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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

Quantifying and comparing sustainability indicators are essential to improve the sustainability of smallholder rice cropping systems. The sustainability of rice production systems can be measured based on economic, environmental, social, and institutional indicators. In this paper, we restrict our assessment to economic and environmental indicators. During 2012–2015, farmers were interviewed from 847 households from intensively irrigated rice production regions in Vietnam, Thailand, Indonesia, Myanmar, Sri Lanka, and China. We assessed the sustainability of their farming practices using economic and environmental indicators, i.e., eight of the 12 performance indicators (PIs), as defined by the Sustainable Rice Platform (SRP). Across the six sites, there was a yield gap of 24–42% and a profit gap of 36–82% between the 10% highest-performing farms (mean of top decile) and the mean-performing farms. In addition, there was a labor productivity gap of 12–32%, a nitrogen use efficiency (NUE) gap of 11–20%, a phosphorus use efficiency (PUE) gap of 1–29%, and a water productivity gap of 12–42%. Deliberate modification of conventional practices, including not flooding the field for >30 days before rice planting, incorporating pre-rice crop residue >30 days before planting, and adoption of mid-season drainage or alternate wetting and drying irrigation rather than continuous flood irrigation during the rice growing period, could substantially reduce the greenhouse gas (GHG) emission in irrigated rice fields without yield penalty. There is an urgent need to adopt improved management strategies for nitrogen (N), phosphorus (P), potassium (K) fertilizer, irrigation water-use efficiency, as well as for decreasing pesticide use frequency, without sacrificing profitability and yield. We identified the following priority interventions for each site: a) increasing fertilizer use and adopting higher-yielding varieties in Bago, Myanmar; b) reducing pesticide application rates in Can Tho, Vietnam; c) reducing fertilizer use in Guangdong, China; d) reducing nitrogen and labor use in Yogyakarta, Indonesia; e) reducing fertilizer and water use in Polonnaruwa, Sri Lanka and; f) reducing fertilizer use in Nakhon Sawan, Thailand. Additional uses of the PI analysis clearly demonstrated that rice yield and profit gaps can sustainably be closed by increasing efficiencies that will also lead to reduced environmental footprint.

Stable carbon (C) isotopes provide valuable information to study C incorporation in soil aggregates. Different soil aggregate fractions have different concentrations of soil organic C (SOC), and changes in the abundance of soil C isotopes are closely linked to aggregate turnover. Soils from rice-wheat rotation fields in a long-term (31 years) experiment established in subtropical Central China were analyzed to improve knowledge of the influence of long-term fertilization (e.g. inorganic fertilizers) on the organic C isotope composition of different aggregate fractions. Aggregate-associated C levels and δ13C values (13C to 12C ratios, relative to a standard) ranged from 19.0 to 23.1 g kg−1, and from −24.8 to −23.0‰, respectively, across all treatments. However, SOC concentrations and δ13C values were higher under treatments including inorganic fertilization than under the control (fertilizer-free, CK) treatment. In addition, δ13C values of micro-aggregates ( 0.25 mm), i.e. the micro-aggregates (

Potassium (K) fertilizer additions can result in high crop yields of good quality and low nitrogen (N) loss; however, the interaction between K and N fertilizer and its effect on N2O emissions and associated microbes remain unclear. We investigated this in a pot experiment with six fertilizer treatments involving K and two sources of N, using agricultural soil from the suburbs of Wuhan, central China. The aim was to determine the effects of the interaction between K and different forms of N on the N2O flux and the abundance of nitrifying and denitrifying microbial communities, using static chamber-gas chromatography and high-throughput sequencing methods. Compared with no fertilizer control (CK), the addition of nitrate fertilizer (NN) or ammonia fertilizer (AN) or K fertilizer significantly increased N2O emissions. However, the combined application (NNK) of K and NN significantly reduced the average N2O emissions by 28.3%, while the combined application (ANK) of K and AN increased N2O emissions by 22.7%. The abundance of nitrifying genes amoA in ammonia oxidizing archaea (AOA) and ammonia oxidizing bacteria (AOB) changed in response to N and/or K fertilization, but the denitrifying genes narG, nirK and norl were strongly correlated with N2O emissions. This suggests that N or K fertilizer and their interaction affect N2O emissions mainly by altering the abundance of functional genes of denitrifying microbes in the soil-plant system. The genera Paracoccus, Rubrivivax and Geobacter as well as Streptomyces and Hyphomicrobium play an important role in N2O emissions during denitrification with the combined application of N and K.

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.

A cotton field experiment was conducted to study the effects of plastic film mulching cultivation (PC) and non-mulching cultivation (NPC) on soil carbon content of an Aridisol, classified as a typic natrargid, in Xinjiang Uygher Autonomous Region, China. The use of PC enhanced the stock of soil organic carbon (SOC) at depths of 0–30 cm, but not at depths of 30–70 cm, compared with NPC. Furthermore, PC enhanced the stock of soil inorganic carbon (SIC) at depths of 30–70 cm but not at 0–30 cm. Overall, PC increased the total carbon (TC) stock at depths of 0–70 cm. The TC stock was higher in PC (16.37 kg C m− 2 year− 1) than in NPC (15.89 kg C m− 2 year− 1). The contribution percentage of SIC (52%) to the net soil carbon (C) accumulation was higher than that of SOC (48%). Our results suggested that adoption of PC could be used as an effective way to increase the carbon sequestration of soils under cotton systems in arid areas.

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.

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.

Understanding the responses of soil organic carbon (SOC) distribution to terrain and land use variations is important for making corresponding measures to enhance the soil quality and its carbon storage. The objective of this study was to characterize the spatial distribution of SOC, and analyze the impacts of environment factors on spatial variation of SOC along the Danjiangkou Reservoir area, China. A village size watershed was selected to investigate the SOC distribution under different terrains and land uses. We found that SOC contents followed a log-normal distribution with arithmetic and geometric means of 6.83 g kg −1 and 6.09 g kg−1, respectively, which were moderately variable (Coefficient of Variation = 49.6%) and demonstrated a moderate spatial dependence according to the nugget ratio (37.8%). The experimental variogram of SOC was best-fitted by a spherical model after the spatial outliers had been detected and subsequently eliminated. From the spatial distribution map of SOC contents, the highest SOC content occurred in the center of the watershed, which were along the main water channel or tributaries and normally had lower altitude. While,the lower values of SOC contents were located at the edge of the watershed, such as in the northwest, southwest and southeast of the area where citrus were normally planted. This spatial distribution pattern of SOC was generally consistent with the spatial structure of terrain and land use on the unique terrain of the agriculture-based reservoir area. Therefore, taking terrain and land use type into account when estimating the spatial variation of SOC pool would increase the accuracy in prediction and modeling of SOC movement at the watershed scale. Keywords: Soil organic carbon, Spatial variability, Terrain, Land use, Kriging