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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.

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.

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.

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.

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

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.