Comparison of crop productivity, economic benefit and environmental footprints among diversified multi-cropping systems in South China

Spatio-temporal variations in carbon sources, sinks and footprints of cropland ecosystems in the Middle and Lower Yangtze River Plain of China, 2013-2022

Cropland ecosystems, which are most affected by human activities, are dual carriers of carbon sources and sinks. It has significant implications for the achievement of the "two-carbon" objective. The Middle and Lower Yangtze River Plain (MLYRP) is the principal grain-producing area of China, which is a great agricultural country. The development of green agriculture in this plain is of vital importance. Nevertheless, there is a lack of attention to the dynamics of the carbon footprints of cropland. Hence, this study was conducted with the help of carbon emission coefficient method. It investigated the spatio-temporal variations of carbon sources, sinks and carbon footprints of cropland ecosystems in this plain from 2013 to 2022. The findings suggest that (1) Carbon uptake was fluctuating up during the study period. Carbon uptake was higher in paddy and wheat. (2) Carbon emissions were declining year by year. Fertilizer and irrigated agriculture produced more carbon emissions. The top four for both indicators were Anhui, Jiangsu, Hubei and Hunan provinces. (3) The carbon footprint declined in fluctuations. This indicator ranked the top four in Hubei, Anhui, Zhejiang and Jiangsu provinces. The spatial distribution pattern of the above three indicators was more in the north and less in the south. (4) Cropland ecosystems exhibited carbon sinks. There were relatively large carbon eco-surplus and high carbon eco-efficiency. Nevertheless, the carbon ecological surplus was decreasing in fluctuation. Consequently, MLYRP should keep popularizing new technologies such as green manure crops and precision agriculture.

Microplastics abundance associated with farmland use types and the impact on soil microbial communities: A case study in Southern China

To investigate the impact of various farmland use types on the spatial distribution of microplastics (MPs) and their correlation with microbial communities, 78 soil samples from distinct farmland use types (orchard, paddy field, and vegetable field) in Southern China were examined. Results revealed that the abundance of MPs ranged from 528 to 39,864 items/kg with a mean abundance of 10,562 items/kg, which were primarily 0-30 µm in size. A total of 32 polymer types were identified, with the main polymer being polyethylene terephthalate (PET, 28.8 %), followed by polyvinyl chloride (PVC, 13.5 %) and fluororubber (FKM, 9.5 %). The abundance of MPs was highest in orchard field (8896 ± 5745 items/kg), followed by paddy field (4176 ± 2976 items/kg) and lastly vegetable field (2967 ± 3698 items/kg). Results of 16 S rRNA gene amplicon sequencing showed that the presence of MPs affected the bacterial distribution patterns. Compared with soil bacterial communities, the spatial dispersion and dissimilarity of plasticsphere communities were less variable. Notably, the predicted sequences related to xenobiotics biodegradation and metabolism became more abundant, thereby affecting the ecological function of soil. Overall, this study provides important data for further research on MP ecosystem risks associated with farmland use types.

Emergy-based evaluation of production efficiency and sustainability of diversified multi-cropping systems in the Yangtze River Basin

Excessive agricultural investment brought about by increased multiple-cropping index may compromise environmental sustainability. There are few studies on the sustainability of diversified multi-cropping systems in the Yangtze River Basin (YRB). Therefore, this study selected five representative locations in the YRB. According to the local climate characteristics and food demand, diversified multi-cropping systems were designed, and the main local winter crops were selected as the previous crops of the corn-soybean strip compound cropping system, with the local traditional double-cropping model as the control (CK). The emergy evaluation method was introduced to quantitatively compare the efficiency and sustainability of diversified multi-cropping systems in the YRB. The results showed that by incorporating soybean by intercropping with corn, compared with the CK, the total energy input, annual energy output, and annual economic output increased by 15.80%, 9.78%, and 33.12% on average, respectively. The unit emergy value (UEV) and unit non-renewable value (UNV) increased by 6.03% and 5.98%, respectively; the emergy yield ratio (EYR) and environmental loading ratio (ELR) decreased by 0.91% and 0.44%, respectively; the emergy sustainability index (ESI) was the same. In the third mature crop selection, compared with that of corn, the ELR of soybean decreased by 14.32%, and the ESI increased by 18.55%. In addition, the choice of winter crops plays a vital role in the system's efficiency and sustainability. Compared with those of other winter crops, the annual economic outputs of potato (upper reaches of the YRB), potato or forage rape (middle reaches of the YRB), and wheat (lower reaches of the YRB) increased by 51.02%, 32.27%, and 0.94%, respectively; their ESI increased by 71.21%, 47.72%, and 12.07%, respectively. Potato-corn/soybean or potato/corn/soybean (upper reaches of the YRB), forage rape-corn/soybean or potato/corn/soybean (middle reaches of the YRB), and wheat-corn/soybean (lower reaches of the YRB) were chosen to facilitate the coexistence of high economic benefits and environmental sustainability. Additionally, promoting mechanization and reducing labor input were essential to improve the efficiency and sustainability of multi-cropping systems. This study would provide a scientific basis and theoretical support for the development of efficient and sustainable multiple-cropping systems in the dryland of the YRB.

Environmental impacts and nitrogen-carbon-energy nexus of vegetable production in subtropical plateau lake basins

Vegetables are important economic crops globally, and their production has approximately doubled over the past 20 years. Globally, vegetables account for 13% of the harvested area but consume 25% of the fertilizer, leading to serious environmental impacts. However, the quantitative evaluation of vegetable production systems in subtropical plateau lake basins and the establishment of optimal management practices to further reduce environmental risks are still lacking. Using the life cycle assessment method, this study quantified the global warming, eutrophication, acidification, and energy depletion potential of vegetable production in a subtropical plateau lake basin in China based on data from 183 farmer surveys. Our results indicated that vegetable production in the study area, the Erhai Lake Basin, was high but came at a high environmental cost, mainly due to low fertilizer efficiency and high nutrient loss. Root vegetables have relatively high environmental costs due to the significant environmental impacts of fertilizer production, transportation, and application. A comprehensive analysis showed that the vegetable production in this region exhibited low economic and net ecosystem economic benefits, with ranges of 7.88-8.91 × 103 and 7.35-8.69 × 103 $ ha-1, respectively. Scenario analysis showed that adopting strategies that comprehensively consider soil, crop, and nutrient conditions for vegetable production can reduce environmental costs (with reductions in global warming potential (GWP), eutrophication potential (EP), acidification potential (AP), and energy depletion potential (EDP) by 10.6-28.2%, 65.1-73.5%, 64.5-71.9%, 47.8-70.4%, respectively) compared with the current practices of farmers. This study highlighted the importance of optimizing nutrient management in vegetable production based on farmers' practices, which can achieve more yield with less environmental impacts and thereby avoid the "trade-off" effect between productivity and environmental sustainability.

Yield and nutrient composition of forage crops and their effects on soil characteristics of winter fallow paddy in South China

In terms of providing additional feeds and improving the soil fertility, planting forage crops during the fallow seasons is an effective strategy to promote resource utilization. The objective of this research was to compare the effects of planting different forage crops on the yields and nutritive compositions of forage and soil properties of winter fallow paddy in southern China. Five forage crops, including alfalfa (Medicago sativa, AF), common vetch (Vicia sativa, CV), milk vetch (Astragalus sinicus, MV), smooth vetch (Vicia villosa, SV) and Italian ryegrass (Lolium multiflorum, IR), were planted by monoculture on the winter fallow paddy in 2017-2018 (season 1) and 2018-2019 (season 2), respectively. The dry matter yield of IR was significantly higher than those of AF, CV, SV and MV (P<0.05). The crude protein yield of IR was significantly higher than those of AF, CV and MV (P<0.05). The neutral detergent fiber and acid detergent fiber contents of CV, SV and IR were significantly lower than those of AF and MV (P<0.05). Forage crops significantly affected the culturable microbial population of soils (P<0.05). The bacteria, actinomyces and fungi numbers on IR were the highest, while azotobacter number was the lowest. The catalase, acid-phosphatase and invertase activities of IR soil were the lowest. The numbers of bacteria, actinomyces and fungi of IR soil were the highest. IR and SV were the best crops to obtain forage and improve the soil. When producers pursue higher forage yield, we recommend planting Italian ryegrass. If the producers want to improve soil characteristics, smooth vetch is the most suitable plant. These results provide useful information to rice growers for cropping management when growing forage crops (based on the yield and nutritional value) or green manure (based on improving the soil fertility) as an alternative to late rice harvest.

Reducing carbon footprints and increasing net ecosystem economic benefits through dense planting with less nitrogen in double-cropping rice systems

Excessive application of nitrogen fertilization in farmland systems can cause nitrogen wastage, environmental pollution, and increase greenhouse gas (GHG) emissions. Dense planting is one of the efficient strategies for nitrogen fertilizer reduction within rice production. However, there are paying weak attention to the integrative effect of dense planting with less nitrogen (DPLN) on carbon footprint (CF), net ecosystem economic benefit (NEEB) and its components in double-cropping rice systems. Herein, this work aims to elucidate the effect via field experiments in double-cropping rice cultivation region with the treatments set to conventional cultivation (CK), three treatments of DPLN (DR1, 14 % nitrogen reduction and 40,000 hills per ha density increase from CK; DR2, 28 % nitrogen reduction and 80,000 hills density increase; DR3, 42 % nitrogen reduction and 120,000 hills density increase), and one treatment of no nitrogen (N0). Results showed that DPLN significantly reduced average CH4 emissions by 7.56 %-36 %, while increasing annual rice yield by 2.16 %-12.37 % compared to CK. Furthermore, the paddy ecosystem under DPLN served as a carbon sink. Compared with CK, DR3 increased gross primary productivity (GPP) by 16.04 % while decreasing direct GHG emissions by 13.1 %. The highest NEEB was observed in DR3, which was 25.38 % greater than CK and 1.04-fold higher than N0. Therefore, direct GHG emissions and carbon fixation of GPP were key contributors to CF in double-cropping rice systems. Our results verified that optimizing DPLN strategies can effectively increase economic benefits and reduce net GHG emissions. DR3 achieved an optimal synergy between reducing CF and enhancing NEEB in double-cropping rice systems.