Late-season Rice Research Articles

Low fertilizer inputs do not adversely affect yield or performance of Indica hybrid rice

The enhancement of rice production numbers can be achieved by using quality rice cultivars and fertilizers. The double rice cropping model has given rise to an important rice production system in southern China. Exploring the possibility of whether hybrid vigor could make a substantial contribution to early and late season rice production, and how the heterosis expression of hybrid rice functions under different levels of fertilizer application is of great significance. The objective of this study was to evaluate the grain yield and associated plant traits of popular hybrid and inbred rice varieties with large–scale promotion under conditions of customary (high) and combined (low) fertilization in the early and late seasons of 2017–18 in Changsha County, Hunan Province, China. We found that hybrid rice varieties displayed their respective advantages in the early and late rice seasons, but the advantages in their relative yield traits varied. The leading advantages of early season rice were effective panicle number per hill (EPN), 1000–grain weight (KGW), harvest index (HI), yield, and nitrogen use efficiency (NUE), whereas in late season rice, the foremost advantages were grain number per panicle (GNP), HI, yield, and NUE. The EPN was the prime advantage of early season hybrid rice with a short growth period, and the GNP was the main advantage of late season hybrid rice with a long growth period. Notably, the main yield advantage of hybrid rice was stronger under combined (low) fertilization than under customary (high) fertilization. Hence, high yield can be achieved by selecting the best hybrid rice varieties supported by combined fertilization (lower fertilizer use with higher efficiency).

Conversion from double-season rice to ratoon rice paddy fields reduces carbon footprint and enhances net ecosystem economic benefit

Ratoon rice (RR) system is an alternative to the double-season rice (DR) system in central China due to its high annual yield and relatively lower cost and labor requirement. However, the effect of conversion from DR to RR on the carbon footprint (CF) and net ecosystem economic benefit (NEEB) remains largely unknown. Here, we elucidated the effect by using two early-season rice varieties (ZJZ17, LY287) and two late-season rice varieties (WY103, TY390) for the DR system, and two RR varieties (YLY911, LY6326) for the RR system. The six varieties constituted four cropping systems, including DR1 (ZJZ17 + WY103), DR2 (LY287 + TY390), RR1 (YLY911) and RR2 (LY6326). The two-year experiment demonstrated that RR had 27.37% lower annual CF than DR, which could be attributed to the significantly lower annual CF (by 87.27%) of ratoon crop in RR relative to that of the late-season rice in DR. Direct greenhouse gas (GHG) emissions contributed the most to annual CF in both systems, accounting for 43.28% and 35.39% in DR and RR, respectively. Furthermore, conversion from DR to RR system significantly increased annual NEEB by 30.95%. This increase could be attributed to the 20.25% higher annual grain yield of main crop in RR relative to early-season rice in DR, and 75.32% and 87.27% lower annual costs for agricultural inputs and CF of ratoon crop than late-season rice in DR, respectively. Rice variety also showed certain effects on the yields and GHG emissions in different RR systems. Compared with RR1, RR2 significantly increased annual yield and annual NEEB, while decreased annual CF and annual yield-scaled CF (CFy). These findings suggest that the conversion of the DR system to LY6326 RR system may be a highly promising strategy to simultaneously reduce CF, promote NEEB and maintain high grain yield in central China.

Urea Application Rate for Crop Straw Decomposition in Temperate China

Returning straw to the field has become the most important straw utilization method in China. The aim of this research was to study the appropriate amount of nitrogen fertilizer applied when returning the straw of three major crops (wheat, rice, and corn) to the field in areas under low to high yield levels based on the demand of nitrogen for microbial decomposition of straw. Under the condition of returning 100% straw to the field, we developed the formula for calculating the nitrogen application rate and estimated the urea application rate for the three major grain crops. The results showed that returning straws of wheat, early-season rice, middle-season rice and late-season rice, and corn to the field with urea application at the rate of about 150 kg/ha, 120～135 kg/ha, 75 kg/ha, and 75～90 kg/ha, respectively, can provide sufficient nitrogen for microbial decomposition. The urea application rate for returning 100% wheat straw to the field in Huang-Huai-Hai region, Middle-Lower Yangtze region, Loess plateau region, and Northwest arid region was 135–230 kg/ha, 110–190 kg/ha, 85–145 kg/ha, and 95–165 kg/ha, respectively. 52.5–98.5 kg/ha of urea was used for 100% early rice straw returning to the field in Middle-Lower Yangtze region and South China. In addition, the urea application rate for 100% middle-late rice straw returning to the field was 95–180 kg/ha, 100–185 kg/ha, 95–175 kg/ha, and 75–140 kg/ha, respectively. The rate of urea application for 100% corn straw returning to the field in Northeast China, Huang-Huai-Hai, Northwest arid region, and Southwest China was 60–135 kg/ha, 50–115 kg/ha, 60–135 kg/ha, and 45–105 kg/ha, respectively. The amount of nitrogen fertilizer required for the total return of crop straw is not only affected by crop straw C : N, yield per unit area, and ratio of grass to grain but also affected by straw returning mode, regional nitrogen application level, and other factors. Therefore, the amount of nitrogen fertilizer should be adjusted according to the type of cropping system, soil, and climatic conditions of the specific location. This substantial N input for stimulating straw decomposition may favor N losses with nitrate leaching and nitrous oxide emissions and hold a potential for soil N eutrophication in the long term if the level is not carefully adjusted to the N requirement of the subsequent crops and changes in soil organic matter levels.

CO2 fluxes over two paddy fields with different management practices in Southern China

Management practices in paddy fields are changing in the Poyang Lake basin, southern China. Investigating CO2 fluxes in paddy fields under different management practices is essential for understanding regional carbon cycles affected by human activities. Two-year CO2 fluxes were collected from paired eddy covariance (EC) towers at two paddy fields in southern China. One site is under the traditional farmers' management (direct-seeded early rice and transplanted late rice with continuous flooding (CF) irrigation, FM site), while the other site is under the promotion of milk vetch rotation and alternate wetting and drying (AWD) irrigation (PM site). The results showed both sites were CO2 sink with annual cumulative net ecosystem exchange of CO2 (NEE) of -744±21 and -645±22 g C m−2 in 2017, and -794±22 and -766±20 g C m−2 in 2018 at the PM and FM site, respectively. After considering the grain carbon, the CO2 budgets were -142±21 and -59±22 g C m−2 in 2017, and -170±22 and -173±20 g C m−2 in 2018 at the PM and FM site, respectively. The partitioning of NEE into gross primary productivity (GPP) and ecosystem respiration (Reco) showed that the PM site had higher GPP and Reco, which was mainly caused by the milk vetch growth. The AWD irrigation did not affect the field water conditions of the early rice season, but resulted in 16 more drying days and 5.6% more Reco for the late rice season compared to the FM site. Overall, our results imply that the field with milk vetch rotation and AWD irrigation was able to fix more CO2 in 2017, while it had similar CO2 budgets to the traditional farmers’ field when the light and heat conditions during the direct seeded early rice were affluent in 2018.

Effects of iron-modified biochar with S-rich and Si-rich feedstocks on Cd immobilization in the soil-rice system

Fe-modified biochar has been shown to have high sorption ability for cadmium (Cd), while Cd immobilization effects of Fe-modified biochars with Si-rich and S-rich feedstocks have been rarely addressed. To explore the effects of Fe-modified Si-rich and S-rich biochars on Cd translocation in the soil-rice system, a pot experiment was carried out with an acidic Cd-contaminated sandy loam paddy from central South China and a late season rice cultivate during July to November 2018. Rice straw and rice husk were chosen as Si-rich feedstocks, and rape straw was applied as S-rich feedstock, these feedstocks were further collected and pyrolyzed at 450 °C. Pristine and Fe-impregnated rice straw (BRS/BRS-Fe), rice husk (BRH/BRH-Fe) and rape straw (BRE/BRE-Fe) biochars were applied at 0 and 10 t/ha, respectively. The reductions in Cd concentrations in rice grains were 23.8%, 22.3% and 46.1% with treatments of BRE, BRS and BRH, respectively, compared to the control. Compared to other pristine biochars, BRH is more effective in Cd remediation in paddy soil. For Fe-modified biochars, BRE-Fe achieved the highest reductions in Cd concentrations in rice grains with 46.7% and 30.1%, compared with the control and BRE, respectively. BRE-Fe decreased Cd remobilization from leaves to grains. Only BRE-Fe enhanced the formation and Cd sorption capacity of iron plaque. BRS-Fe and BRH-Fe enhanced Fe content in rice plants, which might induce the reduction in iron plaque formation. Fe and S-contained complexes contents increased in the contaminated pristine biochar particles, but reduced in the contaminated BRE-Fe particles. Therefore, Fe modification could not enhance Cd immobilization effect of Si-rich biochar, while Fe modified S-rich biochar has promising potential for Cd remediation with enhancement in iron plaque formation and Cd fixation in rice leaves.

Combined Effects of Soil Amendment and Zinc Fertilizer on Accumulation and Transportation of Cadmium in Soil-Rice System

A field experiment was conducted in moderately and severely Cd contaminated paddy fields in Beishan Town, Changsha City, Hunan Province. This study examined the effects of LS amendment (limestone+sepiolite), in combination with soil application and foliar spraying of Zn fertilizer, on Cd uptake in early and late rice plants. The results showed that: ① the application of LS (2250 kg·hm-2 and 4500 kg·hm-2) significantly increased pH and CEC values in paddy soil during the early and late rice seasons, but the addition of Zn fertilizer (90 kg/hm2) to soil and through foliar spraying (0.2 g·L-1 and 0.4 g·L-1) had no significant effects on the pH or CEC of the soil. ② LS application decreased concentrations of TCLP-Cd and CaCl2-Cd in the soils, by 11.5%-38.8% and 24.0%-81.0%, respectively, while neither of the treatments involving the addition of Zn fertilizer to soil or through foliar spraying had any significant effects on the concentrations of TCLP-Cd and CaCl2-Cd. ③Single treatments involving only LS amendment, Zn fertilizer in soil, or foliar spraying of Zn fertilizer also reduced Cd concentrations in brown rice, but to a lesser degree than the combined treatments. The combined treatments (L1Z1F1, L1Z1F2, L2Z1F1, and L2Z1F2) reduced Cd concentrations in brown rice by 64.9%-67.5% and 56.1%-80.6%, for early and late rice, respectively, while L2Z1F1 (4500 kg·hm-2 LS+90 kg·hm-2 Zn fertilizer+foliar spraying 0.2 g·L-1 Zn fertilizer) resulted in the largest reduction in Cd concentration in brown rice. ④ The Cd/Zn ratio in brown rice was significantly positively correlated with Cd concentrations, indicating that increased Zn concentration in different rice tissues was one of the key reasons for decreased Cd concentration in brown rice. Clearly, as a remediation technology, combining LS amendments with zinc fertilizer is an effective method for achieving the safe utilization of moderately and severely Cd contaminated paddy fields, by effectively inhibiting the uptake, accumulation, and transportation of Cd in rice plants and decreasing Cd concentrations in brown rice.

Comparison of yield performance between direct-seeded and transplanted double-season rice using ultrashort-duration varieties in central China

Labor scarcity requires double-season rice to be planted by direct seeding as an alternative to transplanting. Only ultrashort-duration varieties can be used in direct-seeded, double-season rice (DSD) in central China where thermal time is limited. Whether ultrashort-duration varieties grown in DSD can be as productive and efficient in nitrogen (N) use as transplanted double-season rice (TPD) remains unclear. Field experiments were conducted in Hubei province, central China with two establishment methods (DSD, TPD) and three N rates in the early and late seasons of 2017 and 2018. Nitrogen treatments included zero-N control (N0), total N rate of 60 kg N ha−1 with equal splits at basal, midtillering, and panicle initiation (N1), and weekly N application at 15 kg ha−1 from seeding/transplanting to heading (N2). Both early- and late-season rice under DSD matured within 95 days, on average 9 days shorter than rice under TPD. The grain yield of DSD was comparable to or higher than that of TDP in both seasons, although the daily yield was significantly higher under DSD than under TDP. Before heading, DSD had higher leaf area, stem number, intercepted radiation, and radiation use efficiency than TPD, which compensated for the negative effect of short growth duration on biomass production. Total dry weight and harvest index under DSD were comparable to or higher than those under TDP. In general, the recovery efficiency of fertilizer-N under DSD was higher than that under TPD, but the reverse was true for physiological N use efficiency. Thus, there was no significant difference in agronomic N use efficiency between DSD and TPD. These results suggested that DSD with ultrashort-duration varieties is a promising alternative to TPD in central China for maintaining high grain yield and N fertilizer use efficiency with less labor input.

Effects of Coconut Chaff Biochar Amendment on Methane and Nitrous Oxide Emissions from Paddy Fields in Hot Areas

Based on the rice-vegetable crop rotation model, in-situ measurements of nitrous oxide (N2O) and methane (CH4) emissions were conducted in double-cropping rice fields in Hainan to determine the impact of coconut chaff biochar on greenhouse gas emissions. The experiment involved four treatments:conventional farming fertilization (CON), nitrogen fertilizer combined with 20 t ·hm-2 biochar (B1), nitrogen fertilizer combined with 40 t ·hm-2 biochar (B2), and no nitrogen fertilizer, as the control (CK). The N2O and CH4 emissions were measured using static chamber-gas chromatography during the two paddy seasons, and the global warming potential (GWP) and greenhouse gas intensity (GHGI) were also estimated. The results show that N2O emission dynamics during the early rice season are closely related to the mineral nitrogen content of the soil. The N2O is emitted at the rice seedling and tillering stages after fertilization. The cumulative N2O emission during the early rice season was 0.18-0.76 kg ·hm-2. Compared with the CON treatment, the biochar treatments reduced N2O by 18%-43%, and the B2 treatment resulted in a significant reduction. The addition of biochar may promote the reduction of N2O at the early rice seedling stage and increase N2O emissions by improving the soil NO3--N content at the early rice tillering stage. During the late rice season, N2O is emitted during the heading and maturity stages, and the cumulative N2O emission was 0.17-0.34 kg ·hm-2. The B1 treatment reduced emissions by 37%, and B2 increased emission by only 3%, which is not a significant difference. The peak of CH4 emissions from rice fields appeared in the late phase of the early rice season and prophase of the late rice season. The cumulative emission of CH4 in the early rice season was 3.11-14.87 kg ·hm-2. Compared with CON, the CK treatment increased emission by 39%. The biochar treatment may increase soil aeration and limit the ability of CH4 production in the early rice season, as B1 and B2 treatments reduced CH4 emissions by 28% and 71%. The cumulative CH4 emission in late rice season was 53.1-146.3 kg ·hm-2, and the emission dynamics were significantly positively correlated with NH4+-N content. CK and B1 treatments increased CH4 emissions by 52% and 99%, respectively compared with CON, and the B2 treatment significantly increased CH4 emissions by 176%. Compared with CON, the B1 and B2 treatments increased the yield by 12.0% and 14.3% when applied in the early rice season and by 7.6% and 0.4% when applied in the late rice season, respectively. Due to the increased methane emissions in the late rice season, biochar amendment increased the GWP of the double-cropping rice field, in which the high amount of biochar reached a significant level; different amounts of biochar had no significant effect on the GHGI of the double-cropping rice field. Thus, the application of coconut chaff biochar for the reduction of greenhouse gas emission, from rice fields in hot areas, requires further research.

Optimizing agronomic traits and increasing economic returns of machine-transplanted rice with side-deep fertilization of double-cropping rice system in southern China

• Machine-transplanted rice with side deep fertilization (MRSF) could optimize agronomic traits and yield components. • MRSF increased grain yield by 0.5 %–20.2 % compared with conventional fertilization (CF). • MRSF increased economic return by 9.9 %–31.8 % compared with CF. • MRSF enhanced NPK fertilizer uptake but reduced their application rates. • MRSF combined with decreased nitrogen input by 20–30 % is the appropriate system. Machine-transplanted rice with side-deep fertilization (MRSF) is a recommended strategy to reduce labor cost and nitrogen (N) fertilizer loss in sustainable double-cropping rice production in China. However, the effects of MRSF on double-cropping rice profitability and agronomic traits are unclear. Here, experiments were conducted in two sites at Dongting Lake to determine the yield and economic benefits of MRSF and the optimal N application rate. Six fertilization treatments for early- and late-season rice at various N rates (0/0, 90/99, 105/116, 120/132, 135/149, and 150/165 kg N ha −1 ) were tested. The grain yield of early-season rice (ESR) was the highest (8.7 t ha −1 ) under 70 % deep fertilization (DF), whereas that of late-season rice (LSR) was the highest (6.1 t ha −1 ) under 80 % DF treatment in Miluo. The grain yield of ESR and LSR (7.5 and 7.9 t ha −1 , respectively) were the highest under 80 % DF treatment in Yiyang. Compared with conventional fertilization (CF), MRSF significantly enhanced grain yield by 0.5 %–20.2 % and 5.3 %–15.0 % in Miluo and Yiyang, respectively. The high grain yield under MRSF can be attributed to higher leaf area index, chlorophyll content, nutrient uptake, biomass accumulation, and spikelet number per m 2 . Relative to CF, MRSF increased the panicle bearing tiller rate by 8.4 %–24.6 % (Miluo) and 3.3 %–12.2 % (Yiyang), thereby improving dry matter accumulation and nutrient uptake. Furthermore, the economic benefit under MRSF increased by 9.9 %–31.8 % (Miluo) and 15.0 %–25.7 % (Yiyang) compared with that under CF. N reduction in the MRSF treatments resulted in fewer effective panicles than the 100 % DF treatment. Improved yield and nutrient uptake in double-cropping rice were associated with deep fertilizer placement rather than N application rate. The number of filled grains per panicle had the strongest influence on ESR and LSR grain yield. Overall, MRSF is recommended as an alternative approach to increase grain yield, profitability, and agronomic traits while lowering the N application rate in the double-cropped rice systems near Dongting Lake, southern China.

Water‐use efficiency and greenhouse gas emissions of rice affected by water saving and nitrogen reduction

AbstractWe investigated the effects of reduced irrigation and N application, using green manure and rice straw, on the water‐use efficiency (WUE) and greenhouse gas (GHG) emissions of machine‐transplanted rice (Oryza sativa L.) to provide theoretical and technical guidance for water and N management in double‐cropping rice. Field trials were conducted from 2014 to 2016 using two irrigation methods (flood irrigation, W0; intermittent irrigation, W1) and three N application methods (no nitrogen application, N0; chemical nitrogen constant application, N1; chemical nitrogen reduction combined with green fertilizer and straw, N2). Methane (CH4) and nitrous oxide (N2O) emissions, water consumption, and grain yield were compared for the different treatment measures. Under the same N fertilizer management, intermittent irrigation reduced cumulative emissions of CH4 of early and late season rice by 14.54–37.37% and 16.70–52.25%, respectively, whereas N2O emissions increased by 12.50–35.29% and 23.08–34.09%, compared with flood irrigation. Under identical irrigation conditions, the cumulative CH4 and N2O emissions of early and late rice were N2 > N1 > N0. Compared to W0N1 treatment, W1N2 decreased the annual average water consumption by 4.40 and 5.53% for early and late rice, whereas yield and WUE increased by 4.27 and 3.98% and 9.54 and 9.71%, respectively. In addition, the annual global warming potential and greenhouse gas intensity of double‐cropped rice increased by 47.62 and 41.77%, respectively. The incorporation of green manure and rice straw with reduced N fertilizer application using intermittent irrigation in double rice cropping systems reduced water consumption and increased grain yield but also increased GHG emissions.

Effects of Water and Fertilization Management on CH4 and N2O Emissions in Double-rice Paddy Fields in Tropical Regions

Paddy soils are widely considered a main source of methane (CH4) and nitrous oxide (N2O). Comprehensively evaluating CH4 and N2O emissions from double-rice systems in tropical regions with different water irrigation and fertilizer applications is of great significance for addressing greenhouse gas emissions from such systems in China. In this study, eight treatments were evaluated:conventional irrigation-PK fertilizer (D-PK), conventional irrigation-NPK fertilizer (D-NPK), conventional irrigation-NPK+organic fertilizer (D-NPK+M), conventional irrigation-organic fertilizer (D-M), continuous flooding-PK fertilizer (F-PK), continuous flooding-NPK fertilizer (F-NPK), continuous flooding-NPK+organic fertilizer (F-NPK+M), and continuous flooding-organic fertilizer (F-M). CH4 and N2O emissions in double-rice fields in tropical region of china were monitored in situ by closed static chamber-chromatography method and crop yields as well as global warming potential (GWP) and greenhouse gas intensity (GHGI) were determined. The results show that:① The cumulative CH4 emissions from early rice and late rice are 10.3-78.9 kg·hm-2and 84.6-185.5 kg·hm-2, respectively. Compared with F-PK and F-NPK treatments, F-NPK+M and F-M treatments significantly increased the cumulative emissions of CH4 from early rice season. Under the same fertilizer conditions, the cumulative CH4 emissions under continuous flooding condition were significantly higher than that under conventional irrigation condition. Irrigation and fertilization had extremely significant effects on CH4 emission in the early rice season. ② The cumulative N2O emissions across all treatments were 0.18-0.76 kg·hm-2 in early rice season and 0.15-0.58 kg·hm-2in late rice season, respectively. During early rice season, compared with F-PK, F-NPK significantly increased the cumulative N2O emission; however, compared with D-PK, D-NPK, D-NPK+M, and D-M treatments significantly increased the cumulative N2O emissions. Compared with F-PK, other three treatments under continuous flooding condition significantly increased N2O cumulative emission in late rice season; compared with D-PK, D-NPK, and D-M treatment significantly increased the cumulative N2O emission. Irrigation and fertilization had significant impacts on N2O emissions in late rice season, and fertilization had significant impacts on N2O emission in early rice season. ③ Early and late rice yields were 7310.7-9402.4 kg·hm-2 and 3902.8-7354.6 kg·hm-2, respectively. Early rice yields in both F-NPK and F-M treatments were significantly higher than those in F-PK, D-PK, and D-NPK treatments. Compared with PK, the other three fertilization treatments under the same irrigation condition significantly increased late rice yield. The GWP and GHGI in early rice season were 580.8-2818.5 kg·hm-2and 0.08-0.30 kg·kg-1, respectively. There was no significant difference in GWP among four fertilizer treatments under conventional irrigation condition in the early rice season. However, F-NPK+M and F-M treatments had a significant increase in GWP compared with F-PK. The GHGI in F-NPK+M and F-M treatments were significantly higher than that in other treatments. The GWP and GHGI in late rice season were 3091.6-6334.2 kg·hm-2 and 0.50-1.23 kg·kg-1, respectively. Irrigation significantly affected GWP and GHGI in both early and late rice seasons but fertilization had no significant impact on GWP and GHGI in late rice season. ④ Correlation analysis results showed that soil NH4+-N content and soil temperature below 5 cm soil layer had an extremely significant negative correlation with CH4 emissions. Soil pH was extremely significant positive correlated with CH4 emissions but significantly negatively correlated with N2O emission. Soil NH4+-N and NO3--N concentrations were extremely significantly negatively correlated with N2O emission. Given crop yield, GWP, GHGI, and D-NPK+M can be recommended for local water and fertilizer management to reduce greenhouse gas emissions while maintaining rice yields.

Stronger impact of urea application than incorporation of Chinese milk vetch (Astragalus sinicus L.) on nirK-denitrifying bacterial communities in a Chinese double-rice paddy

ABSTRACT The impact of Chinese milk vetch (Astragalus sinicus L., CMV) incorporation on the nirK-denitrifying bacteria remains unknown. Here, the diversity and the composition of nirK-denitrifying bacterial communities in a double-rice paddy soil were estimated by using Illumina MiSeq sequencing under four fertilisation treatments: no fertilisation (CK), vetch incorporation (CMV), urea (N200) and combined application of vetch and urea (CMV+N100). Compared with CK, N200 increased Shannon index by 10.5% in early rice season, whereas CMV did not change the Shannon index and Chao1 index in both seasons. Proteobacteria and Bradyrhizobium were the most abundant phylum and genus for nirK-denitrifying bacterial communities, respectively. Most variations in abundance of genus components of nirK-denitrifying bacterial communities as affected by the application of urea were detected in late rice season. Principal coordinates analysis showed that effect of CMV on the nirK-denitrifying bacterial communities was weaker than application of inorganic fertiliser (N200 and CMV+N100). Furthermore, redundancy analysis showed that soil was the key factor driving nirK-denitrifying bacterial communities. Our results indicated that the response of the nirK-denitrifying bacterial communities is more sensitive to urea than vetch, suggesting the combination of vetch and urea can be considered as an alternative N resource to inorganic fertiliser.

Effect of substituting nitrogen fertilizer with nitrogen-fixing cyanobacteria on yield in a double-rice cropping system in southern China

The efficient use of nitrogen fertilizer to increase rice production is essential for food security in China. However, the high-input of chemical nitrogen fertilizer has also resulted in soil N losses and environmental pollution. Here we investigated the possibility of using biofertilizer to reduce nitrogen fertilizer use via partial substitution of chemical nitrogen fertilizer (NF) with nitrogen-fixing cyanobacteria (NFC) in red soil. The effects of 100% NF (N10C0) and different substitution rates of NF with NFC (70%, 50%, 30%, and 0% NF plus 30%, 50%, 70%, and 100% N obtained through NFC, labeled as N7C3, N5C5, N3C7, and N0C10, respectively) on rice yield and soil properties were assessed in a double-rice system in greenhouse (six treatments) and field experiments (four treatments) from 2018 to 2019. The N10C0 and N7C3 treatments had no significant effect on grain and straw yields and the nutrient uptake in the greenhouse experiment. The higher substitution treatments could not sustain stable rice yields and the nutrient uptake in either greenhouse or field experiments, which indicated that 30% substitution was appropriate to sustain rice yields. For rice growth traits, higher substitution rates (70–100%) significantly decreased the number of tillers/plant and panicles/plant. In general, soil TN and TP contents in the 0–15 cm layer increased with increasing substitution rate during the early and late rice seasons. Compared to the N7C3 and N5C5 treatments, there were no significant differences in NH4+-N and NO3−-N contents under the N10C0 treatment. Compared to the application of NF as the sole nitrogen source, 30% substitution with NFC could result in monetary savings of approximately 5.77 US$ ha−1. Taken together, our findings demonstrate that substituting NF with an appropriate amount of NFC is beneficial for improving the productivity and sustainability of paddy fields under the double-rice cropping system.

Producing more potatoes with lower inputs and greenhouse gases emissions by regionalized cooperation in China

The Chinese government has projected that 30% of the total potato consumed as a staple food, to meet the yield demand for staple food anticipated by population growth and the recommended tuber consumption for a healthful diet. This policy has significantly promoted potato development in China in recent years. Nevertheless, it is urgent to determine where is it suitable to grow potatoes in China and how to match the future demand for potatoes with lower inputs and environmental costs. In the present study, we compared the integrated efficiencies of the six Chinese potato-production regions by analyzing the normalization scores of the Partial Factor Productivity of new nitrogen (N) and phosphorus (P) inputs (PFPN and PFPP), and greenhouse gas (GHG) intensity (GHGI) indicators, to reply to the first question. Then we predicated the national potato demand based on the historical trends of per capita tuber consumption in China’s urban and rural areas, and estimated the national new N and P inputs, irrigation water consumption, and total GHG emissions when meeting the future potato demand, by scenario analysis, to answer the second question. We found that the Chinese mean per capita tuber consumption is expected to rise to the recommended standard (50 g cap.−1 d−1) by 2026. If current increasing trends continue, potato yield will need to increase by 42.2% relative to 2015. The normalization score of the PFPN, PFPP, and GHGI indicators shows that northeast (NE, 3.0), northwest (NW, 1.4), and southwest (SW, 1.1) China have considerable advantages for growing potatoes, compared to the middle and lower reaches of the Yangtze River (MLRYR, 0.3), southeast China (SE, 0.4) and north China (NC, 0.1). Chinese potato production has the potential for mitigating total potato-sown area, new N and P inputs, irrigation water consumption, and total GHG emissions by 1.6–7.7%, 2.2–11.1%, 2.3–11.2%, 1.0–5.1% and 6.7–33.3%, respectively, relative to a business-as-usual scenario, with no compromise in yield. The combined measures include converting a small proportion of maize land to potato production in the NE, NW and SW regions, properly increasing winter potato planting after the late-rice season in MLRYR, SW and SE, and enhancing potato yield by adopting optimized agricultural practices in the six production regions. The proportions and combinations in which these three measures are promoted depend on the degree of difficulty for each region. Our results can not only help guide potato farming toward lower inputs and cleaner production in China by regionalized cooperation, but can also provide regionalized parameters for resource inputs and GHG emissions for further simulation models of Chinese potato production.

Effects of green manure planted in winter and straw returning on soil aggregates and organic matter functional groups in double cropping rice area.

To explore the mechanism of exogenous organic materials enhancing soil organic carbon and soil fertility, based on a long-term experiment located in Hengyang Red Soil Experimental Station, we examined the effects of winter green manure and straw returning patterns (CK, winter fallow; MV, winter Chinese milk vetch; S, early-season rice straw total returning; DS, early-season and late-season rice straw total returning; SMV, winter Chinese milk vetch + early-season rice straw total returning; DSMV, winter Chinese milk vetch + early-season and late-season rice straw total returning) on soil aggregates and organic functional groups. The results showed that the proportion of super aggregates (>2 mm) and macroaggregates (0.25-2 mm) in double cropping rice soil was the highest with a ratio of about 72.1%-81.8%, and the organic carbon content in the two kinds of aggregates was as high as 12.1-20.7 g·kg-1, accounting for 22.7%-59.0% of the total organic carbon. The main organic functional group in paddy soil was polysaccharides, followed by aliphatic carbon and aromatic carbon. The abundance of all those groups was affected by winter Chinese milk vetch growing and straw returning. Compared with other treatments, DSMV significantly increased the proportion of super aggregates (>2 mm) and macroaggregates (0.25-2 mm) and favored the accumulation of inert carbon such as aromatic carbon in the two kinds of aggregates. DSMV could enhance the stability of soil aggregates and organic matter, which had high potential in the real agricultural production.

Contrasting effects of straw and straw-derived biochar applications on soil carbon accumulation and nitrogen use efficiency in double-rice cropping systems

Increasing cropland soil carbon (C) sequestration and improving crop nitrogen use efficiency (NUE) are vital for sustainable agriculture and environmental protection. The incorporation of straw and application of straw-derived biochar to croplands may help to achieve these goals; however, the long-term effects on soil C sequestration and NUE in double-rice cropping systems are poorly understood. Here, a 6-y field experiment was conducted in a double-rice cropping system to investigate the variations in soil C sequestration and NUE with straw and straw-derived biochar amendments. The treatments were as follows: control with zero nitrogen (N0); conventional chemical fertilizer application (NPK); NPK plus 3 t rice straw dry matter (DM) incorporated per ha−1 season−1 (NPK + LS); NPK plus 6 t rice straw DM incorporated per ha−1 season−1 (NPK + HS); NPK plus 24 t straw-derived biochar DM incorporated per ha−1 (NPK + LC) applied once; and NPK plus 48 t straw-derived biochar DM incorporated per ha−1 (NPK + HC) applied once. Both the straw and biochar additions increased the soil C content in the topsoil, and the NPK + LC treatment sequestered 2.6-fold more soil C than the NPK + HS treatment over the 6-y period, when the input amounts of straw as well as the straw derived C were similar for both treatments. Besides input C directly into the fields, biochar application also increased soil original organic C accumulation in the NPK + LC treatment. Compared with NPK, 50 % and 100 % straw incorporation to the field increased the mean NUE by 22.3 % and 39.8 %, respectively, in the late rice season of 4–6 y, mainly due to increasing soil organic C. Rice grain yields decreased in the early rice season for the first 3 y of the straw treatments but increased in the first season when the biochar was applied, when compared with NPK. However, in the second 3 y after straw application, the grain yield of NPK + HS was significantly higher than that of NPK in late rice season. This investigation has indicated that biochar application had a higher potential in soil carbon sequestration than straw incorporation, and long-term (> 3 y) straw incorporation favored for the enhancement of NUE in paddy fields.

Increases in Genetic Diversity of Weedy Rice Associated with Ambient Temperatures and Limited Gene Flow.

Simple SummaryIncreased genetic diversity in plants is probably associated with greater ambient temperatures. To test this hypothesis, we studied genetic diversity and differentiation of weedy rice populations occurring in the early- and late-season rice cultivation fields in Leizhou of southern China. Data collected from 10-year climatic records showed a higher average temperature in the late rice-cultivation seasons than in the early rice-cultivation seasons. Results obtained based on 27 SSR (simple sequence repeat) loci indicated greater genetic diversity in the late-season weedy rice populations, in addition to the considerable genetic differentiation between the early- and late-season weedy rice populations. We therefore conclude that a higher ambient temperature might be an important factor to promote the formation of genetic diversity in the late-season weedy rice populations.Hypotheses regarding the association of increased species or genetic diversity with gradually warmer regions as a global pattern have been proposed, but no direct and solid experimental data are available to approve the association between plant genetic diversity and ambient temperatures. To test the diversity-temperature hypothesis, we studied genetic diversity and genetic differentiation of weedy rice (Oryza sativa f. spontanea) populations occurring naturally in early- and late-season rice fields that share nearly the same ecological conditions but with slightly different temperatures. Data collected from 10-year historical climatic records indicated a ~2 °C higher average air temperature in the late rice-cultivation seasons than in the early seasons. Results based on molecular fingerprints of 27 SSR (simple sequence repeat) loci showed a higher level of genetic diversity in the late-season weedy rice populations than in the early-season populations. In addition, a positive correlation was detected between the increased proportion of genetic diversity (ΔHe) and genetic differentiation among the weedy rice populations, suggesting limited gene flow. Therefore, we conclude from this study that increased genetic diversity in the late-season weedy rice populations is probably caused by the higher ambient temperatures. This finding provides evidence for the possible association between genetic diversity and ambient temperatures.

Comprehensive effects of combined application of organic and inorganic fertilizer on yield, greenhouse gas emissions, and soil nutrient in double-cropping rice systems

We carried out a 3-year field experiment with three treatments: 1) no fertilizer application (CK), 2) chemical fertilizer application (F), and 3) combined organic and chemical fertilizer (FM) in which the total nitrogen inputs were equal with F (organic fertilizer applied in the early rice season). We evaluated the variations of crop yield, CH4 and N2O emission, and soil nutrient. The results showed that fertilizer application could increase rice yield in both early and late rice seasons. Compared with F treatment, FM treatment increased rice yield by 5.6% and 7.2% for early and late rice, respectively. The enhancement of yield was positively correlated with years. Compared with F treatment, CH4 emission in early rice season, late rice season and whole year in the field in FM treatment was increased by 8.2%, 4.8% and 6.7%, respectively, while the N2O emission was deceased by 31.4%, 5.0% and 18.8%, respectively. Organic fertilizer application reduced the greenhouse gas intensity (GHGI) by 6.8% and 8.5%, but there was no significant differences in global warming potential (GWP) across treatments in 2018 and 2019. Compared with F treatment, the content of organic matter, total nitrogen, available phosphorus and available potassium were increased by 9.7%, 4.1%, 30.9% and 2.5%, respectively. Overall, our results suggested FM application in early rice season is an effective measure to increase crop yield, improve soil nutrient, and reduce GHGI.

Soil Threshold Values for Zn Based on Soil-Rice System and Health Risk Assessment in a Typical Carbonate Area of Guangxi.

Zinc (Zn) is enriched in carbonate area related to geological genesis. To ensure safety of rice, soil threshold values of Zn in soil-rice systems were assessed based on analysis of soil-rice Zn concentration in relation to human health risk. Models for the prediction of Zn concentration of early-season and late-season rice grain were accurately established on the basis of significant partial correlations between log10 (BAFs) and log10 (soil properties). The rice threshold value ranged from 10.67 to 37.90 mg/kg, which might not suitable for male and urban residents. The soil safety threshold of early-season rice and late-season rice in carbonate area ranged from 148-200 mg/kg, 119-200 mg/kg with pH below 6.5, 148-250 mg/kg, 119-250 mg/kg with pH ranging from 6.5 to 7.5; 148-300 mg/kg, 119-300 mg/kg with pH above 7.5, respectively.

Controlled-release N fertilizer to mitigate ammonia volatilization from double-cropping rice

Controlled-release nitrogen fertilizer (CRNF) can effectively enhance crop yields and raise the efficiency of nitrogen fertilizer in agroecosystems. In the present study, the volatilization of NH3 was determined by airflow enclosure chamber technique after the application of different CRNF rates in double-cropping rice fields in southern China for continuous 3 years. The early and late season rice (ESR and LSR) were cultivated each year. The results showed that the total NH3 volatilization losses ranged from 25 to 56 kg N ha−1 in ESR and from 32 to 61 kg N ha−1 in LSR. The loss of N to the total applied N ranged from 12 to 29% in ESR and from 12 to 27% in LSR. The application of CRNF significantly reduced the cumulative NH3 volatilization losses by 20–43% for ESR and by 20–32% for LSR compared with conventional urea application. CRNF in LSR was less effective to reduce NH3 volatilization than that in ESR. Furthermore, the application of 80% of N rate in the form of CRNF gave higher grain yield and apparent nitrogen recovery efficiency (ANRE) than that of application of 100% of N rate from conventional urea. CRNF can effectively reduce NH3 volatilization, and increase rice yield and ANRE. Considering higher price of CRNF, the application of CRNF at lower (20% applied N) rate than conventional urea in LSR may be a reasonable fertilization strategy for improving N use efficiency, environment effectiveness, and sustaining the development of rice production systems in double-cropping rice.