Analysis and Research on Production Effects of Full-Film Double Ridge-Furrow Mulching with Polyethylene Film and Biodegradable Film Based on AquaCrop

Abstract

Water is an important factor limiting the development of arid rain-fed agriculture. Film mulching is an effective way to ensure yield in arid areas. However, whether biodegradable film can be used instead of polyethylene film for agricultural production in arid areas is a matter of contention. In this study, AquaCrop model simulation and field experiment were used to analyze the production effect of corn whole film double ridge furrow sowing technology covering polyethylene film (PM) and biodegradable film (BM) in Dingxi City from 2016 to 2020. The results showed that the AquaCrop simulation data have a high fitting with the field test data, and the model was suitable for simulating dry farming in Dingxi City. The best sowing time in Dingxi City is to select the average temperature to be stable at about 15 °C (around 15 April to 25 April each year), and the yield is the highest after sowing during this period. Although BM can achieve environmental protection and energy saving, it is weaker than PM in water storage and soil evaporation inhibition in arid areas. The average yield, aboveground biomass, water productivity, and harvest index of PM were 63.95%, 18.57%, 76.35%, and 38.22% higher than those of BM, respectively. In drought years, BM water stress on leaf expansion, induced stomatal closure, and premature senescence were 61%, 17%, and 9.5% higher than PM, respectively, and the stress time was 28.5 d, 5 d, and 26 d, respectively. The maximum canopy coverage and effective root zone water content were 24.5% and 30.49% lower, respectively. In the wet year, water stress under BM only had a certain effect on the leaf expansion of crops but had no effect on the induction of stomatal closure and premature senescence. The maximum canopy coverage and effective root zone water content were 13.56% and 31.35% lower, respectively. The above studies show that BM has a certain ability to store water and preserve moisture, but the parameters of PM are better than BM. Especially in dry years, the crop production efficiency of PM is more significant. It can be seen that in rain-fed agricultural areas with rainfall less than 500 mm, biodegradable film can not replace polyethylene film.

1. Introduction

The majority of China’s northwest inland region is characterized by rain-fed agriculture, which accounts for 46.3% of the total cultivated land area [1]. The northwest inland region of China experiences a continental monsoon climate, is rich in solar radiation, and possesses considerable potential for agricultural production. However, water resources have emerged as the primary limiting factor for agricultural development [2,3,4,5]. In recent years, the frequency of drought years has increased due to global climate change, exacerbating the shortage of agricultural water [6,7]. Water-harvesting and water-saving agriculture have been vigorously pursued to ensure food security in the country.

With the continuous development of agricultural technology, a new drought-resistant technology of whole film double ridge furrow sowing was proposed for the rain-fed arid area of Northwest China. This technology has the characteristics of covering and inhibiting evaporation, ridge and furrow rainwater harvesting, ridge and furrow planting, etc. It can realize the functions of water storage and moisture conservation, catchment infiltration, rainwater enrichment and superposition, water and fertilizer conservation, increasing surface temperature, improving water and fertilizer utilization rate, and reducing weeds and pests in the field [8,9,10,11,12,13,14]. At present, the whole film double ridge furrow sowing technology is mainly covered with polyethylene film in order to have better soil moisture conservation, evaporation inhibition and improving temperature. However, due to the unclean recovery of polyethylene film, improper treatment after recovery, and the time-consuming and laborious recovery, the recovery cost is high. Therefore, a large amount of polyethylene film is left in the field after crop harvest, which causes soil and environmental pollution; affects soil water infiltration, water content, and air permeability; hinders water and fertilizer migration and soil compaction; and causes difficulties in crop root growth and development [8,15,16,17].

In recent years, people have realized the seriousness of environmental pollution caused by polyethylene film. The research on mulch film has gradually turned to biodegradable mulch film, and it is believed that biodegradable mulch film can replace polyethylene film [18,19,20]. With the end of the crop physiological period, the biodegradable mulch film is gradually decomposed into soil nutrients without recycling, thereby reducing the cost of recycling mulch film and treating mulch film. At present, the common biodegradable films on the market are additive biodegradable polyethylene film and completely biodegradable film. The completely biodegradable film is decomposed into CO₂ and H₂O by soil microorganisms with the harvest of crops, and the decomposition will not pollute the soil environment. In recent years, relevant researchers have performed a lot of research on biodegradable film to improve water retention and thermal insulation. Existing research shows that biodegradable film has the same effect as polyethylene film and has no pollution to the soil.

However, most of the existing studies are short-term experimental studies, and few people consider the impact of biodegradable film on crop yield and water productivity due to differences in rainfall in different years, resulting in more one-sided research results. Huang et al. [7] studied the effects of long-term continuous mulching of biodegradable film and polyethylene film on maize yield and crop water productivity in different years through field experiments and did not use simulation software for auxiliary research. At present, no researchers have covered biodegradable film in the whole film double ridge furrow sowing technology, and no simulation software has been used to analyze the influence of biodegradable film on crops. In this study, AquaCrop model simulation and field test analysis and comparison were used to study the biodegradable film and polyethylene film in the whole film double ridge furrow sowing technology, and the differences in corn yield, water productivity, and soil moisture were compared. The software was used to analyze whether biodegradable film could replace polyethylene film in rain-fed arid agricultural areas.

The AquaCrop model is a water-driven model for crop growth proposed by the Food and Agriculture Organization of the United Nations. The model has simple data input, a friendly user interface, and accurate data output. It is the only simulation software that separates soil evaporation and crop transpiration, mainly using water as the driving force to determine water productivity [5,21,22]. At present, Shan et al. used the AquaCrop model to analyze the corn film mulching planting [23,24]. Zhang et al. [25] used the AquaCrop to simulate the whole film double furrow corn production in dry land and optimize the management measures. Pan et al. [5] used the AquaCrop to analyze the effects of polyethylene mulch on corn yield and soil moisture under different planting patterns. In this study, the AquaCrop model is proposed to be used to simulate the study of corn whole-membrane double-row furrow sowing technology covered with biodegradable and polyethylene mulch in the northwest dry zone and to analyze the effects of different mulch films on corn yield, water productivity, soil moisture, etc., with a view to providing the corresponding technical support for the adaptation of biodegradable mulch film in the whole-membrane double-row furrow technology in the dry zone of Northwest China.

2. Materials and Methods

2.1. General Situation of Test Site

The experiment was carried out in Dingxi City, Gansu Province (104°62′ E, 35°58′ N) from 2016 to 2020. It is located in the Loess Plateau of Northwest China, with an altitude of 1894.5 m. It belongs to the typical semi-arid climate of the Loess Plateau. The annual average temperature is 6.7 °C, and the annual rainfall is 386.6 mm, mainly concentrated from July to September and mostly in the form of rainstorms. The annual evaporation is as high as more than 1400 mm, and the spring is dry and rainy. The total solar radiation is 5923.8 MJ/m², and the frost-free period is about 140 d. The soil is loessial soil, and the groundwater is greater than 10 m. It is a typical rain-fed agricultural area with large surface runoff and serious soil erosion.

2.2. Research Materials and Methods

2.2.1. Test Materials

In this experiment, the plots (100 m × 100 m) were randomly selected, the test area groups were randomly distributed, and the north–south and east–west directions of each test area were divided into four blocks on average, as shown in Figure 1. Each piece of land was separated by a one-meter interval. The corn variety ‘Xianyu 335’ was selected, and the planting mode was full-film double-ridge furrow sowing technology. No. 1 and No. 3 were covered with polyethylene film, and No. 2 and No. 4 were covered with biodegradable film. The rotary tillage, fertilization, ridging, film mulching, soil mulching, and sowing operations were completed at the same time by using the combined sowing machine. The two types of polyethylene film (Polyethylene film (left) and biodegradable film (right) were purchased from Nanjing Qiqi Agricultural Technology Co., Ltd., Nanjing, China) covered by the surface are shown in Figure 2.

2.2.2. Performance of Two Types of Film to Inhibit Evaporation

We aimed to reduce the influence of soil capillary rise and other external factors on the experimental results. There was no rainfall in the experimental site recently. Six sampling points were randomly selected to remove surface debris. Soil samples with a size of 20 cm × 20 cm and a sampling depth of 0–25 cm were collected by a soil shovel. The soil samples were loaded into self-sealing bags and brought back to the laboratory. The soil moisture content was measured by a moisture measuring instrument and then loaded into six flower pots, as shown in Figure 3. The soil surface was covered with polyethylene film and biodegradable film, respectively. After ten days on the balcony of the laboratory, samples were taken from the flowerpots, respectively, and then the soil moisture content was measured by water measuring instrument to analyze the effect of two kinds of film on inhibiting surface evaporation.

2.2.3. Determination of Aboveground Biomass and Yield of Maize

When measuring the above-ground biomass and yield of maize in the test area, after the maize was ripe, 6 samples of maize plants with uniform growth were randomly selected in the middle of each test area, and they were taken back to the laboratory for drying and weighing. The average value of the above-ground biomass and yield of each maize plant was calculated, and the above-ground biomass and yield of the test area were calculated by planting density.

2.2.4. AquaCrop Principle

AquaCrop is a crop-water productivity model developed by the Food and Agriculture Organization of the United Nations to address food security and assess the impact of environment and management on crop production. AquaCrop simulates the yield response of herbaceous crops to water, especially when water is a key limiting factor in crop production. The AquaCrop model ensures its broad applicability by using only a small number of explicit parameters and most intuitive input variables that can be determined in a simple way. There are also some limitations in the AquaCrop model. The AquaCrop model can only simulate a single growth cycle; it is assumed that the field is uniform, and there is no spatial difference in crop development, transpiration, soil characteristics, or management; only vertical inflow (rainfall, irrigation, and capillary rise) and outflow (evaporation, transpiration, and deep infiltration) water fluxes are considered. The AquaCrop model evolved from the Ky method, separating the actual evapotranspiration (ET) into soil evaporation (E) and crop transpiration (Tr) and separating the final yield (Y) into biomass (B) and harvest index (HI):

$$ET=E+Tr$$

(1)

$$Y=HI\cdot B$$

(2)

The separation of soil moisture into soil evaporation and crop transpiration avoids the confounding effect of non-productive water consumption (soil evaporation), especially when the initial planting or sparse planting leads to incomplete ground coverage. The yield is separated into biomass and harvest index, and the corresponding functional relationship can be divided according to environmental conditions. These reactions are actually fundamentally different, and their separation avoids the confounding effects of water stress on B and HI. The core formula of the AquaCrop growth engine derived from the above changes is as follows:

$$B=WP\cdot {\displaystyle \sum Tr}$$

(3)

where

• Tr—crop transpiration, mm.
• Wp—water productivity parameters (biomass per square meter (kg) and evapotranspiration per millimeter accumulated during the period of biomass production).

2.2.5. Model calibration and evaluation

Due to some non-restrictive factors in the simulated environment, there are some differences with the field experiment; in order to better adapt to the test site, it is necessary to calibrate the non-restrictive parameters of the model. Using the calibrated model simulation, the simulation data are compared with the field test data to evaluate the adaptability of the model. Pearson correlation coefficient (r), root mean square error (RMSE), normalized root mean square error (CV (RMSE)), Nash efficiency coefficient (EF), and consistency index (d) were used to test the simulation accuracy of the model.

$$r={\displaystyle \sum _{i=1}^n(O_i-\overline{O_i})(P_i-\overline{P_i})}/\sqrt{{\displaystyle \sum _{i=1}^n{(O_i-\overline{O_i})}^2{(P_i-\overline{P_i})}^2}}$$

(4)

$$RMSE=\sqrt{{\displaystyle \sum _{i=1}^n(P_i-O_i{)}^2/n}}$$

(5)

$$CV(RMSE)=1/O_i\sqrt{{\displaystyle \sum _{i=1}^n{(P_i-O_i)}^2/n}}\times 100$$

(6)

$$EF=1-{\displaystyle \sum _{i=1}^n{(P_i-O_i)}^2}/{\displaystyle \sum _{i=1}^n{(O_i-\overline{O_i})}^2}$$

(7)

$$d=1-{\displaystyle \sum _{i=1}^n{(P_i-O_i)}^2}/{\displaystyle \sum _{i=1}^n({\left|P_i-\overline{O_i}\right|}^2+{\left|O_i-\overline{O_i}\right|}^2)}$$

(8)

where O_i is the observed value; P_i the simulated value; $\overline{O_i}$ is the mean value of O_i; $\overline{P_i}$ is the mean value of P_i; and n is the number of observations.

In the simulation evaluation test, the value of r is −1~1, and the closer r is to 1, the closer the simulated value is to the real value, and the simulation effect is better. The value of RMSE is 1~+∞, and the closer the value is to 0, the better the simulation effect is. The value of CV (RMSE) is less than 10%, indicating that the simulation effect is excellent. The simulation effect is good at 10–20%, and the simulation effect is general at 20–30%. The closer the value of EF and d is to 1, the better the simulation effect is.

2.3. Data Source

The simulated meteorological data are from the China Meteorological Data Network, and the time step is 1 d. The meteorological data include daily minimum temperature Tn (°C), daily maximum temperature Tx (°C), daily rainfall (mm), sunshine hours (h), wind speed at 2 m from the ground (m/s), reference evapotranspiration (calculated by using the ETo calculator in the AquaCrop model), and atmospheric CO₂ concentration. The recommended value is used in the model. The meteorological data are shown in Figure 4.

The soil data consisted mainly of soil profile data and groundwater data. Soil profile data include soil thickness, texture, bulk weight, wilting coefficient, field water holding capacity, percentage of saturated water content, and saturated hydraulic conductivity, as shown in

Table 1. Soil physical and chemical properties of experimental station.

Soil Thickness (cm)	Texture	Bulk Weigh (g/cm3)	Wilting Coefficient (vol%)	Field Water Holding Capacity (vol%)	Saturated Water Content (vol%)	Saturated Hydraulic Conductivity (mm/day)
0–20	loam	1.08	7.68	26.05	55.25	250
20–100	silt loam	1.23	7.13	26.45	43.61	150

. Groundwater depths exceeding the maximum of the modeled set range were not considered for crop impacts.

Using the corn model in AquaCrop, the parameters in the model were corrected according to the actual planting density and planting mode of corn planted by local farmers: planting density, sowing time, initial canopy coverage, maximum canopy coverage, growth cycle, flowering cycle and growth period, etc. The crop harvest index was determined according to the actual planting situation.

The field management data were set according to the local farmers’ planting mode. The biomass production in aoil fertility was set as ‘moderate’, and the soil cover by mulches in mulches was set as ‘complete’. The parameters in the type of surface mulches were set as ‘synthetic (plastic) mulches’ (reduction of evaporation losses 100%) and ‘organic plant materials’ (reduction of evaporation losses 59.4%). Because it is a full-film double-ridge furrow planting technology, field surface practices are set as soil bunds, and there is no surface runoff. The film had the effect of inhibiting weeds in the field, weed management was set as ‘perfect’, and the weed coverage rate was 0.

3. Results and Analysis

3.1. Calibration and Applicability Analysis of AquaCrop

The AquaCrop model was used to simulate the corn planting in the typical arid area of Dingxi City. The meteorological data of Dingxi City from 2016 to 2020 obtained from the China Meteorological Data Network were imported, and the corn parameters were corrected by the trial and error method. By comparing and analyzing the simulated values of corn yield from 2016 to 2020 with the experimental values in the field, the corn parameters in the model were adjusted so that the simulated values of corn were compatible with the experimental values in the field.

The relative error of corn yield in Dingxi City from 2016 to 2020 was almost 10%. The AquaCrop model can accurately simulate the yield and other indicators of corn in typical arid areas of Dingxi City. The AquaCrop model was used to simulate the yield of corn full-film double-furrow planting technology in Dingxi City from 2016 to 2020. As shown in

Table 2. Analysis of yield simulation accuracy of corn whole film double ridge furrow sowing technology.

Year	r	RMSE	CV (RMSE)/%	EF	d
2016	0.93	0.10	1.66	0.94	0.91
2017	0.89	0.24	2.10	0.91	0.90
2018	0.91	0.18	1.87	0.90	0.92
2019	0.93	0.22	1.98	0.94	0.93
2020	0.92	0.18	1.68	0.93	0.90

, the model has good simulation accuracy for corn full-film double-furrow planting technology in arid areas. Ding et al. [26] used the AquaCrop model to simulate the cumulative temperature compensation effect of polyethylene film mulching. The R2 distribution of soil water storage in the 1.2 m soil layer was 0.10–0.94, the RMES distribution was 14.3–28.9 mm, and the NRMSE distribution was 4.5–9.6%. Zhang et al. [25] used the AquaCrop model to simulate the overall standardized root mean square error and conformity of the yield of maize cultivation in dryland with full film mulching and double ridges were 8.5% and 0.97, respectively. The above research and this study show that the simulated value of the AquaCrop model has a high degree of fitting with the field experimental value, which can better simulate the crop growth state of dry land mulching planting, saving time cost and capital cost for later research, reduce the experimental error caused by uncertain factors in the environment, and improve the applicability and feasibility of the research results.

3.2. AquaCrop Model to Determine Sowing Time

Ma et al. [27] studied the effects of sowing time and density on the physiological indexes of the summer corn population in the Guanzhong irrigation area. The total effect of sowing time on the physiological indexes of the corn population was significantly greater than that of density. The sowing time of corn is greatly affected by temperature. Due to the high altitude and low temperature in Dingxi City, the sowing time is generally from the end of April to the beginning of May. After the corn is sown, only when the ground temperature is stable at 12 °C at 10 cm below the surface will it germinate for 7 days. If the temperature is too low, the time of corn seeds in the soil is too long, which will affect the germination rate of seeds or the formation of weak seedlings after germination. Sowing too early not only leads to low yield but also increases the incidence of pests and diseases. If the sowing is too late, it will result in a short growth cycle of corn, and if the corn grain is not full, production will decrease. The rainfall before the sowing time will also affect the seed germination time. There is an imbibition stage after sowing. If the soil water content is too low, it will affect the seed germination time. After a preliminary study, the best sowing time in Dingxi City is as shown in

Table 3. Relationship between average temperature and yield in different sowing times from 2016 to 2020.

Year	2016	2017	2018	2019	2020
Best Sowing time	4/30	4/28	4/17	4/15	4/16
Average Daily Temperature	22.8 °C	20.2 °C	19.2 °C	17 °C	13.2 °C

, when the average daily temperature is stabilized at about 15 °C (around 15–25 April) sowing is the best [5].

3.3. Effects of Water Stress on Crops under Different Film Mulching Modes

Water is an important factor affecting crop growth in arid areas of northwest China. Soil moisture has an important impact on crop leaf expansion, stomatal closure, and early canopy senescence. Aiming at the two corn planting modes of PM and BM covered on the whole film double ridge furrow sowing ridge in Dingxi City, Gansu Province, the optimal sowing time determined by the AquaCrop model was used to simulate the effect of soil moisture on crops under the two film mulching modes during the whole growth period. In 2016 and 2017, the rainfall was less than 300 mm, which was a dry year. In 2018, 2019, and 2020, the rainfall was more than 300 mm, which was a wet year. During the whole growth period, the whole growth process of corn was simulated by the AquaCrop model, and the results are shown in Figure 5.

The analysis of derived data showed that the effect of water stress of PM on crop leaf expansion was significantly less than that of BM under the two planting patterns. As shown in Figure 5, the leaf expansion of water stress was mainly at the jointing stage of corn (about 40–85 days after sowing). In 2016 and 2017, the stress effect of BM on leaf expansion was up to 97% and 100%, respectively, and the stress days were 37 d and 56 d, respectively, while the stress effect of PM was up to 28% and 47%, respectively, and the stress days were 18 d. In 2018, 2019, and 2020, there was more rainfall during the growth period. The maximum stress effects of BM on leaf expansion were 51%, 12%, and 29%, respectively, and the stress days were 31 d, 27 d, and 41 d, respectively. The maximum stress effects of PM were 15%, 1%, and 7%, respectively, and the stress days were 10 d, 1 d, and 10 d, respectively. The stress percentage and stress days of PM on leaf expansion were better than those of BM.

The higher the stress effect on leaf expansion, the more detrimental to crop growth. Especially in dry years, the stress effect of soil moisture on maize leaf expansion is significantly greater than that in wet years. Compared with BM, the stress effect of reducing soil moisture on maize leaf expansion under PM is also significantly greater than that in wet years.

As shown in Figure 6, water stress-induced stomatal closure mainly occurs after the corn canopy coverage reaches the maximum (90 days after sowing). Stomatal closure will not be conducive to crop respiration and organic matter accumulation, affecting crop yield. After the canopy coverage reached the maximum in 2016, the total rainfall was only 40.3 mm. The maximum water stress-induced stomatal closure of BM is 57%, which is 10% higher than PM. After the canopy coverage reached the maximum in 2017, the total rainfall was 193.4 mm, and the maximum stomatal closure induced by water stress of BM was 44%, which was 24% higher than that of PM. Compared with 2016 and 2017, 2018, 2019, and 2020 were wet years, and water stress had no effect on stomatal closure. The simulation data showed that the effect of water stress-induced stomatal closure in 2016 was significantly stronger than that in 2017, while the effect of PM on reducing water stress was higher than that of BM. PM could improve the effect of water stress on maize respiration.

As shown in Figure 7, the trend of crown premature senescence caused by water stress is similar to that of induced stomatal closure. Due to less rainfall in the later stage and lower soil moisture content, some physiological activities of crops are affected, and crown premature senescence is caused. Premature senescence of canopy will shorten the growth cycle of maize, reduce the accumulation time of organic matter, make maize grains not full, and reduce the yield and quality of maize. In 2016, the water stress of BM caused the maximum crown premature aging of 27%, and the stress percentage of PM was 18%. In 2017, the maximum stress percentage of BM was 17%, and the maximum stress percentage of PM was 7%. The stress time of BM was about 5 days earlier than that of PM, and there was no effect in the wet years of 2018, 2019, and 2020.

AquaCrop was used to simulate the effect of water stress on crops during the whole growth period of corn under different mulching modes in Dingxi City, Gansu Province. The results of simulation data are shown in Figure 5, Figure 6 and Figure 7. The expansion of water-stressed leaves is mainly in the jointing stage of corn (about 40–85 days after sowing). In 2016, the expansion time of water-stressed leaves in BM was 17 days earlier than that in PM, the maximum difference in water stress percentage was 69%, and the whole process of water stress was 21 days longer than that in PM. Stomatal closure induced by water stress mainly occurred after the maximum canopy coverage of crops (90 days after sowing). The time of stomatal closure induced by water stress in BM was 6 days earlier than that in PM, and the maximum percentage of water stress was 10% different. The trend of water stress under the two film mulching modes was the same, and the stress effect of the biodegradable film was great. Water stress-induced canopy senescence mainly occurred at the filling stage of corn (after 90 days after sowing). The time of water stress-induced canopy senescence in BM was 5 days earlier than that in PM, and the maximum difference in water stress percentage was 9%. After the filling stage of corn, water stress-induced canopy senescence continued until corn harvest.

3.4. Differences in Canopy Coverage and Crop Transpiration under Different Film Mulching Modes

Corn film mulching planting will reduce soil evaporation, increase soil water productivity, and increase soil water content. Wang et al. [28] used soil moisture sensors, a miniature evaporation and permeation meter, and eddy covariance systems to detect that film mulching can increase surface soil temperature by 4.9%, increase soil volumetric water content by 19.5%, reduce corn evapotranspiration by 6.0% during the whole growth period, reduce soil evaporation by 57.5%, and increase water productivity by 22.6%. The difference in soil moisture under different film mulching modes has a great influence on the canopy coverage during the growth period of corn. The effective root zone water content directly affects the growth of crops during the whole growth period. The relationship between the effective root zone water content and the canopy coverage is shown in Figure 8.

In the drought years of 2016 and 2017, the maximum canopy coverage of BM was 27.4% and 21.6% lower than that of PM, respectively, and the maximum difference of effective root zone water content was 30.35% and 30.64%, respectively. In the wet years of 2018, 2019, and 2020, the maximum canopy coverage of BM was 14%, 13.2%, and 13.5% lower than that of PM, respectively, and the maximum difference of effective root zone water content was 34.83%, 31.28%, and 27.96%, respectively. In dry years, the water content of the effective root zone has been declining, and the canopy coverage has reached the maximum value and then decreased with the decrease of the water content of the effective root zone and the change of the canopy coverage of BM is more significant. In wet years, the effective root zone water content has been in a stable state, and the canopy coverage is also in a stable state after reaching the maximum value.

There are differences in soil moisture between PM and BM modes, which makes the canopy coverage of corn different. The greater the canopy coverage, the greater the transpiration coefficient of crops and the greater the transpiration. As shown in Figure 9, PM is 27.4% and 21.6% higher than BM canopy coverage in the 2016 and 2017 dry years, respectively. The maximum crop transpiration coefficients during the growth period are 0.28 and 0.34 higher, respectively, and the total crop transpiration is 85.3 and 76.1 mm higher. In the wet years 2018, 2019, and 2020, PM was 14%, 13.2%, and 13.5% higher than BM canopy coverage, respectively. The maximum crop transpiration coefficients during the growth period were 0.34, 0.28, and 0.28, respectively, and the total crop transpiration was 42.9, 31.8, and 31.5 mm higher. The difference in total crop transpiration between the two models in dry years was greater than that in wet years.

From 2016 to 2020, the effective water content in the root zone under PM was higher than that under BM. The canopy coverage and crop transpiration coefficient of PM were stable compared with BM, and the variation range was small. It can be seen that PM is more conducive to crop growth and can ensure the continuous and stable yield of crops.

3.5. Changes in Aboveground Biomass, Yield, and Water Productivity under Different Polyethylene Film Mulching Patterns

The difference in soil total water content under different film mulching modes has a great influence on aboveground biomass, yield, harvest index, and water productivity. The simulation results are shown in Figure 10. The aboveground biomass, yield, water productivity, and harvest index of PM mode in 2016–2020 are higher than those of BM. The aboveground biomass of PM was 23.89%, 21.5%, 16.87%, 15.18%, and 15.42% higher than that of BM, respectively. The yield of PM was 70.98%, 66.02%, 62.59%, 59.92%, and 60.22% higher than that of BM, respectively. The water productivity of PM was 63.54%, 68.45%, 87.56%, 81.37%, and 80.82% higher than that of BM, respectively. The harvest index of PM was 37.79%, 36.52%, 39.13%, 38.83%, and 38.82% higher than that of BM, respectively. In the dry year, PM had a larger increase in above-ground biomass and yield than BM and a smaller increase in water productivity and harvest index. In the wet year, PM had a smaller increase in above-ground biomass and yield than BM and a larger increase in water productivity and harvest index, and the harvest index basically tended to a value.

In the drought years of 2016 and 2017, the coefficients of variation of aboveground biomass of PM and BM were 2.16% and 3.03%, the coefficients of variation of yield were 2.54% and 3.98%, the coefficients of variation of water productivity were 2.21% and 0.73%, and the coefficients of variation of harvest index were 0.39% and 0.86%. In the wet years of 2018, 2019, and 2020, the coefficients of variation of aboveground biomass of PM and BM were 2.16% and 1.74%, the coefficients of variation of yield were 2.12% and 1.64%, the coefficients of variation of water productivity were 2.96% and 2.96%, and the coefficients of variation of harvest index were 0 and 0.1%. Under the two modes, the coefficient of variation of aboveground biomass, yield, and harvest index in dry years is higher than that in wet years, while the coefficient of variation of water productivity in dry years is lower than that in wet years, and the coefficient of variation of PM in dry years is lower than that in BM mode. The coefficient of variation of PM in wet years is slightly higher than that of BM because PM in dry years is more significant than BM in regulating rainwater distribution and covering anti-steaming. The ability of water saving and drought resistance is stronger, and the parameters of crops tend to be stable. In wet years, rainwater is abundant, soil moisture is not an important factor limiting crop growth, and the crops of BM also tend to be stable.

For PM rather than BM aboveground biomass and yield with the increase of rainfall during the reproductive period, the growth decreases gradually, while the water productivity with the increase of rainfall during the reproductive period, growth increases gradually; thus, the soil water content in the model of full-film double-monopoly furrow covered with polyethylene mulch is relatively high compared with the model of mulching biodegradable mulch, reducing the stress of water and temperature on corn in all growth periods, increasing corn yield, and the effect in the drought years The simulation results were in agreement with the results of the literature [7].

3.6. The Relationship between Different Soil Depth and Rainfall

In the rain-fed agricultural area of Northwest China, soil moisture content directly affects crop growth, and the change in soil moisture content is mainly determined by rainfall. Based on the AquaCrop simulation data, as shown in Figure 11, the soil moisture content of 0–200 mm soil layer under the two film mulching methods fluctuates greatly with rainfall, especially in the soil above 100 mm. Due to the effect of ridge and furrow rainwater harvesting, as long as there is rainfall, the soil moisture content fluctuates greatly. The groundwater in Dingxi City is less than 10 m, and there is no capillary rise. Therefore, the deep soil moisture content will only change when the crop roots grow in the deep soil. Especially in 2016 and 2017, which were dry years, the deep soil moisture shows a downward trend. The years 2018, 2019, and 2020 were wet, and the deep soil moisture was on the rise or flat.

In the same year, the soil water content of PM mode was significantly higher than that of BM mode, especially in the deep soil. In the two dry years of 2016 and 2017, the soil water content of BM mode below 780 mm did not change about 20 days after sowing, while the soil water content of PM mode increased by about 7%. About 90 days after sowing, the deep soil moisture content of BM decreased significantly, and the final soil moisture content of PM and BM was the same, while the water supply of PM to corn growth was significantly greater than that of BM, which ensured crop yield. In the three wet years of 2018, 2019, and 2020, the variation trend of soil water content above 400 mm in the two mulching modes was basically the same, while the soil water content below 400 mm was quite different. The average water content of PM was about 10% higher than that of BM in deep soil. It can be seen that the coverage and evaporation inhibition effect of PM was significantly better than that of BM, especially in dry years.

3.7. Economic Benefit Analysis of Film Mulching Planting

Film mulching can improve soil temperature and soil moisture and prevent soil nutrient loss, so it can improve crop yield and quality. Compared with the common planting mode [5], PM and BM planting in the whole film double ridge furrow planting technology has better environmental benefits in maize yield, soil moisture, field management, soil protection, and quality improvement. From 2016 to 2020, the average yield of PM and BM was 6.21 t/hm² and 1.42 t/hm², higher than that of the common planting mode, respectively. According to the market price, the income increased by USD 2238.8/hm² and USD 512/hm², respectively. Both film mulching can inhibit surface evaporation, collect rainwater infiltration, and increase water productivity. Especially in arid rain-fed agricultural areas, water is the only factor limiting agricultural development. Soil moisture directly affects crop yield. PM and BM inhibit invalid evaporation of soil surface by 100% and 59.4%, respectively. The average soil water content of PM and BM in 5 years after crop harvest is 56.47% and 31.84% higher than that of ordinary planting mode, respectively. The higher the soil water content after harvest, the more conducive to the next crop planting and sustainable development and the improvement of environmental benefits. Mulching planting inhibits weeds in the field and reduces crop pests and diseases. Compared with ordinary planting patterns, it saves the cost of cultivation and protection (according to the survey of local labor efficiency and labor costs, it costs USD 250/hm²) and reduces pesticide pollution to the environment. Film mulching can protect soil quality and structure, reduce soil nutrient loss, prevent soil compaction, improve soil fertility, reduce the cost of loosening soil, and increase the long-term yield of crops.

Paving two kinds of film in arid areas will increase maize yield, but at the same time, the film material and labor costs will also increase. In the process of laying, because PM and BM are laid mechanically, the cost of labor and machinery is the same, but the material cost of BM is more expensive than that of PM, and PM needs to be recycled after crop harvest. BM is directly buried in the soil without recycling, which reduces the cost of recycling. According to the local labor service fee and film price, the cost of BM is USD 138.3/hm² higher than that of PM, and the overall economic benefit of PM in Dingxi City, Gansu Province, is higher than that of BM. BM is gradually degraded into fragments after harvest and is decomposed into water and carbon dioxide that are pollution-free to the environment after tillage. PM needs to be recycled after harvest. Improper long-term recycling will cause environmental white pollution, affecting soil water and fertilizer migration and crop root growth. However, the current degree of mechanization is high, and the residual film can be completely recycled and standardized, which has little impact on the environment. Therefore, film mulching planting has good economic benefits, especially in arid areas, polyethylene film has good adaptability, which can improve the income of farmers and enhance the economic value of land.

4. Discussion

AquaCrop simulation was used to study the adaptability of PM and BM in whole film double ridge and furrow sowing technology of maize in Dingxi City and to determine whether BM can replace PM. Existing studies have shown that [7], through a large number of field experiments in the Loess Plateau of China, when the rainfall is greater than 600 mm and less than 800 mm, the maize productivity of BM is higher than that of PM, which can achieve a win-win situation of yield increase and environmentally friendly development. When the rainfall is less than 600 mm, the maize productivity under PM is significantly higher than that under BM, and the economic benefit of BM is lower than that of PM. In Xinjiang, where the annual rainfall is only 50–250 mm [29,30], BM can replace PM to increase cotton yield because irrigation is used to ensure cotton yield throughout the growth period. In this study, the experimental site was a rain-fed agricultural area with a rainfall of 300–500 mm. The results showed that the maize productivity of PM in the whole film double ridge furrow sowing technology was significantly higher than that of BM. Therefore, BM could not replace PM in maize planting in Dingxi City, China, which was consistent with the results of the literature [7].

The simulation results of AquaCrop simulation of maize whole film double ridge furrow sowing technology are slightly larger than the field test results because when the model is input into the field management data, there are seepage holes and seeding holes on the film surface after film mulching and sowing, the film coverage rate is less than 100%, and there is some surface evaporation, but the damaged film area is very small and cannot be measured and calculated, so the film coverage rate in the model is set to 100%. Mulching can not completely inhibit the growth of weeds in the field, and there is a lack of data on the impact of weed maize growth, affecting maize yield. The whole film double ridge furrow planting technology has a large ridge and a small ridge, which is set as ridge planting in the model, and the surface runoff is 0. However, due to the influence of plot and terrain, there will be certain surface runoff in the experiment, resulting in uneven rainwater infiltration and reduced corn yield.

In the follow-up study, the input data in the model was further improved, the regional differences of each test plot were input into the model, and the weed infestation data and field management data were collected to make the model more suitable for field experiments. The effects of N, P, K fertilizer and film interaction on crop yield and water productivity should be considered to increase crop yield and increase farmers’ benefits.

5. Conclusions

(1) In this study, the AquaCrop model was used to simulate the whole film double ridge furrow sowing technology of maize in Dingxi City from 2016 to 2020, and the applicability of the AquaCrop model was verified. By comparing the field test data with the simulation data, r was higher than 0.89, RMSE was distributed between 0.01 and 0.24, CV (RMSE) was distributed between 1.66% and 2.10%, EF was higher than 0.90, and d was higher than 0.90. The calibrated AquaCrop model was used to determine the sowing time of maize, and the relationship between soil total water content, aboveground biomass, yield and water productivity, and the effect of water stress on crop growth under the biodegradable film and polyethylene film planting patterns were studied.

(2) The analysis of AquaCrop simulation results shows that the sowing time of maize in Dingxi City has a significant impact on the yield, and premature or late sowing will significantly reduce the yield. The best sowing time in Dingxi City is when the average temperature is stable at about 15 °C (15–25 April), and the yield is the highest.

(3) Through comparative analysis of simulation results and field experiments, in dry years, the effect of water stress on crop leaf expansion under BM was 61% higher than that under PM, and the number of stress days was 28.5 days more than that under PM. The effect of water stress on stomatal closure was 17% higher than that under PM, and the effect of water stress on crown premature senescence was 9.5% higher than that under PM, and the stress time was about 5 days earlier than that under PM. In wet years, the effect of water stress under BM on leaf expansion was 23% higher than that of PM, and the number of stress days was 26 days more than that of PM. There was no stress effect on stomatal closure and premature senescence of the canopy.

(4) The simulation results show that in dry years, the effective root zone water content of BM is 30.5% lower than that of PM in the same period, resulting in the maximum canopy coverage under BM being 24.5% lower than that of PM. In wet years, the effective root zone water content of BM is 31.57% lower than that of PM in the same period, resulting in the maximum canopy coverage under BM being 13.57% lower than that of PM. And the soil water content in the dry year has been in a downward trend, and the wet year is basically stable. Because the greater the canopy coverage, the greater the crop transpiration, the crop transpiration under PM is greater than that under BM, and the difference between the total crop transpiration of the two models in dry years is significantly greater than that in wet years.

(5) The above-ground biomass, yield, harvest index, and water productivity under PM were significantly higher than those under BM, and the indexes under PM were more stable than those under BM. Especially in dry years, the advantage of PM is more significant. In dry years, the deep soil moisture of both models showed a downward trend, and the soil moisture was in an overdraft state, while the decline under PM tended to be gentler than that under BM. In the wet year, the deep soil moisture remained stable or rising. Therefore, the water retention of PM is better than that of BM, and its adaptability in arid areas is stronger.

The AquaCrop model was used to simulate the whole film double ridge furrow sowing technology of maize. The simulation results were highly fitted with the field test data, and the adaptability of the model was good. The research and analysis showed that the biodegradable film could not replace the polyethylene film in corn planting in Dingxi City, which provided certain data support and technical means for corn planting and had certain guidance for the optimization and improvement of the agronomic technology of the whole film double ridge furrow sowing technology of maize. In the later research, the distribution of soil moisture and fertilizer in the whole film double ridge furrow sowing technology and its influence on crop growth should be considered so that the model can more accurately simulate the planting mode of the whole film double ridge furrow sowing technology in arid areas, and provide more reliable data for the research.