To determine the significant differences between Conventional and Biodynamic treatments in vineyard in terms of soil bulk density, water infiltration and penetrometer resistance
McLaren Vale vineyard - Experimental site and management
The experimental site as figured above is 9.3 ha of own rooted cv. Cabernet Sauvignon (V. vinifera) vines. The project site was established in 1989 and is part of a 108 ha commercial vineyard in McLaren Flat, South Australia. There are two 1.6 ha blocks (each block consisting of 4 treatments and each replicated twice). Each replicate (0.2 ha) consists of 8 rows, with 40 vines per row making up 1,666 vines/ha. Four treatments (organic, biodynamic, low input conventional and conventional) were defined by a steering committee in September 2008. Of four, two treatments were selected - Biodynamic and Conventional each replicated twice. In this study, a comparative assessment has been done between soils in a biodynamic and a conventional treatment. For each treatment, soil samples were collected for calculating the bulk density and measurements for water infiltration rates and penetrometer resistance were taken.
Approach to Biodynamic
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Biodynamic is a term coined by an Austrian philosopher Rudolf Steiner in 1924. Bio-dynamics is "a holistic approach that emphasises soil building and a high diversity of crops, animals, and wildlife habitat". Biodynamics makes use of biodynamic preparations (500-508) without further addition of nutrients but are claimed to stimulate the processes of nutrient and energy cycling (Koepf et al. 1990).
Conventional approach in itself is difficult and broad. Conventional treatment makes use of herbicides, synthetic pesticides, fungicides and insecticides as a means to suppress weeds and disease pressure. However, conventional approach can now be defined as "low input" and may use traditional organic practices, such as sowing cover crops, adding compost and using soft chemical. However, less attention has been drawn in conventional treatments in order to maintain a biologically active soil (Gehlen 1988).
Difference between biodynamic and conventional system
Studies of biodynamics and conventional management indicate that soil properties are negatively affected by conventional practices, or alternatively it is positively influenced by biodynamic practices. Distinguishing between biodynamic and conventional systems, the greatest difference that arises is the compost addition and weed control. Compost is a major component of organic and biodynamic systems (Madge 2007). It is beneficial to all components of vineyard soil fertility (Buckerfield and Webster 2000). Compost when used as mulch has been found to improve water retention and soil infiltration rates (Mundy and Agnew 2003, Webster 2003) and reduce vineyard weed growth (Buckerfield and Webster 2002). It also increases earthworm numbers and soil biological activity (Mundy and Agnew 2003). It has been claimed for long that biodynamic practices increase soil biological properties and biodiversity (Lotter 2003). However, other factors such as soil type, time of measurement and specific management practices (eg: compost additions) may play a greater role, than whether the management is biodynamic or conventional (Bossio et al. 1998, Abbott and Murphy 2003).
Biodynamic practices generally support greater biological activity than conventional methods (Reganold et al. 1993, Carpenter-Boggs et al. 2000c). It has been proposed that biodynamic treated vineyards have 50 - 300% higher levels of microbial biomass, earthworm counts as compared to conventional vineyard (Gehlen 1988).
Soil properties have been defined by many soil scientists in terms of physical and chemical parameters for successful plant growth and nutrition; however, biological properties are more difficult both to quantify and qualify (Abbott and Murphy 2003). Only one long-term study has compared biodynamic and conventional treatments with respect to soil properties (Gehlen 1988). Soil properties - Bulk density, water infiltration and penetrometer resistance have been measured and analysed in both the treatments and significant conclusions were drawn as which treatment has higher levels of infiltration rates and how well structured the soil is in terms of bulk density.
Soil structure is important because it provides storage and the capacity for movement of water, gases and heat, which in turn determines the availability of nutrients to the plant (Robertson et al. 1999). Good soil structure provides a habitat for soil organisms enables root growth and limits damage from erosion. Structure can be measured by bulk density, aggregate stability, pore size, air capacity and water holding capacity (Kasperczyk and Knickel 2006). Comparative studies have often found biodynamic management improves soil structure as compared to conventional practices (Reganold et al. 1987). However, it has been concluded that benefits in biodynamic practices are due to the organic principles (Carpenter Boggs et al. 2000b).
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Bulk density is defined as the mass of oven dried soil per unit volume and depends on densities of constituent soil particles like organic matter, clay etc. (White R.E. 1997). Biodynamic system, high in organic matter the bulk density values range from <1g/cm3 - 1.2 whereas for conventional system it ranges from 1.2-1.8g/cm3 (compacted horizons in clay soils).
Material and method
Measurements for bulk density were made on soil surface by driving a steel cylinder of known volume in initial soil depth of 0-5 cm followed by 5-10 cm and then to 10-15 cm. This is because the dimensions were made in the first 50cm of the soil as different management practices are easily tracked and evident mainly in the topsoil (Droogers P. and Bouma J. 1996). The cylinder is drawn in intact soil core and the soil sample was collected, oven-dried and weighed. The diameter of the cylinder should be 10times its thickness so as to avoid additional compaction of the soil core.
NOTE: Cup weight: 15.26 g
Soil volume in cylinder = (2.5)2*3.1415*5 = 98.17 cm3
Results and discussion
Volumetric water content (cm3/cm3)
Bulk Density (g/cm3)
Soil depth (cm)
Wet soil + cup weight (g)
Bulk density (g/cm3)
Gravimetric water content (g/g)
Volumetric water content (cm3/cm3)
Av Biodynamic (R1 R2 R3 R4)
Av Conventional (R1 R2 R3 R4)
From Figure 1 above, it has been analysed that bulk density increases with soil depth which can be explained on the fact that density at depth of soil is less convenient to measure. Bulk densities were found to be lower for the biodynamic as compared to conventional system (Table 1&2). This is because the biodynamic treatment is enriched with organic matter and as the organic matter increases the bulk density decreases and vice versa (White R.E. 1997). Furthermore, there is an increase in organic matter with soil depth leading to decline in bulk density values. In case of conventional treatment, bulk densities were higher because of decreased organic matter. In biodynamic treated surface soils (0-15 cm) had significantly higher organic matter content, thicker topsoil and microbial activity as a result of which the bulk density is lower than the conventional treated soil (Reganold J.P. 1995). In addition, there is an inverse relationship between bulk density and total porosity and can be assessed when the soil aggregates are in coherence. Presence of organic matter in biodynamic soil resulted in modifying these properties. The biodynamically treated soils are less compacted which means more porosity and thereby reduced/low bulk density while in conventional system compaction resulted in reduced porosity and hence increase in bulk density. This can be further explained as the larger organic matter content is due to the biodynamic manure preparation that increase the organic matter in comparison to mineral fertilizers and to the intermittent applications of compost (Hitchins J.A.L. et al 1994). It is well known fact that soil strength tends to increase with bulk density. For a good soil structure aggregates are important that aids in movement and storage of soil water. The test above confirms that biodynamic soil were found to have numerous aggregates and the soil surface was soft in contrast to conventional treatment where there were few aggregates and the soil surface was hard. This observation points out that conventional system has more soil strength and hence higher bulk density.
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The overall impression was that there are relatively small structural differences. Soil compaction leading to large structural elements with low internal porosity appeared to be more pronounced for the conventional soil despite of being actively present in both the systems. There are significant differences in soil organic matter (SOM) content and water availability in favour of Biodynamic treated soils and therefore, soil density, and thus compaction, was lower in Biodynamic soil (Turinek M. 2009).
Infiltration is defined as the movement of water into the soil from above. Suction gradient is an important element while measuring the water infiltration rate. The gradient is predominant in early stages of wetting a dry soil. The relationship between infiltration and suction gradient is inversely proportional which means that as the depth of wet soil increases, the suction gradient declines. Initially, water infiltration follows a preferential flow down macropores but once critical value for surface detention reaches, runoff occurs. When a soil is structurally homogeneous and if water continues to move over the soil surface and travels down at a constant rate, it is known as infiltration capacity or infiltrability of the soil.
Material and method
For measuring the water infiltration rate of the soil, a steel ring of 100mm diameter called ring infiltrometer is used. The infiltrometer is driven into 50mm top soil surface at a short distance and water is allowed to move to a known depth inside the ring infiltrometer. When infiltration is achieved, infiltration capacity/rate is then estimated by measuring the rate of loss of water from the ring. After few minutes the ring would be topped-up with a measured volume of water and the infiltration assessed.
Results and discussion Table 3
Infiltration rate (cm/h)
It was found that the soils treated with biodynamic system have higher water infiltration rates, porosity than the conventionally farmed soils. This could be due to improved soil structure and better water relations in biodynamic soil in contrast to conventional soil. Figure 4 above illustrates a sharp change in water content at wetting front (wetting zone) which clearly shows that biodynamically treated soils have higher infiltration rates which is possible due to the rapid flow of water down the channels and cracks thereby flow of bulk water penetrates into the micropores and aggregates (known as matrix flow). In addition, as the soil in biodynamic treatment possess good structure due to good C respiration and soil organic matter water takes up a preferred potential position of minimum potential energy in the smallest pores and does not move at a appreciable rate unless the large pores down the channel begins to fill. The overall result is that the hydraulic conductivity decreases at saturation. From figure 4 it can be seen that the infiltration of the biodynamically managed soil was double the conventionally managed soil with a steady state infiltration being about two times higher. Water infiltration is an indirect measure of soil structure. It was observed that water movement was less impeded in biodynamic soil than conventional treatment which means that on conventional treatment high rainfall intensities could not be absorbed immediately (Podolinsky A. 2000).
The third soil property is the penetration resistance. This soil property measures the compaction of soil profile with a standard instrument called Penetrometer. It should be noted that penetration resistance is highly variable and so a number of readings were taken. The measurement of Penetrometer resistance depends largely on soil moisture content and it is best used in comparative sense rather than used as absolute sense (White R.E. 1997).
Material and method
Penetrometer resistance is measured using a Penetrometer comprised of a rod of about 1m long with a conical tip and provided with a proving ring and strain gauge at the top. It is done by driving the rod into the soil, the ring is distorted and the force is recorded by the gauge. Penetrometer is simple, reproducible and an effective measure of soil compaction. It is effective both in wet and dry conditions (Podolinsky A. 2000).
Result and discussion
Average - Penetrometer resistance
It has been found that conventional treatment required more blows to penetrate the soil profile and the rod went deeper into the soil which suggests that the conventional soil profile was harder to penetrate as compared to biodynamically managed soil. When relate to the bulk density it was found that biodynamic soil has reduced bulk density and hence less compaction whereas in case of conventional soil, bulk density was higher due to soil strength and more compaction.
In conclusion, it can be said that biodynamic soil had lower bulk density, higher organic matter, high water infiltration rates and less penetration resistance as compared to soil in conventional system. These results were drawn with sufficient statistical representation. Soil properties in biodynamic system have potential to allow faster infiltration, less compaction and lower bulk densities. The descriptions relevant to soil structure are highly qualitative and non-diagnostic. Therefore in the end it can be concluded that biodynamic management has favourable effects on soil structure thus providing a positive contribution to the sustainability analysis.
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