Effects of nitrogen application rate and hill density on rice yield and nitrogen utilization in sodic saline–alkaline paddy fields

Soil salinity and alkalinity can inhibit crop growth and reduce yield,and this has become a global environmental concern.Combined changes in nitrogen (N) application and hill density can improve rice yields in sodic saline–alkaline paddy fields and protect the environment.We investigated the interactive effects of N application rate and hill density on rice yield and N accumulation,translocation and utilization in two field experiments during 2018 and 2019 in sodic saline–alkaline paddy fields.Five N application rates (0 (control),90,120,150,and 180 kg N ha^(-1) (N0–N4),respectively) and three hill densities(achieved by altering the distance between hills,in rows spaced 30 cm apart:16.5 cm (D1),13.3 cm (D2) and 10 cm (D3))were utilized in a split-plot design with three replicates.Nitrogen application rate and hill density significantly affected grain yield.The mathematical model of quadratic saturated D-optimal design showed that with an N application rate in the range of 0–180 kg N ha^(-1),the highest yield was obtained at 142.61 kg N ha^(-1) which matched with a planting density of 33.3×10^(4) ha^(-1).Higher grain yield was mainly attributed to the increase in panicles m^(–2).Nitrogen application rate and hill density significantly affected N accumulation in the aboveground parts of rice plants and showed a highly significant positive correlation with grain yield at maturity.From full heading to maturity,the average N loss rate of the aboveground parts of rice plants in N4 was 70.21% higher than that of N3.This is one of the reasons why the yield of N4 treatment is lower than that of the N3 treatment.Nitrogen accumulation rates in the aboveground parts under treatment N3 (150 kg N ha^(-1)) were 81.68 and 106.07% higher in 2018 and 2019,respectively,than those in the control.The N translocation and N translocation contribution rates increased with the increase in the N application rate and hill density,whereas N productivity of dry matter and grain first increased and then decreased with the increase in N application rate and hill density.Agronomic N-use efficiency decreased with an increase in N application rate,whereas hill density did not significantly affect it.Nitrogen productivity of dry matter and grain,and agronomic N-use efficiency,were negatively correlated with grain yield.Thus,rice yield in sodic saline–alkaline paddy fields can be improved by combined changes in the N application rate and hill density to promote aboveground N accumulation.Our study provides novel evidence regarding optimal N application rates and hill densities for sodic saline–alkaline rice paddies.

Study of Dynamics of Floodwater Nitrogen and Regulation of Its Runoff Loss in Paddy Field-Based Two-Cropping Rice with Urea and Controlled Release Nitrogen Fertilizer Application

The article deals with the effects of urea and controlled release nitrogen fertilizer （CRNF） on dynamics of pH, electronic conductivity （EC）, total nitrogen （TN）, NH4^＋-N and NO3 -N in floodwater, and the regulation of runoff TN loss from paddy field-based two-cropping rice in Dongting Lake, China, and probes the best fertilization management for controlling N loss. Studies were conducted through modeling alluvial sandy loamy paddy soil （ASP） and purple calcareous clayey paddy soil （PCP） using lysimeter, following the sequence of the soil profiles identified by investigating soil profile. After application of urea in paddy field-based two-cropping rice, TN and NHa＋-N concentrations in floodwater reached peak on the 1st and the 3rd day, respectively, and then decreased rapidly over time; all the floodwater NO3--N concentrations were very low; the pH of floodwater gradually rose in case of early rice within 15 d （late rice within 3 d） after application of urea, and EC remained consistent with the dynamics of NH4^＋-N. The applied CRNF, especially 70% CRNF, led to significantly lower floodwater TN and NH4^＋ concentrations, pH, and EC values compared with urea within 15 d after application. The monitoring result for N loss due to natural rainfall runoff indicated that the amount of TN lost in runoff from paddy field- based two-cropping rice with urea application in Dongting Lake area was 7.47 kg ha^-1, which accounted for 2.49% of urea- N applied, and that with CRNF and 70% CRNF application decreased 24.5 and 27.2% compared with urea application, respectively. The two runoff events, which occurred within 20 d after application, contributed significantly to TN loss from paddy field. TN loss due to the two runoffs in urea, CRNF, and 70% CRNF treatments accounted for 72, 70, and 58% of the total TN loss due to runoff over the whole rice growth season, respectively. And the TN loss in these two CRNF treatments due to the first run-off event at the 10th day after application to early rice decreased 44.9 and 44.2% compared with urea, respectively. In conclusion, the 15-d period after application of urea was the critical time during which N loss occurred due to high floodwater N concentrations. But CRNF decreased N concentrations greatly in floodwater and runoff water during this period. As a result, it obviously reduced TN loss in runoff over the whole rice growth season.

Effects of Nitrogen Dosage on the Yield and Nitrogen Use Efficiency of Machine Transplanted Rice Using Dry Soil Preparation in Rice Paddy Field

[Objective] The aim was to analyze the effects of nitrogen dosage on the yield and nitrogen use efficiency of machine transplanted rice using the technology of dry soil preparation in rice paddy field. [Method] With conventional Japonica rice cultivar Shengdao 18 as the study material, the effect of nitrogen dosage on stem and tillers dynamics, yield components and nitrogen use efficiency were investigated using the technology of dry soil preparation in rice paddy field. [Result] The highest yield was 10 957.20 kg/hm^2 as the nitrogen application was 315.00 kg/hm^2. Meanwhile, the roughness ratio, grain-straw ratio and nitrogen use efficiency remained at a higher level. Low nitrogen application could not obtain high yield. In contrast, high nitrogen application quantity led to a significant decline in nitrogen use efficiency. [Conclusion] The study could provide a scientific basis for the further promotion of the technology of dry soil preparation in rice paddy field.

Effect of Different Winter Cover Crops on Carbon Dioxide Emission in Paddy Field of Double Cropping Rice Area in Southern China

In this study, a two-year experiment was conducted by suing a static chamber method to observe the effects of straw recycling of winter cover crops measure on CO2 emission fluxes in southern China. Three patterns of winter use were performed in the paddy field, including RRR （rice-rice-ryegrass （Lolium multiflorum L.） cropping system）, CRR （rice-rice-Chinese milk vetch （Astragalus sinicus L.） cropping system） and FRR （rice-rice cropping system with winter fallow）. During the winter, the average daily CO2 fluxes were greater （P 〈 0.05） in the RRR and CRR than the FRR. During the winter crop growing seasons, both the average daily CO2 fluxes and the total CO2 emissions were different as the following orders： RRR 〉 CRR 〉 FRR. The average CO2 fluxes during early rice and late rice season were similar. The highest CO2 flux was found at rice tillering stage with an order as the follows： RRR 〉 CRR 〉 FRR and CRR 〉 RRR 〉 FRR both in 2009 and 2010, respectively. The annual CO2 emissions of RRR and CRR were significantly higher respectively by 857.0 g.CO2-C.m2 and 607.4 g.CO2-C.m-2 than the FRR. The results show that straw recycling of winter cover crops measure may strongly influence the CO2 emission in paddy field in southern China.

Effects of straw and biochar addition on soil nitrogen,carbon,and super rice yield in cold waterlogged paddy soils of North China

The additions of straw and biochar have been suggested to increase soil fertility, carbon sequestration, and crop produc- tivity of agricultural lands. To our knowledge, there is little information on the effects of straw and biochar addition on soil nitrogen form, carbon storage, and super rice yield in cold waterlogged paddy soils. We performed field trials with four treatments including conventional fertilization system （CK）, straw amendment 6 t ha^-1 （S）, biochar amendment 2 t ha^-1 （C1）, and biochar amendment 40 t ha^-1 （C2）. The super japonica rice variety, Shennong 265, was selected as the test Crop. The results showed that the straw and biochar amendments improved total nitrogen and organic carbon content of the soil, reduced N2O emissions, and had little influence on nitrogen retention, nitrogen density, and CO2 emissions. The S and C1 increased NH4^＋-N content, and C2 increased NO3^--N content. Both S and C1 had little influence on soil organic carbon density （SOCD） and C/N ratio. However, C2 greatly increased SOCD and C/N ratio. C1 and C2 significantly improved the soil carbon sequestration （SCS） by 62.9 and 214.0% （P〈0.05）, respectively, while S had no influence on SCS. C1 and C2 maintained the stability of super rice yield, and significantly reduced CH4 emissions, global warming potential （GWP）, and greenhouse gas intensity （GHGI）, whereas S had the opposite and negative effects. In summary, the biochar amendments in cold waterlogged paddy soils of North China increased soil nitrogen and carbon content, improved soil carbon sequestration, and reduced GHG emission without affecting the yield of super rice.

Discrepancy in Response of Rice Yield and Soil Fertility to Long-Term Chemical Fertilization and Organic Amendments in Paddy Soils Cultivated from Infertile Upland in Subtropical China

From 1990,over 17 years field experiment was carried out in paddy field cultivated from infertile upland to evaluate the response of rice productivity,soil organic carbon（SOC）,and total N to long-term NPK fertilization or NPK combined with organic amendments.The field trials included NPK（N,P,K fertilizer）,NPKRS（NPK combined with rice straw）,NPK2RS（NPK combined with double amount of rice straw）,NPKPM（NPK combined with pig manure） and NPKGM（NPK combined with green manure） and the cropping system was rice-rice（Oryza sativa L.） rotation.Annual rice yield,straw biomass,and harvesting index increased steadily with cultivation time in all treatments.Average annual rice yield from 1991 to 2006 was ranged from 7 795 to 8 572 kg ha-1 among treatments.Rice yields in treatments with organic amendments were usually higher than that in treatment with NPK.Contents of SOC and total N also increased gradually in the cultivation years and reached the level of 7.82 to 9.45 and 0.85 to 1.03 g kg-1,respectively,in 2006.Soil fertilities in treatments with chemical fertilization combined with organic amendments were relatively appropriate than those in treatment with NPK.There was obvious discrepancy between cumulative characters of rice yield and soil organic fertility in newly formed paddy field.Compared with relatively high rate of crop productivity improvement,cumulative rates of SOC and total N were much lower in our study.SOC and total N contents were still less than half of those in local highly productive paddy soils after 17 years cultivation in subtropical China.Present work helps to better understand the development of infertile paddy soils and to estimate the potential of yield improvement in this region.

Effects of cracks and some key factors on emissions of nitrous oxide in paddy fields

Paddy field is a primary agricultural landscape in the south of China and is often regarded as one of main sources emitting nitrous oxide to atmosphere. The nitrous oxide emissions under a variety of paddy field practices, such as fertilization, flooding/draining management were investigated to study on agricultural activities on paddy field affect the dynamic process of the emission. Under no addition of fertilizers the average emission flux of nitrous oxide was 8 55 μg/(m 2·h) during the rice( Oryza Sativa L.) growth season. The results indicated that most of nitrous oxide emissions occurred during the crack forming and expansion period when paddy field was being drained. The diurnal emissions peak of nitrous oxide appeared at 20∶30 at night in cracked rice fields. The statistical analysis suggested that the correlation of nitrous oxide emissions flux( Y ) with soil water content( X 1), soil temperature( X 2), and E h( X 3), could be described in a regression equation: Y =-1498 95+2895 48 X 1+50 63 X 2-96 99 X 1· X 2+0 006 X 2· X 3 There were the different power equations to simulate the correlations between the everyday dynamic N 2O emissions and the mean surface area of cracks, mean volume and depth of cracks respectively during paddy soil drying by soil columns incubation experiments. Taken all together, the current study presented a dynamic analysis of nitrous oxide emission of paddy field under various conditions, therefore provided a basis for the management to balance between environmental effect and paddy field activities.

Effects of Micro-Topographic Reestablishment on Paddy Impoundment and Rice Yield

From a perspective of cultivation measures, it was needed to develop a new paddy impoundment model to achieve higher rice yield with higher water utilization efficiency. This study was conducted to quantify the effect of ridge- tillage terrace ecological rice farming （RT）, bed ecological rice farming （B） and conventional ecological rice farming （CK） on the paddy impoundment model and rice yield, and determine dry matter accumulation （DMA）, rice yield, yield component, and parameters of the ridge tillage and the bed. The RT could be used to achieve the dual improvement in the capacity of natural precipitation storage and in soil aeration by dry-wet alternation damp irrigation. Water storage capacity in the RT was 29% higher than that of the CK and most of the water was stored in the ditch. The grain yield of each of different rice cultivars （except the cultivar Huanghuazhan in 2011） in the RT was significantly higher than that of the CK. The total DMA in the RT was 16.5% in 2011 and 28.2% in 2012 higher than that of the CK, respectively. The variation of DMA before and after the full-heading stage among rice cultivars was inconsistent. Consequently, the RT was an effective measurement of micro- topographic reestablishment for changing paddy impoundment model, increasing water storage capacity, especially the natural precipitation storage, and increasing rice yield.

Effects of Green Manure Rotation on Rice Growth Dynamics and Nitrogen Uptake and Utilization

This study aimed to comprehensive evaluation of different winter green manure on characterization of nitrogen uptake and utilization, to provide the basis for N fertilizer reasonable operation and characteristics improvement of nitrogen nutrition in rice high-yield cultivation. This experiment was set to compare milk vetch, rapeseed,ryegrass and mixed of green manure on rice yield, rice growth dynamics and nitrogen uptake and utilization in rice. The results showed that among 4 different winter green manure, the treatment of MV-R-R（milk vetch-rice-rice） for the early rice yield was the most than others treatments. Compared with RG-R-R（ryegrass-rice-rice）, RPR-R（rapeseed-rice-rice）, MS-R-R（mixed green manure-rice-rice）, the treatment of MVR-R inceased by 6.61%, 3.29%, 0.78%, respectively. The treatment of MV-R-R in N content in plant of rice was maximized in the tillering, booting, heading and maturity periods, respectively higher than the average of other treatments 9.68%, 19.72%,6.23% and 8.66%. At tillering, booting, heading and maturity, the treatment of MV-R-R were the highest in N uptake, RP-R-R minimum. The N periodic accumulation for MV-R-R were higher than other treatments in the tillering to booting, booting to heading and heading to maturity periods. The rates respectively were 21.81%, 68.73% and286.5%. In addition, N periodic accumulation and its ratio to total in the heading to maturity was minimum, maximum before tillering under green manure rotation system.So the cropping system of milk vetch-rice-rice could increase nitrogen use efficiency and improve N cycling.

Characteristics of Soil Fertility of Buried Ancient Paddy at Chuodun Site in Yangtze River Delta, China

Field investigation and laboratory analysis of 22 ancient paddy soils excavated at Chuodun site, Kunshan City, Jiangsu Province, China were carried out in 2003 to （1） understand the basic characteristics of ancient paddy soils, （2） compare the difference of soil fertility between ancient paddy soils and recent paddy soils, and （3） inquire into mechanisms of the sustainability of paddy soil. The oldest paddy soils at Chuodun site can be dated back to Neolithic age, around 6000 aBP. These ancient fields were buried in about 1-m deep from the soil surface and their areas ranged from 0.32 to 12.9 m^2 with an average of 5.2 m^2. The paddy soils with 〉 5 000 pellets phytolith g^-1 soil were termed intensively cultivated paddy soils （ICPS） and those with 〈5000 pellets phytolith g^-1 soil were called weakly cultivated soils （WCPS）. The contents of organic carbon （OC）, and total N in the former were significantly higher than that in the latter. Ancient paddy soils had higher soil pH and C/N, total and available P, and lower contents of OC, DOC, total N, S, Cu, Fe, and available K, S, Fe, Mn, and Cu compared with recent paddy soils, which were attributed to application of chemical and manure fertilizers, pollution and acidification in recent paddy soils. The variation coefficients of OC and other nutrients in ancient paddy soils with higher PI were greater than that in ancient paddy soils with low PI, which indicated that human activities had a great impact on the spatial variability of soil nutrients. The contents of OC, total N, P and S in ancient paddy soils were higher than that in ancient moss of the same age, which indicated that planting rice during Majiabang culture period was beneficial to the accumulation of those life elements.

A possible mechanism of mineral responses to elevated atmospheric CO_2 in rice grains

Increasing attentions have been paid to mineral concentration decrease in milled rice grains caused by CO2 enrichment, but the mechanisms still remain unclear. Therefore, mineral （Ca, Mg, Fe, Zn and Mn） translocation in plant-soil system with a FACE （Free-air CO2 enrichment） experiment were investigated in Eastern China after 4-yr operation. Results mainly showed that： （1） elevated CO2 significantly increased the biomass of stem and panicle by 21.9 and 24.0%, respectively, but did not affect the leaf biomass. （2） Elevated CO2 significantly increased the contents of Ca, Mg, Fe, Zn, and Mn in panicle by 61.2, 28.9, 87.0, 36.7, and 66.0%, respectively, and in stem by 13.2, 21.3, 47.2, 91.8, and 25.2%, respectively, but did not affect them in leaf. （3） Elevated CO2 had positive effects on the weight ratio of mineral/biomass in stem and panicle. Our results suggest that elevated CO2 can favor the translocation of Ca, Mg, Fe, Zn, and Mn from soil to stem and panicle. The CO2-led mineral decline in milled rice grains may mainly attribute to the CO2-1ed unbalanced stimulations on the translocations of minerals and carbohydrates from vegetative parts （e.g., leaf, stem, branch and husk） to the grains.

The Effect of Bamboo Charcoal Application on Soil Nutrients and Heavy Metals in Rice

Soil heavy metal pollution is becoming more and more serious.Biomass charcoal application can play an important role in alleviating the toxicity of heavy metals in soils.Compared with other biochar,bamboo charcoal has more unique properties and may have a unique effect on heavy metal pollution.Zhejiang Province of Southeastern China is rich in bamboo resources.However,few studies related to bamboo charcoal application for heavy metal remediation in farmland were reported.In this study,four treatments with different amounts of bamboo charcoal application were set up through a field experiment,namely BC0(no bamboo charcoal application),BC1(2500 kg⋅ha^(−1)),BC2(5000 kg⋅ha^(−1)),and BC3(10000 kg⋅ha^(−1)),and each treatment was replicated three times.The results showed that(1)The application of bamboo charcoal significantly increased the soil pH and organic matter content.Compared with BC0,the pH and organic content of BC3 increased by 7.4%and 17.4%(P<0.05)respectively.(2)The HCl-extractable Cd content of paddy soil in the BC1 treatment was significantly lower than other treatments(P<0.05),and decreased by 15.3%,compared with BC0.The soil HCl-extractable Zn and Cu content did not differ significantly between treatments(P>0.05).(3)With the increase of bamboo charcoal application,the Cd content in rice gradually decreased,the BC3 treatment significantly decreased by 39.0%(P<0.05),and the Zn and Cu contents in rice did not differ significantly between treatments(P>0.05),compared with BC0.(4)Soil pH,organic matter and Cd in rice seeds were significantly negatively correlated(P<0.01).The heavy metal content in rice does not change with the change of heavy metal content with HCl-extractable state in soil.It means bamboo charcoal does not reduce heavy metal content in rice by simply declining the heavy metal content with HCl-extractable state.The mechanism of action is relatively complicated,and further study is needed.

江汉平原典型种植模式稻田土壤中农药残留特征

在江汉平原中稻-油菜/小麦轮作田、一季中稻田及再生稻田3种种植模式稻田采集土壤样品86个。调查了土壤样品中滴滴涕(DDTs,包括o,p′-DDT、p,p′-DDT、p,p′-DDE、p,p′-DDD)、六六六(HCHs,包括α-HCH、β-HCH、γ-HCH、δ-HCH)、甲胺磷、甲基对硫磷、氧乐果、乐果、敌敌畏、乙酰甲胺磷、毒死蜱、氯虫苯甲酰胺、吡蚜酮、吡虫啉、啶虫脒、三环唑、戊唑醇、氰氟草酯、二氯喹啉酸、乙草胺及异丙甲草胺等25种农药及其代谢产物的残留。结果表明,检出率最高的3种农药为当前常用杀虫剂氯虫苯甲酰胺(87.21%),杀菌剂三环唑(91.86%)及戊唑醇(72.09%),其残留均值分别为0.0397、0.0734 mg/kg及0.0276 mg/kg;已经禁用的有机氯农药滴滴涕(o,p′-DDT、p,p′-DDT、p,p′-DDE、p,p′-DDD)仍能检出,检出率为36.05%~66.28%。3种模式田块中检出的滴滴涕主要来源于历史上滴滴涕的使用。杀虫剂吡蚜酮及杀菌剂三环唑在再生稻田的残留量均值显著高于中稻-油菜/小麦轮作田及一季中稻田;但其他农药在不同种植模式稻田中的残留没有显著差异。本研究为江汉平原农药残留的治理及农药的合理使用提供了参考信息。

施氮量对川东南冬水田稻鱼共作系统下杂交稻产量和土壤养分的影响

【目的】利用川东南冬水田区连续多年稻鱼共作系统,研究施氮(N)量对免耕栽培杂交稻产量形成和土壤养分的影响,为制定稻鱼共作系统下免耕栽培杂交稻长期、合理的氮肥管理策略提供理论依据。【方法】于2018—2022年在川东南冬水田区开展了5年大田定位试验,供试杂交稻品种为蓉优1015和内6优103,耕作方式为免耕。设置N 0、45、90、135 kg/hm^(2)4个施氮水平,分别记作N_(0)、N_(45)、N_(90)、N_(135)。在水稻收获期,调查杂交稻产量及产量构成因素,分析0—20 cm土层土壤全量和速效氮、磷、钾含量,以及有机质含量和pH,通过回归分析,研究施氮量与水稻产量和土壤养分因子含量变化之间的关系。【结果】稻鱼共作系统下,年份、施氮量对杂交稻产量及产量构成的影响达极显著水平。5年间,杂交稻产量与施氮量均呈极显著正相关(r=0.9070^(**)~0.9720^(**)),与低氮量处理N_(45)相比,N_(90)和N_(135)处理杂交稻产量分别增加了6.37%~26.53%、9.11%~25.11%,单位面积有效穗数和每穗粒数也显著增加。而N_(90)处理杂交稻产量与N_(135)处理相当或更高。逐步回归分析结果表明,杂交稻产量构成(单位面积有效穗数、每穗粒数、结实率和千粒重)与产量的偏相关系数达显著或极显著水平(t=2.20*~9.17^(**))。通径分析结果表明,杂交稻单位面积有效穗数和每穗粒数对产量的直接贡献(分别为0.8754和0.4987)和总贡献(分别为0.6364和0.3598)较大,表明单位面积有效穗数和每穗粒数是影响产量的主要因素。在N_(0)、N_(45)处理下,土壤全氮、碱解氮含量随稻鱼共作年限的增加而下降,而在N_(90)、N_(135)处理下随稻鱼共作年限的增加而增加。土壤全氮、碱解氮含量随施氮量增加而提高,而全磷、全钾、速效磷、速效钾含量则随施氮量增加而下降。杂交稻产量与土壤养分含量呈极显著正相关,可见提高磷素、钾素供给能力是稻鱼共作系统杂交稻高产的重要基础。【结论】川东南冬水田区稻鱼共作系统下,年施氮90 kg/hm^(2)可以提高杂交水稻的单位面积有效穗数和每穗粒数,进而维持甚至提高水稻产量。连续施用中、高量氮肥还可以提升土壤有机质、全氮、全磷、全钾、碱解氮、速效磷和速效钾含量,且随稻鱼共作年限延长呈增加趋势;土壤pH值则随稻鱼共作年限延长呈下降趋势。

稻萍共生对水稻磷素吸收和磷肥利用效率的影响

稻萍共生是我国传统的稻作方式,能提高水稻产量和氮肥利用效率,然而目前还鲜有研究关注稻萍共生对水稻磷肥利用效率的影响。通过田间试验,探讨稻萍共生处理对稻田土壤理化性质、水稻产量和磷肥利用效率的影响。结果表明:稻萍共生处理未显著改变土壤有机质、总氮、总磷和有效磷含量,但显著提高土壤硝态氮含量(P<0.05)。稻萍共生促进了水稻的磷吸收,显著增加了籽粒磷吸收量(P<0.05)和地上部总磷吸收量(P<0.05)。此外,稻萍共生还提高了水稻的磷肥回收利用率(P<0.05),说明稻萍共生处理能有效提高水稻磷肥利用效率,为水稻磷肥的高效利用提供了参考途径。

节水灌溉下秸秆还田形式对黑土区稻田N_(2)O排放与产量的影响

为探寻不同灌溉模式下秸秆还田形式对黑土区稻田N_(2)O排放与产量的影响,于2023年进行大田试验,设置常规灌溉(F)与控制灌溉(C)两种灌溉模式,同时设置秸秆还田(S)、秸秆炭化为生物炭还田(B)、秸秆过牛腹为有机肥还田(O)3种还田形式,以及秸秆不还田(N)作为对照组,共计8个处理。分析不同灌溉模式下秸秆还田形式对稻田N_(2)O排放通量与水稻产量的影响,测定了水稻各生育期稻田土壤铵态氮含量、硝态氮含量、微生物氮含量、pH值,并分析了N_(2)O排放总量和水稻产量与土壤环境因子之间的关系。结果表明:除返青期外,与秸秆不还田处理相比,秸秆还田与有机肥还田处理土壤铵态氮含量、硝态氮含量、微生物氮含量均表现为增加。相同秸秆还田形式下,控制灌溉模式下各处理生育期内土壤平均铵态氮含量、硝态氮含量较常规灌溉模式高36.23%~60.82%、14.16%~19.61%。同时,秸秆还田与生物炭还田能提高稻田土壤pH值。相同灌溉模式下,与秸秆不还田处理相比较,秸秆还田与有机肥还田处理N_(2)O排放总量分别增加14.44%~24.09%、8.22%~14.44%,生物炭还田处理N_(2)O排放总量降低14.31%~23.90%。生物炭还田与有机肥还田各处理水稻产量提高3.28%~13.07%,其中控制灌溉模式下生物炭还田处理产量最高。综上所述,控制灌溉下生物炭还田可以实现节水、增产、减排的目的。

不同矿物调理剂对Cd污染水田土壤性质及水稻Cd含量的影响

【目的】探究不同矿物调理剂对广西镉(Cd)污染水田土壤性质及水稻Cd含量的影响,为利用水田生产安全稻米提供参考依据。【方法】选用钙镁硅调理剂A和B、钙硅调理剂C和钙镁调理剂D(分别设为A、B、C和D处理),在广西某受Cd污染水田开展Cd污染大田修复治理试验,以不施用调理剂为对照(CK)。处理后于水稻成熟期测定土壤的pH、阳离子交换量(CEC)、总Cd和土壤有效态Cd含量及水稻根、茎、叶和籽粒的Cd含量,分析不同矿物调理剂对Cd污染水田土壤的修复治理效果及Cd在水稻各部位的残留状况,并对土壤总Cd含量、CEC和pH与有效态Cd含量进行相关分析。【结果】施用矿物调理剂可显著提高Cd污染水田的土壤pH和CEC(P<0.05,下同),二者分别较CK提高15.0%~16.6%和20.4%~23.8%;可显著降低Cd污染水田的土壤有效态Cd含量,较CK下降14.0%~19.3%。施用矿物调理剂后水田的土壤有效态Cd含量与pH呈显著负相关,pH的对数ln(pH)值与土壤有效态Cd含量的相关系数为0.4053;ln(pH)值与CEC呈极显著负相关(P<0.01),相关系数为0.6326;随着土壤pH和CEC的上升,土壤有效态Cd含量持续下降。施用矿物调理剂均可有效降低水稻根、茎、叶和籽粒的Cd含量及水稻地上部Cd的富集系数,其中,水稻籽粒的总Cd含量下降35.9%~50.2%,水稻地上部(茎、叶和籽粒)Cd的富集系数分别下降19.5%~33.5%、32.1%~44.9%和38.6%~52.6%。【结论】施用不同矿物调理剂均可显著提升水田土壤pH和CEC,从而降低土壤有效态Cd含量,抑制Cd从土壤向水稻根、茎、叶和籽粒迁移,有效降低水稻Cd含量,减少Cd在水稻地上部(茎、叶和籽粒)富集。

硝化抑制剂双氰胺施用对水稻产量和温室气体排放的影响

为探究施用硝化抑制剂双氰胺对水稻产量和温室气体排放的影响,以常规粳稻品种南粳9108为供试材料进行盆栽试验,设置常规氮肥(CK)和常规氮肥配施硝化抑制剂双氰胺(DCD)2个处理。采用静态箱-气相色谱法连续监测稻田温室气体排放动态变化。结果表明,与CK相比,DCD显著提高了水稻产量(15.1%)和地上部生物量(28.4%),并且显著降低了稻田甲烷(CH_(4))累积排放量(22.2%)、氧化亚氮(N_(2)O)累积排放量(56.0%)、综合温室效应(GWP)(24.4%)和温室气体排放强度(GHGI)(31.7%)。可见,常规氮肥配施硝化抑制剂双氰胺可以协同实现水稻丰产和稻田温室气体减排。

稻蛙生态种养模式碳足迹评价

【目的】开展稻蛙生态种养模式碳足迹系统性研究,为该模式的可持续发展提供科学依据和优化建议。【方法】采用生命周期评价法,对常规水稻种植(Traditional rice monoculture,TR)、绿色稻蛙种养(Green rice-frog coculture,GF)和有机稻蛙种养(Organic rice-frog coculture,OF)模式进行碳足迹评价。【结果】GF和OF的单位面积碳足迹分别为5985.20和5632.99 kg CO_(2)e·hm^(−2),相比TR分别降低5.98%和11.51%,单位利润碳足迹分别下降45.10%和45.87%,单位营养密度碳足迹分别下降14.63%和12.17%。GF和OF净生态系统经济效益提高了50%以上,其中GF的高达71.77%。与TR相比,GF的产量差异不显著,OF的产量降低了16.73%;GF和OF的CH4排放分别增加了58.13%和131.18%,N2O排放分别降低了41.06%和63.12%;GF和OF具有更高的全球增温潜势和温室气体排放强度,其中,OF的影响更为显著。GF和OF中,有机物料如紫云英、菜籽饼和有机肥的投入表现为净碳固定效应。碳足迹构成和敏感性分析显示,TR的碳足迹构成中温室气体排放(57.07%)和化肥施用(32.88%)占比较高;OF的碳排放和固定均高于GF,CH4排放和尼龙防护网使用对GF和OF的贡献最大。不确定性分析表明,GF和OF的单位面积碳足迹分别为5907.29和5647.25 kg CO_(2)e·hm^(−2),低于TR,变异系数小于7.5%。【结论】稻蛙共作模式(GF和OF)相较于TR模式具有更低的碳足迹以及更突出的碳固定效应和环境友好等特点,为气候变化背景下我国水稻产业的绿色低碳发展提供了新的科学依据。

稻田不同水旱复种模式对土壤团聚体及碳氮的影响

【目的】探寻更适合南方稻田可持续发展的水旱复种模式。【方法】在江西农业大学科技园开展紫云英−早稻−晚稻(CK)、紫云英−早稻−晚玉米||晚大豆(CRI)、油菜−早稻−晚玉米||晚大豆(RRI)、油菜−早稻−晚稻(RRR)水旱复种模式的田间对比试验。【结果】土壤有机碳、全氮含量均为CK>RRR>CRI>RRI。种植紫云英模式的R0.250(粒径≥0.250 mm的团聚体含量)比种植油菜模式的高,土壤结构的稳定性更强。CRI的早稻产量高于其他处理。【结论】在南方地区推行紫云英−早稻−晚玉米||晚大豆种植模式(CRI),有利于农业的可持续发展。