石灰性土壤上两种磷效率小麦根际特征差异

采用三室根箱实验,选用黑垆土和潮土两种石灰性土壤,对两种磷水平的磷低效型小麦京411和磷高效型小麦小偃54,进行植株生物量及吸磷量、根际土壤pH值、磷酸酶含量、水溶性磷含量的测定,旨在研究两种磷效率小麦在不同石灰性土壤上的根际特征差异.结果表明,不施磷条件下,两种土壤上,小偃54的根部生物量分别为0.85和4.62 g,均显著高于京411的0.68和3.65 g;小偃54根际土壤的pH值分别比京411低0.07,0.11个单位;在施磷条件下,小偃54的根际土壤水溶性磷分别低于京411 837,1588 μg/kg,达到显著性差异.根际磷酸酶在不同土壤上存在明显的差异,黑垆土在不施磷条件下小偃54的根际土壤磷酸酶含量显著高于京411,在潮土上呈现相反的趋势.试验结果表明,两种磷效率,小麦根际特征在不同土壤上有一定的相似性,同时存在明显差异.     

不同磷供应水平下小麦根系形态及根际过程的变化特征

以石麦15和衡观35两个品种小麦为试验材料,应用根袋栽培方式,研究了不同施磷量对小麦根系形态和根际特征的影响。结果表明,与施磷量P2O5 0.1 g/kg相比,高量供磷（P2O5 0.3 g/kg）条件下石麦15地上部生物量和磷累积量增加幅度大于衡观35;但不施磷处理衡观35地上部生物量降低幅度小于石麦15,磷含量和累积量高于石麦15,衡观35耐低磷能力较强。土壤供磷不足时,衡观35总根长中直径0.16 mm细根所占比例高于石麦15,根系平均直径较小;而高磷供应下,石麦15根系中直径0.16 mm细根长度较长,在总根长中所占比例较高。总根长和直径0.16 mm的细根长度与植株地上部磷累积量之间呈显著正相关关系。总根长越长尤其是细根越多,有利于促进植株对磷的吸收。与非根际土壤相比,高磷供应下根际土壤有机磷含量增加,微生物量磷含量降低;而供磷不足时根际土壤碱性磷酸酶活性较高,有机磷含量较低。与施磷量P2O5 0.1 g/kg相比,高量供磷下根际土壤pH值升高、碱性磷酸酶活性下降,不施磷处理根际土壤pH值降低。本研究表明,供磷不足时,小麦根系形态和根际过程均发生适应性变化,而高量供磷条件下,小麦植株根系形态的改变因品种而异。     

磷肥对日光温室番茄磷营养和产量及土壤酶活性的影响

采用盆栽方法进行了不同施磷（P2O5）水平下,日光温室番茄产量、不同生育期番茄磷素分配、干物质积累、土壤速效磷含量和酶活性研究,并确定了适宜番茄生长的最佳施磷量与土壤速效磷含量。结果表明,随着磷肥施用量的增加,土壤速效磷含量及番茄各组织含磷量相应增加;当施用P2O5达到0.53 g/kg（处理5）,土壤速效磷含量在60～77 mg/kg时,较适宜番茄生长,番茄产量和单果重达最高,根系和茎叶干物质积累也达到最好水平。当施磷量超过0.53 g/kg时,造成土壤和植株磷累积过高,易引起土壤盐害,降低土壤酶活性,从而降低干物质积累和番茄产量,影响土壤的可持续利用。     

施磷量对玉米 -大豆间作根际红壤无机磷形态及磷吸收的影响

通过盆栽模拟试验,探讨不同施磷量对玉米 -大豆间作作物生长及磷吸收的影响,并分析根际红壤中各无机磷形态的变化。结果表明:与单作相比,玉米 -大豆间作显著提高了作物地上部生物量及磷素吸收量,并具有明显的产量优势。与常规施磷水平(P100)下的单作相比,玉米 -大豆间作条件下,磷肥减施 1/2(P50)并未降低作物籽粒产量与玉米的磷吸收量。间作种植显著降低了玉米、大豆根际红壤总无机磷含量,并且无机磷减少量主要以O-P、Fe-P和 Ca-P为主。玉米、大豆根际土壤Fe-P、Al-P、Ca-P与 O-P占土壤总无机磷含量的比例主要受磷水平的调控,而种植模式对玉米和大豆根际土壤中各无机磷形态的比例(除 Fe-P外)均没有影响。在本试验条件下,玉米 -大豆间作通过根系交互作用主要促进土壤中 Fe-P、Ca-P和 O-P的活化来增加玉米与大豆的磷吸收,并具有节约磷肥、维持作物产量和磷吸收的潜力。     

小麦蚕豆间作对红壤有效磷的影响及其与根际pH值的关系

在云南红壤上采用田间小区试验,通过测定分蘖～拔节期、孕穗～抽穗期、灌浆～乳熟期不同土层深度小麦根际土壤有效磷(available phosphorus)含量和根际pH值,比较研究了小麦蚕豆间作对小麦根际土壤有效磷含量和pH值的影响,探讨了间作小麦根际pH与根际土壤有效磷之间的相互作用.结果表明,与小麦单作相比,小麦蚕豆间作显著地促进了小麦产量的提高.同时,小麦蚕豆间作促进了小麦根际土壤有效磷含量的提高,分蘖～拔节期、孕穗～抽穗期0-10 cm、10-20 cm土层单、间作差异显著;间作显著降低了分蘖～拔节期10-20 cm土层、孕穗～抽穗期0-10 cm、10-20 cm、20-30 cm土层小麦根际土壤pH.分蘖～拔节期、灌浆～乳熟期,单、间作小麦根际土壤有效磷含量与根际pH呈负相关关系.试验表明,在红壤上间作小麦根际土壤有效磷含量的提高与间作降低根际pH有密切关系.     

不同磷水平下玉米-大豆间作对红壤无机磷组分及有效磷的影响

通过2年盆栽试验，探讨不同磷水平下玉米–大豆间作根际土壤无机磷组分、土壤有效磷含量及作物磷吸收的差异，明确土壤无机磷组分、土壤有效磷与作物磷吸收之间的相互关系。试验设置玉米单作、大豆单作、玉米–大豆间作3种种植方式以及3个P2O5施用水平(0、50、100 mg/kg，分别记作P0、P50、P100)，共9个处理。结果表明：与单作相比，2018年和2019年在P0、P50和P100水平下，间作显著提高玉米和大豆的籽粒产量，并显著提高玉米和大豆植株的磷素吸收量。与常规施磷水平(P100)下的单作处理相比，玉米–大豆间作在磷肥减少50%(P50)的条件下，并未降低玉米和大豆的磷吸收量与籽粒产量。3个磷水平下，间作提高了玉米和大豆根际土壤有效磷含量，而降低了根际土壤总无机磷以及Fe-P、Al-P、Ca-P、O-P的含量；同时适当增施磷肥显著提高了玉米和大豆根际土壤总无机磷及各无机磷组分的含量。本试验条件下，间作促进土壤中Fe-P、Al-P、Ca-P和O-P的活化(尤其是Fe-P)，是低磷胁迫下间作土壤有效磷含量与作物磷吸收量增加的重要原因。玉米–大豆间作具有节约磷肥、维持作物产量及根际土壤有...     

稻鸭生态种养系统直播水稻根表和根际土壤营养特性研究

采用田间小区试验对比分析了直播方式下稻鸭生态种养系统和水稻单一种植系统水稻根表和根际土壤的氮、磷、钾和有机碳含量及pH的变化。结果表明:与水稻单一种植系统相比,稻鸭生态种养系统水稻根表和根际pH分别升高4.41%、0.85%,全氮含量分别降低0.11g·kg-1、0.11g·kg-1,全磷和全钾含量变化不明显。水稻根表速效氮和速效钾含量分别增加30.80mg·kg-1、17.93mg·kg-1,速效磷含量降低8.66mg·kg-1;水稻根际速效氮和速效钾含量分别减少15.13mg·kg-1、7.61mg·kg-1,速效磷增加9.66mg·kg-1。稻鸭生态种养系统水稻根表活性有机碳和高活性有机碳分别增加2.17g·kg-1、0.56g·kg-1,全有机碳含量减少0.99g·kg-1;根际土壤全有机碳、活性有机碳和中活性有机碳含量分别减少2.39g·kg-1、2.64g·kg-1、0.72g·kg-1。稻鸭生态种养改变了速效磷、速效钾和活性有机碳在水稻根域土壤的相对富集部位,即速效钾和活性有机碳富集部位主要在根表土壤,速效磷则主要在根际土壤。表明稻鸭生态种养明显改善了水稻根表和根际土壤营养状况,这可能对水稻根系吸收和利用土壤养分具有积极意义。     

不同施磷水平下生物质炭用量对土壤磷素状况及棉花养分吸收的影响

通过两年温室盆栽试验,研究不同施磷水平(0、0.25、0.5 g kg-1)下,生物质炭用量(0%、1%和2%)对土壤磷素状况和棉花生长及养分吸收的影响。研究结果表明:施用生物质炭可提高土壤水溶性磷、速效磷和全磷含量,三种磷素的影响表现为:水溶性磷全磷速效磷。生物质炭用量对施用后第二年的土壤磷素影响更明显,高磷(0.5 g kg-1)水平下土壤水溶性磷和速效磷含量随生物质炭用量的增加而显著增加。不施磷和低磷(0.25 g kg-1)水平下,施用生物质炭显著提高了棉花植株总干物质重,但1%和2%用量间差异不显著;高磷(0.5 g kg-1)水平下,两年的试验结果不一致。生物质炭显著增加了棉花的氮、磷和钾吸收量;尤其是在高磷水平下,棉花磷素吸收量随生物质炭用量(0%到1%以及2%)显著增加。因此,生物质炭和磷肥合理配施可显著增加土壤磷素,促进棉花生长和养分吸收。     

生物黑炭对玉米苗期根际土壤氮素形态及相关微生物的影响

生物黑炭被作为土壤改良剂应用逐渐被认可,但其应用机制特别是生物黑炭对氮素形态和根际微生物的影响机理尚不明确,影响其推广。本文采用盆栽试验,研究了玉米和水稻秸秆烧制的生物黑炭按不同量施入土壤后,对玉米苗期株高、生物量和根际土壤氮素形态及相关微生物的影响。结果表明,施入60 g·kg-1玉米黑炭和40~60 g·kg-1水稻黑炭均对玉米苗期株高有显著(P0.05)降低作用,其中水稻黑炭的降低效果更为明显;分别施入60 g·kg-1玉米黑炭和20~60 g·kg-1水稻黑炭后,玉米植株地上部生物量均显著降低。施入60 g·kg-1玉米黑炭后根际土壤含水量和微生物量氮显著提高。随两种生物黑炭施入量的不断增加,玉米苗期根际土壤全氮、硝态氮含量以及固氮作用强度也显著增加,且均在60 g·kg-1施用量下达最大值。施用40 g·kg-1玉米黑炭可显著提高玉米苗期根际土壤氨态氮含量。同时,施用两种生物黑炭后,均不同程度地抑制了玉米根际土壤中细菌总体数量,促进了固氮菌和纤维素降解菌的生长,其中施入60 g·kg-1玉米黑炭的效果最为明显。综上,玉米和水稻秸秆生物黑炭的适量施用,可以促进玉米根际土壤氮素的循环转化,影响相关微生物的群落结构,且与水稻秸秆相比,玉米秸秆生物黑炭的施用效果更加明显。本文针对作物生长、土壤氮素形态及相关微生物数量3个方面研究生物黑炭施入土壤对氮有效性的影响,能够更全面、更准确地将生物黑炭如何影响土壤氮素转化展现出来,促进生物黑炭的深入开发利用,对黑土肥力保护具有一定意义。     

降水酸度对马尾松根际环境中铝形态的影响

为了探明降水酸度对植物根际环境中铝形态的影响,以马尾松为例,采用根箱栽培、配制不同pH值的模拟酸雨以室外模拟酸雨喷淋法研究马尾松根际及非根际土壤中铝形态的特征及规律.研究结果表明:酸雨对土壤中铝化合物具有溶蚀作用,可促进土壤里活性铝离子(Al3+)溶出,并且酸雨pH值越低,活性铝离子累积溶出量越大,溶出的铝所形成的铝形态在马尾松根际土壤与非根际土壤以及根际不同土层之间存在一定差异,马尾松根际pH值和根系分泌物协同影响铝形态的动态变化.根际土壤中有机铝结合态含量增加.交换态铝含量则稍稍下降.     

Phosphorus uptake of maize as affected by ammonium and nitrate nitrogen - Measurements and model calculations -

Phosphorus uptake is often enhanced by ammonium compared to nitrate nitrogen nutrition of plants. A decrease of pH at the soil-root interface is generally assumed as the cause. However, an alteration of root growth and the mobilization of P by processes other than net release of protons induced by the source of nitrogen may also be considered. To study these alternatives a pot experiment was conducted with maize using a fossil Oxisol high in Fe/Al-P with low soil solution P concentration. Three levels of phosphate (0, 50, 200 mg P kg^?1) in combination with either ammonium or nitrate nitrogen (100 mg N kg^?1) were applied. Plants were harvested 7 and 21 d after sowing, P uptake measured and root and shoot growth determined. To assess the importance of factors involved in the P transfer from soil into plants, calculations were made using a model of Barber and Claassen. In the treatments with no and low P supply NH₄-N compared to NO₃-N nutrition increased the growth of the plants by 25 % and their shoot P content by 38 % while their root growth increased by 6 % only. The rhizosphere pH decreased in the NH₄-N treatments by 0.1 to 0.6 units as compared to the bulk soil while in the NO₃-N treatments it increased by 0.1 to 0.5 units. These pH changes had a minor influence on P uptake only, as was demonstrated by artificially altering the soil pH to 4.7 and 6.3 respectively. At the same rhizosphere pH, however, P influx was doubled by the application of NH₄-compared to NO₃-N. It is concluded that in this soil the enhancement of P uptake of maize plants after ammonium application cannot be attributed to the acidification of the rhizosphere but to effects mobilizing soil phosphate or increasing P uptake efficiency of roots. Model calculation showed that these effects accounted for 53 % of the P influx per unit root length in the NO₃-N and 72 % in the NH₄-N supplied plants if no P was applied. With high P application the respective figures were only 18 and 19%.     

RESPONSE OF MAIZE GROWN IN AN ALFISOL OF SRI LANKA TO INOCULANTS OF PLANT GROWTH PROMOTING RHIZOBACTERIA

Field experiments were conducted to assess the ability of rhizobacterial inoculants to enhance growth and yield of maize. Performances of two phosphorus (P)-solubilizing bacteria in combination with a fertilizer mixture containing rock phosphate and triple super phosphate (PFM), and five diazotrophs combining either with 150 kg or 100 kg nitrogen (N) ha^?1 supplied as urea were compared with non-inoculated-fertilized controls. Shoot P and N and soil available P and N contents were assessed and shoot biomass and ear weights were recorded at harvest. Pseudomonas cepacia resulted in significantly higher available P (51 mg P kg^?1 soil), P accumulation (3.6 g kg^?1 dry matter) and 13% increase in shoot biomass over control. Azospirillum sp. and dual inoculant comprising Enterobacter agglomerans + Agrobacterium radiobacter led to significantly higher available N (74–94 mg kg^?1 soil) and 19 to 26% increase in shoot biomass over the control. However, inoculants did not increase the yield significantly.     

Wheat response to combined application of nitrogen and phosphorus in a saline sandy loam soil

Fertilization with nitrogen (N) or phosphorus (P) can improve plant growth in saline soils. This study was undertaken to determine wheat (Triticum aestivum L; cv Krichauff) response to the combined application of N and P fertilizers in the sandy loam under saline conditions. Salinity was induced using sodium (Na⁺) and calcium (Ca²⁺) salts to achieve four levels of electrical conductivity in the extract of the saturated soil paste (EC_e), 2.2, 6.7, 9.2 and 11.8?dS?m^?1, while maintaining a low sodium adsorption ratio (SAR; ≤1). Nitrogen was applied as Ca(NO₃)₂?·?4H₂O at 50 (N50), 100 (N100) and 200 (N200)?mg?N?kg^?1 soil. Phosphorus was applied at 0 (P0), 30 (P30) and 60 (P60)?mg?kg^?1?soil in the form of KH₂PO₄. Results showed that increasing soil salinity had no effect on shoot N or P concentrations, but increased shoot Na⁺ and chlorine ion (Cl^?) concentrations and reduced dry weights of shoot and root in all treatments of N and P. At each salinity and P level, increasing application of N reduced dry weight of shoot. At each salinity and N level P fertilization increased dry weights of shoot and root and shoot P concentration. Addition of greater than N50 contributed to the soil salinity limiting plant growth, but increasing P addition up to 60?mg?P?kg^?1 soil reduced Cl^? absorption and enhanced the plant salt tolerance and thus plant growth. The positive effect of the combined addition of N and P on wheat growth in the saline sandy loam is noticeable, but only to a certain level of soil salinity beyond which salinity effect is dominant.     

Bioavailability and Accumulation of Cadmium and Zinc by Sedum plumbizincicola after Liming of an Agricultural Soil Subjected to Acid Mine Drainage

A glasshouse pot experiment was conducted to study the effects of liming on plant growth and zinc (Zn) and cadmium (Cd) accumulation by Sedum plumbizincicola in a heavy-metal-contaminated acidified paddy soil. Lime application significantly increased the soil pH, which reached a maximum of 5.53 after addition of 4.0 g kg^?1 lime to soil, about 1.4 units more than that of the control. Sedum plumbizincicola grew larger after lime application but aboveground biomass did not increase significantly with increasing soil pH. Liming significantly reduced shoot Zn and Cd concentrations and uptake except at the lowest lime application rate (0.5 g kg^?1 lime to soil). This indicates that S. plumbizincicola can grow well in acidic soil at a soil pH of 4.15, and application of lime did not increase plant heavy-metal extraction. Consequently, it is promising to use this plant for Cd and Zn phytoextraction from agricultural soils polluted with acid and metals.     

Root-induced changes in the rhizosphere: Importance for the mineral nutrition of plants

Root-induced changes in the rhizosphere may affect mineral nutrition of plants in various ways. Examples for this are changes in rhizosphere pH in response to the source of nitrogen (NH₄-N versus NO₃-N), and iron and phosphorus deficiency. These pH changes can readily be demonstrated by infiltration of the soil with agar containing a pH indicator. The rhizosphere pH may be as much as 2 units higher or lower than the pH of the bulk soil. Also along the roots distinct differences in rhizosphere pH exist. In response to iron deficiency most plant species in their apical root zones increase the rate of H⁺ net excretion (acidification), the reducing capacity, the rate of Fe^III reduction and iron uptake. Also manganese reduction and uptake is increased several-fold, leading to high manganese concentrations in iron deficient plants. Low-molecular-weight root exudates may enhance mobilization of mineral nutrients in the rhizosphere. In response to iron deficiency, roots of grass species release non-proteinogenic amino acids (?phytosiderophores”?) which dissolve inorganic iron compounds by chelation of Fe^III and also mediate the plasma membrane transport of this chelated iron into the roots. A particular mechanism of mobilization of phosphorus in the rhizosphere exists in white lupin (Lupinus albus L.). In this species, phosphorus deficiency induces the formation of so-called proteoid roots. In these root zones sparingly soluble iron and aluminium phosphates are mobilized by the exudation of chelating substances (probably citrate), net excretion of H⁺ and increase in the reducing capacity. In mixed culture with white lupin, phosphorus uptake per unit root length of wheat (Triticum aestivum L.) plants from a soil low in available P is increased, indicating that wheat can take up phosphorus mobilized in the proteoid root zones of lupin. At the rhizoplane and in the root (root homogenates) of several plant species grown in different soils, of the total number of bacteria less than 1 % are N₂-fixing (diazotrophe) bacteria, mainly Enterobacter and Klebsiella. The proportion of the diazotroph bacteria is higher in the rhizosphere soil. This discrimination of diazotroph bacteria in the rhizosphere is increased with foliar application of combined nitrogen. Inoculation with the diazotroph bacteria Azospirillum increases root length and enhances formation of lateral roots and root hairs similarly as does application of auxin (IAA). Thus rhizosphere bacteria such as Azospirillum may affect mineral nutrition and plant growth indirectly rather than by supply of nitrogen.     

有机、无机肥料施用后土壤生物量C、N、P的变化及N素转化

研究结果表明,有机、无机肥施用后,土壤微生物量C、N、P开始增加很快,随着时间的推移,土壤微生物量C又有所降低,但生物量N和P则基本保持稳定。硫铵施入土壤后,微生物对肥料¹⁵N的生物固持10天后达到最高峰,以后被固持在体内的¹⁵N有一部分被逐渐释放出来,但一个月后仍有17%左右的¹⁵N被固持在微生物体内。硫铵与有机肥配合施用时,微生物对硫铵¹⁵N固持比例有所增加。有机肥中的¹⁵N被微生物固持的比例也较大,在肥料施入20天左右达到最大值,一个月后仍有19-25%存在于微生物体内。硫铵施用一个月后¹⁵N损失高达18%,有机肥中的N也有少量被损失。     

缓释肥对紫色土油菜生长和养分吸收利用的影响

分析缓释专用配方肥与当地常用肥对油菜生物量、氮磷钾养分吸收利用及其在土壤中累积的影响,为油菜节肥高效生产提供依据。通过大田试验,以油菜品种三峡油5号为试验材料,设置6种施肥处理：以不施肥（F₀）和常规施肥(F_c)为对照处理,缓释专用配方肥设置4种施肥水平(F₃₇₅: 375 kg·hm^-2,F₅₂₅: 525 kg·hm^-2,F₆₇₅: 675 kg·hm^-2,F₈₂₅: 825 kg·hm^-2)。结果表明,不同施用量的缓释专用肥料对油菜产量、单株有效角果数以F₆₇₅处理最大,F₈₂₅处理次之,F₃₇₅处理最小,其分别较F_c 处理增产43.54%、36.82%、13.88%;施用缓释专用配方肥油菜氮养分损失率从F_c处理的78.30%降低至53.97% ~ 73.66%;磷养分损失率从F_c处理的56.65%降低至20.53% ~ 46.13%;施用缓释专用肥料油菜收获期根区土壤全氮、全磷与全钾含量从F_c处理的0.651 0 g·kg^-1、0.404 4 g·kg^-1与20.74 g·kg^-1上升至0.661 7 ~0.691 4 g·kg^-1、0.407 2~0.496 0 g·kg^-1与28.96~29.50 g·kg^-1。施肥大幅增加油菜生物量,缓释专用配方肥的施用不仅利于提升肥料利用率,同时使得根区土壤养分含量变化较小,结合农业可持续发展,实际生产应该施用缓释专用肥。     

Influence of nitrogen fertilizer forms and crop straw biochars on soil exchange properties and maize growth on an acidic Ultisol

Effects of repeated application of urea (UN) and calcium nitrate (CN) singly and together with crop straw biochars on soil acidity and maize growth were investigated with greenhouse pot experiments for two consecutive seasons. Canola straw biochar (CB), peanut straw biochar (PB) and wheat straw biochar (WB) were applied at 1% of dried soil weight in the first season. N fertilizers were applied at 200 mg N kg^?1. In UN treatments, an initial rise in pH was subjected to proton consumption through urea hydrolysis, afterwards nitrification of NH₄⁺ caused drastic reductions in pH as single UN had soil pH of 3.70, even lower than control (4.27) after the 2nd crop season. Post-harvest soil analyses indicated that soil pH, soil exchangeable acidity, NH₄⁺, NO₃^? and total base cations showed highly significant variation under N and biochar types (P < 0.05). Articulated growth of plants under combined application with biochars was expressed by 22.7%, 22.5%, and 35.7% higher root and 25.6%, 23.8%, and 35.9% higher shoot biomass by CB, PB and WB combined with CN over UN, respectively. Therefore, CN combined with biochars is a better choice to correct soil acidity and improve maize growth than UN combined with biochars.     

Soil‐solution speciation by MINEQL+4.6 model and plant uptake of Cd and Zn by barley (Hordeum vulgare L.) after application of different phosphate fertilizers

A greenhouse experiment was conducted to investigate the immediate effect of application of mono‐ammonium phosphate (MAP), single superphosphate (SSP), and triple superphosphate (TSP) fertilizers containing varying concentrations of Cd on (1) chemical speciation of Cd and Zn in soil solution by chemical‐equilibrium calculations (MINEQL+4.6 model), (2) growth of barley plants, (3) concentrations of Cd, P, and Zn in soil solution and plant tissue, as well as total plant accumulation of Cd, P, and Zn, and (4) monitoring pH and element changes during incubation periods following phosphate application. Results show that, in general, the pH of soil solution increased during the first 40 d of incubation, then declined. Also, at the end of incubation period, pH of soil solution was affected by fertilization source and fertilization rate. The concentration of Cd in soil solution changed with time. Phosphate fertilization (p < 0.05) or fertilizer source (p < 0.05) showed consistent effects. Also, the application of phosphate fertilizers with three rates significantly increased Zn concentrations in soil solution during the first half (0–30 d) of incubation period and then decreased but still more than in the control. In general, application of different sources of phosphate at 100 g kg^–1 did not change the dominant forms of Cd in soil solution during all incubation time intervals. Speciation of Zn in the control after 30 d of incubation had changed, in comparison to 10 d of incubation, and the dominant forms were Zn²⁺, ZnOH⁺, ZnHCO₃, ZnCO₃(aq), and Zn(OH)₂(aq). Adding phosphate fertilizer significantly increased both shoot and root dry weight compared to control, indicating P was a growth‐limiting factor in the control plants. The Zn concentrations in shoot and root were lower in the TSP‐ and SSP‐fertilizers treatment than those in the MAP and fertilizer treatments at all rates of fertilization. Adding phosphate increased the Cd : Zn and P : Zn ratios in the shoot and root tissue, with the effect being greater with increasing fertilization rate. Phosphate fertilization greatly increased the total accumulation of Cd of barley compared with the control plants (p < 0.001), with the effect being greater with increasing fertilization rate. Source and rate of fertilizers, and their interactions had significant effect (p < 0.05) on Cd accumulation in the whole plant.     

Earthworm (Aporrectodea trapezoides)–mycorrhiza (Glomus intraradices) interaction and nitrogen and phosphorus uptake by maize

The interactive impacts of arbuscular mycorrhizal fungi (AMF, Glomus intraradices) and earthworms (Aporrectodea trapezoides) on maize (Zea mays L.) growth and nutrient uptake were studied under near natural conditions with pots buried in the soil of a maize field. Treatments included maize plants inoculated vs. not inoculated with AMF, treated or not treated with earthworms, at low (25 mg kg⁻¹) or high (175 mg kg⁻¹) P fertilization rate. Wheat straw was added as feed for earthworms. Root colonization, mycorrhiza structure, plant biomass and N and P contents of shoots and roots, soil available P and NO₃⁻–N concentrations, and soil microbial biomass C and N were measured at harvest. Results indicated that mycorrhizal colonization increased markedly in maize inoculated with AMF especially at low P rate, which was further enhanced by the addition of earthworms. AMF and earthworms interactively increased maize shoot and root biomass as well as N and P uptake but decreased soil NO₃⁻–N and available P concentrations at harvest. Earthworm and AMF interaction also increased soil microbial biomass C, which probably improved root N and P contents and indirectly increased the shoot N and P uptake. At low P rate, soil N mobilization by earthworms might have reduced potential N competition by arbuscular mycorrhizal hyphae, resulting in greater plant shoot and root biomass. Earthworms and AMF interactively enhanced soil N and P availability, leading to greater nutrient uptake and plant growth.