Biochemical quality and accumulation of soil organic matter in an age sequence of <Emphasis Type="Italic">Cunninghamia lanceolata</Emphasis> plantations in southern China

Purpose

Biochemical protection is an important mechanism for maintaining the long-term stability of the soil carbon (C) pool. The labile and recalcitrant pools of soil organic matter (SOM) play different roles in regulating C and N dynamics; however, few studies have characterized the capacity of soil C sequestration while considering the biochemical quality of SOM. The aim of the present study was to assess the changes in the soil organic carbon (SOC) and nitrogen (N) pools during a traditional rotation period (25 years) of a Chinese fir (Cunninghamia lanceolata) plantation with an emphasis on SOM biochemical quality.

Materials and methods

Three different forest stand development stages—young (6 years old), middle-aged (16 years old) and mature (25 years old)—were selected for soil sampling to a depth of 100 cm. Total C and total N of the soil was analysed to determine the changes in the SOC and N stocks among the three development stages using an equivalent soil mass (ESM) approach. Bulk soils were fractionated into labile and recalcitrant fractions using the acid hydrolysis method to identify the quality of SOM.

Results and discussion

The mineral soil organic carbon pool at a 1-m depth slightly decreased from the young stand to the middle-aged stand and rapidly increased by 28 % to reach a maximum in the mature stand. SOC accumulation in the surface soil predominated the changes in total SOC stocks in all three stands. The increased N was reflected in the entire depth, and the highest soil N accumulation was in the mature stand. The recalcitrant C concentration and SOC were positively correlated. The non-hydrolysable C proportion was lower in the middle-aged stand versus the young stand (8.69 % loss), while the labile C percentage was higher (13.89 % gain). In the mature stand, the recalcitrant C index increased to 39.84 %. The recalcitrant index of C decreased with an increasing soil depth, whereas the recalcitrant index of N dramatically increased.

Conclusions

These results highlighted the significant effect of the stand age and the soil depth on the storage and biochemical availability of SOM in Chinese fir plantations of southern China. The recalcitrant index of C changed with the change in SOC concentration, indicating that biochemical protection mechanism plays an important role in soil C sequestration. In addition, more attention should be paid to subsoil C protection in the management of Chinese fir plantations because of low biochemical stability.

     

Long-term fertilization increases soil nutrient accumulations but decreases biological activity in navel orange orchards of subtropical China

Purpose

With its high economic benefits, navel orange (Citrus sinensis) has been widely planted and fertilizer has been increasingly applied in the subtropical China in the last 30 years. Comprehensive assessments are needed to explore the long-term fertilization impacts on soil chemical and biological properties in the navel orange orchards.

Materials and methods

Through a large number of soil and leaf samples from the young, middle-aged, and mature navel orange orchards, this study examined the impacts of stand age (corresponding to the fertilization year using compound chemical fertilizer) on seasonal variations in major soil properties and leaf nutrients in the subtropical China.

Results and discussion

Soil total nitrogen (N) and mineral N were significantly higher in the middle-aged and mature orchards than in the young orchard. Total phosphorus (P), available P, labile P, slow P, occluded P, weathered mineral P, total exactable P, and residual P generally increased with fertilization years (P?<?0.05), and the increasing percentages for soil P fractions were much higher than those for N variables. The total N and P use efficiencies (plant uptake/soil input) were 20–34 and 10–15 %, respectively. Soil microbial biomass, invertase, urease, and acid phosphatase activities showed significant seasonal variations and decreased with fertilization years. Leaf N concentration significantly decreased with fertilization years, but no difference was found for P.

Conclusions

Soil self-fertilization was impeded, and less fertilizer amount should be applied especially in the older navel orange orchards since N and P accumulations do not increase leaf nutrients but worsen soil biological quality.

     

Soil pH,organic matter,and nutrient content change with the continuous cropping of <Emphasis Type="Italic">Cunninghamia lanceolata</Emphasis> plantations in South China

Purpose

Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) is an important native tree species in China. Consecutive cropping traditionally occurs in Chinese fir plantations (CFPs), but this practice has resulted in productivity declines in subsequent rotations. This study was designed to better understand the change of soil properties in the continuous cropping CFPs.

Materials and methods

We investigated soil pH, soil organic matter (SOM), and nutrient contents in different soil layers and in rhizosphere soil (RS) and non-rhizosphere soil (NRS) under CFPs of different ages and in different rotations.

Results and discussion

In the upper (0–20 cm) soil layer, soil pH decreased, while SOM increased, beneath mature CFPs with consecutive rotations. Total nitrogen (TN), available potassium, and available phosphorus contents in the upper soil layers did not differ significantly with consecutive rotations. Soil pH in RS was significantly lower than in NRS under mature plantations of the third rotation. Soil organic matter, TN, and available nitrogen did not differ between RS and NRS. Available phosphorus in RS was consistently lower than in NRS, and was highly deficient in the third rotation.

Conclusions

We conclude that no severe soil nutrient degradation occurred in the continuous cropping CFPs examined in this study, with soil acidification and phosphorus deficiency being two primary problems observed.

     

Stoichiometric variation of carbon,nitrogen, and phosphorus in soils and its implication for nutrient limitation in alpine ecosystem of Eastern Tibetan Plateau

Purpose

The main objectives of this research are to decipher the stoichiometric characteristics of carbon (C), nitrogen (N), and phosphorus (P) in soils from the alpine ecosystem and to obtain information about nutrient limitation on plants and microbes.

Materials and methods

The soils were sampled along an altitudinal gradient (2000 to 4300 m above sea level) from the eastern slope of Gongga Mountain in eastern Tibetan Plateau. In total of 102 soil samples in profiles and 27 soil microbial biomass (SMB) samples from five vegetation zones were collected to analyze the concentrations of C, N, and P as well as their ratios. The concentrations of C and N were measured using an automated C/N analyzer, total P was detected by inductively coupled plasma-atomic emission spectrometer, and the concentrations of microbial biomass C, N, and P were measured by the chloroform fumigation-extraction method. Soil P fractions were extracted by modified Hedley sequential extraction method.

Results and discussion

The concentrations of C, N, and P in the soils and SMB varied spatially, whereas the variation of their ratios was constrained. The C:N:P ratios were 556:22:1 for the O horizon, 343:16:1 for the A horizon, 154:7:1 for the B horizon, and 63:3:1 for the C horizon, indicating a significant decrease with depth. The mean ratio in the SMB was 51:6.6:1. Microbial biomass C, N, and P were important components of soil nutrients, especially the microbial biomass P which accounted for 40.8 % of soil available P. The C:P and N:P were higher in the soils of broadleaf-coniferous and coniferous forests, whereas the ratios in the SMB were higher in the broadleaf forest. The ratios of C and N to available P in the soils decreased significantly with altitude.

Conclusions

The local climate, vegetation succession, and soil development in the high mountain resulted in the soil nutrient cycling different from that in other terrestrial ecosystems. Among the different vegetation zones, the P-limitation of plants and microbial communities might be possible in the soils of lower land forests in the long term.

     

Fly ash and zeolite amendments increase soil nutrient retention but decrease paddy rice growth in a low fertility soil

Purpose

Fly ash (FA) and zeolite (Z) are known to increase nutrient retention in paddy soils through the immobilization of phosphorus (P) by FA and nitrogen (N) by Z. However, there is a possibility that the co-application of the amendments may hamper rice growth due to reduced availability of the nutrients. This study was conducted to investigate the effects of the co-application of FA and Z on soil N and P availability and rice growth.

Materials and methods

Rice was cultivated in soils without the amendment (control) and with the amendment: FA alone, Z alone, and both FA and Z. Tiller number, dry matter (DM), rice uptake of N and P, and soil N and P concentrations were determined.

Results and discussion

The application of FA and Z increased N and P concentrations in the soils; however, such increased nutrient retention did not translate to DM increases. Results suggested that reduced mobility of nutrients hampered tillering in the early growth period, eventually leading to a reduction in DM accumulation at the harvest. Due to the nutrient limitation caused by FA and Z, the rice grown with both FA and Z did not survive at the harvest.

Conclusions

Our study shows that the application of FA and Z does not always improve rice growth due to nutrient limitation, especially in a low fertility soil. Furthermore, the co-application of FA and Z should be avoided, as the negative impact of FA or Z on nutrient limitation became more severe when FA and Z were co-amended.

     

Consistent profile pattern and spatial variation of soil C/N/P stoichiometric ratios in the subalpine forests

Purpose

The vertical patterns of soil carbon (C), nitrogen (N), and phosphorus (P) stoichiometry are still controversial, and relative contribution of their controlling factors also is rarely understood for the whole soil profile. This study aimed to assess the vertical variation of both C/N, N/P, C/P ratios and their determining factors along soil profiles in subalpine forests of the eastern Tibetan Plateau.

Materials and methods

Soil samples at five depths (0–10, 10–20, 20–30, 30–50, and 50–100 cm) were collected from 132 forest sites to evaluate the vertical distribution of soil C/N, N/P, and C/P ratios. Eleven relevant environmental factors (e.g., altitude, latitude, longitude, soil pH, soil bulk density, relative stone contents, soil order, slope, position, forest type, and dominant tree species) were measured to examine their relative contribution on stoichiometric ratios within each soil layer using boosted regression tree (BRT) analysis.

Results and discussion

Soil C/N, N/P, and C/P ratios consistently decreased with increasing soil depth. BRT models accurately predicted the soil C/N, N/P, and C/P ratios in the upper four layers (R ² = 49–97 %). For soil C/N and N/P ratios, altitude associated with latitude had the highest contribution across five soil layers, while the contributions of soil pH and bulk density were significant within soil layers closer to the surface. Independently, soil bulk density and altitude were the most important factors of C/P ratios in 0–30- and 30–100-cm soil layers.

Conclusions

This study indicated that soil C/N/P stoichiometric ratios, and the relative importance of their controlling factors, shifted within soil profiles across Tibetan Plateau forests. Further research will be needed to understand the regulatory mechanism of soil stoichiometry and biogeochemistry in response to environmental change at whole soil profiles.

     

“Fertile island” effects of <Emphasis Type="Italic">Tamarix chinensis</Emphasis> Lour. on soil N and P stoichiometry in the coastal wetland of Laizhou Bay,China

Purpose

As a useful comprehensive index for reflecting nutrient cycling in soils, nitrogen (N) and phosphorus (P) stoichiometry is subject to influences of many external environmental and biological factors. Studies on such influences were limited, and the influential mechanism remains unclear. The purpose of this research is to investigate soil N and P stoichiometric variations and analyze “fertile island” effects of Tamarix chinensis Lour. (T. chinensis) in the coastal wetland of Laizhou Bay in China.

Materials and methods

Soil samples beneath clusters and communities of T. chinensis were collected respectively in July 2012. Amounts of ammonium, nitrate, and available phosphorus in the soil samples were measured through the corresponding standard methods for material measuring.

Results and discussion

In general, there were significant vertical variations in soil N and P stoichiometry beneath clusters and communities of T. chinensis. A downtrend was observed for N and P contents with the increase in soil depth. On the contrary, the N/P ratio revealed a trend of going up first and then dropping off along with the increase of the soil depth. Comparatively, the horizontal variations in the soil N and P stoichiometry beneath a single cluster of T. chinensis were greater in the topsoil than those in the subsoil. The N and P contents gradually decreased from the canopy center to the outside. On the contrary, an opposite trend was found for the N/P ratio. For the horizontal variations beneath T. chinensis communities, there were no significant differences for either N and P contents or N/P ratios.

Conclusions

Similar to the ecosystems in arid and semi-arid areas, vegetations in many semi-humid areas could also form fertile islands and exert significant influences on the soil nutrient cycle. The formation of fertile islands beneath a single cluster of T. chinensis could have significant influence on soil N and P stoichiometry. Under the influence of fertile islands beneath T. chinensis, the limiting element of the biogeochemical processes in the coastal wetland of Laizhou Bay might change from N to P. However, the influences of fertile island effects on soil N and P stoichiometry beneath T. chinensis communities were relatively small, illustrating that the influences of fertile island effects was not significant at the community level. Thus, the impacts of environmental factors on soil N and P stoichiometry might be greater than that of the fertile island effects in the wetland on a larger scale.

     

Effects of biomass ash,bone meal,and alkaline slag applied alone and combined on soil acidity and wheat growth

Purpose

The purpose of this study is to examine the effects of combined application of biomass ash (BA), bone meal (BM), and alkaline slag (AS) on soil acidity, nutrient contents, uptake of the nutrients by wheat, and wheat growth.

Materials and methods

A pot experiment with an Ultisol collected from Anhui province, China, was conducted to compare the effects of BA, BM, and AS applied alone and combined on soil acidity; soil nutrient contents; uptake of N, P, K, Ca, and Mg by wheat, and wheat growth.

Results and discussion

Application of BA, BM, and AS alone and combined increased soil pH and decreased soil exchangeable Al³⁺. BA + BM + AS showed the greatest ameliorating effect on soil acidity, and soil pH of the treatment increased by 1.24 units compared with control. Application of BA + BM + AS reduced soil exchangeable Al³⁺ and increased soil exchangeable calcium and magnesium to a greater extent than BA + BM and single application of the amendments. The BM-containing amendments substantially increased soil available phosphorous by 66–93% compared with control. Application of the amendments alone and combined enhanced the uptake of N, P, K, Ca, and Mg by wheat and thus promoted wheat growth and increased yield of wheat grains. Application of BA + BM + AS and BA + BM showed greater effects on nutrient uptake and wheat growth than single application of the amendments. Wheat straw weights of the two treatments were 11.1 and 10.1 times greater than that of control. The data were 2.7, 4.8, and 5.6 times for the treatments of BA, AS, and BM. The contents of Cd, Cr, Zn, and Cu in wheat grains were lower than standard limits, except for the single BA treatment.

Conclusions

BA + BM + AS is the best choice for amelioration of acid soils and promotion of crop production.

     

Appraisal for site specific plant nutrient management through spatial variability and mapping in hilly areas of northern Pakistan

Purpose

The main purpose of this research work was to assess soil nutrient, spatial variability, and their mapping through GIS for better fertilizer recommendation and management.

Materials and methods

Soil samples (0–20-cm depth) were collected from major crop areas of district Chitral, northern Pakistan during April 2014. The crops areas were divided into eight main sampling units. Each sampling location was recorded through GPS point. The samples were then brought to laboratory of Soil and Environmental Sciences, for further analysis.

Results and discussion

The overall results showed that Zn content was the most deficient nutrient followed by K with 86 and 64% of samples, respectively. These results are different from other plain and agricultural areas which are dominantly deficient in order of N > P > K that could be associated to steep topography, climatic condition, and parent materials. The analyzed nutrients varied independently as indicated by their lower correlation values but showed stronger spatial patterns. Gaussian, linear, and exponential models were used depending on mean prediction error (MPE), root mean square standardize prediction error (RMSSPE), and nugget values for semivariogram analysis and consequent mapping of different nutrients through GIS.

Conclusions

The N and P were weakly distributed, while K and all micronutrients had strong spatial pattern suggesting that only N and P were managed during farming practices and that varied irregularly in the sampled area. In contrast to other plain agricultural areas of the country, the Zn and K were the most deficient elements and should be applied with suitable Zn and K fertilizers for optimum crop production in the area. This low Zn and K contents would be associated to the parent materials, low pH, and high organic matter contents especially in high altitude and comparatively high P content in the soil. The prepared maps can help on site-specific recommendation of fertilizers for farmers, researcher, and planners.

     

Improved nutrient status affects soil microbial biomass,respiration, and functional diversity in a Lei bamboo plantation under intensive management

Purpose

Intensive management, such as fertilization and organic mulching, is applied frequently in Lei bamboo (Phyllostachys praecox) plantations to achieve higher production in subtropical China. However, responses as well as key impact factors of soil microbial properties under such management remain uncertain. We analyzed the relationships between nutrient changes and microbial properties and assessed the main factors determining microbial biomass, activity, and functional diversity in soils under intensive management in a Lei bamboo plantation.

Materials and methods

Soil samples of treatments of no fertilization (control), chemical fertilization (CF), and chemical and organic fertilization combined with organic mulching (CFOM + M) were taken before mulching. The soil organic carbon (SOC), dissolved organic carbon, and total and available nitrogen (N), phosphorus (P), and potassium (K) were measured. Microbial biomass carbon (MBC), basal respiration, and mineralization were also analyzed. Community level of physiological profile (CLPP) of microorganisms was analyzed by BIOLOG method to estimate the functional diversity and carbon (C) source utilization patterns of microbes. Principal component analysis (PCA), principal response curve (PRC), correlation analysis, regression analysis, and redundancy analysis (RDA) were performed to clarify changes in variables and determine the factors influencing microbial properties.

Results and discussion

SOC and total and available N, P, and K increased as follows: CFOM + M > CF > control. However, C/P and N/P ratios showed an opposite trend. MBC and respiration were not affected, but microbial quotient and metabolic quotient declined under intensive management. McIntosh diversity index was much higher in CFOM + M. The PCA showed that microorganisms in CFOM + M had a stronger ability to use most C sources. Weaker utilization of serine indicated an alleviation of nutrient deficiency in CFOM + M. PRC of CLPP showed a significant treatment effect and that utilization of serine sensitively responded to nutrient status over the whole incubation time. RDA showed that total and available N, total K, and C/P were the main factors influencing utilization of C sources by microbial communities.

Conclusions

Fertilization combined with organic mulching increased soil nutrients, microbial biomass, and respiration in a Lei bamboo plantation. Abundant nutrients also increased C source use efficiency of microorganisms under intensive management. Changes of N and K and C/P might have led to a shift in microorganisms toward a different life strategy and determined the change in C source utilization patterns of microbial communities.

     

Relationships between soil–litter interface enzyme activities and decomposition in <Emphasis Type="Italic">Pinus massoniana</Emphasis> plantations in China

Purpose

Enzyme activities in decomposing litter are directly related to the rate of litter mass loss and have been widely accepted as indicators of changes in belowground processes. Studies of variation in enzyme activities of soil–litter interface and its effects on decomposition are lacking. Evaluating enzyme activities in this layer is important to better understand energy flow and nutrient cycling in forest ecosystems.

Materials and methods

Litter decomposition and the seasonal dynamics of soil–litter enzyme activities were investigated in situ in 20- (younger) and 46-year-old (older) Pinus massoniana stands for 540 days from August 2010 to March 2012 by litterbag method. We measured potential activities of invertase, cellulase, urease, polyphenol oxidase, and peroxidase in litter and the upper mineral soils, and evaluated their relationships with the main environment factors.

Results and discussion

Remaining litter mass was 57.6 % of the initial weights in the younger stands and 61.3 % in the older stands after 540-day decomposition. Levels of enzyme activity were higher in the litter layer than in the soil layer. Soil temperature, litter moisture, and litter nitrogen (N) concentration were the most important factors affecting the enzyme activities. The enzyme activity showed significantly seasonal dynamics in association with the seasonal variations in temperature, water, and decomposition stages. Remaining litter dry mass was found to be significantly linearly correlated with enzyme activities (except for litter peroxidase), which indicates an important role of enzyme activity in the litter decomposition process.

Conclusions

Our results indicated the important effects of biotic (litter N) and abiotic factors (soil temperature and litter moisture) on soil–litter interface enzyme activities. Overall significant linear relationship between remaining dry mass and enzyme activities highlighted the important role of enzyme activity in affecting litter decomposition processes, which will further influence nutrient cycling in forest ecosystems. Our results contributed to the better understanding of the mechanistic link between upper soil–litter extracellular enzyme production and litter decomposition in forest ecosystems.

     

Determinants of the biodiversity patterns of ammonia-oxidizing archaea community in two contrasting forest stands

Purpose

The variation in soil microbial community patterns is primarily influenced by ecological processes associated with spatial distance and environmental heterogeneities. However, the relative importance of these processes in determining the patterns of soil microbial biodiversity in different successional forests remains unclear.

Materials and methods

Based on the species data from denaturing gradient gel electrophoresis (DGGE) analysis, we described the composition and beta diversity of ammonia-oxidizing archaea (AOA) community, an important functional microbial group in regulating nitrogen cycle, in a middle-succeed stand (60 years of secondary succession) and an undisturbed native stand in a subtropical forest in southern China. The composition pattern was examined using a multi-response permutation procedure (MRPP), and the beta diversity was described using the Sørensen index. The relative influence of edaphic, vegetational, spatial, and topographical factors on AOA composition and beta diversity was assessed by variation partitioning and multiple regression on distance matrices (MRM), respectively.

Results and discussion

We did not find any stand-specific patterns in AOA community composition in the two stands; however, the influential variables were different between the two stands; 7.3 and 4.5 % of the total variation in AOA community composition could be explained by edaphic (i.e., available potassium and total phosphorus) and spatial variables, respectively, in the middle-succeed stand, while 3.7 and 2.8 % of the variation were explained by spatial variable and available phosphorus, respectively, in the native stand. Soil total phosphorus influenced the beta diversity of AOA community most in the middle-succeed stand, while genetic distance of tree species was found to be the most important factor in driving the beta diversity pattern in the native stand.

Conclusions

Soil nutrients influenced the beta diversity of AOA community in the middle-succeed stand more than that in the native stand, while vegetation is more important in the native stand. The substantial unexplained variations were possibly due to the effects of other unmeasured variables. Nevertheless, dispersal process is more important in controlling AOA community composition in the native stand, while processes associated with environmental heterogeneities are more important in the middle-succeed stand in this subtropical forest.

     

Effects of different fertilization regimes on nitrogen and phosphorus losses by surface runoff and bacterial community in a vegetable soil

Purpose

Vegetables are major economic crops in China. Their cultivation usually involves high fertilizer application rates leading to significant losses of N and P to the wider environment, resulting in water contamination and low nutrient use efficiency. Hence, it is a matter of urgency to understand the mechanisms and factors that affect N and P losses in vegetable production systems in order to develop optimum fertilization regimes.

Materials and methods

Different fertilization regimes were applied in a long-term chili (Capsicum spp. L.) production soil to study the effects on nitrogen (N) and phosphorus (P) runoff losses, microbial biomass, microbial community, and crop yields. Three fertilization regimes were implemented: control (no fertilizer; CK), farmer’s fertilization practice (FFP), and site-specific nutrient management (SSNM). A fixed collection device was used to quantify the total volume of water output after each precipitation event. All water samples were analyzed for total nitrogen, ammonium nitrogen (NH₄⁺-N), nitrate nitrogen (NO₃^?-N), total phosphorus (TP), and available phosphorus (AP). Soil samples were collected for analysis of the physicochemical properties and for DNA extraction after chili harvest. High-throughput sequencing was used to further investigate the relationship between the microbial community and nutrient losses.

Results and discussion

The SSNM fertilizer regime resulted in a 23.3% yield increase and enhanced agronomic N use efficiency from 11.87 to 15.67% compared with the FFP treatment. Soil available nutrients (i.e., AN and AP) and ATP content increased significantly after SSNM implementation. Under the SSNM regime, N losses decreased by 25.8% compared with FFP but did not lead to significantly different P losses. High-throughput sequencing results showed that each treatment formed a unique microbial community structure. VPA results revealed that the microbial community structure was mainly (50.56%) affected by the interactions between N and P. Mantel results indicated that the soil properties that significantly affected soil microbial community structure followed the order: AP, AK, and salinity.

Conclusions

Our study has demonstrated that SSNM not only generates lower N losses but also provides higher contents of soil available nutrients and plant yield, which were mainly attributed to the multiple top dressings and meeting of the plants’ demand with adequate nutrient supplies. The combined data showed that the microbial community differentiation between the different fertilizer regimes was mainly linked to the interactions between N and P in the soil.

     

Plant–soil interaction affects the mineralization of soil organic carbon: evidence from 73-year-old plantations with three coniferous tree species in subtropical Australia

Purpose

Plantation is an important strategy for forest restoration and carbon (C) storage. Plantations with different tree species could significantly affect soil properties, including soil pH, soil nutrient content, soil microbial activities, and soil dissolved organic C. Changes in these abiotic and biotic factors could regulate mineralization of soil organic C (SOC). However, it remains unclear to what extent these factors affect the mineralization of SOC under different tree species plantations.

Materials and methods

Soil was collected at 0–10 cm depth from plantations with Pinus elliottii Engelm. var. elliottii, Araucaria cunninghamii, and Agathis australis, respectively, in southeast Queensland, Australia. Soil samples were assayed for soil organic C; organic N and mineralization of SOC; soil particle size; total C, N, and P; and pH. In addition, a 42-day laboratory incubation with substrate additions was done to examine the influence of different substrates and their combinations on bio-available organic C.

Results and discussion

Our results suggested that SOC mineralization was mainly determined by soil pH and soil C content among plantations with different tree species, whereas SOC mineralization was not correlated with soil N and P contents. These results were further confirmed by the substrate addition experiments. SOC mineralization of soils from slash pine showed greater response to C (glucose) addition than soils from other two plantations, which suggested significant differences in SOC mineralization among plantations with different tree species. However, neither N addition nor P addition had significant effects on SOC mineralization.

Conclusions

Our results indicated that plantations with different tree species substantially affect the mineralization and stability of soil organic C pool mainly by soil pH and soil C content.

     

Impact of fertilization on soil polyphenol dynamics and carbon accumulation in a tea plantation,Southern China

Purpose

The strong role that soil polyphenols play in soil organic matter (SOM) formation affects soil carbon sequestration. N deposition, which comes from man-made fertilizer, influences plant growth and soil biochemical properties therefore greatly regulates soil polyphenol metabolism. The objective of this experiment was to understand the effect of fertilizer form and rate on soil polyphenol dynamics as well as to understand the potential relationship between soil phenols and C accumulation.

Materials and methods

Urea, rapeseed cake, and chicken manure, respectively, referred as N, B, and F in the text, were applied at three rates (low N, medium N, and high N, referred as 1, 2, and 3 in the text, respectively); plots without fertilization were set as control (CK, for short). Seasonal dynamics of soil total polyphenol (Tp) and bound polyphenol (Bp) concentrations were monitored. Polyphenol oxidase (PPO), peroxidase (POD), and soil fluorescein diacetate (FDA) hydrolysis activities, all factors relevant to polyphenol metabolism, were measured simultaneously. The relationship between soil polyphenols and soil C concentration was also determined.

Results and discussion

N-fertilization altered the seasonal change pattern and the accumulation level of soil Tp and Bp, which possibly resulted from the enhancement of soil microbial activities and the change of soil nutrient status. Positive linear correlation was observed between soil Tp and TC (total C) contents, which means fertilization could influence C accumulation through affecting the metabolism of soil polyphenols. Soil chemical characteristics and enzyme activities that relate to soil polyphenol metabolism were influenced by fertilization as well. Mitigated TC increment was observed in most fertilization treatments mainly due to the increased SOM decomposition rate.

Conclusions

Our findings reveal the important role of soil phenols played in C accumulation in a tea plantation due to the significant, positive linear relationship between soil Tp and TC. Long-term studies, combined with soil microorganism community structure, soil humification, and tea leaf litter decomposition experiments, are necessary for fully understanding the role that polyphenols play in soil C cycle.

     

Micronutrients (Fe,Mn, Zn and Cu) balance under long-term application of fertilizer and manure in a tropical rice-rice system

Purpose

The balance of micronutrients in soils is important in nutrient use efficiency, environmental protection and the sustainability of agro-ecological systems. The deficiency or excess of micronutrients in the plough layer may decrease crop yield and/or quality. Therefore, it is essential to maintain appropriate levels of micronutrients in soil, not only for satisfying plant needs in order to sustain agricultural production but also for preventing any potential build-up of certain nutrients.

Materials and methods

A long-term fertilizer experiment started in 1969 at Central Rice Research Institute, Cuttack, Odisha, India. Using this experiment, a study was conducted to analyze the balance of micronutrients and their interrelationship. The experiment was composed of ten nutrient management treatments viz. control; nitrogen (N); N + phosphorus (NP); N + potassium (NK); nitrogen, phosphorus and potassium (NPK); farmyard manure (FYM); N + FYM; NP + FYM; NK + FYM; and NPK + FYM with three replications. Micronutrients in soil (total and available), added fertilizers and organic manures and in rice plant were analyzed. Besides, atmospheric deposition of the micronutrients to the experimental site was also calculated. A micronutrient balance sheet was prepared by the difference between output and input of total micronutrients.

Results and discussion

Application of FYM alone or in combination with chemical fertilizer increased the diethylenetriamine pentaacetate (DTPA)-extractable Fe, Mn and Zn over the control treatment. The treatment with NPK + FYM had the highest soil DTPA-extractable Fe, Mn, Zn and Cu after 41 years of cropping and fertilization. Application of chemical fertilizers without P decreased the DTPA-extractable Zn over the control while the inclusion of P in the fertilizer treatments maintained it on a par with the control. The application of P fertilizer and FYM either alone or in combination significantly increased the contents of total Fe, Mn, Zn and Cu in soil mainly due to their micronutrient content and atmospheric depositions. A negative balance of Zn was observed in the N, NP, NK and NPK treatments, while a positive balance observed in the remaining treatments. The balance of Mn was negative in all the treatments, due to higher uptake by the rice crop than its addition.

Conclusions

Long-term application of chemical fertilizers together with FYM maintained the availability of micronutrients in soil and, thus, their uptake by rice crop.

     

Soil quality assessment under different <Emphasis Type="Italic">Paulownia fortunei</Emphasis> plantations in mid-subtropical China

Purpose

Paulownia, one of the fastest growing broad-leaved tree species in the world, is widely distributed in the warm temperate regions of China. However, there are few commercial-scale Paulownia plantations, and there is only limited information available about the most suitable soil quality for Paulownia fortunei growth in mid-subtropical, Hunan Province, China.

Materials and methods

To understand the effect of the growth of P. fortunei on soil conditions, 25 soil property parameters under Paulownia plantations were studied in Hunan Province, China. Seventy-two standard plots of eight different stand types were analyzed by three statistical approaches to assess soil quality (SQ) in the different P. fortunei plantations.

Results and discussion

The results revealed that a majority of the soil characteristics when intercropping with oilseed rape and the pure P. fortunei (plantation III) were better than intercropping with Camellia oleifera, orange trees, and Cunninghamia lanceolata (Lamb.). Available calcium, available magnesium, available potassium, available phosphorus, soil thickness, slope, soil organic matter, available sulfur, available copper, dehydrogenase, and available zinc were selected as the minimum data set (MDS). The SQ index (SQI) showed that three classes for soil quality among the eight P. fortunei plantations ranged from 0.48 to 0.88 and these were correlated with standing volume (p?<?0.05).

Conclusions

From the results, we concluded that selected MDS indicators can describe the soil fertility quality of P. fortunei plantations, and that the relationship between SQI and standing volume has a biological significance. P. fortunei plantations intercropped with Camellia oleifera, orange trees, and Cunninghamia lanceolata (Lamb.) caused a deterioration in SQ, but intercropping oilseed rape and pure P. fortunei plantations produced an improvement in SQ.

     

Effects of phosphate on trace element accumulation in rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.): a 5-year phosphate application study

Purpose

Phosphate (P) fertilizers are being widely used to increase crop yield, especially in P-deficient soils. However, repeated applications of P could influence trace element bioaccumulation in crops. The effects of 5-year P enrichment on trace element (Cu, Zn, Cd, Pb, As, and Hg) accumulation in Oryza sativa L. were thus examined.

Materials and methods

Two paddy soils with different initial P availabilities were amended with and without P fertilizer from 2009 to 2013. Trace elements and P levels in rice and soils were analyzed.

Results and discussion

In soil initially with limited P, P amendment enhanced grain Pb, As, and Hg concentrations by 1.8, 1.5, and 1.4-fold, respectively, but tended to decrease the grain Cd level by 0.73-fold, as compared to the control. However, in soil initially with sufficient P, P amendment tended to reduce accumulation of all examined elements in rice grain.

Conclusions

Phosphate amendment in initially P-limited and P-sufficient soils had different effects on trace element availability in soil (as reflected by extractable element) and plant physiology (growth and metal translocation), resulting in contrasting patterns of trace element accumulation in rice between the two types of soils. Our study emphasized the necessity to consider the promoting effects of P on Pb, As, and Hg accumulation in grain in initial P-deprived soil.

     

Root plasticity,whole plant biomass,and nutrient accumulation of <Emphasis Type="Italic">Neyraudia reynaudiana</Emphasis> in response to heterogeneous phosphorus supply

Purpose

The aims of this study were to examine the adaptive mechanisms of Neyraudia reynaudiana, a pioneer species rapidly colonizing degraded sites, to heterogeneous phosphorus (P) distribution, and how foraging P distributed in patches affects whole-plant biomass and nutrient accumulation.

Materials and methods

Plants were grown in equally divided sand-culture boxes using different concentrations of P applied either heterogeneously (0/5, 0/15, 5/15, 0/30, and 15/30 mg KH₂PO₄ solution/kg dry soil) or homogeneously (2.5/2.5, 7.5/7.5, 10/10, 15/15, and 22.5/22.5 mg kg^?1) to each of the split boxes.

Results and discussion

After 4 months of treatment applications, a significant (p < 0.05) variation in specific root length plasticity was detected between patches of heterogeneous P availability. The largest patch strength difference (0/30 mg/kg) induced the greatest change in specific root length relative to the smallest patch strength difference (0/5 mg/kg). Root P content was not changed by the heterogeneous treatments. Although the whole plant biomass was unaffected by the P distribution pattern, the accumulation of P in the whole plant was slightly higher in the homogeneous treatment than in the heterogeneous treatment.

Conclusions

Plasticity of root morphological appears to be the main adaptation mechanism by which this species forages patchily distributed P. The benefit of this strategy is not reflected in increased whole-plant productivity or nutrient accumulation when P is heterogeneously distributed. The results are fundamental to understanding the mechanisms of foraging nutrient-patches and adapting to poor soil conditions.

     

Short-term effects of organo-mineral biochar and organic fertilisers on nitrogen cycling,plant photosynthesis,and nitrogen use efficiency

Purpose

Organo-mineral biochar fertiliser has the potential to replace conventional biochar and organic fertiliser to improve soil quality and increase plant photosynthesis. This study explored mechanisms involved in nitrogen (N) cycling in both soil and ginger plants (Zingiber officinale: Zingiberaceae) following different treatments including organic fertiliser, commercial bamboo biochar fertiliser, and organo-mineral biochar fertiliser.

Materials and methods

Soil received four treatments including (1) commercial organic fertiliser (5 t ha^?1) as the control, (2) commercial bamboo biochar fertiliser (5 t ha^?1), (3) organo-mineral biochar fertiliser at a low rate (3 t ha^?1), and (4) organo-mineral biochar fertiliser at a high rate (7.5 t ha^?1). C and N fractions of soil and plant, and gas exchange measurements were analysed.

Results and discussion

Initially, organo-mineral biochar fertiliser applied at the low rate increased leaf N. Organo-mineral biochar fertiliser applied at the high rate significantly increased N use efficiency (NUE) of the aboveground biomass compared with other treatments and improved photosynthesis compared with the control. There was N fractionation during plant N uptake and assimilation since the ¹⁵N enrichment between the root, leaf, and stem were significantly different from zero; however, treatments did not affect this N fractionation.

Conclusions

Organo-mineral biochar fertiliser has agronomic advantages over inorganic and raw organic (manure-based) N fertiliser because it allows farmer to put high concentrations of nutrients into soil without restricting N availability, N uptake, and plant photosynthesis. We recommend applying the low rate of organo-mineral biochar fertiliser as a substitute for commercial organic fertiliser.