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Balancing the relationship between straw returning and fertilizer, especially nitrogen fertilizer application is vital for achieving the goal of reducing fertilization and improving soil fertility. To better understand their combined effects on crop yield and nitrogen utilization, a study was conducted to explore the effects of straw returning and nitrogen fertilizer application on crop yield and nitrogen utilization. In contrast to straw return, nitrogen fertilizer application had a more significant effect on the crop yield. Straw ploughing led to significantly higher crop yield under the nitrogen fertilizer application rates of 0, 90, 150 kg/ha compared to straw mulching (P < 0.05). No significant differences for > 150 kg/ha concerning their effects on crop yield were observed between straw ploughing and mulching. The optimal residual return amount was 9000 kg/ha and straw return was not decisive to crop yield under the same nitrogen fertilizer application rate. Straw ploughing better promoted nitrogen uptake, utilization, harvest and retention than straw mulching and no residue addition when combined with nitrogen fertilizer application. These findings demonstrate that straw ploughing and 150 kg/ha nitrogen fertilizer application rate is a better combination for implementing stable production and enhancing nitrogen utilization synchronously in the chernozem of Northeast China. [ABSTRACT FROM AUTHOR]

In order to mitigate the degradation of black soil organic matter, this paper designed a field microplot experiment with different proportional mixtures of corn straw and peat with an equal carbon amount. Treatments included (ⅰ) no organic materials applied (CK), (ⅱ) Application of peat (P), (ⅲ) Peat and corn straw are 2:1(2/3P), (ⅳ) Peat and corn straw are 1:2(1/3P) and (ⅴ) Application of corn straw (0P). The humus composition and humic acid (HA) structural characteristics of black soil were studied using elemental analysis, Fourier transform infrared (FTIR) spectroscopy, fluorescence spectrum and thermogravimetric analysis. The results demonstrated that water-soluble substances carbon (WSS-C) content increased with the increase of straw application amount, SOC, humification rate (PQ) and carbon content of other humus fractions increased with the increase of peat application amount. In addition, the higher peat applied, the stronger the aromatic nature of HA structure, the more stable and complex the structure of HA, the higher corn straw applied, the stronger the aliphatic nature of HA structure, and the simpler the structure of HA. With the consideration of the humus composition and HA structural characteristics of black soil, the appropriate ratio of the application of corn straw and peat deemed 2:1. [ABSTRACT FROM AUTHOR]

Bursaphelenchus xylophilus became one of the most damaging forest pests in recent years in Hunan province, and caused remarkable losses of pine tree. In order to explore the effect of fire disturbance on the prevention of Monochamus alternatus and B. xylophilus. forests dominated by Pinus massoniana were taken as the object of the study in Daolin town, Ningxiang city, Hunan province, China. Three kinds of forest were selected, such as healthy forest of Pinus massoniana (Control I), infected forest without prevention(II), and infected forest with prevention(III). Then, 6 plots were set in every object forest. Three were the control plot, and the other three were treated with prescribed burning. We continuously investigated the number of M. alternatus and B. xylophilus before and after low intensity prescribed burning. The results indicated that the quantity of female M. alternatus in the three kinds of fire disturbance plots were reduced by 88.24%, 75.00% and 94.74%, respectively, while the males were reduced by 77.78%, 81.82% and 88.89% before and after the fire. There were significant differences for the quantity of M. alternatus before and after the prescribed burning (P<0.05). The results showed that the prevention efficacy of II-2 was the best. Within 10 to 20 days after the fire, the quantity of B. xylophilus carried by M. alternatus changed significantly. The average quantity of B. xylophilus carried by female and male M. alternatus dropped from 1135 to 6 and from 397 to 35, respectively. It showed that prescribed burning could reduce the population density of M. alternatus and carrying quantity of B. xylophilus of each M. alternatus. So prescribed burning could control the spread of pine wilt disease and prevent its outbreak. Prescribed burning has an important theoretical and practical significance in pine wilt disease prevention. [ABSTRACT FROM AUTHOR]

The effects of agricultural waste return on the emissions of greenhouse gases (CO2, N2O and CH4) from corn farmland in the black soil region of Northeast China and its potential to increase temperature were studied to provide a theoretical basis for formulating reduction measures of agricultural greenhouse gas emissions. This study was conducted at the Experimental Station of China Agricultural University in Quanyangou, Lishu County, Siping City, Jilin Province. Static greenhouse gas chromatography was used to monitor soil greenhouse gas fluxes under different fertilization measures, and the different fertilization treatments were analyzed for comprehensive differences in greenhouse effects among corn fields. The results showed that the average CO2 fluxes and total emissions in response to the straw return treatment were the highest, reaching 388.96 mg⋅m-2⋅h-1 and 14718.97 kg⋅hm-2, respectively, and nitrogen topdressing fertilizer significantly increased CO2 emissions. With respect to CH4 emissions, single fertilizer-treated plots had the highest average absorbed flux and total absorption--0.042 mg⋅m-2⋅h-1 and 1.36 kg⋅hm-2, respectively, and with respect to N2O fluxes, the highest flux and amount were 0.153 mg⋅m-2⋅h-1 and 5.75 kg⋅hm-2, respectively. The global warming potential of the straw in situ treatment was significantly higher than that of the other treatments, and the global warming potential of the cattle manure treatment was lower than that of the single chemical fertilizer treatment, but the differences were not significant. Moreover, straw mulch increased CO2 emissions from black soils, and dry soils were shown to be important sinks of atmospheric CH4. Combinations of organic and inorganic fertilizers and individual fertilizers can reduce N2O emissions from soils. Therefore, to achieve higher corn yields and to reduce greenhouse gas emission intensities simultaneously, applications of organic and inorganic fertilizers constitute an ideal soil fertility method in the black soil region of Northeast China. [ABSTRACT FROM AUTHOR]

Soil organic carbon decomposition is regulated by soil physical and chemical properties, such as soil nitrogen (N) and soil substrate quality. In this study, soil samples from both N fertilization and control plots were collected at two depths in a Larix gmelinii plantation to determine if N addition elicits consistent responses in microbial respiration in bulk and rhizosphere soil, and to determine the temporal and spatial dynamics of soil organic carbon decomposition. Soil bulk and rhizosphere microbial respiration were determined using the NaOH solution absorption method. Soil microbial biomass was determined by a modified CHCL3 fumigation-extraction method. The greatest soil bulk and rhizosphere microbial respiration occurred in July. Soil rhizosphere microbial respiration was higher than bulk respiration at 0-10 cm and 10- 20 cm. The biggest reductions in soil microbial respiration induced by fertilization were 15.0% (bulk) and 19.6% (rhizosphere) at 0-10 cm in July, and 6.4% (bulk) and 7.9% (rhizosphere) at 10-20 cm in September. Fertilization did not influence the rhizosphere priming effect except for at 10-20 cm in May. Structural equation modeling revealed that soil microbial biomass carbon (MBC) and nitrogen (MBN) contributed directly to soil microbial respiration. Moreover, soil total N and organic carbon content were associated with soil microbial respiration through MBC and MBN. These results suggest that N fertilization suppresses soil organic carbon decomposition by decreasing soil microbial biomass, while C input induced by root exudates determined the rhizosphere priming effect, not soil microbes in the rhizosphere. [ABSTRACT FROM AUTHOR]

The effect of different long-term (2001-2016) tillage practices on soil nitrogen forms in different soil layers were studied to provide a scientific basis for evaluating soil fertility and establishing rational fertilization measures. Soil contents of total nitrogen (TN), particulate organic nitrogen (PON), microbial biomass nitrogen (MBN), water soluble organic nitrogen (WSON), NO3-N content, NH4-N content ammonium nitrogen and organic acid nitrogen component contents were measured under notillage (NT) and mould plow (MP) treatments based on a long-term (16 year) conservation tillage experiment in Northeast China. The results showed that no-tillage increased soil total nitrogen, active nitrogen, inorganic nitrogen and organic nitrogen content, which varied with soil depth. Compared with MP, NT significantly (p < 0.05) increased total nitrogen and active nitrogen content in the surface soil (0- 30 cm); TN, PON, MBN and WSON increased significantly (p < 0.05) by 28.32%, 23.07%, 15.13% and 25.21% in 0-5 cm and by 10.17%, 19.4%, 15.97%, and 31.33% in 5-10 cm, respectively. For soil inorganic nitrogen, the content of ammonium nitrate at 0-5 cm and at 5-10 cm under NT was significantly (p < 0.05) higher than that of MP by 28.1% and 32.13%, respectively, and the content of ammonium nitrogen in soil at 0-5 cm was significantly (p < 0.05) higher, by 12.86%, than that of MP. No-tillage significantly increased the content of total hydrolysable nitrogen, hydrolysable ammonia nitrogen, hydrolysable amino acid nitrogen and hydrolysable unidentified nitrogen in the 0-10 cm soil layer, but no significant effect was found on the content of hydrolysable amino sugar nitrogen. Soil nitrogen content was closely related to tillage practices. These results suggest that no-tillage was beneficial in augmenting soil nitrogen supply capacity by increasing soil total nitrogen, active nitrogen, inorganic nitrogen and organic nitrogen content. [ABSTRACT FROM AUTHOR]

It is often claimed that earthworms exert a huge influence on soil macroporosity. Nevertheless, gaps still exist in our knowledge of rangeability in soil macroporosity caused by earthworm activity. Earthworms are generally recognized as ecosystem engineers vital for soil ecosystem function and services, but the potential mechanism of earthworm response to the combination of extreme drought and conservation tillage has not yet been identified. To improve understanding of the effect of the earthworm on soil macroporosity and how earthworms, through soil macroporosity, respond to extreme drought and conservation tillage, a study was conducted to compare soil macroporosity under different tillage treatments with the same number of earthworms in incubation conditions and soil structural properties (soil penetration resistance, infiltration rate, saturated hydraulic conductivity) associated with macroporosity, together with crop yields under different tillage systems and drought stress in field conditions. The results show that earthworms only increase the volume of large macropores (>100 μm) rather than small macropores (30-100 μm) under different tillage systems. Earthworms played a positive role in the development of large macropores, as evidenced by the formation of paths of least resistance under high penetration resistance, higher infiltration rate and saturated hydraulic conductivity and no obvious yield loss under extreme drought and conservation tillage in a Chinese Mollisol. [ABSTRACT FROM AUTHOR]