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The Discrete Element Method (DEM) for describing the action mechanism between soil and sweep tool can be used to perform a detailed analysis of draft force, soil cutting, clod-crushing and loosening by taking into account the tillage speed and the three soil phases. This study describes the simulation of the 3D DEM soil model and a cultivator sweep digitized with a 3D scanner, showing the soil—sweep interaction as a function of implement draft force and implement operating speed.

The suitability of the model is validated by comparing the results of laboratory and simulated shear tests (static validation) with the results of soil bin tests (dynamic validation). The mechanical parameters of the sandy soil used for the soil bin tests were measured using the direct shear box test. Cohesion for the soil model used during simulations was set using the parallel bond contact model, where the determining factors were the Young modulus for particle contact (E c ) and bonding (Ē c ), the Poisson’s ratio (nu), the normal (σ) and shear (τ) bond strength and the radius of the related volume (cylinder). Once the DEM model parameters were set, the draft force values measured during dynamic testing were harmonized using the value for viscous damping (c i ).

The dynamic soil—sweep model was validated using the viscous damping applied based on the simulated and measured draft force values. The validation of the Young modulus to 0.55e6 Pa (K n = 1.73e4 N/m, K s = 8.64e3 N/m) enabled us to set the draft force values of the model for different speeds (0.8–4.1 m/s) with an accuracy of 1–4%.

During the analysis of changes in tillage quality, the developed dynamic soil—sweep model showed a high degree of porosity (48%) due to grubbing in the attenuated speed range (0.5–2.1 m/s), and a decreasing tendency (0.41–0.39%) in the non-damped speed range (2.1–4.1 m/s). After the initial equilibrium state, the ratio of average particle contacts for the given porosity decreased in the attenuated speed range (coord number: 4.8), and a slight decrease was also found above speeds of 2.1 m/s (coord number: 5.2). In the model, clod-crushing was examined based on the ratio of sliding contacts, and we found a continuous increase (sliding fraction: 2–15%) in the speed range used for the simulation (0.8–4.1 m/s).

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A lot of attention is being paid to the understanding of the influence of soil degradation on human life at the beginning of the 21 st century. Among the many types of degradation processes, structural degradation is widespread on huge areas in Europe. For better control, it is needed to get familiar with all the driving forces, the main reasons that lead to soil degradation (Várallyay, 2003; ESB, 2002). In addition to unfavourable natural conditions, inappropriate land use has an important impact on micro-aggregate stability and the rate of tolerance to deformation forces, such as cultivation and erosion.  Rheological measurements provide new quantitative information on particle-particle interaction, the colloidal stability and structure of concentrated suspensions in general. Field samples from loess derived agricultural soils were investigated. In addition to general laboratory analyses (soil organic matter content, CaCO 3 content, CEC), conventional, simple aggregate stability, and water retention measurements and rheology were applied for investigating the micro-aggregate stability of the samples. The evaluation of pseudoplastic flow curves indicated close relationships between the strength and stability of the physical network and the composition of the suspensions. These soil properties have strong, well-defined connection with tolerating cultivation and capability for erosion. 

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Agrokémia és Talajtan
Authors:
Éva Lehoczky
,
M. Kamuti
,
N. Mazsu
,
J. Tamás
,
D. Sáringer-Kenyeres
, and
G. Gólya

Plant nutrition is one of the most important intensification factors of crop production. The utilization of nutrients, however, may be modified by a number of production factors, including weed presence. Thus, the knowledge of occurring weed species, their abundance, nutrient and water uptake is extremely important to establish an appropriate basis for the evaluation of their risks or negative effects on crops. That is why investigations were carried out in a long-term fertilization experiment on the influence of different nutrient supplies (Ø, PK, NK, NPK) on weed flora in maize field.The weed surveys recorded similar diversity on the experimental area: the species of A. artemisiifolia, S. halepense and D. stramonium were dominant, but C. album and C. hybridum were also common. These species and H. annuus were the most abundant weeds.Based on the totalized and average data of all treatments, density followed the same tendency in the experimental years. It was the highest in the PK treated and untreated plots, and significantly exceeded the values of NK fertilized areas. Presumably the better N availability promoted the development of nitrophilic weeds, while the mortality of other small species increased.Winter wheat and maize forecrops had no visible influence on the diversity and the intensity of weediness. On the contrary, there were consistent differences in the density of certain weed species in accordance to the applied nutrients. A. artemisiifolia was present in the largest number in the untreated control and PK fertilized plots. The density of S. halepense and H. annuus was also significantly higher in the control areas. The number of their individuals was smaller in those plots where N containing fertilizers were used. Contrary to them, the density of D. stramonium, C. album and C. hybridum was the highest in the NPK treatments.

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