Soil bulk density
Soil bulk density — ratio of the mass of soil of undisturbed structure to its volume.
Equilibrium soil bulk density — equilibrium state between porosity and the solid phase of soil, which occurs under natural conditions in the absence of tillage for 1–2 years under the influence of gravity, precipitation, and other natural factors.
Dry soil bulk density (ρds) is calculated by the formula:
where
- md
- — mass of absolutely dry soil with undisturbed structure;
- V
- — volume of absolutely dry soil with undisturbed structure.
Bulk density depends on particle-size composition, humus content, number of water-stable aggregates, and moisture content. With a heavy particle-size composition with a large proportion of silt fraction and humus, soils are subject to significant swelling upon wetting and loosening, which leads to a change in equilibrium and optimum density.
Optimum density
Optimum density — soil density at which the most favorable conditions develop for plant growth and the activity of soil microorganisms. Optimum density for most crops is considered to be 1.0–1.2 g/cm3 (according to other data, 1.0–1.3 g/cm3). A density above 1.55–1.6 g/cm3 is considered critical.
Studies of plant response to the physical state of soils of different genesis have made it possible to determine the ranges of optimum density values for grain and row crops. For example, modeling of the bulk density of sod-podzolic medium loamy soil showed that the optimum density in years with average moisture for cereal grain crops is 1.1–1.3 g/cm3, for potatoes — 1.0–1.2, for sugar beet — 1.1–1.5 kg/m3, and for other row crops — 1.0–1.2. The equilibrium density of the same soils is 1.35–1.50 g/cm3.
Table. Equilibrium and optimum soil bulk density for field crops (according to A. I. Puponin, 1986), g/cm3.
| Soil | Particle-size composition | Equilibrium density | Optimum density for crops | |
|---|---|---|---|---|
| grain crops | row crops | |||
| Sod-podzolic | Sandy | 1.5–1.6 | - | 1.4–1.5 |
| row | Sandy loam | 1.3–1.4 | 1.2–1.35 | 1.10–1.45 |
| row | Loamy | 1.35–1.50 | 1.1–1.3 | 1.0–1.2 |
| Sod-carbonate | Loamy | 1.4–1.5 | 1.1–1.25 | 1.0–1.2 |
| Sod-gley | Loamy | 1.4 | 1.2–1.4 | - |
| Meadow floodplain | Loamy | 1.15–1.2 | - | 1.0–1.2 |
| Bog | Degree of peat decomposition 35–40% | 0.17–0.18 | - | 0.23–0.25 |
| Gray forest | Loamy | 1.35–1.4 | 1.15–1.25 | 1.0–1.2 |
| Chernozem | Loamy | 1.0–1.3 | 1.2–1.3 | 1.0–1.3 |
In structured soil, the gap between optimum and equilibrium density is minimal, and in well-cultivated soils they may coincide, for example, in chernozems. Chernozem soils with a high humus content have an equilibrium density of 1.0–1.3 g/cm3, coinciding with the optimum, which makes it possible to reduce the intensity and depth of tillage. Optimal conditions for the emergence of cereal crops seedlings, as well as for reducing moisture evaporation, are formed in chernozem heavy loamy soil when the density of the upper 7-cm layer is 0.98–1.04 g/cm3, and that of the lower layer at a depth of 7–30 cm is 1.18–1.20 g/cm3. To achieve such a combination of densities, a combination of different-depth moldboard and nonmoldboard tillage with surface tillage is used.
List of sources
- Bazdyrev G. I., Loshakov V. G., Puponin A. I., et al. Agriculture. Textbook for universities. Moscow: Kolos Publishing House. 2000.
- Mineev V. G., Sychev V. G., Gamzikov G. P., et al. Agrochemistry. Textbook. / Ed. by Mineev V. G. Moscow: Publishing House of the All-Russian Research Institute of Agrochemistry named after D. N. Pryanishnikov. 2017.
- Yagodin B. A., Zhukov Yu. P., Kobzarenko V. I. Agrochemistry. / Ed. by B. A. Yagodin. Moscow: Kolos. 2002.
- Klenin N. I., Kiselev S. N., Levshin A. G. Agricultural machines. Moscow: KolosS. 2008.
- Khalansky V. M., Gorbachev I. V. Agricultural machines. Moscow: KolosS. 2004.
