Radical Reclamation of Sandy Soils Using Peat Suspension

F. A. Malyshev, P. E. Anikhovskaya, M. N. Bryantseva

The natural fertility of sod-podzolic light soils is low and depends to a considerable degree on the water regime [8]. The water regime can be improved by changing the physical and chemical properties of soils through the introduction of peat suspension into them. For this purpose, the All-Union Scientific Research Institute of Peat developed the mechanization and technology for applying peat suspension [1] and studied its effect on the radical change of the water-physical properties of light soils and on increasing their fertility.

After peat suspension is poured onto the surface of fields, with the liquid phase seeping into the soil, fine peat particles penetrate into the soil. The phenomenon of peat-particle penetration into the depth has a decisive influence on the change in the water-physical and mechanical properties of the soil below the arable layer and on increasing its fertility [2].

When peat suspension with a solids content of 4% is applied to sandy soil, on plots with peat at rates from 50 to 500 t/ha (calculated at 60% moisture), over three days below the arable soil layer (20 cm) from 1.7 to 6.7% of the peat particles penetrated.

The content of organic matter in the soil after the application of hydropeat increases with depth down to one meter. On plots fertilized with peat at a rate of 280–380 t/ha, the arable layer contains 3–6% more organic matter than the control plots. At a depth of 20–40 cm on plots with hydropeat, the excess of organic matter reaches 2%; at a depth of 40–60 cm, up to 0.4%; at a depth of 60–80 cm, up to 0.3%. Below the indicated depth, on some plots with peat, compared with the controls, the content of organic matter is also somewhat increased.

A higher content of organic matter in the arable and underlying layers fertilized with hydropeat is observed over a number of years (Table 1).

In the process of peat suspension seeping into the soil, fine peat particles are deposited; i.e., the concentration of peat in the suspension decreases with depth. As the suspension seeps into the soil and the number of peat particles in it decreases, the viscosity of the suspension decreases, approaching more and more the viscosity of water.

Peat suspension seeps through the soil pores first of all where there is less resistance to its movement, i.e., through the larger pores, which are occupied to a lesser extent by physically bound water [3, 4].

The most important physical property of soil is porosity. It determines a number of very important soil qualities, such as moisture capacity, water permeability, air permeability, and the rate and height of the rise of water from the lower soil layers to the upper ones.

Table 1

Organic-matter content in the sixth year after the application of peat suspension

In soils heavier in mechanical composition, porosity is made up of finer pores. Sandy soil has a large number of coarse pores and an insignificant number of fine ones. Water entering it quickly seeps through the coarse pores into the lower layers and is retained only slightly in the arable horizon.

The porosity in sandy loam and sandy soils after the application of peat suspension and its incorporation into the upper layer at a depth of 0—20 cm becomes greater by 5–8% than in the controls. Below 20 cm, porosity decreases in both plots; however, in the plot with peat the decrease proceeds more sharply, as a result of which porosity there is lower than in the control (Table 2).

Table 2

Change in porosity in the second year after the application of hydropeat—30 t/ha to sandy-loam soil

It should be noted that in the thirteenth year after the application of 380 t/ha of peat, recalculated to 60% moisture content, porosity in the arable layer was 9% higher, and with the application of 140 t/ha—4% higher, than in the control.

This regularity in the change of porosity is observed in all cases where hydropeat was applied, with the only difference that in soils heavier in mechanical composition these phenomena are less pronounced.

The change in soil porosity depends on the size of the peat fractions from which the peat suspension is prepared; i.e., a finer fractional composition of peat results in greater seepage of particles into the underlying layers. After the application of a suspension prepared from a fraction \(>5\) mm, porosity increases markedly in the arable layer and changes to a lesser extent in the lower layers. When a suspension prepared from a fraction \(<2\) mm is applied, the opposite phenomenon occurs: porosity in the arable layer increases to a lesser extent and decreases more noticeably in the lower layers. It follows from this that, if we seek to reduce porosity with soil depth below the arable layer, it is necessary to increase the processing of peat during excavation of the deposit, and also to select a deposit with a higher degree of decomposition. If it is necessary to increase porosity in the arable layer, peat that is less processed and has a lower degree of decomposition should be added to the soil.

With the addition of a large quantity of peat to the soil, its specific gravity decreases somewhat.

The bulk density of the soil, both in its natural state and of its solid phase, changes more sharply after the addition of hydropeat than does its specific gravity.

The bulk density in the natural state in the arable layer varies over a fairly wide range; however, on plots with peat at 280–380 t/ha it is lower than in the control by \(0.06\)—\(0.30\) g/cm\(^3\). In the underlying layers, the difference in bulk density between the plots with peat and the control is observed to a lesser extent; moreover, on the plots with peat it is higher by \(0.01\)—\(0.08\) g/cm\(^3\) down to a depth of 50–60 cm.

The bulk density of the solid phase changes according to the same regularity as the bulk density in the natural state; however, the difference between the plots with peat and the control is greater than for the bulk density of the soil in its natural state.

Owing to the lower bulk density of peat in comparison with mineral soil, the mechanical mixture formed in the arable layer after peat application (if considered from the standpoint of its physical state) has a lower bulk density (after plowing in the peat) than the soil. The arable layer does not completely accommodate the peat particles in its pore space, as a result of which it increases in volume and rises somewhat in height, thereby reducing its bulk density.

The increase in the bulk density of the soil deeper than the arable layer is explained by the fact that the peat particles that have seeped down fill the pore space and do not increase the volume of the soil in these layers, as a consequence of which the content of solid matter per unit volume increases.

Fine fractions in the soil mainly affect its physical and chemical properties [6].

At present, soils are classified according to the ratio of mechanical fractions. With a larger percentage content of particles \(<0.01\) mm, they are assigned to heavier soils and, conversely, with a smaller content—to light soils [6, 7].

Peat has a significantly greater dispersion than mineral light soils. Consequently, the addition of peat increases the dispersion of the soil; at the same time, together with the liquid phase of the suspension, the finest peat particles penetrate deep into the soil, owing to which the content of particles \(<0.01\) mm increases in light soils. In the 3rd year after the application of peat suspension at the rate of 200 t/ha of peat, particles \(<0.01\) mm on the plot with peat at a depth of 20–40 cm amounted to 11.79%, and in the control to 7.07%; at a depth of 40–60 cm on the plot with peat, 8.88%, and in the control, 5.59%; i.e., the content of particles \(<0.01\) mm after the application of hydropeat at the indicated depths increased by 4.72 and 3.21% (Table 3).

Table 3

Mechanical composition of sandy soil in the fourth year after the application of peat suspension

A decrease in porosity below the plow layer, an increase in dispersion, and an increase in the amount of organic matter after the introduction of hydromorphic peat into the soil cause a sharp improvement in the water properties of light soils.

After the introduction of 200–400 t/ha of hydromorphic peat, its moisture capacity increases, the filtration coefficient decreases, and the water-lifting capacity increases; as a result, plants receive more moisture for their development and growth.

Fig. 1. Amount of moisture that plants can use for their development and growth in the fourth year after the introduction of peat suspension

Thus, in meter-long monoliths taken from the soil in the sixth year after the introduction of hydromorphic peat, over 26 hours the water rose to a height of one meter, and the moisture content in the upper ten-centimeter layer increased from 15.7 to 17.8%. In the 20–50 cm layer, counting from the top, the moisture content in the monoliths increased by 2.0–2.5%. When the experiment was continued to 188 hours, the moisture content in the monoliths from the control plot did not increase in the upper layer.

In monoliths taken from sandy soil in the eighth year after the introduction of hydromorphic peat, after 209 hours the moisture content in the upper layer increased from 9.1 to 11.3%.

The moisture content in the plow layer throughout the entire season is higher in soils with peat; moreover, as the amount of peat increases, the moisture content also increases.

As a result of the improvement of the water properties of light soils after the introduction of peat suspension, plants can obtain more moisture from the soil for their development and growth (Fig. 1).

The introduction of hydromorphic peat into the soil in an amount of 200–400 t/ha sharply increases the humus content in the plow and subplow layers. It should be noted that a number of special studies have been devoted to the change in soil humus and its influence on increasing the stable fertility of soils. Data relating to this question can be found in monographs

I. V. Tyurin [9] and M. M. Kononova [10]. This question is considered in a number of other works, both domestic and foreign.

When peat is introduced into the soil, incompletely decomposed bog plants and humus are added. Further decomposition of the peat takes place in the soil, as a result of which the humus content in it increases.

Fig. 2. Nitrogen content in sandy loam soil in the 6th year after application of peat suspension

The amount of humus in the 0–20 cm layer when 380 t/ha of hydropeat was applied in the fourth year was greater than in the control by 2.65%; when 280 t/ha of hydropeat was applied—by 2.1%; and when 140 t/ha was applied—by 0.85%.

A higher humus content in soil with peat, relative to the control, is observed down to a depth of 1 m.

The application of hydropeat to the soil affected the change in the depth of the humus horizon, the thickness of which depends somewhat on the compaction of the plow layer. Therefore, measurements of the humus horizon of the soil were made in spring, summer, and autumn, before the plow layer was loosened. When hydropeat was applied at rates from 140 t/ha to 380 t/ha, the depth of the humus horizon increased by 2–7 cm.

In the sixth year after the application of 140–380 t/ha of hydropeat, the sandy loam soil contained from 0.20 to 0.30% total nitrogen, while the control contained 0.13%. Soil with a higher content of total nitrogen also contains more mobile, readily hydrolyzable nitrogen. On the plot with peat, the content of mobile nitrogen increased in comparison with the control by 0.70–3.70 mg per 100 g of soil (Fig. 2).

The presence in the soil of a large amount of hydrolyzable nitrogen is of great importance from both the theoretical and practical standpoint.

Hydrolyzable nitrogen characterizes those reserves of it which, under favorable conditions, pass into forms available for plant nutrition.

Of great importance for characterizing soil fertility is the capacity of soils to absorb from solutions certain substances that play a positive role in plant development.

Peat in its natural state, compared with soil, has a higher absorption capacity, which for various lowland peats ranges from 77.7 to 178 mg-eq per 100 g of organic matter [11].

The absorption capacity of the soil in the 6th year after the application of hydropeat increased from 42 to 102%.

The ultimate aim of the present work is to increase the fertility of light soils. As a result of a significant improvement in the water-physical, mechanical, and chemical properties of light soils after the application of hydropeat, their fertility increases considerably.

Table 4

Yield of agricultural crops on plots with hydropeat, 380 t/ha

The yield increase on sandy and sandy-loam soils over the course of 13–15 years (with the application of hydropeat at 200–380 t/ha) amounted to from 20 to 150%. The yield of agricultural crops on all the other plots treated with hydropeat was significantly higher throughout the entire elapsed period.

After the sandy soil in the “16 Partisans” collective farm of the Pukhovichi District was flooded with hydropeat in 1951, a soil which previously had not been cultiva-

... the rye yield in the first year was 16.5 centners/ha. On this same plot, the yield of rye—the seventh crop after the application of hydropeat (1957)—was 15.8 centners/ha. In fertility this plot at present is not inferior to soils cultivated earlier.

Long-term observations show that the productivity of agricultural crops on soil with peat does not decline over time (Table 4). The duration of the effect of hydropeat on increasing yields has not yet been established; however, taking into account the changes in the water-physical, mechanical, and chemical properties of the soil, it may be assumed that, provided other agrochemical measures are observed, hydropeat will act for decades.

The application of hydropeat at a rate of 200–400 t/ha makes it possible to save a considerable quantity of mineral fertilizers. Thus, on a plot treated with hydropeat in 1953, mineral fertilizers during the first 8 years were applied at the rate of 8.5 centners/ha of superphosphate, 4.5 centners/ha of potassium chloride, and 2 centners/ha of ammonium nitrate. Over 8 years, calculated as active ingredient \(N_{45}P_{45}K_{45}\), the following mineral fertilizers were applied: nitrogen—17%, phosphorus—47%, and potassium—56%. In subsequent years mineral fertilizers were applied in larger quantities.

The costs of procuring peat over 11 years were recouped seven- to ninefold. The final effectiveness of applying hydropeat can be established after the yield increase relative to the control has ceased.

LITERATURE

1. F. A. Malyshev. Hydromechanization of Peat Extraction for Fertilizer. Minsk, 1947.

2. F. A. Malyshev. The seepage of solid peat particles from hydromass into the depth of the soil. Transactions of the Institute of Peat, vol. VIII, 1959.

3. A. A. Rode. Soil Moisture. Goslesbumizdat, 1952.

4. L. S. Leibenzon. Movement of Natural Liquids and Gases in a Porous Medium. Gostekhizdat, 1947.

5. A. A. Rode. Soil Science. Goslesbumizdat, 1955.

6. N. A. Kachinskii. Methods of Mechanical and Microaggregate Analysis of Soils. Publishing House of the USSR Academy of Sciences, 1943.

7. I. S. Lupinovich. Light soils of the non-chernozem zone of the European part of the USSR and the tasks of science in their reclamation. Increasing the Fertility of Light Soils. Moscow, 1960.

8. V. I. Shempel. The current state of the question of cultivating sandy soils of the Polesie Lowland. In: On the Question of Reclamation and Development of the Productive Forces of Polesie. Minsk, 1949.

9. I. V. Tyurin. Organic Matter of Soils. Selkhozgiz, 1937.

10. M. M. Kononova. The Problem of Soil Humus and the Current Tasks of Its Study. Publishing House of the USSR Academy of Sciences, 1951.

11. P. I. Belkevich, L. R. Chistova. Ion-exchange property of peat. Communications I–IV. Transactions of the Institute of Peat, Academy of Sciences of the BSSR, vol. 6, 1957.