Effects of successive soil freeze-thaw cycles on nitrification potential of soils

Abstract

In our previous report (Yanai et al. 2004: Soil Sci. Plant Nutr., 50, 821–829), we demonstrated that soil freeze-thaw cycles caused a partial sterilization of the soil microbial communities and exerted limited effects on the potential of organic matter decomposition of soils. In the present study, the effects of soil freeze-thaw cycles on the nitrification potential of soils were examined and the impacts of the freeze-thaw cycles on the nitrifying communities were analyzed. Samples of surface soils (0 to 10 cm depth) were collected, from tropical arable land sites, temperate forest, and arable land sites~ Nitrification potential was assayed by the incubation of soils with or without the addition of 200 fig N of ammonium sulfate per g soil to reach a moisture content adjusted to 60% of maximum water-holding capacity at 27~wC following four successive soil freeze-thaw cycles (-13 and 4°C at 12 h-intervals). Nitrification potential of the soils, in which the decrease in the microbial biomass following the freeze-thaw cycles was less appreciable, was not inhibited by the soil freeze-thaw cycles. On the other hand, the nitrification potential of the soils, in which the decrease in the microbial biomass following the soil freeze-thaw cycles was relatively more appreciable, was clearly inhibited by the freeze-thaw cycles or was undetectable even in the unfrozen control. Surprisingly, nitrate production in the samples of an arable soil collected from Vietnam was inhibited by the addition of ammonium sulfate, and thus the effects of counter-anions of ammonium salts on the nitrification potential of the soils were examined. Since a much larger amount of nitrate was produced in the Vietnam soil with the addition of ammonium acetate and ammonium hydrogen carbonate than that in the soil with the addition of ammonium sulfate, it was considered that ammonium sulfate inhibited nitrification in the soil. These results indicated that ammonium sulfate may not always be a suitable substrate for estimating the nitrification potential of soils. Relationship between soil physicochemical properties and the effect of the soil freeze-thaw cycles on the nitrification potential was evaluated and it was considered that the soil pH(KCI) was likely to be responsible for the difference in the responses among soils, assuming that the pH values changed in unfrozen water under the frozen conditions of soils.     

干湿循环强度与频度对花岗岩红壤孔隙分布的影响

为探明干湿循环频度与强度对花岗岩红壤孔隙分布的影响,该研究通过测定不同干湿循环条件下土壤水分特征曲线计算孔隙分布,并采用孔隙分形维数量化干湿循环效应对土壤孔隙结构变异的影响。结果表明：干湿循环对＜0.2 μm、＞3～15 μm和＞57 μm三类当量孔隙产生了显著影响。孔隙结构的再分布主要集中于前4次干湿交替之中,其后干湿交替的影响效应随着频度的增加逐渐减小并趋于稳定。随着强度增强,非活性孔隙（＜0.2 μm）和中孔隙（0.2～30 μm）逐渐发育成大孔隙（＞30 μm）。同时,干湿循环强度对大孔隙（＞30 μm）影响显著（P＜0.05）,贡献率达65.2%,而干湿循环频度对非活性孔隙（＜0.2 μm）影响显著（P＜0.05）,贡献率达91.9%。此外,土样孔隙分形维数D经干湿循环后逐渐减小,且与强度呈负相关（R2=0.868）,表明孔隙结构向大孔隙均质化方向发展。研究结果说明季节性降雨干旱引发的干湿循环效应主要影响大孔隙的生成,增强了土体的均质性和导水能力,加剧了岩土体失稳崩塌的风险。     

Characteristics of microbial biomass and soil organic matter in newly reclaimed wetland rice soils

Microbial biomass C, N, total organic C, N and mineralizable N were measured in newly reclaimed wetland sandy loam rice soil with a very low nutrient status. Microbial biomass C increased 5.4–10.4 times due to application of barnyard manure, but decreased drastically to 24–27% during rice cultivation. Organic C and N contents also decreased during cultivation, but to a lesser extent to 59–76%. At the tillering stage of the rice plant, microbial biomass N was highly correlated with mineralizable N (r=0.986).     

Responses of soil organic matter and microorganisms to freeze-thaw cycles

Soil organic matter (SOM) biomarker methods were utilized in this study to investigate the responses of fungi and bacteria to freeze-thaw cycles (FTCs) and to examine freeze-thaw-induced changes in SOM composition and substrate availability. Unamended, grass-amended, and lignin-amended soil samples were subject to 10 laboratory FTCs. Three SOM fractions (free lipids, bound lipids, and lignin-derived phenols) with distinct composition, stability and source were examined with chemolysis and biomarker Gas Chromatography/Mass Spectrometry methods and the soil microbial community composition was monitored by phospholipid fatty acid (PLFA) analysis. Soil microbial respiration was also measured before and during freezing and thawing, which was not closely related to microbial biomass in the soil but more strongly controlled by substrate availability and quality. Enhanced microbial mineralization (CO₂ flush), considered to be derived from the freeze-thaw-induced release of easily decomposable organic matter from microbial cell lyses, was detected but quickly diminished with successive FTCs. The biomarker distribution demonstrated that free lipids underwent a considerable size of decrease after repeated FTCs, while bound lipids and lignin compounds remained stable. This observation indicates that labile SOM may be most influenced by increased FTCs and that free lipids may contribute indirectly to the freeze-thaw-induced CO₂ flush from the soil. PLFA analysis revealed that fungal biomass was greatly reduced while bacteria were unaffected through the lab-simulated FTCs. Microbial community shifts may be caused by freezing stress and competition for freeze-thaw-induced substrate release. This novel finding may have an impact on carbon and nutrient turnover with predicted increases in FTCs in certain areas, because fungi and bacteria have different degradation patterns of SOM and the fungi-dominated soil community is considered to have a higher carbon storage capacity than a bacteria-dominated community.     

冻融循环与沸石掺配对黑土物理性质的影响

冻融循环作用是东北黑土区发生土壤侵蚀的原因之一,施加土壤改良剂是减弱土壤侵蚀的有效方法。该研究以未经冻融循环作用和未经沸石掺配的黑土作为对照,将天然沸石与黑土按不同比例掺配,探究冻融循环作用和沸石掺配对黑土物理性质的影响,研究表明:1)冻融循环作用增大黑土容重、粘聚力、微孔占比、次大孔占比,减小土壤总孔隙度和内摩擦角,沸石掺配可以降低冻融循环作用对除内摩擦角以外土壤物理性质的影响;2)沸石掺配黑土增大黑土容重、粘聚力、内摩擦角、微孔占比,减小土壤总孔隙度,冻融循环作用对沸石掺配黑土的作用会产生负面影响,但是随着沸石掺配比例增大,冻融循环作用的影响减弱。     

Plant biomass influences rhizosphere priming effects on soil organic matter decomposition in two differently managed soils

We used a continuous labeling method of naturally ¹³C-depleted CO₂ in a growth chamber to test for rhizosphere effects on soil organic matter (SOM) decomposition. Two C3 plant species, soybean (Glycine max) and sunflower (Helianthus annus), were grown in two previously differently managed soils, an organically farmed soil and a soil from an annual grassland. We maintained a constant atmospheric CO₂ concentration at 400±5 ppm and δ¹³C signature at −24.4‰ by regulating the flow of naturally ¹³C-depleted CO₂ and CO₂-free air into the growth chamber, which allowed us to separate new plant-derived CO₂-C from original soil-derived CO₂-C in soil respiration. Rhizosphere priming effects on SOM decomposition, i.e., differences in soil-derived CO₂-C between planted and non-planted treatments, were significantly different between the two soils, but not between the two plant species. Soil-derived CO₂-C efflux in the organically farmed soil increased up to 61% compared to the no-plant control, while the annual grassland soil showed a negligible increase (up to 5% increase), despite an overall larger efflux of soil-derived CO₂-C and total soil C content. Differences in rhizosphere priming effects on SOM decomposition between the two soils could be largely explained by differences in plant biomass, and in particular leaf biomass, explaining 49% and 74% of the variation in primed soil C among soils and plant species, respectively. Nitrogen uptake rates by soybean and sunflower was relatively high compared to soil C respiration and associated N mineralization, while inorganic N pools were significantly depleted in the organic farm soil by the end of the experiment. Despite relatively large increases in SOM decomposition caused by rhizosphere effects in the organic farm soil, the fast-growing soybean and sunflower plants gained little extra N from the increase in SOM decomposition caused by rhizosphere effects. We conclude that rhizosphere priming effects of annual plants on SOM decomposition are largely driven by plant biomass, especially in soils of high fertility that can sustain high plant productivity.     

添加无定形铝氧化物对雷竹林土壤有机质矿化的影响

土壤中无定形铝氧化物对有机质的存在有很大的影响,由于雷竹特殊的经营方式导致土壤中有机质快速积累,为了解无定形铝氧化物对土壤中快速积累的有机质分解产生的影响,本文通过往不同种植年限的雷竹林土壤中增加不同量的无定形铝氧化物(0、2、10、20、40 g/kg)以及室内密闭培养法测定CO2的释放量来反映有机质的分解状况,以便了解无定形铝氧化物对快速增加的雷竹林土壤有机质分解的影响,了解集约经营下的雷竹林土壤有机质的变化趋势及稳定性.结果表明,无定形铝氧化物的加入可显著抑制土壤有机质的分解,当无定形铝氧化物的加入量为40 g/kg时,对0年(水稻)、1年、5年、15年雷竹林土壤有机质分解的抑制率分别为56.97%、60.75%、58.87%、44.25%;0年(水稻)土壤加入无定形铝氧化物0、2、10、20、40 g/kg,对有机质分解的抑制效率分别为7.49%、38.04%、50.79%、56.98%.无定形铝氧化物对有机质分解的抑制效率随其加入量的增加而提高,但随土壤有机质含量的增加而下降.     

氨化秸秆还田对土壤孔隙结构的影响

【目的】土壤孔隙性质是土壤结构性的反映,直接影响着土壤的肥力和水分有效性。定量研究氨化秸秆还田对土壤不同大小等级孔隙数量和孔隙分布的影响,可以为土壤培肥提供科学依据。【方法】采用室内试验方法,设置氨化秸秆加入量为土壤总质量的 0(CK)、 0.384%(S1)、 0.575%(S2)、 0.767%(S3)4个处理,室内培养。在培养0、60、120和180 d,取样测定土壤水分特征曲线(SWRC)数据,利用双指数土壤水分特征曲线模型(DE模型,Double-exponential water retention equation),分析氨化秸秆对土壤剩余孔隙、基质孔隙和结构孔隙的影响; 基于DE模型的微分函数,探究不同氨化秸秆处理对土壤孔隙分布的影响。【结果】不同处理的土壤水分特征曲线SWRC实测值和DE模型模拟值之间的均方根误差介于0.0036和0.0041 cm3/cm3之间,R2介于0.998和0.999之间,土壤含水量模拟值和实测值非常接近1 ∶1,表明DE模型可以准确反映添加氨化秸秆后土壤含水量随吸力的变化规律,较准确地估算土壤不同大小等级孔隙数量变化。培养120 d内,氨化秸秆对土壤剩余孔隙、基质孔隙和结构孔隙影响不显著; 培养180 d时,各处理土壤结构孔隙度表现出随着氨化秸秆添加量的增加而增加的趋势; 此时S3对土壤剩余孔隙影响不显著,显著减小了土壤的基质孔隙度(P0.05),极显著地增加了土壤的结构孔隙度(P 0.01)。在孔隙分布中,氨化秸秆促进了土壤已有孔隙向较大孔隙的发育,显著增加了土壤结构孔隙分布数量; 随着氨化秸秆添加量的增加,土壤结构孔隙的分布数量越大,且峰值出现的越早。氨化秸秆增加了土壤中有机质含量; 土壤结构孔隙和总孔隙均与有机质含量呈显著的正相关关系(P 0.05); 有机质可以黏结团聚土壤的矿物颗粒,有效地促进了土壤结构孔隙的发育; 氨化秸秆对土壤孔隙的影响随着时间的进行越来越明显。【结论】氨化秸秆增加了土壤中有机质含量,促进了土壤孔隙结构的发育,增加了土壤的结构孔隙度和总孔隙度,这对改良和培肥土壤、改善土壤耕性具有重要意义。     

The effect of rice straw on the priming of soil organic matter and methane production in peat soils

Rice residue management often leads to increased methane (CH₄) emissions but the outcomes of edaphic and management factors are not always predictable. Rice residue can act as a substrate for CH₄ production; however the role it plays in priming (mineralization) of soil organic matter (SOM) to release additional substrates for CH₄ production are not well established. We anaerobically incubated a highly organic soil with ¹³C-enriched rice straw for 3 months to investigate its priming effect (PE) on SOM and source of C for CH₄ production. Anaerobic decomposition of SOM was accompanied by iron (Fe) reduction with minimal CH₄ production when straw was absent. Straw addition enhanced Fe reduction and increased CH₄ production concurrently with a clear succession of microbial community structure and function assessed with phospholipid fatty acid (PLFA) profiling. The PE on CH₄ production from SOM was strong and positive during the entire experiment. Overall, PE on SOM (CO₂ plus CH₄ production) was slightly positive at the end of the experiment, associated with only a 32% mineralization of the added straw-C (as CO₂ plus CH₄). Straw addition also released large amounts of dissolved organic carbon (DOC) from SOM. Our results suggest that straw addition effects on PE of SOM and CH₄ production can last for a long period of time showing that straw will cause non-linear response in CH₄ production and potentially result in significant losses of soil C as DOC by leaching or direct exports in histosols.     

Effects of soil organic matter on pH-dependent phosphate sorption by soils

Effects of soil organic matter (80M) on P sorption of soils still remain to be clarified because contradictory results have been reported in the literature. In the present study, pH-dependent P sorption on an allophanic Andisol and an alluvial soil was compared with that on hydrogen peroxide (H₂0₂)-treated, acid-oxalate (OX)-treated, and dithionite-citrate- bicarbonate (DCB)-treated soils. Removal of 80M increased or decreased P sorption depending on the equilibrium pH values and soil types. In the H₂O₂ OX-, and DCB-treated soils, P sorption was pH-dependent, but this trend was not conspicuous in the untreated soils. It is likely that 80M affects P sorption of soils through three factors, competitive sorption, inhibition of polymerization and crystallization of metals such as AI and Fe, and flexible structure of metal-80M complexes. As a result, the number of available sites for P sorption would remain relatively constant in the wide range of equilibrium pH values in the presence of 80M. The P sorption characteristics were analyzed at constant equilibrium pH values (4.0 to 7.0) using the Langmuir equation as a local isotherm. The maximum number of available sites for P sorption (Q _max) was pH-dependent in the H₂0₂-, OX-, and DCBtreated soils, while this trend was not conspicuous in the untreated soils. Affinity constants related to binding strength (K) were less affected by the equilibrium pH values, soil types, and soil treatments, and were almost constant (log K ≈ 4.5). These findings support the hypothesis that 80M plays a role in keeping the number of available sites for P sorption relatively constant but does not affect the P sorption affinity. By estimating the Q _max and K values as a function of equilibrium pH values, pH-dependent P sorption was well simulated with four or two adjustable parameters. This empirical model could be useful and convenient for a rough estimation of the pH-dependent P sorption of soils.     

冻融状态和初始含水率对土壤力学性能的影响

冻融状态影响土壤的抗剪强度从而威胁季节性冻土地区的工程安全、边坡稳定以及土壤流失。通过直剪试验测定了不同冻融状态和初始含水率对青藏地区（S1）和北京地区（S2）土体抗剪强度的影响。结果显示,2种土在未冻和已融状态下的抗剪强度相似,且均随着土含水率的增加而减小,但S1土抗剪强度比S2土大7.5%～9.7%;在冻融状态下,S1土抗剪强度随着土含水率的增加而增大,而S2土则随之减小。S1冻融土抗剪强度在低含水率（≤13.5%）时小于未冻土和已融土,而在高含水率（≥24.5%）时则反之;S2冻融土抗剪强度小于未冻土和已融土。在冻融状态下2种测试土的内摩擦角显著小于未冻土和已融土,而黏聚力整体上则大于未冻土和已融土。与未冻土或已融土相比,2种土在冻融状态下的强度相对较低,宜作为季节性冻土地区工程设计以及土壤流失防治的基本状态。     

冻融对土壤分离能力及侵蚀阻力的影响

冻融后坡面为水力侵蚀产沙提供了大量有效物质源,是河道泥沙的主要策源地。该研究利用室内模拟冻融和径流冲刷试验,设置不同冻融循环次数、坡度和流量梯度,分析冻融对土壤分离能力及侵蚀阻力的影响机制。结果表明,冻融条件下,坡度、流量和冻融循环次数均对土壤分离能力有显著影响（P<0.05）,贡献率分别为17.94%、19.96%和18.43%。冻融前后,土壤分离能力基本均随坡度和流量的增加而增大,冻融后的均值（5.28±2.48 g/(cm2·min)）显著大于冻融前（2.39 ±1.71 g/(cm2·min)）,但冻融后的增幅明显小于冻融前。不同坡度和流量条件下,冻融1次后,土壤分离能力均显著增大（P<0.05）,但其随冻融循环次数增加的变化趋势差异较大,只有在坡度与流量同时较小（10°和≤18L/min）或较大（15°和≥18L/min）时,呈显著增大趋势。冻融循环1、5、10次后,土壤细沟可蚀性分别增大1.25、1.66和1.72倍,随冻融次数的增加逐渐趋于稳定;土壤临界剪切力冻融后显著降低,与冻融次数无明显关系。冻融后土壤平均容重、水稳性团聚体和抗剪强度分别降低了6.61 %、24.77 %和21.35 %,土壤孔隙度和三相结构指数变化与之相反。冻融条件下,土壤细沟可蚀性与水稳性团聚体和抗剪强度呈显著负相关关系,而与孔隙度呈显著正相关关系。     

冻融交替对黑土氮素转化及酶活性的影响

以黑土为试验材料,通过室内培养实验,研究了不同冻融循环(-25—5℃、-10—5℃)对黑土氮素转化速率和土壤酶活性的影响。结果表明:随着冻融频次的增加,铵态氮含量和硝态氮含量均逐渐增加。除了中强度冻融(-10—5℃)的土壤铵态氮在培养第1周期内的含量最低外,剩余培养周期内,铵态氮含量均表现为中强度冻融(-10—5℃)高强度冻融(-25—5℃)对照组(5℃);硝态氮含量对不同冻融温度的响应差异显著。与对照组相比较,冻融循环整体上降低了土壤的矿化速率和硝化速率,但实验末期有促进硝化的趋势,不同强度冻融对矿化速率和硝化速率影响显著。受土壤温度和冻融交替的影响,土壤的脲酶活性和转化酶活性均低于对照组,且脲酶活性和转化酶活性均表现为中强度冻融高强度冻融(第1周期除外)。综上,冻融作用对黑土的供氮能力和土壤酶活性具有重要影响。     

A study on decomposition of organic matter and aggregate formation

It is universally accepted that grassland soils have a good crumb structure, and the aggregation of soil particles is mainly attributed to the organic matter supplied from grass roots, and to certain organic aggregating agents accumulated in the decomposition process.     

Effects of deficit irrigation and transplanting methods of irrigated rice on soil physical properties and rice yield

This study evaluated how deficit irrigation and method of transplanting irrigated rice affected soil physical properties in the short term and rice yields under cultivation that did not involve wet levelling (puddling). Field experiments were conducted in 2009 and 2010 at Sakha Agric. Res. Sta., Egypt. Planting methods were as follows: traditional transplanting into flat flooded soil (M₁), transplanting into furrows (M₂) and into beds (M₃). The deficit irrigation treatments were as follows: irrigation every 6 days between transplanting and 2 weeks before harvesting, reference method (I₁), irrigation as in I₁ but with a continuous period of 12 days without irrigation (i.e. one irrigation event missed) at heading (I₂), irrigation as in I₁ but with an event missed at the beginning of tillering and at the start of head development (I₃) and irrigation as in I₁ but with 3 missed events, one each at the beginning of tillering, the start of the head development and panicle initiation (I₄). Results showed that relative to soil conditions before planting, both rice transplanting methods and deficit irrigation decreased soil bulk density, water holding pores percentage, fine capillary pores percentage and soil shear strength, whereas drainable porosity percentage increased. Soil cracked more under the reference treatment than under the other treatments. Rice transplanting into beds and maintaining irrigation every 6 days without any irrigation skip, treatment (I₁ × M₃), appeared appropriate for growing rice. This combination resulted in soil physical properties favourable for plant growth, producing the largest grain and straw yields of all the treatments.     

黄土高原典型土壤全氮和微生物氮剖面分布特征研究

为阐明黄土高原典型土壤全氮和微生物氮含量随土壤类型、土层和土地利用方式变化规律,研究了从北向南依次分布的干润砂质新成土(神木)、黄土正常新成土(延安)和土垫旱耕人为土(杨陵)等典型土壤的全氮和微生物氮含量的变化特征。结果表明,不同土壤类型、不同土层全氮和微生物氮含量存在显著差异。从南到北,全氮和微生物氮含量显著下降(P0.05)。对同一土壤类型,全氮和微生物氮含量在060.cm随土层深度增加下降很明显,60120.cm有轻微下降,120.cm以下低而稳定。微生物氮含量随土壤类型的变化趋势与全氮完全相同,其与土壤全氮、有机碳及微生物碳含量均存在极显著正相关关系(P0.01)。土壤微生物氮与全氮比值变化在0.42%9～.44%之间。虽然土地利用对土壤全氮和C/N比影响不显著,但却显著影响微生物氮含量和微生物氮与全氮的比值;与农田土壤相比,草地土壤微生物氮含量和微生物氮与全氮比值均明显增加。这一结果说明微生物氮含量和微生物氮与全氮比值更能有效、快速地反映土壤质量的变化。     

Effects of organic matter application on microbial biomass and available nutrients in various types of paddy soils

Abstract

The effect of the addition of bromacil (pesticide) or/and a sewage sludge on the urease, phosphatase and dehydrogenase activities of soil was studied. Urease and phosphatase activities increased initially with the addition of bromacil. This effect disappeared after 28 d of soil incubation. The increase in the urease and phosphatase activities caused by the addition of sewage sludge was more pronounced than that of bromacil. The combined addition of sewage sludge and bromacil also led to an increase in the activity of both hydrolases. Dehydrogenase activity was affected negatively by the addition of bromacil and positively by the sewage sludge addition. When sewage sludge and bromacil were added simultaneously, dehydrogenase activity was higher than when sewage sludge alone was added.