Structure and self-similarity in silty and sandy soils: the fractal approach

Soil structure was studied using the concept of fractals and related to soil texture and aggregate properties such as surface charges and aggregate stability. The mass and porosity fractal dimensions (D_m and D_p) of silty and sandy soils were determined on in situ soils using a variety of soil sections (thin, very-thin and ultra-thin), by image analysis on a continuous scale from m to 10^?9 to 10^?1m. Surface fractal dimensions (D_s) of these soils were determined on < 2 mm air-dried samples using mercury porosimetry and the fractal cube generator model. The results suggest that soils are not pore fractals but mass and surface fractals with D_m= 1.1 D_s when the dimension of the embedding Euclidean space d is 3. The soil structures could possibly be described by fractal diffusion-limited aggregation with complex interconnected aggregates or by fractal cluster–cluster aggregation models. As a preliminary conclusion, the fractal approach appears to be a potentially useful tool for understanding the underlying mechanisms in the creation or destruction of soil structure.     

Effects of alternative tillage systems on soil quality and yield of spring cereals on silty clay loam and sandy loam soils in the cool, wet climate of central Norway

Tillage trials were established on a poorly drained silty loam overlying silty clay loam and on a freely drained sandy loam overlying medium sand, in 1988 and 1989, respectively. Autumn and spring ploughing and two ploughless systems were compared for 12–13 years, with three replications at each site. The ploughless treatments comprised deep versus shallow spring harrowing until 1999, and thereafter autumn plus spring harrowing versus spring harrowing only. In 6 years, treatments with and without fungal spraying of the cereal crops were included. In other years, fungicides were not used. Perennial weeds were controlled by herbicides as necessary, on nine occasions up until 2001. Average spring barley (Hordeum vulgare L.) and spring oat (Avena sativa L.) yields were similar with spring ploughing as with autumn ploughing at both sites. In treatments without ploughing, average yields on the silty loam over clay were 93% of those obtained with ploughing, and on the sandy loam over sand they were 81%. Smaller and non-significant yield differences were found between spring harrowing versus deep spring harrowing, and between autumn plus spring harrowing versus spring harrowing only. Fungal spraying increased yields markedly at both sites (25%), but there was no significant interaction between this treatment and tillage system. Oat was compared with barley in 2 years, with oat performing better under ploughless tillage. At both sites increases in penetrometer resistance occurred in the topsoil of unploughed treatments. These were considered particularly limiting on the sandy loam. On the silty loam there was an increase in surface horizon porosity in the absence of ploughing, which was associated with an increase in topsoil organic matter content. On this soil there was also a tendency toward lower penetrometer resistance at >30 cm depth on autumn plus spring harrowed soil than on ploughed soil, indicating that the plough pan may have diminished. This was supported by observations of greater earthworm activity on unploughed soil. Soil chemical analyses revealed that mineral N and plant-available P and K accumulated in the upper horizon under ploughless tillage. The percentage yields obtained in individual years with autumn as opposed to spring ploughing, were positively correlated with air temperature during 0–4 weeks after planting on the silty loam, and with precipitation during 0–12 weeks after planting on the sandy loam. In the case of yields obtained with spring harrowing only, relative to spring ploughing, positive correlations were found with 0–4 week temperature on both soil types, suggesting that low early season temperatures may limit yields under ploughless tillage.     

Crust formation on sandy soils in the Sahel I. Rainfall and infiltration

Sandy soils of the Sahel area in West Africa, mainly cropped to millet (Pennisetum typhoides) are very sensitive to crust formation. Crusts strongly reduce infiltration capacity. In this area most fields are gently sloping (1–3%) and hence runoff is a widespread phenomenon; on the average 25% of the rain (mainly in the form of a few large storms during the rainy season) is lost by runoff. The causes of crust formation and its effect on the infiltration rate are discussed. On untilled soils the presence of a crust is a permanent feature. Rainfall characteristics play a key role in crust formation. Major rainfall characteristics of the Sahel differ significantly from those of other semi-arid areas.     

Effects of tillage and application of cattle slurry on carbon pools and aggregate distribution in temperate grassland soils

The objective was to study the effects of tillage and cattle slurry application on organic C dynamics in grassland soils. Treatments included long‐term grassland and reinstalled grassland (after tillage and winter wheat cropping) with and without cattle slurry application (240 kg N ha^–1 y^–1). A period of 4 y slurry application sufficed to increase microbial activity 1.6‐fold in surface soil (0–10 cm). Tillage affected aggregate distribution and basal respiration in the surface soil.     

挪威北部土壤微生物活性的季节变化

Seasonal development of soil microbial activity and bacterial biomass in sub-polar regions was investigated to determine the impacts of biotic and abiotic factors, such as organic matter content, temperature and moisture. The study was performed during spring thaw from three cultivated meadows and two non-cultivated forest sites near Alta, in northern Norway. Samples from all five sites showed increasing respiration rates directly after the spring thaw with soil respiration activity best related to soil organic matter content. However, distributions of bacteria] biomass showed fewer similarities to these two parameters. This could be explained by variations of litter exploitation through the biomass. Microbial activity started immediately after the thaw while root growth had a longer time lag. An influence of root development on soil microbes was proposed for sites where microorganisms and roots had a tight relationship caused by a more intensive root structure. Also a reduction of microbial activity due to soil compaction in the samples from a wheel track could not be observed under laboratory conditions. New methodological approaches of differential staining for live and dead organisms were applied in order to follow changes within the microbial community. Under laboratory conditions freeze and thaw cycles showed a damaging influence on parts of the soil bacteria. Additionally, different patterns for active vs. non-active bacteria were noticeable after freeze-thaw cycles.     

陕北沙区不同利用方式风沙土的养分特征

通过分析陕北沙区榆林市不同利用方式形成的流动风沙土、半固定风沙土、固定风沙土(紧沙土)和由人类生产活动形成的耕种固定风沙土、耕灌固定风沙土的养分特征,发现随着植被的增加,流动沙丘逐渐被固定,流动风沙土、半固定风沙土、固定风沙土含有较多养分的细颗粒增多使表层养分逐渐增加。耕种固定风沙土由于生产活动,加速了土壤有机质的矿化,使土壤有机质、氮素含量降低;而磷肥的使用,使土壤有效磷增加。耕灌固定风沙土作为当地的基本农田受人类活动影响,引水拉沙,增加土壤细颗粒含量,且大量施肥,使这种土壤的肥力有了较大地提高。     

Using time domain reflectometry to characterize cattle and pig slurry infiltration into soil

Abstract. The rate and extent to which cattle or pig slurry infiltrates into soil after application is one of the important factors determining the rate and extent of subsequent ammonia (NH₃) volatilization. Better characterization of the infiltration process is required to improve predictive models of NH₃ losses after land spreading. This paper describes a laboratory system using time domain reflectometry to measure slurry infiltration into soil columns. This system enabled semi-continuous, non-destructive infiltration measurements to be made, assessing the influence of slurry type, dry matter (DM) content, soil type and soil water tension. Differences were noted in the infiltration behaviour of cattle and pig slurries. For cattle slurry, DM content (range 1.7–7.1%) was the main influencing factor. Infiltration rate rapidly decreased with increasing DM content and there was no influence of soil type or water tension. For pig slurry, all of the slurry infiltrated into a sandy clay loam soil within the first hour, regardless of DM content (range 1.5–4.7%), whereas only 60% infiltrated into a clay loam soil over the same time period (slurry DM content 2.1%).     

Soil properties following cultivation and non-grazing of a semi-arid sandy grassland in northern China

Cultivation and overgrazing are widely recognized as the primary causes of desertification of sandy grassland in the semi-arid region of northern China. Very little is known about the effect of cultivation and overgrazing on soil physical, chemical and biological properties in this region. The objective of this study was to quantitatively evaluate the magnitude of changes in soil properties due to 3 years of cultivation (3CGS) and 5 years of ungrazed exclosure (5RGS) in a degraded grassland ecosystem of the semi-arid Horqin sandy steppe. Short-term cultivation resulted in a 18–38% reduction in concentration of soil organic C, and total N and P in the 0–15 cm plow layer. Cultivation had a significant influence on N and P availability and soil biological properties, with lower basal soil respiration (BSR) and enzyme activities than the grassland soils. This was mostly due to strong wind erosion when sandy grassland was cultivated. Data indicated a considerable difference in soil particle size distribution between the cultivated and grassland soils, and fine fraction (<0.1 mm) in the cultivated soil was lower than that in the grassland soils. Moreover, grassland vegetation recovery in the 5RGS resulted in significant improvement in soil properties measured at the 0–7.5 cm depth. From the perspective of soil resource management and environmental conservation, a viable option for these sandy grasslands would be to stop conversion of grassland to cropland and adopt proper fencing practices to limit overgrazing.     

施肥措施对砂姜黑土水分入渗性能的影响

土壤水分入渗是降雨和灌溉水转变为土壤有效水的过程,是降水、地表水、土壤水和地下水相互作用的环节,是影响作物水分利用效率的重要因素。砂姜黑土黏粒含量高,具有楔型结构等障碍因子,水分入渗性能和持水能力较弱,作物水分利用效率低。改良土体结构是提高土壤入渗与持水能力,增加作物水分利用效率的重要途径。为研究施肥措施对砂姜黑土理化性质及水分入渗性能的影响,设置不施肥对照(CK)、测土配方施肥(PF)、测土配方施肥+秸秆还田(PF+JG)和测土配方施肥+粉煤灰(PF+FMH)4个试验处理,进行小麦-玉米田间轮作试验。研究了土壤容重、颗粒组成、总孔隙度和有机质含量的变化规律,分析了土壤水分入渗特征及其与土壤理化性质之间的关系。结果表明,PF+JG、PF+FMH处理使土壤有机质含量分别较CK和PF提高18.01%、8.92%和11.18%、2.61%,土壤容重分别降低12.90%、11.29%和4.48%、2.98%,土壤总孔隙度分别增加13.89%、5.87%和12.46%、4.56%,土壤水分累积入渗量分别增加98.08%、90.39%和34.64%、29.41%。PF+JG(1.18×10-4 m·s-1)和PF+FMH(1.13×10-4 m·s-1)处理的土壤水分稳定入渗速率分别是CK(5.92×10-5 m·s-1)和PF(8.73×10-5 m·s-1)的1.99倍、1.91倍和1.35倍、1.29倍。土壤水分稳定入渗速率与有机质及总孔隙度显著正相关(P0.01),与土壤容重呈显著负相关(P0.05)。该研究表明,秸秆还田和粉煤灰处理,可提高土壤有机质含量,降低土壤容重,增加土壤孔隙度,提高土壤水分稳渗速率,可为土壤水分入渗性能提升提供理论依据。     

土壤性质对砂土亚表层磷迁移的影响

The soil factors influencing the potential migration of dissolved and particulate phosphorus （P） from structurallyweak sandy subsoils were evaluated by means of soil column leaching experiments. Soil colloids were extracted from two types of soils to make the colloid-bound forms of P solution. Eight sandy soils with diverse properties were collected for packing soil columns. The effects of influent solutions varying in concentrations of colloids, P, and electrolyte, on the transport of P and quality of leachates were characterized. P migration in the soils was soil property-dependent. High soil electrical conductivity values retarded the mobility of colloids and transportability of colloid-associated P （particulate P）. Soil electrical conductivity was negatively correlated with colloids and reactive particulate P （RPP） concentrations in the leachates, whereas, the total reactive P （TRP） and dissolved reactive P （DRP） concentrations in the leachates were mainly controlled by the P adsorption capacity and the P levels in the subsoil. The reactive particulate P in the leachates was positively correlated with the colloidal concentration. Increased colloidal concentration in the influent could significantly increase the colloidal concentration in the leachates. Elevated P concentration in the influent had little effect on P recovery in the leachates, but it resulted in significant increases in the absolute P concentration in the leachates.     

Effects of pig slurry application on soils and soil humic acids

The effect of three annually consecutive additions of pig slurry at two rates (90 and 150 m3 x ha(-1) x year(-1) on soils and soil humic acids (HAs) was investigated in a field experiment under semiarid conditions. Soils and pig slurries were analyzed by standard methods. The HAs were isolated from soils and pig slurry by a conventional procedure based on alkaline extraction, acidic precipitation to pH 1, purification by repeated alkaline dissolutions and acidic precipitations, water washing, dialysis, and final freeze-drying. The HAs obtained were analyzed for elemental (C, H, N, S, and O) and acidic functional group (carboxylic and phenolic) composition, and by UV-vis, FT-IR, fluorescence, and ESR spectroscopies. With respect to the control soil, the pig slurry amended soils had greater pH and electrical conductivity, slightly larger total N content, and smaller values of C/N ratio. A decrease of total organic C was observed only in soils amended for 2 and 3 years at the higher slurry rate. With respect to control soil HA, pig slurry HA was characterized by larger contents of S- and N-containing groups, smaller acidic functional group and organic free radical contents, a prevalent aliphatic character, extended molecular heterogeneity, and smaller aromatic polycondensation and humification degrees. Amendment with pig slurry HA determines a number of modifications in soil HAs, including increase of C, S, and COOH contents, C/N ratios, and aliphaticity and decrease of extraction yields and N, O, phenolic OH, and organic free radical contents. These effects are generally more evident after the first year of slurry application and tend to disappear with increasing number of treatments. Most probably, over the years the slightly humified slurry HA is mineralized through extended microbial oxidation, whereas only the most recalcitrant components, such as S-containing, phenolic, and aliphatic structures, are partially accumulated by incorporation into soil HA.     

Nitrogen and potassium mineralization from winery solid waste composts in sandy and sandy loam soils

This study aimed at quantifying nitrogen (N) and potassium (K) released from winery solid waste (WSW) composts during laboratory incubation to address deficiency in two texturally distinct soils. Composts had 4, 10, 20, 30, 40% (w/w) of filter materials (FMs) mixed with grape marc and pruning canes. The composts were mixed with the soils at equivalent rate of 200 kg N ha^?1 and incubated for 42 days. Quantitatively higher (p < 0.05) ammonium N content was recorded in sandy than sandy loam soil during the incubation duration while exchangeable K was increased in K-deficient sandy soil. Cumulative total mineralized N (TMN) measured during the incubation duration ranged from 59 mg kg^?1 to 672 mg kg^?1 depending on compost type and soil texture while a 10-fold increase in compost FMs content resulted in 144% and 139% increases in cumulative mineralized K in sandy and sandy loam textured soil, respectively. Percent N mineralized from the composts relative to the amount applied during the incubation duration was less than 54% reflecting the composts and soils inherent characteristics. The high ammonium N and K mineralized suggests that farmers must be cautious in utilizing these composts for field crops production due to the potential environmental risks.     

耕作方式对新垦沙地农田杂草群落结构的影响

通过田间调查的方式,研究了黑河中游边缘绿洲新垦沙地农田杂草分布状况,并对不同耕作方式下农田杂草群落结构特征进行了分析。调查中共记录杂草16种,隶属10科。新垦沙地农田杂草群落基本组成为藜(Chenopodium album)+牛筋草(Eleusineindica)+狗尾草(Setaria viridis)+反枝苋(Amaranthus retroflexus)。与当地传统的地膜覆盖、秋耕和玉米连作耕作方式相比,秸秆覆盖、减少秋耕和玉米-大豆轮作均可增加农田杂草物种丰富度、多样性指数和群落优势度(P0.05)。与当地传统耕作方式相比,秸秆覆盖可增加杂草群落中牛筋草优势度比,降低藜和反枝苋优势度比;减少秋耕可增加狗尾草、反枝苋、灰绿藜(C.glaucum)和米瓦罐(Silene conoidea)优势度比,降低牛筋草优势度比;玉米-大豆轮作可增加米瓦罐优势度比。不同耕作方式对偶见种杂草在田间的分布和组成影响不明显。可以看出,新垦沙地农田杂草物种较少,群落组成单一;不同耕作方式对新垦沙地农田杂草物种多样性和群落结构组成有明显影响,进一步深入研究对沙地农田杂草合理防除具有重要的指导意义。     

Effects of cropping system and rates of nitrogen in animal slurry and mineral fertilizer on nitrate leaching from a sandy loam

Abstract. Leaching of nitrate from a sandy loam cropped with spring barley, winter wheat and grass was compared in a 4-year lysimeter study. Crops were grown continuously or in a sequence including sugarbeet. Lysimeters were unfertilized or supplied with equivalent amounts of inorganic nitrogen in calcium ammonium nitrate (CAN) or animal slurry according to recommended rates (1N) or 50% above recommended rates (1.5N).
Compared with unfertilized crops, leaching of nitrate increased only slightly when 1N (CAN) was added. Successive annual additions of 1.5N (CAN) or 1N and 1.5N (animal slurry) caused the cumulative loss of nitrate to increase significantly. More nitrate was leached after application of slurry because organic nitrogen in the slurry-was mineralized.
With 1N (CAN) the leaching losses of nitrate were in the following order: continuous spring barley undersown with Italian ryegrass < continuous ley of perennial ryegrass < spring barley in rotation and undersown with grass < perennial ryegrass grown in rotation = winter wheat grown in rotation < sugarbeet in rotation < continuous winter wheat < continuous barley < bare fallow.
At recommended levels of CAN (1N), cumulative nitrate losses over the four years were similar for the crops when grown in rotation or continuously. When crops received 1.5N (CAN) or animal slurry, nitrate losses from the crops grown continuously exceeded those from crops in rotation. Including a catch crop in the continuous cropping system eliminated the differences in nitrate leaching between the two cropping systems.     

N mineralization process of the surface soils under shifting cultivation in northern Thailand

N mineralization process (ammonification plus nitrification) in the surface 0-5 cm soil layers under shifting cultivation in northern Thailand was studied. Labile pool of organic matter extracted with a K₂S0₄ solution at 1l0°C in an autoclave (fraction A) or by shaking at room temperature (fraction B) was used as factor to evaluate the N mineralization process which was examined in an incubation experiment. In the soils, in which the N mineralization pattern was fitted to a first order kinetics model, the content of (organic + NH₄ ⁺)-N in fraction B determined the initial rate of N mineralization. The soils, which showed a short lag time of less than 7 d both in the N mineralization and nitrification processes, had a high ratio of organic C to (organic + NH₄ ⁺)-N in fraction B, exceeding the value of 7. The soils, which showed a long lag time of more than 7 d only in the nitrification process, had a low pH(KCI) (less than 4.2). Thus, the rate of N mineralization was affected by the labile pool in fraction B or soil pH. On the other hand, there was a correlation between the N ₀ + N _max (inorganic N at 0 d + maximum amount of mineralizable N) value and the labile pool in the fraction A, suggesting that the N ₀ + N _max value depended on the contents of the labile pool.     

Bacterial community structure and microbial activity in different soils amended with biogas residues and cattle slurry

Anaerobic digestion of organic materials generates residues of differing chemical composition compared to undigested animal manures, which may affect the soil microbial ecosystem differently when used as fertilizers. This study investigated the effects of two biogas residues (BR-A and BR-B) and cattle slurry (CS) applied at rates corresponding to 70 kg NH₄⁺-N ha⁻¹ on bacterial community structure and microbial activity in three soils of different texture (a sandy, a clay and an organic clay soil). 16S rRNA genes were targeted in PCR reactions and bacterial community profiles visualized using terminal restriction fragment length polymorphism. General microbial activity was measured as basal respiration (B-resp), substrate-induced respiration (SIR), specific growth rate (μ_SIR), metabolic quotient (qCO₂) and nitrogen mineralization capacity (NMC). Non-metric multidimensional scaling analysis visualized shifts in bacterial community structure related to microbial functions. There were significant differences in bacterial community structure after 120 days of incubation (+20 °C at 70% of WHC) between non-amended (control) and amended soils, especially in the sandy soil, where CS caused a more pronounced shift than biogas residues. Terminal-restriction fragment (TRF) 307, the predominant peak in CS-amended sandy soil, was identified as possibly Bacillus or Streptococcus. TRF 226, the dominant peak in organic soil amended with BR-B, was classified as Rhodopseudomonas. B-resp significantly increased and SIR decreased in all amendments to organic soil compared with the control, potentially indicating decreased efficiency of heterotrophic microorganisms to convert organic carbon into microbial biomass. This was also reflected in an elevated qCO₂ in the organic soil. The μ_SIR level was higher in the sandy soil amended with BR-A than with BR-B or CS, indicating a shift toward species capable of rapidly utilizing glucose. NMC was significantly elevated in the clay and organic soils amended with BR-A and BR-B and in the sandy soil amended with BR-B and CS. Thus, biogas residues and cattle slurry had different effects on the bacterial community structure and microbial activity in the three soils. However, the effects of biogas residues on microbial activities were comparable in magnitude to those of cattle slurry and the bacterial community structure was less affected. Therefore, we do not see any reason not to recommend using biogas residues as fertilizers based on the results presented.     

Zokor activity promotes soil water infiltration in the Mu Us sandy land of northern Shaanxi, China

Zokors are common subterranean rodents that inhabit agricultural fields, shrublands, and grasslands in the arid and semi-arid regions of China. Zokor burrowing activities can alter soil structure and affect soil hydrological processes; however, there are few studies regarding their effects on soil preferential flow in the Mu Us sandy land. An evaluation of the effects of zokor disturbance on their habitat and soil water is important for understanding the ecological role of zokors in the soil eco...