Multiple Cropping Systems for Improving Crop Yield and Soil Quality—Series II

Optimized fertilizer use improves crop yield and mitigates environmental pollution associated with crop production. Fertilizer and plant density are core strategies to ensure food security and cope with climate change. However, little is known about the long-term interactive effect of reduced nitrogen (N) and increased density on yield and C (Carbon) balance. In this study, field experiments were conducted in a double-cropping rice region to evaluate long-term effects on yield and carbon footprint (CF) by crop-based and soil-based methods. Treatments were set for 10% reduction in N coupling with conventional density (N1D1), 20% higher density (N1D2), 40% higher density (N1D3), and 20% reduction in N coupling with conventional density (N2D1), 20% higher density (N2D2), and 40% higher density (N2D3), with the prevailing practices as control, conventional plant density, and fertilizer dose. Results showed that the yield continued to increase with increasing density; under the same density, reducing N by 10% is more beneficial for yield improvement and for CH₄ emission reduction. Compared with CK, reducing N application by 10% generally increased the annual yields by 7.34–23.25% on average, and reduced CH₄ emissions by 16.19–22.11%, resulting in a reduced crop-based carbon footprint of 22.24–26.82%, and a reduced soil-based carbon footprint of 22.08–32.85%. While reducing N application by 20% increased the annual yields by 5.00–20.19% and reduced the CH₄ emission by 1.66–4.93%, it reduced crop-based carbon footprints by 1.81–10.05% and reduced soil-based carbon footprints by 7.22–19.86%. As density increased, the crop-based CF decreased, whereas the soil-based CF increased. Overall, the highest yield and the lowest soil-based CF and unit yield CF (CFy) were observed in N1D3. Regarding sustainability, a 10% reduction in N, along with an increase in density to 40%, can be recommended for double-cropping rice production. Full article

Crop straw and N fertilizer applications impact paddy rice yield and greenhouse gas (GHG) emissions. However, their interactive effects have not been well documented. This study investigated the effects of straw (S), no straw incorporation (NS), and three levels of N fertilization rates (N0, N1, and N2) on single rice (SR), double rice (DR), and rice-wheat (RW) cropping systems. Straw incorporation significantly increased total CH₄ emissions by 118.6%, 8.0%, and 79.0% in the SR, DR, and RW, respectively, compared to the NS. The total GHG emissions in DR are significantly 72.6% and 83.5% higher than those in RW and SR, respectively. Compared to NS, straw incorporation significantly increased yield-scaled emissions by 27.8%, 15.0%, and 89.0% in SR, DR, and RW, respectively. Straw with N application significantly increased average rice yield over N1 and N2 by 39.4%, 50.0%, and 6.7% in SR, DR, and RW, respectively. There was a significant correlation between methyl coenzyme M reductase (mcrA) and CH₄ emissions in r_SR = 0.87 (p < 0.05) and r_RW = 0.85 (p < 0.05), except in r_DR = 0.06 (p > 0.05). This study scientifically supports straw incorporation combined with a moderate N application rate in rice-based cropping systems to maintain high rice yields and mitigate GHG emissions. Full article

A multiple cropping system is beneficial for utilizing natural resources, while increasing the grain production and economic outputs. However, its impact on greenhouse gas emissions is unclear. The objective of this study was to evaluate the influence of rice-based cropping systems on methane (CH₄) and nitrous oxide (N₂O) emissions, the carbon footprint (CF), grain yields, and net economic returns in eastern China. Four treatments were applied: rice–fallow (as a control), rice–milk vetch, rice–wheat, and rice–rapeseed. Methane and N₂O emissions were measured every 7 days via static chamber and gas chromatography methods from the 2019 rice season to the 2021 non-rice season. The CF was calculated based on the life cycle assessment. The results showed that multiple cropping systems significantly increased the annual grain yield by 1.2–6.4 t ha⁻¹ and the annual CH₄ and N₂O emissions by 38–101 kg CH₄-C ha⁻¹ and 0.58–1.06 kg N₂O-N ha⁻¹, respectively. The average annual net returns for rice–wheat and rice–rapeseed were 131–150% greater than those for rice–milk vetch and rice–fallow. The annual CFs increased in the following order: rice–wheat (19.2 t CO₂-eq ha⁻¹) > rice–rapeseed (16.6 t CO₂-eq ha⁻¹) > rice–milk vetch (13.9 t CO₂-eq ha⁻¹) > rice–fallow (11.5 t CO₂-eq ha⁻¹). The CH₄ emissions contributed to the largest share of the CF (60.4–68.8%), followed by agricultural inputs (27.2–33.7%) and N₂O emissions (2.9–5.9%). Moreover, nitrogen fertilizer accounted for 65.6–72.4% of the indirect greenhouse gas emissions from agricultural inputs. No significant difference in the CF per unit grain yield was observed between the four rice-based cropping systems. The CF per net return of rice–wheat and rice–rapeseed significantly decreased by 37–50% relative to that of rice–fallow and rice–milk vetch. These findings suggest the potential to optimize rice-based cropping systems for environmental sustainability and grain security. Full article

Increasing agricultural yields and reducing greenhouse gas (GHG) emissions are the main themes of agricultural development in the 21st century. This study investigated the yield and GHGs of a jujube–alfalfa intercropping crop, relying on a long-term field location experiment of intercropping in an arid region. The treatments included four planting densities (D1 (210 kg ha⁻¹ sowing rate; six rows), D2 (280 kg ha⁻¹ sowing rate; eight rows), D3 (350 kg ha⁻¹ sowing rate; ten rows)) and four nitrogen levels (N0 (0 kg ha⁻¹), N1 (80 kg ha⁻¹), N2 (160 kg ha⁻¹), and N3 (240 kg ha⁻¹)) in the jujube–alfalfa intercropping system. The results showed that the jujube–alfalfa intercropping system is a the “source” of atmospheric CO₂ and N₂O, and the “sink” of CH₄; the trend of CO₂ fluxes was “single peak”, while the trend of N₂O and CH₄ fluxes was “double peak”, and there was a tendency for their “valley peaks” to become a “mirror” of each another. The magnitude of emissions under the nitrogen level was N3 > N2 > N1 > N0; the content of soil total nitrogen, quick-acting nitrogen, and the global warming potential (GWP) increased with an increase in the amount of nitrogen that was applied, but the pH showed the opposite tendency. The D2N2 treatment increased the total N, quick N, SOC, and SOM content to reduce the alfalfa GHG emission intensity (GHGI) by only 0.061 kg CO₂-eq kg⁻¹ compared to the other treatments. D2N2 showed a good balance between yield benefits and environmental benefits. The total D2N2 yield was the most prominent among all treatments, with a 47.64% increase in yield in 2022 compared to the D1N0 treatment. The results showed that the optimization of planting density and N fertilization reduction strategies could effectively improve economic efficiency and reduce net greenhouse gas emissions. In the jujube–alfalfa intercropping system, D2N2 (eight rows planted in one film 160 N = 160 kg ha⁻¹) realized the optimal synergistic effect between planting density and nitrogen application, and the results of this study provide theoretical support for the reduction in GHGs emissions in northwest China without decreasing the yield of alfalfa forage. Full article

Developing rubber agroforestry systems is crucial to ensure the sustainable development of natural rubber cultivation. This study focuses on the starch crop Maranta arundinacea (arrowroot) and assesses its productivity and influencing factors when intercropped in 6–7-year-old conventional single-row and double-row rubber plantations. We analyze various aspects, including light resources, root distribution, soil nutrients, arrowroot growth characteristics, and product quality. The results indicate that the daily average photosynthetically active radiation (PAR) in the double-row rubber agroforestry system intercropping area ranges from 896.4 to 940.2 μmol·m⁻²·s⁻¹. Additionally, the rubber tree roots near the intercropping area are less dense (107.0 g cm⁻³). In contrast, the conventional single-row rubber agroforestry system has a significantly lower daily average PAR of only 145.7 μmol·m⁻²·s⁻¹, and the nearby rubber tree roots are more abundant (616.2 g cm⁻³). Although soil nutrient levels were slightly lower in the intercropping area on the double-row treatment compared to the single-row treatment, there was no statistical difference (p < 0.05). Arrowroot’s photosynthetic capacity in the double-row rubber agroforestry system intercropping area is significantly greater than in the single-row rubber agroforestry system intercropping area. The yield per unit area in the former (23.46–27.47 t·ha⁻¹) is also significantly higher than in the latter (2.87–4.75 t·ha⁻¹, p < 0.05), with higher starch content. Therefore, arrowroot exhibits higher productivity when intercropped in double-row rubber agroforestry systems, making it suitable for establishing a “rubber–arrowroot” agroforestry model to enhance the yield per unit area of rubber plantations. Full article

Optimizing Cropping patterns is important for the improvement of regional agricultural economic efficiency and sustainable development. However, there are few studies on the sustainability of cropping patterns in hilly areas. Here, we studied four new three-maturing cropping patterns in a typical ecological site in the hilly areas of southwest China. An analytical method combining economic efficiency evaluation and energy value analysis was used to evaluate and compare the economic efficiency and sustainability of the new cropping model and the traditional cropping model. We explored the construction of a new three-crop cropping model suitable for the southwest hilly area to improve the economic benefits of agricultural production and improve the sustainability of agricultural production. To solve the above problems, we constructed eight cropping patterns and classified them as follows: The Traditional Double Cropping System: T1, oilseed rape-summer soybean; T2, oilseed rape-summer maize; T3, wheat-summer maize. Traditional Triple Cropping System: T4, wheat/spring maize/summer soybean. Novel Triple Cropping System: T5, forage oilseed rape-spring maize/summer soybean; T6, forage oilseed rape-spring maize/peanut; T7, potato-spring maize/peanut; T8, potato-spring maize/summer soybean. The results of the study showed that compared with the Traditional Double Cropping System and the Traditional Triple Cropping System, the Novel Triple Cropping System increased the economic yield by an average of 100.39% and 49.18%, the economic production capacity by 71.32% and 36.48%, the biological yield by 12.53% and 4.90%, and the biological production capacity by 13.59% and 5.80%. The economic benefits of the Novel Triple Cropping System were significantly improved, with economic profits increased by CNY 9068 ·hm⁻² and CNY 7533 ·hm⁻² compared with the Traditional Double Cropping System and the Traditional Triple Cropping System. The energy value analysis further revealed the characteristics of the Novel Triple Cropping System as a high input and high output model. The Novel Triple Cropping System increased energy value inputs by 6.56% and 4.25%, and energy value outputs by 13.69% and 4.27% compared with the Traditional Double Cropping System and the Traditional Triple Cropping System, respectively. This high level of inputs stems mainly from a significant increase in labor inputs. Meanwhile, the energy-value indicator analysis of the Novel Triple Cropping System shows its lower dependence on natural resources, greater production intensification, and increased system stability. As a result, the Novel Triple Cropping System showed higher sustainable production capacity. In summary, the results of this study can provide a theoretical basis for optimizing cropping patterns and promoting high-yield and the sustainable development of agriculture. Full article

In response to the limitations of traditional double rice cropping models, this study constructed five typical rice planting models in the middle reaches of the Yangtze River, namely “Chinese milk vetch-early rice-late rice (CK/CRR), Chinese milk vetch—early rice—sweet potato || late soybean (CRI), rapeseed—early rice—late rice (RRR), rapeseed—early rice—sweet potato || late soybean (RRI) and potato—early rice—late rice (PRR)” to study the annual emission characteristics of greenhouse gases under different planting models. The results showed the following: (1) From the perspective of total yield in two years, the CRI treatment reached its maximum, which was significantly higher than that of other treatments by 9.30~20.29% in 2019 (p < 0.05); in 2020, except for the treatment of RRI, it was significantly higher than other treatments by 20.46~30.23% (p < 0.05). (2) The cumulative emission of CH₄ in the double rice treatment is generally higher than that in paddy-upland rotation treatment, while the cumulative emission of N₂O in the paddy-upland rotation treatment is higher than that in the double rice treatment, but the total amount is much lower than the cumulative emission of CH₄. Therefore, CH₄ emissions from rice fields still occupy most of the GHGs. (3) The global warming potential (GWP) and greenhouse gas emission intensity (GHGI) of different planting patterns in rice fields in 2020 were higher than those in 2019, and the GWP and GHGI of double rice cropping treatment is higher than that of paddy-upland rotation treatments. During the two years, the GWP of CRR treatment reached its maximum and was significantly higher than that of other treatments by 48.28~448.90% and 34.43~278.33% (p < 0.05). The GHGI of CRR was significantly higher than that of CRI and RRI by 3.57~5.4 and 1.4~3.5 times (p < 0.05). Based on the comprehensive performance of greenhouse gas emissions over the two experimental years, RRI and CRI have shown good emission reduction effects, which can significantly reduce greenhouse gas emissions from paddy fields, are conducive to reducing global warming potential and greenhouse gas emission intensity and conform to the development trend of “carbon neutrality”. Therefore, considering high-yield, low-temperature chamber gas emissions, the Chinese milk vetch—early rice—sweet potato || late soybean model performs well and has the best comprehensive benefits. It is of great significance for optimizing the rice field planting mode in the middle reaches of the Yangtze River. Full article