Rice-based Rotations Research Articles

Carbon footprint research and mitigation strategies for rice-cropping systems in China: a review

Reducing greenhouse gas (GHG) emissions and quantifying the carbon footprint (CF) of rice-cropping systems in the context of food security is an important step toward the sustainability of rice production. Exploring the key factors affecting emission reduction in rice production is important to properly evaluate the impact of China’s rice-cropping systems on global climate change. This review provides an overview of the direct and indirect CF in rice-cropping systems; analyzes the influencing factors in terms of rice-based cropping systems, varieties and agronomic practices; and proposes mitigation strategies. Different studies have shown that direct and indirect GHG emissions in rice-based cropping systems accounted for 38.3 to 95.5% and 4.5 to 61.7% of total emissions, respectively. And the CFs of ratoon rice, rice–wheat, rice–maize, rice–rapeseed, and rice–fish systems ranged from 316,9 kg CO2-eq kg−1 to 258,47 kg CO2-eq kg−1, which are lower than that in a double-rice planting system. High-yielding rice, drought-resistant rice, and other hybrids can mitigate GHG emissions from paddy fields by 3.7 ~ 21.5%. Furthermore, organic matter, water, tillage, straw incorporation, conservation tillage, reduced nitrogen fertilizer use, and added biochar and methane inhibitors could reduce emissions. Therefore, through reasonable agronomic measures, variety selection and optimal layout of rice-based rotation systems, the carbon neutral rate of rice production can be improved to help the national carbon sequestration and emission reduction target.

Contrasting regulating effects of soil available nitrogen, carbon, and critical functional genes on soil N2O emissions between two rice-based rotations

Contrasting regulating effects of soil available nitrogen, carbon, and critical functional genes on soil N2O emissions between two rice-based rotations

Long-term impact of legume-inclusive diversification and nutrient management practices on phosphorus dynamics in alkaline Fluvisol

An insight into the dynamics of soil phosphorus (P) pools with long-term cropping/management practices would help in designing efficient and sustainable management module(s). The study aimed to investigate the long-term impact of diversified rice-based rotations and variable nutrient management practices on the dynamic composition of P pools and their influence on systems’ base-crop productivity in an alkaline soil of Indo-Gangetic plain (Fluvisol). Treatments consisted of four rotations [rice–wheat (R–W), rice–wheat–mungbean (R–W–Mb), rice–wheat–rice–chickpea (R–W–R–C), rice–chickpea (R–C)] each with three nutrient treatments [control (CT), integrated nutrient management (INM), sole-chemical fertilizers (CF)]. Notably, R–C exhibited higher levels of bioavailable-P (soluble-P, Ca2-P, labile-Po), particularly in subsurface soil depth (0.2–0.4 m) compared to other rotations. Likewise, the inclusion of chickpea every alternate year (R–W–R–C) resulted in higher Ca2-P (40%), labile-Pi (15%), labile-Po (11%), and moderately labile Po (8%) compared to R–W rotation demonstrating an increased significance of chickpea in maintaining a favorable soil P regime in alkaline soil. Both R–C and R–W–R–C reduced the surface-to-subsurface depth ratio (SSBR) of soluble-P and Ca2-P while increasing the ratio for microbial biomass P. Even with a suboptimal fertilizer-P rate, INM significantly increased soluble-P (4–33%), labile-Po (13–17%), microbial biomass P (10–26%), moderately labile-Po (4–17%) compared to CF and exhibited higher SSBR values. Correlation analysis demonstrated the substantial influence of very-labile carbon, microbial and phosphatase activities on P availability. The treatment-induced changes in labile-P pools significantly influenced rice (base-crop) yields. In conclusion, chickpea-inclusive diversification and INM could be a sustainable approach to enhance P bioavailability and crop productivity in tropical rice soils.

Optimal Straw Retention Strategies for Low-Carbon Rice Production: 5 Year Results of an In Situ Trial in Eastern China

Crop straw retention in the rice-based rotation cropland has been widely accepted as an effective method to improve soil quality in China. Rice–wheat rotation cropland is one the most prevalent rice-based rotation patterns, where it only exploits a small proportion of the total agricultural land yet feeds the majority of the Chinese population. Previous studies indicated that the incorporation of fore-rotating crop straw can effectively facilitate soil carbon sequestration in rice paddy fields. However, the application of crop straw may increase methane (CH4) emissions from rice paddies due to the anaerobic soil condition. To mitigate CH4 emissions from rice paddies while still preserving their soil carbon sequestration ability, a field experiment was conducted in the 2012–2016 rice growing seasons to determine the optimal low-carbon crop straw retention strategy. Five treatments with different wheat straw retention strategies were employed in this study, including non-fertilization and non-straw (Control), conventional fertilization without straw incorporation (CF), conventional fertilization with wheat straw incorporation (FS), slow-release fertilizer combined with wheat straw (SFS), and conventional fertilization with wheat-straw-derived biochar (FB). The results indicated that FS, SFS, and FB treatments significantly increased soil carbon sequestration in comparison with CF treatment. However, the increment of soil carbon sequestration was offset by raw wheat straw induced excess CH4 emissions under FS and SFS treatments. In contrast, the application of wheat-straw-derived biochar significantly promoted soil carbon sequestration, but showed no significant effect on CH4 emissions. Collectively, to the farmers, who aim to achieve agricultural carbon neutrality, the application of straw-derived biochar is worthy of consideration in rice cultivation processes.

Reduced tillage and crop diversification can improve productivity and profitability of rice-based rotations of the Eastern Gangetic Plains.

Intensive rice (Oryza sativa)-based cropping systems in south Asia provide much of the calorie and protein requirements of low to middle-income rural and urban populations. Intensive tillage practices demand more resources, damage soil quality, and reduce crop yields and profit margins. Crop diversification along with conservation agriculture (CA)-based management practices may reduce external input use, improve resource-use efficiency, and increase the productivity and profitability of intensive cropping systems. A field study was conducted on loamy soil in a sub-tropical climate in northern Bangladesh to evaluate the effects of three tillage options and six rice-based cropping sequences on grain, calorie, and protein yields and gross margins (GM) for different crops and cropping sequences. The three tillage options were: (1) conservation agriculture (CA) with all crops in sequences untilled, (2) alternating tillage (AT) with the monsoon season rice crop tilled but winter season crops untilled, and (3) conventional tillage (CT) with all crops in sequences tilled. The six cropping sequences were: rice-rice (R-R), rice-mung bean (Vigna radiata) (R-MB), rice-wheat (Triticum aestivum) (R-W), rice-maize (Zea mays) (R-M), rice-wheat-mung bean (R-W-MB), and rice-maize-mung bean (R-M-MB). Over three years of experimentation, the average monsoon rice yield was 8% lower for CA than CT, but the average winter crops yield was 13% higher for CA than CT. Systems rice equivalent yield (SREY) and systems calorie and protein yields were about 5%, 3% and 6%, respectively, higher under CA than CT; additionally, AT added approximately 1% more to these benefits. The systems productivity gain under CA and AT resulted in higher GM by 16% while reducing the labor and total production cost under CA than CT. The R-M rotation had higher SREY, calorie, protein yields, and GM by 24%, 26%, 66%, and 148%, respectively, than the predominantly practiced R-R rotation. The R-W-MB rotation had the highest SREY (30%) and second highest (118%) GM. Considering the combined effect of tillage and cropping system, CA with R-M rotation showed superior performance in terms of SREY, protein yield, and GM. The distribution of labor use and GM across rotations was grouped into four categories: R-W in low-low (low labor use and low GM), R-M in low-high (low labor use and high GM), R-W-MB and R-M-MB in high-high (high labor use and high GM) and R-R and R-MB in high-low (high labor use and low GM). In conclusion, CA performed better than CT in different winter crops and cropping systems but not in monsoon rice. Our results demonstrate the multiple benefits of partial and full CA-based tillage practices employed with appropriate crop diversification to achieve sustainable food security with greater calorie and protein intake while maximizing farm profitability of intensive rice-based rotational systems.

Intensification of rice-pasture rotations with annual crops reduces the stability of sustainability across productivity, economic, and environmental indicators

CONTEXTIntegrated crop-livestock systems are facing the pressure to intensify worldwide, yet decoupling crops and livestock can lead to specialized systems relying on greater external inputs and potential negative externalities. OBJECTIVEOur goal was to compare rice-pasture, as the business-as-usual rotation, with two intensified systems, rice-soybean and rice-cover crop, to address the following objectives: 1) quantify partial carbon footprint (CF) including both crop and livestock, 2) develop a multi-criteria performance index based on productivity, economic, and environmental indicators at the systems-level, and 3) evaluate the stability of this index over the study period. METHODSTo understand how increasing the frequency of annual grain crops influences whole-system sustainability, we evaluated 10 productivity, economic and environmental indicators as well as a multi-criteria performance index and its stability in three rice-based rotation systems over 7 years in Uruguay. Treatments were: (a) rice–pasture [a 5 yr rotation of rice–ryegrass (Lolium multiflorum Lam.)–rice, then 3.5 yr of a perennial mixture of tall fescue (Festuca arundinacea Schreb.), white clover (Trifolium repens L.), and birdsfoot trefoil (Lotus corniculatus L.)], (b) rice–soybean [a 2-yr rotation of rice–ryegrass–soybean (Glycine max [L.] Merr.)– Egyptian clover (Trifolium alexandrinum L.)], and (c) rice–cover crop (an annual rotation of rice–Egyptian clover). RESULTS AND CONCLUSIONSRice-soybean had medium productivity and energy use, resulting in the highest nitrogen and energy use efficiency and among the lowest yield-scaled C footprint. Field greenhouse gas emissions and embodied energy in fuel and agrochemicals were similar in rice-pasture and rice-soybean, but the increase in soil organic carbon in pasture rotating with rice was able to offset this by almost 50%. Rice-cover crop had the highest economic incomes but also the highest input costs, translating into the lowest gross margin. Although the rice-soybean and rice-pasture had a similar gross margin, the variability in rice-pasture was lower and with lower input costs. Rice-soybean and rice-pasture had a multi-criteria performance index 65% higher than rice-cover crop (0.35). Rice-pasture had the highest overall stability across four different stability parameters calculated. We conclude that the intensification of rice-pasture with annual crops could reduce the stability of sustainability without increasing economic performance, even for rice-soybean that showed the best the multi-criteria performance but with less stability across indicators. SIGNIFICANCEThe findings of this study demonstrate how the integration of rice and pastures with livestock achieves the best combination of stability across profitability and environmental performance, thus mitigating vulnerability to external stressors.

Long-term Conservation Agriculture increases sulfur pools in soils together with increased soil organic carbon compared to conventional practices

Long term depletion of sulfur (S) in soils is common in many cropping systems globally, and especially in intensive, rice-based rotations in Asia. We hypothesized that Conservation Agriculture (CA) practices (minimal soil disturbance and crop residue retention) will increase S in soils primarily through changes in soil organic carbon (SOC). A long term experiment was sampled after 24 crops of continuous practice of (A) contrasting soil disturbance (strip planting = SP and conventional tillage = CT) and (B) two levels of crop residue retention (low residue = LR and high residue = HR). Sulfur fractions and dynamics in soil at five depths (0–5, 5–15, 15–30, 30–45 and 45–60 cm) along with bulk density (BD), pH, SOC, total nitrogen (TN) and extractable nutrients were determined. Levels of total S (584 – 668 mg kg−1), organic S (50.0– 153 mg kg−1), available S (7.9 – 21.6 mg kg−1) and water soluble S (6.0 – 17.0 mg kg−1) were the highest in SP with HR (P < 0.05), while inorganic S (505 – 533 mg kg−1) and adsorbed S (2.3 – 4.4 mg kg−1) were significantly higher (P < 0.05) in HR plots irrespective of tillage systems at 0–30 cm soil depth. All the S fractions were positively and strongly correlated with SOC and except for inorganic and adsorbed S, all other S fractions were positively correlated with TN, extractable P, Zn, B and Fe. All S fractions were negatively correlated with BD. Inorganic S was the dominant S fraction but highly significant and positive correlations of available S with organic S (r = 0.92) and water–soluble S (r = 0.92) suggests these two fractions were the main sources of plant available S. This study suggests that both minimal soil disturbance and increased crop residue retention, core components of CA, increased S pools in soils primarily due to increased SOC sequestration.

Methane emission, methanogenic and methanotrophic communities during rice-growing seasons differ in diversified rice rotation systems

Appropriate crop rotation in rice field is an important measure to maintain soil fertility and rice productivity. However, the effects of different rice rotation systems on methane (CH4) emission and the underlying mechanisms, as well as rice grain yields have not been well assessed. Here, a 2-year field study involving three rice rotation systems (Wh-PR: wheat-flooded rice rotation, Ra-PR: rapeseed-flooded rice rotation, Ra-UR: rapeseed-aerobic rice rotation) was conducted. CH4 emissions, methanogenic and methanotrophic communities and rice grain yields were measured during rice growing seasons to determine which rice rotation pattern can reduce CH4 emissions and improve rice grain yields. The average cumulative CH4 emission was 136.19 kg C ha−1 in Ra-PR system, which was significantly higher than that in Wh-PR and Ra-UR systems by 60.6 % and 14.6-fold, respectively. These results were mainly attributed to the low soil dissolved organic carbon in Wh-PR system and the well aerated soil condition in Ra-UR system, as compared with Ra-PR system. Rice grain yields exhibited no significant differences among the three rotation systems in 2019 and 2020. The abundances of methanogens in Ra-PR system were obviously higher than those in Wh-PR and Ra-UR systems. While the abundances of methanotrophs were comparable between Ra-PR and Wh-PR systems, which exhibited significantly lower abundances than that in Ra-UR system. CH4 fluxes showed markedly positive relations to the abundances of methanogens, while exhibited no relationship with the abundances of methanotrophs. Both methanogenic and methanotrophic community compositions differed considerably in Wh-PR and Ra-UR systems in comparison with Ra-PR system. Specifically, the relative low abundances of Methanothrix and Type I methanotrophs occurred in Wh-PR and Ra-UR systems, whereas Methanosarcina, Methanocella, Methanomassiliicoccus and type II methanotrophs (Methylocystis and Methylosinus) were found in higher relative abundances in Wh-PR and Ra-UR systems. Overall, changing the preceding upland crop types or introducing aerobic rice to substitute flooded rice in rice-based rotation systems could diminish CH4 emissions, mainly by regulating soil properties and eventually changing soil methanogenic and methanotrophic communities.

Continuous Practice of Conservation Agriculture for 3–5 Years in Intensive Rice-Based Cropping Patterns Reduces Soil Weed Seedbank

When farmers first shift from conventional tillage (CT) to conservation agriculture (CA) practices, the control of weeds may be more difficult, due to the absence of tillage. However, continuous CA, over several years, may alter the weed seedbank. The nature of the weed seedbank changes over time, in intensively cropped rice-based rotations that are typical of the Eastern Gangetic Plain, are not well understood. Two on-farm CA experiments were sampled (in Beluapara after 3 years and Digram after 5 years) in Bangladesh for the effects of strip planting (SP) and bed planting (BP) at both the sites, plus no-tillage (NT) in Beluapara, and increased retention of the residue of previous crops (20% vs. 50%). The conventional tillage (CT) and 20% residue was the control treatment. The weed seedbank in 0–15 cm soil was quantified by assessing the emergence of weeds from soils collected from the field after irrigation, (Boro) rice in Digram and wheat in Beluapara, and they were allowed to emerge in trays in a shade-house experiment. The year-round count of emerged weeds at both the locations revealed the fewest number of weed species (especially broadleaf weeds), and the lowest weed density and biomass in SP, followed by CT, BP, and NT, with 50% crop residue mulch. Relative to CT, the SP, BP, and NT produced relatively more perennials weeds, as follows: Alternanthera denticulata ((R.) Brown.), Cyperus rotundus (L.), Dentella repens (L.), Jussia deccurence (Walt.), Leersia hexandra (L.), and Solanum torvum (Sw.), which was the opposite of CT that was enriched with the following annual weeds: Cyperus iria (L.), Digitaria sanguinalis (L.), Euphorbia parviflora (L.), Fimbristylis miliacea (L.), Lindernia antipoda (L.), L. hyssopifolia (L.), and Monochoria hastata (L.). The soil weed seed bank reduced by 13% in SP, while it increased by 19% and 76% in BP and NT, respectively, compared with CT. The species diversity reduced in SP and NT, by 24% and 11%, respectively, but increased by 2% in BP. In 50% residue, the soil weed seed bank and species diversity reduced by 16% and 14%, respectively, relative to that of 20% residue. The continuous practice of CA, for 3 or more years, in two rice-based crop rotations, decreased the size of the weed seedbank, but increased the relative proliferation of specific perennial weeds.

Long-term rice-oilseed rape rotation increases soil organic carbon by improving functional groups of soil organic matter

Aggregate carbon (C) pools, which are closely associated with soil organic C (SOC) stability and agricultural productivity, are greatly affected by the composition of soil organic matter (SOM) functional groups. However, the long-term effect of different rice-based rotations on the composition of SOM functional groups remains elusive. In this work, a 10-year field experiment was conducted to assess the effect of different rice-based rotations (rice-wheat [RW] and rice-oilseed rape rotation [RR]) on the composition of SOM functional groups and soil aggregate C pools. The composition of SOM functional groups was determined by the nuclear magnetic resonance spectroscopy method. Aggregate C pools were isolated through density gradient fractionation. After 10 years of rice-based rotation, compared with RW, RR significantly reduced the proportion of macromolecular functional groups (nuclear magnetic resonance zone (NMR) > 110 mg kg–1) in SOC, especially that of aromatic C (by 25.0%) and carboxyl C (by 26.8%), but significantly increased the contents of SOM compounds, particularly those of polysaccharides (by 30.7%), nitrogen carrier (by 28.4%) and lipids (by 34.7%). RR enhanced the proportions of large macroaggregate (by 56.0%) and intra-microaggregate particulate organic C (iPOC) (by 13.0%), as well as the SOC content (by 12.7%) relative to RW. Structural equation modeling revealed that RR could promote aggregate development and the stock of SOC as iPOC by enhancing the proportion of small functional groups in SOM (NMR < 110 mg kg–1) and promoting SOM compound formation, thereby improving soil C pool stability and content relative to RW in the long-term rotation.

Strip Tillage and Crop Residue Retention Decrease the Size but Increase the Diversity of the Weed Seed Bank under Intensive Rice-Based Crop Rotations in Bangladesh

Cropping under conservation agriculture (CA) has become increasingly attractive among farmers in recent years. However, weed control may be more difficult during the transition to CA from conventional establishment methods due to the reduction in tillage intensity. Conversely, CA changes to weed dynamics can alter the weed seed bank in the longer run. In Bangladesh’s intensively cropped rice-based rotations, the nature of weed seed bank shifts over time after adopting CA are poorly known. Two 2-year studies were sampled from on-farm CA experiments under wheat-mungbean-winter rice and monsoon rice-mustard-winter rice rotations. We investigated the effects of reduced soil disruption in the form of strip-tillage (ST) combined with increased deposition of standing reside from previous crops (0 vs. 50%). The weed seed bank in 0–5, 5–10, and 10–15 cm depths of soil were quantified in a shade-house experiment by measuring weed emergence over 12 months in seedling trays. After 2 years of field study, the year-round count of emerged weeds from the seed bank showed that ST plus 50% mulch had a lower weed abundance and biomass and fewer weed species than that of conventional tillage (CT) without residue. The perennial weeds Ageratum conyzoides L., Alternanthera philoxeroides L., Cynodon dactylon L., Cyperus rotundus L., Jussia decurrence Walt., Leersia hexandra L., Scirpus mucronatus (L.) Palla., and Solanum torvum Sw. were enriched in the smaller-sized ST seed banks in terms of both density and biomass. The CT, on the other hand, was dominated by annual weeds: Cyperus difformis L., Cyanotis axillaris Roem., Echinochloa crus-galli (L.) Beauv., Eleusine indica L., Fimbristylis miliacea (L.) Vahl., and Rotala ramosior L. Overall, ST plus 50% residue had a more diverse seed bank than CT without mulch. The majority of weed seeds were amassed in the 0–5 cm soil depth of the ST, while most of them were accumulated in the 10–15 cm layer of the CT. The wheat-mungbean-winter rice rotation had a more diverse floristic composition with many more weed species than the monsoon rice-mustard-winter rice rotation.

Evaluation on environmental consequences and sustainability of three rice-based rotation systems in Quanjiao, China by an integrated analysis of life cycle, emergy and economic assessment

The rice-based cultivation system in the middle and lower reaches of the Yangtze River of China is changing gradually during recent years which arouses more attentions and concerns on environmental performance and sustainability. In this study, the integrated analysis of life cycle assessment (LCA), emergy evaluation (EME) and economic analysis (ECA) were applied and Quanjiao county was selected as a case study to estimate the pollution emissions, emergy efficiency and economic benefits of three typical rice-based rotation systems depended on a detailed farming practice filed investigation of 157 valid samples under structured questionnaire. The three typical rice-based rotation systems are rice-wheat rotation (RW), rice-fallow rotation (RF) and rice-crayfish rotation (RC), respectively. The LCA results showed that the area-based potential environmental impact for RW, RF and RC are 34.08, 13.71 and 39.98, the profit-based potential environmental impacts are 2.62, 1.16 and 1.98. The EME results indicated that the RC shows the highest emergy input, around 1.23E+17 sej/ha/yr, more than that of RW and RF, around 3.88E+16 sej/ha/yr and 3.40E+16 sej/ha/yr, respectively. From the emergy indices of the three systems, the RC results in higher environmental pressure and lower sustainability compared with the RW and RF. Fertilizer, diesel oil, water, electricity and forage are the crucial factors of environmental consequences, herein forage, water and electricity inputs are becoming new factors that are increasingly prominent and often neglected. From an economic perspective, the cost and income of the RC are highest because of more input and higher sale value, the area-based profit of the RC (20142 ¥/ha) is higher than that of RF (11848 ¥/ha) and RW (13031 ¥/ha). Generally, during the rice planting system transferring, the development of farming technologies and standards should be promoted to avoid the disorder of agricultural production, and then gearing up to the better economic performance and environmental sustainability for the rice-based rotation systems. Moreover, proper agricultural development policies should be made and promoted to stimulate farmers’ willingness to adopt advanced farming practices and techniques to reduce environmental emissions and enhance agricultural system sustainability as well as increasing farmers' income.

Weed populations of intensive rice based cropping system as affected by tillage and increased crop residues in Bangladesh

When farmers first shift from conventional tillage (CT) to conservation agriculture (CA), weeds control may be more difficult due to the absence of tillage. However, in the longer term (3-5 years), CA changes to weed dynamics may alter the weed seedbank. The nature of weed seedbank changes over time in intensively cropped rice-based rotations typical of the Eastern Gangetic Plain of Bangladesh is not well understood. Three long term CA experiments were sampled (at Rajbari after three years and Rajshahi after five years) for effects of decreased soil disturbance strip planting (SP) and bed planting (BP) at both sites and Zero tillage (ZT) at Rajbari, increased retention of standing residues of previous crops (20 vs. 50%. The weed seedbank in 0-15 cm soil was quantified by assessing emergence from trays in a net-house experiment during January-December 2016. The year-round count of emerged weeds revealed the fewest number of weed species (especially broadleaf weeds) and lowest weed density in SP, followed by CT, BP, and ZT with 50% crop residues. The SP, BP, and ZT produced a higher number of perennials weeds than annual weeds, which was the opposite of CT. The continuous practice of SP and increased crop residue retention for three or more years decreased the size of weed seedbank but increased the relative proliferation of perennial weeds compared to CT. Weed seedbank size in SP was even smaller than BP and ZT.

Rice-pasture agroecosystem intensification affects energy use efficiency

Sustainable rice production systems are key to food security. Diversified farming systems are essential for ecological intensification and environmental enhancement. Energy use efficiency is one of the main sustainability indicators in agroecosystems. Thus, an assessment of consumption and efficiency of energy in contrasting cropping systems can discriminate their management practices and components sustainability. The goal of this study was to evaluate the energy performance through energy return on investment (EROI) in four rice-based rotation systems that belong to a long-term experiment located in the Temperate Grassland Terrestrial Ecoregion, at the Atlantic side of South America. Rotations analyzed consisted in: a) continuous rice (Rc); b) rice-soybean (R−S); c) rice-pasture for 1.5 years (R−PS); and, d) rice-pasture for 3.5 years (R−PL). The EROI estimations considered all the inputs and outputs of energy from cradle to farm gate. The greatest EROI was observed in R–S (7.2 MJMJ−1) and the lowest energy consumption in R−PL (10,607 MJ(hayr)−1). The R−PL’s EROI (6.7 MJMJ−1) was 6.5% and 8% higher than Rc and R−PS EROI, respectively. Rotations without pastures produced 79% more energy compared with rotations including pastures. However, energy inputs of rice-pasture rotations were 40% lower than either R−S or Rc. The EROI (without animal production) of R−PS, R–S and Rc was 25%, 28% and 43% lower than the EROI of R−PL (10 MJMJ−1), respectively. For the analyzed South American ecoregion, EROI assessments of four business as usual rice production systems allowed to discriminate and hierarchize their sustainability and diversity.

Including grain legume in rice–wheat cropping system improves soil organic carbon pools over time

Deterioration of soil physical quality and depletion of soil organic carbon (SOC) are widespread challenges in tropical rice–wheat growing regions. Consequently, soil productive capacity, production sustainability, and resource use efficiency have declined in this agro-ecosystem. Ecological engineering approach such as legume inclusion in cropping system offers several ecosystem services, and thus, may serve an important role in the restoration of soil health. Given that, a long-term (2003–2015) field experiment was conducted to assess the impact of four rice-based crop rotation treatments [rice–wheat, rice–chickpea, rice–wheat–mungbean, rice–wheat–rice–chickpea] each with three levels of nutrient management treatments [control, integrated nutrient management, chemical fertilizers] on soil aggregation, soil carbon pools, and carbon stabilization. Legume inclusive rotations increased water stable macro-aggregates (WSMA) over rice–wheat rotation in both surface (0–0.2 m) and subsurface (0.2–0.4 m) soil depths. In surface soil, WSMA was the highest in rice–wheat–mungbean rotation (65%) followed by rice–chickpea rotation (57%) and was the least in rice–wheat rotation (50%). Subsequently, grain legume inclusive rotations had the higher aggregate ratio and mean weight diameter over rice–wheat rotation, being the highest in rice–wheat–mungbean rotation. Rice–wheat–mungbean and rice–chickpea rotations had higher carbon concentration in coarse macro-aggregates, meso-aggregates, and coarse micro-aggregates as compared with rice–wheat rotation. Grain legume inclusive rotations increased active carbon pool (9–18%), SOC (6–17%), and carbon management index (5–7%) over rice–wheat rotation, and the order was rice–wheat–mungbean > rice–chickpea ≥ rice–wheat–rice–chickpea > rice–wheat. Integrated nutrient management treatment resulted in higher macro-aggregate (7%), mean weight diameter (6%), active carbon pool (22%), passive carbon pool (16%), SOC (20%), and carbon management index (22%) over the chemical fertilizer treatment. Thus, it is concluded that inclusion of grain legume in lowland rice-based rotation and integrated nutrient management could improve soil aggregation, carbon concentration in aggregates, and soil carbon pools in the tropical soils. The study highlights the prospects of strategic designing of legume inclusive rotation/s for rice agro-ecosystem health and its sustainability.

Nitrogen use efficiency in different rice-based rotations in southern China

Experiments in fields and micro-plots were conducted to investigate the optimal cropping system and nitrogen (N) fertilizer application rate and timing. The treatments consisted of Chinese milk vetch–rice (CMV–R) rotation with five N fertilizer application rates (0, 120, 180, 240, 300 kg N ha−1) during the rice-growing season, and fallow–rice (F–R) and wheat–rice (W–R) rotations with only one N application rate (240 kg N ha−1) each. Rice yield increased with increasing N fertilizer application rate under CMV–R rotation, and achieved highest yield under CMV–R180. There is a decreasing trend when N application rate exceeded 180 kg N ha−1. Rice yield was always higher under CMV–R240 compared to W–R240 and F–R240. During the 2012 rice season, the fertilizer N-use efficiency, residual N fertilizer in soil and N fertilizer recovery efficiency of CMV–R180 reached largest under CMV–R rotation with different N treatments. Furthermore, the fertilizer N-use and recovery efficiencies of CMV–R240 and F–R240 were far higher than those of W–R240. In 2013, fertilizer N-use efficiency was the highest (> 50%) at the heading stage, which was nearly twice as much as the efficiencies during the basal and tillering stages. The N fertilizer loss rate during the basal stage was significantly higher than that at the tillering and heading stages, which was up to 60%. CMV–R rotation with 180 kg N ha−1 achieved the highest rice yield of 9454 kg ha−1 and high fertilizer N-use efficiency (40.6%) under a relatively lower N application rate. Therefore, Chinese milk vetch–rice cropping system could be a promising approach for decreasing fertilizer inputs to prevent N pollution problems and increasing rice yield, especially for the intensive rice-based cropping systems in southern China.

Crop establishment with conservation tillage and crop residue retention in rice-based cropping systems of Eastern India: yield advantage and economic benefit

Continuous practice of tillage intensive puddled rice-based systems in South Asia has developed serious issues related to soil health and production sustainability. This has exaggerated the need for sustainable alternatives. Here, the impact of four tillage cum crop establishment practices [conventional puddled transplanted rice followed by conventional till maize/wheat (CTTPR-CT), non-puddled transplanted rice followed by zero-till maize/wheat (NPTPR-ZT), zero-till transplanted rice followed by zero-till maize/wheat (ZTTPR-ZT), zero-till direct seeded rice followed by zero-till maize/wheat (ZTDSR-ZT)], two residue management [residue removal, residue retention (~ 33.0%)] and two rice-based rotations (rice–wheat, rice–maize) on crop performance, system productivity, and production economics were evaluated. At 4th and 5th year of rotation, complete zero-tillage-based crop establishment (ZTDSR-ZT, ZTTPR-ZT) enhanced the grain yield of rice (9.3–20.6%), wheat (18.4–22.6%), and maize (10.8–11.8%) over CTTPR-CT, whereas yield advantage in NPTPR-ZT was marginal for all the crops. The higher grain yield of rice and wheat in ZTDSR-ZT and ZTTPR-ZT treatments was mainly attributed to higher tiller production (rice 11.5–23.2%; wheat 29.5–34.9%). Likewise, the higher aboveground biomass, cob length, cob weight, and grains weight cob−1 led to higher maize yield in conservation tillage treatments (NPTPR-ZT, ZTDSR-ZT, and ZTTPR-ZT). Retention of crop residue improved (p < 0.05) the yield of all crops being higher in maize (6.9–10.3%) followed by wheat (5.3–10.5%). The reduced cost of cultivation and higher return from produce in ZTDSR-ZT, ZTTPR-ZT, and NPTPR-ZT enhanced the net income by INR 48164, 35800, 25632, respectively, over CTTPR-CT. Thus, zero-tillage-based crop establishments with crop residue retention were found as potential alternative for improving crop productivity, profitability and sustainability of rice-based production systems.

Chinese Milk Vetch Improves Plant Growth, Development and 15N Recovery in the Rice-Based Rotation System of South China

Chinese milk vetch (CMV) is vital for agriculture and environment in China. A pot experiment combined with 15N labeling (including three treatments: control, no fertilizer N and CMV; 15N-labeled urea alone, 15NU; substituting partial 15NU with CMV, 15NU-M) was conducted to evaluate the impact of CMV on plant growth, development and 15NU recovery in rice-based rotation system. The 15NU-M mitigated oxidative damage by increasing antioxidant enzymes activities and chlorophyll content while decreased malondialdehyde content in rice root and shoot, increased the biomass, total N and 15N uptake of plant shoots by 8%, 12% and 39% respectively, thus inducing a noticeable increase of annual 15N recovery by 77% versus 15NU alone. Remarkable increases in soil NH4+ and populations of bacteria, actinomycetes and azotobacter were obtained in legume-rice rotation system while an adverse result was observed in soil NO3− content versus fallow-rice. CMV as green manure significantly increased the fungal population which was decreased with cultivating CMV as cover crop. Therefore, including legume cover crop in rice-based rotation system improves plant growth and development, annual N conservation and recovery probably by altering soil nitrogen forms plus ameliorating soil microbial communities and antioxidant system which alleviates oxidative damages in plants.

The Rice-based Rotation Systems and Material Circulation in Northern Italy

The Rice-based Rotation Systems and Material Circulation in Northern Italy

Effects of crop rotation on properties of a Vietnam clay soil under rice-based cropping systems in small-scale farmers' fields

In tropical deltas, intensive monoculture with three rice crops per year (RRR) has been the standard for decades. However, in recent years some farmers have started rice-based rotations with one or more upland crops per year. The trends for increased grain yields with this new system raises the question as to whether the introduction of upland crops affects properties of alluvial clay paddy soil. This was evaluated in the present study, which was performed at 40 paddy fields in the Vietnamese Mekong Delta under four different cropping systems (10 farms per system) on paddy rice soils: RRR; crop rotation with two rice crops and one upland crop per year (RUR); crop rotation with one rice and two upland crops per year (RUU); and upland crop (UUU). Soil samples were collected at depths of 0–10, 10–20 and 20–30cm. Most soil properties differed significantly between the RRR and the RUR, RUU or UUU. The RUR, RUU and UUU systems alleviated soil compaction, resulting in reduced penetration resistance and bulk density and increased total and macroporosity at 20–30cm depth. In addition, aggregate stability index and plant-available water capacity were higher for RUR, RUU and UUU compared with RRR at the 20–30cm depth. Average soil organic carbon (SOC) stocks ranged from 59.3tha–1 in UUU to 72.3tha–1 in RUR, with SOC stocks in RRR and RUU being intermediate (66.4 and 68.3tha–1) and not significantly different to that of the RUR system. Carbon hydrolysable by HCl (Chydrolysable) was 74–84% greater in the RUR, RUU and UUU than in RRR systems. In conclusion, rice–upland crop systems may alleviate soil degradation resulting from continuous rice monoculture.