Optimized Ridge–Furrow Ratio to Decrease Greenhouse Gas Emissions and Increase Winter Wheat Yield in Dry Semi-Humid Areas

Abstract

The plastic-mulched ridge–furrow rainwater harvesting (RF) system has been widely adopted worldwide due to its visible economic benefits. However, few and inconclusive studies have focused on greenhouse gas (GHG) emissions. In addition, it is still unknown whether different coverage ratios under RF have an impact on greenhouse gas emissions. Here, we evaluate the effects of various coverage ratios on the soil hydrothermal characteristics, global warming potential (GWP), greenhouse gas intensity (GHGI), and yield productivity in dry semi-humid areas. A control (FP, conventional flat planting without mulching) and three different ridge–furrow ratios (40:40 (RF40), 40:60 (RF60), and 40:80 (RF80)) were tested in 2017–2019. Compared with FP, RF increased the soil temperature and promoted soil moisture in the furrows during the vegetative growth period. However, the soil temperature of the furrows slightly increased with furrow width, whereas the soil moisture obviously decreased under the three RF practices. In a wet year (2017–2018), FP significantly increased the winter wheat yield (43.6%) compared with RF, while the opposite was the case in a normal year (2018–2019). Among the three RF treatments, RF40 and RF80 significantly increased the yield by 13.9% and 17.2%, respectively, compared with RF60. Compared with FP, all of the RF treatments increased the flux of N₂O and CO₂ emissions but reduced CH₄ absorption. Compared with FP, RF with ridge–furrow ratios of 40:40 cm, 40:60 cm, and 40:80 cm increased the GWP by 99.6%, 53.4%, and 31.3%, respectively, and increased the GHGI by 55.8%, 45.3%, and 0.7%, respectively. Therefore, conventional flat planting in wet years and a ridge–furrow ratio of 40:71 cm in normal years can reduce GHG emissions, sustaining crop productivity, and promote the sustainable development of agriculture and the environment.

1. Introduction

The increase in atmospheric greenhouse gases (GHGs), such as N₂O, CO₂, and CH₄, leads to global warming and frequent extreme meteorological events, which have caused serious impacts on the sustainable development of the environment and agriculture, as well as having directly threatened food security [1,2]. Therefore, limiting climate change by reducing greenhouse gas emissions has become the focus of attention. As population growth and food demand increase, the pressure on the cultivated land ecosystem continues to increase, and the increase in agricultural intensity will lead to a continuous increase in greenhouse gas emissions [3,4]. Reducing greenhouse gas emissions while increasing food production is the key to sustainable agricultural development.

The plastic-mulched ridge–furrow rainwater harvesting system (RF) is widely used around the world as an effective method to increase soil temperature, reduce water evaporation, and control nutrient leaching and weeds [5,6,7]. RF mulching can cause changes in soil temperature and humidity, which in turn have an important impact on greenhouse gas emissions between the soil and the atmosphere [8,9,10]. The current research on GHG emissions from ridge–furrow mulching has mainly focused on different mulching materials, mulching methods, and different fertilization rates or irrigation amounts [8,11,12,13], and the results on the effect of RF on greenhouse gases are still inconsistent. For example, studies have shown that RF can reduce CO₂ emissions [11] and CH₄ absorption [14], as well as increase N₂O emissions [14]. Xu et al. [10] showed that under the same irrigation level, the ridge–furrow mulching system can decrease CO₂ and N₂O emissions compared with FP, and with a decrease in irrigation amount, the absorption of CH₄ increases in winter wheat farmland. Cuello et al. [12] showed that the ridge–furrow mulching system increased the emissions of N₂O and CH₄ compared with non-mulching. In addition, different ridge–furrow ratios under RF improve soil micro-topography heterogeneity, which also has certain effects on soil moisture, temperature, and yield [15,16]. At present, the research on different ridge–furrow structures mainly focuses on the effects of different ridge–furrow ratios on soil hydrothermal characteristics and crop yields [16,17,18]. The change in soil hydrothermal characteristics is bound to affect the greenhouse gas emissions between the soil and the atmosphere, but there is little research on whether GHG emissions can be affected by changing the ridge–furrow ratio in RF.

Hence, this study aimed to (1) determine the effects of various ridge–furrow ratios under RF on N₂O, CO₂, and CH₄ emissions, as well as their relationship with soil hydrothermal characteristics and (2) to propose an appropriate combination of ridge–furrow ratios that could mitigate GHG emissions while increasing crop yield.

2. Materials and Methods

2.1. Experimental Description and Weather Conditions

Field experiments were conducted in the 2017–2018 and 2018–2019 growth seasons in the same field at the Experimental Station of Northwest A&F University, Shaanxi Province (108°04′ E, 34°20′ N), which is a typical winter wheat planting area in the Guanzhong Plain and has a representative dry semi-humid climate condition. The precipitation was concentrated from July to September. The average annual precipitation was 592.3 mm; the average precipitation during the growth period of winter wheat was 287.5 mm, and the temperature was 10.3 °C. The physicochemical characteristics of the soil (0–20 cm layer) were as follows: organic matter, 11.97 g kg⁻¹; total nitrogen, 1.31 g kg⁻¹; alkaline nitrogen, 20.53 mg kg⁻¹; available phosphorus, 22.34 mg kg⁻¹; available potassium, 97.37 mg kg⁻¹; soil bulk density, 1.25 g cm⁻³; and pH, 8.1.

The weather conditions during the study years differed substantially in terms of air temperature and precipitation (Figure 1). The annual precipitation in 2017–2018 and 2018–2019 was 687.6 mm and 608.4 mm, respectively. The precipitation during the winter wheat growth period was 183.8 mm and 169.2 mm, respectively. The average precipitation for the annual and the winter wheat was 592.3 mm and 287.5 mm over a 40 y period, respectively. According to the drought index (DI) (Guo et al., 2012), 2017–2018 was a wet year, but 2018–2019 was a normal year (DI = 0.64 > 0.35; −0.35 < 0.11 < −0.35); the winter wheat growth periods in 2017–2018 and 2018–2019 were both dry (DI = −1.78 < −0.35, −2.03 < −0.35). The temperature of the summer maize growth period in 2017–2018 was slightly higher than that in 2018–2019.

2.2. Experiment Design

The experiment was a completely randomized design comprising four treatments (Figure 2), including (a) conventional flat planting without mulch (FP); (b) RF40 (plastic-mulched ridge–furrow rainwater harvesting system with a ridge–furrow ratio of 40:40 cm); (c) RF60 (RF with a ridge–furrow ratio of 40:60 cm); and (d) RF80 (RF with a ridge–furrow ratio of 40:80 cm). Each treatment was replicated three times, and each plot was 5 m long and 4.4 m wide, with an area of 22 m².

We used the winter wheat variety Xinong 979 at a sowing rate of 225 kg ha⁻¹ in each plot with a row spacing of 20 cm, which was planted on 18 October 2017 and 11 October 2018. Basal fertilizer containing 225 kg ha⁻¹ urea (N = 46%), 75 kg ha⁻¹ diammonium phosphate (P₂O₅ = 46%, N = 18%), and 150 kg ha⁻¹ potassium sulfate (K₂O = 45%) was evenly broadcasted over the RF system furrows and plowed to a depth of ~20 cm in the soil layer. The crops were harvested on 7 June 2018, and 2 June 2019. Weeding and pest control were carried out regularly during the growth period.

2.3. Sampling and Measurements

The closed chamber method was used to measure greenhouse gas (GHG) emissions during the growth period of winter wheat from 2017 to 2019 [10,19]. The chamber consisted of a base (height: 15 cm) and a heat-insulated steel chamber (length: 40 cm, width: 30 cm, and height: 40 cm) with a triple valve to collect gas. Gas was collected between 9:00 and 11:00 a.m. every 3 days for the first 15 days after fertilization using a 60 mL syringe and then taken during the main growth period of winter wheat (the overwintering, jointing, flowering, grain-filling, and maturity stages), as well as after precipitation. The gas samples were collected at 10 min intervals (0, 10, 20, and 30 min) after chamber closure. The concentrations of CO₂, N₂O, and CH₄ in a gas sample were analyzed within 42 h using a gas chromatograph (Shimadzu, Japan) with an electron capture detector (ECD) and a flame ionization detector (FID). The CO₂, N₂O, and CH₄ gas emission fluxes were calculated as follows (Chen et al., 2017):

$$\mathrm{F}=\rho \times h\times \frac{dc}{dt}\times \frac{273}{T}$$

(1)

where F is the flux rate of CO₂, N₂O, and CH₄ (mg m⁻² h⁻¹), ρ is the standardized stage gas density of CO₂, N₂O, and CH₄ (mg cm⁻³), h is the height of the chamber (m), $\frac{dc}{dt}$ is the rate of greenhouse gas accumulation in the chamber, and T is the absolute temperature (273+ mean temperature in the box, °C).

Seasonal cumulative GHG emissions were calculated as follows:

$$\mathrm{Seasonal} \mathrm{emission}={\displaystyle {\sum }_i^n\left(R_i\times D_i\right)}$$

(2)

where R_i is the greenhouse gas emission rate (kg ha⁻¹ day⁻¹) in the i-th sampling interval, D_i is the number of days in the i-th sampling interval, and n is the number of sampling intervals.

Global warming potential (GWP, kg CO₂-eq hm⁻²) and greenhouse gas intensity (GHGI, kg CO₂-eq hm⁻² grain) were calculated as follows:

$$\mathrm{GWP}={\mathrm{N}}_2\mathrm{O}\times 265+{\mathrm{CH}}_4\times 28+{\mathrm{CO}}_2$$

(3)

$$\mathrm{GHGI}=\frac{\mathrm{GWP}}{Y}$$

(4)

where N₂O, CH₄, and CO₂ are the seasonal cumulative GHG emissions, respectively. Y is the winter wheat yield (kg hm⁻²).

Automatic temperature probes were used to record the soil temperature daily at a soil depth of 5 cm. Soil volumetric water content (%) dynamics at a soil depth of 10 cm were measured using time domain reflectometry (Field Scout™ TDR 300 Soil Moisture Meter, Spectrum Technologies, Inc., Aurora, IL, USA) in real time.

At the physiological maturity stage, the plants were harvested (two rows of 0.5 m in length) to determine the grain yield of each plot.

2.4. Statistical Analysis

Statistical analyses were conducted using SPSS 23 (IBM SPSS Statistics, Armonk, NY, USA). One-way ANOVA was used to analyze the effects of the ridge–furrow ratio on the soil moisture, temperature, and GHG emissions. Two-way ANOVA was used to analyze the effects of the planting pattern and precipitation year on the crop yield, GWP, and GHGI. The relationships among CO₂, N₂O, CH₄, soil temperature, and moisture were determined using correlation analyses. A regression analysis was used to evaluate the relationship between crop yield and GHG emissions. The significant differences among the treatments were identified by using an F test (p < 0.05), and a post hoc analysis was conducted with Fisher’s protected LSD test to identify significant differences between the factor means at p = 0.05. OriginPro 2020 was used to produce the figures.

3. Results

3.1. Soil Temperature and Soil Moisture

The soil temperature under the two planting patterns showed a similar seasonal dynamic as the air temperature across two years (Figure A1). The two-year seasonal variation in the surface soil temperature in each treatment was basically the same, which was mainly affected by the daily air temperature. All RF showed a higher soil temperature in the vegetative growth period than FP (0.61 °C), while FP showed a higher soil temperature in the reproductive growth period than RF (1.06 °C) (Figure 3A). Under the three RF treatments, the soil temperature showed a slight increase with an increase in the furrow width; the temperature with a furrow width of 80 cm was higher than that of 60 cm and 40 cm (0.20 °C, 0.46 °C), but there was no significant difference among the treatments.

The seasonal variation in the soil moisture in the furrows and ridges was basically the same and was mainly affected by precipitation. The alternating ridges and furrows under the RF system showed obvious topographical heterogeneity (Figure A2). Under the three RF treatments, the soil moisture in the furrows was significantly higher than that on the ridges (14.1%). In addition, the soil moisture in the furrows under the RF treatments was significantly higher than that of FP, but there was no significant difference between the ridge and FP (Figure 3B). The average soil moisture in the furrows of RF40, RF60, and RF80 was 15.4%, 9.8%, and 10.3% higher than FP, respectively.

3.2. Greenhouse Gas Emissions

In the two-year experiment, the flux trends in the N₂O emissions were basically the same, reaching the first peak after fertilization and tillage. After that, as the growth process of winter wheat advanced, the N₂O fluxes of each treatment gradually decreased and tended to be stable (Figure 4A,B). The N₂O flux began to increase from day 1 and peaked at about day 7 under FP and RF, respectively. During the growth period of winter wheat, the N₂O emissions flux of RF was significantly higher than that of FP, and its cumulative emissions flux was significantly increased by 419.84% compared with FP. In addition, in the three ridge–furrow ratio treatments, the cumulative emissions flux of RF80 was basically the same as that of RF40, but higher than that of RF60, and there was no significant difference between the treatments (Figure 5A).

The fluxes in CO₂ emissions had obvious seasonal variation and experienced two peaks—one week after tillage and fertilization and around 200 days after sowing (early stage of the grain-filling stage) (Figure 4C,D). Compared with FP, RF significantly increased the CO₂ emissions flux during the growth period of winter wheat, and its cumulative emissions flux increased by 52.58% compared with FP. For RF treatments, RF40 had the highest cumulative emissions, followed by RF60 and RF80 (Figure 5B).

In winter wheat cultivation, the emissions of CH₄ were negligible and mainly absorbed from the atmosphere, indicating that wheat fields are the sink of CH₄ (Figure 4E,F). In the two-year experiment, the CH₄ absorption of FP was higher than that of RF, and the cumulative absorption flux increased by 42.72% compared with RF (Figure 5C). For the RF treatment, with the width of the furrow, the CH₄ cumulative absorption flux increased, and RF80 was the highest, which was significantly different from RF40.

3.3. Relationships of Greenhouse Gas Emissions with Soil Moisture and Soil Temperature

The relationship between the GHG fluxes and soil temperature was closer than that between the GHG fluxes and soil moisture (Figure 6). The soil temperature closely correlated with N₂O and CO₂ fluxes, irrespective of various practice patterns; it was in a quadratic parabolic relationship, that is, as the temperature increased, the emission flux first increased and then decreased. However, soil temperature had a weaker correlation with CH₄. The relationships of N₂O fluxes with soil temperature in FP and the three RF treatments were identical, but the relationship of CO₂ fluxes with soil temperature in the RF treatment was higher than that in FP, and RF80 was the highest. Although the relationship between soil moisture and N₂O flux was weak, it also presented a quadratic parabola. Soil moisture had a weaker correlation with CO₂ and CH₄.

3.4. Crop Yield, GWP, and GHGI

The precipitation year and planting pattern had a significant impact on the winter wheat yield. The yield in 2017–2018 was significantly higher than that in 2018–2019. The planting patterns were not significantly different between RF40, RF80, and FP, but they were all significantly higher than RF60 (Figure 7A,B). Similarly, the precipitation year and planting pattern also had significant effects on the GWP and GHGI. In terms of the precipitation year, although the GWP and GHGI in 2018–2019 were higher than those in 2017–2018, the differences were not significant (p < 0.05). In terms of the planting pattern, the GWP and GHGI of RF40 were significantly higher than those of FP. However, there was no significant difference between RF40, RF60, and RF80 for the GWP, and no significant difference between RF40 and RF80 for the GHGI, but they were all significantly higher than RF60 (Figure 7C–F).

Here, the assumption was that the FP corresponded to a furrow width = 0 cm. The standardized crop yield and GHG emissions were analyzed regressively. The furrow width associated with the highest yield and lowest GHG emissions was 0 cm in 2017–2018 and 71.3 cm in 2018–2019 (Figure 8A,B).

4. Discussion

4.1. Soil Temperature and Soil Moisture

In the RF practice, different ridge–furrow ratios changed the distribution of the solar radiation received by the land surface due to the change in the micro-topography heterogeneity and then changed the hydrothermal conditions of the farmlands [18]. In this study, compared with FP, RF increased the soil temperature in the vegetative growth period and also increased the furrow soil moisture, while FP mainly increased the soil temperature in the reproductive growth period. This is mainly because the small canopy in the early growth stage of the crop and solar radiation can increase the surface soil temperature through the canopy. However, in the later growth stage, the soil temperature decreased due to the overshadowing effect and ridge sealing of the RF practices. Similar results were reported by Li et al. [15]. There were no significant differences in the soil temperature and moisture among the three RF treatments, probably because the warming effect of the RF practices was mainly through the light energy absorbed by the mulched- ridge and transferred laterally to the planting furrow, as well as the light energy absorbed directly by the planting furrow. Therefore, the soil temperature of RF80, the widest planting furrow, was higher than that of RF60 and RF40. Similarly, due to the rainwater harvesting effect of the RF system, the highest water content resulted in being that of the narrowest planting furrow of RF40, while the higher water content had a larger specific heat capacity and thermal energy for evaporation, therefore leading to a lower soil temperature. This result was consistent with Liu et al. [16]. We also found that RF40 increased the soil moisture in the furrow compared with RF60 and RF80 (see Figure 3B).

4.2. Greenhouse Gas Emissions

In previous studies, the fluxes of N₂O peaked after sowing and were mainly related to pre-sowing soil hydrothermal characteristics and fertilization [20]. Similar results were found in our study. In the present study, the soil N₂O peaked about 7 days after sowing and fertilization. After that, soil N₂O fluxes almost leveled off and were at low levels as winter wheat growth progressed. This may be due to the intense competition for sources of N by winter wheat plants, which grew fast after the re-greening and jointing stage resulted in low N₂O emission levels for a long period of time in each treatment. Xu et al. [10] also showed that in years with more precipitation, fluxes in N₂O emissions in winter wheat remained at a steady level for each treatment after the jointing stage. In the RF practices, due to the improvement in soil hydrothermal characteristics, the soil microbial population and activity are positively affected, and the mineralization process of the microorganisms is accelerated, resulting in the emission of greenhouse gases (N₂O, CO₂, and CH₄) [21,22]. In the present study, we found that RF significantly increased the flux in N₂O emissions compared with FP, and the cumulative emissions of RF40 and RF80 were almost the same under the three RF treatments, but both were higher than RF60. This may be because RF40 and RF80 have higher soil moisture and soil temperature, respectively, and the increase in soil moisture and temperature can enhance microbial activity and soil respiration, thereby increasing the cumulative emissions of N₂O [23]. Previous studies have found that the soil microbial respiration rate can reach its maximum value under appropriate temperature or moisture conditions, and soil microbial respiration will be decreased if the soil temperature or moisture is too low or too high [24]. The same result was obtained in this study. It was found that both soil moisture and soil temperature had a quadratic parabola form for the flux in N₂O emissions, indicating that there was a certain trade-off between soil moisture, soil temperature, and N₂O.

CO₂ emissions are affected by soil moisture, temperature, and physical as well as chemical properties [25]. Ridge–furrow mulching directly or indirectly affects these factors, which in turn affect CO₂ emissions. In the present study, RF increased CO₂ emission fluxes compared with FP, indicating that ridge–furrow mulching can absorb more carbon. These results were consistent with those reported by Gong et al. [26]. In different precipitation years, CO₂ emission fluxes showed similar seasonal patterns. All peaked after sowing, then gradually decreased and peaked again at about 200 days, mainly because pre-sowing fertilization and soil moisture stimulated microbial activity and accelerated the decomposition of organic matter, thus promoting the increase in CO₂ fluxes. In addition, the temperature rose and precipitation increased after the re-greening and jointing stage, and stronger photosynthesis stimulated the activity of aerobic microorganisms, thus accelerating root respiration and releasing more CO₂. Similar results were obtained by Cuello et al. [12] and Chi et al. [27]. We also found that the cumulative emissions of RF40 were higher than those of RF60 and RF80. This indicates that proper soil moisture is conducive to soil respiration and thus increases CO₂ emissions. Soil temperature can indirectly affect root respiration and thus CO₂ emissions by affecting root growth. Through controlled experiments, McMichael and Burke et al. [28] found that there was an optimal temperature for root growth and that the root growth rate accelerated with an increase in temperature until it reached an optimal temperature, beyond which it began to decrease. This is consistent with the relationship between soil temperature and CO₂ emissions found in this study.

Different from N₂O and CO₂, in the present study, both planting patterns resulted in the uptake of CH₄ in the two growing seasons with a small uptake flux. This was mainly because dryland soils often act as CH₄ sinks due to aerobic soil conditions [29]. Similarly, the cumulative absorption of CH₄ in FP was significantly higher than that in RF, while the difference between the three RF treatments was not significant. This indicated that the higher soil moisture content under RF facilitated higher CH₄ emissions as compared to those under no-mulching. Other studies on dryland regions obtained similar results [8,10]. In addition, CH₄ emission fluxes were not closely related to soil temperature and moisture, which is consistent with Chen et al. [8].

4.3. Crop Yield and GHGI

In dryland agriculture, crop yields depend on annual and seasonal precipitation [7]. In the present study, we found that annual precipitation had an important effect on the winter wheat yield. Although the growth period of winter wheat in the two-year experiment was in a dry year, the yield in a wet year (2017–2018) was significantly higher than that of normal year (2018–2019). Among the planting patterns, the yield of FP was higher than that of RF and not significantly different from RF40 and RF80 but significantly higher than that of RF60. This was mainly because for dense crops, such as wheat, the mulched-ridge of the RF planting practice reduced the wheat per unit of the planted area, thereby decreasing the yield [30]. In years with more precipitation, for winter wheat, the yield increase caused by the increase in the soil moisture could not compensate for the loss of yield due to the reduction in the planted area, which may have contributed to the higher yield of FP than RF. The annual precipitation had a significant effect on the spikes number, m⁻², and the grain number, spike⁻¹ (

Table A1. Average spike number per m², grain number per spike, and 1000-grain weight (g) of winter wheat under different treatments in two growth seasons.

Treatments	Spike Number m−2	Grain Number Spike−1	1000-Grain Weight
FP	434 ab	38.3 b	44.2 a
RF40	387 c	41.9 a	43.8 a
RF60	401 bc	38.0 b	43.4 a
RF80	465 a	41.2 a	42.6 a
Y	**	**	ns
P	*	**	ns
Y×P	**	*	ns

Note: Y, precipitation year; P, planting pattern. Values within a column followed by the different lowercase letters indicate a significant difference at p < 0.05 using the LSD method. ns indicates non-significant difference; * Significant at p < 0.05 and ** Significant at p < 0.01, respectively.

). In the RF system, different ridge–-furrow structures changed the heterogeneity of the soil micro-topography, which also affected precipitation collection and yield components. For RF40, the loss in yield due to the reduced planting area was compensated by an increase in the grain number, spike⁻¹, due to the better water harvesting effect of its narrower furrow. The difference in the yield between RF40 and RF80 was not significant due to the wider furrow of RF80 compensating for the loss in the yield by increasing the spikes number, m⁻², and the grain number, spike⁻¹. However, for RF60, its water collection and warming effect were not as effective as those of RF40 and RF80, and the increase in the spikes number, m⁻², could not offset the yield loss due to the decrease in the grain number, spike⁻¹, so its yield was significantly lower than that of RF40 and RF80, which may have contributed to the significantly higher yield of FP than RF60.

Crop yield and greenhouse gas emissions determine the GWP and GHGI of each treatment. In the present study, the precipitation year had no significant effect on the GWP and GHGI, and RF increased the GWP and GHGI compared with FP. This result was consistent with Cuello et al. [12]. There was no significant difference in the GWP among the three RF treatments. However, the GHGI of RF40 and RF60 was significantly higher than that of RF80. This may be attributed to the decrease in the crop yield, which usually leads to a lower carbon input, and thus, relatively high greenhouse gas emissions [25].

In agricultural production, increasing food production without sacrificing farmland crops productivity and minimizing environmental problems are the basis of sustainable agricultural development [22]. Through a regression analysis, we found that when crop yields reach their maximum and greenhouse gas emissions are at the lowest, the optimal ridge– furrow ratio in a wet year (2017–2018) was 0:0 cm (that is, conventional flat planting), while the optimal ridge–furrow ratio in a normal year (2018–2019) was 40:71.3 cm. Therefore, in order to increase the crop yield and reduce the environmental impact in dryland wheat planting, we suggest that conventional flat planting is more suitable in years with more annual precipitation, and a 40:71.3 cm ridge and furrow system is more suitable in years with less annual precipitation.

5. Conclusions

During the winter wheat growing season, spatiotemporal changes in soil moisture and soil temperature are closely related to grain yield and GHG emissions. The effect of different furrow widths on soil moisture was greater than that of soil temperature. In a wet year, due to the poor rainwater harvesting effect of RF, there was a higher GHGI because of the decreased crop yield compared with FP. However, the effective rainwater harvesting effect of RF in a normal year reduced the GHGI by increasing the crop yield, although more GHG was discharged. Changes in the GHG emissions from agricultural soils were related to soil hydrothermal characteristics, and GHG emissions could be regulated through various ridge–furrow ratios. In the higher precipitation year, the appropriate ridge–furrow ratio was 0:0 cm (i.e., conventional flat planting), while in the lower precipitation year, the appropriate ridge–furrow ratio of 40:71.3 cm was a sustainable strategy to increase the crop yield while reducing GHG emissions in dry semi-humid areas.