Department of Plant Nutrition, China Agricultural University; Key Laboratory of Plant Nutrition and Nutrient Cycling, Ministry of Agriculture; and Key Laboratory of Plant–Soil Interactions, Ministry of Education, Beijing 100193, China AND Lancaster Environment Centre, University of Lancaster, Lancaster LA1 4YQ, UK
Abstract
In recent years, agricultural growth in China has accelerated remarkably, but most of this growth has been driven by increased yield per unit area rather than by expansion of the cultivated area. Looking towards 2030, to meet the demand for grain and to feed a growing population on the available arable land, it is suggested that annual crop production should be increased to around 580 Mt and that yield should increase by at least 2% annually. Crop production will become more difficult with climate change, resource scarcity (e.g. land, water, energy, and nutrients) and environmental degradation (e.g. declining soil quality, increased greenhouse gas emissions, and surface water eutrophication). To pursue the fastest and most practical route to improved yield, the near-term strategy is application and extension of existing agricultural technologies. This would lead to substantial improvement in crop and soil management practices, which are currently suboptimal. Two pivotal components are required if we are to follow new trajectories. First, the disciplines of soil management and agronomy need to be given increased emphasis in research and teaching, as part of a grand food security challenge. Second, continued genetic improvement in crop varieties will be vital. However, our view is that the biggest gains from improved technology will come most immediately from combinations of improved crops and improved agronomical practices. The objectives of this paper are to summarize the historical trend of crop production in China and to examine the main constraints to the further increase of crop productivity. The paper provides a perspective on the challenge faced by science and technology in agriculture which must be met both in terms of increased crop productivity but also in increased resource use efficiency and the protection of environmental quality.
Key words
• Food security
• environmental quality
• genetic improvement
• integrated soil-crop systems management
• resource use efficiency
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Trends in crop production
Increased crop production and yield
Over the last 50 years there has been remarkable growth in agricultural production in China. This has created the so-called ‘Miracle in China’ with 7% of the world's arable land feeding 22% of the world's population.
Chinese cereal production has increased steadily from 83.4 Mt in 1961 to 474.2 Mt in 2009 (Fig. 1A), accounting for 9.5% of total global cereal production in 1961 and 21.8% in 2009. The net increase over this period is 390.8 Mt with an annual growth rate of 3.7%, which is substantially higher than the world mean growth rate in cereal production of 2% during the same period. In 2009, China was responsible for approximately 29.1% of global rice production, 20% of maize, and 16.9% of wheat production (National Bureau of Statistics of China, 1950–2010; FAO, 2010). The success of crop production in China has impacted on both global food supply and on natural resource use and availability and both of these changes have received global recognition.
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Fig. 1.
Production and cultivation areas of cereal crops (rice+wheat+maize) (A), grain yields of rice, wheat, and maize (B) and trends in all fertilizer and N fertilizer consumption in China from 1961 to 2009. The consumption is the apparent whole consumption in China based on the calculation of balance (production+imports–exports). Source: China Agriculture Yearbook. FAO STAT electronic databases (http://apps.fao.org)
Historically, cereal production has been dominant in the south of the country and practised less in the north of China. However, over the last few decades the balance has shifted to some extent. From 1980 to 2008, total cereal cultivation area decreased by 3.77 Mha in the Yangtze River Basin, by 3.27 Mha in south China, and by 0.81 Mha in South-West China, where rice-based cropping systems are dominant. In contrast, the cereal cultivation area increased by 5.42 M ha on the North China Plain and in North-East China. Total cereal production in the north increased from 129 Mt in 1980 to 283.5 Mt in 2008, which accounted for 41.4% of the national total cereal production in 1980 and 57.5% in 2008 (National Bureau of Statistics of China, 1950–2010). As a result, the North China Plain and the North-East of China have become important cereal production and food-commodity supply regions. In these regions, however, water availability for agriculture is becoming a major issue for the nation.
The increase in total crop production in China has arisen mainly as a result of increases in yield per unit area rather than from increases in the cultivated area. For example, from 1961 to 2009 there was a 3.2-fold increase in the productivity of rice (from 2041 kg ha−1 to 6585 kg ha−1), an 8.5-fold increase in the productivity of wheat (from 557 kg ha−1 to 4739 kg ha−1), and a 4.6-fold increase in the productivity of maize (from 1139 kg ha−1 to 5258 kg ha−1) (Fig. 1B). Over the same period the total cultivated area of cereals increased by only 30% (from 65.5 Mha in 1961 to 85.1 Mha in 2009) (National Bureau of Statistics of China, 1950–2010; Fig. 1A).
Intensification of crop production contributes to increased yield
Intensification of crop production over the last 50 years has come to be known as the ‘green revolution’ and has been achieved by the use of modern high-yielding varieties while greater benefits have been realized from chemical fertilizers, irrigation, and weed and pest control.
The consumption of fertilizer in China has increased linearly since 1961. The total consumption of chemical fertilizers exceeded 64 Mt in 2009, and this is nearly 35% of the total global fertilizer consumption. Use of nitrogen (N) fertilizer has increased from 0.5 Mt in 1961 to 46.6 Mt in 2009 (Consumption=production+import–export, Revised from National Bureau of Statistics of China, 1950–2010, Fig. 1C). The area of irrigated farmland has expanded by 32% since the 1970s and the effective area of irrigated farmland has now reached 58.5 Mha. This is 48% of the total arable land area in China, but it produces 75% of the national grain production and 90% of the products from cash crops (National Bureau of Statistics of China, 1950–2010). Chemical use increased from 0.76 Mt in 1991 to 1.76 Mt in 2005 (National Bureau of Statistics of China, 1950–2010). As the second-largest producer and consumer of pesticides, use in China accounts for 14% of the world total and the country has now become a net exporter (Liu and Diamond, 2005). Without the use of synthetic fertilizers, irrigatio, and chemicals, China's food production could not have increased at the rates recorded.
Figure 2 shows that intensification of maize production has occurred with time. Improvements in maize varieties and cropping techniques have contributed to increased grain yield per unit area since 1960s in China (Li and Wang, 2009). In the 1960s, double-cross hybrids were dominant and use was combined with planting technologies focused on improving the condition of farmland. Planting density was also increased at this time. Since the 1970s, single-cross hybrids have been extensively used. The main trends in the development of breeding strategies to increase maize yield potential included selection for disease-resistance traits, the improvement of above-ground plant architecture, stay-green and late-maturing characteristics. Planting technologies were characterized by the use of chemical fertilizers, irrigation, weed and pest control, higher planting density, and soil quality improvement. As management intensity increased, planting technologies shifted from the use of novel individual techniques to more technical integration. For example, chemical fertilizer use was largely just N fertilization in the 1970s with both N and P additions common in the 1980s and use of combined NPK fertilizers used much more often in the 1990s and 2000s. Chemical fertilizer rate has increased greatly since the 1990s.
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Fig. 2.
The main varieties and techniques of maize production from the 1960s to the 2000s in China. In the 1960s, double-cross hybrids were dominant with main planting technologies characterized by improving farmland condition and increasing planting density. Since the 1970s, single-cross hybrids have been extensively used. The main trends in the development of breeding strategies to increase maize yield potential including disease-resistant gene selection, plant canopy architecture improvement, stay green, and late-maturing. Planting technologies were characterized by the use of chemical fertilizers, irrigation, weed and pest control, higher plant density, and soil quality improvement. However, increased management intensity was observed: planting technologies had shifted from individual techniques to technical integration. For example, chemical fertilizer types were used from sole N in the 1970s to N and P in the 1980s, and even to the combination of NPK in the 1990s and 2000s. Chemical fertilizer rate has greatly increased since the 1990s. (Adapted from Li and Wang, 2009, and reproduced by kind permission of the Chinese Academy of Agricultural Sciences.)
Declining rates of yield increase
Despite the achievement of increased crop production and grain yield per unit area, annual growth rates of cereal yields are gradually declining. For example, the average growth rate of cereal yields decreased from 4% in the 1970s to 1.9% in the 1990s. Over the last 10 years, rice and maize yields have shown declining or stagnant trends in most provinces in China. Inappropriate crop management practices, especially poor nutrient, soil, and water management, are likely to be responsible (Dawe et al., 2000; Peng et al., 2002; Ladha et al., 2003; Zhang et al., 2007; Peng, 2011). Nevertheless, wheat yields have increased in most regions. This may be due to increasing rainfall in the autumn and winter in northern China providing better conditions for wheat growth and increased incentives for farmers to plant grass, fruit trees, and other alternative crops in some regions with low wheat yields.
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The main constraints in further improving crop production
If it is assumed that dietary trends in China continue and that the Chinese population will stabilize at around 1.6 billion after another 20 years, the demand for grain can only be met and the population fed on the remaining arable land if annual crop production can be increased to around 580 Mt. To achieve this, grain yield in China must increase by 2% annually over the next 20 years (Fan et al., 2010). However, further increases in crop production will be more problematic than has been the case for the last 50 years. The availability of water and good soil are major limiting factors for China. Agricultural inputs must be reduced, especially N and phosphorus (P) fertilizer, overuse of which have led to environmental problems such as increased greenhouse gas emissions and severe water pollution in parts of China. Furthermore, climate change will also aggravate crop stresses such as heat, drought, salinity, and submergence in water.
Limited arable land and poor soil quality
A long history of arable farming and steady increases in human population have led to the depletion of arable land reserves in China (Li and Sun, 1990). For example, the population has more than doubled since the 1950s to its current level of 1.3 billion but the total arable land area has expanded by only 29% to the current 134.5 Mha (National Bureau of Statistics of China, 1950–2010). The per capita arable land area is 0.1 ha at present, which is 45% of the world average (Wang et al., 2009a). China has used almost every piece of available land for agriculture. The potential to increase grain area will therefore be limited in the future, and more food will need to be produced from the same amount of (or even less) land. Now, it is clear that it will become more important to adopt technological and policy measures to improve the sustainability of agriculture as well as to increase grain yield per unit area of arable land.
Most arable land in China has poor soil quality, so that it is difficult to achieve high crop yields. For instance, in North-East China, grain yields on low productivity soils were less than 1500 kg ha−1, but the corresponding average value was 7595 kg ha−1 on high productivity land (Fan et al., 2010). The areas of high, medium, and low productivity land account for 28.7, 30.1, and 41.2% of the total arable land in China, respectively (Wang, 2005). Soil organic matter (SOM), a key indicator of soil quality, is still low in Chinese cropping systems although recent studies show SOM in croplands has increased since the 1980s (Xie et al., 2007; Huang and Sun, 2006; Lu et al., 2009; Piao et al., 2009). The average content of SOM in topsoil from cropland is 10 g kg−1 in China compared with 25-40 g kg−1 in European countries and the United States (Fan et al., 2010). Soil degradation, a reduction in soil quality as a result of human activities, is a very serious problem in China. Of the total degraded land area in the world estimated to be 1964 Mha (Oldeman et al., 1991), degraded land in China comprises 145 Mha or 7.4% of the world total (Lal, 2002). The average thickness of topsoil in China over a 50-year period progressively decreased from 22.9 cm in the 1930s to 17.6 cm in the 1980s (Lindert, 2000). Some soils are likely to be even thinner now due to the intensity of erosional and depositional processes.
To enhance crop production in China with efficient resource utilization, improvement in soil quality is critical. By definition, low quality soil has a lower resource buffer than exists in good soil and this decreases the margin of error for nearly all crop management practices. Improving the recycling of organic manures such as animal and human excreta, crop straw and stalks, and green manure can be an important step towards saving natural resources and, simultaneously, stabilizing and optimizing soil quality in crop production systems. Novel soil management practices should be developed and promoted in China. For example, biochar addition to soils is an ancient practice which has recently begun to attract wider notice. Incorporation of biochar represents a means of sequestrating carbon and there is increasing evidence that although there may be some negative effects of incorporation, it can also reduce nutrient leaching and impact positively on the slow release of nutrients to enhance crop yields (Marris, 2006; Lehmann, 2007). Zero-till or reduced till practices, which have rarely been practised in China until now, have reportedly allowed sustained yields with largely positive effects on ecosystem services in some parts of the world. Although there is some doubt about positive effects on greenhouse gas emissions (Rochette, 2008), there are reports of fewer weeds, more beneficial insects and improved water use efficiency resulting from this practice (Hobbs et al., 2008). Reduced till may be especially beneficial on low productivity land.
Water shortage
Of all China's environmental woes, the biggest threat to livelihoods and food security may be looming water shortages (Li, 2010, Peng, 2011). China's total fresh water volume is 2.81×1012 m3, with 2.7×1012 m3 of surface water and 0.83×1012 m3 of groundwater (The Ministry of Water Resources of the People's Republic of China, 2009). Although this water resource is large in absolute value, ranking sixth in the world, the per capita water resource is only 25% of the world average (Wang et al., 2008). China is listed as one of the 13 countries which are shortest of water. Moreover, the distribution of water resources is spatially and seasonally uneven. The north of the country, similar in land area and population to the south, holds only 18% of the total water despite having 65% of the total arable land. By contrast, the south receives water from summer rainfalls, which is often ‘wasted’ through flooding (Piao et al., 2010).
Agricultural water use is a major part of all water used annually. However, increased water shortage associated with overuse of surface water, declining groundwater levels and water pollution is threatening the sustainability of agricultural production. The share of irrigation in total water use in China has declined from 80% in 1980s to 65% in 2009 (The Ministry of Water Resources of the People's Republic of China, 2009). Annual water shortage in agriculture amounts to 30×1010 m3 in China. By 2030, China's total water deficit could reach 130×1010 m3 (Li, 2006).
The outlook for water shortage is especially dire on the North China Plain (NCP), one of the main grain production areas in China. This plain comprises 33.8% of the national arable land, but only has 3.85% of the national water resources. Over the past 40 years, NCP's water table has fallen steadily as some 120×1010 m3 more water has been pumped from the land than the amount replaced by rainfall (Li, 2010). The current plan for a northern diversion of the Yangtze would not, however, benefit agriculture.
Agricultural water use efficiency (WUE) which is defined as grain produced per unit of water consumed is still very low in China due to poor irrigation management practices (Wang et al., 2002; Deng et al., 2006) and lack of investment in infrastructure (Xu and Zhao, 2001; Lohmar et al., 2003). The average WUE of three main grain crops in China is 1.12 kg m−3 with 0.85 kg m−3 for rice, 1.01 kg m−3 for wheat, and 1.51 kg m−3 for maize, respectively (Li and Peng, 2009). Zwart and Bastiaanssen (2004), who reviewed 84 literature sources for experiments around the world which are not older than 25 years, found that the average WUE of rice, wheat, and maize was 1.09, 1.09, and 1.80 kg m-3, respectively. Thus, the overall WUE of grain production in China has fallen behind the world average. This implies that there are tremendous opportunities for China to reduce water consumption with no reduction or even an increase in grain yield (Wang et al., 2002; Hu et al., 2006). However, increasing crop productivity in China still requires innovative approaches to water saving in agriculture.
Low nutrient use efficiency and environmental pollution
Increase in fertilizer nutrient input has made a significant contribution to the improvement of crop yields in China. Fertilizer consumption has increased almost linearly (Fig. 1C). China is currently the world's largest consumer of fertilizer.
Unfortunately, since about 1990, the increase in grain production has been associated with a major decline in fertilizer nutrient use efficiency, especially N, and with widespread environmental damage. According to yearly data for grain yield and synthetic N consumption (National Bureau of Statistics of China, 1950–2010), the partial factor productivity of applied N (PFP, the ratio of yield to the amount of applied N) has been halved over the last 30 years. The recovery efficiency of N (% fertilizer N recovered in above-ground crop biomass, REN) for cereal crops was 35% on average in the 1990s. However, this value has gradually reduced since then and the current REN is 28.3% for rice, 28.2% for wheat, and 26.1% for maize (Zhang et al., 2008a), all of which are lower than the world values (40–60%). Similarly, Ma (2006) reported that the contribution of synthetic N to increased grain yield in China was 30.8% between 1978 and 1984 but declined to 10.4% between 1999 and 2003.
The low nutrient use efficiency may be attributed to fertilizer overuse and high nutrient loss resulting from inappropriate timing and methods of fertilizer application, especially in high-yielding fields. For example, the average amount of N applied for the winter wheat–summer maize double-cropping system in the North China Plain increased from 143 kg ha−1 in 1967 to about 384 kg ha−1 in 1988 and 670 kg ha−1 in 2000 (Zhen et al., 2006). The average fertilizer N application rate for rice of 150 kg ha−1 is higher than in most countries and as much as 67% above the global average, but application rates of 150–250 kg N ha−1 are common in China and can reach 300 kg N ha−1 in some places (Roelcke et al., 2004; Peng et al., 2010). Following an on-farm country-wide survey, Li et al. (2010) found that N fertilizer rates for cereal crops still show an increasing trend: the rates were 204 kg N ha−1 for wheat, 199 kg N ha−1 for maize, and 217 kg N ha−1 for rice in 2000. In 2007, rates had increased to 229 kg N ha−1 for wheat, 237 kg N ha−1 for maize, and 231 N kg ha−1 for rice. Fertilizer application is not often based on real-time nutrient requirements of the crop and/or site-specific knowledge of soil nutrient status. For example, in rice production systems most farmers apply N in two split dressings (basal and top-dressings) within the first 10 d of the rice growing season (Fan et al., 2007). In the intensive wheat–maize system in China, applying large amounts of N fertilizer before planting or at the early growth stage constitutes standard management practice to ensure adequate N for the whole growing season, and this N supply rate is usually about 50% of the total amount given (Cui et al., 2010). This large amount of basal fertilizer-N is prone to loss over an extended period because the plants require time to develop their root systems and a significant demand for N.
Irrational fertilizer utilization has led to substantial environmental pollution. For example, losses of N and P through leaching and runoff have led to drinking water pollution which affects 30% of the population and results in the eutrophication of 61% of lakes in the country. Annual synthetic fertilizer N-induced N2O emission from Chinese croplands has increased from 120 Gg N2O-N yr−1 in the 1980s to 210 Gg N2O-N yr−1 in the 1990s (Zou et al., 2010). Another case study shows that soil pH in the major Chinese crop-production areas has declined significantly from the 1980s to the 2000s because of excessive N fertilizer inputs (Guo et al., 2010).
In conclusion, rationalization of nutrient application to deliver greater nutrient use efficiency and reduced environmental risks is urgently required in China. There is now overwhelming evidence that the quantities of fertilizer applied could be reduced with no detrimental effect on yield. Crop yields might even be increased by a reduced use of fertilizer (Wilkinson et al., 2007; Fan et al., 2008). The great challenge ahead is to determine how crop productivity can be further increased to feed a growing population while minimizing nutrient loss and any subsequent environmental damage for China. In reality, achieving such a target represents one of the greatest scientific challenges facing humankind (Tilman et al., 2002).
The impacts of climate change on agriculture
Climate change and its impacts on crop production are major forces with which China will have to cope in the twenty-first century (Editorial Board of Science Press, 2007; Godfray et al., 2010). Rising temperature, altered rainfall patterns, and more frequent extreme events will increasingly affect crop production, often in those places that are already most vulnerable (Morton, 2007). In China, the clear warming has occurred in recent decades. The average temperature has increased by 1.2 °C since 1961. Precipitation patterns show significant regional trends. The drier regions of northeastern China (including North China and North-East China) are receiving less and less precipitation in summer and autumn. By contrast, the wetter region of southern China is experiencing more rainfall during both summer and winter (Piao et al., 2010). China is at risk from heavy rainfalls, heat waves, and drought (Zhai et al., 2005; Su et al., 2008; Wei and Chen, 2009).
Countrywide, a 4.5% reduction in wheat yields is thought to be due to rising temperatures over the period 1979–2000 (You et al., 2009). Maize yields may also have been sensitive to recent warming, with data from eight Chinese provinces showing a negative response to rising temperature during the period 1979–2002. By contrast, rice yields in the north east appear to have increased by 4.5–14.6% per °C in response to night-time warming between 1951 and 2002 (Tao et al., 2008). However, improvements in crop management have been so influential that they prevent a clear conclusion on the net impact of historical climate change on agriculture in China (Piao et al., 2010). For instance, the autonomous adoption of new crop varieties seems to have compensated for the negative impact of climate change on both wheat and maize production in the North China Plain (Liu et al., 2010).
IPCC global climate models suggest that the climate warming trend will continue and China's average temperature is estimated to increase further by 1–5 °C by 2100 (Meehl et al., 2007). Cereal yields may benefit globally from the synergy of climate change and the fertilizing effect of elevated CO2 (Chavas et al., 2009; Xiong et al., 2009), but the impacts of climate change on crop production is still largely uncertain (Piao et al., 2010). This is because the magnitude of the CO2 fertilization effect on crop yield is still uncertain and a matter of debate (Baker, 2004; Bannayan et al., 2005; Sakai et al., 2006; Li et al., 2007; Ma et al., 2007; Ziska, 2008) and not all the effects of climate, for example, O3 pollution, are included in the current projections (Piao et al., 2010; Wilkinson and Davies, 2010). Another important source of uncertainty in current projections lies in the potential of crop production to adapt to climate change. This implies that the future adverse effect of climate change might be ameliorated by developing and using improved agronomic practices and improved crop germplasm (Lobell et al., 2008).
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The way forward
Intensification leading to increased yields per unit area provided most of the recent doubling of agricultural production. The potential for a further doubling in yields now attracts increasing attention and research. The need to revitalize yield growth with few resources and in a sustainable manner is not under question. Several conceptual frameworks have been proposed for such an advance, such as ‘Ecological Intensification’ (Cassman, 1999), ‘Evergreen Revolution’ (Swaminathan, 2000), and ‘Sustainable Intensification’ (Baulcombe et al., 2009). However, the key question is how are we to achieve this objective in the face of several constraints, including land and water scarcity, environmental degradation, and climate change.
Two issues are emphasized which are crucial if crop productivity is to be increased with efficient resource use while limiting environmental degradation (Fig. 3). The initial challenge is how to apply good governance to change suboptimal crop and soil management practices using existing agricultural sciences and technologies. At the same time, advances in crop productivity will be needed. Two pivotal components are required to follow new trajectories: (i) the development of integrated soil–crop systems management (ISSM), which will address key constraints in existing crop varieties, and (ii) the production of new crop varieties that offer higher yields but use less water, fertilizer or other inputs and are more resistant to drought, heat, submersion, and pests and diseases.
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Fig. 3.
Conceptual model for optimal crop production to achieve synchronously increasing crop productivity, improving resource use efficiency, and environmental protection in China. (A) The current status in crop productivity on farm fields. (B) Scenario of crop productivity upon application of the existing technologies. (C) Scenario of crop productivity upon improved soil and crop management such as integrated soil—crop systems management, in existing crop varieties. (D) Scenario of crop productivity upon improved soil and crop management and improved crop varieties.
Application and extension of existing technologies countrywide
Despite the fact that cereal yields per unit area have shown a remarkable increase since 1961, inappropriate crop management practices are still very common in China today. Available evidence suggests that the yield gap between average farm yields and the regional variety test experiments for major cereal crops are derived from factors such as: (i) low profitability of crop production; (ii) limited access to new agricultural technologies, and (iii) poor soil and crop management by farmers (Lobell et al., 2009; Fan et al., 2010). China has devoted great effort to developing easy-application and low-cost technology in agriculture, and has recently made remarkable progress. For example, since 2003, a strategy has been followed which promotes the integrated use of nutrients from various resources and N management and emphasizes the synchronization of supply and crop demand (Fan et al., 2008). Integrated nutrient management techniques can, on average, increased grain yield by 9.2–14.6%, and raise N fertilizer partial productivity by 10.5–18.5%, compared with conventional agricultural practice with cereal crops (Table 1). In a recent study, a triangular transplanting pattern and split N fertilizer application in the South-West of China has led to 22% increase in rice yields with improved REN of 119% (Fan et al., 2009). It has been well recognized that the WUE can be improved with maintained or even increased crop yield by use of water-saving techniques (Davies et al., 2010). Examples of these are alternate wetting and drying irrigation for rice (Yang and Zhang, 2010), mulching (plastic film or crop straw) for both rice and upland crops (Fan et al., 2005a, b; Zhang et al., 2008b; Wang et al., 2009b), deficit irrigation for upland crops (Fereres and Soriano, 2007), and alternate furrow irrigation for maize (Du et al., 2010). Net reductions in some greenhouse gas emission can potentially be achieved by changing agronomic practices. For example, improving N management can greatly reduce greenhouse gas (GHG) (N2O and CO2) emissions from Chinese croplands (Huang and Tang, 2010).
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Table 1.
On-farm evaluation of performance of integrated nutrient management in yield and partial productivity of N fertilizer (PFP-N) compared with farmers’ conventional practices in major cereal cropping systems in 110 agricultural counties in China
Our view is that the most effective near-term strategy for improving crop productivity for China is application and extension where possible of existing technologies in current agricultural systems. The situation is a little similar to the case of the African smallholder farmers, for example, in Malawi, where maize yields were doubled, even tripled within 2–3 years on a national scale. This was achieved through improved seed and fertilizer use, and good governance from an input subsidy programme supported by both international agencies and local government (Denning et al., 2009).
However, the key issue is how existing agricultural technologies can be quickly accessed and adopted by farmers? Currently, the efficiency of the agricultural technology extension system in China is low. There have been serious difficulties such as lack of investment, and poor training of technicians (Research Centre of Rural Economy of Ministry of Agriculture, 2005). Due to small-scale farming, economic benefits derived from improved management practices generally do not translate into economic incentives which induce farmers to adopt new technologies voluntarily. Therefore, incentive measurements such as farming subsidies may be useful to encourage the farmer to adopt new technologies and change inappropriate management practices. A multiple approach of extension, involving official extension systems, enterprise and non-government organizations (NGOs) such as farmers’ special associations should be pursued simultaneously to promote the dissemination of technologies. A lack of appropriate extension services have been identified as a problem in many farming systems around the world (Baulcombe et al., 2009)
Advances in crop production
Development of integrated soil–crop systems management:
Existing knowledge and technology can, to a certain extent, improve management practices of farmers, but will be unlikely to increase production to the level that is needed to allow a response to international challenges with a doubling of food production by 2030. Greater advances in crop production, which must follow new trajectories, are needed during the next 20 years to ensure a substantial increase in cereal yield and ensure food security. The science of crop and soil management and agricultural practice needs to be given particular emphasis as part of a food security grand challenge (Baulcombe et al., 2009). Despite the enormous importance of the subject and the growing number of specific studies, a multi-disciplinary synthesis of novel understanding and even the established understanding of plant science, agronomy, soil science, and agroecology is scarce in China. The development of more ecologically-influenced agricultural systems that integrate features of traditional agricultural knowledge and add new ecological knowledge into the intensification process will be needed (Matson and Vitousek, 2006).
An ISSM approach is advocated here, addressing the key constraints to yield in existing crop varieties. Such constraints may be low soil fertility, water shortage, low nutrient use efficiencies, and impacts of climate change etc (Fig. 4). In this approach, advances are needed to help us understand coupling mechanisms between plants and climate, plants and soil, plant/microbial biology and ecology, and rhizosphere interaction and management (Zhang et al., 2010). In this area, the key proposals are: (i) take all possible measures to improve soil quality, (ii) integrate the utilization of various nutrient resources and match nutrient supply to crop requirements, and (iii) integrate soil and nutrient management with high yielding cultivation systems (Zhang et al., 2011).
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Fig. 4.
Conceptual model of an integrated soil–crop systems management approach. Note: Temp., temperature; Prec. precipitation. (Figure taken from Chen et al., 2011, and reproduced by kind permission of the National Academy of Sciences.)
Recently, an ‘integrated soil–crop systems of management for maize’ has been demonstrated. This involves the use of the Hybrid-Maize simulation model to maximize the use of solar radiation and the exploitation of temperature changes. To design crop and nutrient management for given ecological conditions, it also uses a root-zone in-season N management strategy to synchronize N supply from soil and fertilizer and the N demand of the crop (Chen et al., 2011). Current studies on the NCP show that this ISSM system could generate 14.6 t h−1 maize grain yields with 265 kg N ha−1 fertilizer application. This yield level is 2.4 times higher than that achieved by farmers’ practices, but the amount of N fertilizer applied is similar to farmers’ practice. Thus, N efficiency is increased 2.4 times above farmers’ practices (Fig. 5).
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Fig. 5.
Performance of an integrated soil–crop systems management (ISSM) in the North China Plain. The ISSM uses the hybrid-maize simulation model to maximize the use of solar radiation and temperature, a root-zone in-season N management strategy by synchronizing the N supply from soil and fertilizer and the N demand of crop. Right: ISSM with grain yield of 14.6 t ha−1, and partial factor productivity of applied N (PFP-N) of 56 kg kg−1, Left: farmer's practices (FP) with grain yield of 6 t ha−1, N fertilizer PFP of 20 kg kg−1.
The above research for maize has illustrated the potential for substantial improvements in yield with higher input efficiency by ISSM approaches. Much more analysis is required for maize, and also for other major crops to establish how yield can be increased as the result of genotype, environment, and management interaction. This type of analysis permits an understanding of the factors that lie behind regional and crop differences in limitations in yield improvement. These insights can then be used to apply more targeted research and develop ISSM as needed.
Continued genetic improvement in crop varieties:
Improving yield potential of crop varieties through plant breeding will be a critical component for future food security (Foulkes et al., 2010). Yield potential is defined as the yield of a crop cultivar when grown in environments to which it is adapted, with nutrients and water non-limiting and pests and diseases effectively controlled (Evans, 1996). When average farm yields reach about 80% of the yield potential ceiling, it becomes more difficult for farmers to sustain yield increases through fine-tuning in soil, crop, water, nutrient, and pest management (Cassman, 1999). Rice yield, especially in those productive regions, appear to be at or near 80% of yield potential in China (Cassman et al., 2003). Recently, it was found that an ISSM approach to management of rice led to a significant increase in N use efficiency but only a small increase in grain yield. This may suggest that further increases in rice yield will mostly depend on the improvement of yield potential. However, there is less certainty over how close we are to delivering yield potential in Chinese maize and wheat production. For example, in the last ten years, wheat yields increased by 2.7% per year in China. Chen et al. (2011) reached nearly 12.8 t ha−1 maize managed by ISSM across several ecological regions of China. This is twice the response to current farmers’ practices (see above). Therefore, closing the current yield gaps for maize and wheat may be a priority for agricultural researchers to ensure food security in China. For a long-term view, plant breeders still need to focus on the traits with the greatest potential to increase wheat and maize yields.
In the context of global environmental changes and other constraints to increase yield for China further, the efficient use of nutrient, especially N, and water have emerged as two key targets. New crop varieties will need to be more efficient in their use of reduced levels of nutrients (Godfray et al., 2010; Tester and Langridge, 2010). Crop varieties with increased tolerance to drought are also required in many parts of the world but particularly in China (Morison et al. 2008).
In the last half-century, traditional plant breeding has occurred almost entirely under management regimes that include fumigated soils with extravagant additions of nutrients and sufficient water (Boyer, 1982). This has potentially selected against traits that allow plants to maintain high net primary productivity (NPP) and yields under non-saturating nutrient conditions (Jackson and Koch, 1997). For example, breeding for increased rice yield potential has been focused on increasing panicle size and improving lodging resistance with thick stems in China. Therefore, rice breeders in China often select progenies with “tolerance to high N” in the breeding nursery with high N application. As a result, the most recently released cultivars and hybrid combinations will not lodge even at a very high N rate (Peng et al., 2002). Research to improve the yield potential of cereal grains in low nutrient environments has been sporadic, with mixed results until a recent concerted effort showed that it is possible to improve the yields of wheat and maize in low input environments (Bänziger and Cooper, 2001; Drinkwater and Snape, 2007). Therefore, there is an urgent need for Chinese breeders to invest more in the capacity to strengthen this strategy.
Traditional breeding methods need to be combined with advanced breeding technologies such as marker-assisted selection (MAS) and genetic modification (GM). This allows for more efficient selection of favourite germplasms across multiple traits and accelerates the breeding cycles. In China, the largest plant biotechnology capacity outside North America is now being built (Huang et al., 2002). Since 2008, the Chinese government has already rolled out a $3.5 billion research and development (R&D) initiative on GM plants (Stone, 2008). Challenges ahead are: (i) to identify the candidate genes and traits valuable for breeding; (ii) incorporate these into elite cultivars and to evaluate their performance under real agricultural field conditions (Zhang, 2007); and (iii) adopt new approaches for generating GM crops to reduce the constraints on regulatory approvals and increase consumer acceptance.
Previous SectionNext Section
Conclusions
Global food production now faces greater challenges than ever before. There is no simple solution to delivering increased crop productivity while improving resource use efficiency and protecting environmental quality. In this review, the focus has been on science and technology, but a broad range of options including social and economic factors such as technology extension and access to technologies by farmers also needs to be pursued. The path from the application of existing technologies to the delivery of improved soil–crop systems management and improved crops must be explored step by step.
Above all, future work will require a mult-disciplinary approach that involves not just soil scientists, agronomists, and farmers, but also ecologists, policy-makers, and social scientists. Our strong view is that governments of the world must allocate more funds to both fundamental plant science and applied crop research and, despite substantial current spending, China is no exception to this. However, global co-operation is needed to avoid duplication of effort and low efficiency and to ensure faster progress.
Previous SectionNext Section
Acknowledgments
We thank the National Basic Research Program of China (973 Program: 2009CB118608), the Special Fund for the Agriculture Profession (201103003), the Innovative Group Grant of the National Science Foundation of China (30821003), the National Natural Science Foundation of China (41171195), the Research Councils UK Science Bridge programme, and the EU DROPS programme, for financial support.
Abbreviations
N
nitrogen
P
phosphorus
SOM
soil organic matter
NCP
North China Plain
WUE
water use efficiency
REN
recovery efficiency of N
PFP
the partial factor productivity
ISSM
integrated soil–crop systems management
NGOs
non-governmental organizations
NPP
net primary productivity
MAS
marker-assisted selection
GM
genetic modification
• © The Author [2011]. Published by Oxford University Press [on behalf of the Society for Experimental Biology]. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com
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