膜下滴灌条件下水分对棉花根系分布特征的影响

通过分层土柱挖掘法，研究膜下滴灌条件下不同滴灌量棉花（Gossypium hirsutum L．）根系的分布特征。结果表明：直径〉1mm的粗根只分布在40cm以上的土层；随着土层深度增加，棉花根系生物量逐渐减少；但随着滴灌量减少，土壤深层根系生物量有增加趋势。不同处理的根系生物量的分布与土层深度呈显著的负指数关系，棉花细根生物量、根长、根表面积在土壤中垂直分布都呈“单峰型”曲线变化规律；但随着滴灌量的减少，棉花根系消弱系数β呈增加趋势。     

Morphological analysis of viral communities in the floodwater of a Japanese paddy field

Capsid size distributions of viral communities in the floodwater of a Japanese paddy field under a long-term fertilizer trial were surveyed during the rice cultivation period by using transmission electron microscopy. The capsid size distributions were monophasic, and the median values fell within the range of 50-70 nm. The quartile intervals were narrow from either 40-50 nm or 50-60 nm to either 60-70 nm or 70-80 nm for most samples. There was no clear seasonal variation in the capsid size distribution of viral communities. The difference in size distributions among different fertilizer plots was also not found. Viral communities in the floodwater were predominated by isometric icosahedral forms. Viruses with octahedral capsids and elongated ones were rare and sporadic in the floodwater.     

A new approach for modelling vertical stress distribution at the soil/tyre interface to predict the compaction of cultivated soils by using the PLAXIS code

Soil compaction by agricultural machines can have adverse effects on crop production and the environment. Different models based on the Finite Element Method have been proposed to calculate soil compaction intensity as a function of vehicle and soil properties. One problem when modelling soil compaction due to traffic is the estimation of vertical stress distribution at the soil surface, as the vertical stress is inhomogeneous (non-uniform) and depends on soil and tyre properties. However, uniform stress distribution at the soil/tyre interface is used to predict the compaction of cultivated soils in most FEM compaction models. We propose a new approach to numerically model vertical stress distribution perpendicular to the driving direction at the soil/tyre interface, employing the FEM models of PLAXIS code. The approach consists of a beam (characterised by its geometric dimensions and flexural rigidity) introduced at the soil surface and loaded with a uniform stress with the aim to simulate the action of a wheel at the soil surface. Different shapes of stress distribution are then obtained numerically at the soil surface by varying the flexural rigidity of the beam and the mechanical parameters of the soil. PLAXIS simulations show that the soil type (soil texture) modifies the shape of the stress distribution at the edges of the contact interface: a parabolic form is obtained for sand, whereas a U-shaped is obtained for clay. The flexural rigidity of the beam changes the shape of distribution which varies from a homogenous (uniform) to an inhomogeneous distribution (parabolic or U-shaped distribution). These results agree with the measurements of stress distributions for different soils in the literature. We compared simulations of bulk density using PLAXIS to measurement data from compaction tests on a loamy soil. The results show that simulations are improved when using a U-shaped vertical stress distribution which replaces a homogenous one. Therefore, the use of a beam (cylinder) with various flexural rigidities at the soil surface can be used to generate the appropriate distribution of vertical stress for soil compaction modelling during traffic.     

Modeling vertical movement of organic matter in a soil incubated for 41 years with C labeled straw

The distribution of organic matter (OM) in the soil profile reflects the balance between inputs and decomposition at different depths as well as transport of OM within the profile. In this study we modeled movement of OM in the soil profile as a result of mechanisms resulting in dispersive and advective movement. The model was used to interpret the distribution of ¹⁴C in the soil profile 41 years after the labeling event. The model fitted the observed distribution of ¹⁴C well (R²=0.988, AIC_c=−82.6), with a dispersion constant of D=0.71 cm² yr⁻¹ and an advection constant of v=0.0081 cm yr⁻¹. However, the model consistently underestimated the amount of OM in the soil layers from 27 to 37 cm depth. A possible explanation for this is that different fractions of OM are transported by different mechanisms. For example, particulate OM, organomineral colloids and dissolved OM are not likely to be transported by the same mechanisms. A model with two OM fractions, one moving exclusively by dispersive processes (D=0.26 cm² yr⁻¹) and another moving by both dispersive (D=0.99 cm² yr⁻¹) and advective (v=0.23 cm yr⁻¹) processes provided a slightly better fit to the data (R²=0.995, AIC_c=−83.6). More importantly, however, this model did not show the consistent underestimation from 27 to 37 cm soil depth. This corroborates the assumption that differing movement mechanisms for different OM fractions are responsible for the observed distribution of ¹⁴C in the profile. However, varying dispersion, advection, and decay of OM with depth are also possible explanations.     

Soil porosity and water infiltration as influenced by tillage methods

The relations between soil pore structure induced by tillage and infiltration play an important role in flow characteristics of water and solutes in soil. In this study, we assessed the effect of long-term use of various tillage systems on pore size distribution, areal porosity, stained (flow-active) porosity and infiltration of silt loam Eutric Fluvisol. Tillage treatments were: (1) ploughing to the depth of 20 cm (conventional tillage (CT)); (2) ploughing to 20 cm every 6 years and to 5 cm in the remaining years (S/CT); (3) harrowing to 5 cm each year (S); (4) sowing to the uncultivated soil (no tillage (NT)), all in a micro-plot experiment. Equivalent pore size distribution was derived from the water retention curve, areal porosity – from resin-impregnated blocks (8 cm × 9 cm × 4 cm) and stained porosity – from horizontal sections (every 2 cm) of column samples (diameter: 21.5 cm, height: 20 cm) taken after infiltration of methylene blue solution. The pore size distribution curves indicated that the textural peaks of the pore throat radius of approximately 1 μm were mostly defined under NT, whereas those in the structural domain of radii of 110 μm radius—under CT. The differences among the tillage treatments were more pronounced at depth 0–10 cm than 10–20 cm. At both depths, the differences in pore size distribution between the tillage treatments were relatively greater in structural than those in the matrix domain. CT soil had the greatest areal porosity and stained porosity. The stained porosity as a function of depth could be well described by logarithmic equations in all treatments. Cumulative infiltration (steady state) as measured by the double ring infiltrometer method was the highest under CT (94.5 cm) and it was reduced by 62, 36 and 61% in S/CT, S and NT soil, respectively. Irrespective of tillage method, cumulative infiltration rates throughout 3 h most closely correlated with stained porosity in top layers (0–6 cm). Overall, the results indicate that soil pore system under CT with higher contribution of large flow-active pores compared to reduced and no tillage treatments enhanced infiltration and water storage capacity.     

Spatial distribution of earthworms [Lumbricidae] in recultivated soils of the Rhenish lignite‐mining area,Germany

The spatial distribution of earthworms was studied by means of combined formalin expulsion and hand sorting in three arable fields of the Rhenish lignite‐mining area that differed in their recultivation age (6, 12, 24 yr). In addition, pH and the spatial distribution of penetration resistances were measured to see if they are corresponding with the distribution of earthworms. Already the 6 yr old field had a rich population of endogeic, anecic, and epigeic earthworms (119 ind. m^–2, 48 g m^–2, 6 species). This quantity was similar to the 24 yr old site. The 12 yr old field was only sparsely populated by earthworms (5 ind. m^–2, 5 g m^–2, 3 species). In the 6 yr old field, the spatial distribution pattern showed a center of maximal earthworm abundances, corresponding to the distributional pattern of penetration resistances. In the old field (24 yr), the species varied in their spatial distribution, and there was no correspondence with the distribution of penetration resistance. In general, the penetration resistance at the youngest site was clearly lower than at the two older sites. The earthworm population in the 6 yr old field can be explained by cocoons contained in the dumped material. A calculation using literature data on earthworm‐population dynamics shows that a founding population of 400–600 reproductive individuals per hectare and a continuity of favorable growth conditions during the time of soil management is necessary for the development of the situation found at the 6 yr old site in this study.     

华北平原冬小麦-夏玉米轮作体系中标记15N的去向及残效

A field experiment was conducted to investigate the fate of ¹⁵N-labeled urea and its residual effect under the winter wheat (Triticum aestivum L.) and summer maize (Zea mays L.) rotation system on the North China Plain. Compared to a conventional application rate of 360 kg N ha^-1 (N360), a reduced rate of 120 kg N ha^-1 (N120) led to a significant increase (P < 0.05) in wheat yield and no significant differences were found for maize. However, in the 0-100 cm soil profile at harvest, compared with N360, N120 led to significant decreases (P < 0.05) of percent residual N and percent unaccounted-for N, which possibly reflected losses from the managed system. Of the residual fertilizer N in the soil profile, 25.6%-44.7% and 20.7%-38.2% for N120 and N360, respectively, were in the organic N pool, whereas 0.3%-3.0% and 11.2%-24.4%, correspondingly, were in the nitrate pool, indicating a higher potential for leaching loss associated with application at the conventional rate. Recovery of residual N in the soil profile by succeeding crops was less than 7.5% of the applied N. For N120, total soil N balance was negative; however, there was still considerable mineral N (NH₄⁺-N and NO₃^--N) in the soil profile after harvest. Therefore, N120 could be considered agronomically acceptable in the short run, but for long-term sustainability, the N rate should be recommended based on a soil mineral N test and a plant tissue nitrate test to maintain the soil fertility.     

郑州市夏玉米生物量积累与增长分配规律分析

根据郑州市1994—2006年夏玉米生物量观测资料分析了不同生育期单株各器官的生物量变化和增长分配规律，得出：在玉米整个生长期，单株各器官的重量变化在不同生育阶段不同，结果导致各部分干重占全株干重百分比的差异。总体上看，拔节前叶片增长较快，占比率最高，达68％～88％；叶鞘增长也快但所占比例一直不大，最高时占20％；茎在拔节一抽雄期增长较快，最高时占41％；果穗在抽雄后直线增长，最高时占63％。同时，通过定量分析得到了各器官在整个生育期增长分配率的变化过程，模拟取得不同气候年型生物量积累曲线，研究结果可为当地玉米生长的定量化模拟提供参考。     

蒸发和灌水频率对土壤水分分布影响的研究

通过室内均质土柱试验，对不同灌水频率下有无蒸发土壤中的水分分布规律进行了分析。结果表明，灌水频率可改变土壤水分的空间分布和土壤蓄水量。在相同灌水量条件下，灌水频率加大，上部土层水分含量在一定范围内增高，且湿润锋深度变浅，上部土层蓄水量增加；适宜的灌水频率可增加土壤蓄水量。有无蒸发条件下土壤水分差异在灌水初期主要体现在上部土层，随灌水次数增多，上部土层水分差异减少，且灌水频率越高，这种差异减少得越快，而下部土层水分差异增加。     

Carbon mineralisation in soil adjacent to plant residues of contrasting biochemical quality

A fraction of the C of residues incorporated into soil diffuses into the adjacent soil where it is eventually mineralised by microorganisms. Our aim was to quantify the contribution of this adjacent soil to the overall mineralisation of residue-C. For this, we incorporated two different residues labelled with ¹³C, with contrasting biochemical characteristics, namely mature wheat straw and young rye leaves, in soil cores. When 15% mineralisation of residue-C was measured for both residues, we separated a particulate fraction (the residues), the adjacent soil (4-5 mm thick) and a distant soil fraction, and incubated them separately for 5 h. We found that 76% of the mineralised wheat straw-C came from the particulate fraction and 23% from the soil adjacent to the residues. For rye leaves, 67% of the evolved CO₂ came from the particulate fraction and 33% from the adjacent soil. It showed that the adjacent soil had a significant role in the mineralisation of carbon from the residues, even if the main source of residue-derived CO₂ was the particulate fraction itself. The functional importance of the soil adjacent to the residues increased with the amount of soluble organic compounds that had been leached from the residue into the adjacent soil, suggesting a strong interaction between the initial quality of the crop residue and the resulting spatial heterogeneity of the decomposing microorganisms and C within the soil.