Soil structure and its agronomic value. The formation of structural aggregates is a complex natural process, and mechanical effects on the soil with tillage tools, as a rule, destroy its structure. In this regard, one of the main tasks of tillage is to minimize the destruction of the structure and create the best conditions for its accelerated recovery. Depending on the size of the aggregates, the soil structure is subdivided (according to P.V. Vershinin) into the following groups: cloddy (aggregates over 10 mm), macrostructure (10-0.25 mm), coarse microstructure (0.25 − 0.01 mm), and fine microstructure (less than 0.01 mm). Agronomically valuable fractions are considered to be all fractions in the range from 10 to 0.25 mm. The soil structure is of high quality when the amount of agronomically valuable particles in the soil is more than 55%. Aggregates larger than 10 mm are clods and the cloddy structure, as known, is far from the best condition of the soil, just as the dominance of particles smaller than 0.25 mm of the silty part of soil aggregates. Therefore, the following qualitative assessments of the structure are used based on the number of aggregates of this very agronomically valuable range, 10-0.25 mm.
Structure coefficient (Cstr) is determined by the following formula [25]:
$${C}_{str}=\frac{\sum (10-\text{0,25} mm)}{\sum (>10 mm, <\text{0,25} mm)}$$
Agronomically correct choice of a particular system of basic and presowing soil, timely and high-quality performance of all scientifically based operations, taking into account specific conditions, is a mandatory requirement and an important prerequisite for obtaining high and sustainable rice yields.
Fall (primary) plowing. In the Kyzylorda region, rice production is concentrated mainly on meadow-boggy soils, characterized by a low level of natural fertility, contains little humus–0.74–1.55%, total nitrogen – 0.084–0.106%, and total phosphorus – 0.149–0.171% [26]. Such soils, when poorlytilled, lead to a deterioration of its agrophysical properties, which negatively affects the size and quality of the rice yield.
The quality of fall plowing of the soil is largely determined by the soil and climatic conditions, the technical condition of the unit, the timing of the work, the skill of the machine operator, as well as the correct choice of tillage tools. In a field plowed since autumn, in spring, the workability of soil begins faster, which makes it possible to start its presowing preparation earlier and carry out sowing in the optimal agrotechnical terms.
In our studies, fall plowing of the soil on the experimental field was carried out in agrotechnical terms after the harvesting of rice and crop residues (the second decade of October).
As a criterion for assessing tillage, the ridgenessof the plowed field (height of the ridges) and thecloddiness (number of clods and area under clods) were determined, the special significance of which these indicators acquire in fields intended for sowing rice, the cultivation of which requires careful soil preparation.
The first observations of the experiments showed that when plowing with the Lemken Juwel 7 swing plow, the layers of meadow-boggy soils were tightly and evenly adjoined to each other, and the ridges were clearly defined. Therefore, due to the formation of the same size and shape of the layers, as well as their location at the same distance from each other, the ridgenesscoefficient in these fields was 1.09. This indicator was somewhat higher (1.15) on plots where plowing was carried out with the PLN-5-35 traditional plow (Table 6).
Table 6
Influence of various tillage tools on the ridgeness and cloddiness of meadow-boggy soils (average for 2019–2020)
Primary tillage to a depth of 25–27 cm | Ridgeness, cm | Ridgeness coefficient | Cloddiness, pcs/m2 | Area under clods, m2 |
profile line length | projected length* |
PLN-5-35 | 13.8 | 12.0 | 1.15 | 18.0 | 0.28 |
Lemken Juwel 7 | 13.1 | 12.0 | 1.09 | 17.2 | 0.16 |
Note: * – the projected length is equal to the registration plot width, i.e. 12.0 m. |
The fall-plowed field should not be excessively cloddy, since additional tilling of such a fall-plowed field with the help of heavy disc harrows and rollers does not always eliminate its flaws. In addition, poor-quality fall-plowed field creates additional difficulties in the spring, reducing the efficiency of subsequent operations of secondary tillage for the cultivated crop.
From the obtained experimental material, it follows that the number of clods (lumps of soil with a diameter of more than 5.0 cm) on the check surface of the experimental fields when plowing with the PLN-5-35 plow was 18.0 pcs/m2, the occupied area was 0.38 m2, slightly less – 17.2 pcs/m2 was recorded when plowing with the Lemken Juwel 7 swing plow. However, in this variant, the smallest area occupied by them was noted, and, therefore, cloddiness was 0.16 m2 (Fig. 1).
In general, the ridgeness coefficient and the number of clods on the surface of the plowed field largely depended not only on the physical condition of the soil, but also on the design features of the plows being compared. It should also be noted that when using the swing plow, there was no need to divide the checks into lots, as a result of which there were no back furrows and center ridges on it.
Secondary tillage (disk fall plowing). The correct system of secondary tillage for rice can only be carried out under the condition of good winter tillage. It should create an insulating layer on the soil surface in order to preserve soil moisture, eliminate compaction in the plowing layer, provoke weeds to germinate, create a grainy-silty topsoil that allows sowing rice seeds to a depth of 1.5-2.0 cm, and level the field surface with an accuracy of ± 3–5 cm.
Disk fall plowing to a depth of 16–18 cm with various tools was carried out in the spring at the onset of workability of the soil (2nd decade of April) on the experimental fileds, plowed with the PLN-5-35 and Lemken Juwel 7 plows. The results of the research indicate that various tillage tools influenced the natural processes of structure formation and led to a change in the content of agronomically valuable aggregates ranging in size from 10 to 0.25 mm (Table 7).
Table 7
Aggregate composition of the soil in a layer of 0–10 cm after disk fall plowing with various tools to a depth of 16–18 cm (%by weight of the sample), (average for 2019–2020)
Fall plowing | Disk fall plowing to a depth of 16–18 cm | Sizes of aggregates (mm) and their contents (%) | Structure coefficient |
> 25 | 25 − 10 | 10 − 1 | 1-0.25 | < 0.25 |
PLN-5-35 (control) | BDT-3 in two tracks (control) | 30.5 | 37.5 | 27.8 | 5.3 | 0.9 | 0.49 |
BDM-Agro | 22.3 | 35.2 | 30.8 | 9.6 | 1.1 | 0.67 |
Lemken Juwel 7 | BDT-3 in two tracks | 25.8 | 36.4 | 30.6 | 8.4 | 0.8 | 0.63 |
Horsch Terrano 4 FX | 18.2 | 32.6 | 33.6 | 11.7 | 1.9 | 0.82 |
LSD05 (least significant difference) | | | | | | 0,05 |
The smallest quantityof agronomically valuable aggregates (33.1%) with a predominance of the cloddy fraction (30.5%), where BDT-3 was used in two tracks, was noted. It also follows from the data in the table that the use of combined tools such as BDM-Agro and Horsch Terrano 4 FX have promoted active crumbling of the plowing layer of soil, mixing of soil particles with plant residues, which is accompanied by the formation of fine soil particles. Thus, the share of cloddy aggregates (> 10 mm) accounted for 6.2–8.7%, and fine earth accounted for 19–23%. Lemken Juwel 7 + Horsch Terrano 4 FX is dominated by the 3–5 mm fraction.
In these variants, there was a tendency to an increase in the structure coefficient due to an increase in the content of agronomically valuable particles and a decrease in the number of fractions with a size of < 0.25.
Secondary tillage.Violation of the quality of presowing preparation of the soil surface leads to the formation of a waterlogged layer, deterioration of the water and air and thermal regime, deviation from the established sowing depth, which contributes to blindness in seedlings, a decrease in field germination and yield of cultivatedsmall-seeded crops.
Preference is given to those tools that have the ability to loosen and crumble the plowing horizon of soil so that before sowing in a layer of 0–10 cm there are no fractions larger than 25 mm, i.e. exceeding the seeding depth of rice by its sizes.
When studying the physical properties of the soil in the 0–10 cm layer in comparison with disk fall plowing to a depth of 16–18 cm (Table 7), significant changes are observed in the structural and aggregate composition towards their improvement under the influence of different tillage tools. So, in the control variant, where the BDT-3 disc harrow (incorporation of nitrogen-phosphorus fertilizers) and the ZKKSh-6 star-wheeled roller recommended in the zone were used as surface tillage, the number of agronomically useful sizes was 50.7% (Table 8). In addition, on the control plots, in comparison with other variants of the experiment, a sharp differentiation was recorded between the cloddy (11.8%) and dusty fraction (2.1%).
Table 8
Aggregate composition of the soil in a layer of 0–5 cm before sowing rice (%, by weight of the sample), (average for 2019–2020)
Fall plowing to a depth of 25–27 cm | Disk fall plowing to a depth of 16–18 cm | Secondary tillage to a depth of 8–10 cm | Sizes of aggregates (mm) and their contents (%) | Structure coefficient |
> 25 | 25 − 10 | 10 − 1 | 1-0.25 | < 0.25 |
PLN-5-35 (control) | BDT-3 in two tracks (control) | BDT-3 + ZKKSh-6 (control) | 11.8 | 37.4 | 36.6 | 14.1 | 2.1 | 1.02 |
BDM-Agro | BDM-Agro | 6.8 | 38.4 | 42.6 | 10.5 | 1.7 | 1.13 |
Lemken Juwel 7 | BDT-3 in two tracks | BDT-3 + ZKKSh-6 | 4.7 | 40.2 | 44.1 | 9.6 | 1.4 | 1.15 |
Horsch Terrano 4 FX | Horsch Terrano 4 FX | 2.1 | 9.6 | 48.2 | 11.2 | 0.9 | 1.46 |
LSD05 (least significant difference) | | | | | | 0,08 |
The analysis of the results obtained by us showed that in the soil tilled with the disk header BDM-Agro 3x4, the content of aggregates ranging in size from 1 to 10.0 mm in a layer of 0–5 cmwas 53.1%. This is explained by the specifics of the work of the BDM-Agro concave disks, itis good to crumble the soil and crush its buckshot structure, and the slat-spiral rollers, installed at the back, finally breaking the soil into even lumps, leave a perfectly flat loose surface (Fig. 2). At the same time, it was noticed that when using the Horsch Terrano 4 FX cultivator, an increase in the amount of agronomically valuable structural aggregates was followed by a decrease in the silt fraction up to 0.9% of the total amount of aggregates.
One of the reasons for the positive effect on the soil structure of the Horsch Terrano 4 FX cultivator is due to the prolonged presence of the cultivated soil in the working area and the special shape of the tines, which allows achieving better mixing quality. In addition, relying on the tractor mounting mechanism in the front and the compaction roller in the back, this cultivator on the experimental fields made it possible to maintain strictly the specified placement depth of mineral fertilizers (8–10 cm).
It should also be noted that when cultivating the soil with the Horsch Terrano 4 FX cultivator, 59.4% of the aggregate composition remained in the surface layer, not deeper than 5 cm. After tilling with the BDT-3 disc harrows, these aggregates, for the most part, were embedded on the bottom of the furrow, and hard-to-break clods were partially tilted out on to the soil surface. Therefore, in the fields tilled with these tools, the 0–5 cm layer contained fractions larger than 25 mm.
The soil structure coefficient, at a depth of 0–5 cm, according to the variants of the experiment has been in the range from 1.13 to 1.15, this indicates that in all variants, except for the control one, the soils have a good aggregate state before sowing, with the exception of the variant with plowing using a swing plow, which has an excellent aggregate state of 1.46.
The content of the most agronomically valuable aggregates of the plowing layer of soil was (0.25-10.0 mm) according to the variants in the range of 55.3–60.5%, which, firstly, characterized a good aggregate state, since the values were included in the group of 40–60%; secondly, there were no significant differences between the tillage methods in comparison with the control variant (PLN-5-35).
The bulk density has a soil-zonal pattern and depends on the content of humus in it, its granulometric composition and structure. Rice, like most agricultural plants, grows and develops better at a soil density of 1.1–1.3 g/cm3. In the studies of N. S. Kandaurov and other researchers, it was found that the rice yield decreases both on loose (< 0.9 g/cm3) and on dense (more than 1.3 g/cm3) soil within the range of 16–32% [27].
As a result of soil analysis, it was revealed that the freezing of the soil plowed in autumn under the influence of the weather conditions of the winter season contributed to its natural loosening. In this connection, by the beginning of the spring presowing cultivations (2-nd decade of April), the soil density was relatively the samein all variants of the experiment and amounted to 1.25–1.26 g/cm3 (Table 9).
Table 9
Soil density in the 0–20 cm layer of the plowing horizon under rice, g/cm3 (average for 2019–2020)
Fall plowing to a depth of 25–27 cm | Disk fall plowing to a depth of 16–18 cm | Secondary tillage to a depth of 8–10 cm | Soil density in the 0–20 cm layer, g/cm3 |
Before disk fall plowing | Before sowing |
PLN-5-35 (control) | BDT-3 in two tracks (control) | BDT-3 + ZKKSh-6 (control) | 1.26 | 1.30 |
BDM-Agro | BDM-Agro | 1.26 | 1.28 |
Lemken Juwel 7 | BDT-3 in two tracks | BDT-3 + ZKKSh-6 | 1.25 | 1.30 |
Horsch Terrano 4 FX | Horsch Terrano 4 FX | 1.25 | 1.27 |
Further study of soil density in the 0–20 cm layer indicates that the studied tools and tillage methodshad an unequal effect on the soil density ratio before rice sowing. Thus, the highest soil density in the 0–20 layer was recorded on the control plots, where the traditional technology with commercial tools was used (1.30 g/cm3), while the disk fall plowingto a depth of 16–18 cm using the BDM-Agrodisk headerfollowed by disking and rolling, significantly reduced theseratio by an average of 0.02 g/cm3. A slight increase in density in the control variant of the experiment could be explained by the fact that there were a large quantity of coarse fractions (Table 7), which together had a fluffy consistency.
In the fields where fall plowing was carried out with the Lemken Juwel 7 swing plow, the soil density of the disk fall plowingto a depth of 16–18 cm with BDT-3 and two cultivations with the same tool after applying mineral fertilizers was 1.28 g/cm3. In the variant where the incorporation of mineral fertilizers and rolling was carried out in one pass with Horsch Terrano 4 FX, the soil density was minimal – 1.27 g/cm3.
Thus, analyzing the data on the density of the soil consistency, it should be noted that by the spring, under the influence of meteorological factors in the autumn-winter period, the soils occupied by rice in the conditions of the Kyzylorda region, despite the plows used, acquire an optimum value. Minimization of presowing cultivation of meadow-boggy soils by combining disking and rolling in one technological process leads to a decrease in the density of the 0–20 cm soil layer by an average of 0.02–0.05 g/cm3.
When preparing the soil for sowing rice, it is necessary to take into account the index of its hardness. High hardness worsens the physical-mechanical and agrophysical propertiesof the soil, hinders the germination of plants, prevents the development of their root system, and requires additional energy consumption during its cultivation [28, 29].
The results obtained show that before the start of fall plowing, i.e. after harvesting rice, the soil had a slight hardness in creasing with the depth in all variants of the experiment. After all the winter and presowing cultivations, by the beginning of rice sowing, only the 0–5 cm layer (4.0-4.3 kg/cm2) remained uncompacted, and deeper in the 5–10 cm layer, the hardness value increased sharply in comparison with the initial one, and was on average 11.6–12.6 kg/cm2 in all variants of the experiment, regardless of the tools used and the number of operations performed, in the 10–20 cm layers, the hardness value was 12.0–13.0 kg/cm2, which was a good indicator for rice (Table 10).
Table 10
Soil hardness in different layers of the plowing horizon under rice, kg/cm2 (average for 2019–2020)
Fall plowing to a depth of 25–27 cm | Secondary tillage | Sample depth, cm |
Disk fall plowing to a depth of 16–18 cm | Diskingto a depth of 8–10 cm and rolling |
before fall plowing | before sowing |
0–5 | 5–10 | 10–20 | 0–5 | 5–10 | 10–20 |
PLN-5-35 (control) | BDT-3 in two tracks (control) | BDT-3 + ZKKSh-6 (control) | 4.3 | 5.8 | 5.6 | 5.1 | 12.6 | 13.0 |
BDM-Agro | BDM-Agro | 4.3 | 5.8 | 5.6 | 5.0 | 12.2 | 12.8 |
Lemken Juwel 7 | BDT-3 in two tracks | BDT-3 + ZKKSh-6 | 4.0 | 5.6 | 5.6 | 4.8 | 11.8 | 12.1 |
Horsch Terrano 4 FX | Horsch Terrano 4 FX | 4.0 | 5.6 | 5.6 | 4.6 | 11.6 | 12.0 |
Thus, the results of research on the effect of tillage tools on agrophysical properties show that on meadow-boggy soils, the incorporation of mineral fertilizers with further soil rolling can be completely replaced with modern tools such as BDM-Agro and Horsch Terrano 4 FX.
The yield of an agricultural crop depends on the number of plants per unit area and their productivity. The first component of the yield structure is largely determined by the field germination of seeds. Field germination is the number of seedlings expressed as a percentage of the number of germinating seeds sown.
In the Kyzylorda region, throughout the development of rice growing, a stable increase in yield is limited by the low field germination of rice seeds, which does not exceed 30% [10]. Therefore, obtaining optimal seedlings in terms of density in the amount of 300–350 plants per 1 m2 is one of the current problems of rice sowing, the successful solution of which largely depends on how correctly an integrated tillage system is made for specific conditions.
The different aggregate composition of the soil plays a significant role in the initial stages of growth and development of rice plants. The predominance of fractions of 1–10 mm in the sowing layer makes it possible to increase the field germination of rice seeds, reduce the number of days from sowing to emergence of seedlings, and provide favorable conditions for the formation of the root system. So, according to A.K. Butov, the presence of aggregates from 1 to 10 mm in size in the upper layer (0–5 cm), after sowing rice, doubles the field germination of seeds [30].
In our studies, the first seedlings of rice seeds on the experimental field appeared 5–7 days after sowing. As the first records showed, the primary and secondary tillage with different tools began to affect rice plants from seed sprouting, i.e. their field germination (Table 11).
In the course of fall plowing, where cultivation was carried out with the PLN-5-35 plow, the highest field germination of seeds of 218.2 pcs/m2 was provided by the BDM-Agrodisk header, their smallest number of 204.2 pcs/m2was in the control variant, where BDT-3 in two tracks was used. The lower germination of rice seeds on this field can be explained by the fact that during the initial flooding of the checks with water, soil fractions < 0.25 mm in size tighten the seeds, and > 10.0 mm cover the seeds after swelling. As a result, the rice seeds are at a greater depth, which, if there is a layer of water in the checks, the seedlings cannot overcome.
Table 11
Field germination of seeds and preservation of plants for harvestingrice depending on the tillage tools used (average for 2019–2020)
Fall plowing to a depth of 25–27 cm | Disk fall plowing to a depth of 16–18 cm | Secondary tillage to a depth of 8–10 cm | Field germination | Preservation of plants for harvesting |
pcs/m2 | % | pcs/m2 | % |
PLN-5-35 (control) | BDT-3 in two tracks (control) | BDT-3 + ZKKSh-6 (control) | 204.2 | 30.6 | 135.7 | 66.5 |
BDM-Agro | BDM-Agro | 218.2 | 31.1 | 142.7 | 65.4 |
Lemken Juwel 7 | BDT-3 in two tracks | BDT-3 + ZKKSh-6 | 219.0 | 31.2 | 146.0 | 66.6 |
Horsch Terrano 4 FX | Horsch Terrano 4 FX | 223.8 | 31.9 | 150.0 | 67.0 |
LSD05 (least significant difference) | | 0,72 | | 0,81 |
From the above data it can be seen that in the experiments, the largest number of germinating rice seeds, 223.8 pcs/m2, was obtained in the variant where fall plowing was carried out with the Lemken Juwel 7 swing plow, and disk fall plowing and secondary tillage was carried out with the Horsch Terrano 4 FX cultivator, i.e. where in the 0–5 cm soil layer the fractional composition was represented mainly by the size of aggregates from 1 to 10 mm. The number of sprouted plants in the variant using Lemken Juwel 7 and BDT-3 was 219.0 pcs/m2.
Field germination, as known, is correlated with the index of the degree of plant preservation, which characterizes the number of plants preserved for harvesting as a percentage of the number of sprouted ones. In the course of research, we found that the preservation of rice plants before harvesting in all variants of the experiment, including control, did not have a significant difference and ranged within 65.4–67.0%. This indicator can be considered relatively optimal for the study area. The existing differences in 2..3 plants according to the variants of the experiment, in principle, reflect not the influence of the agrophysical properties of soils during the growing season, but the accuracy of the formation of the density of the rice plants.
Yield is the most important indicator of agricultural crops. Establishing the relationship between the yield and the agrophysical properties of the soil makes it possible to change them in the desired direction by improving the tillagesystem and the optimum set of tillage tools.
The analysis of the data obtained shows that, in general, the rice yield in all experiments has been formed to be quite high throughout the years of research. The results of the experiments once again confirm the effectiveness of using the Lemken Juwel 7 swing plow in conjunction with the Horsch Terrano 4 FX cultivator, where it provided the highest rice yield of 6,83 t/ha, and the yield increase was 0,71 t/ha compared to the control (Table 12).
Table 12
Rice grain yield depending on the tillage tools used, t/ha (average for 2019–2020)
Fall plowing to a depth of 25–27 cm | Disk fall plowing to a depth of 16–18 cm | Secondary tillage to a depth of 8–10 cm | Rice grain yield, t/ha | Addition to the control, c/ha |
PLN-5-35 (control) | BDT-3 in two tracks (control) | BDT-3 + ZKKSh-6 (control) | 6.12 | - |
BDM-Agro | BDM-Agro | 6.54 | + 0.42 |
Lemken Juwel 7 | BDT-3 in two tracks | BDT-3 + ZKKSh-6 | 6.32 | + 0.2 |
Horsch Terrano 4 FX | Horsch Terrano 4 FX | 6.83 | + 0.71 |
LSD05 (least significant difference) | 0.21 | |
This is primarily due to more optimal agrophysical properties and a high coefficient of soil structure (1.46) before sowing rice, and secondly, due to higher field germination of seeds in the studied variant.
Rice harvest accounting in the variant where the PLN-5-35 traditional plow was used for plowing, as well as the use of the BDM-Agrodisk headers disk, fall plowing, and incorporating mineral fertilizers with subsequent presowing rolling of the field also contributed to obtaining an additional yield in the quantity of 0,42 t/ha.