•No significant interactions between fertilizer types for both gases were observed.•Organic amendments stimulated N2O emissions but didn’t affect NO emissions.•Chemical fertilizer application significantly stimulated N2O and NO emissions.•Emission factor of N2O was higher than that of NO irrespective of fertilizer type.In China, the rapid conversion of traditional rice-wheat rotation to orchard-induced management practices has resulted in changes in soil N2O and NO emissions. However, quantification of emissions from orchard fields characterized by a high rate of organic and chemical N fertilization application has not yet been widely carried out. In this study, we measured soil N2O and NO emissions from a typical peach orchard in the Taihu region over a 2-year period using a combination of static chamber and gas chromatography techniques. Four treatments were examined: organic manure alone (OM), chemical fertilizers alone (CF), organic manure plus chemical fertilizers (OF + CF), and no fertilizers as a control (CK). No significant effects of organic amendments × chemical fertilizer application on soil N2O and NO emissions were observed. The mean annual N2O emission over the 2-year period was 3.2 kg N ha−1 under CK treatment, and increased to 9.3, 10.3, and 20.1 kg N ha−1 under OF, CF and OF + CF treatment, respectively. In contrast, cumulative NO emissions were relatively low, ranging from 0.14 to 1.99 kg N ha−1 yr−1. The NO emissions were enhanced by approximately eight fold following mineral fertilization application either alone or in combination with organic manure, and to a lesser extent (45%, nonsignificant) by organic manure application alone. Overall, NO accounted for approximately 14.5 and only 2.9% of the total (NO + N2O)-N emissions under CF and OF treatment, respectively. Over the 2-year observation period, the N2O emission factor averaged 1.69%, 1.32% and 1.86% and the NO emission factor averaged 0.03%, 0.27% and 0.17% under OF, CF and OF + CF treatment, respectively. Overall, our results suggest that fertilized peach orchard soil in the Taihu region is an important source of N2O emissions.

•Effects of simple and complex C on microbial NO3− immobilization were different.•NO3− immobilization was enhanced with simple C addition at rates >500 mg C kg−1.•NO3− immobilization was enhanced with complex C addition of C/N ratios >18.•It is possible to add exogenous C to increase soil microbial NO3− immobilization.The accumulation of NO3− in the soil has resulted in increased nitrogen (N) loss through runoff, leaching, and gaseous emissions. Microbial immobilization of NO3− as an important process in reducing soil NO3− accumulation has been for a long time neglected due to the predominant viewpoint that microbes preferentially immobilize NH4+-N. Microbial NO3− immobilization is generally carbon (C)-limited, and thus exogenous organic C input may enhance microbial NO3− immobilization. However, the effect of the quality and quantity of exogenous organic C input on soil microbial NO3− immobilization is poorly understood, and a synthetic assessment on such an effect is lacking. We thus assessed the impact of exogenous organic C type, the application rate of simple organic C (glucose and acetate), complex organic C type (animal manure, plant residue) and the C/N ratio of complex organic C on soil microbial NO3− immobilization rate using a meta-analysis. We found that the quality and quantity of exogenous C input affect soil microbial NO3− immobilization: microbial NO3− immobilization was enhanced with the addition of simple organic C at rates >500 mg C kg−1, or complex organic C with C/N ratios >18. Furthermore, a positive relationship between the natural log of response ratio of soil microbial NO3− and NH4+ immobilization indicates the simultaneous utilization of NH4+ and NO3− under elevated C availability. We conclude that specific exogenous organic C input at a high rate or with a high C/N ratio can enhance microbial NO3− immobilization and reduce soil NO3− accumulation.

The nitrogen (N) isotope method reveals that application of fertilizer N can increase crop uptake or denitrification and leaching losses of native soil N via the “added N interaction”. However, there is currently little evidence of the impact of added N on soil N losses through NH3 volatilization using 15N methodologies. In the present study, a three-year rice/wheat rotated experiment with 30% 15N-labeled urea applied in the first rice season and unlabeled urea added in the following five crop seasons was performed to investigate volatilization of NH3 from fertilizer and soil N. We found 9.28% of NH3 loss from 15N urea and 2.88–7.70% declines in 15N-NH3 abundance occurred during the first rice season, whereas 0.11% of NH3 loss from 15N urea and 0.02–0.21% enrichments in 15N-NH3 abundance happened in the subsequent seasons. The contributions of fertilizer- and soil-derived N to NH3 volatilization from a rice/wheat rotation were 75.8–88.4 and 11.6–24.2%, respectively. These distinct variations in 15N-NH3 and substantial soil-derived NH3 suggest that added N clearly interacts with the soil source contributing to NH3 volatilization.

Yak and Tibetan sheep grazing is a common phenomenon on natural grasslands in the Qinghai-Tibetan Plateau, and large amounts of excrement are directly deposited onto alpine grasslands. However, little is known about the effects of excrement return on soil N supply and N retention capacity. This study investigated the short-term effects of yak and Tibetan sheep dung on gross N transformation rates determined by 15N tracing technique of alpine steppe (AS) and meadow (AM) soils at 60 % water holding capacity (WHC) under laboratory conditions. Cumulative gross N mineralization and NH4+ immobilization over the 21-day incubation period in AM soil were around 2.8 and 2.0 times as high as that in AS soil, respectively. Cumulative gross nitrification in AM soil was 0.96 times higher, while the value of gross NO3− immobilization rate was 0.65 times lower than in AS soil, resulting in higher NO3− accumulation in AM soil. Dung addition increased soil gross N mineralization and NH4+ immobilization rates by 12–35 % and 17–59 %, respectively. Amending yak and sheep dung decreased gross nitrification rates by 3–23 % but increased gross NO3− immobilization rates by 25–190 %, which led to a decreased net NO3− accumulation and NO3− losses risk through leaching. The cumulative CO2 emissions over the 21 days of incubation period were enhanced by 65 and 120 % for AS and AM soil, respectively. The application of dung stimulated cumulative N2O emissions, but the stimulation was only significant in AM soil. In general, yak and sheep dung return has a positive effect on soil N supply and retention owing to the increase in NH4+ availability for plant with simultaneously decreasing NO3− accumulation in soils.

In the Taihu Lake Region (TLR) of China, farmers’ injudicious and excessive use of phosphorus (P) fertilizer has led to a dramatic spike in P accumulation. In view of that, the water flooding practice can increase soil P release and enhance P availability in rice season, compared with the strong P fixation in wheat season; it seems possible to save P fertilizer in rice season with the aim of reducing P loads without any crop yield declines.To validate this possibility, a 4-year pot experiment encompassing eight rice/wheat seasons and using four paddy soils with varying Olsen-P contents (6.16 to 40.95 mg kg−1) was conducted to compare rice/wheat yield, inorganic and organic P accumulation under four different P regimes, P fertilization for both rice and wheat (PR + W; conventional practice), P fertilization only for wheat (PW), P fertilization only for rice (PR), and no P fertilization for both seasons (Pzero).Compared with conventional PR + W treatment, PR treatment significantly decreased wheat yields, especially in medium- and low-P soils, with an Olsen-P concentrate decline of 34.4–62.8 %. In contrast, PW treatment showed no significant difference in the rice/wheat yields over 4 years irrespective of high-, medium-, and low-P-concentrated soils, despite the soil Olsen-P concentration declining by 34.9–64.4 %. This highlights the feasibility of omitting P fertilizer application to flooded rice for at least 4 years in rice/wheat cropping paddy fields while maintaining crop yields and reducing environmental risk. In four paddy soils, available inorganic P was the dominant effective P source and increased with the concentration of Olsen-P. Without P fertilization over time, the concentration of soil inorganic P fractions declined and organic P remained relatively constant.According to the P supply capacity of different soils under the regime of omitting P fertilization for rice, how to utilize the bioavailability of P in different P supply capacity soils when P fertilization is omitted for rice crops will be required in future work.

Long-term nitrogen (N) fertilization has been shown to stimulate N2O emissions from acidic soil in tea plantations. However, the potential mechanism behind this stimulation remains unclear. We aimed to investigate the effects of 6 years of fertilizer application on N2O emission pathways and the N2O emission ratio from heterotrophic and autotrophic nitrification in tea plantation.We performed a 15N-tracing experiment under 40 and 60 % water-holding capacity (WHC) to investigate the effects of 6 years of fertilizer application on N2O-emission pathways and emission ratios from heterotrophic and autotrophic nitrification in soil from tea plantations.Six years of fertilizer application stimulated both heterotrophic and autotrophic nitrification, particularly under conditions of higher soil moisture. Autotrophic nitrification was the predominant pathway for N2O emission in tea soils, being responsible for 66.7–75.9 % and 50.4–56.9 % of N2O emission in unfertilized and fertilized soils, respectively. Fertilizer application significantly increased the contribution of denitrification to N2O emission (10.5–35.7 %), independent of soil moisture conditions, which could be due to a fertilizer-induced reduction in soil pH Fertilizer application and a subsequent reduction in pH resulted in a 3–4 and 8–9 fold increase in the ratio of N2O emissions from heterotrophic nitrification and autotrophic nitrification, respectively.The increase in N2O emission following N fertilizer application was attributed to increased heterotrophic and autotrophic nitrification rates and an increased ratio of N2O emission from heterotrophic and autotrophic nitrification. Our results suggest that pH was a critical factor regulating the ratio of N2O emission from heterotrophic and autotrophic nitrification and thus controlling N2O emission from the tea soils studied.

Organic materials with low C/N ratio, such as animal manure and compost, have been largely applied to orchard soil to maintain soil organic matter and improve soil fertility. However, little is known about the decomposition characteristics and nitrogen (N) mineralization of added organic materials. Thus, a laboratory incubation study using 15N tracing technique was carried out to investigate the effects of organic materials with low C/N ratio (rapeseed meal and chicken manure) on gross N transformations in a vineyard soil. Our result showed that carbon (C) mineralization of organic material depended on C/N ratio and lignin/N ratio of organic material, while N mineralization was associated with substrate N concentration. The application of organic material with low C/N ratio increased gross N mineralization, NH4+ immobilization, autotrophic nitrification rates, and CO2, N2O, and NO emissions. Heterotrophic nitrification and NO3− immobilization did not occur, irrespective of organic material amendments. Organic material amendments increased more total inorganic N production (mineralization + heterotrophic nitrification) than total inorganic N consumption (immobilization of NH4+ and NO3−), leading to increasing net N mineralization rates. In addition, NO3− consumption (NO3− immobilization + dissimilatory NO3− reduction to NH4+) increased to a lesser extent than NO3− production (heterotrophic + autotrophic nitrification) following organic material amendments, leading to more rapid accumulation of NO3− in soils. Our results suggest that organic material with a low C/N ratio can provide readily available N as N fertilizers but accompanied by enhanced risk of N losses through gaseous N emissions and possibly NO3− leaching and runoff.

Few studies have examined the effects of biochar on nitrification of ammonium-based fertilizer in acidic arable soils, which contributes to NO3− leaching and soil acidification.We conducted a 42-day aerobic incubation and a 119-day weekly leaching experiment to investigate nitrification, N leaching, and soil acidification in two subtropical soils to which 300 mg N kg−1 ammonium sulfate or urea and 1 or 5 wt% rice straw biochar were applied.During aerobic incubation, NO3− accumulation was enhanced by applying biochar in increasing amounts from 1 to 5 wt%. As a result, pH decreased in the two soils from the original levels. Under leaching conditions, biochar did not increase NO3−, but 5 wt% biochar addition did reduce N leaching compared to that in soils treated with only N. Consistently, lower amounts of added N were recovered from the incubation (KCl-extractable N) and leaching (leaching plus KCl-extractable N) experiments following 5 wt% biochar application compared to soils treated with only N.Incorporating biochar into acidic arable soils accelerates nitrification and thus weakens the liming effects of biochar. The enhanced nitrification does not necessarily increase NO3− leaching. Rather, biochar reduces overall N leaching due to both improved N adsorption and increased unaccounted-for N (immobilization and possible gaseous losses). Further studies are necessary to assess the effects of biochar (when used as an addition to soil) on N.

A pot study spanning four consecutive crop seasons was conducted to compare the effects of successive rice straw biochar/rice straw amendments on C sequestration and soil fertility in rice/wheat rotated paddy soil.We adopted 4.5 t ha−1, 9.0 t ha−1 biochar and 3.75 t ha−1 straw for each crop season with an identical dose of NPK fertilizers.We found no major losses of biochar-C over the 2-year experimental period. Obvious reductions in CH4 emission were observed from rice seasons under the biochar application, despite the fact that the biochar brought more C into the soil than the straw. N2O emissions with biochar were similar to the controls without additives over the 2-year experimental period. Biochar application had positive effects on crop growth, along with positive effects on nutrient (N, P, K, Ca and Mg) uptake by crop plants and the availability of soil P, K, Ca and Mg. High levels of biochar application over the course of the crop rotation suppressed NH3 volatilization in the rice season, but stimulated it in the wheat season.Converting straw to biochar followed by successive application to soil is viable for soil C sequestration, CH4 mitigation, improvements of soil and crop productivity. Biochar soil amendment influences NH3 volatilization differently in the flooded rice and upland wheat seasons, respectively.

Biochar has been increasingly used as a method for C sequestration and soil improvement. To understand how feedstock and pyrolysis conditions affect biochar characteristics, we investigated two wood-based biochars (bamboo and elm) and five crop-residue-based biochars (wheat straw, rice straw, maize straw, rice husk, and coconut shell), which were pyrolyzed at 500 or 700 °C and remained at that temperature for 4, 8, and 16 h under oxygen-limited conditions. For a given feedstock, increasing pyrolysis temperature from 500 to 700 °C resulted in increases in ash content, BET surface area, pH, and total P and Ca contents (P < 0.05) and decreases in yield, cation exchange capacity (CEC), total acid, and total N (P < 0.01). Prolonging residence time (from 4 to 8 or 16 h), the BET surface area and ash content of biochars increased (P < 0.05), whereas the yield decreased (P < 0.01). Fourier-transform infrared spectroscopy (FTIR) analysis showed that more recalcitrant and aromatic structures were formed in the biochars with increased temperature. The three straw-based biochars consistently exhibited far greater ash percentage (14.5–40.3 wt %), CEC (14.1–34.8 cmol kg–1), and the contents of total N (0.24–2.81 wt %), P (0.60–8.41 wt %), Ca (0.63–1.48 wt %), and Mg (0.24–0.63 wt %) and generally had higher yield (19.0–37.6 wt %), pH (9.2–11.1), and contents of total acid (0.15–0.53 mmol g–1), C (41.7–55.1 wt %), Na (0.27–6.72 wt %), and K (6.56–28.1 wt %) than the two wood-based biochars. The BET surface area of straw-based biochars with 700 °C pyrolysis temperature could be mostly as high as 112–378 m2 g–1, a comparable level with that of wood-based biochars. Despite the high variability in biochar properties, these results demonstrate that biochars from crop straw may be more effective and desirable for improving soil fertility and C sequestration in Chinese vast soils.

•P fertilization to the wheat-growing season only produced high crop yields.•P fertilizer reduction ensured an adequate labile P supply and microbial community.•P fertilization to the wheat-growing season only is suitable for rice–wheat rotation system.•The first evidence of P fertilizer reduction in rice–wheat rotation for fields.Crop production in the Taihu Lake Region (TLR) of China has been greatly improved by increasing phosphorus (P) fertilizer input. However, overuse has led to accumulation of P and increased the risk of environmental pollution. In this study, we investigated the effects of four P fertilization regimes in paddy soils at two field stations (CS1 and CS2) during four years of a rice-wheat cropping system. The fertilization regimes were as follows: P fertilization only during the wheat-growing season (PW), P fertilization only during the rice-growing season (PR), P fertilization during both the rice- and wheat-growing seasons (PR + W, current farming practice), and no P fertilization during either season (Pzero, control). The PW treatment did not reduce crop yield in either CS1 or CS2 compared to the PR + W. Moreover, soil Olsen-P concentrations during each rice-wheat rotation were maintained, and a positive increase in phosphate utilization efficiency by 1.2–3.6% (p > 0.05) was observed over the four rice-wheat rotations. In contrast, the PR treatment reduced the straw and grain yield of wheat by 8.74–43.2 and 19.4–47.7%, respectively, as did the Pzero treatment by 7.21–60.0 and 19.6–84.1%, respectively (p < 0.05). During the rice season, the PW treatment showed no significant differences in P fractionation and microorganism communities compared to the PR and PR + W treatments. The results suggest that the PW fertilization regime is suitable for rice–wheat rotation systems in agro-ecosystems such as the Taihu Lake Region of China.