Potassium forms in aerated and anoxic soils of different management and potassium fertilizer history

The potassium forms and dominant clay mineralogy were studied in naturally well-drained (Hapludalfs, Eutropept) and poorly-drained soils (Fragiudalfs, Fragiaquept), both composed of the same parent materials (silty-clay or silt loam or clayey-loam). The well-drained soils (i.e. aerated) were cultivated and received larger amounts of K fertilizer; the poorly-drained types (i.e. anoxic) were grasslands and received low amount of K fertilizer. The different aspects investigated-exchangeable and nonexchangeable K, potassium fixation capacity and clay X-ray diffraction diagrams-indicated that the potassium status and the behavior of K-containing clays significantly differed between naturally well-drained aerated soils and anoxic poorly-drained soils. The aerated soils were high in both exchangeable and nonexchangeable K; the K saturation rate was high whereas fixation capacity was moderate. However, the anoxic soils showed a large K depletion and high fixation capacity. The silty-clayey soils studied were more affected by moisture regimes than the silt loam or clayey-loam.The differing K status between aerated and anoxic soils can be explained by several processes and factors, including soil weathering and management and K fertilizer history.     

Possible processes releasing nonexchangeable potassium from the rhizosphere of maize

The source and the releasing processes of nonexchangeable K from the rhizosphere were evaluated by using a 0.01 M HCl sequential extraction that enables the detection of subtle depletion of nonexchangeable K in the rhizosphere. Rhizobox experiments were conducted in which maize (Zea mays L.) plants were grown on different K sources (non-allophanic Andosol, Fluvisol, biotite and orthoclase) for 17 days. Nonexchangeable K decreased significantly in the rhizosphere of Andosol, Fluvisol and biotite, but not of orthoclase. The width of depletion was about 0–1 mm from the root-accumulating compartment regardless of the K sources, and was much less than that of exchangeable (5–10 mm) and water-soluble (50 mm) K. Rhizosphere pHs were above 4.5 in any treatment. These results suggested that the main source of nonexchangeable K for maize was interlayer K in 2:1 type phyllosilicate, and that the releasing process involved was cation exchange of the K rather than mineral dissolution by protons. For the exchange of interlayer K, a decrease of solution K⁺ below a certain threshold is known as a prerequisite. But the concentration of solution K⁺ at the root compartment of Andosol or Fluvisol, estimated to be more than 100 M, was relatively higher than the known thresholds. Moreover, the significant release of nonexchangeable K from biotite occurred only at the root compartment where marked depletion of solution K⁺ was not observed. We therefore suggest that the release of interlayer K from the rhizosphere can occur even without a marked depletion of solution K⁺ through the following processes; (1) accumulation of cations such as Ca²⁺, Mg²⁺ or Na⁺ in the rhizosphere, (2) their adsorption on 2:1 type clay minerals near the edge of interlayer but inaccessible and nonexchangeable by NH₄ ⁺, (3) concomitant removal of the NH₄ ⁺-nonexchangable K even above the known thresholds of solution K⁺, which is followed by the expansion of the interlayer space, and (4) further removal of the deeper K by repetition of the above processes.     

Simple empirical intensity and buffering capacity measurements to predict potassium uptake by white clover

Summary This experiment examined the feasibility of predicting K uptake in white clover by the use of simple and relatively rapid tests that would dispense with the need of knowing the quantity of plant available potassium. Potassium uptake was found to correlate highly (R=>0.9) in linear bivariate regressions using K concentration in the soil solution displaced by centrifuging and an empirical estimate of potassium retention. There was no advantage in determining activity ratios because in at least some of the soils used the ratio law did not apply. Exchangeable potassium alone correlated rather poorly with uptake except at very low soil potassium status. This was not because nonexchangeable potassium was an important source of this nutrient to white clover but because of the large differences in the retention of K amongst the soils used.     

Effect of soil K, Ca and Mg saturation and endomycorrhization on growth and nutrient uptake of sugar maple seedlings

Nutrient imbalances of declining sugar maple (Acer saccharum Marsh.) stands in southeastern Quebec have been associated with high exchangeable Mg levels in soils relative to soil K and Ca. A greenhouse experiment was set up to test the hypothesis that the equilibrium between soil exchangeable K, Ca, and Mg ions influences the growth and nutrient status of sugar maple seedlings. Also tested was whether endomycorrhization can alter nutrient acquisition under various soil exchangeable basic cations ratios. Treatments consisted of seven ratios of soil exchangeable K, Ca, and Mg making up a total base saturation of 58%, and a soil inoculation treatment with the endomycorrhizal fungus Glomus versiforme (control and inoculated), in a complete factorial design. Sugar maple seedlings were grown for 3 months in the treated soils. Plant shoot elongation rate, dry biomass and nutrient concentrations in foliage were influenced by the various ratios of soil cations. The predicted plant biomass and foliar K concentration were highest at a soil Ca saturation of 38%, a soil K saturation of 12%, and a soil Mg saturation of 8%. Potassium concentration in foliage was dependent on the level of Ca and Mg saturation in the soil when soil K saturation was close to 12%. Foliar Ca and Mg levels were more dependent on their corresponding levels in soil than foliar K. Colonization by G. versiforme did not influence seedling growth and macronutrient uptake. The results confirm that growth and nutrition of sugar maple are negatively affected by imbalances in exchangeable basic cations in soils.     

闽江河口互花米草入侵湿地土壤无机硫赋存形态及其影响因素

选择闽江河口鳝鱼滩的互花米草湿地为研究对象，基于时空互代法，探讨了不同互花米草入侵年限（SA1： 5-6 年；SA2： 8-10 年；SA3： 12-14年）湿地土壤的无机硫赋存形态及其主要影响因素。结果表明，随着互花米草入侵年限的增加，湿地土壤的水溶性硫（H₂O-S）含量整体呈增加趋势，而吸附性硫（Adsorbed-S）、盐酸可溶性硫（HCl-Soluble-S）和盐酸挥发性硫（HCl-Volatile-S）含量整体均呈降低趋势。相对于SA1，SA2、SA3土壤的H₂O-S含量分别增加了10.02%和2.68%，而其Adsorbed-S、HCl-Soluble-S和HCl-Volatile-S含量分别降低了9.02%、10.95%、7.57%和15.61%、32.89%、15.14%。湿地土壤的总无机硫（TIS）含量、TIS储量及其占全硫（TS）储量的比例均随互花米草入侵年限的增加而降低，且这种降低主要取决于Adsorbed-S、HCl-Soluble-S和HCl-Volatile-S的贡献。此外，随着互花米草入侵年限的增加，影响湿地土壤不同形态无机硫赋存的环境因子均发生了较大变化，其中土壤颗粒组成、EC和pH的改变对无机硫赋存形态的影响最为明显。研究发现，随着互花米草入侵年限的增加以及该区对互花米草定期刈割活动的进行，湿地土壤无机硫养分可能将继续降低并逐渐趋于缺乏状态，长期而言将减弱互花米草自身的入侵能力。     

黄河口新生湿地土壤磷赋存形态及其动态变化对外源氮输入的响应

选择黄河口新生湿地为研究对象,基于野外原位氮输入模拟试验,探讨了不同氮输入梯度下(NN:对照处理;LN:低氮处理;MN:中氮处理;HN:高氮处理)湿地土壤磷赋存形态的动态变化特征。结果表明,不同氮处理下土壤中闭蓄态磷(HCl-P_i和Residual-P)均是TP的主体(87.75%—90.04%),而活性磷(Resin-P、NaHCO_3-P_i和NaHCO_3-P_o)和中等活性磷(NaOH-P_i、NaOH-P_o、Sonic-P_i和Sonic-P_o)占TP的比例均较低,分别为4.81%—5.58%和5.14%—6.57%。相对于NN处理,MN和HN处理下的活性磷含量分别增加了9.16%和12.44%,而LN、MN和HN处理下的中等活性磷含量分别增加了2.25%,6.92%和24.24%,说明外源氮输入整体增加了土壤中的活性磷含量。与之相比,闭蓄态磷含量在LN、MN和HN处理下均呈降低趋势,其值相对于NN处理分别降低了3.08%、3.08%和5.22%。尽管不同氮处理下土壤养分条件、水盐及酸碱状况均是影响不同磷形态赋存的关键因素,但随着氮输入量的增加,影响磷赋存形态的养分类型发生了明显改变,即由NN和LN处理下主要受N和S影响逐步转变为MN和HN处理下主要受P影响。研究发现,外源氮输入不但可能影响不同磷形态之间的转化,而且亦可能通过改变植物生长节律以及土壤养分及酸碱状况来影响土壤中各形态磷的赋存。     

The cation status of some indigenous plants from a Cango valley limestone-sandstone transition,South Africa

Leaf tissue of four representative species from a limestone-sandstone transition, together with their respective soils, were analysed for cations. The species studied comprisedLeucospermum cuneiforme (Proteaceae) from the acid sandstone,Indigofera sp. nov. (Fabaceae) from the base-rich limestone,Elytropappus rhinocerotis (Asteraceae) from the transition zone andDodonaea angustifolia (Sapindaceae) which occured on all three substrates. The sandstone substrate is low in cations, particularly K and it is suggested that the Leucospermum may supplement its K nutrition with Na. Despite growing on soils of differing cation content, Dodonaea maintained a constant leaf cation content over the three substrates.     

Site factors,foliar nutrient levels and growth of Cordia alliodora plantations in the humid lowlands of Northern Costa Rica

Within the perhumid, Atlantic lowlands of northern Costa Rica, Cordia alliodora plantations were studied in order to explain the observed pattern of growth irregularities. The soils, that were partly used as pastures over long periods, could be classified roughly into two units: (i) red, deeply weathered, slightly acidic soils from Mg-enriched parent material and (ii) brown, strongly acidic soils with high saturation of exchangeable Al (up to 80%).Leaf analysis revealed that Cordia is a highly demanding species in respect to macronutrients. Poorly growing trees in slope position suffered from an insufficient supply of N and P. K/Mg ratios of chlorotic leaves are very low. Soil analysis showed that nutrient deficiencies were related to (i) insufficient soil nutrient reserves of the poor, tropical soils or (ii) to an inhibition of nutrient uptake by soil physical or chemical factors.All sites are characterized by very low K reserves and losses of nutrients that are organically bound (N, P) caused by erosion. In the Mg-rich red soils, low amounts of K lead to K/Mg imbalances. Soil compaction caused by cattle grazing occurs on both soil units. In negatively influences the root development of Cordia, and hence nutrient uptake. In the brown soils, high amounts of exchangeable Al hinder a sufficient supply of nutrients (e.g.P) to the assimilation organs.     

Distribution of soil fractions and location of soil bacteria in a vertisol under cultivation and perennial grass

Effects of soil management on soil characteristics were investigated on the rhizosphere (RPP) and the nonrhizosphere (NRPP) soil of a re-grass vertisol underDigitaria decumbens and in the soil under continuous cultivation (CC). A low energy technique allowed to separate eight size and density fractions, including macro- and micro-aggregates while preserving soil bacteria. Organic C and N, microbial biomass C and the number of total bacteria (AODC) and ofAzospirillum brasilense and their distribution were determined in soil fractions isolated from the CC, NRPP and RPP soils. Soil macroaggregates (>2000 m) were similarly predominant in the NRPP and RPP soils when the dispersible clay size fraction (<2 m) respresented more than 25% of the CC soil mass. The main increase of C content in RPP originated from the macroaggregates (> 2000 m) and from the root fraction, not from the finer separates. The proportion of organic C as microbial biomass C revealed the low turnover of microbial C in the PP situations, especially in the clay size fraction of the NRPP soil. A common shift of AODC toward the finer separates from planted soils (CC and RPP) revealed the influence of living plants on the distribution of soil bacteria. The relative abundance ofA. brasilense showed the presence of the active roots ofDigitaria in the macroaggregates and their contact with the dispersible clay size fraction of the rhizosphere soil.     

Phytoextraction of cadmium and zinc by Salix from soil historically amended with sewage sludge

Short rotation coppice (SRC) such as Salix spp. can be grown as an energy crop and offers some potential for economic and practical phytoextraction of marginally contaminated arable soil. This study tested various soil amendments intended to increase soil metal availability to Salix, investigated the distribution of metal between different tree fractions and assessed the viability of phytoextraction using SRC on arable soils. Several Salix genotypes were grown in field trials over 4 years. Cd and Zn concentrations were generally ranked in the order leaves > bark > wood. Metal concentrations in wood increased towards the top of the willow stems, whereas concentrations in leaves showed the opposite trend. None of the amendments significantly increased uptake of Zn by willow. However, in response to a range of soil HCl treatments, mean Cd concentrations in stems and leaves were 112% and 130% of control values. Data from the current experiment, and previous studies, were combined to develop a predictive model of Cd and Zn stem uptake by Salix. The minimum biological concentration factor (BCF) required to achieve a prescribed soil metal target was also calculated based on typical proportions of bioavailable Cd in sludge-amended soils for a 25-year Salix rotation. The best Salix genotypes investigated achieved less than 20% of the uptake rate required to remove one third of the soil Cd content (equivalent to the average isotopically exchangeable Cd fraction in soils at the study site).     

Resource-island soils and the survival of the giant cactus,cardon, of Baja California Sur

Early survival and growth of some plants in arid environments depends on facilitation by a nurse plant. Amelioration of soil temperature extremes through shading and accumulation of mineral nutrients near nurse-plants are mechanisms of facilitation. We investigated the effects of shading (soil temperature) and soil type on survival and growth of the giant columnar cactus, cardon (Pachycereus pringlei). Cardon was grown either in a sandy clay-loam soil obtained from resource islands formed under mature mesquite (Prosopis articulata) or in the loamy-sand soil from plant-free bare areas that surround the islands. Seedlings were potted in these soils and the pots were buried to ground level in the open. We also determined plant responses to fertilization with N, P, K or NPK in the bare-area soils. Enhancement of survival and growth in the resource-island soils compared to that in the bare-area soils was highly significant. Plants survived and grew better in resource-island soils than in bare-area soil, an effect that was enhanced by shading (one-half of full sun). Greater root/shoot ratios of plants grown in bare-area soil indicated increased resource allocation to roots under limiting conditions. Significant interactions (analysis of variance) indicated that the soil and sun factors of the experiment were not independent of one another. Plant growth in bare-area soil improved considerably (>200%) in response to N fertilization (screenhouse conditions), and approximated that of plants in resource-island soil without N amendment. The growth response to P was small (<50%), while K did not affect growth significantly. Responses to NPK were similar to those to N alone. The results suggested that shading and nutritional effects interact in determining early survival and growth of cardon in different soils. This revised version was published online in August 2006 with corrections to the Cover Date.     

闽江口芦苇与短叶茳芏空间扩展对湿地土壤磷赋存形态的影响

选择闽江口鳝鱼滩的芦苇湿地、短叶茳芏湿地以及芦苇与短叶茳芏空间扩展形成的交错带湿地为对象，研究了不同湿地土壤磷赋存形态的分布特征及其主要影响因素。结果表明，不同湿地土壤中各形态磷含量整体表现为HCl-Pi > NaOH-Pi > Residual-P > NaHCO₃-Pi > NaOH-Po > Sonic-Pi > Resin-Pi > NaHCO₃-Po。其中，难分解态磷占TP的比例最高（Resin-Pi、NaHCO₃-Pi、NaHCO₃-Po），为48.3%-51.1%；中等易分解态磷次之（NaOH-Pi、NaOH-Po、Sonic-Pi、Sonic-Po），为37.4%-38.8%；而易分解态磷最低（HCl-P、Residual-P），为11.5%-12.9%。交错带湿地土壤中易分解态磷、中等易分解态磷和难分解态磷含量相对于纯群落湿地均发生了明显改变，其值相比芦苇湿地分别提高了10.6%、19.2%和22.6%，相比短叶茳芏湿地分别提高了1.6%、11.5%和16.6%，原因主要与二者空间扩展过程中交错带湿地土壤的理化性质特别是粒度组成、pH以及Fe、Al含量均较纯群落湿地发生明显改变有关。芦苇与短叶茳芏的空间扩展整体改变了湿地土壤的全磷（TP）含量和储量，相对于芦苇湿地和短叶茳芏湿地，交错带湿地土壤的TP含量分别增加了20.0%和7.1%，而磷储量分别增加了12.0%和18.0%。研究发现，芦苇与短叶茳芏的空间扩展不但改变了湿地土壤中磷的赋存状况，而且亦可能改变不同磷形态之间的转化。交错带湿地土壤磷赋存状况有助于缓解芦苇与短叶茳芏空间扩展过程中对磷养分的竞争压力，从而可能在一定程度上维持交错带湿地系统的相对稳定。     

外源氮输入对闽江河口芦苇湿地土壤磷形态赋存特征的影响

河口湿地是响应全球气候变化和人类活动最为敏感的生态系统之一，是外源氮的一个重要"汇"，其对于生源元素循环过程可产生深刻的影响。在当前闽江河口区氮负荷增强背景下，探讨外源氮输入对湿地土壤磷形态赋存及其关键转化过程具有重要意义。为此，选择闽江河口鳝鱼滩的芦苇湿地为研究对象，基于野外原位氮输入模拟试验，研究了不同氮输入水平（N_Nt，对照处理；N_Lt，低氮处理；N_Mt，中氮处理；N_Ht，高氮处理）对湿地土壤磷形态赋存特征的影响。结果表明，外源氮输入不但增加了湿地土壤的TP含量，而且改变了其土层分布特征。除N_Mt与N_Nt处理下的TP含量相当外，N_Lt和N_Ht处理下的全磷（TP）含量相比N_Nt处理分别增加了3.5%和4.4%。氮输入整体上增加了湿地土壤的活性磷和闭蓄态磷含量，但降低了中等活性磷含量。相比N_Nt处理，N_Mt和N_Ht处理下的活性磷含量分别增加了6.5%和12.6%，而N_Lt、N_Mt和N_Ht处理下的闭蓄态磷含量分别增加了3.3%、3.9%和7.0%。中等活性磷在N_Mt处理下的降幅尤为明显，其值相比N_Nt处理降低了6.7%。不同氮处理下湿地土壤以闭蓄态磷占比最高（51.8%-54.1%），中等活性磷次之（38.1%-41.2%），活性磷最低（7.0%-7.9%）。不同氮处理下的各形态磷占比以HCl-P_i、Residual-P、NaOH-P_o和NaOH-P_i较高，Sonic-P_o和NaHCO₃-P_i次之，而NaHCO₃-P_o、Resin-P和Sonic-P_i较低。研究发现，氮输入主要通过改变土壤养分及酸碱状况来进一步影响土壤中各形态磷的赋存。其中，N_Mt和N_Ht处理下活性磷含量的增加主要与Resin-P和NaHCO₃-P_o有关，N_Lt、N_Mt和N_Ht处理下闭蓄态磷含量的增加主要与Residual-P有关，而N_Mt处理下中等活性磷的显著降低主要与NaOH-P_i和Sonic-P_o有关。     

刺槐林魔芋健康高产的土壤微生态机制

通过对刺槐林和农田魔芋健株根区、根表及根外土壤微生物区系及养分含量比较,探索刺槐林魔芋健康高产的土壤微生态机制。结果表明:(1)刺槐林魔芋根外和根表土壤细菌数量分别较农田增加11.8%和588.9%,根区土壤真菌数量较农田显著减少74.4%。(2)刺槐林魔芋根区、根表及根外土壤中的有益优势微生物数量及其比例远高于农田魔芋,有害微生物数量远低于农田魔芋;在刺槐林魔芋根区、根表及根外土壤中,3种优势细菌为放射型根瘤菌(Rhizobium radiobacter)、苏云金芽孢杆菌(Bacillus thuringiensis)及摩氏假单胞菌(Pseudomonas mosselii),其中,根表土壤中放射型根瘤菌及苏云金芽孢杆菌数量分别为农田的25.7倍及13.0倍;2种优势真菌为黒附球菌(Epicoccum nigrum)和疣孢青霉(Penicillium verruculosum),1种优势放线菌为绿淀粉酶链霉菌(Streptomyces viridodiastaticus),其中刺槐林魔芋根表和根外土壤中黒附球菌数量分别较农田高159.2%和120.3%;大量存在于刺槐林下魔芋根外土壤中的疣孢青霉、以及根区、根表、根外土壤中的绿淀粉酶链霉菌在农田魔芋相应部位均未检出。(3)刺槐林下魔芋根外、根区土壤有机质含量分别较农田显著增加167.6%、39.6%,但速效P、K含量较农田分别显著降低85.6%~91.3%、12.4%~13.0%。研究认为,刺槐林魔芋健康高产与其根区、根表及根外土壤中特有的有益优势微生物数量多、有害微生物数量少以及土壤有机质含量高密切相关。     

Evaluation of the phosphorus status of P-deficient podzols in temperate pine stands: combining isotopic dilution and extraction methods

Phosphorus (P) is often a limiting factor of forest growth but our knowledge of the processes governing P availability in forest soils is rather limited. In the present work, we combined a isotopic dilution method with extraction methods to evaluate the P status in Pinus pinaster plantation forests on highly P-deficient soils. Total, organic, and inorganic P, dissolved and diffusive P, i.e. ionic P species that can be transferred from the solid phase to the soil solution due a gradient of concentration, were determined to a soil depth of 120 cm in a gradient of 18 forest sites (seven humid sites, five mesic sites, and six dry sites). Our objective was to assess the potential contribution of organic and inorganic P to plant available P. Based on results and our original assumptions, we observed that the contribution of organic P fractions (mineralization of soil organic P) to P availability related to the contribution of inorganic P fractions (diffusive P for durations up to 1 year) was predominant in litter, less important in top soil horizons, and negligible at depths below 30 cm. This was partly due to a decreasing proportion of organic P and an increasing proportion of diffusive P with soil depth. Owing to a very low amount of diffusive P in the top soils in dry sites, the relative contribution of organic P was actually higher in these sites than in humid and mesic sites, despite a lower overall organic P fraction. The combination of extraction and isotopic dilution methods in our study shed new light on P status in this forest range. In particular, these methods enable assessment of both the size of the pools and their dynamic fractions.     

黑老虎内生真菌及根际土壤真菌的群落结构与生态功能分析

为探讨黑老虎(Kadsura coccinea)根际土壤和组织内生真菌菌群的组成及其生态功能，该研究采用ITS高通量测序技术对成熟黑老虎(根、茎、叶)内生真菌及根际土壤真菌群落结构、多样性和生态功能进行了分析。结果表明：(1)从12个样品中共获得2 241个可操作分类单元(OTU),涉及10门、41纲、95目、212科、367属，内生真菌(根、茎、叶)和根际土壤真菌OTU数分别为386、536、258、1 435个，其中共有的OTU为18个。在门水平上，黑老虎内生真菌及根际土壤真菌优势群落均为子囊菌门和担子菌门，其中子囊菌门在叶和茎中占比分别高达96.99%和95.37%;在属水平上，黑老虎根际土壤真菌中腐生真菌被孢霉属占比较高(为13.5%),叶和茎等生长旺盛的组织中子囊菌门未分类属和痂囊腔菌属占比较高。(2)α多样性分析结果显示，黑老虎根际土壤真菌群落的丰度和多样性明显高于内生真菌，茎中内生真菌丰度显著高于根和叶，而根、茎和叶组织间内生真菌多样性差异不显著；PCoA分析结果显示，叶和茎的真菌群落结构相似性更高。(3)利用FUNGuild数据库进行的功能预测分析结果显示，黑老虎根际土...     

Changes in soil phosphorus fractions following positive and negative phosphorus balances for long periods

The effect of phosphorus (P) balance (addition, in both fertilizers and farmyard manure (FYM), minus removal in crops) on eight soil P fractions determined by sequential extraction, was measured on archived soils from various long-term experiments run by Rothamsted Experimental Station in the United Kingdom. It has been established unequivocally that, for all the soils investigated, no one of the eight P fractions was increased or decreased during long periods of P addition or depletion, respectively. However, changes were mainly in the resin (24–30%) and the inorganic (P_i) component of the four fractions extracted sequentially by 0.5 M NaHCO₃, 0.1 M NaOH, 1.0 M NaOH, 0.5 M H₂SO₄ (41–60%). For the sandy loam there were also consistent changes in the organic (P_o) fraction (25%), especially that extracted by bicarbonate, presumably because the soil contained only a little clay and presumably had low sorption capacity. When the soils were cropped without P addition the largest proportional change was in the P extracted by resin, 0.5 M NaHCO₃ and 0.1 M NaOH, suggesting that the P in these fractions is readily available, or has the potential to become available, for crop growth. This was supported by changes in the overall P balance. On the heavier textured soils, 50–80% of the change in total soil P (P_T) was in these fractions; on the sandy soil this increased to more than 90%. The change in the sum of the first five fractions accounted, on average, for 90% of the P balance. However these changes in the P in the plough layer frequently left large amounts of P unaccounted for in some of the excessively P enriched soils. The amount of P_i extracted by resin and bicarbonate (P_i(r+b)) ranged between 14 and 50% of the sum of the P_i fractions. Soils with the lower percentages were those known to be most responsive to P fertilizers. P_i(r+b) accounted for an average of 70% of the P balance (negative) in P depleting soils where crop offtake was not offset or exceeded by annual P additions (positive balance). The ratio between P_i(r+b) and P_i(sum) could be a guide in defining soils deficient in P and those which are excessively enriched.     

Potassium nutrition effects on seed alkaloid concentrations,yield and mineral content of lupins (Lupinus angustifolius)

To ensure that narrow-leafed lupin (Lupinus angustifolius L.) meets feed quality standards, the concentration of alkaloids must be kept under the maximum acceptable limit of 200 mg kg^–1 DM. One of the factors that may affect seed alkaloid concentration is soil nutrient deficiency. In this paper, we report the results of glasshouse and field experiments that tested the effect of potassium (K) deficiency on seed alkaloid concentrations. In the glasshouse, seed alkaloid concentrations increased by 385, 400 and 205% under severe K deficiency in sweet varieties (Danja, Gungurru and Yorrel, respectively) of L. angustifolius. The concentration of alkaloids in Fest, the bitter variety, was always high regardless of soil K status. At all levels of applied K (0–240 mg kg^–1 soil), lupanine was the predominant alkaloid in sweet varieties, whereas 13-hydroxylupanine prevailed in the bitter variety. Seed yield of all varieties increased exponentially with increasing amounts of applied K, reaching a maximum at 60 mg K kg^–1 soil. In the field, application of K to deficient soils decreased seed alkaloid concentration at Badgingarra, Western Australia (WA) but not at Nyabing, WA, in 1996. In both field trials, seed yield and mineral content were not affected by the amounts of K fertiliser applied. These findings highlighted the need for adequate K fertilisation of deficient soils in WA to avoid the risk of producing low quality lupin seed with high alkaloid concentrations. K deficiency is involved in stimulating alkaloid production in sweet varieties of L. angustifolius.     

Yield and composition of soybean seed as a function of potassium supply

Summary A reduction in K supply to soybean plants to deficiency levels during both vegetative and reproductive development resulted in reductions not only in yield, but also in oil and K concentrations in the seed and a concomittant increase in seed protein concentration. Correlations between mean fruit yield and oil, protein and K concentrations, over a wide range of K regimes, were 0.97, −0.94 and 0.98, respectively. When K supply was increased well above the level necessary to produce maximum yields,i.e. luxury consumption, there was no significant change in K concentration in the seed, indicating a high degree of control in the movement of K to the developing seed under high K regimes. When the K supply to the plant was limiting, the rate of accumulation of oil and carbohydrate fractions, but not of seed protein, declined during the latter part of podfilling. This resulted in a fall in the C/N ratio in the non-structural seed components during this part of seed development. Depriving plants of K only during seed development had no effect on seed composition or yield, whereas resupplying K to deficient plants after anthesis resulted in almost the same seed composition and yield as that which occurred with control plants. Possible mechanisms whereby K deficiency influences soybean seed composition and yield are discussed in terms of movement of carbohydrate and nitrogen to the seed. We suggest that potassium-deficient soils are likely to produce crops with low yields and low seed oil levels; the crop may respond to K fertilizers as late as anthesis.     

Hyperaccumulation of nickel by two Alyssum species from the serpentine soils of Iran

Serpentine soils, which contain relatively high concentrations of nickel and some other metals, are the preferred substrate for some plants, especially those that accumulate Ni in their tissues. In temperate regions more Ni-hyperaccumulator plants are found in Alyssum than in any other genus. In this study, serpentine soils of two areas (Marivan and Dizaj) in the west/northwest of Iran and also perennial Alyssum plants growing on these soils were analyzed for Ni and some other metals. The highest concentrations of total metals in the soils of these areas for Ni, Cr, Co and Mn were 1,350, 265, 94 and 1,150 μg g⁻¹, respectively, while concentrations of Fe, Mg and Ca reached 3.55%, 16.8% and 0.585% respectively. The concentration of exchangeable Ni in these soils is up to 4.5 μg g⁻¹. In this study two Alyssum species, A. inflatum and A. longistylum, have been collected from Marivan and Dizaj, respectively. Analysis of leaf dry matter shows that they can contain up to 3,700 and 8,100 μg Ni g⁻¹, respectively. This is the first time that such high Ni concentrations have been found in these species. The concentrations of other metals determined in these species were in the normal range for serpentine plants, except for Ca, which was higher, up to 5.3% and 3.5%, respectively