Supplemental activated biochar pellet fertilizers (ABPFs) were evaluated as a method to sequester carbon and reduce greenhouse gas (GHG) emissions, and improve rice production. The evaluated treatments were a control (standard cultivation method, no additives applied), activated rice hull biochar pellets with 40% of N (ARHBP-40%), and activated palm biochar pellets with 40% of N (APBP-40%). The N supplied by the ARHBP-40% and APBP-40% treatments reduced the need for supplemental inorganic nitrogen (N) fertilizer by 60 percent. The ARHBP-40% treatment sequestered as much as 1.23 tonne ha⁻¹ compared to 0.89 tonne ha⁻¹ in the control during the rice-growing season. In terms of greenhouse gas (GHG) emissions, CH₄ emissions were not significantly different (p > 0.05) between the control and the ARHBP-40%, while the lowest N₂O emissions (0.002 kg ha⁻¹) were observed in the ARHBP-40% during the crop season. Additionally, GHG (CO₂-equiv.) emissions from the ARHBP-40% application were reduced by 10 kg ha⁻¹ compared to the control. Plant height in the control was relatively high compared to others, but grain yield was not significantly different among the treatments. The application of the ARHBP-40% can mitigate greenhouse gas emissions and enhance carbon sequestration in crop fields, and ABPFs can increase N use efficiency and contribute to sustainable agriculture.

Nitric oxide (NO) plays a critical role in atmospheric chemistry and also is a precursor of nitrate, which affects particle matter formation and nitrogen deposition. Agricultural soil has been recognized as a main source of atmospheric NO. However, quantifying the NO fluxes emitted from croplands remains a challenge and in situ long-term measurements of NO are still limited. In this study, we used an automated sampling system to measure NO fluxes with a high temporal resolution over two years (April 2017 to March 2019) from a rainfed maize field in the Northeast China. The cumulative annual NO emissions were 8.9 and 2.3 kg N ha⁻¹ in year 1 (April 2017 to March 2018) and year 2 (April 2018 to March 2019), respectively. These interannual differences were largely related to different weather conditions encountered. In year 1, a month-long drought before and after the seeding and fertilizing reduced plant N uptake and dramatically increased soil N concentration. The following moderate rainfalls promoted large amount of NO emissions, which remained high until late September. The NO fluxes in both years showed clearer seasonal patterns, being highest after fertilizer application in summer, and lowest in winter. The seasonal patterns of NO fluxes were mainly controlled by soil available N concentrations and soil temperatures. The contribution of NO fluxes during the spring freeze-thaw in both years was no more than 0.2% of the annual NO budget, indicating that the freeze-thaw effect on agricultural NO emissions was minimal. In addition, with high-resolution monitoring, we found that soil not only act as a NO source but also a sink. Long-term and high-resolution measurements help us better understand the diurnal, seasonal, and annual dynamics of NO emissions, build more accurate models and better estimate global NO budget and develop more effective policy responses to global climate change.

Insight in the phosphorus (P) flows and P balances in the food chain is largely unknown at county scale in China, being the most appropriate spatial unit for nutrient management advice. Here, we examined changes in P flows in the food chain in a typical agricultural county (Quzhou) during 1980–2017, using substance flow analyses. Our results show that external P inputs to the county by feed import and fertilizer were 7 times greater in 2017 than in 1980, resulting in a 7-fold increase in P losses to the environment in the last 3 decades, with the biggest source being animal production. Phosphorus use efficiency decreased from 51% to 30% in crop production (PUEc) and from 32% to 11% in the whole food chain (PUEf), but increased from 4% to 7% in animal production (PUEa). A strong reduction in P inputs and thus increase in PUE can be achieved by balanced P fertilization, which is appropriate for Quzhou considering a current average adequate soil P status. Fertilizer P use can be reduced from 7276 tons yr⁻¹ to 1765 tons yr⁻¹ to equal P removal by crops. This change would increase P use efficiency for crops from 30% to 86% but it has a negligible effect on P losses to landfills and water bodies. Increasing the recycling of manure P from the current 43%–95% would reduce fertilizer P use by 17% and reduce P losses by 47%. A combination of reduced fertilizer P use and increased recycling of manure P would save fertilizer P by 93%, reduce P accumulation by 100% and P loss by 49%. The results indicate that increasing manure-recycling and decreasing fertilizer-application are key to achieving sustainable P use in the food chain, which can be achieved through coupling crop-livestock systems and crop-based nutrient management.

Overuse of phosphorus (P) fertilizer and the resulting soil P accumulation in vegetable production increases the risk of P runoff and leaching. However, P transformations under continuous fertilization and their effects on environmental risk are unclear. The current study examined the effects of long-term P fertilizer application on P fractions in different soil layers, and assessed the correlations between P fractions and environmental risks in intensive vegetable production in a subtropical region. A total of 32 fields were studied, including 8 uncultivated fields and 24 fields continuously used for vegetable production for 1–3, 4–9, or 10–15 years. The results showed that excessive P fertilizer input caused soil P surpluses ranging from 204.6 to 252.4 kg ha⁻¹ yr⁻¹. Compared to uncultivated fields, vegetable fields contained higher levels of labile P, moderately labile P, sparingly labile P, and non-labile P. The combined percentage of labile P and moderately labile P increased from 55.2% in fields cultivated for 0–3 year to 65.5% in fields cultivated for 10–15 years. The concentrations of soil P fractions were higher at 0–20 cm soil depth than at 20–40 and 40–60 cm soil depth. Soil available P was positively correlated with all soil P fractions except diluted HCl-Pᵢ or concentrated HCl-Pₒ. Long-term vegetable production increased CaCl₂–P downward movement, which was positively correlated with levels of labile and moderately labile P. The P index indicated a high risk of P losses from the vegetable fields. The P index was on average 3.27-fold higher in the vegetable fields than in uncultivated fields, and was significantly correlated with soil available P and organic and inorganic P fertilizer input. The environmental risk caused by P in vegetable production should be reduced by reducing P fertilizer input so as to maintain soil available P within an optimal range for vegetable production.

Pollution from the paddy fields has posed a threat to surface water quality, and the reactive N in runoff has been recognized as the dominant contributor. In the rice-wheat systems of eastern China, replacing wheat (Triticum aestivum) with Chinese milk vetch (CMV) (Astragalus sinicus) is known to reduce total fertilizer N use and associated N losses during winter; however, the function of the rice-CMV system in controlling the N runoff loss was overlooked during the summer rice-growing season. Over 6 years, we monitored soil mineral N, plant N accumulation, rice grain yield, N agronomic efficiency (AEN), and N runoff in rice-CMV fertilizer N rate-response experiments and made comparisons with the conventional N inputs in rice-wheat rotation. Aboveground CMV residues added 65–116 kg N ha⁻¹ yr⁻¹; therefore, by adjusting the fertilizer time, the rice in this system required 44–56% less N fertilizer to produce rice yields equivalent to the 270 kg N ha⁻¹ (district average, C270) used in the rice-wheat system. In all fertilizer N application treatments, 120 kg ha⁻¹ seemed to be the threshold that ensured the soil N supply, the N accumulation at rice critical stages, and consequently, the current level rice yield. The corresponding runoff N averaged 9.3 kg ha⁻¹ season⁻¹, which was 51.8% less than that in C270 (19.3 kg ha⁻¹ season⁻¹). Cumulative N runoff (total N and NH₄⁺-N) correlated strongly with fertilizer N input for any single year (sample size = 108, P < 0.01). Application of 30–120 kg fertilizer N ha⁻¹ gave an equivalent AEN, which indicated that the integration of CMV and fertilizer N could increase the agronomic efficiency of N fertilizer applied to the rice. Rotating paddy rice with CMV instead of wheat, together with the suitable adjustment of N fertilizer, could sustain rice yield and gain the utmost environmental benefits from rice-based agroecosystems.

Ammonia (NH₃) volatilization is one of the main pathways of nitrogen loss from cropland, resulting not only in economic losses, but also environmental and human health impacts. The magnitude and timing of NH₃ emissions from cropland fertilizer application highly depends on agricultural practices, climate and soil factors, which previous studies have typically only considered at coarse spatio-temporal resolution. In this paper, we describe a first highly detailed empirical regression model for ammonia (ERMA) emissions based on 1443 field observations across China. This model is applied at county level by integrating data with unprecedented high spatio-temporal resolution of agricultural practices and climate and soil factors. Results showed that total NH₃ emissions from cropland fertilizer application amount to 4.3 Tg NH₃ yr⁻¹ in 2017 with an overall NH₃ emission factor of 12%. Agricultural production for vegetables, maize and rice are the three largest emitters. Compared to previous studies, more emission hotspots were found in South China and temporally, emission peaks are estimated to occur three months earlier in the year, while the total amount of emissions is estimated to be close to that calculated by previous studies. A second emission peak is identified in October, most likely related to the fertilization of the second crop in autumn. Incorporating these new findings on NH₃ emission patterns will enable a better parametrization of models and hence improve the modelling of air quality and subsequent impacts on ecosystems through reactive N deposition.

Nitrous oxide (N₂O), an ozone-depleting greenhouse gas, is generally produced by soil microbes, particularly NH₃ oxidizers and denitrifiers, and emitted in large quantities after N fertilizer application in croplands. N₂O can be produced via multiple processes, and reduced, with the involvement of more diverse microbes with different physiological constraints than previously thought; therefore, there is a lack of consensus on the production processes and microbes involved under different agricultural practices. In this study, multiple approaches were applied, including N₂O isotopocule analyses, microbial gene transcript measurements, and selective inhibition assays, to revisit the involvement of NH₃ oxidizers and denitrifiers, including the previously-overlooked taxa, in N₂O emission from a cropland, and address the biological and environmental factors controlling the N₂O production processes. Then, we synthesized the results from those approaches and revealed that the overlooked denitrifying bacteria and fungi were more involved in N₂O production than the long-studied ones. We also demonstrated that the N₂O production processes and soil microbes involved were different based on fertilization practices (plowing or surface application) and fertilization types (manure or urea). In particular, we identified the following intensified activities: (1) N₂O production by overlooked denitrifying fungi after manure fertilization onto soil surface; (2) N₂O production by overlooked denitrifying bacteria and N₂O reduction by long-studied N₂O-reducing bacteria after manure fertilization into the plowed layer; and (3) N₂O production by NH₃-oxidizing bacteria and overlooked denitrifying bacteria and fungi when urea fertilization was applied into the plowed layer. We finally propose the conceptual scheme of N flow after fertilization based on distinct physiological constraints among the diverse NH₃ oxidizers and denitrifiers, which will help us understand the environmental context-dependent N₂O emission processes.

Lakes and lake sediments are significant components of the global carbon (C) cycle, and may store very large amounts of organic matter. Carbon sequestration in lakes is subject to substantial temporal and spatial variation and may be strongly affected by human activities. Here, we report accumulation rates (AR) of organic C (OC), total nitrogen (TN) and total phosphorous (TP), and investigate their responses to anthropogenic impact over the past 150 years by analyzing 62 sediment cores from 11 shallow lakes in the Songnen Plain, northeast China. From the center of each of the lakes, we selected one master core for age determination by ²¹⁰Pb and ¹³⁷Cs radioisotopes. The contents of OC, TN, TP, dry bulk density and mass specific magnetic susceptibility were then determined for all cores. The regional OCAR, TNAR and TPAR up-scaling from the multiple cores yielded mean values of 51.63 ± 15.13, 2.50 ± 0.98, and 0.90 ± 0.21 g m⁻² yr⁻¹, respectively. Nutrient AR in the studied lakes increased by a factor of approximately 2 × from the middle 19th century to the 1950s, and approximately 5 × after the 1950s. Elemental ratios show that the increase in OCAR is mainly the result of C autogenesis from the growth of aquatic plants stimulated by agricultural intensification, including increased chemical fertilizer application and farmland expansion. Significantly enhanced nutrient burial by these lakes after the 1950s resulted from increased anthropogenic impacts in northeast China. More sustainable agricultural practises, including a decrease in P fertilizer use, would result in a lowering of OCAR, TNAR and TPAR in the future.

Brazil is one of the major global poultry producers, and the organic waste generated by the chicken slaughterhouses can potentially be used as a biofertilizer in agriculture. This study was designed to test the hypothesis that continuous use of biofertilizer to the crops, substituting the use of mineral fertilizer promote C-offset for the soil and generate crop energy efficiency for the production system. Thus, the objectives of this study were to evaluate the effects of biofertilizer use alone or in combination with mineral fertilizer on soil organic carbon (SOC) stock, carbon dioxide (CO₂) mitigation, C-offset, crop energy efficiency and productivity, and alleviation of environmental pollution. The experiment was established in southern Brazil on a soil under 15 years of continuous no-till (NT). Experimental treatments were as follows: i) Control with no fertilizer application, ii) 100% use of industrial mineral fertilizer (Min-F); iii) 100% use of organic waste originated from poultry slaughterhouses and hereinafter designated biofertilizer (Bio-F), and iv) Mixed fertilizer equivalent to the use of 50% mineral fertilizer + 50% of biofertilizer (Mix-F). Effects of experimental treatments were assessed for the crop sequence based on bean (Phaseolus vulgaris), soybean (Glycine max) and corn (Zea mays) in the summer and wheat (Triticum aestivum) and black oat (Avena strigosaSchreb) in the winter composing two crops per year, as follow: bean/wheat-soybean/black oat-corn/wheat-soybean/black oat-corn/wheat-bean. The continuous use of Bio-F treatment significantly increased the index of crop energy efficiency. It was higher than that of control, and increased it by 25.4 Mg CO₂eq ha⁻¹ over that of Min-F treatment because of higher inputs of crop biomass-C into the system. Further, continuous use of Bio-F resulted in a significantly higher CO₂eq stock and offset than those for Min-F treatment. A positive relationship between the C-offset and the crop energy efficiency (R² = 0.71, p < 0.001) indicated that the increase of C-offset was associated with the increase of energy balance and the amount of SOC sequestered. The higher energy efficiency and C-offset by application of Bio-F indicated that the practice of crop bio fertilization with poultry slaughterhouse waste is a viable alternative for recycling and minimizing the environmental impacts.

Understanding the comprehensive effect on crop production and quality, soil acidification, and Cd accumulation and distribution for wheat-rice rotation under N fertilization and continuous straw return is important for proper contaminated agricultural soil management. A 2-year paddy field experiment was conducted to study the effects of above factors change in the Zhejiang province, China. Fertilization treatments included: conventional N fertilizer application (N3), 20% reduction of N application (N2), 40% reduction of N application (N1), combined with three portions of straw incorporation: all straws retention (N3), half of the straws into the fields (S2), 20% straws retention(S1). The N1 treatments significantly decreased crop yields compared to N2 and N3 treatments. Except for C2-wheat, soil pH generally decreased with increasing N fertilizer input in the order of N1>N2>N3, regardless of how many straws was amended. Moreover, we found that straw addition plus N fertilization had a intersystem impacts on Cd accumulation, distribution and availability. Although total Cd had different trends among 4 experimental seasons, when the N reduced 20% applied, the DTPA-Cd contents were lowest among 3 out of four experimental seasons, except for that of C2-wheat, where N2 treatments ranked the second lower contents. For most seasons, Cd contents in straws were higher than soils and lowest in grains, and S2N2 treatment performed an intermediate value among all treatments. Furthermore, our study demonstrated that S2 or N2 treatments or S2N2 reduced the potential risk of plant diseases and pests with lower disease index, disease cluster rate. Notably, the relative outbreak of pests was remarkably suppressed under S2 treatments, especially S2N2. Thus, these findings demonstrated that in wheat-rice rotation reducing 20% N fertilization with 50% straw returning may be a win-win practice in this region for the equilibrium between agricultural productivity, quality and low Cd polluted risk.