Late-season Rice Research Articles

Low greenhouse gases emissions associated with high nitrogen use efficiency under optimized fertilization regimes in double-rice cropping systems

The optimization of fertilization management has the potential to improve crop yield, reduce greenhouse gas (GHG) emissions and enhance nitrogen agronomy efficiency (NAE). However, less is known about whether these benefits can be simultaneously achieved by optimizing fertilization regimes in Chinese croplands. We carried out a year-round field experiment to measure methane (CH4) and nitrous oxide (N2O) fluxes, crop yield and NAE under different fertilization regimes in a subtropical double-rice cropping system. Relative to the conventional chemical N fertilizer application (F), alternative fertilization strategies significantly decreased N2O emissions by 26–78% when averaged across the options of chemical N fertilizer application with reduced rates (RF, 30% off), chemical N fertilizer fully replaced by organic N fertilizer with reduced rates (OF, 30% off) and chemical N fertilizer fully replaced by controlled-release N fertilizer with reduced rates (CF, 30% off), with the largest mitigation potential occurring in OF-treated plots, but comparable extents between the early- and late-rice seasons. Soil CH4 emissions had no consistent response to alternative fertilization regimes, showing contrasting seasonal patterns between in the early- and late-rice seasons. Alternative fertilization options consistently increased NAE by 7–36% and 30–38% in the early- and late-rice seasons, respectively, and this benefit was maximized in OF-treated plots. Direct emission factors of N fertilizer for N2O and the combined greenhouse gas intensity (GHGI) of N2O and CH4 were negatively related to NAE while rice yield was positively related to NAE. Our findings suggest that optimized fertilization strategies especially through the option of chemical N fertilizer fully substituted by organic N fertilizer can reconcile low climatic impact and high NAE, but without compromising yield in double-rice cropping systems.

Comprehensive analysis of SUSIBA2 rice: The low-methane trait and associated changes in soil carbon and microbial communities

Rice cultivation is the primary source of anthropogenic methane (CH4), which dramatically impacts global climate change. A growing body of evidence shows that optimizing photosynthate distribution is important for increasing rice yields and mitigating CH4 emissions. Therefore, the molecular rice breeding with a barley HvSUSIBA2 gene that confers elevated photosynthate flux to grains, is predicted to enhance rice yield and mitigate CH4 emissions in paddies. Here, in a series of field experiments with differences in growing season and rice variety, we show that SUSIBA2 rice reduced CH4 emissions from paddies. SUSIBA2 rice grown in the early rice season and late rice season showed similar mitigation effects, with reduction rates of 50.98% for early rice and 50.97% for late rice. The reduction rate of SUSIBA2 rice during the winter rice season was significantly lower (22.26%) than those of other rice seasons. The reduction rates also varied between rice varieties, and SUSIBA2 japonica rice showed a more significant CH4 mitigation effect than SUSIBA2 indica rice. Further yield-scaled CH4 emission analyses indicated that the SUSIBA2 effect did not mitigate CH4 emissions at the expense of yield. Compared with the wild type, SUSIBA2 rice significantly reduced soil organic carbon properties and the abundance of CH4-related microbes, and altered methanogenic and methanotrophic communities, indicating that SUSIBA2 rice released less carbon to the soil, which reduced CH4 production. Furthermore, a comparison of microbial communities between SUSIBA2 japonica and indica rice revealed different responses of methanogenic and methanotrophic communities, which may partly explain their differences in growth performance and CH4 mitigation effect. Thus, our results show that SUSIBA2 rice substantially reduces CH4 emissions and that SUSIBA2 can potentially mitigate the CH4 emissions of japonica and indica rice under distinct cultivation conditions.

Reducing ammonia volatilization and increasing nitrogen use efficiency in machine-transplanted rice with side-deep fertilization in a double-cropping rice system in Southern China

Ammonia (NH3) volatilization contributes to major nitrogen (N) fertilizer loss in rice fields. Deep fertilization can effectively mitigate NH3 volatilization and increase N use efficiency (NUE) in agroecosystems. However, the effects of machine-transplanted rice with side-deep fertilization (MRSF) on NUE and NH3 volatilization from paddy fields in double-cropping systems are still unknown. In this study, a field experiment was conducted with double-cropping rice fields in two regions in Southern China (Miluo and Yiyang). NH3 volatilization was measured during the rice growing seasons using the continuous airflow enclosed chamber method under different N application rates with MRSF treatments. The results show that NH3 fluxes in rice soil subjected to different N application rates varied. The ratio of total NH3 loss to applied N by conventional fertilization (CF) ranged from 41.2 to 45.3% in the early-season rice (ESR) and from 44.9 to 45.2% in the late-season rice (LSR). Unlike CF treatment, MRSF treatments significantly reduced the cumulative NH3 loss by approximately 24.8–26.9 % in Miluo and 20.1–20.8 % in Yiyang for ESR and by 18.6–23.0 % in Miluo and 20.2–21.8 % in Yiyang for LSR. MRSF treatments increased the content of available N in the soil by 0.2–8.8 % and 0.7–6.6 % in Miluo and Yiyang, respectively. Moreover, this mitigation effect is expected to be more effective with lower N application rates. An NH3 accumulation model described by the Elovich equation was established over the study period; notably, the field observations fitted the calculated values well. MRSF with a 20–30 % reduction in N application rate yielded a higher NUE in terms of N recovery efficiency (NRE), by 11.5–27.9 % and 11.7–23.7 % in Miluo and 8.2–17.0 % and 7.0–25.8 % in Yiyang relative to that of the CF treatment in ESR and LSR, respectively. Overall, MRSF can reduce the N loss through NH3 volatilization while improving content of available N in the soil and NUE; therefore, further maximizing the yield and simplifying fertilization practices for a cleaner rice production in Southern China.

Evaluation of Late-Season Short- and Long-Duration Rice Cultivars for Potential Yield under Mechanical Transplanting Conditions

The development of large-scale farming has encouraged the adoption of mechanical transplanting techniques for rice production. However, the increased farming operation times that often occur under large-scale farming conditions necessitate shortening the duration of rice growth, especially that of late-season rice; therefore, rice cultivars with short growth durations are popular under such conditions. A field experiment using two short-duration rice cultivars (SRCs), i.e., Jiuliangyou 3 and Shengyou 9520, and two long-duration rice cultivars (LRCs), i.e., Shengyou 957 and Tianyouhuazhan, was conducted in the late season in Yongan and Santang, Hunan Province, China in 2017 and 2018. The grain yield and yield attributes were compared between the SRCs and LRCs, showing that the SRCs, which exhibited an 11–12-day shorter growth period, revealed similar grain yield to the LRCs. The SRCs also exhibited a 10–31% higher spikelet filling rate and a 13% higher harvest index than the LRCs. Moreover, the biomass accumulation, crop growth rate, and apparent radiation use efficiency of the SRCs were significantly higher than those of the LRCs during the postheading phase. Our results indicate that the higher spikelet filling rate, the harvest index, and the apparent radiation use efficiency of the postheading period were the underlying factors for the SRCs’ grain yield.

Elastic sowing dates with low seeding rate for grain yield maintenance in mechanized large-scale double-cropped rice production

Elastic sowing dates (ESDs) are correlated with rice grain yield. ESD is the easiest factor for farmers to manipulate in mechanized large-scale farming. In this study, field experiments were conducted over a 2-year period to determine the effects of different sowing dates on growth duration, effective accumulated temperature, and yield attributes in two early- and late-season machine-transplanted rice cultivars. In early rice (ER), a delay in the sowing date led to decreased grain yield and shorter growth duration. In late rice (LR), delayed sowing led to significantly lower grain yield and prolonged growth duration. In LR, significantly positive correlations were detected between effective accumulated temperature in the post-heading stage and both filling ratio and yield. Reproductive redundancy increased markedly in LR, by 7.72% over a 5-day interval. We determined that the ESDs for LR were 10 days later than the control, and that of ER was recommend early sowing rather than late sowing. These findings suggest a new strategy to meet the demands of mechanized large-scale rice farming: the development of thermal sensitive high-yield long-duration ER cultivars and high-yield short-duration LR cultivars.

Early sowing increases grain yield of machine-transplanted late-season rice under single-seed sowing

The shift from hand transplanting to machine transplanting has increased seed sowing rates and hence shortened seedling age and delayed sowing for late-season rice. The development of a single-seed sowing system for machine-transplanted rice can reduce seed sowing rates and provides a possible way to determine the performance of machine-transplanted late-season rice with early sowing. In this study, field experiments were conducted in two years with two rice cultivars to compare seedling shoot biomass at transplanting (TP), crop growth characteristics, and yield attributes in machine-transplanted late-season rice under single-seed sowing between two sowing dates, i.e., 30 June (SD30) and 15 June (SD15). Averaged across two cultivars and two years, seedling shoot biomass at TP under SD15 was 352% higher than those under SD30. Specific leaf weight (SLW) at heading (HD), crop growth rate (CGR) and biomass production during TP to HD, harvest index, and translocation of biomass accumulated before HD to the grain were higher under SD15 than under SD30 by 4–21%. SD15 had a 5–6% higher spikelet-filling percentage and grain yield than SD30. These results suggest that early sowing can improve the CGR during TP to HD by enhancing seedling growth and increasing SLW, and consequently, increase the biomass production during TP to HD, biomass translocation, and grain yield in machine-transplanted late-season rice under single-seed sowing.

Biochar addition leads to more soil organic carbon sequestration under a maize-rice cropping system than continuous flooded rice

Crop rotation of flooded rice with an upland crop like maize on previous continuous paddy soils is an emerging cropping system in South China. A four-year experiment was conducted at a research area in Hunan province, having a long history of double paddy-rice cropping throughout the year. Maize was introduced as an upland crop in rotation with paddy rice, thus providing two parallel cropping systems i.e., the previous flooded rice-rice (R–R) and the new maize-rice rotation (M–R) systems. We used three treatments in both cropping systems; namely, farmer’s practice (without external C input) as a control, straw addition, and biochar addition. The straw and biochar were added to soil in late rice season on an equal C input basis (3000 kg C ha−1yr-1). In the R–R plots, rice straw was added while in M–R plots maize straw was added during late rice field preparation. Our results show that there were no changes in soil organic carbon (SOC) concentration when R–R was replaced by M–R rotation. Straw addition had no effect on SOC but improved late rice yield. Biochar addition significantly increased SOC and late rice yield in both cropping systems. Moreover, biochar addition resulted in a more significant accumulation of SOC (9% higher) in M–R than R–R. Among soil aggregates, only the 0.25–2 mm fraction had a significantly higher SOC concentration with biochar relative to the control and straw return; and this increase was significantly more pronounced under M–R (28% higher) than R–R cropping system. In general, a significantly higher proportion of small macro-aggregates (0.25–2 mm) were found under M–R, while smaller aggregates (0.05–0.25 and <0.05 mm) were more abundant under R–R. δ13C analyses from M–R plots reveal that the quantity of maize-derived C was marginally higher in the straw treatment than control, but this was not reflected in any significant impact on total SOC of the bulk soil or of aggregates. In conclusion, no detectable changes in SOC were observed over four years experimental period following shift from R-R to M-R cropping system. M-R system with biochar addition led to higher productivity and environmental benefits.

Nitrogen and phosphorus runoff losses were influenced by chemical fertilization but not by pesticide application in a double rice-cropping system in the subtropical hilly region of China.

As one of the important nitrogen (N) and phosphorus (P) pollution sources of waters, the paddy water N and P runoff losses are still poorly understood in the double rice cropping system under the interaction of chemical fertilizer and pesticide. In the subtropical hilly region of China, we conducted a 1.5-year continuous and high-frequency monitoring of paddy water N and P concentrations, runoff N and P losses, and grain yield in a double rice-cropping system with different chemical fertilizer and pesticide application rates. The results showed that the high-risk periods for N loss were in the first 5days after the base fertilizer (BF) application and the first 10days after the topdressing fertilizer application in both early and late rice seasons, while the high-risk periods for P loss were in the first 5days after BF application in the early rice season and the first 15days after BF application in the late rice season. The N and P runoff losses in the early rice season were greater than those in the late rice season, due to that the N and P fertilizers use efficiencies were lower, and thus paddy water N and P concentrations were higher in the early rice season. The paddy N and P concentrations and N and P runoff losses increased significantly with increased fertilizer application rates, while the pesticide application rate did not significantly affect N and P losses. Therefore, special effects (e.g., avoiding high irrigation, fertilizer deep application) should be taken during the high-risk periods of N and P losses to reduce the N and P runoff losses in the double rice cropping system, especially in the early rice season. There are also potentials to reduce fertilizer and pesticide input without reducing rice grain yield for the double rice cropping system in the subtropical hilly region of China.

Impacts of 1.5 and 2.0°C global warming on rice production across China

The primary goal of the 2015 Paris Climate Agreement is to limit future global warming to less than 2.0 °C above pre-industrial levels. Thus, understanding the impacts of relatively low warming level on rice production is essential to future food security of China. Here, with the latest global warming scenarios from the Half a degree Additional warming, Projections, Prognosis and Impacts (HAPPI) project, we assess the impacts of the two HAPPI scenarios (1.5 °C and 2.0 °C warming above pre-industrial levels) on rice production for two major rice-cropping systems, including single-season rice and double-season rice (early- and late-season rice). A multi-model ensemble approach (three crop models and four climate models) was used to predict the changes of rice production across the main rice-growing regions of China under 1.5 °C and 2.0 °C warming scenarios. Results show that increases in mean rice growing season temperature (GST) under 1.5 °C and 2.0 °C warming scenarios are highest in central China. Likewise, the increase in GST during the reproductive growth phase (GST-r) is greater than that during the vegetative growth phase (GST-v). The whole rice-growing season duration (GSD-w) is shortened by about 3–15 and 4.5–18 days under 1.5 °C and 2.0 °C warming scenarios, respectively. Most of the shortening in GSD-w occurs due to a shortening of the vegetative growth phase (GSD-v). Using a stepwise multiple regression procedure, we find that the yield changes of single-season rice and late-season rice are significantly negatively correlated with both GST-r and GSD-v. When examining early-season rice, yield changes are significantly negatively correlated with both GST-v and GSD-r. Under 1.5 °C and 2.0 °C warming scenarios without carbon dioxide (CO2) fertilization effects, the impact of warming has a negative effect across the main rice-growing regions of China. The reduction is greater in the southern area than that in the northern section of the study regions. However, climatic warming has a positive effect on rice yield in low thermal regions of northeast China with CO2 fertilization effects. In other regions, CO2 fertilization will not offset the negative impacts on rice production due to climatic warming. Our results will aid in making the future adaptation strategies to moderate the negative impacts of climate warming on regional rice production across China.

Co-incorporation of green manure and rice straw improves rice production, soil chemical, biochemical and microbiological properties in a typical paddy field in southern China

The cultivation of green manure or rice straw returns in southern China increases crop yields and soil fertility. Few studies have reported the effects of combining both management techniques on rice performance and soil fertility. A 3-year field study was carried out to analyse the impacts of the co-incorporation practice on soil microbial and biochemical parameters as well as crop yield. Five treatments were tested: (i) no-fertilizer (CK); (ii) chemical fertilizer (F); (iii) F plus green manure (FM); (iv) F plus rice straw (FS); (v) F plus green manure plus rice straw (FMS). The results showed that incorporation of green manure and/or rice straw increased double rice yields by 4.1% (FM), 4.7% (FS) and 9.6% (FMS) compared with F. The FMS treatment enhanced soil organic C (SOC), total N (TN), mineral N (Nmin), and available K (AK) levels by combining the advantage of FM in increasing TN and Nmin and the advantage of FS in increasing SOC and AK in comparison with F. The incorporation of green manure and/or rice straw stimulated microbial growth (total phospholipid fatty acids, PLFAs) and altered the soil microbial community structure relative to F, in which FMS had the greatest effect. The enzyme activities of β-glucosidase, β-cellobiosidase, N-acetyl-glucosaminidase, L-leucine aminopeptidase and phosphatase were higher in the green manure and/or rice straw application treatments than in the F treatment in the order FM ≈ FS < FMS. The partial least squares path model (PLS-PM) analysis indicated that green manure mainly influenced the abovementioned indices in the early rice season, while the effects of rice straw lasted until the late rice season. Our results suggest that co-incorporation of green manure and rice straw is a more effective practice for improving soil fertility and rice yields.

Grain filling of early-season rice cultivars grown under mechanical transplanting.

High yields of mechanized intensive rice-based cropping systems, e.g. double-season cropping using early- and late-season rice, are important to ensure national food security in China. However, few studies addressing the relationship between grain weight and grain yield of early-season rice under machine-transplanted conditions. A field experiment was conducted to determine the critical grain-filling characteristics and related physiological aspects that contribute to high grain weight in machine-transplanted early-season rice. The results showed that grain yield was significantly positively correlated with grain weight but not with panicles per m2, spikelets per panicle, and spikelet-filling percentage. Furthermore, this study demonstrated that there was a significant positive correlation between grain weight and mean grain-filling rate, which was significantly positively correlated with harvest index and grain cytokinin content. These results indicate that high grain-filling rate driven by good transport of assimilates to grains and strong grain sink strength is responsible for high grain weight in machine-transplanted early-season rice.

Experimental warming reduces fertilizer nitrogen use efficiency in a double rice cropping system

Climate warming significantly affects nitrogen (N) cycling, while its effects on the use efficiency of fertilizer N are still unclear in agroecosystems. In the present study, we examined for the first time the response of fertilizer N use efficiency to experimental warming using &lt;sup&gt;15&lt;/sup&gt;N labeling with a free-air temperature increase facility (infrared heaters) in a double rice cropping system. &lt;sup&gt;15&lt;/sup&gt;N-urea was applied in micro-plots to trace the uptake and loss of fertilizer N. Results showed that moderate warming (i.e. an increase of 1.4°C and 2.1°C in canopy temperature for early and late rice, respectively) did not significantly affect grain yield and biomass. Warming significantly reduced N uptake from fertilizer for both early and late rice, while increased N uptake from soil. The N recovery rate of fertilizer was reduced from 35.5% in the control and to 32.3% in the warming treatments for early rice and from 47.2% to 43.1% for late rice, respectively. Warming did not affect fertilizer N loss rate in the early rice season, whereas significantly increased it from 38.9% in the control and to 42.7% in the warming treatments in the late rice season, respectively. Therefore, we suggest that climate warming may reduce fertilizer N use efficiency and increase N losses to the environment in the rice paddy.

Effects of Vegetation Strips, Fertilizer Levels and Varietal Resistance on the Integrated Management of Arthropod Biodiversity in a Tropical Rice Ecosystem.

Integrated biodiversity management aims to conserve the beneficial species components of production ecosystems and reduce the impacts of pests. In 2011 and 2013, experiments were conducted at Los Baños, Laguna, Philippines, to compare arthropod communities in rice plots and on levees with and without vegetation strips. Vegetation strips included spontaneous weeds, sesame and okra (2011), or mung bean (2013). The plots were treated with one of three nitrogen levels and in one experiment were planted with planthopper-resistant (IR62) and susceptible (IR64) rice varieties. Parasitoids and predators of lepidopteran pests and of the ricebug, Leptocorisa oratorius, were more abundant in high-nitrogen rice plots where their prey/hosts also had highest densities. Planthoppers and leafhoppers were more abundant in low-nitrogen plots. Weedy and sesame/okra bunds provided habitat for a range of natural enemies including spiders, parasitoids and predatory bugs, but did not have higher pest numbers than cleared bunds. Higher abundances of the predator Cythorhinus lividipennis and higher parasitism of planthopper (Nilaparvata lugens) eggs by Anagrus sp. were associated with sesame/okra bunds in late season rice plots. Mung bean also provided habitat for key predators and parasitoids that spilled over to adjacent rice; however, mung bean was also associated with higher numbers of lepidopteran and grain-sucking pests in the adjacent rice, albeit without increased damage to the rice. For ricebug in particular, damage was probably reduced by higher parasitoid:pest ratios adjacent to the vegetation strips. Varietal resistance and mung bean strips had an additive effect in reducing abundance of the planthopper Sogatella furcifera and the leafhopper Nephotettix virescens. Reduced numbers of these latter pests close to vegetation strips were often compensated for by other plant-sucking bugs, thereby increasing the intensity of potentially stabilizing interspecific interactions such as competition. We highlight the benefits of diversifying rice landscapes and the need to optimize vegetation strips, e.g., by including lepidopteran trap-plants, for intensive rice production systems.

Influence of green manure and rice straw management on soil organic carbon, enzyme activities, and rice yield in red paddy soil

Both the quantity and quality of organic amendments can influence the accumulation of soil organic carbon (SOC) and agroecosystem functioning. However, the evidences of the effect of combination of quantity and quality of organic amendments on the paddy soil quality and rice yield are scarce. An ongoing field experiment was conducted in Hunan province of China to investigate the effect of different Chinese milk vetch (Astragalus sinicus L.) and rice (Oryza sativa L.) straw management practices on the soil biochemical properties and rice yield. The experiment consisted six treatments: applying Chinese milk vetch (MV), applying early-season rice straw (S), applying early-season and late-season rice straw (DS), applying Chinese milk vetch and early-season rice straw (SMV), applying Chinese milk vetch, early-season and late-season rice straw (DSMV), and unamended organic amendment (CK). Compared with CK, SOC content was significantly increased by 13.0%, 18.5%, 11.1%, 12.3%, and 23.0% for the MV, S, DS, SMV, and DSMV treatments, respectively. No significant correlation was found between SOC content and yearly carbon inputs. Application of organic amendments increased soil hydrolase activities (β-D-cellobiosidase, β-1,4-glucosidase, β-1,4-xylosidase, β-1,4-N-acetyl-glucosaminidase and phosphatase). The geometric mean of the assayed hydrolases followed the order: S > DSMV > SMV > DS > MV > CK. Phenol oxidase was significantly higher in CK than in the applied organic amendment treatments. The lowest ratio of β-1,4-glucosidase: phenol oxidase occurred in the S treatment, suggesting that S treatment decreased microbial substrate use efficiency. The yearly average rice yield was increased by 18.6%, 8.5%, 12.3%, 14.6%, and 24.1% for MV, S, DS, SMV, and DSMV treatment with respect to CK. There was no significant correlation between SOC content and rice yield. In general, after 4-year cultivation, our results highlight the effect of quality of organic amendments on the chemical properties of SOC and its nutrient supply. Applying high quantities of diverse organic amendments is suggested to increase SOC content and rice yield in red paddy soil.

Seasonal differences in N release dynamic of controlled-released urea in paddy field and its impact on the growth of rice under double rice cropping system

Single basal application of bulk blending urea(BBU) which consists of both controlled-released urea(CRU) and conventional urea(U) has been proposed to facilitate fertilization and lower cost of CRU. Nevertheless, its effect on the growth, yield and N use efficiency(NUE) of rice in double rice cropping system under subtropical environment are still unknown. Field experiments were conducted at two different sites(Taishan county and Wengyuan county) simultaneously in Guangdong province to investigate the effects of single basal application of two types of BBU(P-BBU which consists of parabolic pattern CRU, and S-BBU which consists of sigmodial pattern CRU) on soil available N, grain yield and NUE. Conventional high-yield fertilization treatment with four split applications of U(FP) and no-N treatment(CK) were established as controls. The results demonstrated that BBU could provide similar or more adequate N nutrient for rice with FP during late rice season. BBU performed comparably to or better than FP on soil NH4+-N, dry matter, grain yield and NUE during late rice season. During early rice season, BBU performed comparably with FP on soil NH4+-N, N content of rice, dry matter, grain yield and NUE at Taishan site, while at Wengyuan site, it significantly reduced soil NH4+-N, N content of rice, dry matter and NUE compared with FP, and reduced grain yield slightly. Release tests in water and paddy field were conducted in order to evaluate the releasing dynamics of parabolic and sigmodial pattern CRU. Results showed that the N release rate of CRU in paddy field during early rice season was significantly slower than that during late rice season. This was closely correlated with the changing pattern of accumulated temperature. The N release rate of parabolic CRU in paddy field was faster and more sensitive to changing temperature than sigmodial CRU. Non-linear regression analysis shows that the N release patterns of sigmodial CRU in paddy fields were more close to N uptake of rice during both rice seasons. The grain yield of rice and NUE in S-BBU was higher slightly than P-BBU during both rice seasons. These results demonstrated that BBU obtained similar grain yield in double rice cropping system in South China, and S-BBU treatment is better for N requirement of rice during both seasons. Future studies should focus on optimizing and customizing the blending ratio of BBU for each rice season in double rice cropping system to increase crop yield and the robustness of BBU to changing weather conditions.

Leguminous Cover Crop Astragalus sinicus Enhances Grain Yields and Nitrogen Use Efficiency through Increased Tillering in an Intensive Double-Cropping Rice System in Southern China

Chinese milk vetch (Astragalus sinicus L., vetch), a leguminous winter cover crop, has been widely adopted by farmers in southern China to boost yield of the succeeding rice crop. However, the effects of vetch on rice grain yield and nitrogen (N) use efficiency have not yet been well studied in the intensive double-cropped rice cropping systems. To fill this gap, we conducted a three-year field experiment to evaluate the impacts of the vetch crop on yields and N use efficiency in the subsequent early and late rice seasons. With moderate N input (100 kg N ha−1 for each rice crop), vetch cover significantly increased grain yields by 7.3–13.4% for early rice, by 8.2–10.4% for late rice, and by 8.6–11.5% for total annual rice production when compared with winter fallow. When rice crops received an N input of 200 kg N ha−1, vetch cover increased grain yields by 5.9–18.4% for early rice, by 3.8–10.1% for late rice, and by 6.2–11.3% for annual rice production. Moreover, comparable grain yields (11.9 vs. 12.0 Mg ha−1 for annual rice production) were observed between vetch cover with moderate N and fallow with added N fertilizer. Yield components analysis indicated that the increased tillering number was the main factor for the enhanced grain yields by vetch cover. Vetch cover with moderate and higher N input resulted in higher agronomic N use efficiency and applied N recovery efficiency compared with the fallow treatments. Here, our results showed that vetch as a winter cover crop can be combined with reduced N fertilizer input while maintaining high grain yields, thus gaining a more sustainable rice production system.

Availability of existing early-season rice cultivars as resources for selecting high-yielding short-duration cultivars of machine-transplanted late-season rice

AbstractHigh-yielding short-duration cultivars are required due to the development of mechanized large-scale double-season rice (i.e. early- and late-season rice) production in China. The objective of this study was to identify whether existing early-season rice cultivars can be used as resources to select high-yielding, short-duration (less than 115 days) cultivars of machine-transplanted late-season rice. Field experiments were conducted in Yongan, Hunan Province, China in the early and late rice-growing seasons in 2015 and 2016. Eight early-season rice cultivars (Liangyou 6, Lingliangyou 211, Lingliangyou 268, Xiangzaoxian 32, Xiangzaoxian 42, Zhongjiazao 17, Zhongzao 39, and Zhuliangyou 819) with growth durations of less than 115 days were used in 2015, and four cultivars (Lingliangyou 268, Zhongjiazao 17, Zhongzao 39, and Zhuliangyou 819) with good yield performance in the late season in 2015 were grown in 2016. All cultivars had a growth duration of less than 110 days when grown in the late season in both years. Zhongjiazao 17 produced the maximum grain yield of 9.61 Mg ha−1 with a daily grain yield of 108 kg ha−1 d−1 in the late season in 2015. Averaged across both years, Lingliangyou 268 had the highest grain yield of 8.57 Mg ha−1 with a daily grain yield of 95 kg ha−1 d−1 in the late season. The good yield performance of the early-season rice cultivars grown in the late season was mainly attributable to higher apparent radiation use efficiency. Growth duration and grain yield of early-season rice cultivars grown in the late season were not significantly related to those grown in the early season. Our study suggests that it is feasible to select high-yielding short-duration cultivars from existing early-season rice cultivars for machine-transplanted late-season rice production. Special tests by growing alternative early-season rice cultivars in the late season should be done to determine their growth duration and grain yield for such selection.

Interactive effects of liming and straw incorporation on yield and nitrogen uptake in a double rice cropping system

Soil acidification and low fertility limit crop productivity in red paddy soils. Liming and straw incorporation are effective practices to alleviate soil acidification and improve soil fertility, respectively, while their interaction is still unclear. A four-year field experiment was conducted in a double rice cropping system with red paddy soil in Jiangxi province to examine the interactive effect of liming and straw incorporation on rice yield and nitrogen (N) uptake from 2015 to 2018. Either liming or straw incorporation increased grain yield and N uptake in both early and late rice seasons. Lime application increased yield and N uptake by 10.7% and 15.5% under straw incorporation, while by 4.4% and 9.7% with straw removal in the early rice season, respectively. In contrast, liming enhanced yield and N uptake by 18.7% and 24.6% in the straw-incorporated treatments in the late rice season, respectively, whereas only by 10.5% and 5.7% in the straw-removed treatments. The effect of liming on enhancing grain yield, N uptake and soil pH for both early and late rice diminished in the present of time. Neither soil organic matter nor total N content was significantly affected by liming after the four-year experiment. Straw incorporation significantly increased soil organic matter, but had no effect on total N. Therefore, limes should be applied along with straw incorporation to simultaneously increase double rice yield, alleviate soil acidification, and improve soil fertility on acidic paddies. Besides, our results suggest that limes should be applied approximately every four years in the double rice cropping system with acidic red soil.

Greenhouse gas emissions from a rice-rice-green manure cropping system in South China

Green manure crops play an important role in reducing chemical fertilizer applications while enhancing soil fertility. However, the effects of winter-planted green manure crops on rice paddy greenhouse gas (GHG) emissions are poorly understood. Based on a 35 years experiment, we analyzed the impacts of a rice-rice-green manure cropping system on rice yield and GHG emissions during both rice and winter-green manure seasons. Our experiment consisted of four treatments: ryegrass-rice-rice (Ry-R-R), milkvetch rice-rice (Mv-R-R), rapeseed-rice-rice (Rp-R-R) and fallow-rice-rice (Fa-R-R), arranged in a completely randomized design. Incorporation of winter-planted green manure had more impacts on yield and CH4 emission in the early rice season than in the late rice season. Compared to the Fa-R-R, the Mv-R-R, Rp-R-R, and Ry-R-R systems increased annual yield by 15.4%, 11.8%, and 6.1%, respectively. However, Ry-R-R and Rp-R-R significantly increased annual CH4 emissions by 116.73% and 52.45%, respectively, while Mv-R-R reduced CH4 emissions by 16.3%, compared to Fa-R-R. The CH4 emissions showed significant positive correlations with dissolved organic carbon, as well as the biomass and C/N ratio of the incorporated green manure plant materials. Although green manuring reduced N2O emissions in both winter and rice seasons, there was no significant difference in annual cumulative N2O emissions among the treatments. Ry-R-R and Rp-R-R increased annual yield-scaled GWP by 102.6% and 34.8%, respectively, while Mv-R-R was 27.8% lower, compared to the Fa-R-R. Our results suggest that Mv-R-R is the best choice of cropping system for yield sustainability and eco-friendly rice production over the long-term.

Effects of Different Fertilization Modes on Greenhouse Gas Emission Characteristics of Paddy Fields in Hot Areas

Greenhouse gas emissions studies commonly focus on temperate and subtropical regions. As a result, greenhouse gas emissions from agricultural soils in tropical areas are often neglected. Therefore, greenhouse gas fluxes in a Hainan paddy field under different fertilization regimes were studied. This research provides an accurate assessment of CH4 and N2O emissions from paddy fields in China and sound mitigation measures. Through static chamber/gas chromatography techniques, CH4 and N2O emissions, global warming potential (GWP), and greenhouse gas emissions intensity (GHGI) in late rice season under five fertilizer treatments were measured. The treatments included:control (CK), conventional treatment (CON), optimized fertilization treatment (YH), optimized fertilization combined with controlled slow-release fertilizer treatment (ZHY1), optimized fertilization combined with controlled slow-release fertilizer and organic fertilizer treatment (ZHY2). The results showed that the cumulative CH4 emissions in the CK, CON, YH1, ZYH1, and ZYH2 treatments were 175.70, 60.30, 63.00, 62.80, and 56.60kg·hm-2, and the cumulative N2O emissions were 0.78, 3.40, 1.03, 1.44, and 0.44kg·hm-2, respectively. Correlation analysis showed that soil temperature and Eh were the main factors driving CH4 emission. Compared with CK, CON, YH, and ZYH1, the yield of rice in ZYH2 treatment increased by 29.69%, 11.81%, 6.74%, and 10.36%, respectively. While GWP of ZYH2 decreased by 64.80%, 43.23%, 12.93%, and 15.15%, and GHGI decreased by 76.49%, 52.52%, 20.54%, and 23.87%, respectively. Therefore, in terms of yield and greenhouse gas emissions, optimal fertilization combined with sheep manure and slow release fertilizer treatment (ZYH2) is feasible in this region.