Here, we report on a two-years field experiment aimed at the quantification of the emissions of nitrous oxide (N2O) and methane (CH4) from the dominant wheat–maize double cropping system in North China Plain. The experiment had 6 different fertilization strategies, including a control treatment, recommended fertilization, with and without straw and manure applications, and nitrification inhibitor and slow release urea. Application of N fertilizer slightly decreased CH4 uptake by soil. Direct N2O emissions derived from recommended urea application was 0.39% of the annual urea-N input. Both straw and manure had relatively low N2O emissions factors. Slow release urea had a relatively high emission factor. Addition of nitrification inhibitor reduced N2O emission by 55%. We conclude that use of nitrification inhibitors is a promising strategy for N2O mitigation for the intensive wheat–maize double cropping systems.

High nitrogen (N) inputs in Chinese vegetable and cereal productions played key roles in increasing crop yields. However, emissions of the potent greenhouse gas nitrous oxide (N2O) and atmospheric pollutant nitric oxide (NO) increased too. For lowering the environmental costs of crop production, it is essential to optimize N strategies to maintain high crop productivity, while reducing the associated N losses. We performed a 2 year-round field study regarding the effect of different combinations of poultry manure and chemical N fertilizers on crop yields, N use efficiency (NUE) and N2O and NO fluxes from a Welsh onion-winter wheat system in the North China Plain. Annual N2O and NO emissions averaged 1.14–3.82 kg N ha⁻¹ yr⁻¹ (or 5.54–13.06 g N kg⁻¹ N uptake) and 0.57–1.87 kg N ha⁻¹ yr⁻¹ (or 2.78–6.38 g N kg⁻¹ N uptake) over all treatments, respectively. Both N2O and NO emissions increased linearly with increasing total N inputs, and the mean annual direct emission factors (EFd) were 0.39% for N2O and 0.19% for NO. Interestingly, the EFd for chemical N fertilizers (N2O: 0.42–0.48%; NO: 0.07–0.11%) was significantly lower than for manure N (N2O: 1.35%; NO: 0.76%). Besides, a negative power relationship between yield-scaled N2O, NO or N2O + NO emissions and NUE was observed, suggesting that improving NUE in crop production is crucial for increasing crop yields while decreasing nitrogenous gas release. Compared to the current farmers’ fertilization rate, alternative practices with reduced chemical N fertilizers increased NUE and decreased annual N2O + NO emissions substantially, while crop yields remained unaffected. As a result, annual yield-scaled N2O + NO emissions were reduced by > 20%. Our study shows that a reduction of current application rates of chemical N fertilizers by 30–50% does not affect crop productivity, while at the same time N2O and NO emissions would be reduced significantly.

Field trials contribute practical information towards the development of phytoremediation strategies that cannot be provided by laboratory tests. We conducted field experiments utilizing the Cd hyperaccumulator plant Solanum nigrum L., on farmland contaminated with 1.91 mg kg⁻¹ Cd in the soil. Our study showed that S. nigrum has a relatively high biomass. Planting density had a significant effect on the plant biomass and thus on overall Cd accumulation. For double harvesting, an optimal cutting position influenced the amount of Cd extracted from soils. Double cropping was found to significantly increase the amount of Cd extracted by S. nigrum. Fertilizing had no significant effect on plant biomass or on the Cd remediation of the soil over the short-term period. Our study indicates that S. nigrum can accumulate Cd from soils where the concentrations are relatively low, and thus has application for use in decontamination of slightly to moderately Cd-contaminated soil.

Excessive fertilization leads to high nitrogen (N) leaching under intensive plastic-shed vegetable production systems, and thereby results in the contaminations of ground or surface water. Therefore, it is urgent to develop cost-effective strategies of nitrogen management to overcome these obstacles. A 15-year experiment in annual double-cropping systems was conducted to explore impacts of N application rate and straw amendment on mineral N leaching loss in plastic-shed greenhouse. The results showed that seasonal mineral N leaching was up to 103.4–603.4 kg N ha⁻¹, accounting for 12%–41% of total N input under conventional N fertilization management. However, optimized N application rates by 47% and straw addition obviously decreased mineral N leaching by 4%–86%, while had no negative impacts on N uptake and tomato yields. These large decreases of N leaching loss were mainly due to the reduced leachate amount and followed by N concentration in leachate, which was supported by improved soil water holding capacity after optimizing N application rates and straw addition. On average, 52% of water leachate and 55% of mineral N leaching simultaneously occurred within 40 days after planting, further indicating the dominant role of water leakage in regulating mineral N leaching loss. Moreover, decreasing mineral N leaching was beneficial for reducing leaching loss of base cations. Therefore, optimized N application rates and straw amendment effectively alleviates mineral N leaching losses mainly by controlling the water leakage without yield loss in plastic-shed greenhouse, making this strategy promising and interesting from environmental and economical viewpoints.

In order to reveal the mechanism of microbial carbon (C) sequestration in paddy soil under different tillage management and to provide an important theoretical basis for perfecting the mechanism of C sequestration in paddy soil. C can indicate changes of soil nutrient content and soil microbial community, but more research is needed to study how C sources utilization characteristics respond to different tillage management under a double-cropping rice (Oryza sativa L.) paddy field in southern China. Hence, the impact of long-term (2005–2018) tillage management on utilization of microbial carbon sources in rhizosphere and non-rhizosphere soils under a double-cropping rice paddy field was studied by using ¹⁸O–H₂O method in this study. The tillage treatments were included: (1) moldboard plow with all crop residue removed as a control (CT), (2) moldboard plow with all crop residue incorporated (CTS), (3) no-tillage with all crop residue retained on the soil surface (NTS), and (4) rotary tillage with all crop residue incorporated (RTS). The results indicated that Richness, Shannon, and McIntosh indices were increased by application of crop residue management, compared with treatment without crop residue, and soil microbial growth rate, soil microbial biomass C content, and soil microbial basal respiration with CT treatment were significantly lower (p < 0.05) than that of NTS, RTS, and CTS treatments. And the soil C utilization efficiency in rhizosphere soil with NTS, RTS, and CTS treatments was significantly lower (p < 0.05) than that of CT treatment. Compared with CT and CTS treatments, the metabolic capacity of soil microorganisms to exogenous C sources with NTS and RTS treatments was increased, and the different types of exogenous C sources were showed as following: complex compounds < carbohydrate < amino acid < carboxylic acids. The redundancy analysis results showed that utilization characteristics of soil microorganisms to exogenous C sources were significantly changed under tillage and crop residue incorporated conditions. Hence, this result indicated that characteristics of soil C sources utilization were significantly increased combined applied with tillage and crop residue incorporated management.

Agricultural greenhouse gas (GHG) emissions account for 14% of the total greenhouse gas (GHG) emissions from human activities, and the carbon footprint (CF) of agricultural production, which can help to propose positive measures to mitigate greenhouse gas (GHG) emissions, is a general method for assessing the impact of agricultural practices on the external environment. This article calculated the carbon footprint (CF) of rice production and compared the differences between the double-and single-cropping rice regions, which is rarely mentioned in previous literature. Some interesting information was shown. For example, the internal structure of rice production carbon footprint (CF) is prominent. (a) In terms of time evolution, CF of agricultural materials showed an increasing trend year by year, while CF of rice planting remained basically stable. (b) In terms of regional differences, whether single-cropping rice regions or double-cropping rice regions, CF of agricultural materials did not show the previous increasing trend after 2011, especially after 2015. This may be greatly affected by the policy such as the abolishing of the China agricultural tax in 2006. These studies can help us to reveal how agricultural policies and different rice cropping patterns affect each region.

The spatial and temporal variability of soil CO₂ emissions from agricultural soils is inherently high. While tillage and crop residue practices play vital roles in governing soil CO₂ emission, their effects on the variability of soil CO₂ fluxes across depths and seasons are still poorly understood. To address this, an experiment consisting of four treatments, namely conventional tillage with (CT+) and without crop residue application (CT−), as well as no tillage with (NT+) and without crop residue application (NT−), was conducted to investigate soil CO₂ fluxes at top 40 cm soils with 10-cm depth intervals in a winter wheat-summer maize rotation system in the North China Plain. Our results showed soil CO₂ fluxes increased with depth in both the wheat- and maize-growing seasons. However, the dominant factors in regulating soil CO₂ fluxes changed with soil depth and seasons. In the wheat-growing season, increase in soil CO₂ fluxes with depth was attributed to the increase of dissolved organic carbon-to-nitrogen ratio (DOC/DON) and a decline in soil DON concentration along the soil profile. These factors explained about 55–96% of the total variation in soil CO₂ fluxes at different soil depths. In the maize-growing season, the dominant factors were soil DOC/DON ratio, soil DON concentrations, and soil moisture. These factors explained approximately 79–96% of the total variation in soil CO₂ fluxes along the soil depth. Greater soil CO₂ fluxes (except at 30–40 cm depth) were observed in NT− than CT− treatments. Furthermore, crop residue application enhanced soil CO₂ fluxes across different depths, but the enhancement was more prominent in CT+ than NT+. Moreover, soil CO₂ fluxes in the maize-growing season were greater than those in the wheat-growing season. Our results demonstrate that the effects of tillage regimes and crop residue management practices on soil CO₂ emissions are not confined only to the plough layer but can extend to soils of over 30 cm depths. We also need to revisit the general conventional view that no tillage can significantly reduce soil CO₂ emissions compared with conventional tillage for better climate change mitigation.

Controlled release fertilizer can reduce nitrogen losses to the environment while increasing grain yield and improving apparent nitrogen recovery (ANR) of rice. However, few studies have evaluated the comparative efficacy of different polymer-coated urea products on nitrogen (N) losses, ANR, and N uptake of rice. A 2-year field experiment was conducted to compare the effects of three different types of polymer-coated urea fertilizer on nitrogen losses through NH₃ volatilization and surface runoff to the environment, ANR, grain yield, and N uptake as compared to conventional urea of rice. Six treatments including (1) control with 0 kg N ha⁻¹ (CK), (2) basal application of urea (Ub), (3) split application (Uₛ) of urea (50% at transplanting, 25% at tillering, and 25% at panicle stages), (4) CRU-1 (polyurethane-coated urea), (5) CRU-2 (degradable polymer-coated urea), and (6) CRU-3 (water-based polymer-coated urea) all applied at 165 kg N ha⁻¹. It was found that CRU-2 resulted in the highest grain yield and panicle numbers among the N fertilization treatments in 2013 and 2014. Applying CRU could help increase N uptake in rice, reduce N losses through NH₃ volatilization and surface runoff, and hence improve ANR. Its single dose can meet the nutrient demand of the rice plant. Controlled release urea could be adopted as an effective mitigation alternative to retard N losses through NH₃ volatilization and surface runoff while improving ANR of double cropping of late rice.

Soil organic matter (SOM) content and soil aggregation are essential components of soil structure, which plays an important role in soil quality and fertility. Also, the SOM content, aggregation, and humus substances in paddy field were affected by application of fertilization practices. However, there is still limited information about the effects of long-term different fertilization practices on soil aggregation and carbon content in the humic acid (C-HAF), fulvic acid (C-FAF), and humin (C-HUM) fractions under double-cropping rice (Oryza sativa L.) system in Southern China paddy fields. Therefore, the effects of long-term fertilizer application on soil aggregation and C-HUM, C-HAF, and C-FAF contents in 0–5-, 5–10-, and 10–20-cm soil depth under double-cropped rice fields in Southern China were investigated. The experiment located at NingXiang County in Hunan Province, China begins in 1986 and the experiment includes five treatments: without fertilizer input (CK), mineral fertilizer alone (MF), rice straw residues and mineral fertilizer (RF), 30% organic matter and 70% mineral fertilizer (LOM), and 60% organic matter and 40% mineral fertilizer (HOM). The results showed that the soil total organic carbon content in paddy soils with RF, LOM, and HOM treatments was significant higher (P < 0.05) than that of the CK treatment at early and late rice maturity stages. The different sizes of soil aggregates with different fertilization treatments were decreased as HOM > LOM > RF > MF > CK. The HOM treatment had the highest percentage of soil aggregates in each size class and the CK treatment had the lowest percentage of soil aggregates in each size class in 0–5-, 5–10-, and 10–20-cm soil depth at early and late rice maturity stages. The soil C-HAF, C-FAF, and C-HUM contents were increased by long-term combined application of manure with mineral fertilizer practices. Meanwhile, the results indicated that the soil C-HAF, C-FAF, and C-HUM contents with RF, LOM, and HOM treatments were significantly higher (P < 0.05) than that of the CK treatment at early and late rice maturity stages. As a result, the soil total organic carbon content, each size class of soil aggregates, and soil C-HAF, C-FAF, and C-HUM contents were increased by long-term combined application of manure with mineral fertilizer in double-cropped rice fields.

Fertilizer regime is playing an important role in heavy metal cadmium (Cd) accumulation in paddy soils and crop plant. It is necessary to assess the Cd accumulation in soils and rice (Oryza sativa L.) plants under long-term fertilization managements, and the results which help to assess the environmental and food risk in Southern China. However, the effects of different organic manure and chemical fertilizers on Cd accumulation in soils and rice plant remain unclear under intensively cultivated rice conditions. Therefore, the objective was to explore Cd accumulation in paddy soils and rice plant at mature stage under different long-term fertilization managements in the double-cropping rice system. Cd accumulation in the surface soils (0–20 cm) and rice plant with chemical fertilizer alone (MF), rice straw residue and chemical fertilizer (RF), 30% organic matter and 70% chemical fertilizer (LOM), 60% organic matter and 40% chemical fertilizer (HOM), and without fertilizer input (CK) basis on 32 years long-term fertilization experiment were analyzed. The results showed that the soil total Cd content was increased by 0.296 and 0.351 mg kg⁻¹ and 0.261 and 0.340 mg kg⁻¹ under LOM and HOM treatments at early and late rice mature stages, respectively, compared with the CK treatment. And the soil available Cd content was increased by 0.073 and 0.137 mg kg⁻¹ and 0.102 and 0.160 mg kg⁻¹ under LOM and HOM treatments at early and late rice mature stages, respectively, compared with the CK treatment. The bioconcentration factor of Cd across different parts of rice plant was the highest in root, followed by stem and grain, and the lowest in leaves. At early and late rice mature stages, the root Cd concentration of rice plant was increased by 0.689 and 0.608 mg kg⁻¹ with HOM treatment, the stem Cd concentration of rice plant was increased by 0.666 and 0.758 mg kg⁻¹ with RF treatment, and the leaf and grain Cd concentration of rice plant was increased 0.094 and 0.082 mg kg⁻¹ and 0.086 and 0.083 mg kg⁻¹ with LOM treatment, respectively, compared with the CK treatment. The soil Cd single-factor contaminant index (PCd) under different fertilization treatments was as the following HOM > LOM > RF > MF > CK. Meanwhile, the PCd with LOM and HOM treatments was higher than that of the MF, RF, and CK treatments, but there is no significant difference between that of MF and RF treatments. Therefore, long-term application of rice straw residue and chemical fertilizer had no obvious effect on the accumulation of Cd in paddy soils and grain, and soil Cd accumulation was increased as application of organic fertilizer.