Multiple Cropping Systems for Improving Crop Yield and Reducing Environmental Costs

Multiple cropping, characterized as two or more crops planted in the same field either sequentially or simultaneously within a year [1], includes crop rotations, intercropping, relay cropping, and mixed cropping, which could maximize the utilization of land and solar heat resources, enhance land use efficiency, natural resource utilization efficiency, and biodiversity, thus promote the crop production, and enhance farmers’ income [2]. Multiple cropping is also an important strategy for maintaining food security in the context of global population growth and declining land area available for agriculture [2]. Expect for increasing crop production and farmer’s income and improving soil quality, reasonable multiple cropping systems can also reduce environmental costs, for example, greenhouse gas (GHG) emission mitigation and agricultural inputs reduction [3]. Eight articles were published in Special Issue II of Multiple Cropping Systems for Improving Crop Yield and Soil Quality, mainly focused on the effects of multiple cropping on crop yield, soil quality, and GHG emissions.

Tang et al. [4] report that Chinese milk vetch–early rice–sweet potato || late soybean (CRI) has a higher yield compared with the traditional cropping system of Chinese milk vetch-early rice-late rice (CRR) in the middle reaches of the Yangtze River of China. Compared with CRR, the CRI cropping system also significantly reduces GHG emissions from paddy fields, which is conducive to reducing the global warming potential and GHG emission intensity, in line with the development trend of carbon neutrality. This study demonstrates that the CRI cropping system is an optimal planting pattern for the paddy field in the middle reaches of the Yangtze River of China.

Li et al. [5] show that the novel triple cropping systems, including forage oilseed rape spring maize/summer soybean, forage oilseed rape spring maize/peanut, potato spring maize/peanut, and potato spring maize/summer soybean, have higher economic benefits compared to the traditional double cropping system and the traditional triple cropping system, characterized by high input and high output in terms of economy. Initiatives, such as mechanization and reduction in labor inputs, are particularly important in reducing cost inputs and improving economic benefits. From the perspective of sustainability, the novel triple cropping system enhances the soil and water conservation capacity of farmland ecosystems and resource utilization efficiency, showing high levels of intensification and sustainability.

Huang et al. [6] indicate that there are no apparent above-ground or below-ground limiting factors when intercropping arrowroot in a double-row rubber agroforestry system. Therefore, this approach represents a suitable rubber agroforestry model that can effectively increase the output per unit area of younger-aged rubber plantations.

Li et al. [7] show that a medium nitrogen level (160 kg ha⁻¹) is more favorable for improving the alfalfa yield and resource use efficiency, resulting in low soil GHG emissions. The combination of a sowing rate of 280 kg ha⁻¹ planting eight rows and a nitrogen application rate of 160 kg ha⁻¹ contributes to a higher alfalfa yield with less GHG emissions, ensures lower carbon emission intensity, and improves soil structure and physicochemical properties.

Concerning the rice-based cropping system, Hu et al. [8] indicate that rice–wheat and rice–rapeseed have reasonably low carbon footprints, grain yields, and net economic returns, which deserve recommendations for local farmers in eastern China. Bankole et al. [9] report that straw incorporation significantly increased total CH₄ emissions by 118.6%, 8.0%, and 79.0% in single rice (SR), double rice (DR), and rice-wheat (RW), respectively, compared to no straw incorporation (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. At the same time, reduced N application could increase rice yield. This study scientifically supports straw incorporation combined with a moderate N application in rice-based cropping systems that could maintain high rice yields and mitigate GHG emissions. Zhang et al. [10] clarify that increasing plant density can significantly increase rice yield, and appropriate N reduction can reduce CH₄ emissions in the paddy fields of southern China. Their results also indicate that 10% N reduction combined with a 40% increase in planting density significantly increases the yield of double-cropped rice and reduces the carbon footprint per unit yield.

Based on 8571 topsoil (0–20 cm soil layer) samples, Su et al. [11] map the spatial distribution of key soil properties in cropland of Yunan Province, China. The results show that higher soil organic carbon (SOC) is mainly distributed in northern and eastern Yunnanand total nitrogen (TN) and total phosphorus (TP) have similar spatial distributions. Generally, higher total potassium (TK) is mainly distributed in southwestern Yunnan Province. There is a significant positive correlation between SOC and TN and TP contents; however, there is a significant negative correlation between SOC and TK. The study also indicates that elevation, temperature, precipitation, clay content, sand content, and silt content are the most important factors affecting SOC, TN, TP, and TK content.

In conclusion, these studies showed that multiple cropping systems are an effective way for improving crop yield and soil quality as well as mitigating GHG emissions with reasonable management, such as optimal nitrogen, crop residue incorporation, and higher planting density, thus promoting the sustainable development of agriculture. Facing the current challenges, such as global population growth, climate change, arable land reduction, and increasing cost of mineral NPK fertilizers on global markets, it is important to further optimize agronomic management under multiple cropping to achieve higher crop productivity with lower environmental costs. These measurements include partially replacing mineral fertilizers with organic manure to reduce GHG emissions, optimizing varieties, tillage practices, and sowing time to adapt to climate change.