Cotton cultivation technology with Chinese characteristics has driven the 70-year development of cotton production in China

FENG Lu,CHI Bao-jie,DONG He-zhong

1 Zhengzhou Research Base,State Key Laboratory of Cotton Biology,School of Agricultural Sciences,Zhengzhou University,Zhengzhou 450001,P.R.China

2 Cotton Research Center,Shandong Academy of Agricultural Sciences,Jinan 250100,P.R.China

3 College of Agricultural Science and Technology,Shandong Agriculture and Engineering University,Jinan 250100,P.R.China

Abstract Since the founding of the People’s Republic of China in 1949,significant achievements have been made in cotton production in China. China has maintained its position as the world’s largest cotton producer for 33 years (1983–2015),with average annual increases of 3.5 and 3.9% in the unit yield and total output of cotton,respectively. Cotton production has played an extremely important role in the development of the national economy and the improvement of living standards. Although the cotton planting area has been reduced in recent years,the total output has remained relatively unchanged due to the continuous increase in the unit yield. China’s dominant position in global cotton production is undoubtedly attributed to the progress and development of cotton cultivation technology. Over the past 70 years,China has established a high-yielding and high-efficiency cotton cultivation mode that corresponds to its national conditions,including a large population and a limited land area. Furthermore,cotton cultivation technology is constantly being innovated and developed to keep pace with the times. In this paper,we review the development of cotton production and cultivation in China over the past 70 years,with a particular focus on the innovation and development of cotton cultivation technology with Chinese characteristics.This review is intended to provide guidance for the sustainable development of China’s cotton production in the future and to provide a reference for global cotton production.

Keywords:China,cotton,cultivation technology,outlook

Cotton (Gossypium hirsutumL.) planting and cultivation has a long history in China. However,it was not until the founding of the People’s Republic of China (PRC) in 1949 that scientific methods were adopted to cultivate cotton.Over the last 70 years,cotton production has made great progress,and the average annual yield has increased by 3.6%,from 160 kg ha–1in 1949 to 1 688 kg ha–1in 2019. The total output of cotton was 5.93 million tons in 2019,which was 12.7 times higher than that in 1949. China has become one of the largest cotton producers in the world. Many factors have contributed to the rapid development of the yield and output,including the adoption of new cotton cultivars and cultivation techniques. A series of cotton cultivars have been bred in China to meet the needs of cotton production in different periods over the past 70 years. Among them,Junmian 1 was bred in the 1960s and has been planted in the northwest inland cotton-growing region for more than 40 years. Lumian 1,which was bred in the 1970s,yields 39.5% more lint than the controlled cultivar Deltapine 15,and has played an extremely important role in the considerable boost in the national average cotton yield in the 1970s and 1980s. CRI 12 was bred in the late 1980s. It is characterized by strong disease resistance to ensure a high and stable cotton yield,and once accounted for more than half of the nation’s total planting acreage. The development of hybrid cotton cultivars in the 1990s,such as Xiangza 2 and CRI 29,greatly promoted the utilization of heterosis and further improved the cotton yield. After entering the 21st century,the release and extension of transgenic Bt cotton varieties such as Lumianyan 15,CRI 41 and Lumianyan 28 greatly alleviated bollworm infection and reduced the yield loss of cotton. Genetic improvements in cotton varieties contribute greatly to cotton yield increases. However,it is generally believed that cultivation technologies have played an even more important role in the increase of cotton yield.This paper reviews the development of cotton production and cultivation technology in China over the past 70 years,with a particular focus on cultivation technologies with Chinese characteristics. This review will not only help to further improve China’s cotton production technology,but also provide a reference for the world’s cotton production.

1.China’s cotton production over the past 70 years

The main indicators in the development and variation in cotton production are the planting area,yield and total output. Over the past 70 years,the cotton planting area has fluctuated greatly,with a coefficient of variation as high as 16.9%. Cotton yield has increased by 10.4 times from 161 to 1 818 kg ha–1,with an annual growth rate of 3.6%.The total output of cotton has doubled. In 2019,the total output of cotton reached 5.93 million tons,which was 12.7 times higher than that in 1949,and the annual growth rate was 3.87% (Fig.1). According to the supply and demand of cotton,China’s cotton production over the last 70 years can be divided into three periods as follows.

Fig.1 Variation of China’s cotton yield,total output and planting area over the past 70 years. Sourced from Agricultural Statistics in China and United States Department of Agriculture(CRI 2019).

1.1.The period of shortage of domestic cotton supply(1949–1978)

During this period,domestic cotton was in short supply. The cotton planting area was relatively small,with an average annual planting area of 4.94 million hectares. The planting area increased rapidly in the first few years after the founding of the PRC and reached 6.26 million hectares by 1956. In the early 1960s,natural disasters led to a sharp decrease in the planting area to 3.5 million hectares in 1962. Then,the planting area began to recover,and by the end of the 1970s,it was approximately 5 million hectares (Fig.1). The unit yield increased slowly during this period,with an annual increase of 9.79 kg ha–1. The increase in cotton yield was mainly due to the introduction of foreign technologies and the continuous improvement in supporting facilities. The total cotton output continued to increase rapidly with some fluctuations and an annual growth rate of 5.6%. Compared to the first decade (1949–1958),the annual average cotton output increased by 64.2% in the third decade (1969–1978).

During this period,the cotton-producing area was divided into five regions:the Yellow River Valley cottongrowing region,the Yangtze River cotton-growing region,the northern early-maturation cotton-growing region,the northwest inland cotton-growing region,and the southern China cotton-growing region (CRI 1959;Huang and Cui 2002). However,the cotton planting area began to decrease each year in the southern China cotton-growing region(Fig.2).

Fig.2 Cotton planting area,yield and total output of each cotton-growing region over the past 70 years. Sourced from Agricultural Statistics in China (CRI 2019).

1.2.The period of roughly balanced cotton supply and demand (1979–2009)

During this period,the cotton supply and demand were roughly balanced. The cotton planting area was the largest but also fluctuated more dramatically in this period than in other periods,with an annual average of 5.30 million hectares,which was 6.3% higher than that in the first period. The cotton planting area reached 6.92 million hectares in 1984,representing the largest planting area in the last 70 years.The unit yield increased rapidly,with an annual growth rate of 25 kg ha–1. The average total output was 4.92 million tons,with an annual growth rate of 3.8%. In 2007,the total cotton output reached 8.06 million tons,which was the highest amount over the last 70 years.

From the 1990s,the southern China cotton-growing region gradually transitioned into a region that grew cotton sporadically (CRI 1983),and the cotton planting area and total output in the region gradually decreased (Zhu 2009).Since then,China has entered an era of having four major cotton-growing regions. In 1996,Xinjiang was listed as the national key cotton production base,indicating that cotton growth had started to shift to the northwest inland area (Zhu and Wang 2012). In the first decade of the 21st century,the northwest inland area accounted for 35% of the entire cotton planting area and 40% of the total output of the nation. Since then,a“three-pillar”cotton production layout has formed,composed of the Yellow River Valley cotton-growing region,the Yangtze River cotton-growing region and the northwest inland cotton-growing region (Lu 2018) (Fig.2).

1.3.The period of“relative surplus”of cotton supply(2010–2019)

During this period,China’s cotton planting area gradually decreased and then stabilized,and the average annual cotton planting area was 4.03 million hectares. The cotton yield continued to increase at a relatively high rate,and the average yield reached 1 565 kg ha–1,with an annual increase of 54.29 kg ha–1. The substantial increase in cotton yield was closely related to the westward shift in the cotton-growing region,especially the increase in cotton planting area in Xinjiang,which had the highest yield among the areas.During this period,China’s demand for cotton decreased and the total output created a relative surplus. Cotton consumption declined to below 10 million tons. From 2011 to 2019,China’s total cotton output decreased from 6.52 to 5.93 million tons.

In this period,the cotton-growing region shifted further westward (Fig.2). In 2016,the cotton planting area of Xinjiang accounted for 53.7% of the national total (Lu 2018). In 2019,the northwest inland cotton-growing region accounted for 75.0% of the planting area and 84.4% of the total output of the country,and the cotton layout pattern of“one body and two wings”had formed (Wanget al.2019).

Changes in the layout of the cotton growth region were mainly caused by the following major factors.

Economic factorsMarket price is the primary factor influencing the decision of cotton farmers to plant cotton (Wanget al.2015). In developed regions,the competitiveness of cotton is weak due to the relatively lowincome generation,thus leading to a shift in cotton-growing regions. Since the 1990s,non-agricultural industries have flourished in the Yangtze River Valley and the Yellow River Valley cotton-growing regions,and they have promoted the transfer of the rural labor forces. Due to the relatively low comparative benefits of cotton production,the cotton planting area has decreased continuously (Chenet al.2021).In contrast,cotton production has an obvious advantage over the other crops that are grown in the northwest inland cotton-growing region,which has led to an increase in the cotton production area in this region (Luet al.2019).

Natural factorsDue to the high temperature and rainy conditions in South China,the soil is strongly acidic,which is not favorable for cotton production and leads to reductions in planting area. Affected by low temperatures,the cotton yield in the northern early-maturation cotton-growing region is unstable,resulting in a reduction in the cotton planting area. By the 1990s,the planting area in the northern early-maturation cotton-growing region had declined to less than 1% of the cotton planting area in the whole country(Wang 2009;Xiao and Yu 2018). In the Yangtze River Valley cotton-growing region,the cotton planting area was gradually reduced due to serious diseases and the weed damage caused by low temperatures and high humidity,which greatly lowered the cotton fiber quality (CRI 1983;Wang and Zhou 2011). With climate change over the past decade,the Yellow River Valley cotton-growing region has experienced substantial precipitation during harvesting,which causes rotted bolls and reduced yields. In addition,natural disasters have occurred more frequently in this region than in other regions. Therefore,the cotton planting area in this region has also decreased (Maoet al.1997).The northwest inland cotton-growing region is characterized by a dry climate,abundant light and heat resources,fewer people and more land,which are all conducive to promoting large-scale planting and mechanized production;therefore,cotton production has developed rapidly in this region (CRI 1983;Tanet al.2020).

Technological factorsDue to the adoption of plastic film mulching,close planting and drip irrigation under mulching,the northwest inland cotton-growing region has experienced a rapid increase in cotton yield and become the most suitable region for the development of the cotton industry (CRI 1983;Zhanget al.2007;Wang 2011). Cotton production in the Yangtze River Valley cotton-growing region was scattered and low in systematization,and thus was not appropriate for the development of mechanization. Additionally,the contradiction between high labor intensity and low labor efficiency had not been solved at the technological level.Consequently,with the continuous increase in labor costs,the demand for increasing income could not be satisfied and the cotton planting area decreased sharply (Zhong and Hu 2008). In the 1980s,the planting area of the Yellow River Valley cotton-growing region increased significantly due to the application of plastic film mulching. However,since the 1990s,cotton has mainly been intercropped with wheat in this region due to the official focus on grain production,which is time-consuming and difficult to mechanize. As the labor costs increased,it was increasingly difficult to stabilize the cotton planting area in this region (Feng 2017b;Lu 2018).

Social policy factorsWith the development of agriculture and the improvement of living standards,cropping structures have been adjusted accordingly. The cotton planting area in South China has continued to decrease due to the development of subtropical crops,such as sugar and rubber,which provide higher benefits and have greater strategic significance (CRI 1983). The main cotton production areas in the Yellow River Valley cotton-growing region overlapped with the main grain production areas. In recent decades,due to the importance of grain production,cotton production has continued to decline in the planting area and has further shifted to areas in this region that are unsuitable for grain production (CRI 1983). In 1996,China established the largest national commercial cotton base in Xinjiang,giving it a great advantage in large-scale production and driving the rapid development of cotton production in Xinjiang.Since 2014,China has implemented a cotton target price subsidy policy in Xinjiang and has further promoted the growth of cotton production in the northwest inland region(Zhanget al.2007).

2.Development of cotton cultivation technologies

Over the past 70 years,due to the large population and increased cotton consumption,theoretical and technological high-yielding cotton cultivation systems with Chinese characteristics have been established. With the promotion of these technologies,the yield and the total output of cotton in China have increased at annual rates of 3.5 and 3.9%,respectively. The developmental progress of cotton cultivation technology can be roughly divided into three periods according to the sources and characteristics of cultivation technology,which correspond well to the developmental process of cotton production outlined above.

2.1.Introduction of foreign technologies and experience (1949–1978)

Since 1950,enhancing cotton production was listed as one of the main tasks for agricultural production. Cotton,steel,coal,and grain,were specifically listed as the four major targets that the whole nation should strive to produce(CRI 1959;Wang 2015). During this period,China’s cotton cultivation was mainly based on technologies introduced from foreign countries and farmers’ practical experience.The cultivation technologies were expanded through continuous improvement with supporting measures from the government.

Deep plowingProduction practices over the years have proven that deep plowing is beneficial for increasing cotton yield. Since 1950,with the improvement of agricultural tools,deep plowing began to be widely applied. During this period,the depth of plowing changed from 9–12 cm to 15–18 cm.Some fields with high yields even deepened plowing to approximately 50 cm (CRI 1959). In the northern cotton area,the cotton yield increased by 6.5–18.3% at a plowing depth of 18–30 cm compared to the yield at a plowing depth of 10–15 cm. In the southern cotton area,the yield increased by 7.8–10.3% at a plowing depth of 18–20 cm compared to that at a plowing depth of 10–12 cm. Numerous practical studies have indicated that a plowing depth of 30 cm is the most appropriate for yield improvement (Zhu 2009).

Increased fertilizer rate Since 1950,fertilizer manufacturing has been greatly improved and the application of organic fertilizers such as farmyard manure increased significantly.Additionally,the area and rate of fertilizer application continuously increased each year,which provided an important foundation for the increase in cotton yield (CRI 1959). Based on the long-term practices of cotton farmers,the appropriate fertilization technology for high-yielding cotton was determined to be adequate base fertilizer,light fertilizer during the seedling stage,heavy fertilizer at the flowering stage,and supplementary fertilizer after topping (CRI 1959).Improved irrigation During this period,China vigorously developed irrigation in cotton fields,and the irrigated areas continued to expand. Instead of flooding irrigation,furrow irrigation and border irrigation began to be adopted,which not only had a positive effect on water conservation but also played an important role in preventing the soil from becoming saline–alkaline (CRI 1959). The irrigation time was mainly determined by climatic characteristics,soil moisture conditions and cotton requirements in different growth stages. The main method of irrigation application was“l(fā)ow intensity and high frequency”(CRI 1959). To ensure emergence and stand establishment,irrigation before planting was recommended,which mainly included winter irrigation and spring irrigation. Experience has indicated that winter irrigation performs better than spring irrigation without decreasing the ground temperature at sowing. Therefore,winter irrigation should be adopted as much as possible,except in soils with poor water retention.The appropriate time for winter irrigation is when the soil surface has started to freeze (Chen 1957).

Close plantingThe close-planting technique used in the Soviet Union has been studied since 1950. After experiments and studies in various places,the cotton planting density gradually increased,rising to 30 000–45 000 plants ha–1. By 1955,the cotton planting density generally surpassed 45 000 plants ha–1,and the cotton yield increased significantly due to the increased density. After 1956,based on the encouragement of Xinjiang’s experience with cotton cultivation,the cotton planting density was further increased to an average of 60 000 plants ha–1(CRI 1959). After 1973,the appropriate planting densities were determined to be 180 000–225 000,75 000–105 000,60 000–90 000,30 000–45 000,and 225 000–300 000 plants ha–1for the northern early-maturation cotton-growing region,the Yellow River Valley cotton-growing region,the Yangtze River Valley cotton-growing region,the southern China cotton-growing region,and the northwest inland cotton-growing region,respectively (CRI 1959). The planting density was also adjusted according to the soil fertility in each region. In dry and barren land,the planting density was increased appropriately (Shiet al.1963).

Plant pruningIn the first few years after the founding of the PRC,cotton plant pruning techniques,which included removing vegetative branches,performing plant topping and continuously excising old leaves,and removing the growth tips of fruiting branches as well as excess buds and empty fruit branches,were extended throughout China (CRI 1959;Dai and Dong 2014). This expansion was because of the many benefits of plant pruning. These benefits include regulating the distribution and consumption of nutrients within cotton plants,adjusting the plant shape,alleviating the conflicts between individual plants and groups of plants,balancing vegetative growth and reproductive growth,and reducing the occurrence of rotten bolls. The pruning technique was also modified according to the soil fertility.When soil fertility was low and cotton plants had poor growth,pruning was simply conducted by removing the vegetative branches and performing plant topping;however,when the soil was fertile and the cotton plants were tall,the complete five-step pruning was applied (Chen 1957).

2.2.Establishment and application of intensive cultivation techniques (1979–2010)

The Chinese government and scientific researchers have always believed that establishing cultivation theory and technology in line with national conditions is the foundation for the sustainable development of China’s cotton production. During this period,a series of high-yielding cultivation techniques emerged and were widely applied to improve cotton production. Among all the cotton production techniques,seedling transplanting,plastic film mulching and chemical regulation were considered the most important(Maoet al.2019). From 1978 to 2012,the average annual contribution of scientific and technological progress to cotton yield improvement was as high as 73.3% (Qianet al.2014).

Seedling transplantingWith the application of seedling transplanting,chilling injury caused by low temperatures and drought stress at the seedling stage can be avoided.In addition,transplanted cotton seedlings have strong roots and are homogeneous in size,which is good for stand establishment. The cotton growth period has also been advanced,resulting in effectively prolonged flowering and boll forming stages and subsequently increased yields(by 10–20%) (Cheet al.2002). Seedling transplantation began to be adopted in cotton in the 1950s and developed rapidly in the late 1980s. It was first adopted in the Yangtze River Valley cotton-growing region and gradually expanded to the Yellow River Valley cotton-growing region. From the late 1990s to the first 10 years of the 21st century,seedling transplanting was used in approximately 40% of the cotton acreage in China (CRI 2013). Cotton seedlings were initially cultivated in columned soil blocks (5–7 cm in diameter and 8–10 cm in height) made of soil and fertilizer,and this process was time-consuming and labor-intensive(Zhu 1983). Subsequently,this process developed from a labor-intensive process to a technology-intensive process,with the emergence of substrate seedlings (Maoet al.2006),plug seedlings (Chenet al.2004) and water-floating seedlings (Chenet al.2006). Bare seedling transplanting was applied to replace transplanting the seedlings with clay,and this process reduced labor consumption by 80%(Yang and Tan 2003;Liu 2005;Zhanget al.2006;Maoet al.2019). Seedling transplantation provided a method of achieving double or triple cropping in areas with insufficient accumulated heat units and enhancing the multiple crop index and farmer incomes. Therefore,seedling transplanting plays an important role in solving the problem of a large population and insufficient land in China (CRI 2013).

Plastic mulchingPlastic film mulching was first adopted for cotton as early as 1976 in Shanxi Province (CRI 1983).Since the introduction of ultrathin plastic film from Japan in 1978,plastic mulching for cotton production has been studied and applied in cotton production in a number of provinces (Mao 1998;Sun and Chen 1999). After 1980,plastic film mulching was listed as one of the 19 scientific and technological achievements in agriculture promoted in the national key demonstration fields and it contributed tremendously to the increase in cotton planting area. China has become the country with the fastest development rate and the largest application area of plastic film mulching in the world and has formed a technical system with Chinese characteristics for the application of plastic mulching in cotton production (Yanet al.2014). Plastic film mulching has increased cotton yields by 50–100%,which has been described as a“white revolution”(CRI 2013). Plastic mulching increases yield because it (i) promotes early growth by increasing the ground temperature by 1–5°C daily;for example,cotton can be planted 7–10 d earlier by using plastic film mulching because of the increased accumulative heat units (up to 220–440.5°C);(ii) increases photosynthetically active radiation (PAR);for example,some solar radiation is reflected by the plastic film and by water droplets under plastic mulching,which can increase PAR by 29.6% within the cotton canopy;(iii) increases humidity;for example,soil moisture in the soil upper layer is increased because plastic mulching prevents evaporation;(iv)improves soil structure and increases the abundance of soil microorganisms;and (v) reduces weeds and diseases. The high temperatures and poor ventilation under mulching are not conducive to the occurrence of weeds and diseases (CRI 2013,2019;Dai and Dong 2014). A series of techniques related to plastic film mulching have been successively developed,including wide-film mulching,double-film mulching and film-side planting (Liuet al.1996;Chenet al.1997). Driven by plastic film mulching,cotton production in the northwest cotton-growing region has undergone a tremendous change. In the 1980s,an integrative cultivation mode based on“high-density,early-maturity and plastic film mulching”was established (Tianet al.2000;Yao 2004). In the 1990s,narrow plastic film was replaced by wide film due to its higher pest control efficacy (Yao 2004;Hu 2005).In the 21st century,water-saving technology was added to the cultivation mode (Tianet al.2000).

Chemical regulationThis technology was introduced in 1979 and has been widely used since 1983. Mepiquat chloride (DPC) has been applied in 90% of cotton fields in China because it has increased cotton yield by 8–10%(CRI 1959;Mao 2007). Chemical regulation with the application of DPC in China has gone through three stages:the symptomatic application stage,the systematic control stage and the integrated chemical regulation stage. In the first stage,DPC was applied to prevent excessive growth caused by high temperatures and rainfall,and a one-time application was used to resolve emergency short-term situations. In the late 1980s,DPC use entered the second stage,in which multiple times of application occurred during the cotton growth periods to modify the canopy structure. In the 1990s,under the premise of systematic chemical control,conventional cultivation practices,such as plant density,irrigation and fertilizer management were also modified to realize dual regulation. Dual regulation achieves the regulation of not only the cotton plants themselves but also their growing environment to reach the full potential of both plant genetics and natural resource utilization (CRI 2013).

Cotton planting techniques in saline fieldsCotton is recognized as a pioneer crop in the development and utilization of saline land (Xinet al.2005). In China,saline land is the main type of land used for the expansion of cotton fields (Mao 2007;Dong 2012). Excessive salt in the soil inhibits seed germination,emergence and plant growth and development through dehydration,salt ion toxicity and nutritional imbalance. Ultimately,salinity leads to insufficient stands or stunted plants and reduced yield and quality.The control of root-zone salinity is considered a beneficial strategy for improving the emergence and establishment in saline fields. Overirrigation and drainage before planting combined with furrow-bed seeding after salt leaching has been confirmed to reduce the exposure of seeds and seedlings to salinity and is effective for improving emergence and stand establishment. The application of plastic film mulching reduces the salt around the cotton root zone by changing the salt distribution in the field. The negative impact of salinity on emergence and seedling establishment can also be mitigated by avoiding the period of plant growth that is most sensitive to salt damage through the use of seedling transplantation. In addition,increasing the use of organic fertilizers is an effective measure for reducing salinization by improving the soil structure (Donget al.2008,2010;Daiet al.2010;Dong 2010;Wanget al.2019). With the techniques described above,significant economic benefits associated with improved cotton yields in saline land have been achieved.

Cotton–wheat (oilseed rape) double croppingIn China,with the increasing population and limited area of arable land,double cropping has played an important role in increasing the multiple cropping index,relieving the conflicts between grain and cotton in land use and increasing farmer incomes (Baoet al.2006;Mao 2007). In a double-cropping system,cotton growth is slowed in the seedling stage and thus reproductive growth is delayed due to the competition for resources between crops during the intergrowth period.This process has resulted in reduced yields and fiber quality.Since the 1980s,the application of seedling transplanting and film mulching has solved these problems,and the cropping system started to develop rapidly at that time(Huanget al.1991;Maoet al.1998,1999;Baoet al.2006;Dong 2010). In the 1990s,double-cropped cotton in China accounted for 70% of the total cotton planting area. Since the beginning of the 21st century,the cotton and oilseed rape double-cropping system has become the main planting pattern in the Yangtze River Valley cotton-growing region while the cotton and wheat double-cropping system has become the main planting pattern in the Yellow River Valley cotton-growing region (Yanget al.2008). With advantages including making full use of resources,increasing soil organic nutrients and improving microbial activity and the ecological environment of cotton fields,double cropping has achieved double expansion,i.e.,it has increased both the planting area and the yields of grain and cotton (Mao 2007).

2.3.Simplified and high-efficiency cultivation technology (2011 to present)

Since 2010,with the rapid development of urbanization and continuous improvements of the economic level,labor costs have continued to increase. Previous labor-intensive cultivation methods that achieved high yields through high inputs not only faced great challenges but also brought about serious environmental problems. Therefore,modern simplified cotton cultivation techniques were developed.

Precision seedingPrecision seeding technology has been used in China since the end of the 20th century.Compared with conventional seeding,precision seeding can save more than 60% of seeds,increase the cotton yield by 5–10%,advance the development of cotton plants by 3–5 d(Wang 2013),and increase the field management area per capita by 3–7 times (Tang and Lin 2004). Precision seeding has become relatively mature in the northwest inland cotton-growing region,and the precise sowing of cotton seeds at a given quantity and location has been achieved. In addition,the developed precision seeder has achieved an integrated design and the joint operation of multiple processes,including sowing,fertilization,herbicide spraying,drip irrigation pipe laying,soil covering,and plastic film mulching (Dong H Zet al.2016;Baiet al.2017). In the Yellow River Valley cotton-growing region,in monocultured cotton fields of the Yellow River Valley cotton-growing region,the precision seeder sows first and then lays the plastic film,and seedlings thinning is no longer needed (Daiet al.2014a;Luet al.2017). In double-cropped cotton fields in the cotton-growing regions of the Yangtze River Valley and the Yellow River Valley,an extra clearing function has also been included in the precision seeder to achieve grass clearing,stubble elimination and shallow rotation (Daiet al.2014b;Fenget al.2017a).

Simplified pruningPruning is extremely labor-intensive and no longer meets the needs of simplified cotton cultivation.Starting in the 21st century,research has achieved no-pruning and no-topping methods through the effective inhibition of vegetative branching and apical growthviaclose planting and chemical regulation. In the northwest inland cotton-growing region,close planting with a high plant density was adopted to inhibit the growth of vegetative branches and achieve a no-pruning system (Fenget al.2017a). In the Yellow River Valley,a cultivation mode of late-sowing and close-planting with moderate plant density was adopted to achieve a no-pruning system. Rotten bolls and premature senescence can be reduced by late sowing,and the excessive growth of vegetative branches is inhibited by increasing the planting density. A reduction in vegetative branches (by approximately 67.3%) simplifies the process of pruning and improves fiber quality and production income by reducing cotton bolls from the vegetative branches. Further research has shown that the high planting density,low fertilization and no-pruning cultivation mode can increase cotton yield higher than the levels obtained using traditional cultivation (Daiet al.2014a;Dong J Jet al.2016).

Water-saving irrigation and fertigationUnder-mulching drip irrigation has become the most popular water-saving irrigation system implemented in the northwest inland cotton-growing region. This system combines drip irrigation with plastic mulching. A specific seeder was developed to achieve drip irrigation pipe laying,seeding and plastic mulching simultaneously during seeding. Soluble solid or liquid fertilizer can also be dissolved in the water tank and applied to the cotton root zone with irrigation to maintain the appropriate moisture and soil fertility in the root zone(Baiet al.2017). Water consumption from fertigation under mulching was only approximately 12% of that in traditional irrigation methods and 50% of that in sprinkler irrigation because this method reduces evaporation between plants and deep leakage. Additionally,fertilizer use was reduced by 15–20% by reducing fertilizer volatilization and loss and,in particular,by effectively avoiding the volatilization and loss of ammonium and urea nitrogen fertilizers (Dong H Zet al.2016). On this basis,dry seeding and wet emergence (in which neither winter nor spring irrigation is applied,and a small amount of water is appliedviadrip irrigation for seed emergence once the soil temperature meets the requirement for emergence after sowing) and regulated deficit irrigation were also developed to reduce unnecessary water losses for water conservation (Zhanget al.2016;Fenget al.2017a).In the Yellow River Valley,irrigation was improved by leveling the land,and changing flood irrigation into ditch irrigation,and changing wide ditch into narrow ditch to reduce the amount of irrigation (Donget al.2017).

Simplified and efficient fertilizationTwo primary simplified and efficient fertilization methods have been developed. The first determines the application rate of fertilizer in terms of cotton yield. In the Yangtze River cotton-growing region,the seed cotton yield ranged from 3 600 to 4 500 kg ha–1,the appropriate application amount of N was from 240 to 270 kg ha–1,and the N:P2O5:K2O ratio was approximately 1.0:0.4:1.0. In the Yellow River Valley cotton-growing region,the appropriate N application rate was from 195 to 225 kg ha–1for medium-and low-yield fields with an average seed cotton yield of 3 000 to 3 750 kg ha–1and from 240 to 270 kg ha–1for high-yield fields with a seed cotton yield greater than 3 750 kg ha–1. In the northwest inland cotton-growing region,the appropriate N application rate was from 300 to 375 kg ha–1for an average seed cotton yield of 4 500 to 5 250 kg ha–1and the ratio of N:P2O5:K2O was approximately 1.0:0.5:0–0.3. The N application rate can be reduced by approximately 15% when fertigation is implemented (Daiet al.2014a;Dong H Zet al.2016;Baiet al.2017). In the second method,a special slow-release fertilizer for cotton was developed to reduce the number of fertilization applications. In the Yangtze River cottongrowing region,by adopting a one-time basal application of slow-release fertilizer or basal application followed by additional topdressing,the fertilization frequency was reduced to 1–2 times per year. Applying the slow-release fertilizer at an amount equal to 80% of the application rate of the active fertilizer had the same effect as a full application of active fertilizer. In the Yellow River Valley cotton-growing region,a one-time application of slow-release fertilizer was adopted and the fertilization frequency was reduced to one time per year (Genget al.2015;Xin and Yang 2015;Xinet al.2016).

Mechanical harvestingThe premise of mechanical harvesting is concentrated maturity. For this reason,the high-yielding and early-maturing cotton cultivation mode in the northwest inland cotton-growing region has been developed with either wide-narrow row spacing of (66+10) cm or an equal row spacing of 76 cm. For the wide-narrow row spacing mode,the theoretical planting density is 219 000–292 000 plants ha–1and the leaf area index (LAI) is between 4.6 and 5.2,while for the equal row spacing mode,the theoretical planting density is 146 200–202 400 plants ha–1and the optimal LAI is controlled between 4.2 and 4.5 (CRI 2019). To achieve mechanical harvesting in the Yellow River and Yangtze River Valley cotton-growing regions,a row spacing of 76 cm was adopted,and the planting density was basically doubled (75 000–120 000 plants ha–1in the Yellow River Valley and 90 000–120 000 plants ha–1in the Yangtze River Valley) (CRI 2019). Chemical defoliation is also a key step in mechanical harvesting (Menget al.2021).After years of experiments and practices,it was determined that the defoliant was the best applied when the boll opening rate was above 30% or when the last harvestable cotton bolls were more than 35-d-old. After applying the defoliant,a minimum temperature of ≥12.5°C and a daily average temperature of ≥18°C for 7–10 d are required (CRI 2019).

3.Challenges and countermeasures in China’s cotton production

3.1.Challenges in cotton production

China’s cotton production has made remarkable achievements over the past 70 years. However,cultivation methods that rely on high inputs of resources and labor have not only created environmental problems but also posed a series of challenges for China’s cotton production.

Relatively poor fiber qualityFor a long time,China only focused on cotton yield instead of fiber quality,resulting in a large gap between the fibers produced and the fibers required in the textile industry. In China,cotton planting is scattered,and dozens of cotton varieties are used in a single region,which causes low fiber uniformity and poor consistency. In addition,extensive production results in more heterogenous fiber content due to the use of materials such as plastic film and hair,which also reduce fiber quality (Dai and Dong 2014;Fenget al.2017a). In recent years,mechanical harvesting has developed rapidly while agronomic measures and processing techniques have not developed at the same pace;therefore,fiber quality,especially fiber length,has been negatively affected (Li and Jiang 1997;Maoet al.2016). At present,the supply of high-quality cotton in China is seriously insufficient;thus,improving fiber quality has become an inevitable necessity(Maoet al.2019).

Serious environmental pollutionThe increase in cotton yield has been accompanied by the overuse of chemical fertilizers,pesticides and plastic film. According to agricultural statistics,the usage of pesticides,fertilizers and plastic film in cotton production was the highest among the main field crops in China. The ecological environment and limited resources have become the main constraints on sustainable and stable agricultural development in China(Wanget al.2021). At present,the fertilizer and water use efficiency in cotton production in China are only 30–40%,which is much lower than the values observed in Israel,the United States and Australia (almost 60%). The use efficiency of pesticides was only 10–30% for China’s cotton production,and it has a profound impact on soil quality (Li and Jiang 1997;Liet al.2005;Fanet al.2011). In addition,“white pollution”caused by residual plastic film also poses a serious threat to the sustainable development of cotton production by reducing soil fertility and preventing moisture and nutrient transport due to changes in the soil physical structure. Reports showed that the cotton yield was reduced by 10–15% with a residual film amount of 30–45 kg ha–1(Liet al.2005;CRI 2019).

Decline in production benefitsWith the development of the economy and urbanization,labor costs have risen each year,thus leaving cotton production with an insufficient comparative advantage and weak market competitiveness.In 2016,cotton production costs reached 4 940 USD ha–1,which was 345.72% higher than the costs in 2001,and the cost of labor increased the most significantly. In 2016,labor costs accounted for 60.42% of the total costs of cotton production. In 2008,due to the influence of the financial crisis,the net profit of cotton production was negative for the first time. Since 2013,the net profit from cotton has continuously decreased,and it fell by 2.98 times in 2016 compared to that in the early years of the cotton market reform. These decreases have seriously affected the stability of the planting area (Luet al.2019).

Low levels of organization and scale in cottonproductionCotton production in China is mainly based on household production. The average cotton planting area per household is small,and cotton planting is scattered,which has increased the difficulty of fully exploiting modern cotton cultivation technologies to increase farmer income.The lag in socialized services in cotton production,the lack of services for farmers and the disconnection between production and demand have resulted in a shortage of high-grade cotton and an excess of low-grade cotton,which has restricted the development of cotton production (Dong H Zet al.2016).

3.2.Prospects for cotton cultivation in China

Currently and in the future,China’s cotton production needs to proceed from the perspective of sustainable development,rely on scientific progress,and properly address the relationship between increasing yield,improving fiber quality and increasing incomes as well as the relationship between production development and environmental friendliness.There should be an emphasis on making breakthroughs in simplified,mechanized and environmentally-friendly cotton cultivation techniques and developing a new cotton cultivation system with Chinese characteristics.

Further improve simplified and efficient cultivation methodsOn one hand,mechanized production should be continuously developed to reduce labor intensity. On the other hand,cotton management should be simplified to reduce the number of steps in production. The contradiction between simplified management and high yield could be resolved through the integration of agronomic techniques and mechanization.

Develop green cotton cultivation technologiesEfficient,water-saving irrigation technologies should be developed and expanded to control the total amount of agricultural water used in order to further reduce wasted water. Variable fertilization,formula fertilization and one-time fertilization based on the soil fertility and yield should be adopted to reduce fertilization costs and fertilizer application rates.The reasonable use of livestock manure and crop straw as soil amendments could also be adopted to reduce environmental pollution. Biological pest control should be actively developed to reduce the usage of chemical pesticides as well as the costs of pest control. A substitute technology for plastic film should be explored to ensure the effective control of“white pollution”.

Develop“smart”agricultureModern information technology can be applied to traditional agriculture,combining intelligent agricultural technology with simplified,green cultivation technology to achieve intelligent management,including accurate perception,remote control and early warning systems. The reform of traditional management relies on experience to achieve a modern management system and includes accurate monitoring,real-time accurate management,reduced labor costs,increased resource use efficiency,and further improvements to the yield and quality of cotton.

Improve organizational servicesTo realize the application of new cotton cultivation technology,large-scale planting by cotton growers should be encouraged. Small-field cotton growers should learn cultivation techniques from cotton farmers with large fields to improve their yield and income. Professional companies should be established to provide services related to farm machinery,plant protection and fertilizer. The whole cotton production process requires such services,including the selection of cultivars,seeding,formulated fertilization,disease and pest control,mechanized harvesting and transportation. The improvement of organizational services could contribute to the uniformity of cotton varieties planted in a specific region,standardize cotton management,and subsequently improve cotton yield and fiber quality.

4.Summary

Since the founding of the PRC,China has made worldrenowned achievements in cotton production. The substantial increase in cotton yield and total output has made an important contribution to the steady development of China’s cotton production and the establishment of China’s position as a dominant cotton producer in the world.Over the past 70 years,cotton cultivation in China has experienced different developmental periods,including the introduction of foreign technologies,the establishment and application of intensive cultivation techniques with Chinese characteristics,and the development of simplified cotton cultivation technologies (Fig.3). However,China’s cotton production still faces challenges related to an insufficient amount of high-quality cotton,low resource utilization efficiency and low mechanization levels. Therefore,in the future,it is necessary to achieve a greater scale and standardization in cotton production by improving organizational services;improving the core competitiveness of cotton through simplification,environmental friendliness,mechanization and intelligence;and finally realizing the sustainable development of the cotton industry,led by high-quality cotton.

Fig.3 The match between the development of cotton cultivation technology with Chinese characteristics and the development of cotton production over the past 70 years in China.

Acknowledgements

This work was supported by the National Key Research and Development Program of China (2018YFD1000900),the Special Fund for Taishan Scholars Project in Shandong Province,China (tspd20150213) and the China Agriculture Research System of MOF and MARA (CARS-15-15).

Declaration of competing interest

The authors declare that they have no conflict of interest.