Roger Hartmann

Evaporation losses from bare soils as influenced by cultivation techniques in semi-arid regions.

The impact of cultivation techniques on the evaporation from bare soils was investigated in the laboratory. Two soil-types, which are important resources for rainfed cultivation of olives and almonds in semi-arid regions, were selected: a loamy sand soil and a stony (loam) soil. Evaporation from the soil surface is an important loss of soil moisture in these farming systems since a large percentage of the soil is kept bare in order to maximise the water availability for the tree crop. For the loamy sand soil the impacts of a straw mulch and treatment of the topsoil with olive mill effluent (OME) were tested. For the stony soil the effects of different rock fragment contents and distribution within the soil profile were tested. After thoroughly wetting with simulated rainfall and allowing the soil moisture to redistribute, the columns were subjected to evaporation for 46 days. Cumulative evaporation depth of soils treated with OME was 28% lower than that of the control soil. A similar reduction, be it lower (16%) was observed for the soil with a high rock fragment content by volume (Rva 0.35 m 3 m ˇ3 ). The straw mulch and rock fragment mulch did not have an impact on the cumulative evaporation depth after 46 days. Furthermore, the time required to reach half of the total evaporation losses (d0.5) increased from 9 days for the control soil (loamy sand) to 24 days for the soil impregnated with OME and to 15 days for the straw mulch treatment. The same trend was observed for the stony soils: an increase in d0.5 from 4 days for the control soil (Rva 0.19 m 3 m ˇ3 ) to 7 days for the soil with Rva 0.35 m 3 m ˇ3 and to 8 days for the rock fragment mulch. These experiments show that the changes in water retention capacity of the topsoil by treatment with a hydrophobic substance (OME) or an increase in rock fragment content have a

Using the seasonal and temporal precipitation concentration index for characterizing the monthly rainfall distribution in Spain

Summary The concentration of the rainfall in a year is an important aspect of the climate. An unbalanced distribution of rainfall evokes periods of rainfall excess and periods of drought which make plant and crop growth difficult. Rainfall concentration needs to be considered in the assessment and the prediction of soil losses by water erosion. A statistical derived index, known as the Precipitation Concentration Index is presented to be used in quantifying the relative distribution of the rainfall patterns. Based on the available data sets, two different calculation procedures were used for deriving the Precipitation Concentration Index (Seasonal and Temporal). The application of the two procedures on the rainfall data of two meteorological stations from different climatological regions revealed how the two methods can be used in quantifying the seasonal and temporal concentration of the rainfall. The rainfall data from meteorological stations situated in a central transect of Spain were used in this investigation. From the observed results, it can be concluded that in the Southern part of the transect, the concentration of the rainfall is not a seasonal effect (not strongly confined by a typical dry or wet period) but a temporal effect (bounded to the unreliable, unpredictable character of the rainfall).

Composted grape marc as growing medium for hypostases (Hypostases phyllostagya)

The use of composted grape marc (CGM) as a plant growth medium was investigated with Hypostases (Hypostases phyllostagya). Seven media were prepared using CGM mixed, in different ratios, with native peat and perlite. The following mixtures were used: 100% CGM, 75% CGM + 25% peat, 50% CGM + 50% perlite, 25% CGM + 75% peat, 50% CGM + 25%) peat + 25% perlite, 25%, CGM + 50%, peat + 25% perlite and 100% peat. The experiment was arranged in a randomized plot design with four replicates under greenhouse conditions. After a growing period of three months, some horticultural parameters were measured. Besides, some physical and chemical properties of the growing medium were determined. The mixtures of 50% CGM + 50% peat, 25% CGM + 75% peat and 100% peat were found to be most suitable based on the horticultural parameters. This was confirmed through the physical characteristics. Up to 50% composted grape marc can be used in mixtures with peat on account of its low cost and high nutrient content.

Effects of beer factory sludge on soil properties and growth of sugar beet (Beta vulgaris saccharifera L.)

The possible use of beer factory sludge (BFS) for an agricultural purpose was investigated with sugar beet (Beta vulgaris saccharifera L.). BFS was air dried and sieved through a 4 mm mesh before application to a soil (Typic Xerofluvent). Afterwards, the BFS was mixed with soil at a rate 0, 10, 20, 40, 80 and 160 tonnes ha(-1). The mixtures were than put into pots and kept in the greenhouse for an incubation of five months. During the incubation, pH, the electrical conductivity, the organic matter content, NH4+-N and NO3--N content were regularly measured. At the end of the incubation period, sugar beet seeds were sown into the same pots. After a growing period of six-months the sugar beet plants were harvested, and yield and quality parameters were determined. BFS increased leaf and root yield. However, the effect of BFS on leaf growth was more pronounced than on root growth. The highest sugar content, refined sugar content and refined sugar yield were obtained with the application rate of 10 tonnes BFS per hectare. Ten tonnes of BSF per hectare was the most suitable on the basis of root quality parameters and root yield. However BFS should be applied to the soil six or seven months in advance due to the high level of nitrogen released through mineralization.

THE INFLUENCE OF SOIL CONDITIONERS ON THE LIQUID-SOLID CONTACT ANGLES OF SANDS AND SILT LOAMS

The possibility of changing the wettability of soil is one of the most important reasons for using soil conditioners. The influence of soil conditioners on the liquid-solid contact angle, being an index of the hydrophobic or hydrophilic properties of the soil, was studied on sand and silt loam treated with three different soil conditioners: a bitumen emulsion, a polyvinyl alcohol solution, and a polyacrylamide solution. The most adequate method to measure the contact angle in sandy soils is the equilibrium capillary rise method according to Letey et al. (1962b), whereas the capillary absorption procedure of Hammond and Yuan (1968) is best suited for silt loam. The bitumen emulsion gives a highly hydrophobic character to the sand as well as to the silt loam. The treatment with the polyvinyl alcohol and polyacrylamide polymers had a different effect on both textures. The sandy soil became hydrophobic, whereas the silt loam grew more hydrophilic.

COMPARISONS OF THE UNSATURATED HYDRAULIC CONDUCTIVITY OF A COARSE-TEXTURED SOIL AS DETERMINED IN THE FIELD, IN THE LABORATORY, AND WITH MATHEMATICAL MODELS

Several methods for determining the hydraulic conductivity-volumetric water content relationship have been developed. We evaluated on a sand dune soil three different methods for determining hydraulic conductivity values. The first method is known as the internal drainage-instantaneous profile method and was carried out on the field. The second method was analogous to the first but was carried out in the laboratory. The results obtained by these two experimental techniques were then used as a reference for comparing with the hydraulic conductivity functions predicted by the third method, mathematical models. For this numerical approach, the Jackson and the Mualem formulation was selected. For the coarse-textured soil used in this investigation, all three methods resulted in hydraulic conductivity functions that were in fairly good agreement. Moreover, the differences between the laboratory experiment and the field experiment were greater than the deviations of the mathematical models, although subtle differences were found. It seemed that Mualems model for calculating the hydraulic conductivity function, combined with the van Genuchten equation for the soil water retention equation, is the easiest to use and leads to the most accurate results for this particular soil.

Modification of the aggregate stability indices for the wet sieving method and the water drop technique

Abstract Soil samples from an experimental field were investigated. The aggregate stability using the wet sieving method and the water drop technique as well as the soil erodibility using a rainfall simulator was calculated. Since it was found that the soil erodibility increases with increasing soil aggregate stability due to the problem of relativity imposed by the aggregate diameter, subsequently, some modifications were introduced to restore the normal trend.

Evaporation in layered soils under different rates of clay amendment.

This study was devoted to the analysis of the evaporation process under natural conditions on a bare layered soil. The first and third layers are similar in all the plots. The intermediate layer differs from one plot to another by the rate of the clay amendment. The cumulative evaporation was estimated using the water balance method. Experimental results indicate that the amendment of 2% is the most efficient in preventing evaporation losses when a long time scale is considered. Whatever the non-zero rate of the amendment is, the evaporation curves coalesce in a single one when expressed in a dimensionless form. Differential calculus yields the optimal rate of the amendment for which cumulative evaporation is minimal at a fixed time.

Field determined variation of the unsaturated hydraulic conductivity functions using simplified analysis of internal drainage experiments

Experimentally determined values of unsaturated soil hydraulic conductivity are presented for an Alfisol of the county of Piracicaba, S.P., Brazil. Simultaneous measurements of soil water content and pressure head are made along a 125 m transect within an irrigated field during the internal drainage process. Calculations of the soil hydraulic conductivity were made using the instantaneous profile method (Watson, 1966) and the unit gradient method (LIBARDI et al., 1980). The spatial variability of the soil hydraulic conductivity manifested along the transect indicates the need to develop a field method to measure K(q) within prescribed fiducial limits, taking into account quantitative evaluation of spatial and temporal variances associated with the mathematical model, instrument calibration and soil properties.

Effect of application of pig slurry on soil penetration resistance and sugar-beet emergence

Abstract The effect of the application of 50, 100 and 200 t ha−1 of pig slurry on soil penetration resistance, and sealing of the soil surface as a result of rainfall, was studied for a sandy loam soil in the field and under laboratory conditions, respectively. In the field, after slurry application and ploughing, a somewhat higher penetration resistance in the ploughed layer was noticed on the plots that had been fertilized with the liquid pig manure. In the laboratory, a superficial application of the pig manure resulted, after simulated rainfall, in lower penetration resistance of the soil surface. However, mixing the slurry with the soil gave a higher penetration resistance. Additionally, the emergence of sugar beet seeds and the oxygen diffusion rate in the soil under laboratory conditions was monitored. The emergence of the sugar beet seeds was much slower in the soil that received pig manure, but final emergence was similar in all treatments. The oxygen diffusion rate showed no difference at all among treatments. An application of 200 t ha−1 pig slurry increased the soil salinity from 1 to 6 mS cm−1.