Ewa A. Czyż

Plant wilting can be caused either by the plant or by the soil

In this paper, plant wilting is re-analysed and re-interpreted on the basis of previously published work. Wilting is considered only in terms of the stress caused by the matric suction of the soil water. Other factors that can induce wilting, such as salinity and plant pathogens, are not considered. It is found that there is confusion around the subject for two main reasons. First, it is usually assumed that the matric suction of the pore water that exists in soil samples when they are removed from pressure plate extractors is equal to the air pressure that was applied. Second (and this is a special case of the first reason), because the soil water content when most plants wilt is very close to that remaining in soil samples on pressure plates operating with an air pressure of 1.5 MPa, it is assumed that plants wilt at a pore water suction of 1.5 MPa. These assumptions are examined here, and it is shown that neither of them is true. Published results are used for the wilting condition. The recently described double-exponential (DE) equation for soil water retention is used for cases where the water is non-equilibrated because of hydraulic cut-off. The non-equilibrated condition is appropriate for plant roots because they, like pressure plate extractors, extract water from soil by immiscible displacement. The DE equation is used to illustrate the conditions under which plant wilting can be either a plant or a soil property. It is shown how this approach can be used to estimate the pore water suction at which plants would wilt because the soil is no longer able to supply water to their roots. It is demonstrated that the commonly used, but often erroneous, value for the wilting-point suction of h = 1.5 MPa is a consequence of the fact that this is the largest value of air pressure used in pressure cell extractors. It is therefore neither a plant nor a soil property, but is an artefact of the experimental procedure. The use of the DE equation for soil water retention shows that we know only that h ≤1.5 MPa, and that h can be as small as 0.2 or 0.3 MPa. Implications for estimation of plant water availability in soils, for plant breeding, and for soil microbial activity are discussed.

Effects of long-term use of different farming systems on some physical, chemical and microbiological parameters of soil quality

Abstract The aim of this study was to compare the effects of different farming systems (organic, integrated, conventional and monoculture) on some soil properties as: bulk density, contents of readily-dispersible clay, organic matter and particulate organic matter, and enzymatic activity measured in terms of the intensity of fluorescein diacetate hydrolysis. Soil under permanent grass was used as a control. The study was conducted on the 20 years lasting field experiment. Samples of Haplic Luvisol soil were collected twice a year on fields under winter wheat from the layers of 0-5, 5-10, 15-20, and 30-35 cm. Within arable soils the soil under organic farming contained the greatest amount of organic matter, which influenced strongly the readily-dispersible clay content, especially in the layer of 5-20 cm. The readily-dispersible clay content in soil under organic farming was 3 times lower, as compared to the conventional and monoculture farming. The highest contents of particulate organic matter 6.2 and 3.5 mg g−1 air dry soil, on average were measured in the 0-5 cm layer of control soil and soil under organic farming, respectively. Also, soil under organic farming and control soil from the depth of 0-5 cm showed 2-2.5 times greater activity of microorganisms in fluorescein diacetate hydrolysis than soil under conventional and monoculture farming. Increase of concentration of organic matter in soil under organic farming decreased soil bulk density. Statistical analysis showed significant correlations between studied parameters of soil quality and confirmed their effectiveness as indicators of disturbances in soil environment.

Estimation of the density of the clay-organic complex in soil

Abstract Soil bulk density was investigated as a function of soil contents of clay and organic matter in arable agricultural soils at a range of locations. The contents of clay and organic matter were used in an algorithmic procedure to calculate the amounts of clay-organic complex in the soils. Values of soil bulk density as a function of soil organic matter content were used to estimate the amount of pore space occupied by unit amount of complex. These estimations show that the effective density of the clay-organic matter complex is very low with a mean value of 0.17 ± 0.04 g ml−1 in arable soils. This value is much smaller than the soil bulk density and smaller than any of the other components of the soil considered separately (with the exception of the gas content). This low value suggests that the clay-soil complex has an extremely porous and open structure. When the complex is considered as a separate phase in soil, it can account for the observed reduction of bulk density with increasing content of organic matter.

Mechanical dispersion of clay from soil into water: readily-dispersed and spontaneously-dispersed clay

Abstract A method for the experimental determination of the amount of clay dispersed from soil into water is described. The method was evaluated using soil samples from agricultural fields in 18 locations in Poland. Soil particle size distributions, contents of organic matter and exchangeable cations were measured by standard methods. Sub-samples were placed in distilled water and were subjected to four different energy inputs obtained by different numbers of inversions (end-over-end movements). The amounts of clay that dispersed into suspension were measured by light scattering (turbidimetry). An empirical equation was developed that provided an approximate fit to the experimental data for turbidity as a function of number of inversions. It is suggested that extrapolation of the fitted equation to zero inversions enables the amount of spontaneously-dispersed clay to be estimated. This method introduces the possibility of replacing the existing subjective, qualitative method of determining spontaneously-dispersed clay with a quantitative, objective method. Even though the dispersed clay is measured under saturated conditions, soil samples retain a ‘memory’ of the water contents at which they have been stored.

Changes in the matric potential of soil water with time and temperature.

The temperature dependence of the matric potential of soil water was investigated as part of a study of the effects of climate change on soil physical properties. Undisturbed samples of topsoils were collected in cylinders. The pore water suction near the center of each cylinder was measured using two miniature tensiometers. The temperature of the samples was varied in the range of 10°C to 40°C. Three different phenomena were observed. The first was a slow drift to increased pore water suctions with time. This was attributed to the rearrangement of soil particles and has been described as the age-hardening or thixotropic effect. The second was the appearance of pressure transients when the temperature was changed stepwise. These were such that a step increase in temperature produced a rapid reduction of pore water suction that decayed during a period of hours. This was attributed to pressure changes of gas bubbles entrapped within water-filled pores-these pressure changes being transmitted to the pore water. The third (or TISSI) effect was a linear increase in pore water suction with time that started at temperatures around 40°C. This increased rate of change persisted for at least three further days after the temperature was again reduced to 20°C. Tests with sand showed none of the above effects. Several hypotheses were tested in attempts to explain the third phenomenon. These included tests to determine if some soil components were dissolving at higher temperatures. However, neither electrical conductivity nor optical absorbance showed any effects at temperatures up to 45°C and times of up to 7 days. It is conjectured that the TISSI effect is associated with the formation of organic micelles, although this needs further research to confirm it.

Effects of different soil management practices on soil properties and microbial diversity

Abstract The effects of different tillage systems on the properties and microbial diversity of an agricultural soil was investigated. In doing so, soil physical, chemical and biological properties were analysed in 2013-2015, on a long-term field experiment on a loamy sand at the IUNG-PIB Experimental Station in Grabów, Poland. Winter wheat was grown under two tillage treatments: conventional tillage using a mouldboard plough and traditional soil tillage equipment, and reduced tillage based on soil crushing-loosening equipment and a rigid-tine cultivator. Chopped wheat straw was used as a mulch on both treatments. Reduced tillage resulted in increased water content throughout the whole soil profile, in comparison with conventional tillage. Under reduced tillage, the content of readily dispersible clay was also reduced, and, therefore, soil stability was increased in the toplayers, compared with conventional tillage. In addition, the beneficial effects of reduced tillage were reflected in higher soil microbial activity as measured with dehydrogenases and hydrolysis of fluorescein diacetate, compared with conventional tillage. Moreover, the polimerase chain reaction – denaturing gradient gel electrophoresis analysis showed that soil under reduced till-age had greater diversity of microbial communities, compared with conventionally-tilled soil. Finally, reduced tillage increased organic matter content, stability in water and microbial diversity in the top layer of the soil.

Effects of reduced and traditional tillage on soil properties and diversity of diatoms under winter wheat

Abstract The aim of this study was to quantify soil properties, microbial biodiversity and crop yield under two tillage systems used for winter wheat production in monoculture. The study was conducted in the period 2013-2016, on a long-term field experiment on a silt loam at the Krasne Research Station near Rzeszów, Poland. Traditional tillage involved soil inversion whereas reduced tillage was a non-inversion system. The following soil properties: chemical (soil organic carbon, pH, available P, K, Mg), physical (soil bulk density, water content, stability in water), and biological (the diversity of diatoms) were measured on samples collected throughout the growing season and at harvest. Soil organic carbon content, water content and bulk density in the 0-5 and 5-10 cm layers were greater in reduced tillage than in traditional tillage. Under reduced tillage the amount of readily dispersible clay was reduced giving increased soil stability in water. Soil under reduced tillage had greater diversity of diatoms (139 taxa) than that under traditional tillage (102 taxa). Wheat yields were positively correlated with precipitation, soil water content and soil organic carbon, and negatively correlated with readily dispersible clay.

Clay-organic complexes in a Polish loess soil

Abstract Complexes formed between clay and soil organic matter are important for carbon sequestration and for soil physical quality. Here, we use samples of loessial soil from South-East Poland to explore the phenomenon of complexing in loess. Soil samples were collected from a single catchment 8 years after the introduction of strip tillage and their compositions were characterized by traditional methods. Complexing was characterized in terms of the content of non-complexed clay which was estimated in two ways: firstly, by measurement of the content of readily-dispersible clay (which was assumed to be the non-complexed clay); and secondly, by calculation using algorithms that had been developed and evaluated previously. The calculations were based on the concept that, at carbon saturation, the clay/organic carbon mass ratio is equal to n. The calculations were done with a range of values of n. It was assumed that the correct value of n was that which gave the greatest coefficient of correlation between the measured values of clay dispersion and the predicted values of non-complexed clay. For the loess used, the optimum value was n = 14.

Physicochemical Properties of Silt Loamy Soil and Diversity of Diatom Species Under Winter Wheat and Oats

The aim of the research was to investigate the soil properties and the species diversity of diatoms growing in different agricultural fields with silt loamy soil. The field experiment was conducted in 2014 in Kosina, near Łańcut (SE Poland), at three sites (indicated as fields K1, K2, K3) with different soil environmental conditions and plants. The growth of winter wheat Triticum aestivum (cv. Bogatka) in fields K1 and K2 and oats Avena Sativa (cv. Haker) in field K3 under different soil management were studied. The soil samples were collected from the top layers (0–5 cm depth) each month, from April to December. Certain physical and chemical parameters of soil were measured. The pH of soil was acidic and slightly acidic in fields K1 (5.0–5.4), K2 (4.9–5.9) and K3 (4.5–5.1). The soil in field K3 had a significantly greater content of organic matter (1.06–1.30%) and water content (12.9–33.8%, v/v) than fields K1 and K2. A total of 91 diatom taxa were found. The diversity was greatest in field K2 (71 taxa), lower in K1 (54 taxa) and K3 (24 taxa). In K1, the most numerous species were Luticola D.G. Mann cf. mutica, Mayamaea atomus var. permitis (Hust.) LangeBertalot, and Stauroneis thermicola (Petersen) Lund, with more than a 20% share in the assemblage. In K2, very abundant assemblages were formed by Mayamaea atomus (Kütz.) Lange-Bertalot, Mayamaea atomus var. permitis (Hust.) Lange-Bertalot, and Stauroneis thermicola (Petersen) Lund with a 25 to 50% share in the total diatom community. In K3, with oat cultivation, a different diatom species structure was found. Here, the most abundant were Halamphora montana (Krasske) Levkov, Hantzchia amphioxys (Ehrenb.) Grunow, Mayamaea atomus (Kütz.) Lange-Bertalot, and Nitzschia pusilla Grunow, which attained a share in the assemblage exceeding than 20%. The effects of different soil management regimes under different plants on the physical and chemical properties of the soil, and on the diversity of diatoms, were significant (P<0.05). Soil water and organic matter content affects the yield of winter wheat and oats. Significant effects of water content and pH of silt loamy soil on the growth and the diversity of species of diatoms were found.