Crop Physiology || Farming systems in China: Innovations for sustainable crop production

C H A P T E R

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Crop Physiology. DOI: 10.1016/B978-0-12-417104-6.00003-0Copyright © 2015 Elsevier Inc. All rights reserved

3Farming systems in China: Innovations

for sustainable crop productionWeijian Zhang1, Chengyan Zheng1, Zhenwei Song1,

Aixing Deng1, Zhonghu He1,2

1Institute of Crop Sciences, Chinese Academy of Agricultural Sciences, Beijing, China2International Maize and Wheat Improvement Center (CIMMYT) China Office,

Beijing, China

1 INTRODUCTION

China is the world’s largest grain producer and consumer. Chinese grain production was more than 530 Mt in 2012; however, China also became the world’s largest cereal importer in 2013. Increasing crop production is therefore im-portant for both Chinese and world food secu-rity. Although China has successfully increased grain production since 2003, the resource-use ef-ficiency remains low. Resource shortage and en-vironmental pollution are the big challenges to sustainable grain production in China over the next decades, whereas projected climate change represents both challenges and new opportuni-ties. Therefore, it is critically important to evalu-ate the experiences of Chinese farming-system innovations for sustainable crop production.

This chapter focuses on the progress of grain crop production through genetic and agronomic improvements in China. Section 2 summarizes

the abiotic conditions and limitations to main crop production. Lack of information precludes the analysis of historical changes of biotic fac-tors. Section 3 summarizes the basic features of major grain crop production and farming sys-tems. We discuss the contributions of genetic improvement and agronomic innovation to yield increases (section 4) and the resource-use efficiency (section 5) over past decades. Section 6 outlines responses of major grain crops to future climate patterns and outlines adaptive practices.

2 THE ABIOTIC ENVIRONMENTS FOR CROP PRODUCTION

2.1 Climatic conditions and historical changes

There are large spatial (Fig. 3.1) and tempo-ral (Fig. 3.2) variations in air temperature and

44 3. FarmIng systems In ChIna: InnovatIons For sustaInable Crop produCtIon

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precipitation. The annual mean air temperature is below 10°C in the north and west, and above 20°C in the south (Fig. 3.1a). Thus, only one crop can be sown annually in the north and west, and two or more crops can be sown in the south. Annual precipitation ranges from more than 1500 mm in the south to less than 500 mm in the north and the west. Thus, the limitations to crop production are low temperature and precipita-tion in the north and the west, and heat stress

and short sunshine duration in the south and the east. extreme weather events, such as chilling in-jury during early rice seedling and winter wheat booting, heat stress during wheat grain filling and during rice and maize flowering, frequently cause large reductions in crop production.

During the past 100 years, particularly over the last decades, the earth has experienced sig-nificant warming. The mean air temperature has increased about 0.74°C since 100 years ago, and

FIG. 3.1 Spatial differences in (a) annual mean air temperature (°C) and (b) the annual precipitation (mm) in China. Data are the mean values during 1990–2010 period.

FIG. 3.2 (a) Mean surface air temperature anomalies and (b) percentile of annual precipitation anomalies in China (relative to 1971–2000).

2 the abIotIC envIronments For Crop produCtIon 45

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it is expected to rise about 2.0–5.4°C (depending on region and CO2 increase scenarios) by 2100 (IPCC, 2007; Chapter 20). Similar warming trends were observed in China (Fig. 3.2a). The mean annual air temperature in the past 50 years has increased by 1.33°C, and no signifi-cant change in annual precipitation has been re-corded since the early 20th century (Fig. 3.2b). However, rainfall seasonality has changed; the summer rainfall showed an increasing trend, while significant reductions occurred in spring and autumn. extremely high temperature is common, and the frequencies of drought and flooding have increased. Some modeling stud-ies indicate that climate change might reduce crop production in China (Chapter 20), thus po-tentially compromising food security. Section 6, however, shows experimental and modeling evidence for a more diverse range of responses, including significant shifts in the boundaries of cropping opportunities.

2.2 Soil conditions, land use and historical changes

China is one of the world’s largest countries in both area and population; it covers 9.6 mil-lion km2 with a large diversity in landscape and land use. The altitude increases from less than 500 m in the southern hilly region to higher than 1500 m in the northern Loess Plateau region, and from less than 50 m in the eastern plain to higher than 5000 m in the western mountain area.

The land area suitable for agriculture only ac-counts for 17.3% of the total. In 2012, the farmland area was 121.7 million ha, making up less than 7% of the world’s total acreage. The farmland area per capita is about 0.09 ha, 43% of the world average farmland size per capita. Farmland soil quality varies among the cropping regions, and only a fourth of this represents high quality soil. The plow layers of major farmlands are less than 15 cm in depth with diverse physical and chemi-cal limitations for root growth. According to the Chinese second soil survey, finished in the 1980s,

soil organic matter (SOM) below 2.0% accounts for more than 65% of total farmland area. More-over, serious acidification affects soils in the south and salinization in the northern areas.

Long-term cropping intensification plays an important role in farmland soil quality. Intensi-fied maize cropping has caused a large reduction in the concentration of SOM in northeast China, the largest maize-growing region. The main reasons for the reduction of SOM concentration are long-term inorganic fertilizer application without any organic amendment and long-term conventional intensive tillage. In the north and south, however, the SOM concentration showed an increasing trend during the last decades, and higher SOM concentration was found in paddy fields than in the dry land (Wang et al., 2010; Huang et al., 2013). The main reasons for the in-crease in SOM concentration in north China are wheat straw retention and less tillage during the maize growing season; however, this has led to the increased occurrence of head scab for wheat. The higher SOM concentration in paddy fields can be attributed to wheat or rice straw reten-tion and the anaerobic soil condition during rice growing seasons (Huang et al., 2013). Long-term fertilizer application with intensive conventional tillage has degraded soil aggregate structure, though soluble fertilizers combined with organ-ic matter amendments (i.e. crop straw and ma-nure) can enhance soil physical structure (Chen et al., 2010; Huang et al., 2010). Soil acidification is a serious issue. A recent study showed that over-use of nitrogen fertilizer, especially urea, caused significant soil acidification in major Chinese cropping lands (guo et al., 2010). Due to mining, industrial and urban activities, heavy metal pollution is becoming a severe problem in farmland soil, especially in the southeast paddy fields where heavy metal concentration (e.g. Pb and Cd) of grain exceeds the state standard in rice crops around the mining areas. To ensure en-vironmental health and food safety, the Chinese government is allocating resources to research and extend sustainable cropping techniques.


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3 FARMING SYSTEM DIVERSITY AND SPATIAL DISTRIBUTION

3.1 Major grain crops

With only 7% of the world’s arable land, China has produced enough food for 22% of the world’s population. In 2012, China produced 589.6 Mt of grain. As shown in Table 3.1, maize, rice and wheat are the three major grain crops and the production of these three crops accounts for 23.8, 28.4 and 17.9% of the world respectively. Owing to the increased demand from livestock and industrial development, maize has become the largest crop, increased from around 20 mil-lion ha to 35 million ha. Major grain cropping areas are located in the northeast, north, east and south (Fig. 3.3). The major rice cropping ar-eas are located in the south and the east, while maize cropping areas are mainly found in the north and northeast. More than 80% of wheat is sown in autumn in the north plain, which is also the major cropping area of maize.

3.2 Grain-based cropping systems

There is large diversity in Chinese cropping systems including single, double and triple cropping (Fig. 3.4). The major reasons for mul-tiple cropping systems are to increase grain production and to maximize resource-use effi-ciency, which is facilitated by family labor (Zhou et al., 2007). China has a small farmland area per capita with the largest population in the world; hence the role of the multiple cropping systems to ensure food security is crucially important.

In the northeast and the west, only one crop (maize, rice or soybean) can be sown annually due to temperature and precipitation limita-tions. Crops are commonly sown in May and harvested from September to October. Between the great Wall and the northern Huaihe River, the double-cropping system is dominant with two dryland crops annually, such as wheat–maize, wheat–soybean, or wheat–peanut. Wheat is sown in October and harvested in June, and the other crops are sown in June and harvested

TABLE 3.1 sown area, yield and production of the main crops in China in 2012

CropArea(million ha)

Yield(t ha−1)

Production(Mt)

Area ratio to total cropping area (%)

Production ratio to the total of the world (%)

Maize 35.0 5.9 205.6 21.4 23.3

Rice 30.1 6.8 204.2 18.4 28.4

Wheat 24.3 5.0 121.0 14.9 18.0

Rapeseed 7.4 1.9 14.0 4.5 21.5

Soybean 7.2 1.8 13.0 4.4 5.4

Potato 5.5 3.4 18.6 3.4 5.1

Peanut 4.6 3.6 16.7 2.8 40.5

Millet 0.7 2.4 1.8 0.4 6.0

Barley 0.5 3.3 1.6 0.3 1.2

Sorghum 0.6 4.1 2.6 0.4 4.5

Data are from China Statistical Year book (2012) and FAO (2013). The yield of potato is converted into that of grain at the ratio 5:1, i.e. 5 kg of fresh tuber was equivalent to 1 kg of grain.

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in October. From the southern Huaihe River to the yangtze River, the annual double crop-ping changes to rice–wheat, rice–rapeseed, and rice–vegetables (e.g. cabbage, faba bean, cauli-flower, carrot, garlic, potato, etc.). Rice is com-monly sown in May, transplanted in June and harvested in October, and the other crops are sown in October and harvested in June. In the south, an annual double-rice cropping system is dominant.

Rice is sown early or late in the cropping sea-son. early rice is sown in March to April, trans-planted in May and harvested in July, while late rice is sown in June, transplanted in July and harvested in October. During winter, vegeta-bles (e.g. cabbage, faba bean, cauliflower, carrot, garlic, potato, etc.), green manure and rapeseed are planted in the paddy fields. Multiple crop-ping areas decreased recently due to the short-age of rural labor and the development of the

FIG. 3.3 Spatial layouts of sown areas (ha) of (a) rice, (b) maize and (c) wheat in China (2012).


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rural economy. As a consequence, the double rice cropping system is being replaced by sin-gle rice with winter crops in southern China. Wheat–maize rotation or a relay cropping sys-tem is being replaced by spring maize per sea-son in the northwest (gansu and Shaanxi), or in the northern China Plain such as northern He-bei, Tianjin, and Beijing.

Although the cropping system is being simpli-fied due to shortage of rural labor and mechani-cal planting, multiple cropping is still dominant. In the southwest, intercropping, relay cropping and mixed cropping are still widely applied for the dryland due to the combination of sufficient farm labor and farmland shortage. For example, in the dryland area of Sichuan province, maize is commonly sown together with soybean or sweet potato; and pea is sown in the field be-fore the maize harvest and after soybean har-vest. Before the wheat harvest, rice is sown in the wheat field with a direct-seeding method; and wheat is sown in paddy fields before rice harvesting in the wheat–rice cropping system.

Recently, a novel relay strip inter-cropping sys-tem of wheat–maize/soybean has been devel-oping in the southwest which outperforms eco-nomically the traditional wheat–maize cropping system by 30% or more (yong et al., 2012). Before the maize harvest, vegetable crops or wheat are sown. even in the paddy fields, farmers often grow soybean and vegetable crops on the paddy ridges during the rice-growing season. These in-tegrated cropping systems improve the farmers’ income and food production stability.

4 YIELD ENHANCEMENT VIA GENETIC IMPROVEMENT AND

AGRONOMIC INNOVATION

4.1 Trends in grain production

Over the last 60 years, there has been a re-markable growth in crop production in China (Figs 3.5 and 3.6). Production of rice, wheat and maize has increased from 48.6 Mt to 204.2 Mt,

FIG. 3.4 Spatial layout of cropping systems in China, (Liu et al., 2013).

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FIG. 3.5 (a) Sown area and (b) total production of rice, wheat and maize during the period 1949–2012 in China. Data from national Bureau of Statistics of China, 1949–2012.

FIG. 3.6 Changes in sown area, yield and production of rice, wheat and maize between 1990 and 2012. Data from national Bureau of Statistics of China, 1990–2012.


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13.8 Mt to 121.0 Mt, and 12.4 Mt to 205.6 Mt between 1949 and 2012, accounting for 66.2% of the total country cereal production in 1949 and 90% in 2012, respectively.

During the last 20 years, significant changes were observed in sown area and production of the main grain crops. From 1990 to 2012, total rice and wheat acreage decreased by 8.9% and 21.1%; in contrast, the maize area increased by 63.7% (Fig. 3.6). He et al. (2013) also showed that a significant reduction in the soybean area has allowed expansion of the maize area in both the yellow and Huai River Valleys and north-eastern China from 2000 to 2012. However, grain yields increased by 7.9% for rice, 23.2% for wheat and 112.4% for maize, and the corresponding increases in total production were 18.4%, 56.1%, and 29.7%, respectively (Fig. 3.6). Compared to the sown area, yield increase contributed much more to increased production. The main contribution to the increase in grain production was maize in the north and northwest, where the sown area increased by 105% and 73.3% and pro-duction by 160.5% and 171.7%, respectively. Rice acreage increased by 171% and production by 230% in the northeast, and Heilongjiang province became the last rice producer in China. The in-crease in wheat production was mainly in central (72.7%) and eastern (39.2%) regions (Fig. 3.6). Since farmland and natural resources are in short supply, further increase in grain production will mainly depend on the increase in yield rather than extension of the sown area in China as in most of the other world cropping systems.

4.2 Contribution of genetic improvement

grain production depends on the yield po-tential (Chapter 16) and stress tolerance, hence genetic improvement plays an important role in increasing productivity. He et al. (2013) have summarized the genetic improvement of yield potential for major cereals. Conventional breed-ing has played a dominant role in developing new varieties and hybrids, although molecular

marker-assisted selection has also been used (He et al., 2013). Improvement of wheat for the irrigated wheat/maize rotation system in the yellow and Huai River Valleys since the 1960s has produced varieties characterized by reduced plant height, increased harvest index, and sig-nificantly increased yield potential, largely due to the utilization of semi-dwarf genes and the 1B/1R translocation (Zhou et al., 2007). Recent studies indicate that wheat yield in Henan and Shandong, China’s largest wheat-producing provinces, has increased significantly since 1990. In Henan, the average annual genetic gain in grain yield between 1981 and 2008 was 0.60%, or 51.3 kg ha−1 year−1, and it can largely be attributed to increased thousand kernel weight and harvest index (Zheng et al., 2011). These au-thors also found that grain yield was closely and positively associated with stomatal conductance and transpiration rate at 30 days post-anthesis. In Shandong, the genetic gain in grain yield be-tween 1969 and 2006 was 0.85%, or 62 kg ha−1 year−1, mainly due to increased kernels m−2 and biomass as a result of improved photosynthetic efficiency at and after heading (Xiao et al., 2012). Plant height was maintained and harvest index increased, with greater photosynthetic efficien-cy after anthesis, indicating there is potential for a physiological approach to yield improvement.

Historical gains of maize yield recorded in our experiment (Fig. 3.7) were 17.9 g plant−1 decade−1 and 936 kg ha−1 decade−1 over the period 1970–2010 in northeast China, which were similar to previous reports (Xie et al., 2009; Ci et al., 2012). yield improvements were significant from 1950 to 1970 and from 1990 to 2000 (Ci et al., 2013). From 1970 to 2000, the gain in maize yield aver-aged 94.7 kg ha−1 year−1, 53% of which was at-tributed to breeding. new hybrids had increased tolerance to multiple stresses, including lodg-ing resistance, which allowed plant densities to increase from 60 000 to 75 000 plants ha−1 (Ci et al., 2011). A comparison of Chinese and US hy-brids grown at different planting densities from 1964 to 2001 indicated that US hybrids showed

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the highest rate of gain (81 kg ha−1 year−1) at the highest planting density (67 550 plants ha−1), whereas the highest rate of gain for Chinese hy-brids was 62 kg ha−1 year−1 at a medium planting density (52 500 plants ha−1). Pedigree and molec-ular marker data showed that US and Chinese hybrids were based on very different germplasm, with decades-old US germplasm contributing to recently developed and widely used Chinese hy-brids (Li et al., 2011). For comparison, Chapter 2 outlines breeding and agronomic progress in maize-based systems of the USA, including a de-tailed account for the role of sowing density to accommodate hybrids and environments.

The significant yield improvement achieved for the cereal crops in favorable environments in China is in agreement with reports from other countries, in the sense that the yield improvements came from increasing biomass through increased photosynthesis (Fischer and edmeades, 2010). This trend will probably con-tinue in the future, but probably at a lower rate of increase than in the past. Conventional breeding will continue to play a significant role in improv-ing yield potential, with likely larger contribu-tions of biotechnology particularly for pyramid-ing genes for disease resistance and processing quality; Chapters 18 and 19 update the role of

biotechnology on crop improvement. While detailed strategies for improving rice, maize, and wheat yields may be different, there are also many similarities, such as combining high yield potential with broad adaptation, increas-ing spikelet or kernel number per unit area, im-proving lodging resistance under high planting densities suitable for mechanized harvesting, and improving resistance/tolerance to abiotic and biotic stresses. To achieve such goals, a com-bined approach is required, including continued selection of elite parents for crossing, alternative selection in different environments, and multi-location testing at advanced stages. Increasing the number of advanced lines screened in multiple environments will greatly assist in identifying elite genotypes. For all three cereals, international germplasm exchange will continue to play a key role in further yield improvement in China (He et al., 2013).

4.3 Contribution of agronomic innovation

A multiple and proper cultivation system is essential for farmland productivity, food secu-rity and efficient use of agricultural resources. Along with the great development of science

FIG. 3.7 Responses of grain yields (a) per plant and (b) per unit area to plant density for maize hybrids released from dif-ferent eras over the 1970s–2000s.


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and technology and the progress of the soci-ety economy, Chinese cropping techniques have achieved much progress during the past decades, resulting in a large contribution to the increase of grain production. Here we outline three innovations in tillage, cropping season op-timization, and rice production technologies.

4.3.1 Soil tillageTraditional tillage has caused significant soil

erosion and degradation, resulting in large de-creases in SOM and fragile soil physical struc-ture (Tang et al., 2004). To decrease the cost and to avoid the negative impacts of conventional tillage, reduced/no tillage has been encouraged (Xie et al., 2008; Li et al., 2009). However, no tillage could have long-term impacts on weed populations and soil compaction. Thus, some novel tillage practices have been developed to counteract these effects. In the northeast, less tillage combined with sub-soiling tillage was widely adopted in maize cropping. In the north and center, a rotation of conventional tillage for winter wheat and no tillage for summer maize or soybean is becoming dominant. For the an-nual double rice cropping system, a rotation of conventional tillage with less tillage is widely used.

4.3.2 Cropping season optimizationField experiments showed that climate

change benefits late rice and winter wheat pro-duction by promoting plant development and growth, but is detrimental to early and mid rice because heat stress affects floret fertilization and grain filling (Dong et al., 2011; Tian et al., 2012; Chen et al., 2013). To avoid the negative impacts of warming, the cropping seasons have been adjusted greatly over the past decades. In the winter wheat–maize cropping system, wheat sowing and maize harvest have been delayed simultaneously, resulting in a large increase in annual yield. Similarly, wheat sowing and rice harvesting have been delayed in the wheat–rice cropping system. Due to higher air temperature, the sowing of rice, maize and soybean has been significantly advanced with unchanged harvest dates, consequently resulting in a longer growth period in the northeast.

4.3.3 Rice cropping technique innovationDuring the last decades, Chinese rice cropping

techniques have been innovated in three aspects (Fig. 3.8). First, alternate dry-wetting seedling-nursery has progressively replaced continuous flooded seedling-nursery. This technique can save water and enhance rice seedling quality.

FIG. 3.8 Rice cropping technique innovations: (a) seedling nursery, (b) irrigation and (c) planting method in China since 1970s.

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Secondly, alternate dry-wetting (AWD) irrigation has replaced the continuous flooded irrigation in major rice cropping areas. AWD can increase O2 concentration in paddy soil to enhance rice root activity after anthesis, consequently benefiting grain filling and yield. One more innovation is the planting method. Traditional manual trans-planting is being replaced by mechanical trans-planting and dry direct seeding because of the shortage of rural labor. Mechanical rice planting can significantly decrease rice production costs and increase the labor efficiency.

5 ATTEMPTS TO IMPROVE RESOURCE-USE EFFICIENCY

5.1 Conservation agriculture for high water-use efficiency

Conservation agriculture (CA) is an ap-proach developed to manage farmland for sus-tainable crop production, while simultaneously preserving soil and water resources (erenstein, 2011). generally, conservation agriculture relies on three major principles: maintenance of a permanent vegetative cover or mulch on the soil surface; minimal soil disturbance (no/reduced tillage); and diversified crop rotation (FAO, 2013). given the effects of conservation agriculture on soil, water and economic viability,

this management has been widely recommend-ed and adopted with mixed success; Chapter 5 discusses the short- and long-term implications of CA in Africa, and the trade-offs involved in its adoption.

Since the 1970s, large efforts have been made on research and demonstration of conservation agriculture in China, where it has been applied in 6.4 × 106 ha by 2012 with a projected increase to 11 × 106 ha by 2015 (gOV, 2009). Conservation agriculture practices in China include no tillage, reduced tillage, straw application, plastic film mulching, water-saving irrigation, and limited irrigation (Zhang et al., 2013a).

Crop straw and plastic film mulching have been extended because material is easily acces-sible and low cost. In the north China Plain and Loess Plateau, for example, many efforts have been paid to increasing water-use efficiency (WUe, yield per unit evapotranspiration) with an acceptable crop yield (Zhang et al., 2013a). However, the range of WUe was very large for the cropping practices, suggesting opportunities for maintaining or increasing WUe with high yield in the region. Mulching with crop residues can improve water-use efficiency by 10–20% through reduced soil evaporation and increased plant transpiration (Table 3.2). Mulching with crop residues during the summer fallow can increase soil water retention. Wang et al. (2004) demonstrated straw mulching significantly

TABLE 3.2 the effects of mulching on soil evaporation, grain yield and water-use efficiency of wheat and maize

Crop TreatmentEvapotranspiration(mm)

Soil evaporation(mm)

Grain yield(g m−2)

WUE(kg m−3)

Winter wheat Mulching 367 75 714 1.94

no mulching 390 117 669 1.72

Maize Mulching 386 86 712 1.84

no mulching 431 129 666 1.55

Summer fallow Mulching ---- 39 ---- ----

no mulching ---- 107 ---- ----

---- Data not available. Source: Deng et al., 2006.


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increased the harvesting of rainwater and yield. Plastic film mulched furrow-ridge cropping (PMF) is a recent modification of maize crop-ping in the semiarid Loess Plateau. Recent stud-ies indicated that soil evaporation significantly decreased in PMF after the jointing stage of spring maize as compared with uncovered and flat sowing (CK). The grain yield and water-use efficiency in the PMF treatment was increased by 333.1% and 290.6%, respectively. In addition, the harvest index of maize in PMF treatment was 132.5% higher than CK (Wang et al., 2011, 2013). Plastic film mulched furrow-ridge can signifi-cantly enhance maize grain yields and water-use efficiency by reducing soil evaporation and improving precipitation water movement from ridges to furrows and increasing soil tempera-ture. Based on a 20-year experiment, Zhang et al. (2013a) also found the maximum wheat yield and WUe in the fields with plastic film and crop straw mulching. Consequently, mulch-ing has been widely extended on the semi-arid Loess Plateau for maize production.

Although conservation agriculture can benefit crop production (Wang et al., 2012b), it can also reduce crop production through undesirable

effects on soil physiochemical and biological conditions (Deubel et al., 2011; Chapter 5). The key limiting factor to the application of conser-vation agriculture in China is the uncertainty of the long-term effects on soil and crop yield. To quantify the impacts of conservation agriculture practices (i.e. nT: no/reduced-tillage only, CTSR: conventional tillage with straw retention, nTSR: nT with straw retention) on crop yield we con-ducted a meta-analysis to compare with conven-tional tillage without straw retention (CT).

Conservation agriculture significantly increas-ed crop yield by 4.6% compared to the CT (Fig. 3.9), though there were large differences among the practices (Qb, R and P = 0.0346). The yield gains of CTSR and nTSR were 4.9 and 6.3%, respectively, while there was no significant effect in the nT compared to the CT. Meanwhile, the longer duration of conservation agriculture, the higher the increase in crop yield (Qb, R and P = 0.004, Fig. 3.9).

The effects of conservation agriculture on crop yield decreased with increasing annual precipitation (Qb, R and P = 0.042, Fig. 3.10). Significant positive effects occurred where an-nual precipitation is below 600 mm, whereas

FIG. 3.9 Differences in the effect sizes among the conservation agriculture practices and among the experimental dura-tions. numbers between brackets are the observations.

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no clear effects were found when precipitation was above 600 mm. The higher the mean an-nual temperature, the higher yield gains under conservation agriculture, although the differ-ences were not significant between the temper-ature ranges (Qb, R and P = 0.1042, Fig. 3.10). The highest enhancing effects on crop yield occurred when mean annual temperature was higher than 10°C, whereas the effect was not significant when mean annual temperature was lower than 5°C.

5.2 Innovations for improving nitrogen fertilizer-use efficiency

nitrogen (n) is the most important mineral nutrient for cereal production, and an adequate supply is essential for high yields (Chapter 8). global consumption of synthetic n has in-creased from 11.6 Tg in 1961 to 104 Tg in 2006 (FAO, 2013). Furthermore, the annual total glob-al n use is projected to grow to approximately 112 Tg in 2020, and up to 171 Mt in 2050, assum-ing no change in n-use efficiency. China has be-come one of the world’s largest producers and consumers of n, P (P2O5) and K (K2O) fertilizer; its use increased from 8.3 to 24.0 Tg, 2.2 to 8.3 Tg,

and 0.3 to 6.2 Tg between 1979 and 2012, respec-tively (Fig. 3.11).

excessive n application causes environmental pollution, increases the cost, reduces nitrogen-use efficiency and may reduce grain yield. The n-use efficiency (nUe: grain yield per unit n applied, kg kg−1 n), decreased by about 24%, from 43 kg kg−1 n in 1980 to 32 kg kg−1 n in 2005. China’s national average n application rate is higher than the world’s average, hence the aver-age nUe in China is lower than the estimated global average of 44 kg kg−1 (Wang et al., 2011). Huang et al. (2010) indicated that the n-uptake efficiency (% fertilizer n recovered in above-ground crop biomass) in China is 30–35% for the three main crops. Improving n-uptake efficiency in the areas where it is lower than 30–50% could save 2.8–6.6 Tg n year−1 (Huang et al., 2010). To improve synchrony between n supply and crop demand, large efforts have been made in re-search and demonstration. To increase crop yield and reduce fertilizer application, a national soil testing and fertilization recommendation (STFR) project has been conducted since 2006. STFR resolved the conflicts between crop fertilizer demand and soil fertilizer supply, increased crop yields and farmers’ incomes, and improved the

FIG. 3.10 Differences in the effect sizes of conservation agriculture practices in relation to precipitation and air tempera-ture. numbers between brackets are the observations.


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quality of agricultural products. Chinese farm-land under STFR has reached 8 × 107 ha in 2012. Compared to traditional fertilization, STFR in-creased rice, wheat, and maize yields by 3.7, 3.8 and 5.9%, respectively, and reduced fertilization to 700 Mt by 2011.

Site-specific n management (SSnM), where fertilization is based on the crop n demand, was developed to increase fertilizer-uptake efficiency of irrigated rice. During the seedling and booting stages, leaf n status measured with a chlorophyll meter (SPAD) is a good indicator

of crop n demand to adjust predetermined n topdressings at seedling and booting. With this approach, the timing and number of n applica-tions are fixed while the rate of n topdressing changes across the seasons and locations. Aver-aged across 107 farmers, SSnM produced 5% higher grain yield than the farmers’ practice, and the n rate was reduced from 195 to 133 kg ha−1, or 32% (Table 3.3). Consequently, SSnM almost doubled nUe and had a 55% higher partial fac-tor productivity of applied n than the farmers’ fertilization practice. Xue et al. (2013) developed

TABLE 3.3 grain yield, total n rate, yield response to n application, agronomic n-use efficiency, and partial factor productivity of applied n (pFp) of farmers’ fertilizer practice and site-specific n management (ssnm)

Parameters Farmers’ practice SSNM Difference (%)

grain yield (t ha−1) 7.1b 7.5a 5.0

n rate (kg ha−1) 195.0a 133.0b 38.0

n response (t ha−1) 1.4b 1.8a 25.0

Agronomic nUe (kg kg−1) 7.1b 13.4a 61.0

PFP (kg kg−1) 36.3b 56.2a 43.0

Source: Peng et al., (2010). Within a row, means followed by different letters are significantly different at the 0.05 probability level according to the least significant difference (LSD) test.

FIG. 3.11 Fertilizer consumption in China between 1979 and 2012.

Data were from on-farm demonstrations conducted by 107 farmers from six provinces in China between 2003 and 2007. Average grain yield of zero-n control was 5.7 t ha−1 across the 107 farmers.

6 CroppIng responses and adaptatIons to warmIng 57

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an improved rice management system combin-ing both SSnM and alternate wetting and mod-erate drying irrigation technologies (AWMD). Compared with local practice, this system in-creased rice yield, nUe and irrigation water-use efficiency (grain yield over amount of irrigation water) by 14.4, 64.1 and 36.4%, respectively.

An in-season n management strategy (InM) has been developed for the intensive wheat–maize system in the north China Plain. According to this strategy, the total amount of n fertilizer is divided between two or three applications dur-ing the growing season, with the optimal n rate for each application being determined from soil nitrate-n tests in the root zone and a target n value for the corresponding growth period of the crop. In this way, the effect of n mineraliza-tion, immobilization and n losses on plant avail-able n during the previous growth period can be included in the result of the next soil nitrate-n analysis thus affecting the next n fertilization recommendation. When employing the InM in north China, experiments demonstrated that n fertilizer was reduced by 66% compared with regular practices without sacrificing crop yield (Cui et al., 2010).

6 CROPPING RESPONSES AND ADAPTATIONS TO WARMING

6.1 Crop phenology responses

Temperature is the key factor controlling crop development and growth (Chapter 12). even a moderate increase in air temperature can affect crop phenology and growth duration signifi-cantly (Tao et al., 2006; Lobell et al., 2012). The impacts of warming on crop phenology in China have been investigated in the field (Table 3.4) and modeling (Chapter 20) experiments. For example, an air temperature increase of around 1.5°C carried out in the Free Air Temperature Increase (FATI) in the yangtze Delta Plain sig-nificantly advanced crop phenophases of wheat and rice (Dong et al., 2011; Tian et al., 2012). Wheat time to maturity was shortened by 10 days (P < 0.05); this was mainly associated with shorter pre-anthesis phase, while the length of post-anthesis was slightly prolonged (Tian et al., 2012). The length of rice pre-heading phase was shortened by 3.3, 1.7 and 2.0 days in the all-day warming, daytime warming and night-time warming plots compared to the

TABLE 3.4 responses of crop phenology to warming under field conditions in China

Crop Treatment

Length of phenophase (d)

Data sourcePre-anthesis Post-anthesis Entire period

Winter wheat Unwarmed 146 53 198 Tian et al., 2012

All-day warming 134 53 187

Middle rice Unwarmed 72 49 120 Dong et al., 2011

All-day warming 68 50 119

Daytime warming 70 48 118

night-time warming 70 49 118

Maize Unwarmed 82 71 152 Qian et al., 2012

night-time warming 86 70 155

The magnitudes of warming were 1.5°C and 1.1°C in daily mean temperatures in the experiments of Tian et al. (2012) and Qian et al. (2012), respectively. In the experiment of Dong et al. (2011), the air temperature elevations were 2.0°C in the daily mean temperature for the all-day warming treatment, 1.1°C in the daytime mean temperature for daytime warming treatment and 1.8°C in the night-time mean temperature for the night-time warming treatment.


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no-warmed control, while the post-heading phase stayed almost unchanged (Dong et al., 2011). Another experiment conducted in north-east China, showed night-time warming before anthesis advanced the spring maize pheno-phases (Qian et al., 2012).

Similar responses of the crop growth period to warming were found in historical data analy-ses. Wang et al. (2012a) reported that the increase in temperature shortened the growth duration of winter wheat mainly by shortening the period from sowing to jointing at two northern sites. Tao et al. (2013) indicated that single rice transplant-ing, heading and maturity dates were generally advanced, but the heading and maturity dates of single rice in the middle and lower reaches of the yangtze River and the northeast China Plain were delayed between 1981 and 2009. In gen-eral, warming shortened the crop pre-anthesis phase, while the post-anthesis phase was pro-longed or not changed. Chapter 20 provides fur-ther evidence and advances an explanation for this pattern.

6.2 Crop yield responses

The effects of warming on crop production may depend on the crop type, the warming extent and the local background temperature (Lobell et al., 2011; Chapter 20). Theoretically, warming can shorten the length of the crop growth period, likely resulting in reduced bio-mass production and n uptake and accumula-tion. Warming may also aggravate high temper-ature stress potentially decreasing grain number and weight. Because multiple cropping systems dominate in China, the short growing period and the post-anthesis high temperature are the major constraints on crop production. Thus, warming may aggravate the constraints on grain produc-tion. On the other hand, temperature increase may directly reduce frost/chilling and indirectly reduce heat injury due to warming-led earlier anthesis. Since frost/chilling before flowering and high temperature stress after flowering are

common in winter crops, warming may enhance yield and grain quality. For example, based on historical data analysis and the assumption of similar rainfall, Xiao et al. (2008) predicted that warming might increase wheat yield by 3.1% at low altitude and 4.0% at high altitude by 2030. Sommer et al. (2013) predicted that an increase in air temperature may mostly benefit wheat production in central Asia. Obviously, there are still major uncertainties about Chinese crop pro-duction under future climate that need further modeling and experimental work.

Many experiments have been conducted to quantify warming impacts on wheat yield and quality during the past decades. However, many of them were conducted under artificial environments (e.g. greenhouse or open top chambers), rather than an agroecosystem scale under field conditions. Meanwhile, existing experiments in China mainly focused on high temperature impacts on starch and protein dep-ositions in grain during post-anthesis, and only a few studies have been conducted across an entire growing cycle. The impacts of predicted warming on wheat yield and grain quality may have been overestimated. Recently, some warm-ing experiments were conducted under field conditions in China (Tian et al., 2012; Dong et al., 2011). Tian et al. (2012) found that anticipated warming may facilitate winter wheat produc-tion in eastern China (Table 3.5). An increase in air mean temperature of 1.5°C enhanced wheat grain yield by 16.3% (P < 0.05) mainly because of the warming-led increases in green leaf area and grain size. The area of flag leaf and total green leaves at anthesis and grain size were 36.0, 19.2 and 5.9% higher in the warmed plots than the unwarmed control (P < 0.05). Simi-larly, Hou et al. (2012) found that warming by 1.6°C also increased wheat yield in yucheng, the center of Chinese winter wheat cropping, where there was no soil moisture limitation. Fang et al. (2013) reported that warming by 2°C decreased wheat yield under a large moveable rain shel-ter in gucheng, the northern edge of Chinese


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winter wheat cropping, where the irrigation was controlled at 100 mm without any precipitation. With an addition of 20 mm, however, warming increased wheat yield significantly. Together, pre-vious field experiments showed that predicted climatic warming will benefit winter wheat production in east China if there is no limitation in precipitation or irrigation. Similarly, cereal yield is likely to increase in milder climates projected for northern europe, unless increas-ing water stress cancels the benefits of warming (Chapter 4). For the middle rice at the same site, warming slightly decreased the above-ground biomass by an average of 9.1, 10.3 and 3.3%, and the grain yield by an average of 0.9, 6.4 and 6.1% in the all-day warming, daytime warming and night-time warming plots compared to the ambient control, respectively (Table 3.5). Warm-ing tended to decrease rice photosynthesis and stimulate night-time respiration. For maize in the northeast, night-time warming (less than 1.5°C) before anthesis increased maize above-

ground biomass and grain yield by 8.2 and 9.3% (Table 3.5). Maize green leaf area and three-ear-leaves (i.e. the ear leaf, and the leaves immedi-ately below and above the ear) area under night-time warming were 13.5 and 14.6% larger than for the unwarmed control.

6.3 Adaptations of cropping systems to warming in northeast China

Although some reports showed negative effects of climate warming in crop yield, some studies showed that crop production might ben-efit from warming if suitable adaptations are implemented (Lobell et al., 2008), especially in the high latitude areas (Chen et al., 2012; Chap-ter 4). Therefore, many cropping practices have been recommended as adaptations to warming, such as adjusting sowing date and cropping pat-tern, adopting heat-tolerant, higher-yielding va-rieties and improving crop management (Chen et al., 2012; Chapter 20).

TABLE 3.5 responses of crop productivity to climate warming under field conditions in China

Crop Treatment

Effective panicles(plant m−2)

Grain number per panicle(grain spike−1)

1000-Grain weight(g)

Above-ground biomass(g m−2)

Grain yield(g m−2) Data source

Winter wheat

Unwarmed 545.7 38.9 42.4 1546.4 645.2 Tian et al., 2012

All-day warming

558.7 40.4 44.9 1666.6 750.4

Single rice

Unwarmed 248.6 153.6 25.8 2091.7 709.4 Dong et al., 2011

All-day warming

260.1 146.6 24.3 1902.5 702.6

Daytime warming

265.1 147.0 24.9 1864.2 664.9

night-time warming

253.5 148.5 24.7 2021.8 665.6

Maize Unwarmed 5.6 621.5 372.0 1265.0 2460.0 Qian et al., 2012

night-time warming

5.6 617.5 348.0 1160.0 2275.0


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In northeast China, where mean air tempera-ture has increased 1.0°C over the last 20 years, present cropping boundaries can be theoretically extended northward about 80 km with a pro-longed growing period of 10 days compared to the 1970s. For example, based on the records of the rice cropping area of Heilongjiang province in 1970 and 2006, the actual changes of the spatial distributions of rice sowing area were analyzed with gIS (Fig. 3.12). The total area of rice cropping increased by 17.1 times in this period, with a greatest increment occurring in the east of the province. Meanwhile, the crop-ping region has also enlarged over the past years. In 1970, the main cropping region was located south of 46°n, especially around the line of 45°n and extended northward of 47°n, mainly around the line of 46°n during the period 1970–2006. The rice sowing areas north of 46°n increased from 3.6 × 104 ha in 1970 to 130 × 104 ha in 2006. Rice production north of 46°n increased from 11 × 104 t in 1970 to 851 × 104 t in 2006. The gravity center, a point that can maintain a bal-ance of force in all directions in a region space

(griffith, 1984), of rice cropping region shifted from e128°529, n45°379in 1970 to e129°539, n46°299 in 2006. The actual cropping center moved about 80 km northward from 1970 to 2006.

The growth durations of newly approved varieties of rice, maize and soybean have been prolonged by 14.0, 7.0 and 2.7 days since the 1950s, respectively (Fig. 3.13). Significant differ-ences in the growth durations were found among different provinces. The increase in the growth duration of rice over the years of 1950–2008 was 9.1 days for Heilongjiang, 13.4 days for Jilin and 19.7 days for Liaoning province (Fig. 3.13). Simi-lar increases were found for the growth dura-tion of maize and soybean (Fig. 3.13). The rice growth duration showed the greatest increment among the three crops during the variety im-proving process. These changes highlight how crop breeding has contributed to crop adapta-tion to warming.

The adjustment of sowing and harvest dates since the 1990s prolonged the actual growing period of both rice (6 d) and maize (4 d) (Chen et al., 2012). Since the 1980s, improved varieties

FIG. 3.12 Actual spatial distributions of rice cropping area in (a) 1970 and (b) 2006 in Heilongjiang province in northeast China. One dot means 300 ha. Source: Chen et al. (2012).


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were able to compensate for the negative impact of climate in the north China Plain. The variety changes of wheat and maize maintained the length of the pre-flowering period against the shortening effect of warming and extend-ed the length of the grain-filling period (Liu et al., 2010). Historical increase in air temperature before the over-wintering stage enabled late sow-ing of wheat and late harvesting of maize, leading to an overall 4–6% increase in annual production of the wheat–maize system. Mechanical sowing and less tillage also shortened the time for field preparation, which facilitated the later harvest of summer maize. Zhang et al. (2013b) found that a major, temperature-induced change in the rice growth duration was underway in China and that using a short-duration cultivar has been accelerating the process for late rice.

Climate change has shifted the cropping boundary of different cropping systems in China (yang et al., 2010). Compared to the cropping boundary in the period from the 1950s to 1980, the northern limits of double cropping were displaced in Shaanxi, Shanxi, Hebei, Beijing and Liaoning provinces from 1981 to 2007. The northern limits of the three-crop system were displaced in Hunan, Hubei, Anhui, Jiangsu, and Zhejiang provinces. The northern limits of win-ter wheat moved northwards and westwards to different degrees in Liaoning, Hebei, Shanxi, Shaanxi, Inner Mongolia, ningxia, gansu and Qinghai provinces, compared with the period 1950–1980. The northern limits of double-rice cropping in Zhejiang, Anhui, Hubei, and Hunan provinces moved northwards. The stable-yield northern limits of rain-fed winter wheat–summer

FIG. 3.13 Crop growth duration in northeast China for varieties released since 1950s. (a) Rice, (b) maize, (c) soybean and (d) their average. Source: Chen et al. (2012).


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maize moved south-eastwards in most regions, mainly in response to decreased rainfall during recent years. During the past 50 years, warm-ing caused the northwards movement of the northern limits of the cropping system, and the northern limits of winter wheat and double rice.

7 CONCLUDING REMARKS

China has increased grain production con-tinuously for ten years, but there are concerns with the secondary effects of intensive crop-ping on farmland soil and water. To reduce the negative impacts of intensive cropping on natural resources and the environment, the Chinese government plans to decrease the grain self-sufficiency rate. Simultaneously, increasing efforts are allocated to research and application of cropping techniques to achieve the multiple goals of food security, environmental safety and climate change adaptation. Integrated innova-tions in crop breeding and agronomy, informed by crop physiology, will be the key to achieve these goals.

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