WANG Jin-bin, XIE Jun-hong, LI Ling-ling#, ADINGO Samuel

1 State Key Laboratory of Aridland Crop Science/College of Agronomy, Gansu Agricultural University, Lanzhou 730070, P.R.China 2 College of Forestry, Gansu Agricultural University, Lanzhou 730070, P.R.China

3 Faculty of Applied Sciences, University for Development Studies, Navrongo-Upper East 00233, Ghana

Abstract The fully mulched ridge–furrow (FMRF) system has been widely used on the semi-arid Loess Plateau of China due to its high maize (Zea mays L.) productivity and rainfall use efficiency.However, high outputs under this system led to a depletion of soil moisture and soil nutrients, which reduces its sustainability in the long run.Therefore, it is necessary to optimize the system for the sustainable development of agriculture.The development, yield-increasing mechanisms, negative impacts, optimization, and their relations in the FMRF system are reviewed in this paper.We suggest using grain and forage maize varieties instead of regular maize; mulching plastic film in autumn or leaving the mulch after maize harvesting until the next spring, and then removing the old film and mulching new film; combining reduced/notillage with straw return; utilizing crop rotation or intercropping with winter canola (Brassica campestris L.), millet (Setaria italica), or oilseed flax (Linum usitatissimum L.); reducing nitrogen fertilizer and partially replacing chemical fertilizer with organic fertilizer; using biodegradable or weather-resistant film; and implementing mechanized production.These integrations help to establish an environmentally friendly, high quality, and sustainable agricultural system, promote highquality development of dryland farming, and create new opportunities for agricultural development in the semi-arid Loess Plateau.

Keywords: fully mulched ridge–furrow system, semi-arid Loess Plateau, maize productivity, farming system, sustainability

1.Introduction

Dryland crop production is one of the most important parts of global agriculture and plays a crucial role in meeting food security (Waniet al.2009).In China, rain-fed agriculture accounts for more than 70% of the total arable land and is mainly located on the semi-arid Loess Plateau and surrounding areas in the north (Denget al.2006).Agricultural productivity in the semi-arid Loess Plateau is limited by low temperature, water availability, and poor soil fertility (Zhouet al.2009; Zhanget al.2018).Plastic filmmulching is an important measure for crop production that can improve crop yield in low water-limited regions (Xueet al.2017; Yinet al.2017).After the widespread use of film mulch, maize (ZeamaysL.) has become the dominant crop in semi-arid areas.In the 2000s, the fully mulched ridge–furrow (FMRF) system (Fig.1), an advancement of plastic technology, was widely used on the semi-arid Loess Plateau because of its high rainfall use efficiency and improvement in maize yield and water use efficiency (WUE) (Yanget al.2007; Zhouet al.2012; Ganet al.2013).However, the high yields of this system resulted in a depletion of soil moisture and soil nutrients (Liu X Eet al.2014a; Xieet al.2015), which affects long-term sustainability.

Fig.1 Diagram of the fully mulched ridge–furrow system.

As a result, researchers should continue to study ways to optimize the benefits of the FMRF system and produce consistent yields while conserving water and nutrients, as well as reducing ecological and environmental issues.This paper examines the evolution of the FMRF system’s theory and technology and the optimization of crop management methods, such as cropping systems and soil management, to increase soil quality while ensuring crop productivity.Ultimately, to create a foundation for optimizing extremely efficient maize production on the semi-arid Loess Plateau.

2.Development of plastic film-mulching technologies in semi-arid Loess Plateau

2.1.Development of plastic mulch technology

The plastic film-mulching technology has passed through four stages of development in Gansu Province, China, including the experimental, the start-up, the innovation, and the integrated upgrade stages (Fig.2) (Wanget al.1998; Heet al.2009; Li L Xet al.2009; Sunet al.2011; Ganet al.2013).Since 1979, film-mulching technology has been successfully tested on vegetable crops.Later, it was tested with a series of successes on crops such as vegetables and fruits and then on food crops such as maize.Plastic film-mulching technology has begun to be widely applied in semi-arid regions since 1984.The cultivated areas ranged from vegetable and fruit crops to maize and potatoes, with the maize cultivation area reaching about 2 600 ha.The start-up period of plastic film-mulching technology was from 1986 to 1995, during which the cultivated area in Gansu Province increased from 35 500 ha in 1986 to 299 000 ha in 1995, and maize became the most important cereal in the semi-arid regions, with an area of 183 000 ha and a yield of 279 million kg.The period 1996–1999 was the innovation phase of plastic mulching technology.In this phase, mulching technology was developed from half film mulching to whole flat mulching, furrow–ridge mulching, which can reduce ineffective evaporation of soil moisture to maintain high soil moisture content (Li L Xet al.2009).In the 2000s, advancements in plastic filmmulching technology led to integrated upgrades in its use.The continuous evolution of mulching technology, along with the integration of the previous theoretical research on mulching and the generation of practical application results, has led to an unprecedented improvement in the effectiveness of mulching technology.

Fig.2 Development stage of plastic mulching technologies in the semi-arid Loess Plateau.

2.2.Development of the FMRF system

To improve the effect of rainfall collection and the efficiency of rainwater harvesting on dry farmland, researchers proposed the FMRF system (Fig.3) after a comprehensive analysis of maize cultivation with the ridge–furrow system, whole-furrow mulching, and rainwater harvesting in 2003 (Yanget al.2007; Shanget al.2008).This technology represents a significant improvement and innovation of plastic film-mulching technology, which opened up a new way to develop dry farming, solved the problems of unstable development of dry farming, and is an important guarantee of food security in dry farming areas.The development of the FMRF system probably went through three phases: preliminary research, yield-enhancing mechanisms, and technology optimization (Fig.3).The FMRF system was mainly in the preliminary phase of research from 2003 to 2008.During this period, high maize yield and economic benefits were achieved in various rainfed-farming areas, and maize yields increased by more than 30% compared to the traditional filmmulching system (Li L Xet al.2009).In 2008–2012, field experiments were conducted by Northwest A&F University, Lanzhou University, Gansu Agricultural University, and Gansu Academy of Agricultural Sciences to investigate the yield-enhancing mechanisms of maize under the FMRF system in semi-arid Loess Plateau (Renet al.2010; Li S Zet al.2014; Liu X Eet al.2014b; Xieet al.2015).At the same time, since 2008, the FMRF system has been rapidly promoted and applied in large areas in Gansu, Qinghai, Shaanxi, Inner Mongolia, Ningxia, and other semi-arid regions of the Loess Plateau in Northwest China (Jianget al.2018).Studies have found that the FMRF system mainly applies to semi-arid regions with an altitude below 2 300 m, annual rainfall of 250–600 mm, and maize as the main applicable crop (Yanget al.2007; Li L Xet al.2009).However, the high maize yields in this system have led to soil water and nutrient depletion, which affects the sustainability of the system in the long term.Therefore, to ensure the sustainable development of the FMRF system, researchers have conducted optimization trials of this technology through various agricultural management practices since 2012 (Liu C Aet al.2014; Wanget al.2020; Xie J Het al.2020).

Fig.3 Development stage of the fully mulched ridge–furrow system.

3.High yield and WUE under the FMRF system

3.1.Yield and WUE

Peer-reviewed publications were reviewed to collect data on the effects of the FMRF system on maize yield and water use efficiency in China.Google Scholar (https://xs.glgoo.net/) was used to gather data published in English.The China National Knowledge Infrastructure (http://www.cnki.net/) provided data in Chinese.The terms “plastic mulching, maize, or water use efficiency”, “the fully mulched ridge–furrow system” and “China” were used as the keywords in the search.The data from publications were extracted from tables and graphs.Briefly, after scrutinizing the search results, 94 studies were selected for this analysis.Yield and WUE of maize under four plastic mulched systems were analyzed on the semi-arid Loess Plateau based on the comprehensive literature review (Fig.4).The highest yield and WUE were observed under the FMRF system, followed by flatplanting with complete plastic film-mulching system (CFM), and flat-planting with half plastic film-mulching system (HFM).The lowest occurred in flat-planting without mulching system (NFM) treatment.Compared to the CFM, HFM, and NFM systems, the FMRF system resulted in a significant increase in yield by 17.5% (n=32), 28.4% (n=43), and 90.5% (n=36) and in WUE by 25.3 (n=22), 25.6% (n=22), and 114.1% (n=20), respectively.

Fig.4 Yield and water use efficiency (WUE) of maize under different plastic mulch systems.NFM, flat-planting without mulching system; FMRF, fully mulched ridge–furrow system; HFM, flat-planting with half plastic film-mulching system; CFM, flat-planting with complete plastic film-mulching system.The percentage indicates the increase in yield and WUE under FMRF treatment compared to other treatments.

3.2.The mechanisms of high yield under the FMRF system

Water conservationIn the semi-arid Loess Plateau, unstable and limited rainfall is the main water resource for crop production.Therefore, protecting rainfall and improving rainfall use efficiency (RUE) are important ways to improve crop production in the region.The FMRF system increased the rainfall capture zone, collected rainfall from the ridge to the furrow, penetrated the plowed soil along the seepage or seeding holes, and promoted crop growth.Li Wet al.(2017) demonstrated that the water content of the soil under the FMRF system was 17.8% higher, and the yield was 37.6% higher than in the no-film-mulching system.Similarly, the FMRF system also increased soil water retention at a depth of 0–60 cm and increased maize yield by 66.5–349.9% compared to the bare ridge and furrow system.Furthermore, compared to the NFM, HFM, and CFM systems, the FMRF system increased RUE by 1 993.5, 42.5, and 14.5% and increased millimeter water output by 212.3, 21.2, and 7.4%, respectively, in a three-year field experiment (Fig.5).The FMRF system was proposed to collect rainfall into the soil and improve rainfall use efficiency as well as yield.

Fig.5 Rainfall use efficiency and millimeter water output value under different film mulched systems.Data from Xie et al. (2015, 2018).NFM, flat-planting without mulching system; HFM, flat-planting with half plastic film-mulching system; CFM, flat-planting with complete plastic film-mulching system; FMRF, fully mulched ridge–furrow system.

Soil temperatureSoil temperature is the key factor guaranteeing the germination and growth of crops.In the semi-arid Loess Plateau, maize usually cannot be germinated in bare soil due to lower temperatures than in covered soil.Soils mulched with plastic film reduce heat exchange between soil and air by preventing water loss from soil to air.In the sowing stage of maize, the FMRF system can absorb solar energy, causing the topsoil to warm up during the day, and the soil mulched with plastic film cools down slowly by reducing longwave radiation.Thus, sufficient soil temperature ensures good germination of maize (Table 1).In addition, the soil temperature was higher in the FMRF system than in the NFM and CFM systems throughout the growing period of maize, which may shorten the growing period of maize, accelerate the seed-filling rate, and eventually lead to an increase in yield (Table 1).

Maize growth and developmentThe advantage of the FMRF system in rainfed maize production is the promotion of maize growth and development through improving soil moisture and soil temperature.A two-year experiment showed that the emergence rate of maize seed under the FMRF system was 26.2% higher than under the NFM system, and the seeds germinated 1–5 days earlier than under NFM, HFM, and CFM systems (Liet al.2013).Furthermore, the FMRF system has positive effects on maize growth characteristics, including plant height, dry matter accumulation, and leaf area index (LAI).Li Wet al.(2017) and Zhang Xet al.(2019) both found that the FMRF system resulted in significantly higher plant height and LAI of maize compared to the NFM system.Additionally, dry matter accumulation increased by an average of 35% under the FMRF system, promoting a significant increase in both the size and number of maize cobs and ultimately leading to significantly higher maize yields.

Photosynthetic characteristics are the physiological basis for yield formation in maize (Renet al.2020).The FMRF system can effectively improve crop water deficiency, increase photosynthetic rate, transpiration rate, and stomatal conductance, and make photosynthesis more intense.Gaoet al.(2012) found that the FMRF system significantly increased the photosynthetic rate, transpiration rate, stomatal conductance, and water use efficiency of leaves compared to the NFM and HFM systems.Li S Zet al.(2014) demonstrated that maize’s chlorophyll fluorescence kinetic parameters were greater under the FMRF system than under the NFM system.These results suggest that FMRF significantly improves the photosynthetic properties of maize leaves and increases the productivity of maize in semi-arid regions.

4.Disadvantages of the FMRF system

4.1.High input and output, but low benefit

Economic benefit reflects the effectiveness of the use of human, material, and financial resources in all aspects of social reproduction.It is clear that the FMRF system has significantly increased input costs due to plastic film expenditures and labor inputs (Table 2).The output was evaluated using economic yields of grain and straw based on the local price per unit at the time.The output under the FMRF system was higher than under NFM and HFM systems, mainly due to improvements in yield and straw.Although high output under the FMRF system, the output–input ratio was lower under the FMRF system than under the NFM, HFM, and CFM systems.

4.2.Soil nutrients and moisture depletion

Most studies have shown that using the FMRF system can increase maize yield, primarily stimulated by higher soil temperatures and favorable soil moisture conditions.However, while maize yield increased, soil organic carbon and enzyme activity decreased.After two years of experiments, the FMRF system decreased soil organic carbon by 29 and 9% compared to the NFM and HFM systems, respectively (Table 3).Soil mineral nitrogen also decreased significantly compared to the other mulching systems with plastic film (Table 3).Water use by maize increased as yield increased on the semi-arid Loess Plateau (Ronget al.2021).The high yield resulted in a deficit in the deeper water storage of the soil; in addition, excessive depletion of soil moisture causes the soil to dry out.The FMRF system has strong rainwater collection and recharge functions, but the unpredictable low rainfall in the semi-arid Loess Plateau limited the functions of the FMRF system.In dry years, soil water storage was lower than stable water storage after two continuous years of maize planting, which is insufficient for the next season’s crop (Table 4).However, in normal and wet years, the soil water consumed by maize can be replenished by rainfall during the fallow period, preventing the formation of a dry soil layer.Therefore, continuous planting of maize with the FMRF system in low rainfall areas will deplete soil moisture severely.

Table 1 Soil temperature under the plastic film-mulching system

Table 2 Economic benefit under the plastic film-mulching systems

Table 3 Soil properties under the plastic film-mulching systems

Table 4 Soil moisture under the plastic film-mulching systems in years with different rainfall patterns

4.3.Increase in soil pests and diseases

Maize cultivation under the FMRF system in the semi-arid Loess Plateau has the problems of long-term continuousplanting, resulting in the accumulation of pests, diseases, and weeds.Li Qet al.(2014) reported that leaf blight, common rust, and red leaf disease of maize are generally highly prevalent in semi-arid regions, with incidences up to more than 80%.In addition, the FMRF system improved the soil microenvironment, which provides good living conditions for pathogenic microorganisms and pests (Ganet al.2013).This promoted the colonization of pathogenic bacteria and pests, increased the incidence of soil-borne diseases and pests, and finally seriously affected the safe production of maize in the semi-arid Loess Plateau.

4.4.Increase in soil carbon emission

Soil microorganisms and crop root activity have direct effects on soil carbon emission, both of which are in turn influenced by environmental factors such as soil temperature and soil moisture (Zhanget al.2016).Beneficial promotion of soil temperature and soil moisture under the FMRF system improved soil microbial diversity and root activity and consequently altered soil respiration (Chenet al.2017).Zhanget al.(2017) and Liuet al.(2016) reported that soil carbon emission under the FMRF system was significantly higher than that under the conventional flat planting system due to increased soil temperature and soil moisture.Liet al.(2019) found that the FMRF system increased soil carbon emission by 20% compared to the NFM system in a two-year field study.These results suggest that soil factors and the microbial environment change under the FMRF system, which may lead to an increase in soil CO2emission and intensify the greenhouse effect.

5.Optimization for the FMRF system

5.1.Optimization of cropping systems

Crop diversificationDue to the negative impacts of maize monoculture under the FMRF system on soil sustainability in the semi-arid Loess Plateau, it is necessary to optimize the arrangement of crops and reduce the large-scale planting of single crops to improve the use of water and soil resources.Strip intercropping is a typical planting pattern with high and stable productivity and efficient utilization of resources.Intercropping can increase resource use efficiency and optimize the soil environment through temporal and spatial combinations of different crops according to the same interspecific relationship (i.e., competition and complementarity) between crops (Yinet al.2020; Zhuet al.2023).Renet al.(2017) found that intercropping potato and maize significantly increased maize yield by improving maize’s photosynthetic properties compared to maize monocultures in low rainfall years.Gaoet al.(2016) showed that intercropping pea and the FMRF system increased the total yield compared to maizemonocropping by increasing the leaf area index of maize in Yuzhong County, Gansu Province.Xieet al.(2021) showed that intercropping systems used 3–13% less water than monocropping.Moreover, intercropping potato with the FMRF system significantly increased net economic return and energy output by 8 and 24%, respectively, compared to maize monocropping.All these findings indicated that intercropping is not only a solution to the status quo of maize monocropping in the FMRF system but also a way to reasonably allocate water, heat, and fertilizer resources while effectively controlling the pests and diseases caused by maize monocropping.

Crop rotation is the practice of growing a series of crops sequentially over time on the same land.Crop rotation can increase water use efficiency and mitigate drought damage according to the nutrients and water requirements of different crops (Yuet al.2022), which can be beneficial on a large scale without large investments.Soil water and nutrients are significantly decreased after the application of the FMRF system.The FMRF system with crop rotation can effectively mitigate soil water and nutrient depletion.In semi-arid regions, no-till sowing of winter oilseed rape after application of the FMRF system has positive effects on soil moisture, temperature, and crop yield, which increased the yield of winter oilseed rape by 205% compared to the system without plastic mulch (Zhang and Li 2015).Sunet al.(2012) reported that applying the FMRF system increased yield by 16, 37, 28, 25, 31, and 17% under no-till planting for potato, winter rape, winter wheat, caraway, beans, and cereals, respectively when compared to the no mulched system.In addition, the FMRF system with crop rotation can also reduce diseases, pests, and weeds.Therefore, the FMRF system with crop rotation is considered an environmentally friendly strategy for sustainable agriculture, which adequately controls nutrients, water, weeds, pests, and diseases and maintains soil structure and fertility.

Varieties with good quality and high yieldCrop yield and water use efficiency are heritable traits and closely related to crop varieties.For the semi-arid areas of the Loess Plateau, using maize varieties with low water consumption, high photosynthetic efficiency, resistance, and infertility tolerance is an important way to improve maize yield and water use efficiency under the FMRF system.Maize (cv.Shendan 16) was the main variety tested in the initial phase of the FMRF system (Li L Xet al.2009; Liet al.2013; Xieet al.2015).With the largescale application of the FMRF system, the following maize varieties were tested successively:cv.Funong 821,cv.Xianyu 335,cv.Zhengdan 985,cv.Jinsui 1203,cv.Wugu 704,cv.Luyu 36,cv.Nonghua 106,cv.Longsheng 1,cv.Lianchuang 808, andcv.Dika 517 (Penget al.2019).Yanget al.(2007) drew the following conclusions based on variety trials in different regions.Application of latematuring varieties in the regions with an elevation below 1 800 m above sea level, such ascv.Shendan 16 andcv.Jinsui 1; medium-maturing varieties were used in areas with altitudes of 1 800–2 000 m, such ascv.Jiudan 3 and Jinsui 3; early-maturing varieties (cv.Jiudan 4) were selected for application in areas above 2 000 m.In recent years, grain and forage maize has gained significant importance in grain production and the planting industry restructuring; it has been suggested to use grain and forage maize varieties instead of regular maize (Fanget al.2020).In order to meet the development trend of China’s livestock industry, achieve high efficiency of maize grain and straw, ensure higher agricultural production and increase farmers’ income, it is recommended to use grain maize and feed maize in the FMRF system in the future.

Choice of film-mulching periodPlastic film-mulching periods play a crucial role in soil moisture on the semiarid Loess Plateau and can solve the problems of sowing and seedling emergence.For the FMRF system, there are three film-mulching periods (i.e., autumn, spring, and pre-sowing).A study reported that mulching in autumn significantly reduces soil water loss, increases the soil water content in the 0–80 cm soil layer before sowing, and guarantees the emergence rate of maize (Hanet al.2018).Gaoet al.(2015) found that mulching in autumn increased the soil temperature in the 0–20 cm layer, shortened the time to maximum filling, accelerated seed filling, and increased the yield of maize per unit area in Dingxi, Gansu Province.Zhanget al.(2010) found that maize yield and water productivity increased by 16.1 and 34.5%, respectively, with autumn mulching compared to pre-sowing mulching in Yuzhong County, Gansu Province.In addition, Lanzhou University (Liu X Eal.2014b) and Gansu Agricultural University (Xie Jet al.2020) suggest leaving the mulch after maize harvesting until the next spring and then removing the old film and mulching the new film.The old mulch is used to retain moisture in winter.Overall, it is generally believed that after the previous maize is harvested, plastic mulched in winter significantly reduce ineffective evaporation of soil water, capture rainfall for use in the next spring, help maize emergence under dry condition, and facilitate the early growth of maize.

Optimization of plant densityMaize is a dense-tolerant crop.Generally, dense planting is one of the most economical and effective cropping practices to improve crop productivity.The plant density of the FMRF system shows differences depending on the regional climate.It was reported that the plant density of the FMRF system increased with increasing rainfall.The suitable planting densities for the low (<300 mm), medium (300–500 mm), and high (>500 mm) rainfall regions are 42 500, 52 500– 67 500, 75 000–90 000 plants ha–1, respectively (Zhanget al.2015; Li S Zet al.2017; Liet al.2018).Therefore, the proper density of the FMRF system should be selected according to regional rainfall and climate.

Mechanized productionIn the initial stage of the FMRF system, agricultural management is mainly done by manual work.With the development of the FMRF system, the corresponding machinery has also been fully developed.The development of small and mediumsized semi-automatic agricultural machinery is the leading direction for the FMRF system due to the special environmental conditions on the Loess Plateau (Li X Get al.2009).The operation of the FMRF system includes constructing the mulching seedbed, sowing on the film, fertilizing under the film in the middle stage of maize, harvesting maize, and recovering the residual film.The corresponding farm machinery includes stubble rototiller, simple/combined type film spreader, single and double bucket spot seeder/hand pusher (electric type) hole seeder, single and double bucket spot seeder, backpack/self-propelled maize harvester, and pile/box/reel/bale type residual film recycling machine (Daiet al.2019).The mechanized operation significantly reduced the input of the FMRF system, increasing the output–input ratio and the economic benefit.In addition, the use of mechanized film recycling machines can improve the efficiency of film recycling and effectively reduce film pollution effectively.

Reduction and replacement of plastic filmThe issue of pollution from residual mulch is an old topic.With the continuous application of the FMRF system, it is difficult to recycle all film.Thus, there is a growing concern about the white pollution caused by residue in the soil.The following recommendations are proposed for environmentally friendly and sustainable development of the FMRF system and in response to the creation of an environmentally friendly society.Firstly, government agencies should adopt encouraging and supporting measures to improve the recycling of agricultural films, establish recycling stations for agricultural films, and develop enterprises for recycling and processing old films.Secondly, residual plastic film pollution can be reduced by replacing conventional polyethylene films with photodegradable or biodegradable films.Thirdly, the efficiency of recycling film residues can be improved by producing and applying weather-resistant mulch films.Finally, film mulch can be replaced with straw, gravel, or other mulch materials in areas with better water and heat resources.

5.2.Optimization of the soil management system

Plow layer constructionTillage practice can significantly affect soil water storage, soil physical, biological, and chemical properties, crop water use, and production (Hanet al.2022).Conventional tillage is the most important practice for the FMRF system in agricultural production.However, conventional tillage can easily cause soil erosion, damage the ecological environment, form a plow soil layer, destroy soil structure, prevent rainfall infiltration, and affect crop growth, yield, and water use efficiency (Huanget al.2008).Conservation tillage based on reduced or no-till can reduce soil erosion, protect the ecological environment of farmland, increase soil organic matter content, and improve the comprehensive productive capacity of farmland (Penget al.2020; Wanget al.2020; Zhouet al.2021).A fiveyear field study under the FMRF system showed that subsoiling tillage significantly reduced soil bulk density and soil penetration resistance and increased soilsaturated hydraulic conductivity and macro-aggregation compared to conventional tillage (Xie J Het al.2020).Soil organic carbon content was significantly increased under subsoiling and no-tillage compared to conventional tillage (Xie J Het al.2020).In addition, the yield was 13% higher in subsoiling tillage than in conventional tillage (Fig.6).Lampteyet al.(2020) found that subsoiling tillage could increase soil water content at 0–30 cm depth, which promoted leaf area index, chlorophyll content and photosynthetic characteristics of maize, and positively affected yield and water use efficiency.In addition, Luet al.(2015) and Zhouet al.(2021) reported that soil carbon emissions were reduced by 47% in Yangling in Shanxi Province and 13.4% in Dingxi in Gansu Province under no-tillage, compared to conventional tillage under FMRF system.Therefore, in the semi-arid Loess Plateau, subsoiling and no-tillage are the recommended tillage methods for the FMRF system, as they not only improve soil structure, effectively increase crop yield and water use efficiency but also reduce soil carbon emission and mitigate the greenhouse effect.

Fig.6 The effects of different tillage practices on maize yield under the fully mulched ridge–furrow (FMRF) system.Data are from Xie J H et al. (2020).CT, conventional tillage; NT, no-tillage; RT, rotary tillage; SS, subsoiling.Different lowercase letters indicate significant differences at P<0.05 among treatments in the same year.

Straw amendmentsThe FMRF system has been widely used to increase maize productivity in the semiarid region of China.However, this process generates maize residues that are discarded, resulting in a huge waste of straw resources and significant environmental pollution (Fanet al.2005).While the removal of crop residues causes a significant loss of organic carbon from the agroecosystem (Turmelet al.2015), the return of straw can preserve soil organic carbon, which is a widely recognized strategy for improving soil quality and crop productivity (Liet al.2020; Zhanget al.2022).Studies have shown that continuous straw incorporation with the FMRF system improved soil quality with changed soil fungal community, increased soil urease and catalase activities, and soil organic carbon and available phosphorus contents, and promoted significantly increased maize yield compared with no straw treatment (Zhanget al.2021).In addition, straw return also increased total nitrogen accumulation, nitrogen content, and crude protein in maize grain under the FMRF system compared to the no-straw treatment (Liet al.2020).However, numerous maize straw returns promoted soil carbon emission (Wanget al.2021), which may result in a range of environmental problems.Therefore, we suggest that the straw return at a rate of 6 000–8 000 kg ha–1incorporation with the FMRF system according to the literature (Denget al.2019; Heet al.2020; Liet al.2020; Zhanget al.2021), which is conducive to the sustainable development of agriculture in the semi-arid regions.

Optimization of the fertilizationAppropriate fertilization measures are beneficial to the improvement of soil fertility, which can compensate for the loss of soil nutrient storage caused by the harvest of agricultural products and the removal of crop waste from farmland and develop towards high and stable yields.However, improper application of fertilizers may result in a decline in soil quality, nutrient imbalance, and reduced fertilizer use efficiency (Ahmadet al.2023; Yueet al.2023).In recent years, many studies have reported fertilizer management of the FMRF system.Studies have shown that the optimal nitrogen under the FMRF system depends on the rainfall and plant density of maize (Table 5).In some regions with more rainfall, nitrogen application rates increased with the increase in the plant density of maize (Zhanget al.2022).However, areas with less rainfall show lower maize planting density and lower nitrogen application (Tanget al.2015; Lampteyet al.2017).Most studies have demonstrated that the optimal amount of nitrogen under the FMRF system is about 200 kg N ha–1(Table 5).However, these results were based on fertilizer basal application, which resulted in an accelerated growth rate of maize in the early stage but a deficiency of water and nitrogen in the late stage, affecting the growth of maize and reducing the nitrogen use efficiency of maize.An appropriate number of nitrogen fertilizers postponed topdressing enhances the synchrony between nutrient supply and nutrient demand of plants, which not only increases the resource use efficiency of maize (Wanget al.2020) but also promotes soil carbon fixation in the soil (Wuet al.2022) and reduces carbon emission (Xieet al.2019b).

Table 5 The optimal nitrogen (N) rate under the fully mulched ridge–furrow system (FMRF)

Despite the many benefits of proper nitrogen management, long-term reliance on chemical fertilizers leads to a decline in soil quality and nutrient imbalance.The use of organic fertilizer instead of chemical fertilizer can ensure crop productivity, increase soil organic carbon content, and improve soil fertility.Organic fertilizer plus chemical fertilizer under the FMRF system promoted crop growth by regulating soil water and heat environment, improved soil water and fertilizer supply capacity, andincreased soil fertility improvement (Yanget al.2019).Lampteyet al.(2019) and Xieet al.(2019a) found that substituting partial inorganic fertilizer with organic fertilizer enhances maize yield, nitrogen, and water use efficiency through improved soil structure and decreased soil bulk density.However, the improvement of soil fertility through organic fertilizer also increased soil carbon emissions (Xie J Het al.2020).In contrast, replacing chemical fertilizers with organic fertilizers at appropriate rates will not increase carbon emissions.Thus, the optimal substitution rates of inorganic fertilizer with organic alternatives under the FMRF system necessitate further consideration.

In summary, improving soil fertility by optimizing tillage practices, straw recycling, and fertilization can compensate for the loss of soil nutrient storage caused by harvesting agricultural products and removing crop waste from farmland, solve the negative effects of high maize yield, and ensure the environmentally friendly and ecologically sustainable development of the FMRF system in the semi-arid Loess Plateau.

6.Conclusion and prospect

The fully mulched ridge–furrow system is an innovative plastic film-mulching technology for agricultural production that improves maize growth and yield in the semi-arid Loess Plateau, which has been widely used to increase rainfall use efficiency and maize productivity.However, in actual production, long-term mono-cropping and continuous cultivation of maize plus plastic film-mulching resulted in high soil moisture and nutrient depletion, increased pest and disease infestation, white pollution, greenhouse gas emission, and other ecological and environmental problems, which may lead to unsustainable development of the technology.Based on the collaborative concept between cropping systems (planting patterns, varieties, the density of maize, mechanized production, and reduced plastic film) and soil management systems (tillage practices, straw amendments, and optimized fertilization), an appropriate farming system for the ridge–furrow mulching system can be constructed, which is proposed to solve the negative problems of this system.Therefore, we propose the following measures to ensure the sustainable development of the fully mulched ridge–furrow system and establish an environmentally friendly, high-quality, and sustainable agricultural system on the semi-arid Loess Plateau: use grain and forage maize varieties instead of normal maize; mulch plastic film in autumn or leave the mulch after maize harvesting until the next spring, remove the old film, and mulch the new film; combine reduced/no-tillage with straw return; practice crop rotation or intercropping with winter rape, millet, and oilseed flax; reduce nitrogen fertilizer and partially replace chemical fertilizer with organic fertilizer; apply biodegradable or weather-resistant films; and implement mechanized production.

Acknowledgements

This work was supported by the Major Special Research projects in Gansu Province, China (22ZD6NA009), the National Key R&D Program of China (2022YFD1900300), the State Key Laboratory of Aridland Crop Science, Gansu Agricultural University, China (GSCS-2022-Z02), the Fostering Foundation for the Excellent Ph.D.Dissertation of Gansu Agricultural University, China (YB2020002), the Innovation Star Project for Excellent Graduate Student of Department of Education of Gansu Province, China (2021CXZX-369), the Young Instructor Fund Project of Gansu Agricultural University, China (GAU-QDFC-2020-03), and the Science and Technology Project of Gansu Province, China (20JR5RA033).

Declaration of competing interest

The authors declare that they have no conflict of interest.