Microbial Biomass Carbon Trends in Black and Red Soils Under Single Straw Application: Effect of Straw Placement, Mineral N Addition and Tillage

Quantifying trends in soil microbial biomass carbon (SMBC) undercontrasting management conditions is important in understanding thedynamics of soil organic matter (SOM) in soils and in ensuring theirsustainable use. Against such a background, a 60-day greenhousesimulation experiment was carried out to study the effects of strawplacement, mineral N source, and tillage on SMBC dynamics in twocontrasting soils, red sol (Ferrasol) and black soil (Acrisol). Thetreatments included straw addition + buried (T1); straw addition +mineral N (T2); and straw addition + tillage (T3).

Maize (Zea mays L.) and Cotton (Gossypium hirsutum L.) Straw Decomposition in Soil: Effect of Straw Placement, Mineral Nitrogen and Tillage

With the present understanding that decomposing straw may not onlyaffect soil properties, but pos- sibly greenhouse gas emissions aswell, focus among environmental researchers has gradually expanded toinclude understanding of decomposition rate and stability of straw ofdifferent plants in different soils under different managementconditions. Against such a background, a short-term (60 days)greenhouse simulation experiment was carried out to study the effectsof straw placement, external mineral N source and tillage on strawdecomposition of maize and cotton in two contrasting soils, a redsoil (Ferrasol) and a black soil (Acrisol).

Soil mineral nitrogen and yield-scaled soil N2O emissions lowered by reducing nitrogen application and intercropping with soybean for sweet maize production in southern China

The increasing demand for fresh sweet maize （Zea mays L. saccharata） in southern China has prioritized the need to find solutions to the environmental pollution caused by its continuous production and high inputs of chemical nitrogen fertilizers. A promising method for improving crop production and environmental conditions is to intercrop sweet maize with legumes. Here, a three-year field experiment was conducted to assess the influence of four different cropping systems （sole sweet maize （SS）, sole soybean （SB）, two rows sweet maize-three rows soybean （S2B3） intercropping, and two rows sweet maize-four rows soybean （S2B4） intercropping）, together with two rates of N fertilizer application （300 and 360 kg N ha-1） on grain yield, residual soil mineral N, and soil N2O emissions in southern China. Results showed that in most case, inter- cropping achieved yield advantages （total land equivalent ratio （TLER=0.87-1.25） was above one）. Moreover, intercropping resulted in 39.8% less soil mineral N than SS at the time of crop harvest, averaged over six seasons （spring and autumn in each of the three years of the field experiment）. Generally, intercropping and reduced-N application （300 kg N ha-1） produced lower cumulative soil N20 and yield-scaled soil N20 emissions than SS and conventionaI-N application （360 kg N ha-l）, respectively. $2B4 intercropping with reduced-N rate （300 kg N ha-~） showed the lowest cumulative soil N20 （mean value=0.61 kg ha-1） and yield-scaled soil N20 （mean value=0.04 kg t-1） emissions. Overall, intercropping with reduced-N rate maintained sweet maize production, while also reducing environmental impacts. The system of S2B4 intercropping with reduced-N rate may be the most sustainable and environmentally friendly cropping system.

Mixing Alfalfa Straw and Maize Straw to Enhance Nitrogen Mineralization, Microbial Biomass and Enzyme Activity: A Laboratory Study

The quality of straw affects N release after straw retention. As straw with high C： N ratio could result in N immobilization, additional N is needed to compensate N demand of crops. However, more and more N fertilizers have been applied to the soil to improve crop yields in China, which not only increases production cost but also reduces soil quality. Therefore, reasonable application of N fertilizer becomes a key problem after straw retention. This study aimed to assess the effects of applying maize straw with high quality alfalfa straw on mineral N content, microbial biomass and enzyme activity under controlled conditions. The effect of applying maize straw with alfalfa straw was compared with that of maize straw in combination with N fertilizer under the same C： N ratio （25：1）. The laboratory incubation experiment consisted of four treatments： （1） soil with no addition （CK）; （2） soil amended with maize straw （M）; （3） soil amended with alfalfa straw and maize straw with an adjusted C： N ratio of 25：1 （MM）; （4） soil amended with inorganic nitrogen fertilizer and maize straw with an adjusted C：N ratio of 25：1 （MF）. The results showed that application of maize straw leaded to an N immobilization during the 270 d of incubation. Combined application of alfalfa and maize straw and or mineral N fertilizer alleviates the N immobilization and increase soil mineral N content. Compared to MF treatment, MM treatment prolonged N availability during the incubation. MM and MF treatments increased the soil microbial biomass carbon and nitrogen contents, and soil invertase and β-glycosidase activities. There was no difference between MM and M treatment in soil urease activity. MF treatment had significantly negative influence on soil urease activity compared with M treatment. The amount of added N significantly affected mineral N content, soil microbial biomass and enzyme activity. The mixture of alfalfa straw and maize straw sustains higher level of mineral N content, microbial biomass and enzyme activity as it had high N input compared to maize straw in combination with N fertilizer. It is concluded that alfalfa straw may be a better N source than N fertilizer in alleviating N immobilization caused by maize straw retention.

Yield and Nicotine Content of Flue-Cured Tobacco as Affected by Soil Nitrogen Mineralization

Nitrogen(N)supply is the most important factor affecting yield and quality of flue-cured tobacco(FCT).A field experiment and an in situ incubation method were used to study the effects of soil N mineralization in the later stages of growth on yield and nicotine content of FCT in Fenggang and Jinsha,Guizhou Province.The yield and market value of FCT at Fenggang were much lower than those at Jinsha.However,the nicotine content of middle and upper leaves was much higher at Fenggang than at Jinsha when the same rate of fertilizer N was applied,which might be due to a higher N supply capacity at the Fenggang site.At later stages of growth(7-16 weeks after transplanting),the soil net N mineralization at Fenggang(56 kg N ha^(-1))was almost double that at Jinsha(30 kg N ha^(-1)).While soil NH_4-N and NO_3-N were almost exhausted by the plants or leached 5 weeks after transplanting,the N taken up at the later growth stages at Fenggang were mainly derived from soil N mineralization,which contributed to a high nicotine content in the upper leaves.The order of soil N contribution to N buildup in different leaves was:upper leaves>middle leaves>lower leaves.Thus,soil N mineralization at late growth stages was an important factor affecting N accumulation and therefore the nicotine content in the upper leaves.

Effects of Temperature and Water Saturation on CO_2 Production and Nitrogen Mineralization in Alpine Wetland Soils

Relationships between carbon (C) production and nitrogen (N) mineralization were investigated in two alpine wetland soils of the Tibetan Plateau using laboratory incubation under different temperatures (5, 15, 25, and 35 ℃) and water saturation (noninundation and inundation). A significant positive relationship was found between CO2 production and N mineralization under increasing temperatures from 5 to 35 ℃ with the same water saturation condition in the marsh soil (r2 > 0.49, P < 0.0001) and the peat soil (r2 > 0.38, P < 0.002), and a negative relationship with water saturation increasing at the same temperature, especially 25 and 35 ℃, in the marsh soil (r2 > 0.70, P < 0.009) and the peat soil (r2 > 0.61, P < 0.013). In conclusion, temperatures and water saturation could regulate the relationship between CO2 production and net N mineralization in the Tibetan alpine marsh and peat soils.

Effect of Combined Heavy Metal Pollution on Nitrogen Mineralization Potential,Urease and Phosphatase Activities in a Typic Udic Ferrisol

Individual and combined effects of Cu, Pb, Zn and Cd on N mineralization, urease and phosphatase were examined in a Typic Udic Ferrisol in laboratory by employing an uniform design and a single factor design.Soil pollution caused by heavy metals inhibited N mineralization (No value) and urease and phosphatase activities. The combined pollution of metals alleviated their toxicity to N mineralization to some extent,whereas aggravated the toxicity to urease and phosphatase. Phosphorous application could mitigate the toxic effect of heavy metals on phosphatase activities, while alleviating effect of N application on the toxicity of heavy metals to urease was inconsistent. However, the mitigating effect of the fertilizers was limited in heavily polluted soils.

N Mineralization as Affected by Long-Term N Fertilization and Its Relationship with Crop N Uptake

A field experiment established in 1997 was conducted to study the effect of long-term N fertilizer application on N mineralization in a paddy soil determined using a laboratory anaerobic incubation followed with a field incubation and to measure the relationship between in situ N mineralization and crop N uptake. To estimate N mineralization in the laboratory, soil samples were collected from plots with N application at different rates for six years and were incubated. Soils treated with fertilizer N mineralized more N than unfertilized soils and mineralization increased with N application rates. Also, the fraction of total N mineralized increased with increasing N fertilizer application. These findings meant that a substantial portion of previously applied N could be recovered slowly over time in subsequent crops. The field incubation of the plot receiving no fertilizer N showed that the NH4^＋-N concentration varied greatly during the rice-growing season and seasonal changes of N mineralization were due more to accumulation of NH4^＋-N than NO3^-N. Hice N uptake increased up to a maximum of 82 kg N ha^-1 during the season. The close agreement found between in situ N mineralization and rice N uptake suggested that the measurement of in situ N mineralization could provide useful recommendations for adequate fertilizer N application.

Nitrogen Mineralization from Animal Manures and Its Relation to Organic N Fractions

Laboratory aerobic incubation was conducted for 161 d to study N mineralization and the changes of organic N fractions of nine different manures（3 chicken manures, 3 pig manures and 3 cattle manures） from different farms/locations. Results indicated that significant（P〈0.01 or P〈0.001） difference existed in N mineralization between manures. The rapid N mineralization in manures occurred during 56 to 84 d of incubation. First order exponential model can be used to describe N mineralization from chicken manures and pig manures, while quadratic equation can predict mineralization of organic N from cattle manures. An average of 21, 19 and 13% added organic N from chicken manure, pig manure and cattle manure was mineralized during 161 d of incubation. Amino acid-N was the main source of N mineralization. The changes of amino acid-N together with ammonium N could explain significantly 97 and 96% of the variation in mineralized N from manured soils and manures. Amino acid-N and ammonium N are two main N fractions in determining N mineralization potential from manures. Amino acid-N contributed more to the mineralized N than ammonium N.

Interactive effects of soil temperature and moisture on soil N mineralization in a Stipa krylovii grassland in Inner Mongolia, China

Determining soil N mineralization response to soil temperature and moisture changes is challenging in the field due to complicated effects from other factors. In the laboratory, N mineralization is highly dependent on temperature, moisture and sample size. In this study, a laboratory incubation experiment was carefully designed and conducted under controlled conditions to examine the effects of soil temperature and moisture on soil N mineralization using soil samples obtained from the Stipa krylovii grassland in Inner Mongolia, China. Five temperature（i.e. 9℃, 14℃, 22℃, 30℃ and 40℃） and five moisture levels（i.e. 20%, 40%, 60%, 80% and 100% WHC, where WHC is the soil water holding capacity） were included in a full-factorial design. During the 71-day incubation period, microbial biomass carbon（MBC）, ammonium nitrogen（NH4 ^＋-N） and nitrate nitrogen（NO3^--N） were measured approximately every 18 days; soil basal respiration for qCO2 index was measured once every 2 days（once a week near the end of the incubation period）. The results showed that the mineral N production and net N mineralization rates were positively correlated with temperature; the strongest correlation was observed for temperatures between 30℃ and 40℃. The relationships between moisture levels and both the mineral N production and net N mineralization rates were quadratic. The interaction between soil temperature and moisture was significant on N mineralization, i.e. increasing temperatures（moisture） enhanced the sensitivity of N mineralization to moisture（temperature）. Our results also showed a positive correlation between the net nitrification rate and temperature, while the correlation between the NH4 ^＋-N content and temperature was insignificant. The net nitrification rate was negatively correlated with high NH4 ^＋-N contents at 80%–100% WHC, suggesting an active denitrification in moist conditions. Moreover, qCO2 index was positively correlated with temperature, especially at 80% WHC. With a low net nitrification rate and high soil basal respiration rate, it was likely that the denitrification concealed the microbial gross mineralization activity; therefore, active soil N mineralization occurred in 60%–80% WHC conditions.

Soil animals and nitrogen mineralization under sand-fixation plantations in Zhanggutai region,China

The effects of soil animals on soil nitrogen (N) mineralization and its availability were studied by investigating soil animal groups and their amounts of macro-faunas sorted by hand, and middle and microfaunas distinguished with Tullgren and Baermann methods under three Pinus sylvestris var. mongolica Litv. plantations in Zhanggutai sandy land, China. In addition, soil N mineralization rate was also measured with PVC closed-top tube in situ incubation method. The soil animals collected during growing season belonged to 13 orders, 5 groups, 4 phyla, whose average density was 86 249.17 individuals·m^(-2). There were significant differences in soil animal species, densities, diversities and evenness among three plantations. Permanent grazing resulted in decrease of soil animal species and diversity. The average ammonification, nitrification and mineralization rates were 0.48 g·m^(-2)·a^(-1), 3.68 g·m^(-2)·a^(-1) and 4.16 g·m^(-2)·a^(-1), respectively. The ammonification rate in near-mature forest was higher than that in middle-age forests, while the order of nitrification and net mineralization rates was: middle-age forest without grazing < middle-age forest with grazing < near-mature forest with grazing (P<0.05). Soil N mineralization rate increased with soil animal amounts, but no significant relationship with diversity. The contribution of soil animals to N mineralization was different for different ecosystems due to influences of complex factors including grazing, soil characteristics, the quality and amount of litter on N mineralization.

Combined effects of two sulfonylurea herbicides on soil microbial biomass and N-mineralization

The interaction effect of two sulfonylurea herbicides, bensulfuron methyl (B) and metsulfuron methyl(M), were tested on microbial biomass C, N, N mineralization and C/N ratio in a loamy sand soil. The herbicides were applied at various levels of: control (B0M0), 0.01 and 0.01 (B1M1), 0.01 and 0.1 (B1M2), and 0.01 and 1.0 (B1M3) μg/g soil. Determinations of soil microbial biomass C, N and N mineralization contents were carried out at 1, 3, 5, 7, 10, 15, 25 and 45 days after herbicides application. The results showed that the soil microbial biomass C (C mic ) and microbial biomass N (N mic ) decreased consistently with the increasing rates of herbicides. The results further indicated that B1M1 and B1M2 caused a significant reduction in C mic and N mic within first 10 and 7 days of incubation, respectively, as compared with the control. These reductions in C mic and N mic were also significant ( P =0.05) with B1M3 application especially within first 15 days of incubation. A significant reduction in N mineralization (N min) was observed with high doses (B1M2, B1M3) of herbicides within first 5 days of incubation, while low rate (B1M1) failed to produce any significant effect. An increase in the soil microbial biomass C:N ratio was also noted.

Carbon and nitrogen mineralization in soil of leguminous trees in a degraded pasture in northern Rio de Janeiro, Brazil

Use of legume trees can improve soil quality in degraded pastures. The aim of this study was to charac- terize C and N mineralization kinetics and estimate the potentially mineralizable C and N in soil under Mimosa caesalpiniifolia Benth. and Acacia auriculiformis A. Cunn. ex Benth. secondary forest and pasture in red-yellow latosols in southeast Brazil. We conducted a laboratory aerobic incubation experiment using a completely ran- domized design of four replicates and four types of plant cover using a modified version of the Stanford and Smith technique （1972） to study C and N mineralization potential. Potentially mineralizable N （No） ranged from 135 to 170 mg kg-1. The predominant form of mineral N for all types of plant cover was N-NO3-. M. caesalpiniifolia was the only species that had a positive influence on N min- eralization. Neither of the legumes influenced C mineral- ization in pasture or secondary forest. The model of N mineralization corresponded to a sigmoidal curve while C mineralization corresponded to an exponential curve, revealing that the N and C mineralization processes were distinct. N mineralized by M. caesalpiniifolia （216 kg ofN ha-1） was adequate to meet the N requirement for a livestock-forest system.

Mineralization and Transformation of Nitrogen Derived from Plant Materials in Soils over 10 Years

Results of a 10-year decomposition experiment indicated that the annual mineralization rate of organic N in newly-formed humus varied with the type of original plant materials and the water regimes for decomposition, ranging from 0.028 to 0.074. The mineralization rate under waterlogged conditions was higher than that under upland conditions. The proportion of α-amino acid N in humus newly-formed under waterlogged conditions was slightly higher than that under upland conditions. It decreased gradually with time, while the proportion of nonhydrolyzable N showed no consistent trend, irrespective of the water regimes for decomposition. The distribution of amino acids in humus newly- formed from different plant materials under various water regimes was quite similar with that in original plant materials, and only minor differences could be found among them. For example, in comparison to original plant materials, the newly-formed humus contained higher proportions of isoleucine, cystine, γ-amino-butync acid and ornithine, and lower proportions of phenylalanine and proline. Moreover the proportion of phenylalanine was higher in the humus newly-formed under waterlogged conditions than that under upland conditions.

Dynamic response of chlorsulfuron herbicide to nitrogen mineralization and the ratio of microbial biomass nitrogen to nitrogen mineralization in the soil

A laboratory incubation experiment was conducted to elucidate the effect of chlorsulfuron herbicide on nitrogen mineralization and the ratio of microbial biomass nitrogen to nitrogen mineralization (N mic /N min ratio) in loamy sand soil.The herbicide was applied at four levels that were control, field rate 0\^01 (FR), 10 times of field rate 0\^1(10FR),and 100 times of field rate 1\^0 (100FR) μg/g soil. Determinations of N\|mineralization and microbial biomass\|N content were carried out 1,3,5,7,10,15,25 and 45 days after herbicide application. In comparison to untreated soil, the N\|mineralization decreased significantly in soil treated with herbicide at levels 10FR and 100FR within the first 5 days incubation. A more considerable reduction in the N mic /N min ratio was observed in the herbicide treated soil than the non\|treated control.Among the different treatment of chlorsulfuron, 100FR displayed the greatest biocidal effect followed by 10FR and FR,showing their relative toxicity in the order of 100FR>100FR>FR.The results indicated that the side effect of this herbicide on N\|mineralization is probably of little ecological significance.

Effect of N Fertilization on Grain Yield of Winter Wheat and Apparent N Losses

Excessive nitrogen (N) fertilizer application to winter wheat is a common problem on the North China Plain. To determine the optimum fertilizer N rate for winter wheat production while minimizing N losses, field experiments were conducted for two growing seasons at eight sites, in Huimin County, Shandong Province, from 2001 to 2003. The optimum N rate for maximum grain yield was inversely related to the initial soil mineral N content (Nmin) in the top 90 cm of the soil profile before sowing. There was no yield response to the applied N at the three sites with high initial soil mineral N levels (average 212 kg N ha-1). The average optimum N rate was 96 kg N ha-1 for the five sites with low initial soil Nmin (average 155 kg N ha-1) before sowing. Residual nitrate N in the top 90 cm of the soil profile after harvest increased with increasing fertilizer N application rate. The apparent N losses during the wheat-growing season also increased with increasing N application rate. The average apparent N losses with the optimum N rates were less than 15 kg N ha-1, whereas the farmers' conventional N application rate resulted in losses of more than 100 kg N ha-1. Therefore, optimizing N use for winter wheat considerably reduced N losses to the environment without compromising crop yields.

Soil Microbial Biomass Nitrogen and Its Relationship to Uptake of Nitrogen by Plants

The contents of the soil microbial biomass nitrogen (SMBN) in the soils sampled from the Loess Plateau of China were determined using chloroform fumigation aerobic incubation method (CFAIM), chloroform fumigation anaerobic incubation method (CFANIM) and chloroform fumigation-extraction method (CFEM).The N taken up by ryegrass on the soils was determined after a glasshouse pot experiment. The flushes of nitrogen (FN) of the soils obtained by the CFAIM and CFANIM were higher than that by the CFEM, and there were significantly positive correlations between the FN obtained by the 3 methods. The N extracted from the fumigated soils by the CFAIM, CFANIM and CFEM were significantly positively correlated with the N uptake by ryegrass. The FN obtained by the 3 methods was also closely positively correlated with the plant N uptake. The contributions of the SMBN and mineral N and mineralized N during the incubation period to plant N uptake were evaluated with the multiple regression method. The results showed that the N contained in the soil microbial biomass might play a noticeable role in the N supply of the soils to the plant.

Nitrous oxide fluxes from upland soils in central Hokkaido,Japan

Nitrous oxide (N2O) fluxes from soils were measured using the closed chamber method during the snow-free seasons (middle April to early November),for three years,in a total of 11 upland crop fields in central Hokkaido,Japan.The annual mean N2O fluxes ranged from 2.95 to 164.17 μgN/(m2·h),with the lowest observed in a grassland and the highest in an onion field.The instantaneous N2O fluxes showed a large temporal variation with peak emissions generally occurring following fertilization and heavy rainfall eve...

N-cycle gene abundance determination of N mineralization rate following re-afforestation in the Loess Plateau of China

Afforestation effectively improved soil microbial communities and significantly increased soil nitro-gen mineralization rate(Rm).Soil microorganisms drive Rm by regulating soil N-cycling genes.Soil nitrification genes had a major effect on soil Rm than denitrification genes after afforestation.Assessing the function of forest ecosystems requires an understanding of the mechanism of soil nitrogen mineralization.However,it remains unclear how soil N-cycling genes drive soil nitrogen mineralization during afforestation.In this study,we collected soil samples from a chrono-sequence of 14,20,30,and 45 years of Robinia pseudoacacia L.(RP14,RP20,RP30,and RP45)with a sloped farmland(FL)as a control.Through metagenomic sequencing analysis,we found significant changes in the diversity and composition of soil microbial communities involved in N-cycling along the afforestation time series,with afforestation effectively increasing the diversity(both alpha and beta diversity)of soil microbial communities.We conducted indoor culture experiments and analyzed correlations,which revealed a significant increase in both soil nitrification rate(Rn)and soil nitrogen mineralization rate(Rm)with increasing stand age.Furthermore,we found a strong correlation between soil Rm and soil microbial diversity(both alpha and beta diversity)and with the abundance of soil N-cycling genes.Partial least squares path modeling(PLS-PM)analysis showed that nitrification genes(narH,narY,nxrB,narG,narZ,nxrA,hao,pmoC-amoC)and denitrification genes(norB,nosZ,nirK)had a greater direct effect on soil Rm compared to their effect on soil microbial communities.Our results reveal the relationships between soil nitrogen mineralization rate and soil microbial communities and between the mineralization rate and functional genes involved in N-cycling,in the context of Robinia pseudoacacia L.restoration on the Loess Plateau.This study enriches the understanding of the effects of microorganisms on soil nitrogen mineralization rate during afforestation and provides a new theoretical basis for evaluating soil nitrogen mineralization mechanisms during forest succession.

Peashrub Community May Accelerate the Successional Process in a Meadowland-Peashrub-Birch Sere

Net N mineralization and nitrification were determined using the closed_top PVC tube in situ incubation method in a subalpine meadow (Saussurea iodostegia Hance + Carex capillaris L.)→shagspine peashrub (Caragana jubata (Pall.) Poir) shrubland→ribbed birch (Betula costata Trautv.) successional sere. The ability of the three communities to supply available N was comparatively studied. The results showed that there were apparent seasonal changes in the inorganic N pools (including NH + 4_N and NO - 3_N) and net N mineralization and nitrification rates in the three sites. There were generally no significant differences in the inorganic N pools among sampling events. But the NH + 4_N concentration in both birch (P<0.01) and meadow (P<0.01) sites was significantly higher than that in peashrub site in June 1996, and the NO - 3_N concentration in peashrub site was significantly higher than that of meadow site (P<0.05) in August 1996. The annual net N mineralization and nitrification rates in peashrub site (16.01 kg·hm -2 ) were higher than in birch (12.05 kg·hm -2 ) and meadow sites (1.64 kg·hm -2 ). The annual net nitrification rate in peashrub site (11.37 kg·hm -2 ) was higher than in meadow site (10.90 kg·hm -2 ) and much lower than in birch site (14.36 kg·hm -2 ). We conclude that the ability of peashrub shrubland soil to supply available N for plant uptake and the ability to prevent available N from denitrification and leaching were higher than that of the other two sites. The leguminous peashrub might play a potential role in supplying more N, which in turn facilitate the invasion of birch saplings during the successional processes.