Walter Kühbauch

Spatial distribution of growth rates and of epidermal cell lengths in the elongation zone during leaf development in Lolium perenne L.

Relative elemental growth rates (REGR) and lengths of epidermal cells along the elongation zone of Lolium perenne L. leaves were determined at four developmental stages ranging from shortly after emergence of the leaf tip to shortly before cessation of leaf growth. Plants were grown at constant light and temperature. At all developmental stages the length of epidermal cells in the elongation zone of both the blade and sheath increased from 12 μm at the leaf base to about 550 μm at the distal end of the elongation zone, whereas the length of epidermal cells within the joint region only increased from 12 to 40 μm. Throughout the developmental stages elongation was confined to the basal 20 to 30 mm of the leaf with maximum REGR occurring near the center of the elongation zone. Leaf elongation rate (LER) and the spatial distributions of REGR and epidermal cell lengths were steady to a first approximation between emergence of the leaf tip and transition from blade to sheath growth. Elongation of epidermal cells in the sheath started immediately after the onset of elongation of the most proximal blade epidermal cells. During transition from blade to sheath growth the length of the blade and sheath portion of the elongation zone decreased and increased, respectively, with the total length of the elongation zone and the spatial distribution of REGR staying near constant, with exception of the joint region which elongated little during displacement through the elongation zone. Leaf elongation rate decreased rapidly during the phase when only the sheath was growing. This was associated with decreasing REGR and only a small decrease in the length of the elongation zone. Data on the spatial distributions of growth rates and of epidermal cell lengths during blade elongation were used to derive the temporal pattern of epidermal cell elongation. These data demonstrate that the elongation rate of an epidermal cell increased for days and that cessation of epidermal cell elongation was an abrupt event with cell elongation rate declining from maximum to zero within less than 10 h.

Nonstructural Carbohydrates of Wheat Stems as Influenced by Sink-Source Manipulations

Summary Fructans accumulate in stems of wheat ( Triticum aestivum L.) prior to and after anthesis. Degradationof fructans is presumed to support grain growth when current photosynthesis is insufficient. We have investigated the effect of shading and partial inflorescence trimming on stem carbohydrate metabolism and grain growth to gain a better understanding of carbohydrate production and utilization in wheat. Plants were grown outdoors in pots, treatments established at anthesis, and plants sampled at 7 to 10 day intervals beginning at the 2-node stage. At anthesis, stems of control plants contained about 200 mg · stem -1 of water soluble carbohydrates (WSC), whereas final grain yield was 1949 mg · ear -1 , suggesting that pre-anthesis assimilates could not contribute greatly to grain filling. Active deposition of WSC in stems occurred between anthesis and the milk stage of kernels (400mg · stem -1 ); thereafter, WSC in stems decreased to less than 30mg-stem -1 at grain maturity. Trimming of inflorescences at full light resulted in increased WSC deposition into stems (637 mg · stem -1 at milk stage). Conversely, when plants with intact inflorescences were shaded, WSC deposition into stems was depressed (128mg stem -1 at milk stage), with this effect being strongest in the peduncle and subtending internode. Final grain yield in shaded plants was also decreased (60 % of control), but much less than WSC accumulation in stems, indicating that stems are less competitive sinks. Developmental changes as well as treatment effects on stem WSC concentrations occurred mainly due to changes in fructan concentration, whereas the concentration of mono- and disaccharides was relatively stable and did not exceed a threshold level of 130 g · kg -1 dry weight in plants with intact ears in the period of linear kernel growth. Above this concentration fructan deposition occurred.

Identification of broad-leaved dock (Rumex obtusifolius L.) on grassland by means of digital image processing

Digital image processing has the potential to support the identification of plant species required for site-specific weed control in grassland swards. The present study focuses on the identification of one of the most invasive and persistent weed species on European grassland, the broad-leaved dock (Rumex obtusifolius L., R.o.), in complex mixtures of perennial ryegrass with R.o. and other herbs.A total of 108 digital photographs were obtained from a field experiment under constant recording geometry and illumination conditions. An object-oriented image classification was performed. Image segmentation was done by transforming the red, green, blue (RGB) colour images to greyscale intensity images. Based on that, local homogeneity images were calculated and a homogeneity threshold (0.97) was applied to derive binary images. Finally, morphological opening was performed. The remaining contiguous regions were considered to be objects. Features describing shape, colour and texture were calculated for each of these objects. A Maximum-likelihood classification was done to discriminate between the weed species. In addition, rank analysis was used to test how combinations of features influenced the classification result.The detection rate of R.o. varied with the training dataset used for classification. Average R.o. detection rates ranged from 71 to 95% for the 108 images, which included more than 3,600 objects. Misclassifications of R.o. occurred mainly with Plantago major (P.m.). Between 9 and 16% R.o. objects were classified incorrectly as P.m. and 17–24% P.m. objects were misclassified as R.o. The classification result was influenced by the defined object classes (R.o., P.m., T.o., soil, residue vs. R.o., residue). For instance, classification rates were 86–91% and 65–82% for R.o. exclusively and R.o. against the remaining herb species, respectively.

Detection of Heterodera schachtii infestation in sugar beet by means of laser-induced and pulse amplitude modulated chlorophyll fluorescence

Two glasshouse experiments with sugar beet cvs Penta and Macarena inoculated, respectively, with 0 or 1500 and 0, 500, 1000 or 1500 juveniles of Heterodera schachtii, were conducted to estimate the capability of laser-induced chlorophyll fluorescence (LIF) and pulse amplitude modulated (PAM) chlorophyll fluorescence techniques to detect H. schachtii infestation and to differentiate between infestation levels. Fluorescence and gas exchange parameters, nitrogen and chlorophyll content of sugar beet leaves were measured weekly after nematode inoculation. Sugar beet plants responded to H. schachtii infestation initially with a decrease in photosynthesis rate and later with a reduction in nitrogen uptake and chlorophyll concentration. At the early stages of nematode infestation, before visual symptoms were evident, infested sugar beet plants displayed increased fluorescence (F680, F740). Later stages of infection were accompanied by an increase in the F686/F740 ratio, ground fluorescence (Fo) and a decrease in photochemical efficiency (Fv/Fm) induced by degradation of leaf chlorophyll. Sugar beet plants infested with 500, 1000 or 1500 juveniles per 100 cm3 of soil did not differ either in their nitrogen and chlorophyll content or in photosynthesis and transpiration rate. The linear discrimination analysis based on the combination of PAM and LIF parameters resulted in 100% correct classification of control plants and high classification rates (60-100%) of the infested treatments on all the sampling dates. Whether the fluorescence technique will differentiate nematode densities under field conditions needs further study.

Fructan in Wheat Kernels during Growth and Compartmentation in the Endosperm and Pericarp

Summary Growth and water-soluble carbohydrate content of kernels of spring wheat grown in the field was analyzed from anthesis to maturity. Fructans comprized 27 % of kernel dry matter at anthesis, i.e. 0.3 mg • kernel -1 . Most active net synthesis of fructan in kernels occurred during the first week following anthesis when volumetric growth of kernels was most rapid. During the period of most rapid dry matter accumulation (7 to 23 days post-anthesis) fructan content of kernels decreased from 1.2 to 0.4 mg. Fructans were not homogeneously distributed in the kernel. Ten days post-anthesis, when fructan content of kernels was near maximum, 71 % of the fructans wer localized in the peripheral 47 % of kernel dry matter, which comprized all the maternal tissue of the kernel (mainly pericarp) and the embryo. At that time the endosperm contained 29 % of kernel fructan. HPLC elution profiles indicated that pericarp fructans had a significantly higher mean molecular weight than endosperm fructans. The marked decrease in kernel fructan between 10 and 17 days post-anthesis was entirely due to loss of fructans from the pericarp. The latter process may be related to the cessation of assimilate partitioning to the pericarp and degeneration of pericarp tissue at this stage of kernel development.

Nitrat-Austräge auf intensiv und extensiv beweidetem Grünland, erfasst mittels Saugkerzen- und Nmin-Beprobung I Einfluss der Beweidungsintensität

In einem Beweidungsversuch mit Rindern auf Dauergrunland eines niederschlagsreichen Mittelgebirgsstandortes im Bergischen Land wurden in vier Sickerwasserperioden zwischen 1993 und 1997 bei mittleren Jahresniederschlagen von 1.362 mm die NO3-Austrage zweier Standweiden erfasst. Die intensiv bewirtschaftete Weide (= [I]) wurde mit 250 kg N ha—1 a—1 gedungt und mit einer durchschnittlichen Besatzdichte von 4,9 GV ha—1 genutzt, wahrend die deutlich extensiver genutzte Weide (= [E]) ohne N-Dungung einen mittleren Viehbesatz von 2,9 GV ha—1 aufwies bei etwa 15 % Trifolium repens im Pflanzenbestand. Der NO3-Austrag wurde fur vier Winterhalbjahre mittels Saugkerzenmethode (mit mindestens 34 Saugkerzen ha—1) und klimatischer Wasserbilanz bestimmt; parallel dazu fand in zwei Winterperioden eine Nmin-Bodenbeprobung in 0—90 cm Bodentiefe zu Beginn und am Ende des Winters statt, mit mindestens 70 Einstichen ha—1. Folgende Ergebnisse konnen festgehalten werden: (1) Die durch Saugkerzenbeprobung und klimatische Wasserbilanz geschatzte mittlere NO3-Verlagerung machte bei einem Sickerwasservorkommen zwischen 399 und 890 mm in drei Winterhalbjahren bei intensiver Beweidung 85 kg NO3-N ha—1 und bei extensiver Beweidung 15 kg NO3-N ha—1 aus; bei einer Sickerwasserspende von nur 105 mm in der Sickerwasserperiode 1995/96 konnte eine um den Faktor 5 geringere NO3-Verlagerung ermittelt werden. (2) Trotz erkennbarer Abstufungen in den Nmin-Werten zwischen den Weidevarianten zu Beginn des Winters erlauben die Daten dieser Nmin-Beprobung keine sichere Aussage uber das Risiko der NO3-Auswaschung; wahrend 1994/95 uber Winter eine Abnahme der Werte in beiden Weidevarianten auftrat (—33 [I] / —8 [E] kg NO3-N ha—1 bzw. —26 [I] / —21 [E] kg NH4-N ha—1), zeigte sich uber Winter 1996/97 meist sogar ein Anstieg in den mittleren Nmin-Wer-ten der Varianten (+10 [I] / +2 [E] kg NO3-N ha—1 bzw. +10 [I] / —10 [E] kg NH4-N ha—1). (3) Trotz der Methodenabweichungen konnte dokumentiert werden, dass durch extensive Beweidung eine Verminderung der NO3-Austrage erzielt werden kann, die den geringen NO3-Verlusten von geschnittenem Grunland nahe kommt. Nitrate leaching from intensively and extensively grazed grassland measured with suction cup samplers and sampling of soil mineral-N I Influence of pasture management Leaching of nitrate (NO3—) from two differently managed cattle pastures was determined over four winters between 1993 and 1997 using ceramic suction cup samplers (with min. 34 cups ha—1); additionally, vertical soil mineral-N content in 0—0.9 m (Nmin) was measured at the beginning and end of two winters (with min. 70 different sample cores ha—1). The experimental site in the highlands north-east of Cologne, Germany, is characterized by high annual precipitation (av. 1,362 mm between 1993 and 1996). An intensive continuous grazing management (1.3 ha, fertilized with 250 kg N ha—1 yr—1, average stocking density 4.9 LU ha—1, = [I]) was tested against an extensive continuous grazing system (2.2 ha, av. 2.9 LU ha—1; no N-fertilizer but an estimated proportion of Trifolium repens up to 15 % of total dry matter in the final year, = [E]). The results can be summarized as follows: (1) Mean leaching losses of NO3-N, estimated from suction cup sampling and balance of drainage volume, were 85 kg NO3-N ha—1 [I] and 15 kg NO3-N ha—1 [E] during three wet winters with drainage volumes between 399 and 890 mm; in a dry winter with 105 mm calculated percolation, nitrate leaching decreased by a factor of 5 for both grazing treatments. (2) Although the amount of mineral N in soil (Nmin) sampled in late autumn showed differences between intensive and extensive grazing, the Nmin method permits no certain indication of the risk of NO3 leaching. For example, during the winter period 1994/95 a reduction of mineral N in the soil (0—0.9 m) in both grazing treatments was found (—33 [I] / —8 [E] kg NO3-N ha—1 and —26 [I] / —21 [E] kg NH4-N ha—1) whereas during the winter 1996/97 an increase in almost all mean mineral N values occurred (+10 [I] / +2 [E] kg NO3-N ha—1 and +10 [I] / —10 [E] kg NH4-N ha—1). (3) In spite of the differences between both methods, the experiment shows that NO3-N leaching under extensive grazing could be reduced almost to levels close to those under mown grassland.

Image classification approach for automatic identification of grassland weeds

The potential of digital image processing for weed mapping in arable crops has widely been investigated in the last decades. In grassland farming these techniques are rarely applied so far. The project presented here focuses on the automatic identification of one of the most invasive and persistent grassland weed species, the broad-leaved dock (Rumex obtusifolius L.) in complex mixtures of grass and herbs. A total of 108 RGB-images were acquired in near range from a field experiment under constant illumination conditions using a commercial digital camera. The objects of interest were separated from the background by transforming the 24 bit RGB-images into 8 bit intensities and then calculating the local homogeneity images. These images were binarised by applying a dynamic grey value threshold. Finally, morphological opening was applied to the binary images. The remaining contiguous regions were considered to be objects. In order to classify these objects into 3 different weed species, a soil and a residue class, a total of 17 object-features related to shape, color and texture of the weeds were extracted. Using MANOVA, 12 of them were identified which contribute to classification. Maximum-likelihood classification was conducted to discriminate the weed species. The total classification rate across all classes ranged from 76 % to 83 %. The classification of Rumex obtusifolius achieved detection rates between 85 % and 93 % by misclassifications below 10 %. Further, Rumex obtusifolius distribution and the density maps were generated based on classification results and transformation of image coordinates into Gauss-Krueger system. These promising results show the high potential of image analysis for weed mapping in grassland and the implementation of site-specific herbicide spraying.

Loss of biodiversity in European agriculture during the twentieth century

Today, agriculture in Europe can be generally classified as having a low level of biodiversity. This article describes indications of biodiversity in agriculture and of how biodiversity has changed over time. It is highly likely that in the past, over a period of approximately 1,000 years, agriculture in central and western Europe was a matter of biodiversity, due to low-intensity cultivation methods and the principle of self-sufficiency that most farms practised. Biodiversity actually increased between the eighteenth and twentieth centuries due to a growing variety of cultivated crops brought about by the more advanced farming methods used in England and the Netherlands at that time. The loss of biodiversity in recent decades was stimulated primarily by the economic “environment“ which was shaped by rising labour costs and relatively low prices for agricultural products which, in turn, accelerated mechanization and specialization in a few products (crops, animals) and put pressure on farmers to increase their yields. At present, loss of biodiversity is apparent in many ways. The European Union is trying to make biodiverse farming attractive to farmers through and farm ecology programmes. A general shift towards more biodiversity is, however, unlikely to occur because the prevailing political, commercial, administrative and economic forces are against it.

SIR-C polarimetric backscatter features of agricultural land cover types early during the growing season

This study focuses on the polarimetric radar backscatter responses observed for different agricultural land cover types early during the growing season, in two well-separated test sites. These were Oltrepo Pavese in northern Italy and Oberpfaffenhofen in southern Germany. Results show that L-band was better at discriminating between agricultural land cover types than C-band. However effects due to soil roughness and those due to vegetation in the fields were difficult to separate using only backscatter amplitude information. Polarimetric information expressed through the HH-VV correlation coefficients and as polarimetric signatures however, provided additional information on the backscatter mechanisms for various land cover types and allowed for the separation of vegetation and soil effects.

Investigation of agricultural land use in Italy and Germany by means of the multi-band/multi-frequency SIR-C/X-SAR system

This study explored the application of multi-band/multi-frequency SIR-C/X-SAR images to agricultural remote sensing. The sensitivity of the backscattered signal with respect to crop or land cover type as well as crop conditions is evaluated. The ability of classify crops early during the growing season with such multi-parameter data sets and the contribution of the various frequencies to the correct classification of land cover types is also assessed. Data used for the study encompasses two well-separated test sites, one in southern Germany and the other in northern Italy.