Impact of minimum tillage on agrophysical indicators of chernozem

How minimum tillage changes the structure of chernozem soil

The transition from classic mouldboard ploughing to surface tillage or direct sowing (No-Till) has a direct impact on the water, air, and nutrient regimes of the soil. For leached, low-humus, deep, heavy-loam chernozem, this issue is particularly acute, as its physical properties initially limit crop productivity.

In its natural state, the plough layer (0–30 cm) of this soil type possesses the following agrophysical indicators:

• Humus content — 3.5–4.5 %
• Soil density — 1.22–1.32 g/cm³
• Total porosity — 49–53 %
• Water capacity — 28.1–30.4 %
• Wilting point — 15.8–16.4 %

In the sub-plough root-inhabited layer, conditions for plants deteriorate: density increases to 1.36–1.44 g/cm³, total porosity drops to 46 %, and water capacity decreases to 23.5 %. Abandoning mechanical tillage accelerates the compaction of these horizons.

According to long-term field trials in an 11-field grain-row crop rotation (conducted since 1999), after 11 years of direct sowing without tillage, the soil density in the 0–30 cm layer, even at the beginning of spring with sufficient humidity (22–24 %), was 1.32–1.35 g/cm³, and soil hardness was 34–37 kg/cm². This exceeds the indicators of mouldboard ploughing by 0.04–0.07 g/cm³ in density and by 9–13 kg/cm² in hardness.

Dynamics of soil density under winter and row crops

Soil density fluctuates throughout the entire growing season. In winter cereal crops, the loosest structure is observed at the beginning of spring growth: from 1.24 g/cm³ under ploughing to 1.28 g/cm³ in the variant without tillage.

During the season under winter crops, the soil gradually compacts. By the heading stage under ploughing, the density is 1.32 g/cm³, which is lower than direct sowing by 0.07 g/cm³ and surface tillage by 0.04 g/cm³. Before harvesting, the density increases in all variants, but ploughed plots remain the loosest.

When growing row crops (soybean, maize, sunflower, and sugar beet), optimal soil density is maintained only under mouldboard tillage in the improved autumn ploughing system. Even when the soil dries out to the wilting point at the end of the growing season, the density of the plough layer here does not exceed 1.28–1.30 g/cm³. Under surface tillage in the second half of summer, the soil over-compacts above the optimum by 0.05–0.07 g/cm³.

In sugar beet crops (based on average data for 2008–2010), there is a gradual compaction across all horizons of the plough layer. In the top layer (0–10 cm), the density remains within the norm (1.08–1.25 g/cm³) under all technologies. At the same time, under mouldboard ploughing and surface tillage at the beginning of the growing season, minimum density values are recorded — 1.08–1.13 g/cm³.

                                   Soil density, g/cm3 in the layer
    Tillage method
                          0–10 cm        10–20 cm   20–30 cm   0–30 cm
                            at the beginning of growth
 Mouldboard ploughing at
                            1.08           1.16       1.23         1.16
 30–32 cm (control)
 Surface tillage at
                            1.13           1.25       1.29         1.22
 8–10 cm
 Direct sowing              1.19           1.26       1.28         1.24
                        at the middle of growth
 Mouldboard ploughing at
                            1.19           1.23       1.25         1.22
 30–32 cm (control)
 Surface tillage at
                            1.19           1.26       1.34         1.27
 8–10 cm
 Direct sowing              1.25           1.30       1.37         1.30
                           before harvesting
 Mouldboard ploughing at
                            1.19           1.25       1.29         1.24
 30–32 cm (control)
 Surface tillage at
                            1.24           1.29       1.36         1.29
 8–10 cm
 Direct sowing              1.22           1.32       1.38         1.31

In the direct sowing variant, the soil density was the highest — 1.19 g/cm³, which is 0.06–0.11 g/cm³ higher than in other experimental variants.

Inter-row cultivations carried out during the sugar beet growing season helped maintain the density of the top soil layer (0–10 cm) within optimal parameters across the studied variants. However, in all observation periods, the direct sowing variant was characterized by higher soil density. In deeper layers, soil loosening was not performed, which led to its compaction in all experimental variants. A trend of increasing soil density was noted from the beginning of the sugar beet growing season until its harvest.

The worst conditions for root formation were observed under surface tillage and especially in the direct sowing variant, where the soil density in the 10–20 and 20–30 cm layers ranged from 1.25 to 1.36 g/cm³, compared to 1.23–1.25 g/cm³ in the control (mouldboard ploughing).

Thus, the studies conducted established that the bulk density of the arable soil layer following ploughing, averaged over three years, was optimal for the growth and development of sugar beet and ranged from 1.16 to 1.31 g/cm3. Higher values were observed in variants with surface tillage and, particularly, with direct sowing.

The deterioration of agrophysical properties under reduced tillage negatively affected the water, air, and nutrient regimes for the crops in the crop rotation.

For instance, under soybean, corn, and sunflower crops during the middle of the growing season, the total soil porosity in the ploughed variants was 49–51%, while with no-till, it decreased by 4–7%. The air content in the total pore volume under mouldboard tillage was 20–28%, while under direct sowing, it was 6–8% lower.

During the first rotation of the crop rotation, the best indicators of soil structure were observed when growing peas for grain and the subsequent winter wheat. When sowing the latter, the highest soil structure coefficients (2.4–2.6) in the arable layer were found in variants with mouldboard tillage, as well as surface semi-fallow tillage.

In direct sowing plots of wheat after peas at the beginning of the growing season, the soil structure coefficients were 0.4–0.6 points lower compared to the aforementioned tillage methods.

A different trend in the dynamics of soil aggregate composition was observed in row crops. The highest indicators of soil structure coefficients (1.6–2.4) under various tillage methods were recorded at the beginning of the growing season. By the time of harvesting row crops, a noticeable deterioration in soil aggregate composition was observed.

At all determination dates, a more agronomically valuable soil structure in row crops was observed in variants with mouldboard winter tillage.

The lowest soil structure indicators were obtained in the direct sowing variant. Constant surface or shallow winter tillage of the soil with disc implements led to an increase in dust content of up to 9–11%, which is 1.5–2.0 times higher than with mouldboard and no-till practices.

Over the period of the first rotation of the field crop rotation, it was established that different tillage methods with the application of N120P60K40 affected the yield of field crops differently. In the group of cereals and grain legumes, peas responded the least to reduced tillage.

The grain yield of this crop under direct sowing (19.3 cwt/ha) was only 1.5 cwt/ha lower than that under mouldboard tillage.

A more significant shortfall in grain yield per hectare was obtained with direct sowing (no-till) for winter barley compared to winter wheat. For the latter, the grain yield reduction under direct sowing for various predecessors ranged from 6 to 10 cwt/ha, while for barley, it was 12 cwt/ha.

In the group of row crops, a significant decrease in yield compared to the traditional cultivation technology was observed for sugar beet under direct sowing.

To a lesser extent compared to mouldboard winter tillage, the yield of corn grain and soybeans decreased under direct sowing. With reduced tillage, among row crops, this indicator decreased the least for sunflower.