Nitrogen mineralization in the oldest climax communities in the eastern Mediterranean region

In this study,we investigated how tree species affect N mineralization in connection to some soil properties and seconder metabolite levels of litter,in the soil of the old-est native forest communities.In the oldest pure communi-ties of Pinus nigra(PN),Fagus orientalis(FO),and Abies bornmuelleriana(AB)in the mountain range of Mount Uludağ,Bursa,Turkey,annual net yield and N mineraliza-tion in the 0-5-and 5-20-cm soil layers were determined in a field incubation study over 1 year.Sampling locations were chosen from 1300 to 1600 m a.s.l.,and moisture content(%),pH,water-holding capacity(%),organic C,total N,and C/N ratio,and annual net mineral N yield of the soil and hydro-lyzed tannic acid and total phenolic compounds in litter were compared for these forest communities.F.orientalis had the highest annual net Nmin yield(43.9±4.8 kg ha^(-1) a^(-1)),P.nigra the lowest(30.5±4.2 kg ha^(-1) a^(-1)).Our findings show that in the oldest forest ecosystems,the seasonal soil moisture content and tree species play an essential role in N cycling and that hydrolyzed tannic acids and total phenolic compounds effectively control N turnover.Tannic acid and total phenolics in the litter were found to inhibit nitrification,but total phenolics were found to stimulate ammonification.

Spatial distribution and driving factors of sediment net nitrogen mineralization in riparian zone of the Three Gorges Reservoir

Inorganic nitrogen(N)loss through sediment N mineralization is important for eutrophication surrounding riparian zone.Sediment physicochemical properties have been changed at water-level elevation in riparian zone of the Three Gorges Reservoir(TGR)due to differences in hydrological stress and human activity intensity.However,spatial distribution and driving factor of net N mineralization rate(Nmin)and its temperature sensitivity(Q10)based on the changes in sediment physicochemical properties are still unclear at waterlevel elevation in the riparian zone.A total of 132 sediment samples in the riparian zone were collected including 11 transections and 12 water-level elevations on basin scale of the TGR during drying period,to conduct a 28-day incubation at 15℃,22℃,29℃and 36℃.Nmin,total N(TN)and substrate quality(SQ)increased with water-level elevation,while Q10 showed an opposite trend(P<0.001).Results of the structural equation model showed that water-level elevation had direct positive effects on TN and SQ(P<0.01).In addition,TN was the major factor that had a direct positive effect on Nmin,and SQ was the crucial factor that had a direct negative effect on Q10(P<0.001).In conclusion,increases in TN and SQ were major driving factors of Nmin and its Q10 at water-level elevation,respectively,in riparian zone of the TGR during drying period.

Effect of forest thinning on soil net nitrogen mineralization and nitrification in a Cryptomeria japonica plantation in Taiwan

We investigated the effect of forest thinning on soil nitrogen mineralization, nitrification and transformation in a Cryptomeria japoni-ca plantation at high elevation to provide basic data for forest manage-ment. We chose four study plots for control, light, medium and heavy thinning treatment, and three sub-plots for buried bag studies at similar elevations in each treatment plot to measure the net N mineralization and nitrification rates in situ. The contents of soil inorganic N （ammonium and nitrate） were similar between treatments, but all varied with season, reaching maxima in September 2003 and 2004. The seasonal maximum net Nmin rates after four treatments were 0.182, 0.246, 0.303 and 0.560 mg？kg-1？d-1 in 2003, and 0.242,0.258,0.411 and 0.671 mg？kg-1？d-1in 2004, respectively. These estimates are approximate with the lower annual rates of N mineralization for this region. Forest thinning can enhance net N mineralization and microbial biomass carbon. The percentage of annual rates of Nmin for different levels of forest thinning compared with the control plot were 13.4%, 59.8%and 154.2%in 2003, and 0.1%, 58.8%and 157.7%in 2004 for light, medium, and heavy thinning, respectively. These differences were related to soil moisture, temperature, precipita-tion, and soil and vegetation types. Well-planned multi-site comparisons, both located within Taiwan and the East-Asia region, could greatly im-prove our knowledge of regional patterns in nitrogen cycling.

Response of nitrogen mineralization dynamics and biochemical properties to litter amendments to soils of a poplar plantation

Understanding the impact of plant litters on soil nitrogen （N） dynamics could facilitate development of management strategies that promote plantation ecosystem function. Our objective was to evaluate the effects of different litter types on N mineralization and availability, microbial biomass, and activities of L-asparaginase and odiphenol oxidase （o-DPO） in soils of a poplar （Populus deltoides） plantation through 24 weeks of incubation experiments. The tested litters included foliage （F）, branch （B）, or root （R） of poplar trees, and understory vegetation （U） or a mixture of F, B, and U （M）. Litter amendments led to rapid N immobilization during the first 4 weeks of incubation, while net N mineralization was detected in all tested soils from 6 to 24 weeks of incubation, with zero-order reaction rate constants （k） ranging from 7.7 to 9.6 mg N released kg-1 soil wk-1. Moreover, litter addition led to increased （C） 49-128% and increased microbial biomass carbon MBC：MBN ratio by 5-92%, strengthened activities of L-aspaxaginase and o-DPO by 14-74%; Up to about 37 kg N ha-1 net increase in mineralized N in litter added soils during 24 weeks of incubation suggests that adequate poplar and understory litter management could lead to reduced inputs while facilitate sustainable and economic viable plantation production.

Effects of Litter Removal and Addition on Soil Nitrogen Mineralization of Eucalyptus Plantation

[Objectives]This study was conducted to understand the process of soil nitrogen mineralization in Eucalyptus plantations,and to identify the characteristics of soil nitrogen mineralization with different litter inputs.[Methods]With the soil of the Eucalyptus plantation in Fusui County,Guangxi as the research object,the soil nitrogen mineralization of the Eucalyptus plantation under different litter treatments(removing litter,adding litter and retaining litter)was studied by PVC tube closed-top in-situ incubation.[Results]①After 1 year of litter treatment,the inorganic nitrogen(NH_(4)^(+)-N+NO_(3)^(-)-N)in the soil of different treatments ranked as adding litter(20.15 mg/kg)>retaining litter(16.02 mg/kg)>removing litter(11.60) mg/kg),and the differences reached a significant level(P<0.05).②After 30 d of in-situ incubation,there were significant differences in soil nitrate nitrogen content before and after incubation in the three treatments(removing litter,adding litter,and retaining litter)before and after incubation(P<0.05),but no significant differences were observed in soil ammonium nitrogen content(P>0.05).Soil nitrate nitrogen contents increased from 1.47,2.01 and 1.72 mg/kg before incubation to 3.66,6.73 and 5.02 mg/kg,respectively,and soil ammonium nitrogen content increased from 11.60,20.15 and 16.02 mg/kg before incubation to 13.65,21.54 and 17.18 mg/kg,respectively.The net nitrogen mineralization quantities of the three treatments were 4.24,6.11 and 4.46 mg/kg,respectively,and the net nitrogen mineralization rates from large to small were adding litter[0.180 mg/(kg·d)]>retaining litter[0.141 mg/(kg·d)]>removing litter[0.125 mg/(kg·d)].Therefore,both removal and addition of litter affected the soil nitrogen input and nitrogen mineralization rate of the Eucalyptus plantation,thereby affecting soil nitrogen availability and the ability of soil to maintain plant-available nitrogen.[Conclusions]This study provides a theoretical basis for nutrient management in Eucalyptus plantations,especially nitrogen nutrient management.

Carbon and nitrogen mineralization in soils along a desertification gradient in the semiarid Horqin Sandy Land, Northern China

This experiment was conducted in three sites along a desertification gradient in Horqin Sandy Land, Northern China. Soils una-mended and amended with five types of plant residue in a wide range of C：N ratios from 9.9 to 82.2 were incubated for 70 days, during which C and N mineralization were measured. Along the desertification gradient from fixed sand dune to semifixed, and mobile sand dune： cumulative CO2-C produced from the unamended soils was 231.6, 193.3 and 61.9 μg/g, respectively, while net inorganic N was 22.9, 17.6 and 0.9 mg/kg. Soils amended with residues produced more CO2-C than the unamended soils across all sites. During the first 10 days, C mineralization rate of residue-amended soils decreased with the increase of C：N ratio at each site. However, the mineralization rates were poorly correlated with the C：N ratio in subsequent stage of incubation. Soils of mobile sand dune amended with higher C：N ratio （more than 32） residues produced less CO2-C than that of fixed and semifixed sand dune. NO3--N was the predominant form of inorganic N during the mineralization process in sandy soils. Carbon-to-nitrogen ratio （C：N） can be regarded as a predictor of the speed of N mineralization in sandy soil. The more C. microphylla residue with the lowest C：N ratio （9.9） added in soils, the more net inorganic N released. Our results suggest that C. microphylla residue when added to soil would potentially provide short-term plant available N and improve the soil quality in sandy land. The desertification process postponed the release of inorganic N from plant residues.

Black locust coppice stands homogenize soil diazotrophic communities by reducing soil net nitrogen mineralization

Background:Black locust(BL,Robinia pseudoacacia)is considered a promising tree species for reforestation due to its great ability to fix nitrogen.However,after two or three coppice-harvesting rotations,the productivity of BL declines.Whether soil microbial communities are affected and how these groups correlate with the nitrogen mineralization process across multi-generation stands remains unclear.Methods:We investigated the composition and structure of free-living nitrogen-fixing microorganisms(diazotrophs)by sequencing the marker gene nifH and compared these results to levels of soil nitrogen mineralization in the bulk soil and rhizosphere in black locust plantations on Mount Tai,China.Results:The results showed multi-generation BL coppice plantations decreased the total soil nitrogen(N),soil phosphorus(P),soil microbial biomass N(MBN),soil microbial biomass C(MBC),soil nitrification rate(Rn),soil ammonification rate(Ra),and net soil N mineralization rate(Rm),but significantly increased the concentration of soil NH_(4þ)-N to maintain sufficient NO_(3)^(-)N.The dominant species in bulk soil and rhizosphere changed from Rhodopseudomonas(22.62%and 15.76%),unclassified_c_Alphaproteobacteria(22.37%and 29.28%),unclassified_o_Rhizobiales(15.40%and 13.31%),Bradyrhizobium(12.00%and 11.74%)in seedling plantations to Bradyrhizobium(45.95%and 47.86%)and Rhodopseudomonas(43.56%and 41.84%)in coppice plantations,respectively.Mantel test and Redundancy analysis(RDA)revealed that Rn,Ra,and Rm were the most important factors shaping the diazotrophic communities.Conclusions:Our results suggest that the multi-generation BL coppice plantation can homogenize soil diazotrophic communities,which is mainly regulated by the available N loss caused by nitrogen mineralization.Strengthening the management technology of coppice plantations will provide more beneficial external consumption.

Effect of Deficit Irrigation Practice on Nitrogen Mineralization and Nitrate Nitrogen Leaching under Semi-Arid Conditions

Agricultural sector acts as a major consumer of water which accounts for 70 percent of global freshwater use. Water scarcity acts as an imminent threat to agriculture, there is a need to use those irrigation and management practices that could overcome this overwhelming situation of water scarcity. Lab incubation study was designed to evaluate the effect of different moisture levels (50%, 60%, 70%, 80%, 90%, and 100% FC) on nitrogen mineralization rate. Net nitrogen mineralization was shown at 60% and 80% FC levels. Two optimized irrigation levels (I0.6 and I0.8) along with four levels of dairy manure (10, 15, 20, and 25 Mg ha-1) were used in a lysimetric trial. Nitrate-nitrogen was measured at four depths (D1: 30 cm, D2: 60 cm, D3: 90 cm, and D4: 120 cm). Results showed strong interaction of irrigation and dairy manure at all depths. Mean maximum nitrate-nitrogen concentration was shown under full irrigation at 120 cm soil depth with the application of DM ®25 Mg ha-1. Under two levels of deficit irrigation, I0.8 has shown maximum nitrate-nitrogen concentration at 90 cm soil depth with the application of DM25, however, deficit irrigation level I0.6 restricted nitrate-nitrogen movement up to 60 cm soil depth, and high concentration was found at 30 cm soil depth. We concluded that deficit irrigation practice along with dairy manure resulted in more nitrate-nitrogen in the upper 60 cm layer of soil where it can be more available for the crops.

REGIONAL ASSESSMENT OF SOIL NITROGEN MINERALIZATION IN DIVERSE CROPLAND OF A REPRESENTATIVE INTENSIVE AGRICULTURAL AREA

Soil nitrogen mineralization(Nmin)is a key process that converts organic N into mineral N that controls soil N availability to plants.However,regional assessments of soil Nmin in cropland and its affecting factors are lacking,especially in relation to variation in elevation.In this study,a 4-week incubation experiment was implemented to measure net soil Nmin rate,gross nitrification(Nit)rate and corresponding soil abiotic properties in five field soils(A-C,maize;D,flue-cured tobacco;and E,vegetables;with elevation decreasing from A to E)from different altitudes in a typical intensive agricultural area in Dali City,Yunnan Province,China.The results showed that soil Nmin rate ranged from 0.10 to 0.17 mg·kg^(-1)·d^(-1)N,with the highest value observed in field E,followed by fields D,C,B,and A,which indicated that soil Nmin and Nit rates varied between fields,decreasing with elevation.The soil Nit rate ranged from 434.2 to 827.1μg·kg^(-1)·h^(-1)N,with the highest value determined in field D,followed by those in fields E,C,B,and A.The rates of soil Nmin and Nit were positively correlated with several key soil parameters,including total soil N,dissolved organic carbon and dissolved inorganic N across all fields,which indicated that soil variables regulated soil Nmin and Nit in cropland fields.In addition,a strong positive relationship was observed between soil Nmin and Nit.These findings provide a greater understanding of the response of soil Nmin among cropland fields related to spatial variation.It is suggested that the soil Nmin from cropland should be considered in the evaluation of the N transformations at the regional scale.

The rhizosphere effect on soil gross nitrogen mineralization: A meta-analysis

Rhizosphere effects play crucial roles in determining soil carbon(C)and nitrogen(N)cycling.However,the rhizosphere effect on soil gross nitrogen(N)mineralization(Nmin)has not been quantitatively assessed on the global scale.Here we performed a meta-analysis of compiled data from 24 publications and 37 species to synthesize the rhizosphere effect on soil gross Nmin and its influencing factors.We found that the rhizosphere effect significantly enhanced soil gross Nmin by 81%on average.Such rhizosphere effect was significantly higher in woody species than in nonwoody species,and higher in ECM(ectomycorrhizal)associated species than in AM(arbuscular mycorrhizal)associated species.Moreover,the variations of the rhizosphere effect on soil gross Nmin were correlated with those on soil C mineralization,phenol oxidase activity and root biomass rather than with other plant(growth form and mycorrhizal association)and climatic(mean annual temperature and precipitation)factors.These results support the‘microbial activation’and‘microbial N mining’hypotheses of rhizosphere effects and indicate the coupling of soil C and gross N mineralization in the rhizosphere.Overall,these findings provide novel insights into the rhizosphere effect on soil gross Nmin among plant growth forms and mycorrhizal associations,and improve our mechanistic understanding of soil N dynamics in the rhizosphere.

Effects of nitrogen and phosphorus additions on soil microbial community structure and ecological processes in the farmland of Chinese Loess Plateau

Microorganisms regulate the responses of terrestrial ecosystems to anthropogenic nutrient inputs.The escalation of anthropogenic activities has resulted in a rise in the primary terrestrial constraining elements,namely nitrogen(N)and phosphorus(P).Nevertheless,the specific mechanisms governing the influence of soil microbial community structure and ecological processes in ecologically vulnerable and delicate semi-arid loess agroecosystems remain inadequately understood.Therefore,we explored the effects of different N and P additions on soil microbial community structure and its associated ecological processes in the farmland of Chinese Loess Plateau based on a 36-a long-term experiment.Nine fertilization treatments with complete interactions of high,medium,and low N and P gradients were set up.Soil physical and chemical properties,along with the microbial community structure were measured in this study.Additionally,relevant ecological processes such as microbial biomass,respiration,N mineralization,and enzyme activity were quantified.To elucidate the relationships between these variables,we examined correlation-mediated processes using statistical techniques,including redundancy analysis(RDA)and structural equation modeling(SEM).The results showed that the addition of N alone had a detrimental effect on soil microbial biomass,mineralized N accumulation,andβ-1,4-glucosidase activity.Conversely,the addition of P exhibited an opposing effect,leading to positive influences on these soil parameters.The interactive addition of N and P significantly changed the microbial community structure,increasing microbial activity(microbial biomass and soil respiration),but decreasing the accumulation of mineralized N.Among them,N24P12 treatment showed the greatest increase in the soil nutrient content and respiration.N12P12 treatment increased the overall enzyme activity and total phospholipid fatty acid(PLFA)content by 70.93%.N and P nutrient contents of the soil dominate the microbial community structure and the corresponding changes in hydrolytic enzymes.Soil microbial biomass,respiration,and overall enzyme activity are driven by mineralized N.Our study provides a theoretical basis for exploring energy conversion processes of soil microbial community and environmental sustainability under long-term N and P additions in semi-arid loess areas.

Soil-nitrogen net mineralization increased after nearly six years of continuous nitrogen additions in a subtropical bamboo ecosystem

In order to understand the effects of increasing atmospheric nitrogen （N） deposition on the subtropical bamboo ecosystem, a nearly six-year field experiment was conducted in a Pleioblastus amarus plantation in the rainy region of SW China, near the western edge of Sichuan Basin. Four N treatment levels---control （no N added）, low- N （50 kg N ha-1 a-l）, medium-N （150 kg N ha-1 a-l）, and high-N （300 kg N ha-1 a-1）--were applied monthly in the P. amarus plantation starting in November 2007. In June 2012, we collected intact soil cores in the bamboo plantation and conducted a 30-day laboratory incubation experiment. The results showed that the soil N net miner- alization rate was 0.96 4- 0.10 mg N kg-1 day-1, under control treatment. N additions stimulated the soil N net mineralization, and the high-N treatment significantly increased the soil N net mineralization rate compared with the control. Moreover, the soil N net mineralization rate was significantly and positively correlated with the fine root biomass, the soil microbial biomass nitrogen content and the soil initial inorganic N content, respectively,whereas it was negatively correlated with the soil pH value. There were no significant relationships between the soil N net mineralization rate and the soil total nitrogen （TN） content and the soil total organic carbon content and the soil C/N ratio and the soil microbial biomass carbon con- tent, respectively. These results suggest that N additions would improve the mineral N availability in the topsoil of the P. amarus plantation through the effects of N additions on soil chemical and physical characteristics and fine-root biomass.

An assessment of response of soil-based indicators to nitrogen fertilizer across four tropical eucalyptus plantations

Low nitrogen （N） availability often results in reduced productivity of Eucalyptus plantations. We studied the response of four eucalyptus plantations （two plantations of E. tereticornis on the coastal lowlands, and two plantations of E. grandis in the upland region of the Western Ghats, Kerala, India） to N addition and related this response to seasonal N mineralization as well as other indices of N availability, in order to examine the utility of soil based indicators of N mineralization for predicting the response of eucalyptus growth to added N ferti- lizer. Several biochemical indicators were examined for their capacity to predict response to N fertilizer, including total soil N, soil C：N ratio, and N released during anaerobic and aerobic incubation. Results show that nitrogen fertilizer addition increased productivity across the 4 sites from 7% to 70%, N released during an aerobic incubation had the highest correlation with fertilizer response across the 4 sites （R^2=0.92/ p〈0.01）, and that Modelled seasonal soil N mineralisation was a poorer predictor of fertilizer response than N released during an aerobic incubation. Whilst some of these indicators are promising, they need wider validation and testing before they could be routinely applied.

Soil nitrogen transformations varied with plant community under Nanchang urban forests in mid-subtropical zone of China

Soil N transformations using the polyvinyl chloride （PVC） closed-top tube in situ incubation method were studied in Nanchang urban forests of the mid-subtropical region of China in different months of 2007. Four plots of 20 m × 20 m were established in four different plant communities that represented typical successional stages of forest development including shrubs, coniferous forest, mixed forest and broad- leaved forest. Average concentrations of soil NH4^＋-N from January to December were not different among the four plant communities. The concentrations of soil NO3^--N and mineral N, and the annual rotes of ammonification, nitrification and net N-mineralization under the early successional shrub community and coniferous forest were generally lower than that of the late successional mixed and broad-leaved forests （p〈0.05）. Similar differences among the plant communities were also shown in the relative nitrification index （NH4^＋-N/NO3^--N） and relative nitrification intensity （nitrification rate/net N-mineralization rate）. The annual net N-mineralization rate was increased from younger to older plant communities, from 15.1 and 41.4 kg.ha^-1.a^-1 under the shrubs and coniferous forest communities to 98.0 and 112.9 kg.ha^-1.a^-1 under the mixed and broad-leaved forests, respectively. Moreover, the high annual nitrification rates （50-70 kg.ha^-1.a^-1） and its end product, NO3-N （2.4-3.8 mg·kg^-1）, under older plant communities could increase the potential risk of N loss. Additionally, the temporal patterns of the different soil N variables mentioned above varied with different plant community due to the combined affects of natural biological processes associated with forest maturation and urbanization. Our results indicated that urban forests are moving towards a state of＂N saturation＂ （extremely niUification rate and NO3^--N content） as they mature.

Integrated application of February Orchid(Orychophragmus violaceus) as green manure with chemical fertilizer for improving grain yield and reducing nitrogen losses in spring maize system in northern China

The development of more efficient management systems is crucial to achieving high grain yields with high nitrogen use efficiency（NUE）. February Orchid-spring maize rotation system is a newly established planting system with the benefits of ground cover and potential wind erosion in northern China. A field experiment was conducted to evaluate the effects of integrated application of February Orchid as green manure with reduction of chemical fertilizers（INTEGRATED） on spring maize yield, N uptake, ammonium volatilization, and soil residual mineral N in northern China. Compared to farmers＇ traditional fertilization（CON）, integrated application of February Orchid as green manure with 30% reduction of nitrogen fertilizers（INTEGRATED） increased maize grain yield and biomass by 9.9 and 10.2%, respectively. The 0–100 cm soil residual Nmin at harvest was decreased by 58.5% and thus nitrogen use efficiency was increased significantly by 26.7%. The nitrogen balance calculation further demonstrated that the INTEGRATED approach performed better than CON with lower apparent nitrogen loss（decreased by 48.9%） which evidenced by the ammonium volatilization of top-dressing fertilizer was decreased by 31.1%, the N_（min） movement to the deeper soil layers was reduced, and the apparent nitrogen leaching loss nearly equal to 0 under the INTEGRATED treatment. Therefore, in northern China, integrated application of green manure and chemical fertilizers is an efficient management approach for improving maize yields and NUE simultaneously.

The role of green manure nitrogen use by corn and sugarcane crops in Brazil

Three assays were developed from April 3, 1995 to October 10, 2005. The work with corn was conducted in a greenhouse, using velvet bean (Mucuna aterrima) and sunn hemp (Crotalaria juncea) as green manure with 15N labeling of either shoots or roots, in two soils with contrasting textural classes. The mineralization of N from legume plants incorporated into the two soils was investigated too. This work included two green manures: velvet bean and sunn hemp, and the common bean (Phaseolus vulgaris) residues. Nitrogen from the velvet bean accounted for a greater proportion of the soil inorganic N;shoots were responsible for most of N accumulated. Common bean residues caused immobilization of inorganic N. The leguminous species added were intensively and promptly mineralized, preserving the soil native nitrogen. One hundred days after emergence of the corn, velvet bean provided higher accumulation of nitrogen in the soil, higher absorption by corn plants and accumulation in the aerial part. The green manure decomposition was more intense in the medium textured soil. In this soil, highest nitrogen losses were also observed. The sugarcane (Saccharum spp.) was cultivated for five years in the field and was harvested three times;15N recovery was evaluated in the first two harvests. The combination of inorganic fertilizer and green manure resulted in higher sugarcane yields than either N source applied separately;however, in the second cutting the yields were higher where sunn hemp was used than in plots with ammonium sulfate. The recovery of N by the first two consecutive harvests accounted for 19% to 21% of the N applied as sunn hemp and 46% to 49% of the N applied as ammonium sulfate. Very little inorganic N was present in the 0-40 cm soil layer with both N sources.

Short-term effects of yak and Tibetan sheep urine deposition on soil carbon and nitrogen concentrations in an alpine steppe of the northern Tibetan Plateau, China

Yak(Bos grunniens) and Tibetan sheep urine deposited onto the alpine grasslands of the Qinghai-Tibetan Plateau is an important pathway for nutrient return, and it is closely related to soil fertility and alpine grassland productivity. However, hitherto, few studies have reported the effects of yak and Tibetan sheep urine deposition on soil carbon(C) and nitrogen(N) concentrations and the possible functional mechanisms under field conditions in alpine grasslands. To explore the status of soil C and N responding to the immediate N addition from livestock urine, we conducted a 28-d field experiment with three treatments, which include the application of yak urine(YU) and Tibetan sheep urine(TSU) application, and the control(CK, no application of urine). The results showed that YU treatment increased the soil moisture content and p H at 0-10 cm across the 28-day experimental period. Urine application resulted in the fluctuation of soil organic C(SOC) and increased topsoil SOC concentration during the middle and later periods of the experiment. Application of YU evidently increased the soil total N(TN) concentration in the 0-10 cm layer, while it did not affect the SOC concentrations in the 10-20 and 20-30 cm layers. Compared with the control, YU treatment significantly(P<0.05) increased the 0-10 and 10-20 cm soil ammonium-N(NH;-N) concentration throughout the 28 days, while the TSU treatment significantly(P<0.05) increased the 0-10 and 10-20 cm soil nitrate-N(NO;-N) concentration. Urine N input changed soil physicochemical properties, nitrification, denitrification, and N leaching processes, and therefore affected the availability of N accumulation and consumption in soil. Under these conditions, the trade-off between soil NH;-N and NO;-N under the influence of yak and Tibetan sheep urine application would change the form and concentration of available N, thereby altering the plant N uptake and utilization strategy of alpine grassland. The conclusions of this study could provide theoretical references for exploring the change characteristics of soil nutrient under the deposition of urine and optimizing the management strategies of livestock urine in the alpine grassland ecosystem.

Evaluating Nitrogen Behavior in Sugarcane after Fertilization Using Leaf and Sap Extract Analyzes

Nitrogen (N) fertilization is important for sugarcane crops, for both agronomic and environmental reasons. Better use of N from fertilizer is required for crop management, and in order to achieve it, adequate N nutrition monitoring is necessary. Sap extract analysis is a sensitive technique that has been adopted in other crops to tackle this objective, and can be used for sugarcane. The aim of this study was to evaluate the behavior of N and the response of sugarcane after N fertilization, using sap and leaf tissue analysis. The study was undertaken in two experimental areas in 2012/2013 season, using ratoon cane, following application of 0, 50, 100, and 150 kg&middotha-1 of N. The youngest visible leaves were sampled from sugarcane at five time points between 0 and 150 days after fertilization, to evaluate the nitrate, ammonium, and total N content of sap extract, and total N content of leaf tissue. At the first sampling point (30 days after N fertilizer application), mineral N in sap increased as a result of N fertilization in medium-textured soil, and remained high until 120 days after fertilization in clayey soil. The total N content of sap followed a similar behavior. Stalk yield was only observed to increase in sugarcane grown in the clayey soil. Sap analysis proved to be an efficient method for monitoring N status in sugarcane grown in different soil types.

Fire alters the availability of soil nutrients and accelerates growth of Eucalyptus grandis in Zambia

Fire has been used to prepare land during tree plantation establishment for many years but uncertainty about how ecosystems respond to prescribed burning makes it difficult to predict the effects of fire on soil nutrients.The aim of this study was to determine the effect of burning accumulated forest residues(slash)on soil chemical properties and how trees respond.We analyzed 40 burned and unburned sites and compared growth of Eucalyptus grandis W.Hill ex Maiden between sites.Soil pH increased by 39%after fire,suggesting reduced soil acidity and increased liming.Total nitrogen increased by 100%;other nutrients(Ca^2+,Mg^2+and K^+)also increased.Increase in nutrients had a significant effect on the growth of E.grandis;larger and taller trees were associated more with burned than unburned sites.This study provides evidence that burning accumulated slash during land preparation prior to plantation establishment alters soil nutrient status and enhances the growth of E.grandis.

热带四种按树人工林的土壤指标对氮肥反应的评价

Low nitrogen (N) availability often results in reduced productivity of Eucalyptus plantations. We studied the response of four eucalyptus plantations (two plantations of E. tereticornis on the coastal lowlands, and two plantations of E. grandis in the upland region of the Western Ghats, Kerala, India) to N addition and related this response to seasonal N mineralization as well as other indices of N availability, in order to examine the utility of soil based indicators of N mineralization for predicting the response of eucalyptus growth to added N fertilizer. Several biochemical indicators were examined for their capacity to predict response to N fertilizer, including total soil N, soil C:N ratio, and N released during anaerobic and aerobic incubation. Results show that nitrogen fertilizer addition increased productivity across the 4 sites from 7% to 70%, N released during an aerobic incubation had the highest correlation with fertilizer response across the 4 sites (R2=0.92, p<0.01), and that Modelled seasonal soil N mineralisation was a poorer predictor of fertilizer response than N released during an aerobic incubation. Whilst some of these indicators are promising, they need wider validation and testing before they could be routinely applied.