Jürgen Schellberg

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.

The Rengen Grassland Experiment: relationship between soil and biomass chemical properties, amount of elements applied, and their uptake

The Rengen Grassland Experiment (RGE) was established in the Eifel Mountains (Germany) on a low productive Nardetum in 1941. Since then, the following fertilizer treatments have been applied with a late two-cut system: unfertilized control, Ca, CaN, CaNP, CaNPKCl and CaNPK2SO4. We aimed to understand how concentrations of macro (N, P, K, Ca and Mg), micro (Cu, Fe, Mn and Zn) and trace (As, Cd, Cr, Ni and Pb) elements in the plant biomass were affected by long-term fertilizer application, soil chemical properties and biomass production. In 2008, biomass samples from the first cut (early July) and the second cut (mid-October) were collected and analyzed. The simultaneous application of N, P and K decreased nitrogen concentration in the aboveground biomass, but substantially increased biomass production. Late cutting management decreased forage quality in highly productive more than in low productive plant communities. The concentrations of P and K in the plant biomass were positively related to P and K application and, therefore, to plant available P and K concentrations in the soil. The concentrations of some micro (Fe, Mn and Zn) and trace (As, Cd, Cr, Ni and Pb) elements in the plant biomass were negatively correlated with the amount of elements supplied by fertilizers and biomass production, probably because of the dilution effect. Long-term fertilizer application resulted in the accumulation of macro (P, Ca and Mg), micro (Fe and Mn) and trace (As and Cr) elements in the soil, but in many cases this accumulation was not connected with an increase in the concentrations of these elements in the plant biomass. Nutritional status, as indicated by the biomass N:P ratio, was consistent with N or P limitation as indicated by the nitrogen and phosphorus nutrition indices. Furthermore, additional K (co-)limitation was indicated by the N:K and K:P ratios in the biomass from the NP treatment. The results from the RGE indicate that there is no simple positive relationship between the applied elements and their concentrations in the plant biomass.

Are There Consistent Grazing Indicators in Drylands? Testing Plant Functional Types of Various Complexity in South Africa’s Grassland and Savanna Biomes

Despite our growing knowledge on plants’ functional responses to grazing, there is no consensus if an optimum level of functional aggregation exists for detecting grazing effects in drylands. With a comparative approach we searched for plant functional types (PFTs) with a consistent response to grazing across two areas differing in climatic aridity, situated in South Africa’s grassland and savanna biomes. We aggregated herbaceous species into PFTs, using hierarchical combinations of traits (from single- to three-trait PFTs). Traits relate to life history, growth form and leaf width. We first confirmed that soil and grazing gradients were largely independent from each other, and then searched in each biome for PFTs with a sensitive response to grazing, avoiding confounding with soil conditions. We found no response consistency, but biome-specific optimum aggregation levels. Three-trait PFTs (e.g. broad-leaved perennial grasses) and two-trait PFTs (e.g. perennial grasses) performed best as indicators of grazing effects in the semi-arid grassland and in the arid savanna biome, respectively. Some PFTs increased with grazing pressure in the grassland, but decreased in the savanna. We applied biome-specific grazing indicators to evaluate if differences in grazing management related to land tenure (communal versus freehold) had effects on vegetation. Tenure effects were small, which we mainly attributed to large variability in grazing pressure across farms. We conclude that the striking lack of generalizable PFT responses to grazing is due to a convergence of aridity and grazing effects, and unlikely to be overcome by more refined classification approaches. Hence, PFTs with an opposite response to grazing in the two biomes rather have a unimodal response along a gradient of additive forces of aridity and grazing. The study advocates for hierarchical trait combinations to identify localized indicator sets for grazing effects. Its methodological approach may also be useful for identifying ecological indicators in other ecosystems.

Using RapidEye and MODIS Data Fusion to Monitor Vegetation Dynamics in Semi-Arid Rangelands in South Africa

Image time series of high temporal and spatial resolution capture land surface dynamics of heterogeneous landscapes. We applied the ESTARFM (Enhanced Spatial and Temporal Adaptive Reflectance Fusion Model) algorithm to multi-spectral images covering two semi-arid heterogeneous rangeland study sites located in South Africa. MODIS 250 m resolution and RapidEye 5 m resolution images were fused to produce synthetic RapidEye images, from June 2011 to July 2012. We evaluated the performance of the algorithm by comparing predicted surface reflectance values to real RapidEye images. Our results show that ESTARFM predictions are accurate, with a coefficient of determination for the red band 0.80 < R2 < 0.92, and for the near-infrared band 0.83 < R2 < 0.93, a mean relative bias between 6% and 12% for the red band and 4% to 9% in the near-infrared band. Heterogeneous vegetation at sub-MODIS resolution is captured adequately: A comparison of NDVI time series derived from RapidEye and ESTARFM data shows that the characteristic phenological dynamics of different vegetation types are reproduced well. We conclude that the ESTARFM algorithm allows us to produce synthetic remote sensing images at high spatial combined with high temporal resolution and so provides valuable information on vegetation dynamics in semi-arid, heterogeneous rangeland landscapes.

Discrimination and characterization of management systems in semi-arid rangelands of South Africa using RapidEye time series

In South African grasslands, rangeland management is strongly related to land tenure. Communal farms are reported to exhibit less desirable vegetation conditions for livestock than commercial farms. Time series of high spatial and temporal resolution imagery may be useful for improved evaluation of these rangelands as they provide information at a spatial scale similar to the typical scale of field assessments and may thus overcome the limited spatio-temporal representativeness of field measurements. A time series of 13 RapidEye images over one growing season (2010–2011) was used to explore spectral differences between and within two management systems (commercial vs. communal). Isomap ordination was applied to map continuous spectral dissimilarities of sample plots. Using regression with simultaneous autoregressive models (SAR), dissimilarities were subsequently related to ecological variables of plant and soil, including indicators for grazing effects. The largest differences were found between sample plots of communal and commercial farms. Vegetation attributes were significantly related to dissimilarities in reflectance, both from the growing season and the dormant period. However, these relationships did not suggest vegetation degradation on communal farms. They further suggest that a management-related pattern of grazing disturbance in the summer months led to spectral differences between farms but could have impaired the detailed characterization of spectral dissimilarities related to differences in vegetation composition.

Grass strategies and grassland community responses to environmental drivers: a review

Grassland covers about one quarter of the Earth’s land area and is currently estimated to contribute to the livelihoods of over 800 million people. Grassland provides ecosystem goods and services, mainly through the provisioning of milk and meat. Therefore, the proper use of grasslands will be essential for feeding the nine billion people that will inhabit planet Earth by 2050. In the context of a changing climate, we should better understand the interactions of environment, management and grass crop at individual, community and ecosystem levels. Functional ecology focuses on the roles and functions that species play in the community or ecosystem in which they occur. Functional ecology thus aims to understand how plant species adapt to environmental conditions and how management can alter this adaptation. Here, we review the latest advances in plant functional traits research and on species strategies to the main environmental factors occurring in grassland ecosystems: nutrient availability, grazing, cutting and shading. Functional ecology also provides a framework to better understand how species strategies interact with the species composition at the community level. Therefore, the literature on community assembling theories in relation to ecosystem processes most relevant to grassland management and services is also reviewed. Finally, future research questions and some new orientations for grassland experts are offered in order to meet the challenge of maintaining productivity and preservation of these semi-natural environments in the face of global change.

Nutrient Flows in Suckler Farm Systems Under Two Levels of Intensity

The potential release of nutrients from animal farms into soil, water and the atmosphere is a major concern in agronomy. Farm gate balances are widely utilised to validate the compatibility of a farming system to the surrounding environment, although they do not reveal the internal nutrient flow as influenced by production intensity and hence might mask local and spatial nutrient surpluses or deficiencies. In a three years experiment on Rengen Research Station (Eifel Mountains) of the University of Bonn (Germany) we examined the entire nutrient cycle of two suckler farm systems without (extensive, system “A”) and with (intensive, system “B”) nutrient input and with 20 suckler cows on 19 hectare each. Stall and grassland nutrient balance sheets give insight into sources of nutrient surpluses and losses in the farm compartments. The annual budgets of N in system “A” were nearly balanced (−18 to 15 kg N ha−1 yr−1) compared to system “B” which calculated 81–120 kg N ha−1 yr−1 surplus due to considerable N input with forage and higher dry matter contribution of white clover leading to higher annual N2 fixation. The maximum of total annual nutrient flow within the entire systems was 388, 42 and 317 kg ha−1 yr−1 with N, P, and K, respectively. Most of these nutrients circulated with forage and excreta on the pastures. This led to considerable losses mainly of nitrogen (44–50 kg N ha−1 yr−1) even in the extensive system. The intake, excretion and resulting losses of N were mainly determined by the allowance of N rich pasture forage and was mostly independent from nutrient input. Compared to the grazing season, stall balances were similar in both systems and all years and revealed very low surpluses with all nutrients. The authors deduce that internal nutrient flow analyses should be added to conventional balance sheets, including a ranking of nutrients related to chemical bond, solubility, volatility and predisposition to losses in the farm’s compartment and environment.

Frontiers and perspectives on research strategies in grassland technology

Abstract. Grassland scientists and farmers are increasingly faced with emerging new technologies and information systems that have been primarily developed in engineering sciences, in particular, precision agriculture, remote sensing, geographic information and biotechnology. Judgment upon whether the implementation of any of these technologies may be beneficial in economic and ecological respects is challenging, especially to those who have to make on-farm decisions. New technologies have been applied on grassland only partially and with some delay compared with arable land. However, as we will show here, there is scope for successful implementation of new technologies in various climatic regions and for a wide range of applications. The paper presents the most important recent developments of new technologies in agriculture that have scope for application in grasslands. It defines the relevant terms and processes, provides examples of successful implementation, and discusses future directions and research needs.

Die entwicklung der erträge von getreide, hackfrüchten und klee im dauerdüngungsversuch dikopshof von 1906 bis 1996

Auf dem Versuchsgut Dikopshof nahe Bonn wurde im Jahr 1904 ein Statischer Dauerdungungsversuch mit den Fruchtarten der “Rheinischen Fruchtfolge”; (Zuckerruben/Weizen/Roggen/Klee/Hafer) angelegt. Im Jahr 1953 wurde die Fruchtart Hafer durch Kartoffeln ersetzt. In einer Halfte der Versuchsflache sind ungedungte und vollgedungte Parzellen den N‐, P‐, K‐ und Ca‐Mangelvarianten gegenubergestellt (klassischer Mangelversuch), in der anderen Halfte wird in diesen Dungungsvarianten zu Zuckerruben, Roggen und Kartoffeln zusatzlich Stallmist gedungt, der in seiner Nachwirkung auch den jeweiligen Folgefruchten zugute kommt. In dem vorliegenden Beitrag werden die Langzeitertrage ausschlieslich der Nullparzellen und der NPKCa‐Volldungungsparzellen mit und ohne Stallmist vorgestellt. Die Ertrage aller genannten Fruchtarten stiegen seit Versuchsbeginn bei organischer oder mineralischer Volldungung um bis zu 100% an, in den absoluten Mangelvarianten stagnierten sie oder fielen in den vergangenen 20 Jahren aufgrund fehlend...

A site-specific slurry application technique on grassland and on arable crops

There is evidence that unequal slurry application on agricultural land contributes to N losses to the environment. Heterogeneity within fields demands adequate response by means of variable rate application. A technique is presented which allows site-specific application of slurry on grassland and arable land based on pre-defined application maps. The system contains a valve controlling flow rate by an on-board PC. During operation, flow rate is measured and scaled against set point values given in the application map together with the geographic position of the site. The systems worked sufficiently precise at a flow rate between 0 and 25 l s(-1) and an offset of actual slurry flow from set point values between 0.33 and 0.67 l s(-1). Long-term experimentation is required to test if site-specific application de facto reduces N surplus within fields and so significantly contributes to the unloading of N in agricultural areas.