Spatiotemporal variations of wheat and maize grass-grain ratio and analysis of carbon sequestration and emission reduction effects of comprehensive straw utilization

This study aimed to investigate the spatiotemporal variations in the grain-to-straw ratios of wheat and maize. A systematic evaluation was also made on the carbon sequestration and emission reduction potential of the straw utilization. Meta-analysis was conducted to search for the keywords, such as "straw-to-grain ratio," "harvest index," "wheat," "maize," and "biomass" in the China National Knowledge Infrastructure, and then screened the straw-to-grain ratio and crop yield data. The straw-to-grain ratio and straw nutrient analysis were then implemented on the temporal variations in the straw-to-grain ratio and its relationship with the crop yield. A total of 285 wheat and 173 maize samples were collected from 14 counties in Henan Province, China. Straw production and utilization data were integrated from the Crop Straw Resource Accounting Subsystem at the county level. The nutrient content of the straw was calculated to evaluate the carbon sequestration and emission reduction potential of straw utilization. The fertilizer substitution of the straw incorporation was also assessed after calculation. The results show that the grain-to-straw ratio of the wheat and maize decreased by 0.14 and 0.06, respectively, every five years. The grain-to-straw ratio decreased by 0.36 for wheat and 0.09 for maize, particularly for every 1 000 kg increase in yield per hectare. The eastern region shared the highest grain-to-straw ratio for wheat (1.14), while the central and western regions had the lowest (1.00). In maize, the southern region exhibited the highest grain-to-straw ratio (0.9), while the eastern and northern regions had the lowest (0.77). The average annual straw production of wheat and maize was 5 168.9×10⁴ t and 2 788.4 × 10⁴ t, respectively, from 2021 to 2023. In terms of the straw utilization, over 98% of the straw was used for fertilization, feed, and fuel. Specifically, 87.7% of the wheat straw was used for fertilization, 8.7% for feed, and 2.3% for fuel, while 80.9% of maize straw was used for fertilization, 14.7% for feed, and 3.6% for fuel. The straw return was contributed approximately 9 579.9×10⁴ t of wheat straw and 5.751.7×10⁴ t of maize straw to croplands over the past three years, thus returning 102.8×10⁴ t of nitrogen, 36.14×10⁴ t of phosphorus, and 367.87×10⁴ t of potassium to the soil, with an average annual carbon sequestration of 259.44×10⁴ t. The fertilizer, feed, and fuel utilization of the straw was equivalent to carbon emissions reduced by 252.99×10⁴ t annually. The grain-to-straw ratios of the wheat and maize continuously decreased with the time progression and yield improvement. The utilization of the straw can be expected to improve the soil fertility and reduce carbon emissions. Therefore, the straw utilization was integrated for green agriculture in the goals of carbon peaking and carbon neutrality.