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Improving both grain yield and resource use efficiencies simultaneously is a major challenge in rice production. However, few studies have focused on integrating dense planting with delayed and reduced nitrogen application to enhance grain yield, nitrogen use efficiency (NUE) and radiation use efficiency (RUE) in rice (Oryza sativa L.) in the double rice cropping system in South China. A high-yielding indica hybrid rice cultivar (Yliangyou 143) was grown in field experiments in Guangxi, South China, with three cultivation managements: farmers’ practice (FP), dense planting with equal N input and delayed N application (DPEN) and dense planting with reduced N input and delayed N application (DPRN). The grain yields of DPRN reached 10.6 and 9.78 t ha–1 in the early and late cropping seasons, respectively, which were significantly higher than the corresponding yields of FP by 23.9–29.9%. The grain yields in DPEN and DPRN were comparable. NUE in DPRN reached 65.2–72.9 kg kg–1, which was 61.2–74.1% higher than that in FP and 24.6–30.2% higher than that in DPEN. RUE in DPRN achieved 1.60–1.80 g MJ–1, which was 28.6–37.9% higher than that in FP. The productive tiller percentage in DPRN was 7.9–36.2% higher than that in DPEN. Increases in crop growth rate, leaf area duration, N uptake from panicle initiation to heading and enhancement of the apparent transformation ratio of dry weight from stems and leaf sheaths to panicles all contributed to higher grain yield and higher resource use efficiencies in DPRN. Correlation analysis revealed that the agronomic and physiological traits mentioned above were significantly and positively correlated with grain yield. Comparison trials carried out in Guangdong in 2018 and 2019 also showed that DPRN performed better than DPEN. We conclude that DPRN is a feasible approach for simultaneously increasing grain yield, NUE and RUE in the double rice cropping system in South China.

Short basal internodes are important for lodging resistance of rice (Oryza sativa L.). Several canopy indices affect the elongation of basal internodes, but uncertainty as to the key factors determining elongation of basal internodes persists. The objectives of this study were (1) to identify key factors affecting the elongation of basal internodes and (2) to establish a quantitative relationship between basal internode length and canopy indices. An inbred rice cultivar, Yinjingruanzhan, was grown in two split-plot field experiments with three N rates (0, 75, and 150 kg N ha−1 in early season and 0, 90, and 180 kg N ha−1 in late season) as main plots, three seedling densities (16.7, 75.0, and 187.5 seedlings m−2) as subplots, and three replications in the 2015 early and late seasons in Guangzhou, China. Light intensity at base of canopy (Lb), light quality as determined from red/far-red light ratio (R/FR), light transmission ratio (LTR), leaf area index (LAI), leaf N concentration (NLV) and final length of second internode (counted from soil surface upward) (FIL) were recorded. Higher N rate and seedling density resulted in significantly longer FIL. FIL was negatively correlated with Lb, LTR, and R/FR (P 0.05). Stepwise linear regression analysis showed that FIL was strongly associated with Lb and LAI (R2 = 0.82). Heavy N application to pot-grown rice at the beginning of first internode elongation did not change FIL. We conclude that FIL is determined mainly by Lb and LAI at jointing stage. NLV has no direct effect on the elongation of basal internodes. N application indirectly affects FIL by changing LAI and light conditions in the rice canopy. Reducing LAI and improving canopy light transmission at jointing stage can shorten the basal internodes and increase the lodging resistance of rice. Keywords: Internode elongation, Leaf area index, Light intensity, Light quality, R/FR, Light transmission ratio, Leaf N concentration

Increasing evidence shows that improved nitrogen management can enhance lodging resistance and lower internodes play a key role in the lodging resistance of rice. However, little is known about the cellular and molecular mechanisms underlying the enhanced lodging resistance under improved nitrogen management. In the present study, two rice varieties, with contrasting lodging resistance, were grown under optimized N management (OPT) and farmers’ fertilizer practices. Under OPT, the lower internodes of both cultivars were shorter but the upper internodes were longer, while both culm diameter and wall thickness of lower internodes were dramatically increased. Microscopic examination showed that the culm wall of lower internodes under OPT contained more sclerenchyma cells beneath epidermis and vascular bundle sheath. The genome-wide gene expression profiling revealed that transcription of genes encoding cell wall loosening factors was down-regulated while transcription of genes participating in lignin and starch synthesis was up-regulated under OPT, resulting in inhibition of longitudinal growth, promotion in transverse growth of lower internodes and enhancement of lodging resistance. This is the first comprehensive report on the morpho-anatomical, mechanical, and molecular mechanisms of lodging resistance of rice under optimized N management.

The increasing scarcity of irrigation water necessitates the development of water-saving technology in rice production. Our previous studies have shown that “safe” alternate wetting and drying irrigation (AWD15) can effectively save water, improve water productivity while maintain grain yield compared to continuous flooding (CF) and farmer's water management practice (FP) under a single fertilizer-N input. The objectives of this study are (1) to investigate the superiority of this novel water management practice compared with FP; and (2) to examine whether there is an interaction between water and N input and whether fertilizer-N input needs to be adjusted under AWD15. Two field experiments were conducted during the late cropping seasons of 2014 and 2015. A hybrid rice variety Tianyou3618 was grown under two water management (AWD15 and FP) and four fertilizer-N rates (0, 90, 180, 270 kg N ha−1). Grain yield, water productivity and nitrogen use efficiency were determined. Compared to that of FP, irrigation water input of AWD15 was reduced by 24.1% in 2014 and 71.4% in 2015. The number of irrigations decreased and water productivity increased significantly. No significant differences existed between AWD15 and FP in grain yield, biomass, leaf area index and nitrogen use efficiency. Nitrogen input level had significant effects on yield, biomass, harvest index and nitrogen use efficiency in both years. Grain yield increased with N rate and the optimal N rate was 180 kg N ha−1. No significant interaction was found between water and nitrogen rate regarding biomass production and grain yield. Our results demonstrated that no change in N input is needed under AWD15 condition and AWD15 is advantageous over farmer's water management practice under all N levels investigated in South China. This is the first report on the performance of AWD15 under different fertilizer-N levels in South China.

Reducing water input and CH4 emission while maintaining grain yield is important for the sustainable rice production in south China. However, water-saving technology has not been widely adopted by farmers because of constrains in handling, effectiveness and reliableness. Recently a simplified and easy-to-use alternate wetting and drying technology, namely “safe” AWD, has been developed and recommended to farmers in Asian countries. However, the performance of the safe AWD technology has not yet been evaluated in south China. The objective of this study was to determine whether the safe AWD technology could maintain grain yield with reduced water input and CH4 emission as compared to the conventional farmer’s practice (FP) in south China. Two on-station field experiments were conducted in Guangzhou, Guangdong province during 2014 early and late seasons. In the early season, a hybrid rice variety, Tianyou 3618 (TY3618), was arranged in a randomized complete block design with three water treatments, i.e., AWD15, AWD30 and continuous flooding (CF). In the late season, a split-plot design was employed with four water management (AWD15, AWD30, CF and FP) as main plots and two varieties as subplots. The two varieties were TY3618 and Hefengzhan (HFZ, inbred). Field water level and soil water potential were recorded daily and the CH4 emission was monitored at 7-day intervals. Crop growth, grain yield and water productivities were measured. Results showed that grain yields under AWD15 and AWD30 were comparable with CF, while water input and total CH4 emissions were significantly reduced under the two AWD treatments for both seasons. In the late season, there were no significant differences in grain yield among the four irrigation treatments for HFZ. While for TY3618, grain yield in AWD30 was significantly lower than AWD15. Irrigation water input in AWD15 and AWD30 was 19.4% and 29.7% lower, and irrigation water productivity was 31.7–37.6% and 48.4–53.2% higher than FP, respectively. Over all, no significant differences were found in maximum tiller number, leaf area index, total aboveground dry weight, among the four irrigation treatments for HFZ. While for TY3618, the crop growth rate during grain-filling stage in AWD30 was significantly lower than CF and FP. The CH4 emission under AWD15 and AWD30 were 37.4–45.7% and 61.1–77.1% lower than FP, respectively. Multi-location on-farm comparisons were conducted in north, central, and southwest region of Guangdong province and the results confirmed that AWD15 could obtain comparable grain yield as FP with fewer irrigations. These findings suggested that the AWD15 could be used for water-saving and CH4 emission mitigation while maintaining grain yield in rice production in south China. This is the first report on the performance of safe AWD in south China.

Optimized agronomic management improves nitrogen (N) use efficiency in crop production. However, limited information exists about the effect of improved agronomic practices on the N surplus in double rice cropping system. In this study, we conducted field experiments to evaluate the N surplus for the prevailing farmers’ practices (FP), optimized N management (OPTN) and optimized N and water management (OPTNW) during 2016–2017 in Guangdong province, South China. Grain yield, recovery efficiency (REN), partial factor productivity (PFPN) and agronomic efficiency (AE) of applied N in OPTN and OPTNW were substantially higher than FP. The yearly N surplus and environmental N loss in OPTN were 29.4% and 26.2% lower than FP, respectively. The N surplus in OPTNW was 32.1% lower than FP. Annual N losses resulting from runoff and leaching in OPTNW were reduced by 45.0% and 17.4%, respectively, compared with OPTN. Pooled data of 22 on-farm field trials from six sites in 2014–2017 showed that N input in OPTN and OPTNW was 16.2%–33.8% lower than FP. The tradable N output in OPTN and OPTNW was 9.9% and 9.0% greater than FP, respectively. The N efficiency of cropping systems (NUEc) in OPTN and OPTNW was increased by 39.8% and 42.0%, respectively, compared with FP. N surplus notably increased with the increasing fertilizer N input, and decreased with the increasing tradable N output and NUEc. These results suggest that through optimized N and irrigation management, N surplus and environmental risk can be practically reduced in a double rice cropping system without yield penalty.

Nitrogen non-point pollution and greenhouse gas (GHG) emission are major challenges in rice production. This study examined options for both economic and environmental sustainability through optimizing water and N management. Field experiments were conducted to examine the crop yields, N use efficiency (NUE), greenhouse gas emissions, N losses under different N and water management. There were four treatments: zero N input with farmer's water management (N0), farmer's N and water management (FP), optimized N management with farmer's water management (OPTN) and optimized N management with alternate wetting and drying irrigation (OPTN + AWD). Grain yields in OPTN and OPTN + AWD treatments increased by 13.0–17.3% compared with FP. Ammonia volatilization (AV) was the primary pathway for N loss for all treatments and accounted for over 50% of the total losses. N losses mainly occurred before mid-tillering. N losses through AV, leaching and surface runoff in OPTN were reduced by 18.9–51.6% compared with FP. OPTN + AWD further reduced N losses from surface runoff and leaching by 39.1% and 6.2% in early rice season, and by 46.7% and 23.5% in late rice season, respectively, compared with OPTN. The CH4 emissions in OPTN + AWD were 20.4–45.4% lower than in OPTN and FP. Total global warming potential of CH4 and N2O was the lowest in OPTN + AWD. On-farm comparison confirmed that N loss through runoff in OPTN + AWD was reduced by over 40% as compared with FP. OPTN and OPTN + AWD significantly increased grain yield by 6.7–13.9%. These results indicated that optimizing water and N management can be a simple and effective approach for enhancing yield with reduced environmental footprints.

Millions of Chinese smallholder farmers were persuaded to adopt enhanced management practices, which led to a greater yield, reduced nitrogen fertilizer use and improved environmental performance throughout China. Two and a half billion smallholder farmers collectively manage 60 per cent of the world's arable land. How these farmers perform determines their own livelihood, but also affects global food security and ecosystem health. Here, Fusuo Zhang and colleagues show how some straightforward interventions have substantially improved the productivity and environmental performance of smallholder farmers across China over the past ten years. The team carried out more than 13,000 field trials across China's main agroecological zones and found that a series of management practices, collectively termed integrated soil–crop system management, increased maize, wheat and rice yields, nitrogen-use efficiency and farmer profitability. Scaling this approach up to 20.9 million smallholder farmer across 452 counties boosted grain yields to 33 million tonnes over the ten-year period, and reduced fertilizer use by 1.2 million tonnes and greenhouse gas emissions by up to 13 per cent. Sustainably feeding a growing population is a grand challenge1,2,3, and one that is particularly difficult in regions that are dominated by smallholder farming. Despite local successes4,5,6,7,8, mobilizing vast smallholder communities with science- and evidence-based management practices to simultaneously address production and pollution problems has been infeasible. Here we report the outcome of concerted efforts in engaging millions of Chinese smallholder farmers to adopt enhanced management practices for greater yield and environmental performance. First, we conducted field trials across China’s major agroecological zones to develop locally applicable recommendations using a comprehensive decision-support program. Engaging farmers to adopt those recommendations involved the collaboration of a core network of 1,152 researchers with numerous extension agents and agribusiness personnel. From 2005 to 2015, about 20.9 million farmers in 452 counties adopted enhanced management practices in fields with a total of 37.7 million cumulative hectares over the years. Average yields (maize, rice and wheat) increased by 10.8–11.5%, generating a net grain output of 33 million tonnes (Mt). At the same time, application of nitrogen decreased by 14.7–18.1%, saving 1.2 Mt of nitrogen fertilizers. The increased grain output and decreased nitrogen fertilizer use were equivalent to US$12.2 billion. Estimated reactive nitrogen losses averaged 4.5–4.7 kg nitrogen per Megagram (Mg) with the intervention compared to 6.0–6.4 kg nitrogen per Mg without. Greenhouse gas emissions were 328 kg, 812 kg and 434 kg CO2 equivalent per Mg of maize, rice and wheat produced, respectively, compared to 422 kg, 941 kg and 549 kg CO2 equivalent per Mg without the intervention. On the basis of a large-scale survey (8.6 million farmer participants) and scenario analyses, we further demonstrate the potential impacts of implementing the enhanced management practices on China’s food security and sustainability outlook.

Overuse of nitrogen fertilizer represents a considerable environmental problem globally, but especially in China. Recently, a recent approach on an experimental scale based on the diffusion of the so-called Three-Control Technology (TCT) successfully alleviated the overuse of nitrogen fertilizer in southern China villages in the Guangdong Province, serving as a reference point for other rice-producing countries tackling similar challenges. Here, we assessed the correlation between rice yields and reduction in the use of nitrogen fertilizer following the introduction of TCT. Our study was based on the collection of primary data from 248 households randomly selected from four rice-growing areas of Guangdong Province, China. Our results show that TCT significantly improved the efficiency in the use of nitrogen. Crucially, participating farmers, including both full adopters and partial adopters, were found to fundamentally change their application practices of nitrogen fertilizer, resulting in major improvements in the local soil and water systems.

To understand the genetic basis of nitrogen and phosphorus uptake in the cultivated rice, quantitative trait loci (QTL) analysis for 7 nitrogen and phosphorus uptake-related traits including above-ground biomass (AGB), leaf colour value (SPAD) in heading stage, grain nitrogen concentration (GNC), grain nitrogen content of the plant, total nitrogen content (TNC), grain phosphorus concentration, total phosphorus content (TPC) were conducted using SNP markers in a F2 population derived from a cross between GH128 and W6827. A total of 21 QTLs for nitrogen and phosphorus uptake-related traits distributed in 16 regions along 6 chromosomes were detected using a high density genetic map consisting of 1582 bin markers, with QTLs maximum explaining 8.19% of the phenotypic variation. Nine QTLs (42.9% of total QTLs) were detected on chromosome 2. Among them, two QTL clusters including AGB, TNC, TPC and GNC were also detected in the region bin 140 and bin 146 on the chromosome 2. The distance between the two clusters was only 4.1 cM. The presence of QTL clusters has important significance and could be useful in molecular marker assisted breeding. These genomic regions might be deployed for the simultaneous improving the use efficiency of nitrogen and phosphorus in rice breeding.

International audience; 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.

Variety and nitrogen (N) fertilizer input are the two main factors that influence the development of sheath blight (ShB) caused by Rhizoctonia solani in intensive and high-input rice (Oryza sativa L.) production systems. This study was conducted to determine the varietal difference in ShB development and its association with yield loss across N rates. Two indica inbred and two indica/indica F1 hybrid varieties were grown under 0 and 90 kg N ha−1 in 2003 wet season (WS) and under 0, 75, 145, and 215 kg N ha−1 in 2004 dry season (DS). Inoculation was done in 3.2 m2 in each experiment unit to achieve uniform disease development. Disease intensity was quantified by measuring relative lesion height (RLH) and ShB index (ShBI) of inoculated 10 hills at flowering and 14 days after flowering. Plant traits, grain yield, temperature, and relative humidity inside the canopy were also measured. Consistent and significant varietal differences in ShB intensity were observed across N rates in both WS and DS. Among the four varieties, IR72 and IR75217H had higher RLH and ShBI than PSBRc52 and IR68284H at all N rates. Sheath blight index at 14 days after flowering had the closest correlation with yield loss from ShB. Varieties with taller stature, fewer tillers, and lower leaf N concentration such as IR68284H generally had lower RLH and ShBI, and consequently lower yield loss from the disease. Disease intensity and yield loss from ShB increased with increasing N rates, but the magnitude of yield loss varied among varieties. This suggests that fertilizer N should be managed more precisely and differently for varieties with different plant type in order to reduce the disease development and maximize grain yield in the irrigated rice systems.

Rice in China receives high amounts of fertilizer nitrogen (N) that are often not used efficiently by the crop. A recently developed site-specific N management (SSNM) approach enables the application of fertilizer N to dynamically match the field- and season-specific needs of the rice crop for N. We used farmer participatory research for on-farm testing of N fertilization by standard and farmer-modified SSNM for irrigated rice. Our study was done in 14 villages in four provinces of China in 2003 and 2004. Twelve to 15 farmers were randomly selected in each study village in each year for a dialogue with the research team and for a rapid rural technology assessment (RRTA). Based on the information obtained from the RRTA, modified SSNM (MSSNM) schemes were developed through dialogue between a research team and farmers at a workshop in each village. Modification mainly involved decreasing the number of fertilizer-N topdressings and increasing the rate of basal N application. Among the 514 farmers surveyed during the workshops, 95% were willing to adopt SSNM and MSSNM technologies and 76% were willing to conduct SSNM or MSSNM experiments. More than two-thirds of the farmers preferred adopting MSSNM rather than the standard SSNM. Based on the farmers’ willingness, 144 farmers were selected to conduct an experiment to compare SSNM or MSSNM with the farmers’ fertilizer practices (FFP). The rate and distribution of fertilizer N during the growing season of MSSNM were in between those of SSNM and FFP. SSNM and MSSNM, compared with FFP, maintained rice yields with significantly less fertilizer N and no significant increase in total labour input. The reduction in fertilizer-N input averaged 48 kg N/ha for SSNM and 23 kg N/ha for MSSNM. The study suggests that there is potential for large-scale dissemination of SSNM technology in China.

Meeting the future food security challenge without further sacrificing environmental integrity requires transformative changes in managing the key biophysical determinants of increasing agronomic productivity and reducing the environmental footprint. Here, we focus on Chinese rice production and quantitatively address this concern by conducting 403 on-farm trials across diverse rice farming systems. Inherent soil productivity, management practices and rice farming type resulted in confounded and interactive effects on yield, yield gaps and greenhouse gas (GHG) emissions (N2O, CH4 and CO2-equivalent) with both trade-offs and compensating effects. Advances in nitrogen, water and crop management (Best Management Practices—BMPs) helped closing existing yield gaps and resulted in a substantial reduction in CO2-equivalent emission of rice farming despite a tradeoff of increase N2O emission. However, inherent soil properties limited rice yields to a larger extent than previously known. Cultivating inherently better soil also led to lower GHG intensity (GHG emissions per unit yield). Neither adopting BMPs only nor improving soils with low or moderate productivity alone can adequately address the challenge of substantially increasing rice production while reducing the environmental footprint. A combination of both represents the most efficient strategy to harness the combined-benefits of enhanced production and mitigating climate change. Extrapolating from our farm data, this strategy could increase rice production in China by 18%, which would meet the demand for direct human consumption of rice by 2030. It would also reduce fertilizer nitrogen consumption by 22% and decrease CO2-equivalent emissions during the rice growing period by 7% compared with current farming practice continues. Benefits vary by rice-based cropping systems. Single rice systems have the largest food provision benefits due to its wider yield gap and total cultivated area, whereas double-rice system (especially late rice) contributes primarily to reducing GHG emissions. The study therefore provides farm-based evidence for feasible, practical approaches towards achieving realistic food security and environmental quality targets at a national scale.

Irrigated rice in China accounts for nearly 30% of global rice production and about 7% of global nitrogen (N) consumption. The low agronomic N use efficiency (AEN, kg grain yield increase per kg N applied) of this system has become a threat to the environment. The objective of this study was to determine the possibility to improve the AEN of irrigated rice in China by comparing the farmers’ N-fertilizer practices with other N management strategies such as real-time N management (RTNM) and fixed-time adjustable-dose N management (FTNM). Field experiments were conducted in farmers’ fields in four major rice-growing provinces in China in 2001 and 2002. The same experiment was repeated at the International Rice Research Institute (IRRI) farm in the dry seasons of 2002 and 2003. Agronomic N use efficiency was determined by the “difference method” using an N-omission plot. Maximum yield was achieved mostly at 60–120 kg N ha−1, which was significantly lower than the 180–240 kg N ha−1 applied in farmers’ practices at the Chinese sites. With the modified farmers’ fertilizer practice, a 30% reduction in total N rate during the early vegetative stage did not reduce yield but slightly increased yield and doubled AEN compared with the farmers’ practice at the Chinese sites. The total N rate in RTNM and FTNM ranged from 30 to 120 kg ha−1 at the Chinese sites, but their yields were similar to or higher than that of the farmers’ practice. Compared with the modified farmers’ practice, RTNM and FTNM further increased AEN at the Chinese sites. Overall, FTNM performed better than RTNM at the Chinese sites because the total N rate of FTNM was closer to the optimal level than RTNM. A quantum leap in AEN is possible in the intensive rice-growing areas in China by simply reducing the current N rate and by allocating less N at the early vegetative stage.

The impact of projected global warming on crop yields has been evaluated by indirect methods using simulation models. Direct studies on the effects of observed climate change on crop growth and yield could provide more accurate information for assessing the impact of climate change on crop production. We analyzed weather data at the International Rice Research Institute Farm from 1979 to 2003 to examine temperature trends and the relationship between rice yield and temperature by using data from irrigated field experiments conducted at the International Rice Research Institute Farm from 1992 to 2003. Here we report that annual mean maximum and minimum temperatures have increased by 0.35 degrees C and 1.13 degrees C, respectively, for the period 1979-2003 and a close linkage between rice grain yield and mean minimum temperature during the dry cropping season (January to April). Grain yield declined by 10% for each 1 degrees C increase in growing-season minimum temperature in the dry season, whereas the effect of maximum temperature on crop yield was insignificant. This report provides a direct evidence of decreased rice yields from increased nighttime temperature associated with global warming.

The combination of natural resources, genes, weather and management systems largely determines maximum crop yields. Recently, one of those elements was portrayed as the key to releasing hitherto unrecognized, but significant, untapped growth potential in rice. That element, the system of rice intensification (SRI), is an unconventional management system developed in Madagascar, where it was reported to increase rice yields to ‘fantastic’ levels. To investigate the general potency of the SRI, we conducted experiments in three locations in China comparing yields in conventional and SRI management systems. In addition, we used a theoretical model to predict maximum yields and compared those with reported yields for various locations, including China and Madagascar. Our results imply that the SRI has no inherent advantage over the conventional system and that the original reports of extraordinary high yields are likely to be the consequence of error.

Relative tillering rate (RTR) increases linearly as leaf nitrogen concentration (NLV) increases in rice (Oryza sativa L.) plants. Leaf area index (LAI) has a negative effect on the emergence and survival of tillers. The objectives of this paper were to quantify the interactive effect of NLV and LAI on tillering in irrigated rice. Field experiments were conducted at Philippine Rice Research Institute (PRRI) and International Rice Research Institute (IRRI), Philippines during the dry seasons of 1995 and 1998. Two indica cultivars, IR72 and IR68284H, were subjected to various nitrogen (N) treatments. Number of tillers (including main stems), leaf area, and tissue N concentration were measured. The NLV explained a large part of variation in number of tillers m−2 among treatments. However, the residual, defined as the difference between observed and estimated number of tillers m−2, was negatively correlated with LAI (P

A field study was conducted at the International Rice Research Institute (IRRI), Philippines during the dry seasons of 1997 and 1998 under irrigated conditions. The objectives of this study were to quantify the critical leaf area index (LAIc) at which tillering stops based on the relationship between tillering rate and LAI, and to determine the effect of nitrogen (N) on LAIc in irrigated rice (Oryza sativa L.) crop. Results showed that the relative tillering rate (RTR) decreased exponentially as LAI increased at a given N input level. The coefficient of determination for the equation quantifying the RTR-LAI relationship ranged from 0·87 to 0·99. The relationship between RTR and LAI was affected by N input level, but not by planting density. The N input level had a significant effect on LAIc with a high N input level causing an increase in LAIc. Tillering stopped at LAI of 3·36 to 4·11 when N was not limiting. Under N limited conditions LAIc reduced to as low as 0·98. Transplanting spacing and number of seedlings per hill had little effect on LAIc. Results from this study suggest that LAI and plant N status are two major factors that influence tiller production in rice crops. The possibility that LAI influences tillering by changing light intensity and/or light quality at the base of the canopy where tiller buds and young tillers are located is discussed.

Tillering plays an important role in determining rice grain yield. Several models have been developed to predict tiller production in irrigated rice. In this paper we tested three models using data drawn from a wide range of plant densities and N inputs in two field experiments conducted at the International Rice Research Institute, Philippines during the 1997 and 1998 dry seasons. Two rice cultivars (IR64 and IR72) were used in the experiments. Plant samples were taken at intervals to determine number of tillers, leaf area index (LAI), biomass, relative growth rate (RGR) and leaf N concentration. The models were parameterized using an iteration procedure of the simplex method. Previous models (TIL and SINK) using the original values of parameters for IR64 failed to predict the number of tillers of IR64 in 1997. However, when re-parameterized, both models described the 1997 data well for both cultivars. The two models also predicted fairly well the number of tillers of different transplanting spacing and N input treatments of IR72 in 1998 using IR72 parameters derived from the 1997 experiment. A simple RGR model was comparable with the TIL and SINK models in descriptive and predictive ability. It appears that all three models could be used for predicting tiller production of irrigated rice.

In an earlier greenhouse screening, we identified a local indica cultivar HT54 tolerant to high temperature at both seedling and grain-filling stages. In this study, we develop an optimized procedure for fine assessment of this heat tolerance. The results indicated that HT54 seedlings could tolerate high temperature up to 48 °C for 79h. The genetic analysis of F(1) and F(2) offspring derived from the cross between HT54 and HT13, a heat-sensitive breeding line, reveals that the heat tolerance of HT54 was controlled by a dominant major locus, which has been designated as OsHTAS (Oryza sativa heat tolerance at seedling stage). This locus was mapped on rice chromosome 9 within an interval of 420kb between markers of InDel5 and RM7364. The determined candidate ZFP gene has been confirmed to be cosegregated with a single nucleotide polymorphism (SNP) developed PCR-restriction fragment length polymorphism (RFLP) marker RBsp1407 in its promoter region. Another heat tolerance-associated SNP was identified in the first intron of its 5'-untranslated region. The existence of these SNPs thereby indicated that the OsHTAS locus contains at least two alleles. We named the one from HT54 as OsHTAS ( a ) and the one from HT13 as OsHTAS ( b ). Further dynamic expression analysis demonstrated that OsHTAS ( a ) was actively responsive to 45 °C high temperature stress compared with the OsHTAS ( b ) allele.

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.

The MANAGE-N model (Part I; Ten Berge et al., this issue) was tested by comparing predicted and measured final crop biomass production for 48 rice cultivars under application of 0, 30–40, 60–80 and 90 to 120 kg urea-N per ha at Cuttack, India, during seven consecutive wet seasons. The overall coefficient of correlation between predicted and measured values was 0.93 (p < 0.01). The root mean squared prediction error was 1110 kg biomass per ha in long, 769 kg/ha in medium and 1210 kg/ha in short duration cultivars. Data sets from three other experiments at Nanchang (Jiangxi, China), Jinhua (Zhejiang, China) and Cuttack were used to (a) evaluate model-recommended N management (dose M, timing M) against local state-recommended management (dose S, timing TS)); and (b) determine the yield prediction accuracy of the model. Under dose DS,, timing M increased grain yields significantly (p < 0.05) by 5 to 10% at all sites, relative to S. Application of dose M resulted in further yield increases at Jinhua and Cuttack. Negative effects of high N dose on yield were observed but not predicted at Nanchang and Jinhua. Agronomic efficiency (mean yield increment per kg N applied) was at all sites higher in DSTM and DMTM than in DSTS.. Predicted grain yields differed from observed values by less than the least significant difference between field treatments (LSD, p = 0.05) at Nanchang and Jinhua. Differences were larger than LSD at Cuttack. Simulations further indicate that the time window for N application narrows as N input decreases. Simulated effects of crop duration on yield, N response and optimum N dose are discussed.