Yingbin Zou

Current Status and Challenges of Rice Production in China

Abstract Rice production in China has more than tripled in the past five decades mainly due to increased grain yield rather than increased planting area. This increase has come from the development of high-yielding varieties and improved crop management practices such as nitrogen fertilization and irrigation. However, yield stagnation of rice has been observed in the past ten years in China. As its population rises, China will need to produce about 20% more rice by 2030 in order to meet its domestic needs if rice consumption per capita stays at the current level. This is not an easy task because several trends and problems in the Chinese rice production system constrain the sustainable increase in total rice production. Key trends include a decline in arable land, increasing water scarcity, global climate change, labor shortages, and increasing consumer demand for high-quality rice (which often comes from low-yielding varieties). The major problems confronting rice production in China are narrow genetic background, overuse of fertilizers and pesticides, breakdown of irrigation infrastructure, oversimplified crop management, and a weak extension system. Despite these challenges, good research strategies can drive increased rice production in China. These include the development of new rice varieties with high yield potential, improvement of resistances to major diseases and insects, and to major abiotic stresses such as drought and heat, and the establishment of integrated crop management. We believe that a sustainable increase in rice production is achievable in China with the development of new technology through rice research.

Improving nitrogen fertilization in rice by site-specific N management. A review

Excessive nitrogen (N) application to rice (Oryza sativa L.) crop in China causes environmental pollution, increases the cost of rice farming, reduces grain yield and contributes to global warming. Scientists from the International Rice Research Institute have collaborated with partners in China to improve rice N fertilization through site-specific N management (SSNM) in China since 1997. Field experiments and demonstration trials were conducted initially in Zhejiang province and gradually expanded to Guangdong, Hunan, Jiangsu, Hubei and Heilongjiang provinces. On average, SSNM reduced N fertilizer by 32% and increased grain yield by 5% compared with farmers’ N practices. The yield increase was associated with the reduction in insect and disease damage and improved lodging resistance of rice crop under the optimal N inputs. The main reason for poor fertilizer N use efficiency of rice crop in China is that most rice farmers apply too much N fertilizer, especially at the early vegetative stage. We observed about 50% higher indigenous N supply capacity in irrigated rice fields in China than in other major rice-growing countries. Furthermore, yield response of rice crop to N fertilizer application is low in China, around 1.5 t ha− on average. However, these factors were not considered by rice researchers and extension technicians in determining the N fertilizer rate for recommendation to rice farmers in China. After a decade of research on SSNM in China and other Asian rice-growing countries, we believe SSNM is a matured technology for improving both fertilizer N use efficiency and grain yield of rice crop. Our challenges are to further simplify the procedure of SSNM and to convince policy-makers of the effectiveness of this technology in order to facilitate a wider adoption of SSNM among rice farmers in China.

Relationship Between Grain Yield and Yield Components in Super Hybrid Rice

Abstract Chinese super hybrid rice breeding project has developed many new varieties with great yield potential. It is controversial which yield component should be emphasized in super hybrid rice production. The present study was conducted to compare super hybrid rice with common hybrid and super inbred rice and analyze contributions of yield components to grain yield of super hybrid rice under experimental conditions, and evaluate relationships between grain yield and yield components of super hybrid rice in farmers paddy fields. Field experiments were done in Changsha, Guidong, and Nanxian, Hunan Province, China, from 2007 to 2009. Eight super hybrid varieties, one common hybrid variety, and one super inbred variety were grown in each location and year. Rice production investigation was undertaken in high-yielding (Guidong), moderate-yielding (Nanxian), and low-yielding (Ningxiang) regions of Hunan Province, China, in 2009. Grain yield and yield components were measured in both the field experiments and rice production investigation. Super hybrid rice varieties outyielded common hybrid and super inbred varieties across three locations and years. Yield potential has been increased by 11.4% in super hybrid rice varieties compared with common and super inbred varieties. The higher yield of super hybrid varieties was attributed to improvement in panicle size. Panicles per m 2 had the highest positive contribution to grain yield with the exception under yield level of 10.0 to 12.0 t ha- 1 , and was positively related to grain yield in farmer“s field at all of the high-, moderate-, and low-yielding regions. Our study suggests that panicle per m 2 ought to be emphasized in super hybrid rice production.

Changes in soil microbial properties with no-tillage in Chinese cropping systems

No-tillage (NT) has revolutionized agricultural systems because it has potential benefits including soil conservation and reduced production costs though saving in fuel, equipment, and labor. Soil quality is of great importance in determining the sustainability of land management systems, and soil microbial properties are becoming increasingly used to assess the effect of farming practices on soil quality due to their quick response, high sensitivity, ecological relevance, and capacity to provide information that integrates many environmental factors. In China, research and application of NT have developed quickly since 1970s. Numerous studies have been conducted in this country to evaluate the effect of NT on soil microbial properties. From these studies, it is evident that NT can lead to an increase in soil microbial size or activity or both and a consequent increase in soil microbial biomass in upland cropping systems. However, there are still several issues that remain unaddressed or inadequately specified. Further investigations are needed (1) to determine the effect of NT on soil microbial diversity by using molecular biological techniques in both upland and rice-based cropping systems; (2) to fully understand the changes of soil microbial properties with NT in rice-based cropping systems, especially for double rice cropping systems; and (3) to clarify the relationship between rhizosphere microbial properties and crop growth in NT rice cropping systems.

Improving Nitrogen Fertilization in Rice by Site-Specific N Management

Excessive nitrogen (N) application to rice (Oryza sativa L.) crop in China causes environmental pollution, increases the cost of rice farming, reduces grain yield and contributes to global warming. Scientists from the International Rice Research Institute have collaborated with partners in China to improve rice N fertilization through site-specific N management (SSNM) in China since 1997. Field experiments and demonstration trials were conducted initially in Zhejiang province and gradually expanded to Guangdong, Hunan, Jiangsu, Hubei and Heilongjiang provinces. On average, SSNM reduced N fertilizer by 32% and increased grain yield by 5% compared with farmers’ N practices. The yield increase was associated with the reduction in insect and disease damage and improved lodging resistance of rice crop under the optimal N inputs. The main reason for poor fertilizer N use efficiency of rice crop in China is that most rice farmers apply too much N fertilizer, especially at the early vegetative stage. We observed about 50% higher indigenous N supply capacity in irrigated rice fields in China than in other major rice-growing countries. Furthermore, yield response of rice crop to N fertilizer application is low in China, around 1.5 t ha − 1 on average. However, these factors were not considered by rice researchers and extension technicians in determining the N fertilizer rate for recommendation to rice farmers in China. After a decade of research on SSNM in China and other Asian rice-growing countries, we believe SSNM is a matured technology for improving both fertilizer N use efficiency and grain yield of rice crop. Our challenges are to further simplify the procedure of SSNM and to convince policy-makers of the effectiveness of this technology in order to facilitate a wider adoption of SSNM among rice farmers in China.

Effect of Nitrogen Regimes on Grain Yield, Nitrogen Utilization, Radiation Use Efficiency, and Sheath Blight Disease Intensity in Super Hybrid Rice

Poor nitrogen use efficiency in rice production is a critical issue in China. Site-specific N managements (SSNM) such as real-time N management (RTNM) and fixed-time adjustable-dose N management (FTNM) improve fertilizer-N use efficiency of irrigated rice. This study was aimed to compare the different nitrogen (N) rates and application methods (FFP, SSNM, and RTNM methods) under with- and without-fungicide application conditions on grain yield, yield components, solar radiation use efficiency (RUE), agronomic-nitrogen use efficiency (AEN), and sheath blight disease intensity. Field experiments were carried out at Liuyang County, Hunan Province, China, during 2006 and 2007. A super hybrid rice Liangyou 293 (LY293) was used as experimental material. The results showed that RTNM and SSNM have great potential for improving agronomic-nitrogen use efficiency without sacrificing the grain yield. There were significant differences in light interception rate, sheath blight disease incidence (DI) and the disease index (ShBI), and total dry matter among the different nitrogen management methods. The radiation use efficiency was increased in a certain level of applied N. But, the harvest index (HI) decreased with the increase in applied N. There is a quadratic curve relationship between grain yield and applied N rates. With the same N fertilizer rate, different fertilizer-N application methods affected the RUE and grain yield. The fungicide application not only improved the canopy light interception rate, RUE, grain filling, and harvest index, but also reduced the degree of sheath blight disease. The treatment of RTNM under the SPAD threshold value 40 obtained the highest yield. While the treatment of SSNM led to the highest nitrogen agronomic efficiency and higher rice yield, and decreased the infestation of sheath blight disease dramatically as well. Nitrogen application regimes and diseases control in rice caused obvious effects on light interception rate, RUE, and HI. Optimal N rate is helpful to get higher light interception rate, RUE, and HI. Disease control with fungicide application decreased and delayed the negative effects of the high N on rice yield formation. SSNM and RTNM under the proper SPAD threshold value obtained highyield with high efficiency and could alleviate environmental pollution in rice production.

Significance, progress and prospects for research in simplified cultivation technologies for rice in China.

SUMMARY Simplified cultivation technologies for rice have become increasingly attractive in recent years in China because of their social, economical and environmental benefits. To date, several simplified cultivation technologies, such as conventional tillage and seedling throwing (CTST), conventional tillage and direct seeding (CTDS), no-tillage and seedling throwing (NTST), no-tillage and direct seeding (NTDS) and no-tillage and transplanting (NTTP), have been developed in China. Most studies have shown that rice grown under each of these simplified cultivation technologies can produce a grain yield equal to or higher than traditional cultivation (conventional tillage and transplanting). Studies that have described the influences of agronomic practices on yield formation of rice under simplified cultivation have demonstrated that optimizing agronomy practices would increase the efficiencies of simplified cultivation systems. Further research is needed to optimize the management strategies for CTST, CTDS and NTST rice which have developed quickly in recent years, to strengthen basic research for those simplified cultivation technologies that are rarely used at present (such as NTTP and NTDS), to select and breed cultivars suitable for simplified cultivation and to compare the practicability and effectiveness of different simplified cultivation technologies in different rice production regions.

Yield Component Differences between Direct-Seeded and Transplanted Super Hybrid Rice

Abstract Super hybrid rice Liangyoupeijiu was grown by transplanting (TP) at a spacing of 20 cm×20 cm with one seedling per hill and by direct-seeding (DS) at a seeding rate of 22.5 kg ha-1 (about 120 seeds m-2) in Changsha, Hunan Province, China in 2004 – 2010. Grain yield and yield components were measured each year, and some physiological factors were determined in 2009. There was no significant difference in mean grain yield across years between DS and TP. DS produced more panicles per m2 but less spikelets per panicle than TP. The differences in number of spikelets per m2, spikelet filling percentage and grain weight between DS and TP were not significant. A large number of panicles per m2 in DS was derived from the increased number of tillers per m2 rather than increased rate of panicle-bearing tillers, and the number of tillers per m2 was mainly determined by the number of hills per m2 because the number of tillers per hill was small in DS plants. Tillering rate, tillering duration as well as carbohydrate and nitrogen metabolism were critical to the reduced number of tillers per hill in DS. In DS plants with fewer spikelets per panicle, the numbers of primary branches and secondary branches per panicle, spikelets per primary and secondary branches, and also panicle length and spikelets per unit panicle length were smaller. These differences were attributed to the smaller source leaf size as well as lower root activity and the nutritional status at panicle initiation.

Comparisons of Yield and Growth Behaviors of Hybrid Rice Under Different Nitrogen Management Methods in Tropical and Subtropical Environments

Abstract To compare the grain yield and growth behaviors of hybrid rice, field experiments were conducted in a subtropical environment in Changsha, Hunan Province, China, and in two tropical environments in Gazipur and Habiganj in Bangladesh during 2009 to 2011. Three hybrid rice cultivars were grown under three nitrogen (N) management treatments in each experiment. The results showed that grain yield was significantly affected by locations, N treatments and their interaction but not by cultivars. Changsha produced 8–58% higher grain yields than Bangladesh locations. Sink size (spikelet number per unit land area) was responsible for these yield differences. Larger panicle size (spikelet number per panicle) contributed to greater sink size in Changsha. Aboveground total biomass was greater in Changsha than in Bangladesh locations, whereas harvest index was higher in Bangladesh locations than in Changsha. Crop growth rate (CGR) was greater at Changsha than Bangladesh locations during vegetative phase, while the difference was relatively small and not consistent during the later growth phases. Higher leaf area index and leaf area duration were partly responsible for the greater CGR in Changsha. Real-time N management (RTNM) produced lower grain yields than fixed-time N management in more than half of the experiments. Our study suggested that further improvement in rice yield in the tropical environments similar to those of Bangladesh will depend mainly on the ability to increase panicle size as well as CGR during vegetative phase, and the chlorophyll meter threshold value used in RTNM needs to be modified according to environmental conditions and cultivar characteristics to achieve a desirable grain yield.

Improving physiological N-use efficiency by increasing harvest index in rice: a case in super-hybrid cultivar Guiliangyou 2

Field experiments were conducted in 2013 and 2014 to compare grain yield, yield attributes and physiological N-use efficiency between two super-hybrid rice cultivars: (1) with the potential of high harvest index and physiological N-use efficiency (Guiliangyou 2) and (2) a representative super-hybrid rice cultivar (Y-liangyou 1). No significant difference in grain yield was observed between Guiliangyou 2 and Y-liangyou 1, whereas there were obvious differences in yield attributes between the two cultivars. Compared with Y-liangyou 1, Guiliangyou 2 had 8–10% lower biomass production but 14–18% higher harvest index. Consequently, physiological N-use efficiency was 18–20% higher in Guiliangyou 2 than in Y-liangyou 1. The higher harvest index in Guiliangyou 2 was mainly attributed to enhanced remobilization of stored reserves in the growing grain than in Y-liangyou 1. Larger panicle neck diameter and thinner leaves were partially responsible for the enhanced remobilization of stored reserves in Guiliangyou 2 as compared to Y-liangyou 1. Our results suggest that Guiliangyou 2 is a unique super-hybrid rice cultivar that achieves high grain yield by increasing harvest index and N-use efficiency.