水分管理和施用石灰对水稻镉吸收与运移的影响

通过田间试验,研究了间歇灌溉和全生育期淹水2种水分管理结合水稻分蘖期施用石灰对不同水稻生育期的土壤和水稻各组织中Cd分布与运移的影响。研究结果表明,全生育淹水和施用石灰均能升高土壤p H值,降低土壤中有效态Cd含量;施用石灰能降低土壤中酸可提取态Cd所占比例而残渣态所占比例增加。在全生育期淹水条件下施用石灰有利于改善土壤性状并提高土壤中Fe质量百分含量。与不施用石灰相比,在间歇灌溉条件下,施用石灰处理的糙米中Cd质量分数从0.86 mg/kg降低到0.56 mg/kg,而在全生育期淹水条件下,施用石灰处理的糙米中Cd质量分数从0.77 mg/kg降低到0.34 mg/kg;无论间歇灌溉还是全淹水处理条件下,施用石灰均增加了水稻总生物量。施用石灰后,在灌浆期,水稻茎叶中Cd的富集系数显著降低(P0.05);在成熟期,根和稻米中Cd的富集系数显著降低(P0.05);在全生育期淹水条件下,成熟期水稻根到茎叶转运系数和茎叶到米中转运系数均显著降低(P0.05)。水稻糙米中Cd含量与土壤中有效态Cd含量、水稻地上部Cd累积量呈显著正相关,与土壤p H值呈显著负相关。上述研究结果表明,施用石灰能够显著降低稻田土壤中Cd的生物有效性;采用全生育期淹水结合在分蘖期施用石灰是降低稻米中Cd含量有效措施且不会导致水稻减产。     

不同生育阶段间歇灌溉对镉污染稻田双季稻产量构成与镉累积的影响

为给镉污染稻区水稻合理灌溉提供理论与技术参考,通过盆栽试验研究了不同生育阶段间歇灌溉对双季稻产量构成与镉累积的影响。结果表明:(1)2季水稻总产以全生育期淹水灌溉处理最高,其次是全生育期间歇灌溉与齐穗至灌浆中期间歇灌溉处理,孕穗至齐穗期间歇灌溉处理产量显著降低;全生育期淹水灌溉处理有利于提高结实率,而全生育期间歇灌溉与分蘖至孕穗间歇灌溉处理有利于提高有效穗数。(2)灌水方式显著影响水稻各器官成熟期镉含量,其中全生育期间歇灌溉有显著提高效果,而全生育期淹水灌溉有降低效应。孕穗至齐穗、齐穗至灌浆中期间歇灌溉处理早、晚稻籽粒镉含量显著低于其他生育阶段间歇灌溉处理。(3)地上部镉累积量以全生育期淹水灌溉处理最低,全生育期间歇灌溉处理最高;各间歇灌溉处理中,孕穗至齐穗、齐穗至灌浆中期间歇灌溉处理地上部镉累积量相对较低。综上所述,为确保双季稻产量、降低稻米镉含量,镉污染稻区最佳灌溉方式为全生育期淹水灌溉,在水资源较紧张的情况下,齐穗至灌浆中期可采取间歇灌溉方式。     

Growth and Iron Uptake of Lowland and Aerobic Rice Genotypes under Flooded and Aerobic Cultivation

With increasing water shortages in China, rice (Oryza sativa L.) cultivation is gradually shifting away from continuously flooded conditions to partly or even completely aerobic conditions. The effects of this shift on the growth and iron (Fe) nutrition of different aerobic and lowland rice genotypes are poorly understood. A field experiment was conducted to determine the effects of cultivation system (aerobic vs. flooded), genotype (five aerobic rice varieties and one lowland rice variety), and Fe fertilization [no Fe and 30 kg ha^?1 ferrous sulfate (FeSO₄·7H₂O] on rice grain yield and Fe nutrition. Plants were sampled at tillering and physiological maturity. In both aerobic and flooded plots, Fe application significantly increased shoot dry weight, shoot Fe concentration, and shoot Fe content at tillering but not physiological maturity. At physiological maturity, grain yield and Fe and grain harvest indices were significantly lower in aerobic than in flooded plots. Shoot dry weight and shoot Fe content differed among genotypes at tillering and at physiological maturity. The grain harvest index of aerobic rice genotype 89B-271-17(hun) was significantly greater than that of the other five genotypes when no Fe was applied. Because soil Fe fertilization did not improve the Fe nutrition of rice in aerobic plots, the results indicate that the shift from flooded to aerobic cultivation will increase Fe deficiency in rice and will increase the problem of Fe deficiency in humans who depend on rice for nutrition.     

Evaluation of palygorskite for remediation of Cd-polluted soil with different water conditions

Purpose

The study aimed at comparing the effects of different water managements on soil Cd immobilization using palygorskite, which was significant for the selection of reasonable water condition.

Materials and methods

Field experiment was taken to discuss the in situ remediation effects of palygorskite on Cd-polluted paddy soils, under different water managements, using a series of variables, including pH and extractable Cd in soils, plant Cd, enzyme activity, and microorganism number in soils.

Results and discussion

In control group, the pH in continuous flooding was the highest under three water conditions, and compared to conventional irrigation, continuous flooding reduced brown rice Cd by 37.9%, and brown rice Cd in wetting irrigation increased by 31.0%. In palygorskite treated soils, at concentrations of 5, 10, and 15 g kg^?1, brown rice Cd reduced by 16.7, 44.4, and 55.6%; 13.8, 34.5, and 44.8%; and 13.1, 36.8, and 47.3% under continuous flooding, conventional irrigation, and wetting irrigation (p < 0.05), respectively. The enzyme activity and microbial number increased after applying palygorskite to paddy soils.

Conclusions

Continuous flooding was a good candidate as water management for soil Cd stabilization using palygorskite. Rise in soil enzyme activity and microbial number proved that ecological function regained after palygorskite application.

     

Dry cultivation enhances cadmium solubility in contaminated soils but minimizes cadmium accumulation in a leafy vegetable

Purpose

Water management has a strong influence on Cd solubility in agricultural soils, affecting Cd uptake in crops. In the process, sulfur interaction with other metals such as zinc may play an important role. A pot experiment was carried out to investigate the effects of water management coupled with zinc and sulfate amendment on Cd uptake by the leafy vegetable amaranth with a strong Cd accumulation tendency in its edible parts.

Materials and methods

The soils were amended with Cd, Cd+SO₄ and Cd+SO₄+Zn with no amendment as control. Then, the soils were flooded for 1 month, after which amaranth was grown with soil kept saturated (wet cultivation). In the succeeding planting, soils were tilled to aeration condition under which amaranth was grown again (dry cultivation). Soil and crop samples were collected and analysed for various parameters.

Results and discussion

The readily exchangeable quantities of Cd and Zn in the soil decreased under wet cultivation, increasing again under dry cultivation but to levels lower than those in the initial soil. Wet cultivation enhanced plant Cd concentration but reduced Zn accumulation compared to dry cultivation. Zn bioavailability was strongly affected by soil water status but failed to reduce Cd uptake by amaranth. Irreversible or slowly reversible changes occurred in Cd and Zn solubility and phytoavailability as soil water-saturated status was altered by periodic flooding events.

Conclusions

Dry cultivation with lower soil water content ensured high production with low Cd in the edible part of this leaf vegetable and so remains the recommended irrigation regime.

     

阻隔主要外源输入重金属对土壤-水稻系统中镉铅累积的影响

土壤-水稻系统中重金属输入输出调控对稻田污染防治和水稻安全生产具有重要意义。该文研究稻草移除、截断大气沉降、清洁水灌溉等调控措施对稻田土壤-水稻系统中重金属Cd和Pb的累积与运移特征的影响。结果表明,稻草移除、截断大气沉降和清洁水灌溉均能明显降低污染土壤中有效态重金属含量和水稻中重金属的累积量。与稻草还田对照处理相比,除种植早稻后的土壤有效态Pb含量外,稻草移除处理下土壤中有效态Cd、Pb含量均略有降低,且在该处理下,早稻糙米中Pb含量与晚稻糙米中Cd、Pb含量显著降低,降幅分别为3.6%、10.4%和32.4%;稻草移除+截断大气沉降处理下,土壤中有效态Cd、Pb含量均不同程度地下降,种植晚稻后的土壤有效态Pb含量显著降低,除早稻的根和糙米中Cd含量外,其余早晚稻水稻各部位Cd、Pb含量均显著降低,水稻根和茎叶Cd、Pb含量平均降幅分别为32.8%、36.8%和32.2%、24.8%,晚稻糙米Cd、Pb累积量分别显著降低66.3%和22.2%;稻草移除+清洁水灌溉处理下,种植早晚稻后的土壤有效态Cd、Pb含量平均下降幅度分别为11.7%和15.9%,早晚稻各部位Cd、Pb含量降低幅度较大,早晚稻根和茎叶Cd、Pb含量平均降幅分别为38.34%、30.35%和43.4%、13.2%,晚稻糙米中Cd、Pb累积量降幅分别为39.4%、67.2%。分析水稻地上部的Cd、Pb富集与转运系数表明,稻草移除结合截断大气沉降或清洁水灌溉等控源措施可显著降低Cd、Pb在水稻地上部位的富集系数,减少地上部位重金属的累积量。上述结果表明,采用稻草移除结合截断大气沉降或清洁水灌溉措施可进一步降低土壤中有效态Cd、Pb含量和水稻中Cd、Pb富集。因此,控制区域大气污染,净化农田灌溉水等控源措施,同时施行稻草移除等输出污染农田土壤中重金属等策略,可有效实现污染农田土壤安全利用和水稻安全生产。     

Effects of phosphate on trace element accumulation in rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.): a 5-year phosphate application study

Purpose

Phosphate (P) fertilizers are being widely used to increase crop yield, especially in P-deficient soils. However, repeated applications of P could influence trace element bioaccumulation in crops. The effects of 5-year P enrichment on trace element (Cu, Zn, Cd, Pb, As, and Hg) accumulation in Oryza sativa L. were thus examined.

Materials and methods

Two paddy soils with different initial P availabilities were amended with and without P fertilizer from 2009 to 2013. Trace elements and P levels in rice and soils were analyzed.

Results and discussion

In soil initially with limited P, P amendment enhanced grain Pb, As, and Hg concentrations by 1.8, 1.5, and 1.4-fold, respectively, but tended to decrease the grain Cd level by 0.73-fold, as compared to the control. However, in soil initially with sufficient P, P amendment tended to reduce accumulation of all examined elements in rice grain.

Conclusions

Phosphate amendment in initially P-limited and P-sufficient soils had different effects on trace element availability in soil (as reflected by extractable element) and plant physiology (growth and metal translocation), resulting in contrasting patterns of trace element accumulation in rice between the two types of soils. Our study emphasized the necessity to consider the promoting effects of P on Pb, As, and Hg accumulation in grain in initial P-deprived soil.

     

Iron deficiency enhances cadmium uptake and translocation mediated by the Fe2+ transporters OsIRT1 and OsIRT2 in rice

Abstract

Cadmium (Cd) accumulation in rice grains is enhanced if ponded water is released from paddy fields during the reproductive stage (intermittent irrigation). The release of ponded water creates aerobic soil conditions under which Cd becomes soluble and iron (Fe) solubility decreases. We hypothesized that Fe shortage in rice induces Fe uptake and translocation and that Cd is also taken up and translocated throughout this process. Hydroponically cultured Fe-deficient rice absorbed more Cd than did Fe-sufficient rice, and the presence of Fe enhanced the translocation of Cd to the shoots. Yeast mutants expressing OsIRT1 and OsIRT2, which encode the rice Fe²⁺ transporter, became more sensitive to Cd, suggesting that Cd was absorbed by OsIRT1 and OsIRT2. We discuss the possibility that Cd accumulation in rice grains during the reproductive stage is mediated by the Fe transport system.     

Effects of soil amendments, foliar sprayings of silicon and selenium and their combinations on the reduction of cadmium accumulation in rice

Agricultural soil contamination by cadmium (Cd) is becoming one of the most serious environmental issues and public concerns. In this study, factorial arrangements of treatments were designed to explore the effects of two soil amendments, sodium sulfide-biofuel ash (SSBA) and lime (0.1%), and three foliar applications, silicon (Si, 2.5 mmol L^-1), selenium (Se, 40 mg L^-1), and their combination (SS), on Cd reduction in rice (Oryza sativa L.) in a pot experiment, which were then verified in a field experiment. Compared with the control without amendment but with spraying of deionized water, both SSBA and lime significantly reduced concentrations of CaCl₂-extractable Cd in soil by 30%-39% and 31%-40% and Cd in brown rice by 44%-63% and 53%-72% in the pot and field experiments, respectively. Foliar Si, Se, and SS applications significantly reduced Cd accumulation in brown rice by 62%-64%, 72%-83%, and 39%-73%, respectively, increased rice grain yield, and improved antioxidant enzyme activities in rice leaves but with different trends in the pot and field experiments. Combinations of SSBA and lime with Si, Se, and SS had a non-significant synergistic effect on Cd reduction in brown rice compared to only foliar spraying or soil amendment in both pot and field experiments, although SSBA + Se and SSBA + Si reduced Cd concentration in brown rice by 16%-34% and 14%-24% compared to only foliar Si and Se and soil SSBA applications, respectively. Soil lime application and foliar Si spraying were the most cost-effective strategies to reduce Cd accumulation in brown rice in the field and pot experiments, respectively. Although soil amendments and foliar treatments were individually effective, their combinations failed to generate a significant synergistic reduction of Cd concentration in brown rice.     

Arsenic speciation in xylem exudates of rice growing in arsenic-contaminated soil

Rice has a much enhanced arsenic (As) accumulation compared with other cereal crops. How As is transported in xylem exudates of rice growing in soil remains unknown. We quantified the chemical species of As in xylem exudates of rice growing in arsenic-contaminated soil (62.5 mg As per kg soil) under flooded and aerobic conditions. In the aerobic treatment, the predominant species of As in the xylem sap was arsenate [As(V)], accounting for 64–88%, and the remainder was arsenite [As(III)]. In the flooded treatment, dimethylarsinic acid (DMA) was detected in the xylem sap besides As(III) and As(V), and the percentages of the three species As was 11–20%, 26–77%, and 12–54%, respectively. As speciation in the soil solution was dominated by As(V) under aerobic conditions, and dominated by As(III) under flooded conditions. DMA was detected at low concentrations in some of the flooded solution samples. Our results show that As speciation in the xylem sap differs in different water management regimes and correlate with As speciation in the soil solution strongly.     

不同水分管理模式下坡缕石修复稻田土壤镉污染效果

  目的  探究在合理的水分管理模式下提高坡缕石钝化稻田土壤镉的效率,及坡缕石施加对土壤理化性质、环境质量和水稻抗氧化胁迫的影响。  方法  采用盆栽试验方法,试验设置长期淹水、传统灌溉和湿润灌溉3种水分管理措施,每一水分管理模式下设0%、0.5%、1.0%、1.5%、2.0%和2.5% 6个坡缕石施加浓度,共18个处理,通过测定土壤pH、zeta电位、有效态镉、稻米生物量、稻米镉含量、土壤酶和叶抗氧化酶活性,分析不同水分管理措施与坡缕石用量组合修复镉污染的效果。  结果  长期淹水、传统灌溉和湿润灌溉下,坡缕石处理土壤pH分别增加0.49 ~ 1.24、0.49 ~ 1.47和0.42 ~ 1.64个单位,0.025 mol L?1 HCl提取态镉含量分别下降15.4% ~ 46.2%,11.5% ~ 39.7%和11.4% ~ 32.4%,毒性浸出法提取态镉最大降幅分别为47.4%、42.4%和40.2%（P < 0.05）。未施加坡缕石条件下,与传统灌溉比,长期淹水、湿润灌溉的稻米生物量降低11.2%和19.3%（P < 0.05）。3种水分管理模式下,坡缕石处理的稻米镉含量分别下降21.9% ~ 75.0%,17.8% ~ 70.2%和17.4% ~ 66.5%,土壤磷酸酶活性最大增幅分别为40.0%、57.1%和40.9%,叶超氧化物歧化酶活性最大增幅分别为33.9%、50.2%和37.4%（P < 0.05）。  结论  长期淹水下坡缕石钝化土壤镉的效率最高,1.0%坡缕石施加使稻米镉含量降至我国食品污染物含量限量标准0.20 mg kg?1（GB 2762—2012）以下,长期淹水联合坡缕石施加组合为镉污染稻田土壤修复技术。     

田间施用石灰和有机肥对水稻吸收镉的影响

通过大田试验探究不同用量的有机肥与石灰对土壤pH、有机质和Cd有效态含量以及不同生育期水稻各器官中积累Cd的动态变化。结果表明:成熟期水稻各器官Cd含量规律为根>茎>叶片>稻壳>糙米。石灰的施用能显著提高土壤pH,在分蘖期时,低用量石灰与高用量石灰处理下土壤pH分别提高1.35,1.84个单位;有机肥的施用可以增加有机质含量,与对照相比,高用量有机肥处理在分蘖期时有机质含量提高6.60 g/kg,在成熟期提高2.72 g/kg。灌浆期是水稻吸收积累Cd的重要时期,石灰和有机肥的施用均能降低灌浆期土壤中有效态Cd含量,高用量有机肥与高用量石灰处理下土壤有效态Cd含量显著降低,分别降低52.05%和46.87%。有机肥和石灰均能显著降低糙米Cd含量,降Cd效果为高用量有机肥>高用量石灰>低用量有机肥>低用量石灰,高用量有机肥处理的效果最好,糙米Cd含量降低68.20%。     

Environmental assessment of closed greenhouse vegetable production system in Nanjing, China

Purpose

There is growing concern about vegetable safety and environmental contamination resulting from rapid development of greenhouse vegetable production in China.

Materials and methods

This paper presents an integrated study of the quality of soils, vegetables, fertilizers, water, and sediments and indicates the characteristics of primary pollutants such as N, P, and some heavy metals in soils using the spatial analysis. Furthermore, sources of soil pollutants were analyzed combining principal component analysis and vertical mobility results. Also the environment risk was evaluated on greenhouse vegetable production activities in a closed greenhouse vegetable production system in Nanjing City, China.

Results and discussion

Greenhouse vegetable fields, which applied more fertilizers than greenhouse strawberry fields, had serious accumulations of soil N, P, Cd, Cu, Pb, and Zn, suggested both by principal component analysis and vertical mobility results. This accumulation resulted in high Cd in some vegetables and high concentrations of N and P in irrigation water and groundwater. The result of spatial analysis showed the northwest and north-center regions which featured convenient transportation and irrigation water were the hotspots for pollutant accumulation. Concentrations of pollutants decreased from these regions to the periphery gradually; results further supported by correlation analysis.

Conclusions

The environmental management of this kind of production system should pay more attention to supervising and controlling the quality of agriculture inputs and improving the efficiency of fertilizer. Producers should utilize the soil appropriately based upon the environmental risk associated with different media. Finally, soil properties and plant species should be considered in the future when assessing soil environmental quality.     

斜发沸石对干湿交替稻田土壤速效钾和产量的影响

为了进一步探究斜发沸石在干湿交替稻田中的应用潜力,设置不同灌溉模式(淹灌和干湿交替灌溉)和不同斜发沸石用量(0、5、10t/hm2)的大田裂区试验,对2017-2018年稻田土壤速效钾动态变化和产量进行了研究。结果表明:稻田增施斜发沸石显著提高了水稻产量,在10t/hm2水平下产量最高,增产率达8.7%～22.3%。斜发沸石对稻田表层土壤速效钾含量和植株地上部钾素积累的提高有显著正效应,干湿交替灌溉显著提高了各生育期植株地上部钾素积累量,提高幅度分别为11.81%～21.42%(2017年)、9.69%～23.79%(2018年)。通径分析表明,斜发沸石增产是因为其显著增加了分蘖肥期和穂肥期土壤速效钾含量,提高了抽穗开花期和黄熟期地上部钾素积累。研究可为揭示干湿交替灌溉下提高钾肥利用效率的应用潜力,并一定程度上缓解稻田缺钾的局面提供依据。     

不同母质土壤-水稻系统Cd吸收累积特征及差异

通过选取土壤有效态镉(Cd)含量相近、母质不同的水稻土河沙泥(河流冲积物发育)和紫泥田(紫色砂页岩母质发育),添加不同浓度的外源Cd(0,0.5,1,2,5mg/kg)模拟Cd污染稻田土壤进行盆栽试验,研究不同母质稻田土壤Cd胁迫条件下水稻不同生育期对Cd吸收累积的差异,并推算出土壤Cd环境安全临界值。结果表明,水稻生育期2种土壤有效态Cd含量均在分蘖期最高,河沙泥有效态Cd含量平均为0.47mg/kg,紫泥田平均为0.36mg/kg,同一外源Cd水平下,河沙泥土壤有效态Cd含量高于紫泥田。对河沙泥而言,随着外源Cd浓度的增加,水稻总生物量呈现先增加后下降的趋势,当外源Cd浓度为1mg/kg时达到最大生物量,为47.11g/pot;而紫泥田水稻生物量呈现逐渐增加的趋势,但各处理间差异不显著(P0.05)。2种土壤中水稻糙米、谷壳、茎叶、根Cd含量均随外源Cd浓度的增加而增加,整体分布特征为根茎叶谷壳糙米,且河沙泥高于紫泥田;河沙泥水稻平均Cd累积量为51.71μg/pot,紫泥田平均Cd累积量为42.56μg/pot,2种土壤成熟期水稻Cd累积量对比分蘖期分别增加1.45,1.07倍。回归分析表明,河沙泥和紫泥田稻米Cd超标的土壤Cd安全临界值分别为2.03,3.14mg/kg。水稻对Cd的吸收累积特征及土壤Cd安全临界值因土壤母质不同而存在显著差异。     

Effects of deficit irrigation and transplanting methods of irrigated rice on soil physical properties and rice yield

This study evaluated how deficit irrigation and method of transplanting irrigated rice affected soil physical properties in the short term and rice yields under cultivation that did not involve wet levelling (puddling). Field experiments were conducted in 2009 and 2010 at Sakha Agric. Res. Sta., Egypt. Planting methods were as follows: traditional transplanting into flat flooded soil (M₁), transplanting into furrows (M₂) and into beds (M₃). The deficit irrigation treatments were as follows: irrigation every 6 days between transplanting and 2 weeks before harvesting, reference method (I₁), irrigation as in I₁ but with a continuous period of 12 days without irrigation (i.e. one irrigation event missed) at heading (I₂), irrigation as in I₁ but with an event missed at the beginning of tillering and at the start of head development (I₃) and irrigation as in I₁ but with 3 missed events, one each at the beginning of tillering, the start of the head development and panicle initiation (I₄). Results showed that relative to soil conditions before planting, both rice transplanting methods and deficit irrigation decreased soil bulk density, water holding pores percentage, fine capillary pores percentage and soil shear strength, whereas drainable porosity percentage increased. Soil cracked more under the reference treatment than under the other treatments. Rice transplanting into beds and maintaining irrigation every 6 days without any irrigation skip, treatment (I₁ × M₃), appeared appropriate for growing rice. This combination resulted in soil physical properties favourable for plant growth, producing the largest grain and straw yields of all the treatments.     

不同调理剂对农田镉污染稳定效果及水稻吸收的影响

采集浙江杭州郊区富春江沿岸镉(Cd)污染水稻土，选择前期试验筛选的对土壤Cd钝化效果良好、可显著降低稻米Cd的4种调理剂，开展室内培养试验和温室盆栽试验，探讨不同调理剂种类(袁梦YM、祝天峰ZTF、天象一号TX1、永清YQ)、用量(推荐用量、3倍推荐用量)和调理剂与生石灰配施对污染水稻土Cd的稳定效果及对水稻生长和糙米Cd含量的影响。室内培养试验结果发现，添加调理剂能使土壤pH显著升高，落干条件下土壤pH增幅较淹水条件下更为明显；施用推荐用量调理剂，土壤硝酸铵提取态Cd显著下降，调理剂推荐用量+生石灰处理较调理剂推荐用量处理下降更为显著；总体上，同一调理剂3倍推荐用量处理下硝酸铵提取态Cd降幅更大，表明硝酸铵提取态Cd受土壤pH影响显著，且YM、TX1调理剂对硝酸铵提取态Cd的降低效果较好。盆栽试验结果显示，施用石灰和商品调理剂均可实现水稻稳产或增产，并显著降低水稻糙米Cd含量，与调理剂施用后土壤Cd有效性降低相一致。含钙、能调节土壤pH并辅以有机质和养分的复合调理剂因兼具养分作用，对水稻稳产增产、糙米Cd含量降低更为有效。     

水氮互作对冷凉区域稻田氮素特征的影响

[目的]研究寒地稻田不同水肥管理模式下的土壤供氮特征,为筛选环境友好型寒地稻作灌溉施肥模式提供支撑。[方法]在大田试验条件下,设置间歇灌溉、淹灌2种水分管理模式及4个供氮水平(0,75,105,135kg/hm~2),以龙庆稻2号为材料,研究水肥互作模式对水稻产量、土壤供氮特征及氮素利用率的影响。[结果]灌溉模式和供氮水平对水稻产量、地上部氮素积累量、水稻氮素利用率均有显著(p0.05)或极显著影响(p0.01)。间歇灌溉模式下,增加氮肥施用量有利于提高单位面积水稻有效穗数、籽粒产量、生物产量、籽粒氮素累积量,均以施氮105kg/hm~2处理最高;水肥互作对氮素利用率影响明显,水稻的氮肥利用率在21.4%~59.1%;氮肥生理利用率、氮肥农学效率及氮肥偏生产力均随着施氮量的提高而降低,施氮量75kg/hm~2处理的氮素吸收利用各项指标均高于其他处理。相关分析表明,水肥因素是影响氮素积累及氮素吸收利用效率的重要因子。[结论]综合考虑水稻产量及氮素利用率的矛盾,间歇灌溉配合适宜减氮模式应予以高度重视。     

Field survey study on the difference in Cd accumulation capacity of rice and wheat in rice-wheat rotation area

Purpose

In the rice-wheat rotation area, Cd contamination affects food safety of rice and wheat. However, there have been conflicting results and different conclusions on the difference in Cd accumulation capacity of rice and wheat, and the factors that led to the difference were not clear.

Materials and methods

A field survey study was conducted by collecting 60 soil and grain samples in pairs during rice and wheat harvest in 30 long-term rice-wheat rotation areas with clean and mild Cd contamination in Jiangsu Province, China. The soil physicochemical properties, total Cd, soil available Cd, and grain Cd were determined, and the factors affecting Cd accumulation in rice and wheat were analyzed.

Results and discussion

The soil pH during wheat season (22 sampling points) was slightly higher than that during rice season; thus, soil available Cd in wheat was generally lower (with an average three times lower) than that in rice soil. The mean Cd content in rice grain was only half of that in wheat grain, and the Cd concentration in rice and bioconcentration factor of rice at 26 sampling points (86.7% of total samples) were lower than those of wheat, indicating that Cd accumulation capacity of wheat was stronger than that of rice. Pearson correlation coefficient and multivariate linear regression models revealed that the main factors affecting the difference of Cd accumulation in rice and wheat were soil pH and available Cd content in soil.

Conclusions

The Cd accumulation capacity of wheat was higher than that of rice, especially in neutral and alkaline soil, and the Cd contents in rice and wheat grain depended on the soil pH and available Cd content. The food security risk of wheat was more noteworthy than rice in rice-wheat rotation area.

     

Influence of water management on the mobility and fate of copper in rice field soil

Purpose

With widely applied water-saving irrigation techniques, the transformation and availabilities of copper (Cu) as both a micronutrient and a toxic metal are changed. However, little information is available on the binding forms, bioavailability, and fate of Cu in paddy fields with different irrigation management. Thus, we investigated the effects of irrigation management on the binding forms and the fate of Cu in a non-polluted paddy soil.

Materials and methods

Field experiments were conducted in 2011 on non-polluted rice fields in Kunshan, East China. Non-flooding controlled irrigation (NFI) was applied in three replications, with flooding irrigation as a control. Samples of soil, soil solution, irrigation water, and rice plants were collected. Fresh soil samples were digested using the modified European Community Bureau of Reference sequential extraction procedure and the dried crop samples digested at 160 °C using concentrated HNO₃. Cu contents in irrigation water, soil solution, extraction for different binding fractions, and the digested solutions were measured using inductively coupled plasma optical emission spectrometry. Leaching loss of Cu was calculated based on the Cu contents in 47- to 54-cm soil solutions and deep percolation rates, which were calculated using the field water balance principle.

Results and discussion

NFI led to multiple dry–wet cycles and high soil redox potential in surface soil. The dry–wet cycles in NFI soil resulted in higher Cu contents in acid-extractable and oxidizable forms and lower Cu in residual form. High decomposition and mineralization rates of soil organic matter caused by the dry–wet cycles partially accounted for the increased Cu in acid-extractable form in NFI soils. The frequently high contents of Cu in reducible form in NFI fields might be due to the enhanced transformation of Fe and Mn oxides. As a result, Cu uptakes in NFI fields increased by 8.1 %. Meanwhile, Cu inputs by irrigation and loss by leaching in NFI fields were reduced by 47.6 and 46.6 %.

Conclusions

NFI enhanced the transformation of Cu from residual to oxidizable and acid-extractable forms. The oxidizable form plays a more important role than the reducible form in determining the transformation of Cu from the immobile to the mobile forms in NFI soils. NFI helps improve availability and decreases leaching loss of Cu as a micronutrient in a non-polluted paddy soil, but leads to a high concentration of Cu in rice.