Wirkung mechanischer Belastung auf Gefüge und Ertragsleistung einer Löss‐Parabraunerde mit zwei Bearbeitungssystemen

Effect of mechanical stress on structure and productivity of a loess‐derived Luvisol with conventional and conservation tillage In Germany farmers are committed to caring for the land by a soil protection law. Yet vehicles with ever increasing axle load endanger productivity and environmental quality of arable soils. In spring of 1995 a field experiment was startet on a wet silty Luvisol to test the effect of single mechanical loading on soil and crop characteristics, when managed by mouldboard ploughing (PL) or conservation tillage (CT). CT soils are considered to be more resistant against compactive stresses and to recover from degeneration more rapidly than PL soils. Beside an unwheeled control the loading treatments were light (2 × 2.5 t; number of wheel passes times wheel load); medium (2 × 5 t) and high (6 × 5 t). In 1995 even light loading of the PL soil caused a significant yield decline by 50% in spring barley, but this happened on CT soil only with high loading. In subsequent years with winter wheat and winter barley yield decline was less distinct. Loading of PL soil reduced total root length (from 4 to 1 km m⁻²) and rooting depth (from 70—90 to 40—70 cm), but on CT soil only root length was diminished by high loading. A tillage‐traffic pan (30—35 cm) hindered subsoil rooting in PL, which was favored in CT by earthworm channels. High loading caused compaction to at least 50 cm depth. Within the pan of the PL soil, penetration resistance attained 5 MPa and bulk density 1.65 g cm⁻³. In the CT soil the zone of maximum compaction was closer to the surface (15—25 cm). In PL soil the saturated hydraulic conductivity and the O₂‐diffusion coefficient gradually decreased with loading, but in CT soil only with heavy loading. The compacted top soil was broken in subsequent years by ploughing (PL: 25 cm) or rotary implements (CT: 5—8 cm). With PL, structure in the pan layer and subsoil did not recover, and rooting depth was still limited. Some restoration, however, was indicated with CT. Here transmitting properties increased in time, which was attributed to the reconstruction of root and earthworm channels, as demonstrated by computer tomography. We conclude that in silty soils compacted layers below ploughing depth will hardly be regenerated by internal processes. CT soils are less susceptible to loading, but high stresses are harmful too. Therefore recommending CT as a measure for protecting soil from compaction would not be enough, considering the present development towards heavy field machinery.     

Enhanced glucosinolates in root exudates of Brassica rapa ssp. rapa mediated by salicylic acid and methyl jasmonate

Elicitation studies with salicylic acid (SA) and methyl jasmonate (MJ) inducing a targeted rhizosecretion of high levels of anticarcinogenic glucosinolates in Brassica rapa ssp. rapa plants were conducted. Elicitor applications not only led to an accumulation of individual indole glucosinolates and the aromatic 2-phenylethyl glucosinolate in the turnip organs but also in turnip root exudates. This indicates an extended systemic response, which comprises the phyllosphere with all aboveground plant organs and the rhizosphere including the belowground root system and also root exudates. Both elicitor applications induced a doubling in 2-phenylethyl glucosinolate in root exudates, whereas application of MJ enhanced rhizosecreted indole glucosinolates up to 4-fold. In addition, the time course study revealed that maximal elicitation was observed on the 10th day of SA and MJ treatment. This study may provide an essential contribution using these glucosinolates as bioactive additives in functional foods and nutraceuticals.     

Combination of electromagnetic induction and gamma spectrometry using K‐means clustering: A study for evaluation of site partitioning

Today rapid survey methods of proximal soil sensing (PSS) provide an increasing number of different and highly resolved data. These multidimensional data sets can lead to multilayered and complex maps of parameters which are only indirectly related to soil properties and soil functions. However, in applications usually just one clear elementary map is required. It is of increasing importance to tackle this problem utilizing a cluster algorithm for the synthesis and reduction of multidimensional input variables. The cluster algorithm provides a partitioning of the investigated site whereby the units are characterized by the statistics of the PSS data. Therefore, the question that arises is how suitable is the suggested partitioning in terms of the delineation of different soil units. In this study, we investigate the suitability of cluster partitioning through a case study at a medium‐scale test site (≈ 50 000 m²). Two common PSS methods: electromagnetic induction (EMI) and gamma spectrometry (GS) will be employed to create a data set for partitioning by a K‐means cluster. The result of the cluster analysis is a delineation of three different parts. In contrast to previous studies, we evaluate the generated partitions by independent soil properties such as grain size, horizon thickness, and color of stratified randomly taken soil samples. The soil analyses show that one of three clusters significantly differs from the others in terms of grain‐size distribution and horizon thickness. The partitioning of the other two clusters could not be confirmed by the considered soil parameters. Nevertheless, the case study demonstrates the combination of different PSS data by K‐means clustering as a potential approach for site partitioning. An evaluation of the results of the cluster analysis through the collection and analysis of soil samples is highly recommended.     

落叶松胚性愈伤组织诱导培养基中激素的311-A最优回归设计筛选

采用311-A最优回归设计，对落叶松胚性细胞诱导中激素种类与浓度优化筛选，建立胚性愈伤组织量依2，4-D、BA、KT的多基本原则 式回归方程，分析了试验因子的主效应和互作效应，借助此方程获得了3因子的最佳配比组合以及最佳胚性愈伤组织发和亘，2，4-D为1.29mg.L^-1、BA为0.39mg.L^-1和KT为0.58mg.L^-1时，落叶松胚性愈伤组织的诱导量可达到13.9317mg.个^-1(外植体）。结果表明，这是一种简便、实用、科学的优化培养基的途径。     

Beeinflusst Magnetit Wassergehaltsmessungen mit time domain reflectometry (TDR)?

Does magnetite have an influence on measurements of water contents by time domain reflectometry (TDR)? An experiment was carried out to investigate an assumed influence of magnetite on TDR pulses. Sand was enriched with three different magnetite concentrations and six different volumetric water contents. The results of this sand standard experiment showed that magnetite up to a concentration of 6% (w/w) has no distinct influence on TDR measurements. Significantly higher water contents measured by TDR in the treatment with 6% magnetite compared to those with 0, 0.5 and 2% magnetite can be explained by the effect of the heavy clay-size magnetite (<2 μm, ρ = 5.1 g cm⁻³) on soil texture and bulk density. This was confirmed by a comparative investigation of three sandy topsoils. Measurements with vertical vs horizonal TDR-probe position gave the same results.     

Botrytis cinerea — history of chemical control and novel fungicides for its management

Infections caused by Botrytis cinerea are of considerable economic importance in grapes, vegetables and berries world-wide, especially when grown under protection. Newly introduced botryticides are the anilinopyrimidines pyrimethanil, cyprodinil and mepanipyrim, the phenylpyrrol fludioxonil and the hydroxyanilide fenhexamid. Biochemical studies indicate that the anilinopyrimidines inhibit the biosynthesis of methionin by blocking cystathionine-β-lyase. The target site of fludioxonil seems to lie in the osmoregulatory signal transmission pathway. Although the exact biochemical target of fenhexamid is not yet characterized, there are clear indications that it is different from all other botryticides known. Therefore, fenhexamid is an effective tool for anti-resistance management strategies.     

Spectropolarimetric diagnostics of thermonuclear supernova explosions

Even at extragalactic distances, the shape of supernova ejecta can be effectively diagnosed by spectropolarimetry. We present results for 17 type Ia supernovae that allow a statistical study of the correlation among the geometric structures and other observable parameters of type Ia supernovae. These observations suggest that type Ia supernova ejecta typically consist of a smooth, central, iron-rich core and an outer layer with chemical asymmetries. The degree of this peripheral asphericity is correlated with the light-curve decline rate of type Ia supernovae. These results lend strong support to delayed-detonation models of type Ia supernovae.     

Channel initiation and the problem of landscape scale

Since the 1940s it has been proposed that landscape dissection into distinct valleys is limited by a threshold of channelization that sets a finite scale to the landscape. This threshold is equal to the hillslope length that is just shorter than that necessary to support a channel head. A field study supports this hypothesis by showing that an empirically defined topographic threshold associated with channel head locations also defines the border between essentially smooth, undissected hillslopes and the valley bottoms to which they drain. This finding contradicts assertions that landscapes are scale-independent and suggests that landscape response to changes in climate or land use depends on the corresponding changes in the threshold of channelization.