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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]

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]