Exploring site-specific N application rate to reduce N footprint and increase crop production for green manure-rice rotation system in southern China.

Milk vetch (Astragalus sinicus L.) is leguminous green manure (GM) which produces organic nitrogen (N) for subsequent crops and is widely planted and utilized to simultaneously reduce the use of synthetic N fertilizer and its environmental costs in rice systems. Determination of an optimal N application rate specific to the GM-rice system is challenging because of the large temporal and spatial variations in soil, climate, and field management conditions. To solve this problem, we developed a framework to explore the site-specific N application rate for the low-N footprint rice production system in southern China based on multi-site field experiments, farmer field survey, and process-based model (WHCNS_Rice, soil water heat carbon nitrogen simulator for rice). The results showed that a process-based model can explain >83.3% (p < 0.01) of the variation in rice yield, aboveground biomass, crop N uptake, and soil mineral N. Based on the scenario analysis of the tested WHCNS_Rice model, the simple regression equation was developed to implement site-specific N application rates that considered variations in GM biomass, soil, and climatic conditions. Simulation evaluation on nine provinces in southern China showed that the site-specific N application rate reduced regional synthetic N fertilizer input by 29.6 ± 17.8% and 65.3 ± 23.0% for single and early rice, respectively; decreased their total N footprints (NFs) by 23.4% and 49.3%, respectively; and without reduction in rice yield, compared with traditional farming N practices. The reduction in total NF was attributed to the reduced emissions from ammonia volatilization by 35.2%, N leaching by 28.4%, and N runoff by 32.7%. In this study, we suggested a low NF rice production system that can be obtained by combining GM with site-specific N application rate in southern China.

Combined application of chemical fertilizer with green manure increased the stabilization of organic carbon in the organo-mineral complexes of paddy soil.

The influence of the combined application of chemical fertilizer with green manure on the stabilization of organic carbon (C) was explored in the organo-mineral complexes of paddy soil. The organo-mineral complexes were isolated from paddy soil treated with no fertilizer, chemical fertilizer alone, and chemical fertilizer combined with increasing amounts of Chinese milk vetch (CMV). The stability (reflected by mineralizable carbon proportion), the content and chemical composition of organic C, the Fe/Al oxides and their associated organic C in the organo-mineral complexes were investigated. The application of chemical fertilizer in combination with CMV significantly improved the stability of organic C in the organo-mineral complexes. The combined application of chemical fertilizer with CMV slightly decreased the proportion of O-alkyl C (easily decomposed) yet somewhat increased the proportions of carbonyl C and aromatic C (difficultly decomposed) and aromaticity index in the organo-mineral complexes. The treatments of chemical fertilizer combined with CMV showed more Fe oxides and Fe/Al-associated organic C and higher proportion of Fe/Al-associated organic C in the total organic C of the organo-mineral complexes. The mineralizable carbon proportion displayed significantly negative correlations with carbonyl C and Fe/Al oxide-associated organic C in the organo-mineral complexes. The Fe/Al oxides were likely to be preferentially bound with the aromatic C and carbonyl C in the organo-mineral complexes. Overall, the combined application of chemical fertilizer with CMV facilitated the association of difficultly decomposed carbon and Fe/Al oxides, which significantly improved the stabilization of organic C in the organo-mineral complexes of paddy soil.

Seed Priming Improved Antioxidant Defense System and Alleviated Ni-Induced Adversities in Rice Seedlings Under N, P, or K Deprivation.

Excess nickel (Ni) concentration in the growing medium severely hampers the plant growth by disturbing oxidative metabolism and nutrient status. The present study was carried out to investigate the individual and interactive effects of Ni toxicity (0.25 mM NiSO4.6H2O) and nutrient deprivation (no-N, no-P, or no-K) on growth, oxidative metabolism, and nutrient uptake in primed and non-primed rice seedlings. Rice seed was primed with distilled water (hydropriming), selenium (5 mg L-1), or salicylic acid (100 mg L-1). The Ni toxicity and deprivation of N, P, or K posed negative effects on the establishment of rice seedlings. The shoot length and fresh biomass were severely reduced by Ni toxicity and nutrient stresses; the minimum shoot growth was recorded for rice seedlings grown under Ni toxicity and no-N stress. The Ni toxicity reduced the root fresh biomass but did not significantly affect the root length of N-deprived seedlings. The rice seedlings with no-P or no-K recorded similar root fresh biomass compared with those grown with sufficient nutrient supply. The Ni toxicity alone or in combination with nutrient stresses triggered the production of reactive oxygen species (ROS) and caused lipid peroxidation in rice seedlings. Among antioxidants, only glutathione reductase and vitamin E were significantly increased by Ni toxicity under different nutrient stress treatments. The Ni toxicity also reduced the concentrations of N particularly in shoot of rice seedlings. The N-deprived (no-N) seedlings recorded maximum Ni concentration in shoot, while K-deprived (no-K) seedlings showed higher Ni concentrations in root. Seed priming with selenium or salicylic acid was effective to alleviate the detrimental effects of Ni toxicity and/or nutrient stresses on rice seedlings. The better growth and greater stress tolerance of primed seedlings was coordinately attributed to lower ROS production, higher membrane stability, strong antioxidative defense system, and maintenance of mineral nutrient status.

Coordinated effects of lead toxicity and nutrient deprivation on growth, oxidative status, and elemental composition of primed and non-primed rice seedlings.

Rice crop is highly susceptible to the toxic levels of lead (Pb) during early growth stages. Moreover, a sufficient availability of mineral nutrients is critical for survival of plants particularly under stressful conditions. An experiment was carried out to unravel the coordinated effects of Pb stress (1-mM PbCl2) and different nutrient treatments (sufficient nutrient supply, nitrogen (N) deprivation, phosphorus (P) deprivation, and potassium (K) deprivation) on morphological growth, reactive oxygen species (ROS), antioxidants, and nutrient status in primed and non-primed rice seedlings. Seeding were primed with distilled water, 60-µM selenium, or 100-mg L-1 salicylic acid. Results indicated that Pb toxicity did not affect the root growth, but severely reduced the shoot growth (length and biomass) of rice in N- or P-deprived seedlings. Rice seedlings grown with sufficient supply of nutrients or K-deprivation showed no growth reduction under Pb toxicity. Exposure of Pb stress triggered the production of ROS (H2O2, O2˙-, OH-) and lipid peroxidation rate particularly under N- or P-deprivation. Moreover, the shoot accumulations of macronutrients (P in particular) were also restricted under Pb toxicity. Seed priming treatments effectively alleviated the undesirable effects of Pb stress on rice growth. The primed rice seedlings showed minimal oxidative damage caused by excessive generation of ROS under Pb stress and/or nutrient deprivation. Seed priming strengthened the antioxidative defense system of rice seedlings by regulating the activities/levels of superoxide dismutase, catalase, peroxidase, and glutathione in rice leaves. Moreover, better accumulation of essential nutrients in primed rice seedlings prevented the excess uptake and translocation of Pb, as evident by the lowered shoot accumulation of Pb.

Seed Priming Alters the Production and Detoxification of Reactive Oxygen Intermediates in Rice Seedlings Grown under Sub-optimal Temperature and Nutrient Supply.

The production and detoxification of reactive oxygen intermediates (ROIs) play an important role in the plant response to nutrient and environmental stresses. The present study demonstrated the behavior of growth, ROIs-production and their detoxification in primed and non-primed rice seedlings under chilling stress (18°C) and nitrogen-(N), phosphorus-(P), or potassium-(K) deprivation. The results revealed that chilling stress as well as deprivation of any mineral nutrient severely hampered the seedling growth of rice, however, seed priming treatments (particularly selenium- or salicylic acid-priming), were effective in enhancing the rice growth under stress conditions. The N-deprivation caused the maximum reduction in shoot growth, while the root growth was only decreased by P- or K-deprivation. Although, N-deprivation enhanced the root length of rice, the root fresh weight was unaffected. Rate of lipid peroxidation as well as the production of ROIs, was generally increased under stress conditions; the K-deprived seedlings recorded significantly lower production of ROIs than N- or P-deprived seedlings. The responses of enzymatic and non-enzymatic antioxidants in rice seedlings to chilling stress were variable with nutrient management regime. All the seed priming were found to trigger or at least maintain the antioxidant defense system of rice seedlings. Notably, the levels of ROIs were significantly reduced by seed priming treatments, which were concomitant with the activities of ROIs-producing enzymes (monoamine oxidase and xanthine oxidase), under all studied conditions. Based on these findings, we put forward the hypothesis that along with role of ROIs-scavenging enzymes, the greater tolerance of primed rice seedlings can also be due to the reduced activity of ROIs-producing enzymes.

Role of xylo-oligosaccharides in protection against salinity-induced adversities in Chinese cabbage.

Soil salinity is a stringent abiotic constraint limiting crop growth and productivity. The present study was carried out to appraise the role of xylo-oligosaccharides (XOSs) in improving the salinity tolerance of Chinese cabbage. Salinity stress (0.5% NaCl solution) and four levels (0, 40, 80, 120 mg L(-1)) of XOSs were imposed on 20-day-old plants cultured under controlled conditions. Salinity stress decreased the aboveground fresh biomass, photosynthesis, transpiration rate, stomatal conductance, internal CO2 concentration, water use efficiency, and chlorophyll contents but increased the stomatal limitation value of Chinese cabbage compared with control. Such physiological interferences, disturbances in plant water relations, and visually noticeable growth reductions in Chinese cabbage were significantly alleviated by the addition of XOSs under salinity stress. Under salinity stress, application of XOSs significantly enhanced the activities of enzymatic (superoxide dismutase, peroxidase, catalase) and non-enzymatic (ascorbate, carotene) antioxidants and reduced the malondialdehyde content in the leaves of Chinese cabbage. The XOS-applied plants under salinity stress also recorded higher soluble sugars, proline, and soluble protein content in their leaves. Exposure of salinity stress increased the ratio of Na(+)/K(+), Na(+)/Ca(2+), and Na(+)/Mg(2+) in shoot as well as root of Chinese cabbage, however, XOS application significantly reduced these ratios particularly in shoot. Lower levels of XOSs (40 or 80 mg L(-1)) were more effective for most of the studied attributes. The greater salinity tolerance and better growth in these treatments were related with enhanced antioxidative defense system, reduced lipid peroxidation, increased osmolyte accumulation, and maintenance of ionic balance.

Greenhouse gas emissions, soil quality, and crop productivity from a mono-rice cultivation system as influenced by fallow season straw management.

Straw management during fallow season may influence crop productivity, soil quality, and greenhouse gas (GHG) emissions from rice field. A 3-year field experiment was carried out in central China to examine the influence of different fallow season straw management practices on rice yield, soil properties, and emissions of methane (CH4) and nitrous oxide (N2O) from a mono-rice cultivation system. The treatments comprised an unfertilized control (CK), inorganic fertilization (NPK), rice straw burning in situ (NPK + RSB), rice straw mulching (NPK + RSM), and rice straw strip mulching with green manuring (NPK + RSM + GM). The maximum rice yield, soil organic carbon, soil total nitrogen, and available potassium were observed in NPK + RSM + GM treatment. Compared with NPK, the NPK + RSM + GM recorded 9% higher grain yield averaged across 3 years. However, NPK + RSM and NPK + RSB were statistically similar with NPK regarding grain yield. The NPK + RSM and NPK + RSM + GM recorded significantly higher CH4 emission during rice growing season as well as winter fallow; however, the response of N2O emissions was variable. The NPK + RSM and NPK + RSM + GM were statistically similar for annual cumulative CH4 and N2O emissions. The NPK + RSM + GM recorded 103 and 72% higher straw-induced net economic benefits and soil organic carbon sequestration rate, and reduced net global warming potential by 27% as compared with NPK + RSM. Considering the benefits of soil fertility, higher crop productivity, and environmental safety, the NPK + RSM + GM could be the most feasible and sustainable option for mono-rice cultivation system in central China.

Zinc-cadmium interactions: Impact on wheat physiology and mineral acquisition.

Increasing concentration of Cd in soil is of great concern due to risk of its entry into food chain. Zinc (Zn) being antagonist to Cd is an important micronutrient to ameliorate its toxic effects on plants and to limit its entry into food chain. A pot experiment was conducted using Cd contaminated soil (30 mg Cd kg(-1) soil as 3CdSO4 · 8H2O) to investigate the effect of soil and foliar applied Zn on physiological response and Cd concentration in wheat. In soil, Zn was applied at 15 and 30 mg Zn kg(-1) soil as zinc sulfate (ZnSO4 · 7H2O). For foliar applications, 3 and 6 g L(-1) ZnSO4 solution was sprayed on completing eight weeks of growth. Results indicated that Zn application could effectively improve physiological performance and mineral content of wheat grown on Cd contaminated soils. Among different Zn fertilization treatments, foliar application of 3 g L(-1) ZnSO4 solution recorded the maximum soluble proteins and the minimum grain-Cd concentration. Soil application of ZnSO4 or foliar application at 6 g L(-1) did not affect Cd concentration in grains. Zinc application through both the methods significantly increased phosphorus (P), potassium (K) and Zn concentrations in shoots. Concentration of P and K in grains showed positive relationship with that of Zn. In crux, present study suggests that foliar application of Zn at booting stage in a suitable concentration (3 g L(-1) ZnSO4 solution) can effectively ameliorate the adverse effects of Cd and decrease grain-Cd of wheat grown in Cd contaminated soil.

Residual phytotoxicity of parthenium: Impact on some winter crops, weeds and soil properties.

Phytotoxic effects of parthenium residues incorporation and parthenium-infested rhizospheric soil on emergence and seedling growth of winter crops (wheat and canola) and weed species (wild oat and canary grass) were examined in different pot studies. In first experiment, parthenium whole plant residues were incorporated at 6 and 8 g kg(-1) soil five days prior to sowing. Pots without residues incorporation were maintained as control. In a second study, parthenium-infested rhizospheric soil collected from different depths (15 and 22.5 cm) and collar regions (horizontal distance away from plant trunk, 15 and 22.5 cm), was used as growing medium. Parthenium-free soil was used as control. Parthenium residues amendment as well as its rhizospheric soil was detrimental for emergence and seedling growth of all test species. Incorporation of parthenium residues reduced the final emergence of canola, wild oat and canary grass by 11-20%, 20-29% and 20-27%, respectively; however wheat emergence was unaffected. Moreover, seedling biomass of wheat, canola, wild oat and canary grass was reduced in the range of 41-48%, 53-61%, 31-45% and 30-45% by parthenium residues incorporation. In second study, soil collected from a rhizospheric depth of 15 cm and collar distance of 15 cm reduced the emergence and seedling growth by 15% and 40%, respectively averaged across different test species. Parthenium residues incorporation and infested rhizospheric soil increased the soil phenolics, electrical conductivity, organic carbon and nitrogen contents over control soils with the exception of pH that was declined. All test species manifested reduced chlorophyll and increased phenolic contents in response to parthenium residues incorporation and infested rhizospheric soil. The inhibition in emergence and seedling growth of all test species was associated with increase in phenolic contents. Parthenium residues incorporation at 8 g kg(-1) soil and upper parthenium-infested rhizospheric soil (15 cm soil depth and 15 cm collar distance) were more phytotoxic for all test species.

Seed Priming with Selenium: Consequences for Emergence, Seedling Growth, and Biochemical Attributes of Rice.

The present study was undertaken to appraise the role of selenium priming for improving emergence and seedling growth of basmati rice. Seeds of two fine rice cultivars (Super and Shaheen Basmati) were primed with concentrations of 15, 30, 45, 60, 75, 90, and 105 µmol L(-1) selenium. Untreated dry- and hydro-primed seeds were maintained as the control and positive control, respectively. Selenium priming resulted in early commencement of emergence, triggered seedling growth irrespective of rice cultivar over untreated control, and was more effective than hydro-priming except at higher concentrations. Lower electrical conductivity of seed leachates, reduced lipid peroxidation, greater α-amylase activity, higher soluble sugars, and enhanced activities of enzymatic antioxidants (superoxide dismutase (SOD), peroxidase (POX), catalase (CAT), and glutathione peroxidase (GPX)) were observed in seeds primed with selenium. Rice seedlings derived from selenium-primed seeds exhibited more chlorophyll contents, while total phenolics were comparable with those of the control seedlings. The improved starch metabolism, greater membrane stability, and increased activity of antioxidants were considered as possible mechanisms responsible for such improvements in emergence and seedling vigor of rice mediated by selenium priming. Priming with selenium (15-60 µmol L(-1)) favored rice emergence and seedling growth. Nevertheless, soaking seeds in relatively concentrated (90 and 105 µmol L(-1)) selenium solution had overall detrimental effects.

Effect of chemical and biological degumming on the adsorption of heavy metal by cellulose xanthogenates prepared from Eichhornia crassipes.

Cellulose xanthogenates, derived from the straw of Eichhornia crassipes, were prepared as adsorbents for heavy metals by CS(2) sulfonation and magnesium substitution after degumming with alkali, self-isolated A(1) strain and pectase, respectively. The effects of three degumming treatments were compared by functional groups analysis, surface morphology and surface element composition and heavy metal (Pb(2+)) adsorption studies. The results demonstrate that bio-degumming treatments by A(1) strain and pectase have weaker degumming effects than alkali treatment. However, the surface characteristics of the bio-degumming products, especially the pectase degumming product, are more beneficial to heavy metal adsorption. In comparison to that of the raw plant materials, the Pb(2+) adsorption performances of the three xanthogenates improved significantly, although no obvious differences being observed among themselves. From an environmental point of view, the two bio-degumming treatments, especially the pectase degumming treatment, are more beneficial to prepare heavy metal adsorbents than the alkali degumming treatment.