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1.
The rice‐wheat annual double cropping system occupies some 0.5 million ha in the Himalayan foothills of Nepal. Alternating soil drying and wetting cycles characterize the 6–10 weeks long dry‐to‐wet season transition period (DWT) after wheat harvesting and before wetland rice transplanting. Mineral fertilizer use in the predominant smallholder agriculture is low and crops rely largely on native soil N for their nutrition. Changes in soil aeration status during DWT are likely to stimulate soil N losses. The effect of management options that avoid the nitrate build‐up in soils during DWT by N immobilization in plant or microbial biomass was studied under controlled conditions in a greenhouse (2001/2002) and validated under field conditions in Nepal in 2002. In potted soil in the greenhouse, the gradual increase in soil moisture resulted in a nitrate N peak of 20 mg (kg soil)–1 that rapidly declined as soil moisture levels exceeded 40 % water‐filled pore space (equiv. 75 % field capacity). Similarly, the maximum soil nitrate build‐up of 40 kg N ha–1 under field conditions was followed by its near complete disappearance with soil moisture levels exceeding 46 % water‐filled pore space at the onset of the monsoon rains. Incorporation of wheat straw and/or N uptake by green manure crops reduced nitrate accumulation in the soil to < 5 mg N kg–1 in pots and < 30 kg N ha–1 in the field (temporary N immobilization), thus reducing the risk for N losses to occur. This “saved” N benefited the subsequent crop of lowland rice with increases in N accumulation from 130 mg pot–1 (bare soil) to 185 mg pot–1 (green manure plus wheat straw) and corresponding grain yield increases from 1.7 Mg ha–1 to 3.6 Mg ha–1 in the field. While benefits from improved soil N management on lowland rice are obvious, possible carry‐over effects on wheat and the feasibility of proposed options at the farm level require further studies.  相似文献   

2.
王琪  王雅琦  万亚男  李花粉 《土壤》2022,54(6):1101-1107
通过田间试验,研究了不同形态叶面硒肥对水稻吸收和转运硒的影响。与空白对照相比,亚硒酸钠、硒酸钠、硒代蛋氨酸和化学纳米硒在水稻扬花期一次施用(15g/hm2)可使水稻籽粒、颍壳和秸秆的硒含量分别提高0.06～0.64、0.36～0.83和0.32～0.75 mg/kg。籽粒硒的回收率大小顺序为：硒代蛋氨酸(34.6%)>亚硒酸钠(15.7%)>硒酸钠(15.0%)>化学纳米硒(6.6%);硒在水稻各部位中的分配比例的高低顺序为：秸秆>籽粒>颍壳。此外,硒用量与水稻籽粒的硒含量呈极显著线性相关。按照黑龙江省富硒大米的地方标准(DB23T 790—2004),达到一等大米的硒含量指标(0.20～0.30 mg/kg),亚硒酸钠单施的施用量为6.01～10.62 g/hm2,腐植酸+亚硒酸钠复合肥的施用量为4.26～8.63 g/hm2。硒代蛋氨酸的富硒效率高于其他3种硒形态,腐植酸+亚硒酸钠复合肥的富硒效率高于亚硒酸钠单施。  相似文献   

3.
苏南典型区农田土壤硒-镉拮抗作用研究   总被引：3，自引：0，他引：3  
以苏南典型区2027套稻米-土壤样品的Se、Cd含量及其相关的元素地球化学调查数据为基础,通过元素相关性统计分析及生物富集系数(BCF)等分布特征研究,本文探讨了农田土壤中Se与Cd的拮抗作用及其控制因素。结果表明：1)土壤中Se和Cd分布共消长特征明显,两者之间具有显著正相关性、相关系数R最高可达0.87；2)有关岩石、陶瓷原料、河泥等均可成为农田富集Se、Cd的物质来源,且多为富Cd强于富Se,只有源于富硒岩石的富硒土壤可排除Cd污染干扰、其开发利用价值最高；3)稻米Se与Cd的生物富集系数多介于0.1～0.8之间,土壤偏碱性有利于稻籽吸收Se、偏酸性则有助于稻籽吸收Cd,受土壤Se、Cd同富集之影响,富硒米与镉超标大米可能同时出现；4)土壤富Se抑制稻米Cd吸收是有条件的,当土壤Se大于0.4mg/kg、总有机碳大于1.5%时,稻米Cd与土壤Se、Cd生物富集系数与土壤Se之间均存在显著负相关性,相关系数R分别为-0.74、-0.56；5)pH与Cd生物富集系数、TOC与Se生物富集系数之间也有显著负相关性,其相关系数R分别为-0.79、-0.65。  相似文献   

4.
硒对镉胁迫下寒地水稻镉含量与分配的影响   总被引：9，自引：0，他引：9  
【目的】研究施硒对不同镉污染土壤上镉在水稻各器官中的分配及稻米中镉含量的影响,探讨通过施硒降低水稻镉吸收量及在稻米中分配的可行性。【方法】采用盆栽试验,以垦鉴稻6号为材料,研究添加不同浓度镉(0、2、4和8 mg/kg土壤)的条件下,施硒(0、0.07和0.14 mg/kg土壤)对水稻不同器官镉含量和镉分配的影响。成熟期整盆收获,分别测定叶片、叶鞘、茎秆、根系和糙米、精米镉含量、硒含量和干物重,计算镉积累量和分配比例。【结果】1)当土壤镉浓度在0 4 mg/kg时,水稻各营养器官和糙米、精米中镉含量随土壤镉浓度增高而显著增加,但当土壤中镉浓度4 mg/kg时,糙米和精米中镉含量增加不显著。未施硒(Se0)时,Cd2(4 mg/kg)和Cd3(8mg/kg)处理糙米中镉含量分别为0.221 mg/kg和0.234 mg/kg,分别是Cd0处理的15.8和16.7倍,均超过我国国家食品安全标准中稻米镉的限量(0.2 mg/kg),精米镉含量未超过国家食品安全规定的限量,Cd3处理精米中镉含量最高,为0.174 mg/kg。2)相同镉浓度下,随着硒浓度的增加,水稻各营养器官和糙米、精米的镉含量和镉积累量均显著下降,糙米和精米的镉含量均低于我国国家食品安全规定的稻米镉限量,且Se2(0.14 mg/kg)处理优于Se1(0.07 mg/kg)处理。其中Cd1(2 mg/kg)浓度时,Se2处理的精米镉含量下降幅度最大,比Se0降低31.5%(P0.01)。3)镉在各器官中的分配比例为根系茎鞘稻谷叶片。随着硒浓度的增加,镉在根系中的分配比例增加,在地上部的分配比例减少,在稻壳中的分配比例增加,在精米中的分配比例下降。在Cd1浓度时,根系镉分配比例范围为60.9%67.8%,稻谷镉分配比例为12.6%13.8%;Se2处理稻壳中镉分配比例比Se0增加5.2个百分点,而精米中镉分配比例则下降了6.2个百分点。4)相同镉浓度下,随着硒浓度的增加,植株各营养器官干物重均增加,Se2处理对干物重的影响优于Se1处理。Cd1、Cd2和Cd3浓度下,Se2处理比Se0处理稻谷干物重分别增加了6.4%(P0.01)、5.2%(P0.05)和11.3%(P0.01)。【结论】施硒可降低镉污染土壤上水稻各营养器官和糙米、精米的镉含量,并能显著降低精米中镉的分配比例,保证稻米的食用安全性,尤其在Cd加入量为2mg/kg土浓度下,施硒效果最显著,以施Se量为0.07 mg/kg处理的效果最好。  相似文献   

5.
Because of their short life cycle, rapid‐cycling base populations (RCBP) of Brassica can act as model systems for investigating selenium (Se) metabolism in high sulfur (S) accumulating plants. To establish treatment responses for a B. oleracea RCBP, plants were grown in nutrient solutions containing 0, 3, 6, and 9 mg sodium seienate (Na2SeO4) L‐1. Depletion of Se from nutrient solutions increased linearly with in‐creasing Na2SeO4 concentrations. Selenium accumulation ranged from 551 to 1,916 μg Se g‐1 dry weight for leaf tissue, 267 to 1,165 μg Se g‐1 dry weight for stem tissue, and 338 to 1,636 μg Se g‐1 dry weight for root tissue. Selenium additions also resulted in linear increases in S accumulation in leaves and stems. Selenium supplementation has been shown to improve the health of individuals with low Se status. Because Brassica species are important vegetable and forage crops, their enrichment with Se maybe a good delivery system for mammalian diets.  相似文献   

6.
A long‐term experiment on a clayey, kaolinitic, thermic Rhodic Hapludox where dolomitic lime was applied to the surface (either at 4.5 t/ha or at 1.5 t/ha per yr for 3 yr), or incorporated into the topsoil (4.5 t/ha), and gypsum applied to the surface (3, 6, and 9 t/ha), was carried out to evaluate their effects on soil profile chemical properties and yields of corn (Zea mays L.) and soybean (Glycine max L. Merrill). Lime applied to the soil surface at either full or split rates, or incorporated and surface‐applied gypsum had long‐lasting effects on soil acidity or calcium and sulphur availability respectively, as measured 8 yr after application. Grain yields of corn and soybean were not influenced by liming. Gypsum at 9 t/ha significantly increased corn grain yields by 7 and 8% respectively 7–10 yr after application, but did not affect soybean grain yields. The differences in response of the corn and soybean crops to gypsum might be related to the Ca2+ uptake by plants because of cation exchange properties of roots, being smaller for corn than for soybean. The use of gypsum in no‐till systems becomes more viable when corn is grown with a greater frequency in crop rotation.  相似文献   

7.
This model analysis of catch crop effects on nitrate retention covered three soil texture classes (sand, loamy sand, sandy loam) and three precipitation regimes in a temperate climate representative of northern Europe (annual precipitation 709–1026 mm) for a period of 43 years. Simulations were made with two catch crops (ryegrass and Brassica) with different rooting depths, and soil N effects in the next spring were analysed to 0.25, 0.75 and 2.0 m depth to represent the catch crop effect on following crops with different rooting depths. Nitrate retained without a catch crop was generally located in deeper soil layers. In the low precipitation regime the overall fraction of nitrate retained in the 0–2.0 m soil profile was 0.23 for the sandy soil, 0.69 for the loamy sand and 0.81 for the sandy loam. Ryegrass reduced leaching losses much less efficiently than Brassica, which depleted nitrate in the 0–0.75 m soil layer more completely, but also in the deeper soil layer, which the ryegrass could not reach. A positive N effect (Neff, spring mineral N availability after catch crop compared with bare soil) was found in the 0–0.25 m layer (that is shallow rooting depth of a subsequent main crop) in all three soil texture classes, with on average 10 kg N/ha for ryegrass and 34 kg N/ha for Brassica. Considering the whole soil profile (0–2.0 m deep rooting of next crop), a positive Neff was found in the sand whereas generally a negative Neff was found in the loamy sand and especially the sandy loam. The simulations showed that for shallow‐rooted crops, catch crop Neff values were always positive, whereas Neff for deeper‐rooted crops depended strongly on soil type and annual variations in precipitations. These results are crucial both for farmers crop rotation planning and for design of appropriate catch crop strategies with the aim of protecting the aquatic environment.  相似文献   

8.
Poultry litter is widely used as a fertilizer for lowland rice in Taiwan and China. However, the organic‐arsenic compound roxarsone (additive of poultry feed) in poultry litter can be absorbed by the plants and the resulting arsenic (As) contamination may pose a serious threat to human health. This study used various amounts of poultry litter contaminated with roxarsone in pot experiments to evaluate the effect of roxarsone on rice agronomic parameters and the bioaccumulation of total and inorganic As in rice‐plant tissues. Rice‐grain yield decreased significantly with increasing As content of the soil, and the critical threshold that killed rice was 200 mg roxarsone (kg soil)–1. The As concentrations in root, straw, leaf, husk, and grain increased with increasing soil As (p < 1%). At 100 mg roxarsone per kg of soil, the As concentration in the rice grain exceeded the statutory permissible limit of 1.0 mg As (kg dry weight)–1 and at 25 mg roxarsone (kg soil)–1, the inorganic As concentrations in grains exceeded the statutory limit of 0.15 mg of inorganic As kg–1 in China. For all treatments, the As concentrations in various plant tissues at maturity follow the order: root > stem > leaf > husk > grain. Arsenite was the predominant species in root, straw, and grain, while arsenate was the predominant species in leaf and husk. No significant difference existed between the amounts of arsenite and arsenate when various amounts of poultry litter were applied. This result illustrates that large amounts of added roxarsone are not only toxic to rice but also accumulate in grains in the inorganic As forms, potentially posing a threat to human health via the food chain.  相似文献   

9.
We used an isotope dilution method to examine the time‐dependent changes in the partitioning and lability of selenium (Se) in a Sri Lankan rice soil after adding fertilizer with selenite (Se(IV)) and selenate (Se(VI)) (1 mg kg?1) and incubation under anaerobic (submerged) (30 days) and subsequent aerobic (drained) conditions (7 days) in controlled reaction vessels mimicking rice paddy water management practices. The Kd (the ratio of sorbed ion to that in solution) values for Se(IV) were significantly (P≤ 0.001) larger than those for Se(VI) in all treatments and at all sampling times. The Kd values for Se(IV) and Se(VI) decreased significantly (P≤ 0.001) with time during the anaerobic and subsequent aerobic phases. Applied Se(IV) fertilizer was rapidly removed into non‐labile pools during the anaerobic phase (day 0 = 60% labile and day 14 = no labile Se), with no significant increase in the labile pool following short‐term aeration. The results suggest that the rapid decrease in Se(IV) lability may be caused by the strong non‐reversible (at least for 7 days) sorption of Se (IV). In contrast, applied Se(VI) fertilizer was 90% labile at 0 day and decreased during the anaerobic phase to 30% after 30 days. There was no significant change in the lability of Se(VI) following the short‐term aerobic phase following anaerobic conditions. These results indicate that Se(IV) would not be an effective pre‐planting fertilizer for rice production. Selenate is likely to be more effective, but losses to non‐labile forms during the submerged phase of rice production may mean that efficiency of pre‐planting Se(VI) fertilizer is also compromised.  相似文献   

10.
The paper deals with the selenium (Se) accumulation of different genotypes of rice (Oryza sativa Japonica) seedlings at early growth stage and its correlation with the Se content in grains in 151 rice varieties. A field trial showed the Se content in brown rice to range from 29 μg/kg to 103 μg/kg. The results from hydroponic culture with representative varieties of high-, moderate- and low-Se content showed that total Se values for the high-Se genotypes were markedly higher than those of the low-Se varieties. This was true of Se content of the whole plant, Se content of shoots, biomass of shoots, and rate of Se accumulation in shoots. There were, however, no significant differences in values for total Se in roots, rate of accumulation in roots, and biomass of roots between high- and low-Se groups. Selenium content in brown rice was positively correlated with the total Se of the whole plant, shoot, and biomass of shoots. We concluded that the total Se transported from roots to shoots was more important than other factors in Se accumulation and content in brown rice.  相似文献   

11.
Abstract

Alley cropping may promote greater sequestration of soil organic carbon. The objective of this study was to examine spatial variability of soil organic carbon (C) and nitrogen (N) fractions relative to tree rows in established alley cropping systems in north central Missouri. Soils were collected to a depth of 30 cm from two alley cropped sites, a 19‐yr‐old pecan (Carya illinoinensis)/bluegrass (Poa trivialis) intercrop (pecan site) and an 11‐yr‐old silver maple (Acer saccharinum)/soybean (Glycine max)–maize (Zea mays) rotation (maple site). Particulate organic matter (POM) C constituted 15–65% and 14–41% of total organic C (TOC) at the pecan and maple sites respectively, whereas POM N comprised 3 to 24% of total N (TKN). TOC and TKN were on average 13% and 18% higher at the tree row than at the middle of the alley for surface soils (0–10 cm) at the pecan site, respectively. Similarly, POM C was two to three times higher at the tree row than the alley for subsurface soils at the maple site. No differences in microbial biomass C and N between positions were observed. Observed results suggest the existence of spatially dependent patterns for POM C, TOC, and TKN, relative to tree rows in alley cropping.  相似文献   

12.
Selenium (Se) biofortification via crops is one of the best strategies to elevate the daily Se intake in areas where soil Se levels are low. However, Se fertilizer recovery (SeFR) is low and most of the Se taken up accumulates in non‐harvested plant parts and returns to the soil with plant residues. A pot experiment with soil was undertaken to study the efficiency of inorganic Se (Na2SeO4) and Se‐enriched plant residues for biofortification, as well as to identify the bottlenecks in Se utilization by Brassica napus L. The soil was fertilized with Na2SeO4 (0 and 7 µg Se kg?1) or with Se in stem or leaf residues (0 and 7 µg Se kg?1). A treatment with autoclaved soil was included (0 and 7 µg kg?1 as Na2SeO4) to unravel the impact of microbial activity on Se uptake. The Se‐enriched plant residues produced a lower Se uptake efficiency (SeUPE) and SeFR than did inorganic Se, and soil autoclaving enhanced Se accumulation in the plants. The time required for decomposition seems to preclude crop residues as an alternative source of Se. Furthermore, B. napus had a limited capacity to accumulate Se in seeds. The study shows that the bottlenecks in Se biofortification appear to be its low bioavailability in soil and poor loading from the silique walls to seeds. Thus, improved Se translocation to seeds would be a useful breeding goal in B. napus to increase SeFR.  相似文献   

13.
水稻不同生育期对硒的吸收、转运及累积规律   总被引：1，自引：0，他引：1  
管文文  戴其根  张洪程  尹雪斌 《土壤》2018,50(6):1150-1154
采用大田试验,研究土壤施用含硒肥料后水稻中硒的积累和分布的动态变化。结果表明:在水稻不同器官中硒的积累量与含硒肥料施用量呈正相关,相关系数达到0.98以上。水稻成熟期,硒施用量30 kg/hm2和120 kg/hm2处理全株硒浓度分别比对照处理提高了98.9%和313.7%。不同生育期,水稻各个器官中硒含量及累积量不同,水稻硒的生物富集高峰期表现在孕穗期,叶与水稻穗部吸收累积硒有着密切关系。水稻成熟期整个植株中硒的累积量为茎叶精米根颖壳。在整个水稻生育期硒有一定的运转累积规律:水稻分蘖期时,硒从根、茎流向叶片;孕穗期再由叶流向茎;灌浆期又从根运转到叶和穗中;最后成熟期叶中的硒流向穗。苗期施用含硒肥料是一条提高水稻硒含量的有效农艺措施。  相似文献   

14.
To identify crop rotation systems capable of sequestering C and N to 1 metre depth in a subtropical Ferralsol of Southern Brazil managed under long‐term zero‐tillage (21 yrs), we evaluated six crop sequences: wheat (Triticum aestivum)–soybean (Glycine max) [W‐S], the baseline; oat (Avena strigosa, as cover crop)–maize (Zea mays)–wheat–soybean [O‐M‐W‐S]; vetch (Vicia villosa, as legume cover crop)–maize–wheat–soybean [V‐M‐W‐S]; vetch–maize–oat–soybean–wheat–soybean [V‐M‐O‐S‐W‐S]; ryegrass (Lolium multiflorum, for hay)–maize–ryegrass–soybean [R‐M‐R‐S]; and alfalfa (Medicago sativa, for hay)–maize [A‐M]. Compared to W‐S and to 1 metre, the hay‐based system of A‐M showed the largest C and N sequestration rates (0.50 and 0.06 Mg/ha/yr, respectively). Alfalfa, being a perennial legume under cut‐regrowth cycles, possibly added more C and N through roots. The other hay system, R‐M‐R‐S, also sequestered C efficiently (0.27 Mg/ha/yr), but not N (0.01 Mg/ha/yr). The legume‐based system of V‐M‐W‐S sequestered significant amounts of both C (0.29 Mg/ha/yr) and N (0.04 Mg/ha/yr). The grass‐based system of O‐M‐W‐S showed the lowest sequestration of C (0.09 Mg/ha/yr). In all systems, a positive relationship (R2 = 0.71) occurred between estimated addition of root C and soil C stock to 1 metre. Whenever C and N sequestration occurred, more than half of that occurred below 20 cm depth. Results suggest that adoption of legume‐based systems, perennially as A‐M or annually as V‐M‐W‐S, is efficient for C and N sequestration in subtropical zero‐tillage soils and that roots possibly contribute more to that sequestration than aboveground biomass.  相似文献   

15.
本文研究了浙江富阳金属冶炼厂周围水田土壤-水稻系统中As、Se含量特征。所采土壤样品中,As含量高于土壤环境质量一、二和三级标准的分别占总数的21.15%、9.62%和7.69%。该金属冶炼厂周围88.46%的土壤属于富Se土壤。足Se土壤占总样的5.77%,过量Se土壤占3.85%,高Se土壤占5.77%。水田土壤可能受与金属冶炼有关的点源污染影响。糙米的As、Se含量高于全国糙米As、Se背景值,可食部分As、Se浓度均未超过我国规定的水稻卫生标准。  相似文献   

16.
This experiment tested whether it was possible to incorporate broiler litter (BL) or cattle farmyard manure (FYM) into a 7‐yr arable rotation on a sandy soil without causing an increase in nitrate‐nitrogen (NO3‐N) leaching. Four manure treatments (with adjusted fertilizer inputs), varying in frequency and timing of application, were imposed on the rotation and compared with a control that received inorganic fertilizer according to recommended rates. Over seven winters, the annual average NO3‐N leached from the inorganic fertilizer treatment (control) was 39 kg/ha in 183 mm drainage. Total manure N loadings over the period of the experiment ranged between 557 and 1719 kg/ha (80–246 kg/ha/yr) for the four treatments. Three of the four manure treatments significantly increased NO3‐N leaching over the rotation (P < 0.001). Annual applications of FYM (1719 kg/ha manure N or 246 kg/ha/yr) increased NO3‐N leaching by 39%. We hypothesize that this was due to increased mineralization of the organic N accumulating from repeated FYM applications. BL applied each year (1526 kg/ha manure N or 218 kg N/ha/yr) increased NO3‐N leaching by 52% above the control; BL applied 5 of 7 yr (972 kg/ha manure N or 139 kg N/ha/yr on average) and including inadvisable autumn applications increased leaching by 50%. BL applied in late winter or early spring every 2–3 yr (557 kg/ha manure N or 80 kg N/ha/yr on average) resulted in NO3‐N leaching similar to the control. This suggests that to avoid additional NO3‐N leaching from manure use in an arable rotation, manure should not be applied every year and autumn applications should be avoided; there are real challenges where manure is used on an annual basis.  相似文献   

17.
In a 20‐yr‐old long‐term experiment, the impact of continuous application of organic manures and inorganic fertilizers on soil quality and the sustainability of finger millet production was conducted on two cropping systems: finger millet and finger millet–groundnut on an Alfisol of semi‐arid southern India. The study was conducted from 1992 to 2011 at the All India Coordinated Research Project for Dryland Agriculture, UAS, Bangalore, using a randomized block design. The treatments comprised of T1: control [no fertilizer and no farmyard manure (FYM) applied], T2: FYM 10 t/ha, T3: FYM 10 t/ha + 50% of recommended NPK (50:50:25 kg/ha), T4: FYM 10 t/ha + 100% of recommended NPK and T5: 100% recommended NPK. Comparison of long‐term yield data between treatments was used to calculate a ‘sustainability yield index’ (SYI), which was greatest for T4 (FYM 10 t/ha + 100% of recommended NPK), in both rotational (0.68) and monocropping (0.63) situations. Soil quality indices were determined using principal component analysis linear scoring functions. The key indicators which contributed to the soil quality index (SQI) under rotation were organic C; potentially available N; extractable P, K and S; exchangeable Ca and Mg; dehydrogenase activity and microbial biomass C and N. The largest SQI (7.29) was observed in T4 (FYM 10 t/ha + 100% NPK), and the smallest (3.70) SQI was for the control. Application of 10 t/ha FYM together with NPK (50:50:25 kg/ha) sustained a mean yield of 3884 kg/ha.  相似文献   

18.
Seven agroforestry tree species were grown in a clay loam soil treated with different levels of selenate‐Se, viz. 0, 1.25, 2.5 and 5.0 mg/kg supplied through sodium selenate. After 1 year of growth, a progressive decrease in dry matter of leaves, stem and roots was observed with increasing levels of applied Se. However, a significant decrease in dry matter yield was observed only at or above 2.5 mg Se per kg soil and shisham (Dalbergia sissoo) proved to be highly sensitive to the presence of selenate‐Se in the soil. On average, the largest above‐ground and below‐ground biomass was accumulated by arjun (Terminalia arjuna) and the lowest by the acacia tree (Acacia tortillas). The selenium content of leaves, stem and roots of all the tree species increased significantly with increasing levels of applied Se, although a large variation within species was observed. In the stem portion of different trees, the highest concentration of Se was found in dek (Melia azedarach) (5.1 mg/kg) and the lowest in mulberry (Morus alba) (2.6 mg/kg). The efficiency of selenium removal (including leaves, stem and roots) was the highest in arjun followed by eucalyptus (Eucalyptus hybrid) – Clone 10, mulberry, jambolin (Syzygium cumini), dek, shisham and acacia. Effective removal of Se takes place through the stem portion of different trees where it constitutes 30–50% of total Se. Large variation in Se uptake by different tree species suggests that trees vary in their potential for phytoremediation of seleniferous soils. In one growing season, shisham aged 24 years, poplar (Populus deltoides)– Clone G 48 (10 years old) and eucalyptus – Clone 10 (10 years old) could remove 2385, 1845 and 1407 g Se per hectare respectively. Corresponding reductions in Se capital of the soil varied between 24 and 37, 19 and 29 and 14 and 32%, respectively, in the surface layer (0–15 cm) alone or 7–11, 6–9 and 4–7% for the whole soil profile (0–120 cm). Removal further increased to 4207 g Se per hectare under an agroforestry farming system of poplar–mentha/wheat with Se being reduced from 43 to 65% for the surface layer and from 13 to 20% for the whole profile.  相似文献   

19.
Abstract

Kenaf (Hibiscus cannabinus) grown during the wet season in the Ord Irrigation Area of Western Australia was sampled at five growth stages. The samples were separated into bark, wood, tops plus foliage and, where applicable, seed. Each fraction was analysed for zinc, manganese, iron, copper, sodium, potassium, calcium and magnesium by atomic absorption spectroscopy, and for nitrogen and phosphorus by colorimetry. Concentrations of these elements in each plant fraction are presented. Calculation of total above‐ground nutrient content of the crop indicated a high content of potassium throughout the growth cycle (up to .280 kg/ha), an initially high content of nitrogen (150 kg/ha) stabilising at a lower level (about 75 kg/ha) up to maturity, and an increasing content of zinc (150 g/ha to 350 g/ha) and calcium (65 kg/ha to 105 kg/ha) with age. A higher content of iron at maturity was also apparent (up to 1400 g/ha). A comparison with other reported data is made.  相似文献   

20.
Abstract

Phosphorus (P) and potassium (K) requirements of snap bean (Phaseolus vulgaris L.) in North Florida are not well defined in the literature. Response of a bush type snap bean to P and K was determined in a 2‐year test at NFREC, Quincy. The resulting data were used in site specific soil‐test interpretations. Residual soil‐P levels were 7, 11, 29, and 66 mg/kg the first yr and 7, 12, 21, and 42 mg/kg the second yr, no fertilizer K was added either yr. Residual soil‐K was 26, 60, and 73 mg/kg the first yr. Fertilizer K was added the second yr at 0,95, and 190 kg/ha. Soil samples were collected from each plot near the beginning of each growing season for determination of soil‐test P and K levels. Soil type was Norfolk loamy fine sand (fine loamy, siliceous, thermic, Typic Kandiudult). Maximum nutrient levels required for snap bean were: soil‐test P 30 mg/kg and soil‐test K 80 mg/kg. Soil‐test interpretations for P were: low <15 mg/kg, medium 15 to 30 mg/kg, and high >30 mg/kg. Potassium soil‐test interpretations were low <40 mg/kg, medium 40 to 80 mg/kg, and high >80 mg/kg.  相似文献   

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