The water balance of a sugar beet crop: A model and some experimental evidence

For a loes soil with sugar beets (Beta vulgaris L.) a model was developed with which the difficult-to-measure components of the water balance equation can be determined. Basic component of the model is the unsaturated soil moisture flow equation. This equation is solved numerically by a finite difference method. As boundary condition at the soil surface, expressions for the potential and the actual transpiration and for the potential and the actual evaporation are used. Besides the hydraulic functions of the soil, standard meteorological measurements, together with leaf area index and root distribution data of the crop, enter the model. For a period of 316 days, calculated and measured soil suction values in 10 different soil depths, are compared as well as transpiration and seepage vaules. The comparison shows that the model provides acceptable results. The model calculations indicate that of the 519 mm of precipitation received during the 316-day period, 503 mm were used for evapotranspiration and 119 mm left the soil profile as internal seepage.     

Mid-term trends in acid precipitation,streamwater chemistry and element budgets in the strengbach catchment (Vosges Mountains,France)

In the Vosges Mountains (NE of France), integrated plot-catchment studies have been carried out since 1985 in the Strengbach basin to study the influence of acid atmospheric inputs on surface water quality and element budgets. In this paper, available mid-term time series (1985–1991) have been considered to detect obvious trends, if any, in surface water chemistry and element budgets. Air quality data showed a slight decline for SO₂, whereas NO₂ slightly increased over the period, but these trends are not very significant. This is in agreement with increased N concentration (mainly as NH ₄ ⁺ ) and with the stability of SO ₄ ^2? in open field precipitation. Because of a significant decrease in rainfall amount over the period, only inputs of NH ₄ ⁺ increased significantly whereas H⁺ and SO ₄ ²⁺ inputs declined. In spring and streamwaters, pH and dissolved Si concentration increased mainly as a result of a reduced flow. Na⁺, K⁺, Cl^? and HCO-3~^? concentrations remained stable whereas Ca²⁺, Mg²⁺ and SO ₄ ²⁺ concentrations declined significantly. Only NO ₃ ^? concentration increased significantly in springwaters. The catchment budgets revealed significant losses of base cations, Si and SO ₄ ^2? . These losses decreased over the period. Nitrogen was retained in the ecosystem. However, a longer record is needed to determine whether or not changes in surface water chemistry have resulted from short-term flow reductions or long-term changes in input-output ion budgets. This is specially true with N because the decline in SO ₄ ^2? output was accompanied by N accumulation.     

Über Immunität bei Insekten

Ohne Zusammenfassung Mit 13 Abbildungen.