Research Articles

Feasibility analysis of a double-cropping system for the efficient use of farmland on China’s Loess Plateau

  • FENG Weilun , 1, 2 ,
  • LIU Yansui , 1, 2, * ,
  • LI Yurui 1, 2 ,
  • CHEN Zongfeng 1, 2
  • 1. Institute of Geographic Sciences and Natural Resources Research, CAS, Beijing 100101, China
  • 2. Key Laboratory of Regional Sustainable Development Modeling, CAS, Beijing 100101, China
*Liu Yansui (1965-), Professor, specialized in human-earth science and rural sustainability. E-mail:

Feng Weilun (1992-), PhD, specialized in the agricultural development and land use. E-mail:

Received date: 2022-04-18

  Accepted date: 2022-11-29

  Online published: 2023-06-26

Supported by

National Natural Science Foundation of China(41931293)

National Natural Science Foundation of China(41801175)

National Natural Science Foundation of China(42201287)

Postdoctoral Science Foundation of China(2020M680658)


Cropping systems worldwide have been affected by the current trend in global warming and the optimization of cropping systems is an important area of research in the transition of agricultural land. The Loess Plateau is a typical ecologically fragile region with the most serious soil erosion in China. We carried out a field experiment in Yan’an city on the Loess Plateau to explore the effect of sowing date on crop growth and yield. We then analyzed the feasibility of a double-cropping system by considering climatic adaptability, ecological suitability and economic viability. Our results showed that different sowing dates resulted in significant differences in crop growth and that appropriate early sowing can result in higher crop yields for early maturing varieties. We showed that double-cropping systems of sweet maize (Zea mays)-forage rape and feed maize-forage rape are feasible on the Loess Plateau. We discuss the implications for the efficient use of farmland, which is important in guiding agricultural supply-side reform and the development of modern agricultural management.

Cite this article

FENG Weilun , LIU Yansui , LI Yurui , CHEN Zongfeng . Feasibility analysis of a double-cropping system for the efficient use of farmland on China’s Loess Plateau[J]. Journal of Geographical Sciences, 2023 , 33(6) : 1271 -1286 . DOI: 10.1007/s11442-023-2129-3

1 Introduction

Agriculture is the foundation of national economic development and provides food, raw materials and energy for various sectors of the social economy (Liu et al., 2017; Feng et al., 2019). Since the start of the 21st century, global warming has become a general trend and has had a serious impact on natural ecosystems, human survival and agricultural production (Stricevic et al., 2018). Climate change is significantly affecting agricultural cropping systems, production potential and management as a result of changes in temperature and precipitation patterns (Meza et al., 2008; He et al., 2015; Marcinkowski et al., 2018). The Sixth Assessment Report of the Intergovernmental Panel on Climate Change in 2021 showed that the global average surface temperature has increased by about 1°C since 1850-1900. The annual average increase in temperature in China is even higher than the global average and agricultural production and cropping systems have been significantly affected (Zhou, 2015; Yin et al., 2016a). As a result of the monsoon climate in most areas, nearly 57% of China’s arable land is replanted, making China one of the countries with the highest multiple cropping indexes worldwide (Liu et al., 2021). The northern climatic boundaries of double-cropping systems (DCSs) have shifted significantly to the north and west in Liaoning, Hebei, Gansu, Shaanxi and Shanxi provinces (Lv et al., 2020). A warming climate can increase the potential of transforming cropping systems in the crucial agricultural climate zone of northern China (Guo, 2015). With encouragement from various national policies to improve agriculture and the balance of farmland occupation and compensation, the substantial northern shifts in the feasibility of DCSs has become an important way of supplementing cultivated land and expanding the region suitable for growing grain crops (Yin et al., 2016b; Zhou et al., 2020).
Maize (Zea mays) is the third primary crop in China. However, the yield of maize, especially rain-fed maize, is projected to decrease with the current global warming trend if no measures are taken (Ju et al., 2013). In 2017, the Chinese government issued guidelines for the structural adjustment of maize in the so-called Sickle Bend area, proposing that the region should actively adjust agricultural planting patterns to achieve stability from grain-based to grain-economy-feed integrated planting operations. As the key area for the structure adjustment of maize-growing, the Sickle Bend area is located in northeast, north, southwest and northwest China, which shows a sickle bend in China’s topographic map distributed from northeast to northwest. The Loess Plateau lies at the heart of the Sickle Bend region and is an important maize-growing area (Feng et al., 2016). The cropping system in this region has, for a long time, been dominated by a single-cropping system due to the fragile ecological environment and the fragmentation of cultivated land. This has led to low agricultural production and the insufficient utilization of light, heat and water resources (Li et al., 2016). The local government in this region has carried out two major renovation projects—the Green-for-Grain Project and the Gully Land Consolidation Project (GLCP)— since the start of the 21st century, which have greatly improved the local ecological environment and agricultural production and laid a foundation for the optimization of cropping systems (Liu et al., 2015; Wang et al., 2016). Moreover, the average temperature on the Loess Plateau since 2000 has increased by about 2.0C compared with that before 1970 (Liu et al., 2019). The annual accumulated temperature has steadily exceeded 3400℃·days since 1997 (the minimum limit of accumulated temperature required for DCSs), which shows that DCSs are now possible in most areas of the Loess Plateau, especially in areas with good soil conditions and sufficient water resources (Liu et al., 2019).
The optimization of cropping systems with increasing multiple cropping indexes can be used to solve the problem of a shortage of cultivated land resulting from the global climate crisis. This is now an area of active research in current agricultural development (Liu et al., 2014; Zhou et al., 2016). Extensive research has been carried out worldwide on the optimization of cropping systems, mainly focusing on the effects of sowing dates and planting patterns on the growth period, growth shape, quality and yield of field crops such as maize, wheat and rice (Muoneke et al., 1997; Sun et al., 2007; Xia et al., 2011; Hu et al., 2017; Ding et al., 2020). Nagy (2009) showed that early sowing can change the growth period of crops and improve grain yields. Li et al. (2010) verified the interaction between sowing date and crop density. Li (2011) reported that the average dry matter accumulation rate and yield of different maize varieties had a decreasing trend with the postponement of the sowing date. Other studies have shown that the sowing date has a significant effect on crop growth and yield and that the response of different crop varieties is inconsistent (Olasantan et al., 2004). Many researchers have used climate prediction and crop growth models to determine options for adaptation to climate change at the planting pattern level (e.g., changing sowing dates, crop varieties, irrigation and fertilization practices) and quantifying their impact on crop yields (Xiong et al., 2008; Tao et al., 2010; Lv et al., 2013). Appropriate early sowing can effectively promote crop growth and improve crop yields, but there is a risk of poor crop emergence and delayed growth in the later stages. It is therefore important for the sustainable and efficient development of agriculture to scientifically explore crop growth and yields at different sowing dates and suggest directions for the adjustment of cropping systems for regional agricultural development.
This study aimed to (1) explore the effect of sowing date on crop growth and yield for different varieties; (2) discuss the factors influencing the adjustment of sowing dates for DCSs; and (3) to analyze the feasibility of DCSs on China’s Loess Plateau.

2 Materials and methods

2.1 Site description

The field experiment was carried out in the Gutun catchment of Yan’an city (109°14°10”E, 36°10°05”N), which is located in the middle of the Loess Plateau (Figures 1a, 1b and 1c) (Wang et al., 2017). The area of the catchment is 24.12 km2, with altitudes ranging from 1050 to 1298 m. The climate of this region ranges from semi-humid to semi-arid with abundant thermal resources. The average annual precipitation is 556 mm, with 70% of the rainfall in July-September. The soil types include loessial soil, black loess and red clay, among which loessial soils are the most cultivated and most eroded in the basin. The rural industries in the Gutun catchment are dominated by planting, followed by animal husbandry and sideline businesses, with a per capita net income of 4100 yuan. Yan’an city implemented the GLCP in 2013, with a construction scale of 33,300 ha. The Gutun catchment is a sub-project of the GLCP, with a construction scale of 27.84 ha. By the end of 2015, a series of engineering measures in Gutun catchment had greatly improved the production capacity and quality of farmland and the efficiency of land use in this region (Figures 1d and 1e).
Figure 1 Location of the field experiment in Yan’an city (a, b); General view of the experimental field (c): WR, Wanrui No.5; DM, Demeiya No.3; JC, Jichengdan No.3; JK, Jingkenuo No.2000; TR, Tieren No.707; MX, Mexican grass); Comparison of the plot before (d) and after implementation (e) of the GLCP; (f) Maize collected in the experimental area

2.2 Experimental layout

The field experiment was carried out from January 2016 to November 2018. The test variables were the sowing date and crop variety (Table 1). Five targeted sowing dates were set as A1 (4 weeks earlier, March 28), A2 (3 weeks earlier, April 4), A3 (2 weeks earlier, April 11), A4 (1 week earlier, April 18) and CK (normal sowing date, April 25). Six crop varieties were used: Wanrui No.5 (WR, a grain crop), Demeiya No.3 (DM, an early maturing grain crop), Jichengdan No.3 (JC, an early maturing grain crop), Jingkenuo No.2000 (JK, a cash crop), Tieren No.707 (TR, a feed crop), and Mexican grass (MX, a feed crop).
Table 1 Description of different experimental treatments (see text for definitions)
Variable Treatment Classification Description
Sowing date CK April 25 AST, 15.1℃; HT, 20.3℃; LT, 10℃; SH, 15.4%
A1 March 28 AST, 6.8℃; HT, 12.6℃; LT, 2.2℃; SH, 15.9%
A2 April 4 AST, 10.1℃; HT, 14.4℃; LT 7.1℃; SH, 15.3%
A3 April 11 AST, 14.5℃; HT, 19.2℃; LT, 10.2℃; SH, 15.3%
A4 April 18 AST, 10.0℃; HT, 17.0℃; LT, 4.2℃; SH, 16.0%
Crop variety WR Wanrui No. 5 Growth period, 98 days; yield, 9.2 t/ha; plant height, 265 cm
NM Demeiya No. 3 Growth period, 118 days; yield, 10.6 t/ha
JC Jichengdan No. 3 Growth period, 114 days; yield, 9.8 t/ha; plant height, 180 cm
JK Jingkenuo No. 2000 Growth period, 85 days; fresh ears yield, 13.5 t/ha; plant height, 260 cm
TR Tieren No.7 07 Growth period, 100 days; fresh weight yield, 105 t/ha; plant height, 350 cm
MX Mexican grass Growth period, 210 days; fresh weight yield, 150 t/ha

Note: AST, average soil temperature; HT, highest temperature; LT, lowest temperature; SH, soil humidity

Each site was 2 m wide and 5 m long and three repetitions were set to ensure the accuracy of the test results. A 1-m wide separation zone was designed between each sample area to reduce the interaction of the soil properties between the different areas. We excavated a 34 m long, 8 m wide and 0.3 m deep soil pit in April 2015 (the original soil below 0.3 m is uniform) using a bulldozer to level the test sample. The soil type of the test area was loessial soil, which is widely distributed on the Loess Plateau. Its major chemical and physical properties are given in Table 2. The row-to-row distance was 50 cm, whereas the plant-to-plant distance was 40 cm. The whole test plot was plowed to a depth of 30 cm with a plowing machine and rotary tiller on March 26. Crop planting and field management were based on local traditional farming practices. A compound fertilizer containing 90 kg/ha N, 39 kg/ha P and 75 kg/ha K was applied using a fertilizer applicator during seeding.
Table 2 Physiochemical properties of the topsoil in the experimental field
Soil type Particle size (%) Soil organic matter (%) pH Cation exchange capacity (Cmol/kg) Available N (mg/kg) Available K (mg/kg) Available P (mg/kg)
Sand Silt Clay
Loessal soil 23.1 68.7 8.2 1.3 8.57 10.33 88.25 3.95 10.95

2.3 Data collection and analysis

The meteorological data (e.g., air temperature, soil temperature and rainfall) were monitored in real time using a commercially produced micro-weather station. The growth data for the crops in the test field included the plant height, stem diameter, biomass and yield. These data were collected by randomly selecting three plants from each test field every week from the seeding stage. The plant height was measured directly with a tape measure and the stem diameter was measured with vernier calipers. The total biomass of the crops was measured by cutting the above-ground part of the crops and then weighing with an electronic balance after drying to a constant weight in an oven. The crop yield data were collected by weighing the fresh weight and grain yield of the crop and calculating the average value by dividing the test samples into three pieces. Based on our previous planting trials with forage rape (Liu et al., 2017), the preferred time to plant the second round of crops is around July 20. To ensure that the first crop harvest and the second crop sowing did not clash in time, we measured the total biomass and crop yield on July 15 in all 3 years.
A composite soil sample was also obtained. This consisted of a mix of three individual soil samples (0-30 cm depth) taken randomly 4-5 m apart. Each sample was kept in a plastic bag for transport to the laboratory. The residual soil was air-dried and analyzed to determine the physical and chemical properties. Soil bulk density, total porosity, available N, available P and available K were determined according to the Institute of Soil Science of the Chinese Academy of Sciences methods (Lu, 2000; Ma et al., 2020). The soil mechanical composition was measured with a Longbench Mastersizer2000 laser particle size analyzer (Malvern Instruments, Malvern, UK). Soil organic matter (SOM) was measured by hot oxidation with sulfuric acid and potassium dichromate (Yeomans and Bremner, 1988). Soil pH was measured in suspension (the ratio of soil and water 1:2.5) with an automatic acid-based titrator (INESADZB-718). Soil cation exchange capacity (CEC) was determined using flame photometry after treating samples by NaOAc solution and then NH4OAc solution (Lu, 2000).
The one-way analysis of variance was employed to estimate the differences in stem diameter, biomass, seed yield and 1000-grain mass among different treatments. The Duncan’s multiple range test at 5% probability level was applied to determine the significant differences among each treatment. Data analysis methods mentioned above were conducted in SPSS version 22.0 (SPSS Inc., Chicago, IL).

2.4 Feasibility analysis

Feasibility analysis is used to investigate and compare the technical, ecological, economic and engineering aspects of a particular technology, including its main content, implementation conditions and impact (e.g., application background, required conditions, resource supply, market demand and overall benefits) to determine whether the technology is operable in the region. It focuses on comprehensiveness, systematization and synthesis, and needs to be considered in a holistic manner and from multiple perspectives. The feasibility analysis for the DCSs was a comprehensive analysis in terms of climatic adaptability, ecological suitability and economic viability, with the aim of demonstrating that DCSs have both theoretical and practical feasibility in this region. Climatic adaptability refers to the ability to adapt to the regional climatic conditions in terms of temperature, precipitation and sunshine. Ecological suitability refers to the influence on the regional ecological environment—that is, to determine that the model has good ecological benefits and does not cause damage to the local ecological environment. Economic viability means that the model has economic benefits and strong market competitiveness by comparing the input-output ratio with the traditional model.

3 Results and analysis

3.1 Crop growth at different sowing dates

3.1.1 Plant height

The plant height at different sowing dates showed significant differences between crop varieties (Figure 2). The plant heights of WR and TR were significantly correlated with the sowing date. Before June 6, the plant heights of crops with earlier sowing dates were relatively large (A1>A2>A3>A4>CK). However, after June 6, the plant heights of groups A2 and A3 increased rapidly and eventually overtook the other two sample sites (A3>A2> A4>A1>CK). Similarly, when DM, JC, JK and MX were sown between March 28 and April 4, the plant heights were significantly higher than those of crops with other sowing dates and the sequence of plant heights with different sowing dates was A1>A2>A3>A4>CK. These results indicate that the early maturing varieties showed greater tolerance to cold and drought and the advance of the sowing date did not affect their early growth. However, the emergence and growth of common crops were relatively poor under the early sowing condition, which led to the growth of late sown crops gradually falling behind.
Figure 2 Plant heights at different sowing dates (WR, Wanrui No.5; DM, Demeiya No.3; JC, Jichengdan No.3; JK, Jingkenuo No.2000; TR, Tieren No.707; MX, Mexican grass corn)

3.1.2 Stem diameter and biomass

The stem diameter of the main crop varieties were different at different sowing dates, consistent with the total biomass (Figure 3a). WR had the largest stem diameter when sown on April 11, followed by the crops sown on March 28 and April 4, with the smallest stem diameter for crops sown on April 18 and 25. There was no significant difference in the stem diameter of DM at different sowing dates. The stem diameter of JK was largest when sown on March 28, but then suddenly decreased to a minimum and then showed an increasing trend with later sowing dates. The stem diameter of TR increased with the sowing date and reached its peak on April 25.
Figure 3 Crop stem diameter and total biomass for different sowing dates (WR, Wanrui No.5; DM, Demeiya No.3; JK, Jingkenuo No.2000; TR, Tieren No.707). Different lowercase letters indicate significant differences between different treatments at the p<0.05 level.
The total biomass of TR showed an increasing trend with later sowing dates, with the highest at 76 t/ha after sowing on April 25, whereas the total biomass of the crops sown on March 28 was the lowest at 52 t/ha. For WR, DM and JK, there was no significant correlation between the biomass index and the sowing date. The total biomass of WR sown on April 4 and 11 exceeded 39 t/ha, which was higher than for crops sown on other dates. The total biomass of DM sown on March 28 and April 4 and 18 was relatively high (>38 t/ha). The total biomass of JK sown on March 28 and April 25 was relatively high, both exceeding 35 t/ha, whereas that of crops sown on April 4 and 11 were both <30 t/ha.

3.1.3 Seed yield and 1000-grain mass

The seed yield of the main crop varieties at different sowing dates showed significant differences (Figure 4a). WR showed a typical inverted U-shaped curve over the sowing date, with the highest yield on April 11, followed by April 18 and 4, and the lowest on April 25 and March 18. By contrast, DM had the lowest yield when sown on April 11, although the yield trend in other sowing periods was similar to WR. The yield of JK was highest when sown on March 18 and lowest when sown on April 4. The yield of TR showed a gradual increase with later sowing dates, with the highest yield on April 25 and the lowest on March 18.
Figure 4 Seed yield and 1000-grain mass at different sowing dates (WR, Wanrui No.5; DM, Demeiya No.3; JK, Jingkenuo No.2000; TR, Tieren No.707)
The 1000-seed weight of the main crop varieties showed significant differences at different sowing dates (Figure 4b). DM sown on April 18 and 25 and JK sown on April 11 and 25 both had a larger 1000-seed weight. In general, the 1000-grain mass of the late sown crops was higher than that of the early sown crops, which may be because the external environmental conditions (e.g., climate and soil) are more suitable for early root growth and the later grain growth period of crops with later sowing dates.

3.2 Theoretical feasibility analysis of DCS

3.2.1 Climatic adaptability

Yan’an city is a typical area on China’s Loess Plateau and its climate has clear interannual and inter-regional differences. Temperature, precipitation and sunshine all have important effects on the growth periods of crops, such as emergence, flowering and maturity. The annual average temperature, precipitation and sunshine hours in Yan’an city have shown a stable and slightly fluctuating trend since the start of the 21st century, with average values of 10.71°C, 548 mm and 2588 h, respectively (Figure 5a). The monthly average temperature in Yan’an from April to October is relatively high, with all months warmer than 10℃ (Figure 5b). After the end of March, the average temperature in Yan’an gradually exceeds 10℃ and increases to a peak of 23.7℃ in July. The temperature then shows a clear downward trend and decreases to <10℃ in early October, which is not suitable for the growth of field crops. Precipitation in this area is sufficient for crop growth from June to October, exceeding 45 mm per month, but is lower in winter and spring at <20 mm per month (Figure 5c). The number of hours of sunshine in Yan’an is relatively high between March and August (>200 h in all months), whereas the number of sunshine hours in other months is relatively low (Figure 5d).
Figure 5 Characteristics of the climate in Yan’an city from 2001 to 2017 (AT, average temperature; AP, average precipitation; SH, hours of sunshine)
The temperature in Yan’an begins to increase at the end of March. Precipitation and the number of hours of sunshine also gradually increase after this date, reaching a peak around July, and then show a significant downward trend. The area has sufficient sunlight and water for crop growth from March to October and the annual accumulated temperature has steadily exceeded 3400℃·day, giving the theoretical possibility of a DCS. Maize crops prefer high temperatures and short hours of daylight and the growth period is 100-120 days, whereas forage rape crops have a greater demand for water and sunshine and the growth period is about 80 days. A reasonable combination of these two crops is a good choice for DCS in this area—that is, another crop of forage rape can be planted after the harvest of JK, TR or forage rape sown before July 20. Based on our analysis of the climate in Yan’an over a period of years, combined with the results of maize planting experiments in this area, DCS is now feasible in this region.

3.2.2 Ecological suitability

The local government of Yan’an city has carried out the Green-for-Grain Project since 1998, which has effectively improved vegetation coverage, significantly enhanced water and soil conservation, and greatly improved the ecological environment (Cao et al., 2018). The GLCP was also implemented in 2013, which significantly improved the agricultural infrastructure and promoted the development of modern agriculture. The joint implementation of these two projects will preserve the ecological environment and promote agricultural development, forming a virtuous circle of returning farmland to forests on the hills and restoring the land below the hills, thus providing a good ecological guarantee for DCSs.
In turn, a DCS helps to improve the local ecological environment and enhance the utilization efficiency of water and soil resources. First, compared with a single-cropping system, it can significantly increase the time for which vegetation covers the surface of cultivated land, which helps to maintain water and soil and improves the utilization efficiency of water resources. Second, it can increase the type and variety of agricultural crops in the region, which helps to increase the complexity and biodiversity of vegetation. Third, the deep rooting of forage rape loosens the soil and this crop can be used as a green manure to improve soil fertility. Fourth, it increases the supply of fodder crops and helps to promote the development of local aquaculture, generating more animal manure to improve soil fertility. A DCS therefore improves soil quality, maintains the water and soil, and improves the utilization efficiency of water and soil resources.

3.2.3 Economic viability

We carried out a wide range of household surveys in the study area to determine planting costs and the income received from local crops; and obtained the results of 50 valid questionnaires (Figure 6). The results showed that sweet potato, potato and millet were the characteristic agricultural products in Yan’an city and that the net income from these crops was relatively high, reaching 24.8, 17.3 and 16.4 kilo-yuan/ha, respectively. However, their total cost was correspondingly high, especially for the transplantation, irrigation and field management of sweet potatoes. The net income of waxy maize, wheat and forage maize was in the mid-range, about 9-12 kilo-yuan/ha. The mechanization level is relatively high for wheat crops, so the gross income and total costs are low at 18 and 4.8 kilo-yuan/ha, respectively. The net income from soybean, field maize and forage rape was relatively low at <9 kilo-yuan/ha. In particular, maize is planted on a large scale in the study area, but provides a net income of only about 7.4 kilo-yuan/ha.
Figure 6 Cost-benefit analysis of different crops in Yan’an city
We conducted a comprehensive cost-benefit analysis of sloping farmland, single-cropping systems and DCSs. The crops planted on sloping farmland are mainly wheat and soybean, with relatively low incomes of 13.2 and 3.1 kilo-yuan/ha, respectively. The crops planted on cultivated land after GLCP were mainly maize, millet and sorghum, with yields of 7.4, 16.4 and 9.7 kilo-yuan/ha, respectively. The yield of these crops was significantly higher than those on sloping fields and the labor costs were greatly reduced, as agricultural machinery can be used during sowing, fertilization, irrigation and harvesting. The net income of the DCSs (JK-HY and TR-HY) both exceeded 23 kilo-yuan/ha, respectively, a significant improvement compared with the traditional single-cropping system. DCSs of sweet maize-forage rape and feed maize-forage rape can therefore significantly increase the economic yield of the cultivated land and greatly increase the competitiveness of the local agricultural economy.

4 Discussion and implications

4.1 Effect of sowing date on crop growth

Our experimental results showed that the growth of DM and JK sown on March 28 was relatively good and the plant height, stem diameter, total biomass and other indexes were significantly higher than those of other sowing dates. This may be partly because DM and JK are early maturing crop varieties, which have stronger drought tolerance and cold resistance and can adapt to the harsh climatic conditions experienced by early sowings (Berzsenyi and Lap, 2001). In general, appropriate early sowing can improve the yield of maize for crop varieties with cold and drought resistance (Sen et al., 1999; Aghayari et al., 2016). However, if some other conventional crops are sown too early, they may be adversely affected by the harsh growing conditions (e.g., drought and severe cold), resulting in slower growth in the later stages. For example, the indicators for WR and TR with a sowing date of March 28 were poor, probably as a result of the relatively low emergence rate with early sowing and poor growth after the large trumpet period (Opsi et al., 2013). Only crops with cold and drought tolerance can achieve our purpose of increasing crop yields by advancing the sowing date.
These results may also be due to the longer growth duration of the early sowing crops compared with later sowing crops if they are measured on the same date. In contrast with similar relative studies, this study aimed to compare the growth of the first crop at a specific time point in order to facilitate the subsequent feasibility analysis of DCSs. We consider the sowing date that results in a better crop growth to be the optimum sowing time for the DCSs, irrespective of whether this is due to a longer growth duration to mid-July or a better adaptation to the early climatic conditions. With the vast territory and different natural conditions in China, the sowing date in other regions has significant effects on the growth of crops. The practice of agricultural production in Heilongjiang and Shaanxi provinces shows that an early sowing date has a significant effect on the improvement in maize yield because these crops can make full use of the water available in spring, have improved drought resistance and actively use the accumulated temperature in early spring to ensure the maturity of maize (Gao et al., 2011).

4.2 Factors influencing the adjustment of the sowing date for a DCS

The adjustment of sowing date is an important management technique to improve the adaptation of maize crops to climate change. The selection of the optimum sowing date should not simply consider regional climate conditions but should also match the growth characteristics of the maize in each growth period and the demand for various climatic resources (Liu et al., 2020). In general, crops with different sowing dates have different growth periods and these different growth periods also have different requirements for temperature, sunshine and precipitation (Nyakatawa et al., 1998). A high-quality crop of maize requires high temperatures and a short duration of sunshine; a delay in the sowing date will shorten the whole growth period (Molnar et al., 2007). Rainfall is an important meteorological factor affecting the growth and yield of maize crops. The rainfall conditions in the study area are more suitable for every growth stage of early sown maize (Maresma et al., 2019).
By comparing the effects of different sowing dates on the growth and yield of different varieties of maize, Liu et al. (2009) showed that a sowing date of May 15 was more suitable for maize growth on the North China Plain than a date of April 24 and that the rainfall conditions were the most important factor. The growth of maize seeds is not only related to pollination at the time of flowering, but also depends on whether the flower can form effective seeds after fertilization (Zhang et al., 2019). The rate of production of early sown maize, from the big bell opening stage to the mature stage, was higher than that of late sown maize, suggesting that early sowing better meets the needs of crop reproductive growth and promotes the early development and growth of grains (Singh et al., 1987). It is therefore necessary to consider the adaptability of the characteristics of crop growth and the local climate conditions to determine the best sowing date for a DCS.

4.3 Feasibility and prospect of a DCS on China’s Loess Plateau

Cropping systems are an important component of farming systems, which consist of a cropping pattern and interactions with the regional resources, relevant enterprises and the technology available. Cropping systems are first influenced by the local thermal factors, which are usually expressed in terms of the active cumulative temperature (the accumulation of average daily temperatures >10℃ during the year). Under the current trend of global warming, and as a smart strategy to tackle climate change, DCSs have been widely adopted in the arid and semi-arid areas of northern China to meet the growing demands for food (Liu et al., 2020; Wang et al., 2020). The implementation of the GLCP on the Loess Plateau during the last 10 years has not only consolidated the results of returning farmland to forests but also promoted the systematic transformation of the regional agricultural, industrial and management structures (Liu et al., 2017; Li et al., 2021). In particular, a DCS has been successfully demonstrated and promoted in Yan’an city for >14 ha of land during the last 2 years and achieved an annual increase in income of 80%, which has had a positive role in realizing local agricultural efficiency, farmers’ income and the sustainable alleviation of poverty (Zhou et al., 2019; Lu et al., 2020; Feng et al., 2022). DCSs are feasible in terms of climatic adaptability, ecological suitability and economic viability, which is an important direction for the optimization of cropping systems on China’s Loess Plateau (Guo et al., 2014).
The consolidation of agricultural land centered on land reclamation, water and soil allocation and ecological restoration has been widely carried out worldwide and the demand for engineering technology is increasing (Liu et al., 2014; Wu et al., 2019a; 2019b). Land consolidation can effectively improve the regional agricultural infrastructure and help sustainable and efficient agriculture, providing an opportunity for the optimization of cropping systems (Han et al., 2014; Li et al., 2014; Liu et al., 2019; Zou et al., 2019). The objective of any cropping system is to use resources (e.g., land, water and solar radiation) effectively to maintain stable production and obtain higher net returns. Efficient cropping systems based on the local climate and the availability of soil and water need to be evolved to achieve potential production levels through the effective use of existing resources (Liu, 2015; Wang et al., 2019).

5 Conclusions

We analyzed the crop growth at different sowing dates and discussed the effects of sowing date on crop growth based on a field experiment in Yan’an city. We also considered the direction and measurement of the optimum utilization of land after implementation of the GLCP on the Loess Plateau through a theoretical and practical feasibility analysis of DCSs in Yan’an city. Our main conclusions are as follows.
(1) Different sowing dates have significant effects on crop yield and appropriate early sowing effectively promotes crop growth and improves crop yields. However, early sowing may risk poor crop emergence and delayed growth in the later stages. Early maturing maize and fodder maize can be harvested at the end of July, which has practical feasibility for DCSs.
(2) There has been much work worldwide in recent years on the optimization of agricultural cropping systems under the current trend of global warming. DCSs with forage rape as the core have a high feasibility for promotion in terms of climatic adaptability, ecological suitability and economic viability. This is an important direction for the adjustment of modern agricultural planting patterns on China’s Loess Plateau.
(3) Since the 21st century, large-scale ecological construction projects have been widely implemented in China’s traditional single-cropping areas, which have produced a large amount of flat cultivated land suitable for mechanization and laid a foundation for the optimization of cropping systems. Through the coupling analysis of field experiment and multi-dimensional feasibility, we comprehensively analyzed the feasibility of the DCS and provided suggestions for efficient utilization of cultivated land.
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