Effect of Fertilizer Nitrogen (N) on Soil Organic Carbon,Total N,and Soil pH in Long-Term Continuous Winter Wheat (Triticum Aestivum L.)

Carbon sequestration via sound agronomic practices can assist in combating global warming. Three long-term experiments (Experiment 502, Experiment 222, and The Magruder Plots) were used to evaluate the effect of fertilizer nitrogen (N) application on soil organic carbon (SOC), total nitrogen (TN), and pH in continuous winter wheat. Soil samples (0–15 cm) were obtained after harvest in 2014, analyzed, and compared to soil test results from these experiments in 1993. Soil pH decreased with increasing N fertilization, and more so at high rates. Nitrogen application significantly increased TN in Experiment 502 from 1993 to 2014, and TN tended to be high at high N rates. Fertilizer N significantly increased SOC, especially when N rates exceeded 90 kg ha^?1. The highest SOC (13.1 g kg^?1) occurred when 134 kg N ha^?1 was applied annually. Long-term N application at high rates increased TN and SOC in the surface soil.     

长期施用化肥对我国南方水田表土有机碳含量的影响

利用meta分析研究水田土地利用方式下化肥对土壤有机碳含量的影响。结果显示:长期施用化肥处理的表层水稻土土壤有机碳含量较不施肥处理显著提高1.00±0.23 g kg-1,是不施肥处理的1.06倍±1.01倍。分析认为施肥处理下,较高的根系生物量导致较高的碳输入水平,另外相对充足的养分供应提高土壤固碳效率,这是施肥处理下土壤具有较高有机碳含量的两个原因。但不同轮作制度下,化肥对有机碳含量提升作用有差异:稻-稻-旱轮作制下化肥的作用不显著,而稻-旱轮作与稻-稻轮作制度下化肥对有机碳含量的提升作用显著。方差分析发现相同施肥措施下,稻-稻-旱轮作体系下土壤有机碳含量在三种轮作制度中最高,而稻-旱轮作与稻-稻轮作没有显著差异。尽管施用化肥能增加土壤有机碳含量,但评价施用化肥对温室效应的影响还需要综合考虑化肥生产、运输与施用过程中的温室气体排放三要素。     

A review of nitrogen fertilizer and conservation tillage effects on soil organic carbon storage

Abstract. The effects of nitrogen fertilizer and tillage systems on soil organic carbon (SOC) storage have been tested in many field experiments worldwide. The published results of this research are here compiled for evaluation of the impact of management practices on carbon sequestration. Paired data from 137 sites with varying nitrogen rates and 161 sites with contrasting tillage systems were included. Nitrogen fertilizer increased SOC but only when crop residues were returned to the soil; a multiple regression model accounted for just over half the variance (R²=0.56, P=0.001). The model included as independent variables: cumulative nitrogen fertilizer rate; rainfall; temperature; soil texture; and a cropping intensity index, calculated as a combination of the number of crops per year and percentage of corn in the rotation. Carbon sequestration increased as more nitrogen was applied to the system, and as rainfall or cropping intensity increased. At sites with higher mean temperatures and also in fine textured soils, carbon sequestration decreased. When the carbon costs of production, transportation and application of fertilizer are subtracted from the carbon sequestration predicted by the model, it appears that nitrogen fertilizer‐use in tropical regions results in no additional carbon sequestration, whereas in temperate climates, it appears to promote net carbon sequestration. No differences in SOC were found between reduced till (chisel, disc, and sweep till) and no‐till, whereas conventional tillage (mouldboard plough, disc plough) was associated with less SOC. The accumulation of SOC under conservation tillage (reduced and no till) was an S ‐shape time dependent process, which reached a steady state after 25–30 years, but this relationship only accounted for 26% of the variance. Averaging out SOC differences in all the experiments under conservation tillage, there was an increase of 2.1 t C ha^?1 over ploughing. However, when only those cases that had apparently reached equilibrium were included (all no till vs. conventional tillage comparisons from temperate regions), mean SOC increased by approximately 12 t C ha^?1. This estimate is larger than others previously reported. Carbon sequestration under conservation tillage was not significantly related to climate, soil texture or rotation.     

Effect of land‐use on soil nutrients and microbial biomass of an alpine region on the northeastern Tibetan plateau,China

Land‐use patterns affect the quantity and quality of soil nutrients as well as microbial biomass and respiration in soil. However, few studies have been done to assess the influence of land‐use on soil and microbial characteristics of the alpine region on the northeastern Tibetan plateau. In order to understand the effect of land‐use management, we examined the chemical properties and microbial biomass of soils under three land‐use types including natural grassland, crop‐field (50 + y of biennial cropping and fallow) and abandoned old‐field (10 y) in the area. The results showed that the losses of soil organic carbon (SOC) and total nitrogen (TN) were about 45 and 43 per cent, respectively, due to cultivation for more than 50 y comparing with natural grassland. Because of the abandonment of cultivation for about a decade, SOC and TN were increased by 27 and 23 per cent, respectively, in comparison with the crop field. Microbial carbon (ranging from 357·5 to 761·6 mg kg⁻¹ soil) in the old‐field was intermediate between the crop field and grassland. Microbial nitrogen (ranging from 29·9 to 106·7 mg kg⁻¹ soil) and respiration (ranging from 60·4 to 96·4 mg CO₂‐C g⁻¹ C_mic d⁻¹) were not significantly lower in the old‐field than those in the grassland. Thus it could be concluded that cultivation decreased the organic matter and microbial biomass in soils, while the adoption of abandonment has achieved some targets of grassland restoration in the alpine region of Gansu Province on the northeastern Tibetan plateau. Copyright © 2010 John Wiley & Sons, Ltd.     

Dynamics of Soil Moisture,pH, Organic Carbon,and Nitrogen Under Switchgrass Cropping in a Semiarid Sandy Wasteland

Switchgrass (Panicum virgatum L.) is a perennial biofuel crop with a high production potential and suitable for growth on marginal land. This study investigates the long-term planting effect of switchgrass on the dynamics of soil moisture, pH, organic carbon (SOC), total nitrogen (TN), nitrate nitrogen (NO₃^–-N) and ammonium nitrogen (NH₄⁺-N) for soils to a depth of 90-cm in a sandy wasteland, Inner Mongolia, China. After crop harvesting in 2015, soil samples were collected from under switchgrass stands established in 2006, 2008, and 2009, native mixture, and a control that was virgin sand. Averaged across six layers, soil moisture and pH was significantly higher under the native mixture than switchgrass or virgin sand. However, SOC and TN were significantly higher under the 2006 switchgrass stand when compared with all other vegetation treatments and the control. The SOC and TN increased from 2.37 and 0.26 g kg^?1, respectively, for 2009 switchgrass stand, and to 3.21 and 0.42 g kg^?1, respectively, for 2006 switchgrass stand. Meanwhile, SOC and TN contents were 2.51 and 0.27 g kg^?1, respectively, under the native mixture. The soil beneath switchgrass and native mixture showed the highest NO₃^–-N and NH₄⁺-N, respectively. The soil moisture increased with depth while SOC, TN, and NO₃^–-N decreased. An obvious trend of increasing moisture, SOC, TN, and mineral N was observed with increasing switchgrass stand age. Thus, growing switchgrass on sandy soils can enhance SOC and TN, improve the availability of mineral N, and generate more appropriate pH conditions for this energy cropping system.     

Land-use effects on soil carbon and nitrogen in a typical plateau lakeshore wetland of China

Wetland soils (WS) can store a significant amount of soil organic carbon (SOC) and total nitrogen (TN). Surface soils (0–20 cm) were sampled in WS, 20-yr-old conventionally tilled soils (CTS20), 2-yr-old abandoned tilled soils (ATS2), and 6-yr-old abandoned tilled soils (ATS6) to estimate changes in SOC and TN contents due to cultivation and abandonment. Our results showed that SOC and TN contents were significantly higher in WS than those in CTS20, ATS2, and ATS6. As a result of 20-yr cultivation, SOC and TN contents decreased from 43.75 to 24.06 g kg^?1 and from 4.96 to 2.32 g kg^?1, respectively. However, after the abandonment of cultivated wetlands, SOC and TN contents showed a slow increase but the change was not significant among CTS20 and ATS2. The findings of this study suggest that SOC and TN contents in top 20 cm soils of wetlands can be reduced significantly by cultivation, but they are restored slowly after abandonment.     

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.     

碳氮添加对雨养农田土壤全氮、有机碳及其组分的影响

为探明碳氮添加4年后,土壤全氮、有机碳及其组分(可溶性有机碳、微生物量碳、轻组和重组有机碳)的变化特征,依托布设于甘肃省定西市安定区李家堡镇的不同碳源配施氮素田间定位试验,涉及秸秆、生物质炭、氮素3个因素,秸秆设置为不施、施用秸秆2水平;生物质炭为不施和施用生物质炭2个水平;氮素设置为不施氮、施纯氮50 kg/hm^2、施纯氮100 kg/hm^2 3个水平,共9个处理。结果表明:不同处理下土壤全氮、有机碳及其组分的含量均随土层的加深而降低。添加生物质炭对土壤全氮、有机碳及其组分均具有不同程度的提升效应。添加秸秆对土壤全氮、有机碳和可溶性有机碳、微生物量碳、轻组有机碳均具有显著提升效应,仅在0-5 cm土层对重组有机碳有显著提高。添加氮素可显著提升土壤全氮、有机碳和可溶性有机碳、微生物量碳、轻组有机碳含量。较其他处理,添加生物质炭对土壤全氮、有机碳和重组有机碳的提升效应最高,添加秸秆对可溶性有机碳、微生物量碳、轻组有机碳的提升效果最优。从提升土壤质量的角度出发,推荐秸秆配施氮素模式,该模式下土壤碳素有效性高、易于被微生物利用,有利于作物生长。从提高土壤固碳角度考虑,推荐生物质炭配施氮素模式,该模式有利于碳的封存。     

Effects of gravel on grassland soil carbon and nitrogen in the arid regions of the Tibetan Plateau

Many previous studies have focused on soil gravel concentrations and their effect on crop yields in agricultural systems. The extent of carbon and nitrogen sequestration in soils under steppe systems in relation to surface gravel mulch remains largely unexplored. This study investigated the effects of gravel mulches on soil organic carbon and total nitrogen stocks in the arid and windy regions of the Tibetan Plateau. Surface gravel mulches provide a more favorable environment for soil carbon and nitrogen stocks than do non-mulched sites. Soil organic carbon and total nitrogen stocks were highest (46.9 Mg ha^− 1 SOC and 2.8 Mg ha^− 1 TN) in the medium gravel mulch sites with ~ 40-50% gravel, and lowest (29.5 Mg ha^− 1 SOC and 1.4 Mg ha^− 1 TN) in no gravel mulch sites. Analysis of aggregate size fractions indicated that the vast majority of SOC was present in microaggregate fractions throughout the top 30 cm of soil. Considering the low level of soil disturbance in the study area, the carbon contained in the macroaggregate fraction might become stabilized in the soil. Gravel mulches above the soil surface have an important bearing on soil carbon sequestration as they control wind erosion, decrease soil surface evaporation and change soil physical behavior in the arid and semiarid regions.     

Soil Carbon Sequestration in Long-Term Fertilization Under Jute-Rice-Wheat Agro-Ecosystem

Soil organic carbon (SOC) sequestration in response to long-term fertilizer management practices under jute-rice-wheat agro-ecosystem in alluvial soils was studied using a modeling approach. Fertilizer management practices included nitrogen (N), phosphorus (P) and potassium (K) fertilization, manure application, and root-stubble retention of all three crops. Soil carbon (C) model RothC was used to simulate the critical C input rates needed to maintain initial soil C level in long timescale (44 years). SOC change was significantly influenced by the long-term fertilizer management practices and the edaphic variable of initial SOC content. The effects of fertilizer combination “100%NPK+FYM” on SOC changes were most significant over “100%NPK” fertilization. If the 100% NPK fertilizer along with manure applied with stubble and roots retention of all crops, alluvial soils of such agro-ecosystem would act as a net C sink, and the average SOC density kept increasing from 18.18 Mg ha^?1 during 1972 to the current average of ～22 Mg ha^?1 during 2065 s. On an average, the critical C input was estimated to be 5.30 Mg C ha^?1 yr^?1, depending on local soil and climatic conditions. The critical C input could be effectively estimated using a summary model driven by current SOC level, mean annual temperature, precipitation, and soil clay content. Such information will provide a baseline for assessing soil C dynamics under potential changes in fertilizer and crop residues management practices, and thus enable development of management strategies for effectively mitigating climate change through soil C sequestration.     

Carbon sequestration dynamic,trend and efficiency as affected by 22‐year fertilization under a rice–wheat cropping system

The maintenance and accumulation of soil organic carbon (SOC) in agricultural systems is critical to food security and climate change, but information about the dynamic trend and efficiency of SOC sequestration is still limited, particularly under long‐term fertilizations. In a typical Purpli‐Udic Cambosols soil under subtropical monsoon climate in southwestern China this study thus estimated the dynamic, trend and efficiency of SOC sequestration after 22‐year (1991–2013) long‐term inorganic and/or organic fertilizations. Nine fertilizations under a rice–wheat system were examined: control (no fertilization), N, NP, NK, PK, NPK, NPKM (NPK plus manure), NPKS (NPK plus straw), and 1.5NPKS (150% NPK plus straw). Averagely, after 22‐years SOC contents were significantly increased by 4.2–25.3% and 10.2–32.5% under these fertilizations than under control conditions with the greatest increase under NPKS. The simulation of SOC dynamic change with an exponential growth equation to maximum over the whole fertilization period predicted the SOC level in a steady state as 18.1 g kg^?1 for NPKS, 17.4 g kg^?1 for 1.5NPKS, and 14.5–14.9 g kg^?1 for NK, NP, NPK, and NPKM, respectively. Either inorganic, organic or their combined fertilization significantly increased crop productivity and C inputs that were incorporated into soil ranging from 0.91 to 4.63 t (ha · y)^?1. The C sequestration efficiency was lower under NPKM, NPKS, and 1.5NPKS (13.2%, 9.0%, and 10.1%) than under NP and NPK (17.0% and 14.4%). The increase of SOC was asymptotical to a maximum with increasing C inputs that were variedly enhanced by different fertilizations, indicating an existence of SOC saturation and a declined marginal efficiency of SOC sequestration. Taken all these results together, the combined NPK plus straw return is a suitable fertilizer management strategy to simultaneously achieve high crop productivity and soil C sequestration potential particularly in crop rotation systems.     

不同施肥措施对旱地采煤塌陷区复垦土壤结构及玉米品质的影响

研究不同施肥措施对复垦土壤结构及玉米品质的影响,以期深入理解采煤塌陷区复垦土壤有机碳固持机制。采集复垦1年的定位试验各处理耕层(0—20 cm)土样以及玉米籽粒,分析土壤水稳性团聚体(>2,0.25~2,0.053~0.25 mm)及粉黏粒组分(<0.053 mm)中有机碳(SOC)及全氮(TN)含量、玉米籽粒蛋白质、淀粉和脂肪含量的变化。试验设不施肥(CK)、施化肥(NPK)、单施有机肥(M)和有机无机肥配施(MNPK)4个处理。结果表明,同CK相比,NPK处理显著提高TN含量、玉米籽粒产量、淀粉和脂肪含量,增幅分别为11.23%,98.53%,1.16%和12.71%;M处理显著提高SOC、TN、>2 mm和0.25~2 mm团聚体中有机碳含量、籽粒产量、蛋白质、淀粉和脂肪含量,增幅分别为44.77%,13.23%,52.73%,60.22%,255.15%,23.28%,1.67%和12.71%;MNPK处理显著提高SOC、TN、各粒径团聚体及粉黏粒组分中SOC和TN含量(除0.25~2 mm团聚体中TN含量)、玉米籽粒产量、蛋白质、淀粉和脂肪含量,增幅分别为46.21%,29.08%,39.23%(>2 mm-C),49.07%(0.25~2 mm-C),110.41%(0.053~0.25 mm-C),40.35%(<0.053 mm-C),22.48%(>2 mm-N),43.29%(0.053~0.25 mm-N),33.33%(<0.053 mm-N),211.37%,35.34%,0.48%和25.18%。表明当养分投入量相同时,有机无机肥配施(MNPK)有利于采煤塌陷区复垦土壤团聚体对有机碳的物理保护,增加土壤有机碳累积,提升土壤肥力,提高作物产量,改善作物品质。     

Soil Organic Carbon Sequestration by Long-Term Application of Manures Prepared from Trianthema portulacastrurm Linn

ABSTRACT

A 6-year field experiment was conducted at Maharashtra, India, from 2011 to 2017 on a silty clay soil, to study the impact of organic manure prepared from common weed Trianthema portulacastrurm Linn. on soybean-fodder maize crop system and soil organic carbon (SOC) sequestration. Organic manures were prepared from Trianthema as compost, vermicompost, dry leaf powder and were compared with application of Farm Yard Manure (FYM), chemical fertilizer treatment (NPK), and control. All treatments were repeated to same earlier treated plots every year for subsequent 6 years. Soil samples were analyzed before experiment and after harvesting of crops at the end of 6 years. All organic manures prepared from Trianthema and FYM increased SOC, nitrogen, phosphorus, and potassium content in the soil as compared to chemical fertilizer treatment and control. The overall increase in SOC content in the 0–60-cm soil depth in vermicompost treatment was 3.51 Mg C ha^?1 as compared to control at the end of this 6 years experiment at the carbon sequestration rate of 585 kg ha^?1 year^?1. Preparation and use of different manures from Trianthema will increase the carbon sequestration in soil, a measure to mitigate global warming.     

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.     

Key soil nutrient requirements for different yield levels in North China

ABSTRACT

Soil chemical properties are closely related to crop production levels. Understanding the relationships between soil nutrients and different yield levels is important for improving the efficiency of fertilization management programs. The objectives of this study were to understand the key soil nutrient requirements for different crop yield levels using 10 experimental wheat-maize rotation sites and to optimize fertilization applications in North China. The results found significant differences between the soil chemical properties among the study sites, with average contents in the range of 10.07–14.72 g/kg for soil organic carbon (SOC), 0.38–1.29 g/kg for total nitrogen (TN), 56.43–89.77 mg/kg for available nitrogen (AN), 17.36–48.54 mg/kg for available phosphorus (AP), 79.4–184.5 mg/kg for available potassium (AK), 0.78–5.97 mg/kg for soil Cu, and 0.75–2.20 mg/kg for soil Zn. The soil pH values were 6.46–8.19. Significant correlations (p < 0.05) were found between high-level yields and higher contents of SOC, TN, AN, and AP when a suitable soil pH were present. The higher levels of soil SOC and TN were important for maintaining high-level yields in these regions. Soil AN and pH are two key limitations that could significantly (p < 0.05) improve medium-level yields. Although some soil indicators, including SOC, TN, AN, AP, soil pH, soil Zn, and Cu could significantly influence low-level yields, soil amendments with C, N, and available P and having a suitable soil pH were especially important for improving low-level yields. These results could be used to improve conventional methods of fertilization management and increase the efficiency of fertilizer use in North China.     

黄土丘陵半干旱区人工柠条林土壤固碳特征及其影响因素

为了探讨黄土丘陵区不同生长年限的人工柠条林地土壤有机碳含量的变化特征及其影响因素,更好地阐明黄土丘陵区柠条林土壤的固碳机理,本文采用时空替代法,以撂荒2 a的坡耕地为对照,对黄土丘陵半干旱区不同林龄(10 a、17 a、26 a、34 a、40 a、50 a)人工柠条林地土壤有机碳(SOC)、全氮(STN)、全磷(STP)及柠条林的根系生物量和枯落物现存量进行了分析。结果表明:1)在0~60 cm的土层剖面上,0~20 cm土层SOC含量明显高于其他土层,并随土层深度的增加逐层递减,其中柠条林地0~20 cm土层SOC含量变化幅度为2.68~11.44 g·kg-1,而40~60 cm土层SOC含量仅在1.64~2.73 g·kg-1波动;与对照相比,随林龄增加柠条林地0~60 cm土层平均SOC含量先减小后增加最后趋于平稳:10 a和17 a柠条林SOC含量比对照显著降低了34.5%和26.9%,26 a柠条林的SOC含量显著升高,其值是对照的1.43倍,40 a和50 a柠条林SOC含量处于积累与消耗相对稳定的状态。2)对SOC含量与STN、STP含量及根系生物量和枯落物现存量进行相关性分析表明,SOC含量与STN含量、根系生物量及枯落物现存量之间存在极显著线性相关,但与STP含量相关性不明显,说明土壤中氮含量的增加能明显提高土壤的固碳能力,而根系生物量和枯落物现存量的多少能够决定土壤的固碳水平。     

Soil Organic Carbon and Nitrogen Fractions under Different Land Uses and Tillage Practices

Many questions have surfaced regarding long-term impacts of land-use and cultivation system on soil carbon (C) sequestration. The experiment was conducted at Ohio Agricultural Research and Development Center. Only minor variations of soil organic carbon (SOC) and nitrogen (N) fractions with depth under plow tillage (PT). The SOC, total nitrogen (TN), microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) concentrations were higher under grassland and forestland in the top 0–15 cm depth than arable soils. No-tillage (NT) also increased SOC and N fractions concentrations in the surface soils than PT. Compared to arable, grass and forest could significantly improve proportions of MBC and MBN, and reduce proportions of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON). NT and forest also increased the ratio of SOC/TN, MBC/MBN, and DOC/DON. Overall, grass and forest provided more labile C and improved C sequestration than arable. So did NT under arable land-use.     

Long-term effects of recommended management practices on soil carbon changes and sequestration in north-eastern Italy

Management practices can have significant implications for both soil quality and carbon (C) sequestration potential in agricultural soils. Data from two long‐term trials (one at field scale and the other at lysimeter scale), underway in north‐eastern Italy, were used to evaluate the dynamics of soil organic carbon (SOC) and estimate the impact of recommended management practices (RMPs) on soil carbon sequestration. Potential SOC sequestration was calculated as the differences between the change in SOC of treatments differing only for the specified RMP for a period of at least 25 years. The trials compared the following situations: (a) improved crop rotations versus monoculture; (b) grass versus improved crop rotations; (c) residue incorporation versus residue removal; (d) high versus low rates of inorganic fertilizers; (e) integrated nutrient management/organic manures versus inorganic fertilizers. At the lysimeter scale, some of these treatments were evaluated in different soils. A general decrease in SOC (1.1 t C ha^?1 year^?1) was observed after the introduction of intensive soil tillage, evidencing both the worsening of soil quality and the contribution towards global CO₂ emissions. Initial SOC content was maintained only in permanent grassland, complex rotations and/or with the use of large quantities of livestock manure. SOC sequestration reached a maximum rate of 0.4 t C ha^?1 year^?1 comparing permanent grassland with an improved crop rotation. Crop residue incorporation and rates of inorganic fertilizer had less effect on SOC sequestration (0.10 and 0.038 t C ha^?1 year^?1, respectively). The lysimeter experiment highlighted also the interaction between RMPs and soil type. Peaty soil tended to be a source of C independent of the amount and quality of C input, whereas a proper choice of tillage practices and organic manures enhanced SOC sequestration in a sandy soil. The most promising RMPs in the Veneto region are, therefore, conversion to grassland and use of organic manures. Although some of these RMPs are already supported by the Veneto Region Rural Development Plan, their more intensive and widespread implementation requires additional incentives to become economically feasible.     

不同培肥措施下种植制度及撂荒对土壤微生物量碳氮的影响

以黄土高原南部半湿润易旱区已进行17年的田间定位试验为研究对象,研究了不同培肥措施(不施肥、施用氮磷钾及氮磷钾与有机肥配合施用)下两种种植制度(一年1熟及一年两熟)和撂荒对土壤微生物量碳、氮(SMBC、SMBN)及可溶性有机碳、氮(SOC、SON)等含量的影响.结果表明,与一年1熟的小麦一休闲种植制度相比,一年两熟小麦一玉米轮作提高了0～10 cm土层SMBC、SMBN、有机碳(TOC)、全氮(TN)和土壤SOC、SON的含量,而对10～20 cm土层上述测定指标影响不大.与不施肥(CK)或单施化肥处理(NPK)下小麦-休闲和小麦-玉米轮作方式相比,撂荒处理显著提高了0～10 cm土层各测定指标的含量.不同培肥措施相比,氮磷钾配施有机肥显著提高了0～10 cm、10～20 cm土层SMBC、SMBN含量;NPK处理0～10 cm土层SMBN含量显著增加,10～20 cm土层SMBN和0～10 cm、10～20 cm土层SMBC含量增加但未达显著水平.不同培肥措施和种植制度对SMBC/TOC和SMBN/TN的比例无明显影响.     

施肥对灌漠土作物产量、土壤肥力与重金属含量的影响

有机物还田是提升土壤肥力的主要措施,但也存在造成土壤金属污染的潜在风险。为查明不同有机物还田对土壤质量及作物产量的影响,本文通过长期定位试验,研究了无肥对照、常规施化肥(氮磷配施)以及70%常规化肥与牛粪、沼渣、污泥、鸡粪、菌渣和猪粪配施对土壤理化性状、有机碳和氮的固存率、氮磷钾活化系数、作物产量及重金属含量的影响。结果表明:牛粪、沼渣、污泥、菌渣、鸡粪和猪粪与70%化肥配施虽作物产量与常规施化肥相似,但6种有机物处理土壤有机质、全氮和碱解氮含量都较常规施化肥处理显著增加,污泥、鸡粪和猪粪处理土壤全磷与速效磷含量较常规施化肥处理显著增加,而且牛粪、沼渣、鸡粪和猪粪处理的速效钾、土壤磷活化系数和土壤钾活化系数较常规施化肥处理也显著提升。牛粪、沼渣、污泥、菌渣、鸡粪和猪粪处理土壤有机碳固存率为36.42%～71.61%,较常规施化肥处理都显著提高;而其氮固存率为6.47%～49.44%,仅有菌渣处理与常规施化肥处理差异不显著,而其他处理较常规施化肥处理显著增加。长期施鸡粪和菌渣处理的土壤铜含量较常规施化肥处理显著增加,增加量分别为4.17mg·kg~(-1)和14.2mg·kg~(-1);而污泥、鸡粪和菌渣处理的土壤锌含量较常规施化肥处理显著增加,增加量分别为13.53 mg·kg~(-1)、22.60 mg·kg~(-1)和49.73mg·kg~(-1)。综上,等有机质(4 500kg×hm~(-2))的牛粪、沼渣、污泥、菌渣、鸡粪和猪粪可替代30%氮磷肥,作物产量不受影响;不同有机物培肥土壤效果为污泥、鸡粪和猪粪优于牛粪和沼渣,而沼渣的培肥效果略差。为保证土壤环境质量稳定不恶化,种植小麦时有机物铜和锌的年携入量应分别低于53.01g×hm~(-2)和221.30 g×hm~(-2),而种植玉米时应分别低于153.40 g×hm~(-2)和347.04 g×hm~(-2)。