Multi-site validation of a soil organic matter model for arable fields based on generally available input data

The paper describes a simplified carbon balance model, derived from the CANDY model, which works in annual time steps requiring only clay content, soil type of the German classification system “Reichsbodenschätzung”, average air temperature and rainfall as site characteristics, a value for organic carbon content as the initial value as well as crop yield and organic matter amendments as management data.The Candy Carbon Balance (CCB) model has been validated using a dataset from 40 long-term experiments situated in Central Europe including 391 treatments with a total number of 4794 C_org observations. Statistical measures to prove model validity were mean error (ME = − 0.001) and root mean square error (RMSE = 0.119). In addition a number of tests were performed to make sure that the model has no systematic error for different types of site conditions and management activities. After this successful validation the CCB model is considered applicable for advisory service for arable fields on a wide range of site conditions. Due to the poor representation of clay soils in this study some more model tests on these soils would be recommendable.     

Long-term fertilization, manure and liming effects on soil organic matter and crop yields

Yield decline or stagnation and its relationship with soil organic matter fractions in soybean (Glycine max L.)–wheat (Triticum aestivum L.) cropping system under long-term fertilizer use are not well understood. To understand this phenomenon, soil organic matter fractions and soil aggregate size distribution were studied in an Alfisol (Typic Haplustalf) at a long-term experiment at Birsa Agricultural University, Ranchi, India. For 30 years, the following fertilizer treatments were compared with undisturbed fallow plots (without crop and fertilizer management): unfertilized (control), 100% recommended rate of N, NP, NPK, NPK+ farmyard manure (FYM) and NPK + lime. Yield declined with time for soybean in control (30 kg ha⁻¹ yr⁻¹) and NP (21 kg ha⁻¹ yr⁻¹) treatments and for wheat in control (46 kg ha⁻¹ yr⁻¹) and N (25 kg ha⁻¹ yr⁻¹) treatments. However, yield increased with time for NPK + FYM and NPK + lime treatments in wheat. At a depth of 0–15 cm, small macroaggregates (0.25–2 mm) dominated soil (43–61%) followed by microaggregates (0.053–0.25 mm) with 13–28%. Soil microbial biomass carbon (SMBC), nitrogen (SMBN) and acid hydrolysable carbohydrates (HCH) were greater in NPK + FYM and NPK + lime as compared to other treatments. With three decades of cultivation, C and N mineralization were greater in microaggregates than in small macroaggregates and relatively resistant mineral associated organic matter (silt + clay fraction). Particulate organic carbon (POC) and nitrogen (PON) decreased significantly in control, N and NP application over fallow. Results suggest that continuous use of NPK + FYM or NPK + lime would sustain yield in a soybean–wheat system without deteriorating soil quality.     

Chemical and microbial properties of semiarid tropical soils of short-term fallows in Burkina Faso,West Africa

In the soudano–sahelian zone of Burkina Faso, the short-term fallow effect on the soil chemical and microbial properties was evaluated. In four farm experiments, two types of fallows were compared with cultivated fields: a natural vegetation fallow and a fallow enriched with Andropogon gayanus. After 5 to 7 years of experiments, soil chemical and microbial characteristics were determined in laboratory for 0–10 cm soil depth. Soil organic carbon (+64%), nitrogen (+35%), microbial biomass (+76%), basal respiration (+141%), and β-glucosidase activity (+86%) were significantly higher in fallows plots than in cultivated fields. The metabolic quotient was not significantly different on fallows compared to the cropped plots. Also, no significant difference was highlighted between natural vegetation fallows and the A. gayanus-enriched one.     

土壤碱溶有机质的测定研究与应用

本文研究了一种土壤供氮能力快速测定方法-土壤碱溶有机质的测定,以及碱溶有机质与常规土壤有机质的相关性、碱溶有机质与植株氮素吸收的相关性及其在测土推荐施肥中的初步应用。选择我国有代表性的潮土、黑土、红壤土样各50个,研究土壤碱溶有机质与常规方法-丘林法测定的土壤有机质的相关性,结果显示二者呈极显著相关（p>0.01）,相关系数R = 0.9345,相关直线回归方程为：土壤有机质（gkg-1） = 3.3265碱溶有机质（gkg-1）+ 6.9389。选择代表我国主要土壤类型的28个土样进行盆栽试验,研究土壤供氮能力测定方法与植株氮素吸收的相关性,结果表明,土壤碱溶有机质与不施氮处理植株吸氮量相关性极显著（相关系数为0.628,p>0.01）,且其相关系数高于土壤有机质和土壤全氮与植株吸氮量的相关系数。虽然土壤碱溶有机质与植株氮素吸收的相关性低于生物培养方法即好气培养2周后土壤矿质氮（硝态氮+铵态氮）与植株氮素吸收的相关性,但土壤碱溶有机质更适合测土推荐施肥实验室高效快速测定的需要,可见碱溶有机质是可浸提的土壤腐殖质,可用比色法快速测定并能较好估测土壤的供氮能力,值得推荐在测土配方施肥实验室应用。     

Incorporation of nitrogen from crop residues into light-fraction organic matter in soils with contrasting management histories

The proportion of N from crop residues entering the light-fraction organic matter (LFOM) pool was investigated in soils with contrasting soil organic matter and microbial characteristics arising from different management histories. A laboratory experiment was conducted in which ¹⁵N-labelled sugar beet, Brussels sprout or ryegrass shoots, which possessed a range of C/N contents, and hence different biochemical qualities, were incorporated into a sandy–loam soil collected from within a field (FC) or from the field margin (FM). Amounts of C and N incorporated into LFOM were determined after 112 days. The FC and FM soils had organic C contents of 0.9% and 2.5%, respectively. Addition of crop residues increased total LFOM N content and reduced its C/N in FC soil but had no effect on total LFOM N or its C/N in FM soil. Ryegrass incorporation into FC was the only treatment in which there was a net increase in LFOM C. Isotopic analysis indicated that more crop-residue-derived N became incorporated into the LFOM N pool in FM relative to FC soil, with per cent crop residue N incorporated ranging from 25.9% to 35.3% in FC and between 38.9 and 68.5 in FM. Incorporation of crop residues had a positive priming effect on pre-existing LFOM N in FM but not FC soil. We conclude that the characteristics of plant material, together with differences in soil organic matter and microbiology resulting from contrasting management, determined the amount of crop residue C and N incorporated into both HFOM and LFOM.     

土壤碱溶有机质的测定研究与应用

研究了一种土壤供氮能力快速测定方法-土壤碱溶有机质的测定,以及碱溶有机质与常规土壤有机质的相关性、碱溶有机质与植株氮素吸收的相关性及其在测土推荐施肥中的初步应用。选择我国有代表性的潮土、黑土、红壤土样各50个,研究土壤碱溶有机质与常规方法-丘林法测定的土壤有机质的相关性,结果显示二者呈极显著相关(p>0.01),相关系数r=0.9345,相关直线回归方程为:土壤有机质(g kg-1)=3.3265μ碱溶有机质(g kg-1)+6.9389。选择代表我国主要土壤类型的28个土样进行盆栽试验,研究土壤供氮能力测定方法与植株氮素吸收的相关性,结果表明,土壤碱溶有机质与不施氮处理植株吸氮量相关性极显著(相关系数为0.628,p>0.01),且其相关系数高于土壤有机质和土壤全氮与植株吸氮量的相关系数。虽然土壤碱溶有机质与植株氮素吸收的相关性低于生物培养方法即好气培养2周后土壤矿质氮(硝态氮+铵态氮)与植株氮素吸收的相关性,但土壤碱溶有机质更适合测土推荐施肥实验室高效快速测定的需要,可见碱溶有机质是可浸提的土壤腐殖质,可用比色法快速测定并能较好估测土壤的供氮能力,值得推荐在测土配方施肥实验室应用。     

The effect of long-term fertilization with organic or inorganic fertilizers on mycorrhiza-mediated phosphorus uptake in subterranean clover

 A pot experiment was conducted with soil from a long-term (74-year) fertilization field experiment to compare the effects of organic and mineral fertilizers on mycorrhiza formation in clover, and mycorrhiza-mediated plant P uptake. Five treatments were selected from the field experiment representing different forms and levels of P. Mycorrhizal effects on plant growth and P uptake were estimated by comparing plants grown in untreated soil containing indigenous arbuscular mycorrhizal (AM) fungi, with plants grown in pasteurized soil. Short-term versus residual effects of fertilizer/manure were also measured by comparing treatments with or without fertilizers added at the start of the pot experiment. Mycorrhiza formation was greatest in soil that had received no P for 74 years, followed by soil having received 30 or 60 Mg ha^–1 farmyard manure (FYM), and soil having received 25 or 44 kg P ha^–1 in NPK fertilizers. Plant growth and P uptake were severely reduced in the absence of AM fungi for all mineral fertilizer treatments. In contrast, plants growing in soil that had received FYM grew equally well or better when non-mycorrhizal. Recent additions of NK fertilizer and FYM had no effect on mycorrhiza formation, while additions of NPK led to reduced colonization. It thus seems that moderate quantities of FYM have less adverse effects on AM than equivalent amounts of nutrients in NPK fertilizers, a phenomenon that is most likely due to a temporal difference in P availability and its gradual release that balance plant demand. Received: 4 November 1999     

长期不同施肥对稻田土壤有机质和全氮的影响

通过对湖南新化、宁乡、株洲、桃江、武岗5个国家级稻田肥力长期定位试验点18年的田间定位试验,研究了不同施肥方式下0-20 cm土层土壤有机质和全N含量的演变规律。结果显示,中量和高量有机肥与化肥配合处理在提高土壤有机质和全N含量方面效果明显优于单施化肥和秸秆还田处理,且随有机肥用量的增加而增加,表明有机肥与化肥配合施用是提高土壤有机质和N素肥力的重要措施。在不同施肥方式下,稻田土壤有机质总体上呈现出上升或者下降的趋势,但在不同的年份会有波动。     

Land use effects on amino sugar signature of chromic Luvisol in the semi-arid part of northern Tanzania

 Characterizing amino sugar signature in particle size separates of tropical soils is important for further understanding the fate of microbial-derived compounds during the decomposition of soil organic matter (SOM) in tropical agroecosystems. We investigated the impact of land-use changes on the nature, amount and dynamics of amino sugars in soil of the semi-arid northern Tanzania. Samples were collected from the uppermost 10 cm of native woodland, degraded woodland, fields cultivated for 3 and 15 years and homestead fields fertilized with animal manure. The amount of glucosamine, galactosamine, mannosamine and muramic acid were determined in bulk soil and size separates. Compared to the native woodland, a 68% and 72% reduction in total amino sugar contents were found in the 3- and 15-year cultivated fields, respectively. Moreover, 39% of the total amino sugar was lost from the degraded woodland. This may be attributed to accelerated decomposition of amino sugars and/or decreasing microbial biomass input under the semi-arid environment following clear-cutting and cultivation. In contrast, only a 20% decline was found from the fields where animal manure had been applied. Most of the amino sugar depletion occurred from the coarse and fine sand-associated SOM. The decline from the silt and clay-bound amino sugar was relatively small, indicating the importance of organo-mineral associations in the stabilization of microbial-derived sugars in this tropical soil. After 15 years of continuous cultivation, the ratio of glucosamine:galactosamine increased from 1.44 to 2.23, while the ratio of glucosamine:muramic acid increased from 14.5 to 26.5 (P<0.05). These results suggest that cultivation may have led to preferential depletion of bacterial-derived amino sugars (muramic acid and galactosamine) compared with fungal-derived glucosamine. Received: 22 June 2000     

Mixing of different mineral soil layers by endogeic earthworms affects carbon and nitrogen mineralization

The effect of the endogeic earthworm species Octolasion tyrtaeum (Savigny) on decomposition of uniformly ¹⁴C-labelled lignin (lignocellulose) was studied in microcosms with upper mineral soil (Ah-horizon) from two forests on limestone, representing different stages of succession, a beech- and an ash-tree-dominated forest. Microcosms with and without lower mineral soil (Bw-horizon) were set-up; one O. tyrtaeum was added to half of them. It was hypothesised that endogeic earthworms stabilise lignin and the organic matter of the upper mineral soil by mixing with lower mineral soil of low C content. Cumulative C mineralization was increased by earthworms and by the addition of lower mineral soil. Effects of the lower mineral soil were more pronounced in the beech than in the ash forest. Cumulative mineralization of lignin was strongly increased by earthworms, but only in the beech soil (+24.6%). Earthworms predominantly colonized the upper mineral soil; mixing of the upper and lower mineral soils was low. The presence of lower mineral soil did not reduce the rates of decomposition of organic matter and lignin; however, the earthworm-mediated increase in mineralization was less pronounced in treatments with (+8.6%) than in those without (+14.1%) lower mineral soil. These results indicate that the mixing of organic matter with C-unsaturated lower mineral soil by endogeic earthworms reduced microbial decomposition of organic matter in earthworm casts.     

黑河中游荒漠绿洲过渡带斑块植被区土壤水分与有机质空间变异特征

以黑河中游荒漠绿洲过渡带斑块植被区土壤为研究对象,对土壤含水量与土壤有机质含量空间变异特征及两者相关性进行研究,并对土壤含水量和土壤有机质含量的空间变异函数模型进行拟合。结果表明:(1)20~40 cm土层的土壤含水量空间变异性最为强烈,C_V=1.780;而40~60 cm土层的土壤有机质含量空间变异性最为强烈,C_V=0.561。(2)0~120 cm土层的土壤含水量空间变异函数理论模型均为指数模型;0~60 cm土层的土壤有机质含量空间变异函数理论模型为纯块金模型;而60~120 cm土层的土壤有机质含量空间变异函数理论模型为指数模型和球状模型。(3)土壤含水量和土壤有机质含量均随土层深度的增加而相应的增加,且二者之间呈显著对数相关关系,R~2=0.9597。     

Soil C, N and crop yields in Alabama's long-term ‘Old Rotation' cotton experiment

The Old Rotation cotton experiment at Auburn, Alabama, is the oldest, continuous cotton experiment in the world (cf. 1896). Long-term cropping systems provide a unique opportunity to observe the effects of 100 years of cropping on soil organic carbon (SOC). The objective of this paper was to summarize limited data on SOC and N cycling in this historic experiment. Soil organic C has been measured on the 13 plots (6 cropping systems) in 1988, 1992 and 1994. Long-term planting of winter legumes with no other source of N applied resulted in higher SOC (9.5 g C kg⁻¹) in the plow layer (0–20 cm depth) compared to continuous cotton with no winter cover crops (4.2 g C kg⁻¹). A 3-year rotation of cotton–winter legumes–corn–small grain–soybean resulted in 12.1 g C kg⁻¹. There was a significant (P<0.05), quadratic cotton yield response (R²=0.54) to increasing SOC. Winter legume cover crops supplied between 90 and 170 kg N ha⁻¹. Where no N has been applied in fertilizer or from a legume crop, annual N removal in the cotton crop is around 13 kg ha⁻¹, about the same as that fixed in precipitation.     

Impact of cultivation and sugar-cane green trash management on carbon fractions and aggregate stability for a Chromic Luvisol in Queensland, Australia

Technological advances in sugar-cane harvesting and processing is bringing about rapid changes in production systems which could impact on soil physical conditions. An increasing incidence of soil structural decline and depletion of soil carbon levels has increased the risk of soil erosion and crop yield reductions. Soil carbon (C) and aggregate stability were studied on a sugar-cane (Saccharum officinarum L.) green trash blanket trial that had been established on a Chromic Luvisol soil at Mackay, Qld, Australia in 1992. The experiment consisted of blocks with two blocks being harvested early and the remaining two blocks harvested late in the crushing season. Within each block, treatment combinations of trash burnt or green trash blanket, which are either cultivated between rows or not cultivated after harvest, were included. Cropping and cultivation of the soil reduced the different C fractions in the surface 0–100 mm layer by 66–67% when compared to an adjacent uncropped reference soil. The labile C (C_L) concentration was 11% lower in the burnt treatment compared to the trash returned treatment but the opposite was found for total C (C_T). After four years, the no cultivation treatment had higher concentrations of all C fractions measured, compared to the cultivated treatment. When compared to the uncropped reference soil, cropping resulted in marked reductions in aggregate mean weight diameter (MWD) and aggregates >250 μm and an increase in aggregates <125 μm determined by both immersion and tension wetting. The return of the green trash resulted in a 30% greater MWD and a 28% increase in aggregates >250 μm and an 18% reduction in aggregates <125 μm compared to the burnt treatment when immersion wetting was used. Four years of cultivation reduced the MWD, as determined by immersion wetting, by 26% compared to the no cultivation treatment. No significant correlations were found between any measured C fraction and aggregate stability. This study indicates that sustainable sugar-cane cropping systems will likely be those where cultivation is kept to a minimum and trash is retained in the system.     

长期三熟制下谷物产量和土壤氮磷钾及有机质性状的演化

自1973年10月起在麦稻稻三熟制下连续进行了26年定位试验。结果表明,长期配施N肥和猪厩肥可以实现谷物的持续增产,保持土壤有机质的持续增长,并培肥土壤,有机质达到60g/kg的高水平。稻田土壤的有机质数量演化可以幂指数方程表示。土壤N素平衡有余,全N大幅度增加,而有效N的增长差距巨大。全K和速效K显著下降,缓效K变化不大。全P在平衡或盈余时有效P大幅提高。     

土壤含水量对反射光谱法预测红壤土壤有机质的影响研究

研究土壤含水量对有机质预测的影响,可为野外红壤有机质快速测定提供理论依据。本文在实验室条件下测量了不同含水量红壤的可见光-近红外光谱反射率,运用偏最小二乘回归(PLSR)建立不同含水量的土壤有机质预测模型。结果显示,随土壤含水量的增加,有机质与一阶微分光谱的相关性先增加后下降,含水量为100～150 g/kg时相关系数最大。分380～2 400、380～1 300、1 300～2 400 nm三个波段建立不同含水量的有机质预测模型,模型预测精度均随土壤含水量增加而呈现先增加后下降的趋势。利用1 300～2 400 nm建立有机质预测模型可以有效避开氧化铁影响,建立的模型预测精度最高。本研究认为,当土壤含水量小于200 g/kg时,可以利用在室内控制条件下测定的土壤反射率,建立1 300～2 400 nm波段的PLSR模型,进行红壤土壤有机质含量预测。