Agronomical techniques to improve technological and sanitary quality

In spite of variable grain protein contents, baking quality of organic wheat was found to be acceptable to good. Mycotoxin (DON) infestation was generally low on tested grain samples. Choice of wheat cultivar was the most efficient way to obtain higher grain quality. Fertilization with readily available nitrogen and, to a lower extent, association with legumes and green manures with mixtures containing fodder legumes also improved grain quality. Reduced tillage affected soil quality and wheat yield but had little effects on grain quality

Treatment of backscattering in a gas of interacting fermions confined to a one-dimensional harmonic atom trap

An asymptotically exact many body theory for spin polarized interacting fermions in a one-dimensional harmonic atom trap is developed using the bosonization method and including backward scattering. In contrast to the Luttinger model, backscattering in the trap generates one-particle potentials which must be diagonalized simultaneously with the two-body interactions. Inclusion of backscattering becomes necessary because backscattering is the dominant interaction process between confined identical one-dimensional fermions. The bosonization method is applied to the calculation of one-particle matrix elements at zero temperature. A detailed discussion of the validity of the results from bosonization is given, including a comparison with direct numerical diagonalization in fermionic Hilbert space. A model for the interaction coefficients is developed along the lines of the Luttinger model with only one coupling constant $K$. With these results, particle densities, the Wigner function, and the central pair correlation function are calculated and displayed for large fermion numbers. It is shown how interactions modify these quantities. The anomalous dimension of the pair correlation function in the center of the trap is also discussed and found to be in accord with the Luttinger model.Comment: 19 pages, 5 figures, journal-ref adde

Adiabatic quantum pump in the presence of external ac voltages

We investigate a quantum pump which in addition to its dynamic pump parameters is subject to oscillating external potentials applied to the contacts of the sample. Of interest is the rectification of the ac currents flowing through the mesoscopic scatterer and their interplay with the quantum pump effect. We calculate the adiabatic dc current arising under the simultaneous action of both the quantum pump effect and classical rectification. In addition to two known terms we find a third novel contribution which arises from the interference of the ac currents generated by the external potentials and the ac currents generated by the pump. The interference contribution renormalizes both the quantum pump effect and the ac rectification effect. Analysis of this interference effect requires a calculation of the Floquet scattering matrix beyond the adiabatic approximation based on the frozen scattering matrix alone. The results permit us to find the instantaneous current. In addition to the current generated by the oscillating potentials, and the ac current due to the variation of the charge of the frozen scatterer, there is a third contribution which represents the ac currents generated by an oscillating scatterer. We argue that the resulting pump effect can be viewed as a quantum rectification of the instantaneous ac currents generated by the oscillating scatterer. These instantaneous currents are an intrinsic property of a nonstationary scattering process.Comment: 11 pages, 1 figur

A preliminary investigation of woody plant increase in the Western Transvaal and implications for veld assessment.

The relationships between tree density and indices of pasture and soil condition were examined in Western Transvaal grasslands where Acacia karroo had increased following disturbance. The correlation between tree density and pasture condition was not linear, indicating a threshold in condition below which dramatic increase in trees is likely. Some evidence is presented for a second threshold where soil compaction inhibits seedling establishment and tree density declines. The necessity for assessing tree and soil status in addition to pasture condition is discussed and a variety of possible indicators of pasture, woody plant and soil status is considered.Language: EnglishKeywords: acacia karroo; botany; Condition indices; disturbance; Disturbance history; grassland; grasslands; Multiple disturbance; pasture; potchefstroom; seedling establishment; Soil compaction; south africa; Thresholds; tree density; Veld assessment; Western Transvaal; Woody plant

The development of veld assessment in the Northern Transvaal savanna I. Red Turfveld.

Grazing-induced gradients in pasture species composition were characterised for the red turfveld of the Northern Transvaal savanna. A proposed classification of pasture species response to grazing was develop and the influence of state variables and driving forces other than grazing was recognized. It is argued that the present status of woody vegetation reflects a variety of influences on a variety of scales. Its effect on forage production needs quantification. Relationships between a pasture composition index and the density of "tree equivalents" were demonstrated. Differences in fire history, soil type and/or grazing may have accounted for the occurrence of two distinct regressions. "Condition" indices incorporate the assumption that grazing is the only force acting on the veld apart from season, and their value is questioned. Discussion of benchmarks is left to Part II. There was no evidence of soil change as a consequence of grazing but the importance of soil type in vegetation assessment was noted. Pasture yield was not investigated but deserves study. Gaps in knowledge are discussed and some recommendations for research are offered.Keywords: botany; disturbance history; driving forces; forage production; grazing; northern transvaal; pasture; pasture index; red turfveld; savanna; soil assessment; south africa; species classification; status; veld; veld assessment; woody vegetation; yiel

The development of veld assessment in the Northern Transvaal savanna II. Mixed bushveld.

Differences in pasture species composition as a consequence of grazing were used to develop a proposed classification of pasture species response to grazing, for both the Combretum apiculatum and the Acacia tortilis communities of the northern Transvaal mixed bushveld. The limited value of this approach is discussed in view of likely interactions with other driving forces.Woody vegetation changed in response to grazing in Acacia tortilis veld but not in Combretum apiculatum veld. Two thresholds of change were indicated, one of which coincided with soil change.The value of recognizing thresholds in pasture composition rahter than attempting to identify benchmarks is discussed. A different approach is required, using multivariate analysis to assess the effect of interacting driving forces and state variables. Advances in ecological knowledge are needed to complement the development of veld assessment techniques.Recommendations are made for veld measurement techniques.Keywords: acacia tortilis; benchmarks; botany; bushveld; combretum apiculatum; driving forces; grass balance; grazing; interactions; mixed bushveld; multiple disturbance; multivariate analysis; northern transvaal; soil assessment; south africa; species classification; species composition; techniques; thresholds; vegetation; veld assessmen

Threshold changes in vegetation along a grazing gradient in Mongolian rangelands

1.The concept of threshold has become important in ecology, but the nature of potential threshold responses of vegetation to grazing in rangeland ecosystems remains poorly understood. We aimed to identify ecological thresholds in vegetation changes along a grazing gradient and to examine whether threshold changes were expressed similarly at a variety of ecological sites. 2. To accomplish this, we surveyed the vegetation along grazing gradients at 10 ecological sites, each located at different landscape positions in Mongolia's central and southern rangelands. Evidence for a threshold in changes in floristic composition along the grazing gradient was examined by comparing linear models of the data with nonlinear models fitted using an exponential curve, an inverse curve, a piecewise regression and a sigmoid logistic curve. 3. Three nonlinear models (piecewise, exponential and sigmoid) provided a much better fit to the data than the linear models, highlighting the presence of a discontinuity in vegetation changes along the grazing gradient. The shapes of the best-fit models and their fit to the data were generally similar across sites, indicating that the changes in floristic composition were relatively constant below a threshold level of grazing, after which the curve changed sharply. 4. Except for two sites, the best-fit models had relatively narrow bootstrap confidence intervals (95% CI), especially around threshold points or zones where the rate of change accelerated, emphasizing that our results were robust and conclusive. 5. Synthesis. Our study provided strong evidence for the existence of ecological thresholds in vegetation change along a grazing gradient across all ecological sites. This suggests that vegetation responses to grazing in the study areas are essentially nonlinear. The recognition that real threshold changes exist in real grazing gradients will help land managers to prevent the occurrence of undesirable states and promote the occurrence of desirable states, and will therefore permit a major step forward in the sustainable management of rangeland ecosystems

Nitrogen leaching and herbage production on intensively managed grass and grass-clover pastures on sandy soil in Finland

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