and a lower land use intensity are attained in the intercropping system than in the corresponding monocultures. In addition, land equivalent ratio (LER) ranges from 1.85 to 2.20. Moreover, the fate of 15N showed that the N uptake and residual are the highest, whereas N loss in the IMS is the lowest among all planting patterns. Intercropping had an increased N use efficiency by increasing N utilization efficiency, rather than N uptake efficiency. The abundance of ammonia oxidizer and denitrifier indicated that IMS improves the structure of soil microorganisms. Furthermore, the transformation abilities of soil N denoted that intercropping strengthens ammonifying and nitrifying capacities to increase soil N residual while decreasing ammonia volatilization and N2O emission. Finally, the greenhouse warming potential and gas intensity of N2O were significantly lower in the IMS than in the corresponding monocultures. In summary, the IMS system provides an environmentally friendly approach to increasing farmland productivity.

Imbalance Water Deficit Improves the Seed Yield and Quality of Soybean

Water imbalance condition (WIC) in a maize-soybean relay intercropping system is the main abiotic stress limiting biomass production and seed yield and, consequently, seed-quality. This experiment was started to study the effects of WIC on soybean, in which two soybean genotypes ND12 and C103 were grown in pots with roots split equally between two soil column and six WIC treatments (%) T1 (100), T2, (100:50), T3 (100:20), T4 (50:50), T5 (50:20), and T6 (20:20) field capacity on both sides of soybean roots were used. Results showed that both genotypes responded significantly to WIC treatments for all the parameters; however, the level of response differed between genotypes. Maximum osmoprotectants (except proline), biomass, yield and yield-related traits and superior seed quality were observed with ND12. Among WIC treatments, T2 and T3 produced 94% and 85%, and 93% and 81% of T1 biomass and yield, respectively. Similarly, treatments T2 and T3 also improved the oil quality by maintaining the content of unsaturated fatty acids and isoflavone content, while opposite trends were observed for protein content. Overall, moderate water reduction (T2 and T3) can improve soybean seed-quality and by selecting drought-resistant genotypes we can increase the soybean yield under intercropping systems.

Effects of phosphorus application rates and depths on P utilization and loss risk in a maize-soybean intercropping system

In order to explore the advantage of intercropping on phosphorus (P) efficient utilization and the reduction of soil P loss, a field experiment in a maize-soybean intercropping system, which included three P application (P2O5) rates (CP: 168 kg·hm-2; RP1: 135 kg·hm-2; RP2: 101 kg·hm-2) and three P application depths (D1: applied in 5 cm depth; D2: applied in 15 cm depth; D3: 1/2 of P fertilizer applied in 5 cm depth and another 1/2 in 15 cm depth) was carried out to analyze the effects of P application rates and depth on crop aboveground biomass, grain yield, crop P uptake, soil total and available P contents, and soil P adsorption-desorption characteristics. Compared with control treatment, the aboveground biomass, grain yield, crop P uptake, soil total P, and available P content were increased significantly by P application, regardless of P rate and application depth. Under the same application depth, RP1 had similar grain yield but higher crop P uptake compared with CP, and thus higher P apparent utilization efficiency. Under the same P application rate, the application depth of D2 had the highest crop aboveground biomass, grain yield, P uptake, soil total P, and available P. According to the characteristic of soil P adsorption-desorption, the treatment with the rate of RP1 and the depth of D2 had the strongest soil P retention capacity, which had advantage in alleviating P loss. These results suggested that reducing application rate but increasing application depth of P fertilizer could improve P use efficiency and reduce soil P loss without sacrifice in crop production in maize-soybean relay intercropping system.

Optimized nitrogen application methods to improve nitrogen use efficiency and nodule nitrogen fixation in a maize-soybean relay intercropping system

In China, the abuse of chemical nitrogen (N) fertilizer results in decreasing N use efficiency (NUE), wasting resources and causing serious environmental problems. Cereal-legume intercropping is widely used to enhance crop yield and improve resource use efficiency, especially in Southwest China. To optimize N utilization and increase grain yield, we conducted a two-year field experiment with single-factor randomized block designs of a maize-soybean intercropping system (IMS). Three N rates, NN (no nitrogen application), LN (lower N application: 270 kg N ha−1), and CN (conventional N application: 330 kg N ha−1), and three topdressing distances of LN (LND), e.g., 15 cm (LND1), 30 cm (LND2) and 45 cm (LND3) from maize rows were evaluated. At the beginning seed stage (R5), the leghemoglobin content and nitrogenase activity of LND3 were 1.86 mg plant−1 and 0.14 mL h−1 plant−1, and those of LND1 and LND2 were increased by 31.4 and 24.5%, 6.4 and 32.9% compared with LND3, respectively. The ureide content and N accumulation of soybean organs in LND1 and LND2 were higher than those of LND3. The N uptake, NUE and N agronomy efficiency (NAE) of IMS under CN were 308.3 kg ha−1, 28.5%, and 5.7 kg grain kg−1 N, respectively; however, those of LN were significantly increased by 12.4, 72.5, and 51.6% compared with CN, respectively. The total yield in LND1 and LND2 was increased by 12.3 and 8.3% compared with CN, respectively. Those results suggested that LN with distances of 15–30 cm from the topdressing strip to the maize row was optimal in maize-soybean intercropping. Lower N input with an optimized fertilization location for IMS increased N fixation and N use efficiency without decreasing grain yield.

Effects of Reduced Nitrogen on Soil Ammonification, Nitrification, and Nitro-gen Fixation in Maize-soybean Relay Intercropping Systems

Effects of Reduced Nitrogen on Soil Ammonification, Nitrification, and Nitro-gen Fixation in Maize-soybean Relay Intercropping Systems

Effects of reduced nitrogen inputs on crop yield and nitrogen use efficiency in a long-term maize-soybean relay strip intercropping system.

The blind pursuit of high yields via increased fertilizer inputs increases the environmental costs. Relay intercropping has advantages for yield, but a strategy for N management is urgently required to decrease N inputs without yield loss in maize-soybean relay intercropping systems (IMS). Experiments were conducted with three levels of N and three planting patterns, and dry matter accumulation, nitrogen uptake, nitrogen use efficiency (NUE), competition ratio (CR), system productivity index (SPI), land equivalent ratio (LER), and crop root distribution were investigated. Our results showed that the CR of soybean was greater than 1, and that the change in root distribution in space and time resulted in an interspecific facilitation in IMS. The maximum yield of maize under monoculture maize (MM) occurred with conventional nitrogen (CN), whereas under IMS, the maximum yield occurred with reduced nitrogen (RN). The yield of monoculture soybean (MS) and of soybean in IMS both reached a maximum under RN. The LER of IMS varied from 1.85 to 2.36, and the SPI peaked under RN. Additionally, the NUE of IMS increased by 103.7% under RN compared with that under CN. In conclusion, the separation of the root ecological niche contributed to a positive interspecific facilitation, which increased the land productivity. Thus, maize-soybean relay intercropping with reduced N input provides a very useful approach to increase land productivity and avert environmental pollution.

Effects of Shading on Leaf Structure and Photosynthetic Fluorescence Characteristics of Soybean Seedlings in Maize-Soybean Relay Intercropping System

Effects of Shading on Leaf Structure and Photosynthetic Fluorescence Characteristics of Soybean Seedlings in Maize-Soybean Relay Intercropping System

Effect of aboveground and belowground interactions on the intercrop yields in maize-soybean relay intercropping systems

Aboveground and belowground interactions are crucial in the over-yielding of intercropping systems. However, the relative effects of aboveground and belowground interactions on yields of intercrops in maize (Zea mays L.) and soybean [Glycine max (L.) Merr.] relay intercropping systems are still unclear. Field experiments, including measurements of biomass, grain yield, and photosynthetic parameters, were conducted in 2013–2014 to analyze the advantages and effects of aboveground and belowground of interspecies interactions on yield. To analyze the aboveground interactions of intercrops for light interception, this study adopted three different row configurations [(P1) “160cm+40cm” and (P2) “120cm+80cm” maize wide-narrow row planting, where two rows of soybean with a 40-cm row width were planted in the wide rows, and (P3) “100cm +100cm” maize equal-row planting, where one row of maize and one row of soybean with a 50-cm spacing between the adjacent rows of both crops]. Moreover, to identify interspecies belowground competition, no root separation (R1) and root separation (R2) were employed between adjacent maize and soybean rows.The photosynthetically active radiation (PAR) transmittances of maize wide-row were significantly higher than those of maize narrow-row at the sixth leaf stage (jointing stage), twelfth leaf stage (bell stage), and tasseling stage. Specifically, PAR transmittances decreased as maize narrow-row spacing increased. No significant differences in the PAR transmittances of maize narrow-row or wide-row were found between the R1 and R2 conditions. Similarly, no significant differences between intercrop biomass and grain yield were observed between the R1 and R2 conditions. By contrast, different row configuration treatments exhibited significant differences in biomass (whole growth period for soybean and after tasseling stage for maize), grain yield and photosynthetic parameters of intercrops. These results implied that aboveground interactions, such as mutual shading, have more significant contributions to intercrop advantages than belowground interactions. In addition, the intercropped maize yields increased as maize narrow-row spacing (from P1 to P3 treatment) increased. However, contrasting trends were found for intercropped soybean yield and land equivalent ration (LER). No significant differences in LER were observed between R1 and R2 conditions in different row configurations. P1 treatment exhibited the maximum LER (1.64 for 2013 and 1.83 for 2014) and mixed yield (7430kgha−1 for 2013 and 9559kgha−1 for 2014), but the lower maize yield compared with P2 and P3 treatments. This result suggested that reducing the competitive ability of maize while increasing that of soybean significantly improves intercropping advantage in maize-soybean relay intercropping systems.