Long-term impacts of manure, straw, and fertilizer on amino sugars in a silty clay loam soil under temperate conditions

There is increasing evidence that microorganisms participate in soil C sequestration and stabilization in the form of resistant microbial residues. The type of fertilizers influences microbial activity and community composition; however, little is known about its effect on the microbial residues and their relative contribution to soil C storage. The aim of this study was to investigate the long-term impact (21 years) of different fertilizer treatments (chemical fertilizer, crop straw, and organic manure) on microbial residues in a silty clay loam soil (Udolls, USDA Soil Taxonomy). Amino sugars were used to indicate the presence and origin of microbial residues. The five treatments were: CK, unfertilized control; NPK, chemical fertilizer NPK; NPKS₁, NPK plus crop straw; NPKS₂, NPK plus double amounts of straw; and NPKM, NPK plus pig manure. Long-term application of inorganic fertilizers and organic amendments increased the total amino sugar concentrations (4.4–8.4 %) as compared with the control; and this effect was more evident in the plots that continuously received pig manure (P?<?0.05). The increase in total amino sugar stock was less pronounced in the straw-treated plots than the NPKM. These results indicate that the accumulation of soil amino sugars is largely influenced by the type of organic fertilizers entering the soil. Individual amino sugar enrichment in soil organic carbon was differentially influenced by the various fertilizer treatments, with a preferential accumulation of bacterial-derived amino sugars compared with fungal-derived glucosamine in manured soil.     

Stability and saturation of soil organic carbon in rice fields: evidence from a long-term fertilization experiment in subtropical China

Purpose

Soil organic carbon (SOC) sequestration in croplands plays a critical role in climate change mitigation and food security, whereas the stability and saturation of the sequestered SOC have not been well understood yet, particularly in rice (Oryza sativa L.) fields. The objective of this study was to determine the long-term effect of inorganic fertilization alone or combined with organic amendments on SOC stability in a double rice cropping system, and to characterize the saturation behavior of the total SOC and its fractions in the paddy soil.

Materials and methods

Soils were collected from a long-term field experiment in subtropical China where different fertilization regimes have been carried out for 31 years. The total SOC pool was separated into four fractions, characteristic of different turnover rates through chemical fractionation. Annual organic carbon (C) inputs were also estimated by determining the C content in crop residues and organic amendments.

Results and discussion

Relative to the initial level, long-term double rice cropping without any fertilizer application significantly increased SOC concentration, suggesting that double rice cropping facilitates the storage and accumulation of SOC. The partial substitution of inorganic fertilizers with organic amendments significantly increased total SOC concentration compared to the unfertilized control. Total SOC increased significantly with greater C inputs and did not show any saturation behavior. Increased SOC was primarily stored in the labile fraction with input from organic amendments. However, other less labile SOC fractions showed no further increase with greater C inputs exhibiting C saturation.

Conclusions

While the paddy soil holds a high potential for SOC sequestration, stable C fractions saturate with increasing C inputs, and thus, additional C inputs mainly accumulate in labile soil C pools.     

Effectiveness of crop straws,and swine manure in ameliorating acidic red soils: a laboratory study

Purpose

Crop straws and animal manure have the potential to ameliorate acidic soils, but their effectiveness and the mechanisms involved are not fully understood. The aim of this study was to evaluate the effectiveness of two crop (maize and soybean) straws, swine manure, and their application rates on acidity changes in acidic red soils (Ferralic Cambisol) differing in initial pH.

Materials and methods

Two red soils were collected after 21 years of the (1) no fertilization history (CK soil, pH 5.46) and (2) receiving annual chemical nitrogen (N) fertilization (N soil, pH 4.18). The soils were incubated for 105 days at 25 °C after amending the crop straws or manure at 0, 5, 10, 20, and 40 g kg^?1 (w/w), and examined for changes in pH, exchangeable acidity, N mineralization, and speciation in 2 M KCl extract as ammonium (NH₄⁺) and nitrate plus nitrite (NO₃^??+?NO₂^?).

Results and discussion

All three organic materials significantly decreased soil acidity (dominated by aluminum) as the application rate increased. Soybean straw was as effective (sometimes more effective) as swine manure in raising pH in both soils. Soybean straw and swine manure both significantly reduced exchangeable acidity at amendment rate as low as 10 g kg^?1 in the highly acidic N soil, but swine manure was more effective in reducing the total acidity especially exchangeable aluminum (e.g., in the N soil from initial 5.79 to 0.50 cmol₍₊₎ kg^?1 compared to 2.82 and 4.19 cmol₍₊₎ kg^?1 by soybean straw and maize straw, respectively). Maize straw was less effective than soybean straw in affecting soil pH and the acidity. The exchangeable aluminum decreased at a rate of 4.48 cmol₍₊₎ kg^?1 per pH unit increase for both straws compared to 6.25 cmol₍₊₎ kg^?1 per pH unit from the manure. The NO₃^??+?NO₂^? concentration in soil increased significantly for swine manure amendment, but decreased markedly for straw treatments. The high C/N ratio in the straws led to N immobilization and pH increase.

Conclusions

While swine manure continues to be effective for ameliorating soil acidity, crop straw amendment has also shown a good potential to ameliorate the acidity of the red soil. Thus, after harvest, straws should preferably not be removed from the field, but mixed with the soil to decelerate acidification. The long-term effect of straw return on soil acidity management warrants further determination under field conditions.

     

The effect of application of organic manures and mineral fertilizers on the state of soil organic matter and nutrients in the long-term field experiment

Purpose

Soil organic matter (SOM) plays an important role in terrestrial ecosystems and agroecosystems. Changes in the agricultural sector in the Czech Republic within the past 25 years have had a negative impact on SOM content and contribute to gradual soil degradation. The aim of this study is to estimate the effect of long-term application of different mineral fertilizers (NPK) and organic manures (manure, cattle slurry) on soil chemical properties (quality of humus, available nutrients, and soil reaction).

Materials and methods

Soil samples were collected from Luvisol during two selected periods 1994–2003 and 2014–2016 from long-term field experiment carried out in Prague-Ruzyně (Czech Republic). Average annual temperature is 8.5 °C, and annual precipitations are 485 mm. Different fertilization regimes have been applied for 62 years. The crop rotation was as follows: cereals (45%), root crops (33%) and legumes (22%). Soil analysis—soil organic carbon (SOC) was determined by oxidimetric titration method. Short fractionation method for evaluation of humic substance (HS), humic acid (HA) and fulvic acid (FA) content was used. Absorbance of HS in UV-VIS spectral range was measured by Varian Carry 50 Probe UV-VIS spectrometer. Degree of humification (DH) and color index (Q_4/6) were calculated from fractional composition data. Soil reaction was measured by potentiometric method. Available nutrients (phosphorus, potassium, magnesium, calcium) were determined by Mehlich II and Mehlich I methods and by ICP-OES. For data analysis, the following are used: exploratory data analysis, ANOVA, and principal component analysis (PCA).

Results and discussion

PCA analysis differentiated fertilizers into two categories: (1) variant NPK (lower quality of humus)—higher acidity, lower SOC and HS content, predomination of FA, higher DH and lower content of available nutrients; (2) variants with organic manures (higher quality of humus)—lower acidity, higher SOC and HS content, predomination of HA, middle DH, and high content of available nutrients. The main result of presented study is to give a synthesis of effect of different type of fertilizers on a sustainable organic matter management in arable soils, with respect to yields, food security and adaptation to predict climate changes.

Conclusions

Long-term application of mineral fertilizers (NPK) without organic matter input can accelerate humus mineralization and soil quality degradation with all negative consequences such as (nitrogen leaching, higher availability of toxic element for plants, slow energy for soil microorganisms etc.). Application of organic fertilizers (manure and cattle slurry) helps to achieve the long-term stable yields while maintaining soil at optimum quality (long-term sustainable management with SOM). Principal component analysis is a useful tool for evaluation of soil quality changes.

     

长期施肥对黄壤有机碳平衡及玉米产量的影响

基于长期定位试验,以黔中典型黄壤为研究对象,采用单因素方差分析、可持续性指数、稳定性指数等方法对长期定位试验获取的数据进行分析和比较,以探讨长期不同施肥处理对黄壤有机碳含量、有机碳平衡量、玉米产量稳定性、可持续性及其相互关系的影响。结果表明:(1)与施化肥和对照处理相比,施有机肥处理土壤有机碳含量明显升高,按大小排序依次为:MMNPK1/2M+1/2NPK1/4M+3/4NPK;(2)施有机肥处理黄壤有机碳平衡量为正值,且随有机肥施用量增加而增加,相反,施化肥和对照处理均为负值,大小依次为:MNPK、M1/2M+1/2NPK1/4M+3/4NPKNPKNKNPN、CKPK,各处理差异显著;(3)有机肥与化肥配施、有机肥单施及氮磷钾化肥协调施用更有利于提高玉米产量,排序为:MNPK1/4M+3/4NPK、1/2M+1/2NPKNPK、MNPNK、PK、NCK;(4)适量有机肥与化肥配施可提高玉米产量稳定性和可持续性(可持续性指数0.6,变异系数0.3),其中,1/4M+3/4NPK处理玉米产量稳定性和持续性最好;(5)玉米年产量与黄壤有机碳平衡量相关度较高,而玉米可持续性、稳定性则主要受有机碳含量影响。综上,有机肥与化肥配施有利于黄壤有机碳含量提升、玉米维持高产稳产。按适量"减肥"原则,以25%有机肥配施75%氮磷钾化肥效果最佳。     

Distribution of carbon and nitrogen in water-stable aggregates and soil stability under long-term manure application in solonetzic soils of the Songnen plain,northeast China

Purpose

Excessive exchangeable sodium and high pH significantly decrease soil structural stability and permeability. Long-term application of cattle manure is an important management practice that can affect water-stable aggregates (WSAs), as well as aggregate stability and distribution of soil organic carbon (SOC) and total nitrogen (TN) in solonetzic soils.

Material and methods

Experiments were carried out in a randomized complete block design comprising five treatments according to the cattle manure application history: corn (Zea mays) with manure applied for 1, 5, 12, and 17 years were used as the experimental treatments and corn without manure application was used as a control. Soil properties, including WSAs, mean weight diameter (MWD), and SOC and TN concentrations in bulk soils and WSAs, were measured across all treatments. The relationships among the measured soil attributes were determined using stepwise regression analysis.

Results and discussion

Results indicated that micro-aggregates mainly accumulated in soils without manure application, while manure application significantly increased macro-aggregates formation. MWD was highest when manure was applied to the soil for 1 year, decreased after 5 years, and increased again after 12 years. SOC and TN concentrations in bulk soils and WSAs increased with the number of years of manure application, with the highest concentrations observed for 17 years in bulk soils. Stepwise regression analysis showed that WSAs 2–5 mm, SOC in WSAs 0.25–0.5 mm, and TN in WSAs 0.1–0.25 mm were dominant independent variables affecting aggregate stability, and that SOC in WSAs 0.25–0.5 mm and TN in WSAs <0.1 mm were dominant independent variables affecting SOC and TN concentrations in bulk soils, respectively.

Conclusions

Long-term application of manure to a solonetz significantly increased macro-aggregates and aggregate stability as well as SOC and TN in bulk soils and all aggregate sizes. These results are likely related to binding agent production as well as C and N accumulation from manure application.     

Earthworms and phosphate-solubilizing bacteria enhance carbon accumulation in manure-amended soils

Purpose

Application of functional organisms in soil organic amendments has the potential to accelerate organic matter decomposition and stimulate C cycling. In this study, a short-term (a year) field experiment was conducted to investigate the collaborative effects of earthworms and phosphate-solubilizing bacteria on C accumulation in pig manure-amended soil.

Materials and methods

A field experiment was conducted with six treatments established. The first three treatments, including control (CK), pig manure (Pm), and pig manure?+?slurry (Pm?+?S), were set up to evaluate the influences of pig manure on soil C accumulation. The other three treatments, including manure?+?slurry?+?earthworms (Te), manure?+?slurry?+?phosphate-solubilizing bacteria (Tb), and manure?+?slurry?+?earthworms?+?bacteria (T(e?+?b)), were set up to investigate the collaborative effects of functional organisms on soil C cycling. The Pm?+?S treatment was chosen as the control (T) for this purpose.

Results and discussion

The results showed that the soil C pools did not increase significantly under the manure treatment. In contrast, an integrated application of manure, slurry, earthworms, and bacteria significantly increased the various C fractions, such as SOC and humin, indicating a rapid and positive effect of earthworms and bacteria on C accumulation. Besides, C sequestration by the integrated application was as high as 1.35 Mg C ha^?1 soil, half of which was stabilized.

Conclusions

The T(e?+?b) was an efficient strategy to sequestrate and stabilize SOC in arid hillside soils. The bacteria increased the labile OC, especially microbial biomass C, while the earthworms were apparently essential for the increase in stable OC.

     

Nitrous oxide emission,global warming potential,and denitrifier abundances as affected by long-term fertilization on Mollisols of Northeastern China

ABSTRACT

A long-term field experiment was performed to assess the effects of fertilization regimes on greenhouse gas emissions, soil properties, soil denitrifies, and maize (Zea mays) grain yield on Mollisols of Northeastern China. Chemical nitrogen (N), phosphorus (P), and potassium (K) fertilizers plus pig manure (MNPK) treatment significantly increased soil N₂O emissions by 29.9–226.4% and global warming potential (GWP) by 29.8–230.7% compared to unfertilized control (CK), chemical N fertilizer only (N), chemical N, P, and K fertilizers (NPK) and chemical N, P, and K fertilizers plus corn straw (SNPK) treatments. However, the MNPK treatment yielded similar greenhouse gas intensity (GHGI) as compared with other treatments, mainly due to higher maize grain yield. There were also higher gene copy numbers of nirK, nirS, and nosZ in topsoil (0–20 cm depth) under MNPK treatment. Automatic linear modeling analysis indicated that main factors influencing soil N₂O emissions were soil organic carbon (SOC), NO₃^? content, and nirK gene abundance. Although the application of chemical fertilizers plus organic manure increases N₂O emissions due to higher N and C availability and nirK gene activity in the soil, this is still a promising fertilizer management due to its notable enhancement of maize grain yield and SOC content.     

Chemical nature of soil organic carbon under different long-term fertilization regimes is coupled with changes in the bacterial community composition in a Calcaric Fluvisol

Fertilization is an important factor influencing the chemical structure of soil organic carbon (SOC) and soil microbial communities; however, whether any connection exists between the two under different fertilization regimes remains unclear. Soils from a 27-year field experiment were used to explore potential associations between SOC functional groups and specific bacterial taxa, using quantitative multiple cross-polarization magic-angle spinning ¹³C nuclear magnetic resonance and 16S rRNA gene sequencing. Treatments included balanced fertilization with organic materials (OM) and with nitrogen (N), phosphorus (P), and potassium (K) mineral fertilizers (NPK); unbalanced fertilization without one of the major elements (NP, PK, or NK); and an unamended control. These treatments were divided into four distinct groups, namely OM, NPK, NP plus PK, and NK plus control, according to their bacterial community composition and SOC chemical structure. Soil total P, available P, and SOC contents were the major determinants of bacterial community composition after long-term fertilization. Compared to NPK, the OM treatment generated a higher aromatic C–O and OCH₃ and lower alkyl C and OCH abundance, which were associated with the enhanced abundance of members of the Acidobacteria subgroups 6 and 5, Cytophagaceae, Chitinophagaceae, and Bacillus sp.; NP plus PK treatments resulted in a higher OCH and lower aromatic C–C abundance, which showed a close association with the enrichment of unclassified Chloracidobacteria, Syntrophobacteraceae, and Anaerolineae and depletion of Bacillales; and NK plus control treatments resulted in a higher abundance of aromatic C–C, which was associated with the enhanced abundance of Bacillales. Our results indicate that different fertilization regimes changed the SOC chemical structure and bacterial community composition in different patterns. The results also suggest that fertilization-induced variations in SOC chemical structure were strongly associated with shifts in specific microbial taxa which, in turn, may be affected by changes in soil properties.     

Phosphorus and carbon status of a paddy soil under different fertilization regimes

Purpose

Phosphorus (P) in soil particulate fraction (PF; >53 μm) is suggested to have a significant importance in soil P cycling. However, the effects of continuous fertilization on P-PF and its association with soil organic carbon (SOC) in paddy soils have not been well studied.

Materials and methods

We sampled paddy soils at 0–20 cm from a long-term field experiment (initiated in 1981) conducted under humid subtropical conditions in China, which has five fertilization treatments with equivalent P input (135 kg P₂O₅?ha^?1 year^?1) except the control treatment (CK). Changes in total P (Pt), inorganic P (Pi), organic P (Po), and SOC under different fertilization managements were evaluated in the whole soil, in the PF, and in the mineral-associated fraction (MAF; <53 μm).

Results and discussion

Continuous fertilization increased the contents of SOC and P in all soil fractions. Both Po and organic carbon in PF were the most sensitive variables to fertilization, indicating that they constitute a useful tool to detect the effects of management practices. Among the fertilization treatments, organic amendments significantly increased Po-PF contents more than chemical fertilizer applied only (p?<?0.05), although they had equivalent P input. The paddy soil without fertilization showed a more significant decrease in Pi compared with Po. The SOC/Po ratios were significantly lower in fertilization treatments (especially those with manure or straw incorporation) than in CK and decreased from PF to MAF. A significant relationship was found between Po-PF contents and rice P uptake during the growing season.

Conclusions

These results demonstrate that Po-PF may also play a significant role in P cycling of paddy soil, and thus, it would be better to consider Po-PF in soil diagnosis to promote P management of paddy soil, especially for that under long-term organic amendments.

     

Land use changes induced soil organic carbon variations in agricultural soils of Fuyang County, China

Purpose

The purpose of this study is to understand spatial and temporal variations of soil organic carbon (SOC) under rapid urbanization and support soil and environmental management.

Materials and methods

SOC data in 1979 and 2006, of 228 and 1,104 soil samples respectively, were collected from surface agricultural lands in Fuyang County, East of China. Land use data were also gathered at the same time.

Results and discussion

The mean SOC was 17.3 (±4.6) g/kg for the 1979 data and 18.5(±5.8) g/kg for 2006. There was a significant difference in SOC between the 2 years according to the t test result. Geostatistical analysis indicated that SOC had a moderate spatial correlation controlled by extrinsic anthropogenic activities. The spatial distribution of SOC, derived from ordinary kriging, matched the distribution of industry and urbanization. Using a six-level SOC classification scheme (<3.5, 3.5–5.8, 5.8–11.6, 11.6–17.4, 17.4–23.2, and >23.2 g/kg) created by Zhejiang Province, approximately 15 % of soil had SOC increase from low to high levels from 1979 to 2006.

Conclusions

The main cause of SOC variation in the study area was land use change from agriculture to industrial or urbanized uses. The increasing SOC trend near most towns may be attributed to use of organic manure, urban wastes, sewage sludge, and chemical fertilizers on agricultural land.     

Dynamics of soil extractable carbon and nitrogen under different cover crop residues

Purpose

Cover crop residue is generally applied to improve soil quality and crop productivity. Improved understanding of dynamics of soil extractable organic carbon (EOC) and nitrogen (EON) under cover crops is useful for developing effective agronomic management and nitrogen (N) fertilization strategies.

Materials and methods

Dynamics of soil extractable inorganic and organic carbon (C) and N pools were investigated under six cover crop treatments, which included two legume crops (capello woolly pod vetch and field pea), three non-legume crops (wheat, Saia oat and Indian mustard), and a nil-crop control (CK) in southeastern Australia. Cover crops at anthesis were crimp-rolled onto the soil surface in October 2009. Soil and crop residue samples were taken over the periods October?CDecember (2009) and March?CMay (2010), respectively, to examine remaining crop residue biomass, soil NH₄ ⁺?N and NO₃ ^??CN as well as EOC and EON concentrations using extraction methods of 2?M KCl and hot water. Additionally, soil net N mineralization rates were measured for soil samples collected in May 2010.

Results and discussion

The CK treatment had the highest soil inorganic N (NH₄ ⁺?N?+?NO₃ ^??CN) at the sampling time in December 2009 but decreased greatly with sampling time. The cover crop treatments had greater soil EOC and EON concentrations than the CK treatment. However, no significant differences in soil NH₄ ⁺?N, NO₃ ^??CN, EOC, EON, and ratios of EOC to EON were found between the legume and non-legume cover crop treatments across the sampling times, which were supported by the similar results of soil net N mineralization rates among the treatments. Stepwise multiple regression analyses indicated that soil EOC in the hot water extracts was mainly affected by soil total C (R ²?=?0.654, P?<?0.001), while the crop residue biomass determined soil EON in the hot water extracts (R ²?=?0.591, P?<?0.001).

Conclusions

The cover crop treatments had lower loss of soil inorganic N compared with the CK treatment across the sampling times. The legume and non-legume cover crop treatments did not significantly differ in soil EOC and EON pools across the sampling times. In addition, the decomposition of cover crop residues had more influence on soil EON than the decomposition of soil organic matter (SOM), which indicated less N fertilization under cover crop residues. On the other hand, the decomposition of SOM exerted more influence on soil EOC across the sampling times among the treatments, implying different C and N cycling under cover crops.     

Effects of long-term application of various organic amendments on soil particulate organic matter storage and chemical stabilisation of vertisol soil

Current understanding of the effects of long-term application of various organic amendments on soil particulate organic matter (POM) storage and chemical stabilisation remains limited. Therefore, we collected soil samples from the soil profile (0–100?cm) under six treatments in a 31-year long-term fertilisation experiment: no fertiliser (CK), mineral fertilisers (NPK), mineral fertilisers plus 3.8 or 7.5?t?ha^?1?year^?1 (fresh base) the amount of wheat straw (1/2SNPK and SNPK) and mineral fertilisers plus swine or cattle manure (PMNPK and CMNPK). Long-term incorporation of wheat straw and livestock manure amendments significantly (p?<?0.05) increased crop yield and sustainable yield index, and POM storage compared with CK and NPK treatments. The mole ratios of H/C in the POM under organic amendment treatments significantly (p?<?0.05) decreased by 13.8% and 37.1%, respectively, compared with the NPK treatment. Similarly, solid state NMR spectroscopy showed that the O–alkyl carbon content of POM was greatly decreased, whereas aromatic carbon contents and alkyl to O–alkyl carbon ratios were substantially increased under PMNPK and CMNPK treatments. In conclusion, we recommend long-term livestock manure application as a preferred strategy for enhancing POM quantity and quality (chemical stability), and crop yield of vertisol soil in northern China.     

Soil carbon and nitrogen storage in alluvial wet meadows of the Southern Sierra Nevada Mountains,USA

Purpose

Wet meadows formed on alluvial deposits potentially store large amounts of soil carbon (C) but its stability is subject to the impacts of management practices. The objective of this study was to quantify and characterize soil organic carbon (SOC) and nitrogen (N) in mountain wet meadows across ranges of meadow hydrology and livestock utilization.

Materials and methods

Eighteen wetlands in the southern Sierra Nevada Mountains representing a range of wetness and livestock utilization levels were selected for soil sampling. In each wetland meadow, whole-solum soil cores delineated by horizon were analyzed for total and dissolved organic C (DOC) total (TN) and mineral nitrogen and soil water content (SWC). Multiple regression and GIS analysis was used to estimate the role of wet meadows in C storage across the study area landscape.

Results and discussion

Average solum SOC contents by wetland ranged from 130 to 805 Mg ha^?1. All SOC and TN components were highly correlated with SWC. Regression analyses indicated subtle impacts of forage utilization level on SOC and TN concentrations, but not on whole-solum, mass-per-area stocks of SOC and TN. Proportions of DOC and TN under seasonally wet meadows increased with increasing utilization. GIS analysis indicated that the montane landscape contains about 54.3 Mg SOC ha^?1, with wet meadows covering about 1.7% of the area and containing about 12.3% of the SOC.

Conclusions

Results indicate that soil organic C and N content of meadows we sampled are resilient to current light to moderate levels of grazing. In seasonally wet meadows, higher proportions of DOC and N with increasing utilization indicate vulnerability to loss. Partial drying of the wettest and seasonally wet meadows could result in losses of over five % of landscape SOC.     

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.

     

有机物料与化肥配施提高黄泥田水稻产量和土壤肥力

农业有机物料具有资源化再利用的特点,与化肥配施既可以保证作物产量,也可以提升地力。为了建立最适宜的南方低产黄泥田培肥模式,该文在浙江金衢盆地开展3年田间试验研究化肥与不同有机物料(菇渣、紫云英、牛粪和秸秆)配施对水稻产量和土壤肥力的影响。结果表明:1)有机物料与化肥配施可以显著提高水稻产量,化肥+菇渣、化肥+紫云英、化肥+牛粪和化肥+秸秆处理下,水稻三年的平均产量分别比单施化肥提高了9.7%、9.5%、12.3%和9.5%;2)有机物料与化肥配合施用,土壤有机质、土壤养分(全氮、有效磷、速效钾和CEC)及土壤容重较单施化肥处理有一定程度的改善,其中,化肥+牛粪效果最明显,有机质质量分数提高了12.5%,土壤有效磷质量分数提高了37.7%,CEC提高了16.1%;3)与单施化肥相比,化肥+菇渣、化肥+牛粪处理下5 mm机械稳定性大团聚体分别提高了10.4%和6.7%,各配施处理均显著降低了团聚体破坏率。总得来讲,连续三年有机物料与化肥配施较单施化肥处理提高了水稻产量、改善了土壤肥力状况、增加了土壤团聚体稳定性,其中又以牛粪与化肥配合施用效果最佳。     

Effects of cultivation and abandonment on soil carbon content of subalpine meadows, northwest China

Purpose

Land use changes have a significant impact on soil carbon emission and sequestration worldwide. Accurate evaluation of the effect of land use change (cultivation and abandonment) on soil carbon content of subalpine meadows is required to monitor the soil carbon dynamics of rangeland ecosystems in China.

Materials and methods

Based on collection of soil cores and vegetation, investigations of four types of land use (undisturbed natural meadow, land cultivated for 20?years, land abandoned for 3?years following cultivation, and land abandoned for 10?years following cultivation) were undertaken in the headwater area of the Heihe River in northwest China. Three soil carbon fractions [soil organic carbon (SOC), light fraction organic carbon (LFOC), and microorganism biomass carbon (MBC)] were determined in the laboratory, and the relative abundances of LFOC/SOC and MBC/SOC were calculated.

Results and discussion

Repeated cultivation by ploughing reduced the carbon content of the top soil layer, resulting in more uniform vertical distribution of soil organic matter. Ten years after cessation of cultivation, the organic carbon content within the top 10-cm soil layer (0?C10?cm) had reached 90?% of the content in native meadows, equivalent to a mean annual sequestration rate of 1.73?t?C?ha^?1. The rate of LFOC restoration was faster than that of SOC restoration. The variation in the ratio of MBC to SOC (0.91?C1.07?%) was small.

Conclusions

The activity of cultivation reduced all indicators of soil carbon status, which were not completely restored to the level of natural meadow, even after abandonment of cultivation for 10?years. Nevertheless, abandonment of cultivation is a practical, even if long-term, means of improving carbon sequestration in subalpine meadow of China.     

长期施肥下新疆灰漠土有机碳及作物产量演变

为明确长期不同施肥下新疆灰漠土有机碳和作物产量演变特征,依托始于1990年的灰漠土肥力长期定位监测试验,选择对照(CK,不施肥)、施氮磷肥(NP)、氮磷钾平衡施肥(NPK)、氮磷钾配合常量有机肥(NPKM)、氮磷钾配合高量有机肥(h NPKM,有机肥施用量为NPKM的2倍)、氮磷钾配合秸秆还田(NPKS)6个处理,分析不同处理下土壤有机碳和小麦、玉米产量演变特征,探讨碳投入及有机碳与作物产量的关系。结果表明:1)长期耗竭种植(CK)、连续施用NP或NPK肥,灰漠土有机碳含量持续下降,年均下降速率分别为0.094 g·kg~(-1)、0.043 g·kg~(-1)和0.053 g·kg~(-1),表明施化肥(NP、NPK)不能维持土壤有机碳含量,不利于土壤肥力的保持。NPKM和h NPKM处理,土壤有机碳显著增加,年均增加0.360 g·kg~(-1)和0.575 g·kg~(-1),增施有机肥是快速提高灰漠土肥力的重要措施。秸秆还田处理(NKPS),土壤有机碳年均增幅0.006 g·kg~(-1),与NPK处理对比,秸秆还田虽没有大幅度提高土壤有机碳,但维持了土壤肥力。2)较CK,长期化肥有机肥配施(NPKM、h NPKM)显著增加了作物产量(P0.05)。与NP和NPK比较,长期化肥有机肥配施显著提高了小麦产量(P0.05),但玉米产量与施化肥处理差异不显著(P0.05),玉米产量以平衡施肥(NPK)的增幅最高,达到220 kg·hm~(-2)·a~(-1)。小麦的产量变异系数(29.1%~43.9%)高于玉米产量变异(19.0%~32.7%)。化肥配合秸秆还田(NPKS)处理的小麦增产幅度与高量施用有机肥(h NPKM)处理接近,喻示了秸秆还田对作物增产的作用不可忽视。3)碳投入与土壤有机碳和小麦、玉米产量有显著线性正相关(P0.05)。基于以上分析,在干旱区灰漠土增加土壤碳投入(有机肥或秸秆)仍然是最基本的土壤培肥措施。     

Transfer of Cd, Pb, and Zn to water spinach from a polluted soil amended with lime and organic materials

Purpose

The transfer of heavy metals from soil to crops comprises several steps, including soil-to-root and subsequent root-to-shoot tranfer. The purpose of this study was to investigate the different steps of soil-to-crop transfer of Cd, Pb, and Zn.

Materials and methods

This study was carried out with a greenhouse pot experiment using a soil polluted with Cd, Pb, and Zn which was amended with rice straw, pig manure, sheep dung, or peat, with and without lime. Water spinach (Ipomoea aquatica) was used as the test crop and was grown after a season of rice cultivation.

Results and discussion

The results showed that all the amendments promoted the root-to-shoot transfer of Cd, Pb, and Zn. The soil-to-root transfer factors (TFs) of Pb and Zn tended to increase with increasing available Pb and Zn in the soils, while no clear relationship between the TF of Cd and available soil Cd was observed. The root-to-shoot TF of Cd, Pb, and Zn tended to decrease with increasing available amounts in the soils and were negatively correlated with the concentrations of the metals in the roots (r _Cd?=?0.820, r _Pb?=?0.789, r _Zn?=?0.769).

Conclusions

The soil-to-root transfer of Cd, Pb, and Zn was significantly different from the root-to-shoot transfer. The soil-to-root transfer was mainly influenced by the amount of available metal in soil, whereas the root-to-shoot transfer was mainly controlled by the concentrations of the metals in the root.     

Biochar for crop production: potential benefits and risks

Purpose

Biochar, the by-product of thermal decomposition of organic materials in an oxygen-limited environment, is increasingly being investigated due to its potential benefits for soil health, crop yield, carbon (C) sequestration, and greenhouse gas (GHG) mitigation.

Materials and methods

In this review, we discuss the potential role of biochar for improving crop yields and decreasing the emission of greenhouse gases, along with the potential risks involved with biochar application and strategies to avoid these risks.

Results and discussion

Biochar soil amendment improves crop productivity mainly by increasing nutrient use efficiency and water holding capacity. However, improvements to crop production are often recorded in highly degraded and nutrient-poor soils, while its application to fertile and healthy soils does not always increase crop yield. Since biochars are produced from a variety of feedstocks, certain contaminants can be present. Heavy metals in biochar may affect plant growth as well as rhizosphere microbial and faunal communities and functions. Biochar manufacturers should get certification that their products meet International Biochar Initiative (IBI) quality standards (basic utility properties, toxicant assessment, advanced analysis, and soil enhancement properties).

Conclusions

The long-term effects of biochar on soil functions and its fate in different soil types require immediate attention. Biochar may change the soil biological community composition and abundance and retain the pesticides applied. As a consequence, weed control in biochar-amended soils may be difficult as preemergence herbicides may become less effective.