Maize-soybean Intercropping Research Articles

Analysis of Grain Yield Differences Among Soybean Cultivars under Maize–Soybean Intercropping

Shading created by intercropping reduces the photosynthetic capacity of soybean plants but also directly affects the pod setting process of soybean. However, which of the changed aspects induce the yield differences in intercropped soybean cultivars is still unknown. Four soybean cultivars with similar yield and growth and development processes in monoculture were selected by a pre-experiment. Field experiments were carried out from 2015 to 2017 to investigate the leaf photosynthetic parameters, total biomass, reproductive characteristics, yield and yield components of soybean. The yield of soybean cultivars was significantly decreased in intercropping systems and the yield of cultivars (cvs.) ZH39 and QH34 were considerably higher than those of cvs. HD19 and HD20. Besides, the pod and seed number and harvest index were also reduced by intercropping and the yield components of cvs. ZH39 and QH34 in intercropping were significantly higher than those of cvs. HD19 and HD20, other than the seed size. Although the parameters of leaf photosynthetic capacity (leaf area index, net photosynthetic rate, and chlorophyll content) of soybean were changed by intercropping, there was no significant difference among cultivars. Additionally, the CGRR1–R5 (crop growth rate between R1 and R5) of intercropped soybean was lower than that of monoculture, while no significant differences were observed in different cultivars. The reproductive biomass at R5 was significantly different among soybean cultivars, and the reproductive partitioning and seed set efficiency of different cultivars were varied by the reproductive biomass at R5. Therefore, high-yielding cultivars in intercropping can achieve higher yield due to more reproductive structures survived at R5.

Shading of the mother plant during seed development promotes subsequent seed germination in soybean.

The effect of shading during seed development on subsequent germination remains largely unknown. In this study, two soybean (Glycine max) seed production systems, monocropping (MC) and maize-soybean intercropping (IC), were employed to examine the effects of shading of the mother plant on subsequent seed germination. Compared to the MC soybean seeds, which received light, the developing IC seeds were exposed to shade resulting from the taller neighboring maize plants. The IC seeds germinated faster than the MC seeds, although there was no significant difference in the thickness of the seed coat. The concentration of soluble pro-anthocyanidin in the IC seed coat was significantly lower than that in the MC seed coat. Changes in the concentrations of several types of fatty acids in IC seeds were also observed, the nature of which were consistent with the effect on germination. The expression levels of genes involved in abscisic acid (ABA) biosynthesis were down-regulated in IC seeds, while the transcription levels of the genes related to gibberellin (GA) biosynthesis were up-regulated. This was consistently reflected in decreased ABA concentrations and increased active GA4 concentrations in IC seeds, resulting in an increased GA4/ABA ratio. Our results thus indicated that shading of the mother plant during seed development in soybean promoted subsequent germination by mediating the biosynthesis of pro-anthocyanidins, fatty acids, and phytohormones.

Reduced stomatal conductance and irradiance account for soybean [Glycine max (L.) Merrill] yield decline in maize-soybean intercrop

Reduced stomatal conductance and irradiance account for soybean [Glycine max (L.) Merrill] yield decline in maize-soybean intercrop

English

Weed is a very significant enemy of crop production. Its density, diversity and the interaction complexes on the yield and yield component of maize cv “Quality protein” were investigated in the present study. The experiment was laid out in randomized complete block design (RCBD) containing five weed management strategies and a weedy check as treatments in 2015 and 2016. Data were collected on weed density, yield and yield components of maize for the two years. For the years and the treatments, a mixed model factorial in RCBD was employed for the analysis of variance of the data. Significant (P≤0.05) variation exists among the two years; the six treatments and their interaction for the grain yield and its components. The use of Pendimenthalin (330 EC) at 3.0 kg a.i.ha-1 supported the highest grain yield (2.4 tons ha-1); hoe weeding and mulching was next with significantly (P≤0.05) lower grain yield of 2.2 tons ha-1. The weedy check had the lowest grain yield of 1.2 tons/ha. An average yield loss of 42% was obtained by comparing the weed control methods with each of the weedy check. By Shukla variance estimate, maize-soybean intercrop gave the most stable grain yield for the two years. Year 2016 significantly (P≤0.05) favoured grain yield, its components and weed density. The proportion of weed categories in the study was: Broadleaves (52.38%), grasses (33.33%) and sedges (14.28%). Broad leaves and grasses density measured at interval displayed a significant linear trend. The sixth week after planting was most critical for grain yield determination in the tested maize cultivar. Key words: Weed management strategies, maize, grain yield, interaction complexes.  &nbsp

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.

Co-benefits of sustainable farming methods to safeguard food security and environmental health in China: a modelling study

BackgroundModernised farming has contributed significantly to the increased global food supply over the past half-century, albeit while creating severe threats to the environment. Excessive application of chemical fertiliser has in particular led to massive release of reactive nitrogen compounds into the atmosphere, where they become major components of fine particulate matter (PM2·5) pollution, with detrimental effects on human health. Various sustainable farming methods with lower environmental impacts have been experimented with and practised in many countries, but their wider benefits beyond the farm scale have rarely been examined. One such method is intercropping with soybeans, which takes advantage of the nitrogen fixing ability of soybeans to improve nutrient use efficiency and reduce fertiliser use. MethodsWe developed a computational modelling framework using the GEOS-Chem and DNDC models, revising the representation for soil nitrogen processes and crop-crop interaction. We did model experiments to quantify the benefits of nationwide adoption of maize-soybean intercropping systems in China in terms of gains in crop production, decreases in fertiliser consumption, and reductions in ammonia (NH3) emissions. We further examined how the decline in NH3 emissions could reduce the downwind formation of PM2·5 and the associated public health costs. FindingsAnnual mean PM2·5 concentrations can be reduced by up to 1·5 μg/m3 with the nationwide adoption of maize-soybean intercropping, with a corresponding annual net economic benefit of US$67 billion, of which $13 billion arises from saved health costs from reduced air pollution. InterpretationOur study shows the wider economic and environmental value of intercropping systems for promoting both food security and public health, serving as a basis for policy consideration by governments and stakeholders. The same modelling framework can likewise be used to investigate the large-scale impacts of other sustainable farming methods. FundingGeneral Research Fund the Hong Kong Research Grants Council, the Area of Excellence Scheme, and the CUHK Vice- Chancellor Discretionary Fund.

Intercropping and Fertilizer Rate Combinations Impact on Maize (Zea Mays L.) and Soybean (Glycine Max L (Merill)) Productivity: The Case Study in the Guinea Savannah Agro-Ecological Zone of Ghana

Production of food in resource-constrained environments that have poor inherent soil nutrition depends on tillage and cropping systems that provide high yields, preserve soil, water and biodiversity. This research was conducted in the Guinea savannah agroecology of Ghana, during the 2015-2016 cropping seasons to evaluate the impact of tillage and cropping systems on sustainable production of maize and soybean by resource-poor farmers. The experiment was a split-split plot design with four replications. The factors consisted of tillage system at three levels (plough, ripping and direct-seeding) laid out as main plots, fertilizer rate at three levels (0 kg/ha, half the recommended rate of 30-15-15 kg/ha and the recommended optimum rate of 60-30-30 kg/ha NPK) laid as sub-plots and cropping system at two levels (sole maize, maize-soybean intercrop) laid on the sub-sub plot. Apart from leaf area that had significant three-way interaction of tillage, cropping system and fertilizer rate (p < 0.05), all other growth parameters were affected by either two factor interaction or a sole factor. Grain yield of maize was significantly influenced by sole maize and fertilizer rate with highest yield occurring under the full rate (3.4 t/ha) compared with the half rate (2.7 t/ha), amounting to yield difference of about 700 kg/ha. Yield of soybean under the integrated production was affected by interaction of tillage system and fertilizer rate. Highest soybean yield (1.4 t/ha) was recorded under the ploughed condition at the full rate of fertilizer application. Though sole maize, ploughed and with full rate of fertilizer application, gave similar benefit/cost ratio as that of the integrated production with half rate of fertilizer application, the intercropped system with half fertilizer rate resulted in 45% more increases in profit compared to the sole production with full fertilizer rate. Integrated production of maize and soybean, with half the recommended rate of NPK (30-15-15 kg/ha) is therefore recommended to resource-poor farmers in northern Ghana.

Carbon footprint of different agricultural systems in China estimated by different evaluation metrics

Increase of concentrations of greenhouse gases (GHGs) in atmosphere have garnered lots of attention due to the associated risk of global warming. Carbon footprint (CF) is a measure that is extensively used to assess the contribution of an individual, event, organization, or product to global climate change. In the current study, the CF of five agricultural systems with different crop systems in different regions in China was evaluated in terms of CO2 eq per hectare, per kg crop yield, and per unit economic output, association with soil GHGs, agrochemical production and soil organic carbon (SOC) change. The results showed that direct nitrous oxide accounted for 61.9–97.8% of total soil GHG emissions in upland fields (agroforestry system, summer maize-winter wheat rotation tillage system, maize-soybean intercropping system, and continuous maize tillage system), while soil methane accounted for 89.9–95.1% of total soil GHG emissions in the paddy field (double rice-winter crop rotation system). GHGs produced from agricultural inputs varied from 2698.7 to 9781.5 kg CO2 eq ha−1 yr−1 among different agricultural systems. Nitrogen fertilizer was the dominant source of GHGs, which accounted for 47.4–92.4% of the total emission. Annual SOC increase ranged from −639.9–13823.9 kg CO2 eq ha−1 yr−1 in the five agricultural systems. Increases of SOC in the treatment of “reduced tillage with straw return” offset all of the total GHG emissions while “conventional tillage without straw return” decreased SOC storage in the continuous maize tillage system. An increase of SOC in crop systems of the other four agricultural systems could offset 23.2–66.7% of the total GHG emissions. Carbon emissions per hectare in the double rice-winter crop rotation system (7339.93–22994.17 kg CO2 eq ha−1 yr−1) were higher than the other four agricultural systems (−744.96–6523.12 kg CO2 eq ha−1 yr−1). In terms of crop yield, CFs of the summer maize-winter wheat rotation tillage system (0.28–0.34 kg CO2 eq kg−1 yr−1) were lower than those from the other four agricultural systems (0.39–2.83 kg CO2 eq kg−1 yr−1), except for the treatment with reduced tillage and residue return in the continuous maize tillage system. Similarly, CFs, as quantified via per unit economic output of the agroforestry system (0.12–0.19 kg CO2 eq ¥−1 yr−1), were lower than those in other the four systems (0.26–0.89 kg CO2 eq ¥−1 yr−1).Different evaluation methodology greatly affected the CF of different crop systems and mostly likely contributed to the contrary evaluation results, especially in the complex system of various crop systems (agroforestry and double rice-winter crop rotation system) in current study. Evaluation results of the CF of an agricultural system depends highly on the methodology used and may suggest different management decisions for lowering CF to promote the development of cleaner production.

Co-benefits of intercropping as a sustainable farming method for safeguarding both food security and air quality

Large-scale, industrialized farming has contributed significantly to the increased global food supply to feed the fast-growing world population over the past few decades, but it also comes with severe threats to the environment. In particular, the excessive application of chemical fertilizer has led to large emissions of reactive nitrogen compounds into the atmosphere, where they become significant components of fine particulate matter (PM2.5) air pollution. Intercropping has been considered as a sustainable agricultural practice that can reduce the environmental impacts of agriculture, but its potential benefits beyond the farm scale have rarely been examined. Here we develop a new parameterization scheme for belowground mutualistic interactions between intercropped crops in the DeNitificaiton-DeComposition biogeochemical model, which is then used to simulate and quantify the benefits of nationwide adoption of maize–soybean systems in China in terms of gains in crop production, decreases in fertilizer consumption, and reductions in ammonia (NH3) emission. We further examine how such a decline in NH3 emission could lessen the downwind formation of PM2.5 using the GEOS-Chem chemical transport model. We show that annual mean inorganic PM2.5 concentrations can be reduced by up to 1.5 μg m–3 with the nationwide adoption of maize–soybean intercropping, with a corresponding annual net economic benefit of US$67 billion, of which US$13 billion arises from saved health costs from reduced air pollution. This study demonstrates the economic and environmental values of intercropping systems in dually promoting food security and environmental health, which can serve as a basis for policy consideration as governments and stakeholders explore more sustainable farming options.

Reduced Tillage and Intercropping as a Means to Increase Yield and Financial Return in the Drylands of Tigray, northern Ethiopia: A Case Study under Rainfed and Irrigation Conditions

Intensive tillage is a major sustainability concern in cereal dominated cropping systems in the drylands of Tigray, Ethiopia. Hence, on-farm trials were conducted to investigate the yield and economic advantage of reduced tillage and intercropping for two seasons. A factorial experiment in a complete randomized block design was carried out at Adigudom located in Hintalo-Wajirat district in South-Eastern Tigray in 2014 (rain-fed) and 2015 (irrigated). The experiment consisted of four tillage frequencies (zero, one, two and four) and three types of cropping systems (sole maize, sole soybean and maize-soybean intercropping) in three/four replications. Maize, variety “Melkassa 2”, and soybean, variety “Awassa 91” were used. Grain and biomass yields, and harvest index of both crops were analysed. Yield advantage of intercropping was evaluated using land equivalent ratio (LER) and partial budget analysis was used for the financial evaluation. The grain and biomass yields of both crops were significantly increased (p<0.05) as the tillage frequencies increased from zero to four in both seasons but the frequent tillage with sole cropping was not economically viable as the two times tillage with maize-soybean intercropping gave 126% greater net benefit compared to the four times tillage sole maize, which is practiced by farmers in the study area. The net benefit was strongly influenced by the main effects of tillage and intercropping in both seasons (p<0.001) and by their interaction in 2014 (p<0.05). Significantly higher LER (1.87-2.12) was recorded from maize-soybean intercropping over sole cropping in all the tillages and both seasons. Hence, two alternative options are suggested that farmers could apply in the drylands of Tigray: (i) keeping the sole cropping culture of maize production, and reducing number of tillages from 4 to 2 that would give 374%and 705% Marginal Rate of Return (MRR), respectively, under the rainfed and irrigated conditions compared to zero tillage sole maize; or (ii) intercropping maize with soybean and reducing tillage frequency from 4to 2 that would give 608% and 585% MRR in the respective growing seasons, compared to zero tillage maize-soybean intercropping. Taking these results into account, two times tillage combined with maize-soybean intercropping can be a good option in dryland areas of Tigray to achieve higher total intercrop yield at a low cost and larger LER. Moreover, reduced tillage can minimize soil degradation and benefit farmers with poor access to draft power or female-headed households constrained with labour for ploughing. Keywords : Tillage; Intercropping; Maize; Soybean; Tigray; Ethiopia. Please find erratum for this article here: https://dx.doi.org/10.4314/mejs.v11i1.10

Effect of crop diversification and mulching on termite damage to maize in western Ethiopia

Termites are major biotic factors that contribute to crop damage and yield losses to maize (Zea mays L.) in western Ethiopia. This study evaluated mulching maize stover, intercropping maize with soybean (Glycine max (L.) Merr.) and desmodium (Desmodium intortum (Mill.) Urb.), and integration of mulching and intercropping for their effectiveness in reducing damage of Microtermes spp mainly Microtermes vadschaggae Sjostedt and Microtermes adschaggae (Sjosted) to maize. Five termite management treatments and a control (sole maize) were arranged in a randomized complete block design with three replicates on 2 farm sites in 2016 and 7 sites in 2017 cropping seasons in Sibu Sire and Gudeya Billa. Results indicated that application of maize stover as mulch combined with animal manure, maize-soybean intercrops and wood ash, maize-desmodium intercrops, and mulching combined with maize-soybean intercrops consistently reduced termite damage to maize in both cropping seasons. These results were comparable to application of Diazinon 60% EC (standard check). In addition, intercropping maize with desmodium, mulching + intercropping maize with soybean, and Diazinon 60% EC reduced the number of lodged plants per plot compared to control. Maize grain yield in treated plots was significantly higher than maize monocrop control. In order to reduce termite damage and to enhance maize productivity, mulching using maize stover, and intercropping of maize with soybean or desmodium can be used in termite prone areas of western Ethiopia and other countries in Africa with similar agroecologies.

Shade stress decreases stem strength of soybean through restraining lignin biosynthesis

Lodging is the most important constraint for soybean growth at seedling stage in maize-soybean relay strip intercropping system. In the field experiments, three soybean cultivars Nandou 032-4 (shade susceptible cultivar; B1), Jiuyuehuang (moderately shade tolerant cultivar; B2), and Nandou 12 (shade tolerant cultivar; B3) were used to evaluate the relationship between stem stress and lignin metabolism in the stem of soybean. Results showed that the intercropped soybean was in variable light condition throughout the day time and co-growth stage with maize. The xylem area and cross section ratio played a main role to form the stem stress. The B3 both in intercropping and monocropping expressed a high stem stress with higher xylem area, lignin content, and activity of enzymes (phenylalanine ammonia-lyase (PAL), 4-coumarate: CoA ligase (4CL), cinnamyl alcohol dehydrogenase (CAD), and peroxidase (POD)) than those of B1 and B2. Among the soybean cultivars and planting pattern, lignin content was positively correlated with stem stress. However, a negative correlation was found between lignin content and actual rate of lodging. In conclusion, the shade tolerant soybean cultivar had larger xylem area, higher lignin content and activities of CAD, 4CL, PAL, and POD than other soybean cultivars in intercropping. The lodging in maize-soybean intercropping can be minimized by planting shade tolerant and lodging resistant cultivar of soybean. The lignin content in stem could be a useful indicator for the evaluation of lodging resistance of soybean in intercropping and activities of enzymes were the key factors that influence the lignin biosynthesis.

Sustainability Evaluation of the Maize–Soybean Intercropping System and Maize Monocropping System in the North China Plain Based on Field Experiments

Monocropping systems, which currently dominate China’s major grain production regions, contribute to resource scarcity and environmental pollution. Intercropping has the potential to improve resource use efficiency. However, prior studies of intercropping systems have generally focused on ecological, economic, and social consequences. Here, we make a comparative ecological sustainability analysis on energy capture and efficiency of maize monocropping and maize–soybean intercropping systems through emergy evaluation based on field experiments performed from 2012 to 2014. We find that maize monocropping shows higher sustainability than maize–soybean intercropping in the North China Plain at present. Quantitative results indicate that for maize monocropping, the emergy yield ratio (EYR) and emergy sustainability index (ESI) are 13.7% and 21.1% higher than that of intercropping systems, and the environmental loading ratio (ELR) is 7.3% lower than that of intercropping systems. To further test, we applied three levels of nitrogen fertilizer in intercropping systems (120 kg ha−1, 180 kg ha−1, 240 kg ha−1), and find that a reduced rate of N fertilizer for intercropped system leads to higher sustainability (ESI 5.3% higher) but still lower sustainability than maize monocropping. Key drivers of the different sustainability outcomes are decreased energy output and a larger proportion of labor input associated with intercropping systems.

Agronomic and Economic Performance of Maize-Soybean Intercrop under Rhizobia and Soil Amendments in Western Kenya

Agronomic and Economic Performance of Maize-Soybean Intercrop under Rhizobia and Soil Amendments in Western Kenya

Effect of shading on accumulation of soybean isoflavonoid under maize-soybean strip intercropping systems

ABSTRACTMaize-soybean strip intercropping system is an important ecological planting system; the wide development of intercropped soybean has contributed to the soybean industry in China. Soybean growth and seed production were affected by the shading from maize. Previous studies confirmed that relay strip intercropping shading facilitates the accumulation of isoflavone glucosides but does not take advantage of the accumulation of isoflavone aglycone. However, the regulation of isoflavones accumulation under strip intercropping system was unknown; in which soybean and maize were sown at the same time, and soybean was mainly shaded in the reproductive stage. In order to reveal the effects of intercropping shading on the isoflavones accumulation in soybean seed, two independent field experiments were conducted in eastern China. We compared the isoflavones profiles of soybean seeds, which were grown under various maize-soybean intercropping systems with different shade levels. The results showed that the intercropping shading was not benefited to the accumulation of soy-isoflavones, including aglycones and isoflavones glycosides and various forms of isoflavones were decreased with the decline of photosynthetic active radiation. Multivariate statistical analysis and significance analysis showed that acylated isoflavones may be more susceptible to intercropping shading.Abbreviations: HCA: Hierarchical cluster analysis; PAR: photosynthetically active radiation; PCA: Principal component analysis; LC-MS: Liquid chromatography mass spectrometer.

Global warming potential from maize and maize-soybean as affected by nitrogen fertilizer and cropping practices in the North China Plain

Nitrogen fertilizer is required to meet grain targets, but the fossil fuel consumption and greenhouse gas emissions resulting from its use are a barrier to achieve low C agriculture. The objective of this study is to evaluate the net global warming potential (GWP) of maize and soybean monoculture and maize-soybean intercrop systems with an ecosystem-level C budget and determine the optimal N fertilizer requirement of maize-soybean intercrop based on the GWP in CO2 -eq during cropping season. The field experiment had five treatments: maize and soybean monoculture receiving 240 kg N ha−1 and maize-soybean intercrop receiving 120, 180 and 240 kg N ha−1 for three years (2012, 2013, and 2014). Considering greenhouse gas (GHG: CO2, CH4 and N2O) emissions from the field plots, indirect GHG emissions from agricultural inputs (e.g., fertilizer, diesel and pesticides) and CO2 fixation by crops, soybean monoculture was the net C source due to its lower net primary production, while all maize monoculture and intercrop treatments were net C sinks except for the maize-soybean intercrop receiving 240 kg N ha−1 in 2013. Maize monoculture was the largest C sink due to its higher net primary production, even though it had significantly (p < 0.05) greater direct and indirect GHG emission than of the maize-soybean intercrop treatments with lower N rates. Nitrogen fertilizer contributed to direct and indirect GHG emissions, with peak N2O fluxes from field plots up to two weeks after N fertilization and 26%–74% of indirect emission attributable to N fertilizer use. Higher N fertilizer rates did not improve yield in the maize-soybean intercrop, and the nitrogen-scaled GWP showed that maize-soybean intercrops fertilized with 150–182 kg N ha−1 had a comparable C fixation potential to maize monoculture receiving 240 kg N ha−1. In conclusion, we demonstrate the ability of maize-soybean intercrop to function as a C sink, similar to maize monoculture, in the North China Plain.

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.

Greenhouse gas emissions from soil under maize–soybean intercrop in the North China Plain

Intercrop systems can exhibit unique soil properties compared to monocultures, which influences the microbially-mediated processes leading to greenhouse gas emissions. Fertilized intercrops and monocultures produce different amounts of N2O, CO2 and CH4 depending on their nutrient and water use efficiencies. The objective of this study was to compare the fluxes and seasonal emissions of N2O, CO2, and CH4 from a maize–soybean intercrop compared to maize and soybean monocultures, in relation to crop effects on soil properties. The experiment was conducted during 2012, 2013 and 2014 at the WuQiao Experimental Station in the North China Plain. All cropping systems received urea-N fertilizer (240 kg N ha−1 applied in two split applications). The cropping systems were a net source of CO2 and a net sink of CH4, with significantly (P < 0.05 in 2012) and numerically (2013 and 2014) lower N2O flux and smaller seasonal N2O emissions from the maize–soybean intercrop than the maize monoculture. The proportion of urea-N lost as N2O was lower in the maize–soybean intercrop (1.6% during the 3-year study) and soybean monoculture (1.7%), compared to maize monoculture (2.3%). Soybean reduced the soil NO3−–N concentration and created a cooler, drier environment that was less favorable for denitrification, although we cannot rule out the possibility of N2O reduction to N2 and other N compounds by soybean and its associated N2-fixing prokaryotes. We conclude that maize–soybean intercrop has potential to reduce N2O emissions in fertilized agroecosystems and should be considered in developing climate-smart cropping systems in the North China Plain.

MAIZE–SOYBEAN INTERCROPPING FOR SUSTAINABLE INTENSIFICATION OF CEREAL–LEGUME CROPPING SYSTEMS IN NORTHERN NIGERIA

SUMMARYField studies were conducted during the 2014 and 2015 wet seasons at Zaria in the northern Guinea savanna and at Iburu in the southern Guinea savanna of Nigeria to determine the productivity of maize–soybean intercropping system. There were four treatment combinations in the experiment: sole maize; sole soybean; maize spaced at 50 cm and intercropped with soybean; and maize spaced at 65 cm and intercropped with soybean. The experiment was laid out in a randomized complete block design with three replications. The results showed that sole cropped maize and soybean generally outperformed the intercropped component crops. Land Equivalent Ratio (LER) was greater than 1 for all the intercrop treatments, indicating that it is advantageous to grow maize and soybean in association than in pure stands. Except for 2014 in Zaria, LER for intercropped maize spaced at 50 cm was higher than that for maize spaced at 65 cm. Gross Monetary Value (GMV) was generally higher for intercrops than sole crops except in Iburu in 2015 where GMV for intercropped maize spaced at 65 cm was similar to those of sole maize and soybean. Monetary Advantage Index (MAI) was positive for all intercrop treatments in both locations and years, which shows definite yield and economic advantages compared to the sole cropping systems. This suggests that farmers can intercrop soybean and maize with maize spaced at 50 cm and 65 cm.