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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 CO 2 -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: CO 2 , CH 4 and N 2 O) emissions from the field plots, indirect GHG emissions from agricultural inputs (e.g., fertilizer, diesel and pesticides) and CO 2 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 N 2 O 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. [ABSTRACT FROM AUTHOR]

Nitrate pollution from agricultural activities has become a common problem in the North China Plain due to overapplication of N fertilizer. Agroforestry is considered a potentially effective land-use practice for mitigating nitrate leaching. In this study, an agroforestry system of 1–2-year-old poplar (Populus × euramericana cl. ‘74/76’) trees intercropped with winter wheat (Triticum aestivum) and maize (Zea mays) were rotated annually and compared with a sole-crop system in order to quantitatively investigate changes in NO3-N accumulation and water use following introduction of the trees into the farmland. The results revealed that evapotranspiration (ET) decreased by 6.1% and 3.7% during the wheat season and increased by 11.5% and 12.1% during the maize season, for fertilized and nonfertilized treatments intercropped with young poplar trees, respectively. NO3-N concentration decreased significantly in the intercropped system. NO3-N accumulation in the soil after the winter wheat and maize harvests decreased by 29.7 kg N ha-1 and 47.9 kg N ha-1 in the fertilized intercropped system, respectively, compared to the fertilized sole-crop system, while the grain yield of intercropped maize decreased by 31.3% and 33.7% for the fertilized and nonfertilized treatments, respectively. Water use efficiency (WUE) decreased by 38.5% and 40.7%, respectively. These results indicate that poplar tree roots play a significant role in alleviating NO3-N accumulation in the soil profile due to more NO3-N uptake in the intercropped system. However, they severely influenced maize grain yield and WUE. Thus, young poplar trees can be introduced into wheat fields. However, it is impractical to introduce them into a wheat and maize rotation system, in view of sustainable agriculture and environmental protection. [ABSTRACT FROM AUTHOR]

The maize sole cropping system solves problems related to ground water resource shortages and guarantees food security in the North China Plain. Using optimal sowing dates is an effective management practice for increasing maize yield. The goal of this study was to explore an optimum sowing date for high-yield maize. Six sowing dates (SDs) from early April to late June with intervals of 10 to 20 days between SD—SD1 (early April), SD2 (mid to late April), SD3 (early May), SD4 (mid to late May), SD5 (early June), SD6 (late June)—were applied from 2012 to 2017. The results showed that yield was correlated with the sowing date based on the thermal time before sowing (r = 0.62**), which was defined as the pre-thermal time (PTt), and that the yield was steadily maintained at a high level (>10,500 kg ha−1) when PTt was greater than 479 °C. To satisfy the growing degree-days required for maturity, maize needs to be sown before a PTt of 750 °C. Data analysis of the results from 2014, 2015, and 2017 revealed the following: i) Most of the grain-filling parameters of late-sown dates (SD4, SD5 and SD6) were better than those in early-sown dates (SD1, SD2, and SD3) in all years, because of the high daily maximum temperature (Tmax) and wide diurnal temperature (Td) from silking to blister (R1–R2) of early-sown dates. The weight of maximum grain-filling rate (Wmax) of SD3 decreased compare with SD4 by the narrow Td from blister to physiological maturity (R2–R6) in all years (−5, −12, and −33 mg kernel−1 in 2014, 2015, and 2017, respectively). ii) In 2017, the pollination failure rates of early-sown dates were 8.4~14.5%, which was caused by the high Tmax and Td of R1–R2. The apical kernel abortion rates were 28.6 (SD2) and 38.7% (SD3), which were affected by Tmax and Td during R2–R6. iii) Compared with late-sown dates, the wide Td of early-sown dates in R1–R2 was caused by higher Tmax, but the narrow Td in R2-R6 was caused by higher Tmin. Our results indicate that high-yielding maize can be obtained by postponing the sowing date with a PTt of 480~750 °C, which can prevent the negative effects of the high Tmax of R1–R2 and high Tmin of R2–R6 on kernel number and weight formation. Moreover, these above-mentioned traits should be considered for heat tolerance breeding to further increase the maize yield. [ABSTRACT FROM AUTHOR]

To reduce pressure on soybean imports, the Chinese government has implemented maize (Zea mays L.)-soybean (Glycine max (L.) Merr.) intercropping (MǁS). The initiative focuses on mechanized, large-scale agricultural areas in the northern plains, aiming to harvest extra soybean while maintaining maize yield. Although the high production potential of MǁS has been established in small-scale experiments, its effectiveness in large-scale mechanized settings on the plains has been less explored. Such oversight misses the complexities of intercropping in terms of field management and configuration that affect yield in large-scale scenarios. The study evaluated the yield performance of 172 households in the North China Plain (NCP) engaging in both MǁS and maize monoculture. A hierarchical model was constructed to forecast the MǁS's high-yielding potential based on the coupling level of field configuration and field management. Findings revealed that MǁS's total yield was only 1 % higher than monoculture. The principal impediment to total yield enhancement was the 10 %-20 % reduction (compared to monoculture) in intercropped maize yield. The inputs for fertilisers, herbicides, chemical control agents, diesel, machinery, and labor for MǁS were 16 %-156 % higher than for monoculture, highlighting significant field management challenges. The imbalance between labor and machinery inputs in weeding was the MǁS's efficiency constraints. Field configuration-type factors contributed 50 % to yield, surpassing field management (23 %). Planting size emerged as the most pivotal factor influencing yield, followed by fertiliser application. Strategies such as controlling the planting scale to 11 ha, increasing the proportion of maize planted to 60 %, optimizing fertiliser and herbicide application (488 kg ha−1, 3 kg ha−1), and managing weed labor (27 h ha−1) were critical in reducing the intercropped maize yield reduction to 9 %, approaching levels observed in previous fine management experiments. Furthermore, these measures resulted in an increased in the extra soybean yield of 16–26 %. MǁS is therefore eligible for support in the NCP based on the application of yield improvement measures. This study underscores the yield performance of mechanized, large-scale MǁS, providing theoretical support in terms of yield for its promotion in the NCP. • The total yield of large-scale maize-soybean intercropping (MǁS) exceeds maize monoculture by 1 %. • Field configuration type factors contribute 50 % to MǁS yield, surpassing field management (23 %). • At the coupling level of field management and configuration, planting scale is key for MǁS yield. • Large-scale MǁS qualifies for promotion in the North China Plain via yield enhancement measures. [ABSTRACT FROM AUTHOR]

Intercropping of maize and soybean has proven to be a sustainable cropping system all over the world. In recent years, as imports of maize and soybean have increased, the Chinese government has strongly promoted the maize -soybeans intercropping to prevent a decline in maize production and to obtain an extra soybean harvest. It is not clear what the coupling relationship is between the intercropping model and the change in yield of maize and soybean across China. The research searched for articles that fulfilled the criteria related to maize-soybean intercropping in China since 2000. It investigated the yield change through meta-analysis, and analyzed the allocation path of yield increase based on the field configuration level using single factor analysis, multilevel model analysis and random forest analysis. Compared to monoculture, the total yield of intercropping maize and soybean increased by approximately 12%, while the equivalent yield decreased by 8% and 40%, respectively. The proportion of maize area was crucial for the maize intercrop yield. The shading effect of maize on soybean was a key factor in soybean yield reduction. Increasing the distance between the maize and soybean strips lead to an elevation of soybean intercropping yields without compromising maize yield or the total yield. Huang-Huai-Hai Plain Summer Sowing region and Southwest Mountain region were more suitable for promotion. The yield of intercropping was beneficial in this suitable integrated region when the soybean strip width did not exceed 78 cm (soybean row spacing ≤3) and the distance between the maize and soybean strips ≥ 77 cm. Maize-soybean intercropping had great potential for yield improvement, the overall LER was 1.6. In the Huang-Huai-Hai Plain Summer Sowing and Southwest Mountain regions, the yield-advantaged field configurations were: (soybean strip-width ≤61 cm or soybean rows ≤3, distance between strips ≥65 cm) and (soybean strip-width ≤76 cm or soybean rows ≤3, distance between strips ≥73 cm), respectively. Each plantation regions still need to select the optimal distance based on the local farming facilities and traditional farming habits. The research demonstrates the yield changes of maize-soybean intercropping in China, providing a methodology with certain reference value for intercropping yield improvement based on field configuration level. [ABSTRACT FROM AUTHOR]