Keywords

1 Introduction

Planosol, diffusely distributed in Heilongjiang and Jilin provinces, People’s Republic of China [1, 2], is a particular soil variety featuring white dense clayey subsoil. This subsoil structure is hard enough that the plant roots can hardly get through the layer to deeper profiles seeking nutrients and water when suffering a continuous adverse situation. Furthermore, the clayey subsoil is so tight that even the water molecules are incapable of moving up and down easily, which leads to drought in high-temperature weather and waterlogging in rainy conditions for dry crops. Hence, Planosol improvement attaches great importance. However, the albic soil usually recovers to its previous structure after a year’s planting with the normal improving method. Farmers have to implement deep tillage yearly to maintain the soil quality. In this paper, a three-stage subsoil interval mixing four-gang plough (TSIMF) was manufactured to improve the property of planosol soil. The improvement effect can last five years once used, saving labor, material, and financial costs.

2 Materials and Methods

2.1 Albic Soil Structure and TSIMF

A typical original planosol profile in a forest in State Farm 854 in Heilongjiang province, P. R. of China is exhibited in Fig. 1. The first horizon (Ap) with a layer of about 0.2 m is a plant-growth beneficial soil that is of colossal humic acids. The second horizon (Aw) which takes a similar thickness to the first layer comes to an impermeable dense lessivage structure. And there is a diluvial heavy clay in the third horizon (B) beneath 0.4 m depth [3, 4].

Fig. 1.
figure 1

Typical original planosol profile of a forest in State Farm 854, Heilongjiang, China. (Each gradation on the scale represents 0.1 m).

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Plants suffer from both drought and flood in different seasons separately owing to the impermeable Aw horizon. The general plant’s root can hardly penetrate the horizon of which the hardness is over 5.0 MPa and the soil microorganisms also disappear under impermeable layers [5]. We determined the soil hardness with a cone penetrometer, whose cone angle is 30º and base diameter is 16 mm.

A three-stage subsoil interval mixing four-gang plough (TSIMF, Fig. 2) was created in 2016 [6] to make a mixture of the Aw and the B layers in an equal amount with the first (Ap) horizon undisturbed meanwhile. With this mechanism, 2-m working width was obtained, and soft and hard subsoil rows (tilled and untilled subsoil, whose width is 0.5 m each) are alternately produced, so a certain trafficability can be maintained after tilling operation with the TSIMF.

The principle of subsoil mixing of the horizon Aw and B with an equal amount via TSIMF has already been reported in previous researches [7,8,9,10,11]. In this paper, the traction force (draught) of the TSIMF on an actual planosol field was determined. Then the improved soil conditions and the yield harvested from the field tilled with the TSIMF were studied.

Fig. 2.
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Three-stage subsoil interval mixing four-gang plough (TSIMF) created in 2016.

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2.2 Soil Section

Soil sections of 1 m length × 0.7 m depth (Figs. 1 and 3) were prepared at the test fields. Then the soil horizon, soil texture, and root penetration depth were measured.

Triplicate soil samples (total = 18 samples) were taken by the soil sampler (105 mm3) at each soil depth layer (0–0.1, 0.1–0.2, 0.2–0.3, 0.3–0.4, 0.4–0.5 and 0.5–0.6 m) to determine the physical soil properties.

Fig. 3.
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Recent soil section in October 2016 in test field established with TSIMF in May 2016. P and Q: see [6].

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2.3 Traction Force (Draught) Test

A TSIMF set was mounted on an off-powered wheel tractor (the first tractor) for supporting (Fig. 2). It was dragged by the second tractor (not shown) on an actual planosol field with a traction dynamometer which a 150 kN-capacity strain gauge was installed [11, 12]. Therefore, only the TSIMF’s horizontal force (draught) was gauged once the running resistance of the supporting tractor (first tractor) was reduced.

The running resistance of the first (supporting) wheel tractor with the TSIMF mounted was first determined (Fig. 2). The first tractor was drawn by the second tractor without any plough operation of the TSIMF, that is, by lifting the lever of the hydraulic device of the first tractor.

The weight transfer caused by the plough bodies of the TSIMF (Fig. 2) was not included in the running resistance of the first (supporting) tractor.

The draught of three elements of the TSIMF was measured separately as follows. The four 1st-plough bodies were initially operated alone without the 2nd and 3rd plough joined (Fig. 2). Then the two 2nd-plough bodies were attached, and the draught of four 1st-plough bodies and two 2nd-plough bodies was determined. The two 3rd-plough bodies were added subsequently, and the total draught of all eight elements was acquired. Three to five measurements were carried out for each configuration.

The working depth of the 1st plough was set to 0–0.2 m, that of the 2nd plough was 0.2–0.4 m and that of the 3rd was 0.4–0.6 m beneath the soil surface (Fig. 2).

2.4 Test Fields

A field test of 20 hectares was implemented applying the TSIMF in May 2016 on the State Farm 854 in the Three-river Plain of Heilongjiang province, P. R. of China, and all the investigations of soil and crops were implemented in October 2016.

The land prepared by a conventional rotary tiller (0–0.15 m deep) and a subsoiler (0–0.3 m deep) [6] was treated as a control (CK).

2.5 Soil Properties

The basic fertility indicators of the albic soil are: organic matter 26.07 g/kg, pH 6.3, alkali hydrolysable nitrogen 82.46 mg/kg, available phosphorus 8.25 mg/kg, and available potassium 57.23 mg/kg. Soil water (moisture) content in volume %, EC value in dS m-1, and soil temperature in ºC were determined in the actual field by a commercial tester. They were also measured at each soil depth layer (0–0.1, 0.1–0.2, 0.2–0.3, 0.3–0.4, 0.4–0.5, and 0.5–0.6 m).

2.6 Yield

Soybean-corn rotation is treated the same as State Farm 854 does. At the test fields, soybean Kenfeng 16 were seeded in May 2016 and harvested in October 2016.

Pods per Plant and Seeds per Plant.

The average values of pods per plant, which were picked up from thirty other cultivated plants selected randomly in each field, were calculated. And an average of seeds per plant are treated with the same method.

Predicted Yield.

The whole soybean per 3 m2 was harvested at each test field and dehydrated. Three points were selected randomly in each experiment treatment land. The average yield was calculated according to the mass of the dry soybean with a moisture content of about 13% w.b. measured with a pan balance.

3 Results and Discussions

3.1 Soil Profile

Figure 3 shows a recent soil profile in October 2016 in the test field established with the TSIMF in May 2016. An interval blending of the subsoil layers was distinctly observed, in which the uncultured subsoil layer (P) width was around 0.5 m and crop roots could be hardly found beneath 0.2 m (see [6] about points P and Q).

The thickness of the tilled and mixed subsoil layer (Q) also turned to about 0.5 m, in which the Aw horizon (Fig. 1) was already invisible. A few crop roots were even discovered 0.6 m deep. The topsoil of 0–0.2 m in both P and Q included plenty of crop roots.

3.2 Measured Traction Force (Draught)

Figure 4 shows the results of the traction force (draught) test. The running resistance of the wheel tractor mounted (Fig. 2) was about 20 kN (standard deviation was 2.22 kN) on the planosol field, whose value was two times larger than prediction [6].

Fig. 4.
figure 4

Notes: The brackets in the Fig.shows the standard deviation of the traction force, kN.

Results of traction force (draught) test on a planosol field.

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The total traction force of four 1st- the horizon Ap was about 40 kN. Therefore, the traction force of a single 1st-plough body occupied a quarter of the force of the total, which fairly coincided with the predicted value [6]. The traction of the two 2nd-plough bodies tilling the horizon Aw came to be about 20 kN, namely 10 kN each, which conformed to the prediction [6]. And the 3rd-plough bodies which were tilling the horizon B took the same situation as the 2nd-plough bodies [6]. For this combination, the total draught of the TSIMF, which was about 100 kN including the running resistance of the tractor (standard deviation was 3.16 kN), appeared to be a little greater than the previous prediction [6].

3.3 Soil Water Content

The soil water (moisture) content of the planosol soybean field is shown in Tables 1 and 2. The soil moisture in the TSIMF soybean field (Table 2) was an average of 2 volume % greater than that in the CK field (Table 1). This is due to the increase of air and water-space (porous media) of the soil with deep tillage of the TSIMF.

Table 1. Soil properties of planosol in CK (subsoiler) soybean field in October 2016.
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Table 2. Soil properties of planosol in TSIMF soybean field in October 2016.
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3.4 EC Value

The EC values of the planosol in the TSIMF soybean field are also shown in Table 2. There was no big difference between those in the CK field (Table 1) and those in the TSIMF field (Table 2). The EC value at any layer in any field was about 1.0 dS m−1.

3.5 Soil Temperature

The soil temperature in the planosol soybean fields is also shown in Tables 1 and 2. The temperature of the TSIMF field (Table 2) was about 1 ºC higher than that of the CK (Table 1) in most soil layers. Especially at the topsoil layer (0–0.3 m deep), there was about a 1.5 ºC difference. This is due to the increase in the air phase of the soil with deep tillage of the TSIMF.

3.6 Yield

Table 3 shows the average number of pods per plant. In the TSIMF field, it was greater than that in CK. The average number of soybean per plant in the TSIMF field was also greater than that in CK (subsoiler) field. The average yield (kg m-2) is in Table 3. The yield with the usage of the TSIMF was 120% of the CK field.

Table 3. Average yield of soybeans in State Farm 854 in October 2016.
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4 Summary and Conclusions

A new three-stage subsoil interval mixing four-gang plough (TSIMF) was designed, produced, and determined for promoting planosol conditions. The traction force (draught) of the TSIMF on an actual field was determined. Then, soil conditions improved and crop yield from the field tilled with the TSIMF was discussed.

The soft and hard subsoil rows (tilled and untilled subsoil, whose width is 0.5 m each) are alternately produced, so a certain trafficability can be maintained after tilling operation with the TSIMF. The TSIMF’s total draught was around 100 kN including the running resistance of the tractor. The soil moisture in the TSIMF soybean field was about 2 volume % greater than that in the CK field (subsoiler). The soil temperature in the TSIMF field was about 1 ºC greater than those in the CK field (subsoiler). The yield in the TSIMF field was 120% of the CK field (subsoiler). The running cost of TSIMF could reduce by 75% compared with conventional subsoiler operation in a 5-year benefit period.