山西矿区复垦土壤中解磷细菌的筛选及鉴定

【目的】矿区复垦土壤贫瘠、 有效磷含量低。解磷细菌能够将有机磷和难溶性无机磷转化为可溶性磷,促进植物对磷素的利用。因此筛选和鉴定具有解磷能力的菌株,可为解决矿区生态恢复使用的微生物肥料提供菌种资源。【方法】采用平板分离法初筛菌株,得到D/d1.5的菌株,然后以磷酸钙为磷源,通过液体发酵试验复筛菌株,挑选出解磷率高于巨大芽孢杆菌(Bacillus megaterium)As1.223的菌株。以磷矿粉和卵磷脂为磷源,液体发酵试验测定菌株的解磷能力及磷酸酶活性。进行菌株的生长试验以测定菌株温度适宜性、 耐盐性及耐酸碱性。通过形态学、 基因序列分析及脂肪酸组成分析综合进行菌株鉴定。 菌落形态观察用营养琼脂平板培养基培养;菌体形态即细胞形态及其大小采用扫描电镜观察;基因序列分析采用16S rDNA序列测定,基因在线比对采用EzTaxon数据库;使用美国MIDI公司的Sherolock全自动细菌鉴定系统对菌株进行脂肪酸组成分析。【结果】利用无机磷和有机磷平板培养基,从山西省矿区复垦区土壤样品中筛选出19株解磷微生物,其中D/d1.5的有7株。在以磷酸钙为磷源的液体培养试验中,4株菌的解磷率高于巨大芽孢杆菌As1.223,解磷率为7.89%～12.61%,最高的为菌株Y14。4株菌对磷矿粉的解磷率为0.81%～1.21%,最高的为菌株Y14。在以卵磷脂为磷源的液体培养试验中,4株菌的解磷率与酸性磷酸酶活性分别为1.79%～3.07%和24.3～28.4U/L,均高于巨大芽孢杆菌As1.223; 碱性磷酸酶活性为11.9～50.2U/L;菌株Y14的解磷率与磷酸酶活性均最高。4株菌均有较强的环境适应能力,以Y14的适应性最强。H22、 Y11和Y34与假单胞菌属(Pseudomonas sp.)同源性在99%以上,Y14与泛菌属(Pantoea sp.)有99.79%的同源性; H22、 Y11和Y34的细胞脂肪酸组成特征峰与假单胞菌属(Pseudomonas sp.)相一致,Y14与泛菌属(Pantoea sp.)相一致;H22、 Y11和Y34被鉴定为假单胞菌(Pseudomonas sp.),Y14为泛菌属(Pantoea sp.)。【结论】分离、 筛选到4株高效解磷菌,对于磷酸钙和卵磷脂的解磷率均高于巨大芽孢杆菌As1.223。4株菌分别隶属于假单胞菌属(Pseudomonas sp.)和泛菌属(Pantoea sp.)。菌株Y14无机磷与有机磷平板的D/d值分别为3.28与1.59,降解磷酸钙、 磷矿粉、 卵磷脂的解磷率分别为12.61%、 1.21%、 3.07%,酸性与碱性磷酸酶活性分别为28.4 U/L和50.2 U/L,均为4株菌里最高的,且环境适应能力最强,生长温度为20～60℃,能耐受pH 4～11的酸碱梯度和2%～7%的盐分梯度,Y14被鉴定为泛菌属(Pantoea sp.)。4株菌均具有良好的解磷能力及较强的环境适应能力,可望进一步研发成为微生物肥料生产菌种。综合D/d值、 解磷率、 磷酸酶活性和生长试验,本试验最终确定适合山西矿区复垦农田推广的高效解磷菌菌株为Y14。     

Phosphorus compounds in subarctic Fennoscandian soils at the mountain birch (Betula pubescens)—tundra ecotone

Nutrient availability will partly regulate the response of high latitude ecosystems to climate warming, but phosphorus biogeochemistry is poorly understood in Arctic soils. We used NaOH-EDTA extraction and solution ³¹P nuclear magnetic resonance (NMR) spectroscopy to determine phosphorus compounds in subarctic soils from three locations in the Fennoscandian mountains contrasting in latitude and continentality. Soils were taken from open tundra and mountain birch (Betula pubescens Ehrh.) forest at each location. Between 87 and 95% of the total phosphorus was extracted from the surface 2 cm of the organic soil horizons. Most of the extracted phosphorus was orthophosphate monoesters (44-55%), with smaller concentrations of inorganic orthophosphate (15-24%), orthophosphate diesters (12-16%), pyrophosphate (3-18%), inorganic polyphosphate (0-15%) and phosphonates (0-4%). The orthophosphate diesters were further subclassified into DNA (9-13% extracted phosphorus) and phospholipids (1-6% extracted phosphorus), although strong signals in the orthophosphate monoester region of the spectra, consistent with the degradation of phosphatidyl choline in alkaline solution, suggested that phospholipid concentrations were substantially underestimated. The phosphorus composition was broadly similar among soils from the three locations, although no phosphonates were detected in tundra soils from the most southerly site. Deeper organic horizons tended to contain a greater proportion of orthophosphate monoesters than at the surface. The abundance of phosphorus compounds that would be considered readily degradable in temperate environments probably reflects the slow organic matter decomposition in these cold, acidic soils, and suggests that phosphorus availability is unlikely to limit ecosystem productivity on mesic soils at the birch-tundra ecotone during changes induced by climate warming.     

A 31P nuclear magnetic resonance study of the phosphorus species in alkali extracts of soils from long-term field experiments

The different forms of phosphorus (P) in 0.5 m sodium hydroxide extracts of soils from long-term field experiments at Rothamsted were characterized by ³¹P-nuclear magnetic resonance spectroscopy (NMR). The extract from an old grassland soil (pH 4.6) from a plot of the Park Grass Continuous Hay Experiment that had received no fertilizer or lime for at least 125 years contained the following forms of P: inorganic orthophosphate (22% of the extracted P), orthophosphate monoesters (49%), orthophosphate diesters (14%), phosphonates (3%), pyrophosphate (4%) and two unidentified forms of P (7%). The soil extract from a Park Grass plot given inorganic phosphate fertilizer (35 kg P ha^?1) annually for 121 years contained the same forms of P and, in addition, a small amount of polyphosphate. There was also evidence of an increase in the orthophosphate monoester fraction. Another old grassland soil, of pH 6.1, contained more total and organic P than Park Grass but the extract contained fewer forms of P: inorganic orthophosphate (14% of the extracted P), orthophosphate monoesters (39%), orthophosphate diesters (34%) and an unidentified form (13%). An area of this grassland that had been ploughed up 20 years previously, and kept bare since, contained less organic P. The extract contained less of the phosphate diesters but the more stable monoesters remained relatively unchanged.     

31P-NMR-spectroscopic investigations of NaOH-extracts from soils with different land use in Yucatan (Mexico)

In aqueous NaOH-extracts of top-soils (0-10 cm) from typic chromuderts, phosphorus was determined by NMR-spectroscopy. In addition to inorganic orthophosphate, orthophosphate monoesters and diesters were detected. Pyrophosphate was only found in traces after clear-cutting and burning of the forests. The result of clear-cutting and agricultural land use is an increase of inorganic P from 19% (forest) to 33% (maize field). Compost gardens and mature tree gardens contain only 9-13% inorganic P in the NaOH-extract. The organic P-fraction consists mainly of orthophosphate monoesters (57-72%). The orthophosphate diester content is only 10–21%. It could be shown, that the increase of inorganic P in the course of clear-cutting and ploughing is correlated with a decrease of orthophosphate mono- and diesters.     

Isolating the influence of pH on the amounts and forms of soil organic phosphorus

Soil pH influences the chemistry, dynamics and biological availability of phosphorus (P), but few studies have isolated the effect of pH from other soil properties. We studied phosphorus chemistry in soils along the Hoosfield acid strip (Rothamsted, UK), where a pH gradient from 3.7 to 7.8 occurs in a single soil with little variation in total phosphorus (mean ± standard deviation 399 ± 27 mg P kg^?1). Soil organic phosphorus represented a consistent proportion of the total soil phosphorus (36 ± 2%) irrespective of soil pH. However, organic phosphorus concentrations increased by about 20% in the most acidic soils (pH < 4.0), through an accumulation of inositol hexakisphosphate, DNA and phosphonates. The increase in organic phosphorus in the most acidic soils was not related to organic carbon, because organic carbon concentrations declined at pH < 4.0. Thus, the organic carbon to organic phosphorus ratio declined from about 70 in neutral soils to about 50 in strongly acidic soils. In contrast to organic phosphorus, inorganic phosphorus was affected strongly by soil pH, because readily‐exchangeable phosphate extracted with anion‐exchange membranes and a more stable inorganic phosphorus pool extracted in NaOH–EDTA both increased markedly as soil pH declined. Inorganic orthophosphate concentrations were correlated negatively with amorphous manganese and positively with amorphous aluminium oxides, suggesting that soil pH influences orthophosphate stabilization via metal oxides. We conclude that pH has a relatively minor influence on the amount of organic phosphorus in soil, although some forms of organic phosphorus accumulate preferentially under strongly acidic conditions.     

Effect of several germination conditions on total P, phytate P, phytase, and acid phosphatase activities and inositol phosphate esters in rye and barley.

Two assays were conducted to study the evolution of rye and barley phosphatases (phytase and acid phosphatase) and the degradation of its substrates (inositol phosphate esters) during seed germination. In this manner we could obtain a low-phytate, endogenous phosphatase rich ingredient to be used in animal nutrition. In the first assay, the seeds were soaked for 1 and 14 h and germinated for 3 and 5 days with and without the addition of gibberellic acid (GA3). In the second assay, the seeds were soaked for 1 h and germinated for 1, 3, and 5 days with GA3. Phytase (up to 5739 and 3151 U x kg(-1)) and acid phosphatase (up to 18288 and 3151 U x g(-1)) activities, and IP6 (6.09 and 6.01 mg x g(-1)), IP5 (0.48 and 0.48 mg x g(-1)), and IP4 (0.13 and 0.06 mg x g(-1)) were detected in ungerminated rye and barley, respectively. The germination process caused a significant increase of Phy and AcPh activities in rye (up to 112 and 213%) and barley (up to 212 and 634%) and a reduction in the phytate phosphorus content (up to 84 and 58%, respectively). Phytate phosphorus content was affected only by soaking time in the case of rye. Finally, during the course of germination, IP6 and IP5 were rapidly degraded in rye (88 and 79%) and barley (67 and 52%), and IP4 was only a short-living intermediate, which was increased during hydrolysis and degraded to IP3. In conclusion, a marked increase of Phy and AcPh activities in rye and barley with a concomitant decrease in phytate phosphorus content and an increase in the content of lower inositol phosphates were observed during the rye and barley germination.     

Orthophosphate, phytate, and total phosphorus determination in cereals by flow injection analysis

A flow injection spectrophotometric procedure with enzymatic hydrolysis was developed for determination of orthophosphate, phytate and total phosphorus in cereal samples. Phosphorus species were extracted from cereals with 0.05 mol L(-1) potassium hydrogen phthalate buffer solution at pH 5.7. Orthophosphate was directly determined in the extracts by molybdenum blue spectrophotometric method. The phytate was hydrolyzed by the enzyme phytase coupled to a solid phase packed into an enzymatic reactor, and the resulting hydrolyzed orthophosphate was also determined by spectrophotometry at 650 nm. After optimization for phosphorus species extraction and enzymatic hydrolysis, a linear calibration graph was obtained up to 196 x 10(-6) mol L(-1) orthophosphate (P conc = -2.67 + 0.52x, r = 0.9998). Measurements are characterized by relative standard deviation of 1.6% for a standard of 72 x 10(-6) mol L(-1) orthophosphate and no baseline drift was observed during 4 h operation periods. It provides 72 measurements per hour, with 2.4 x 10(-)6) mol L(-1) and 7.9 x 10(-6) mol L(-1) as detection and quantification limits, respectively.     

31Phosphorus‐Nuclear magnetic resonance analysis in extracts of a phosphorus‐enriched volcanic soil of Chile

Abstract

The nature of organic and inorganic phosphorus (P) in fertilized and unfertilized samples of Vilcun soil, a Chilean medial mesic typic Dystrandept which was studied through ³¹phosphorus‐nuclear magnetic resonance (³¹P‐NMR) analysis carried out on a single alkaline extraction. The total P contents ranged from 1,506 mg P kg^‐1 (B horizon, unfertilized soil) to 7,541 mg P kg^‐1 (A horizon, fertilized soil). The magnitude of the P signal (SEM‐EDAX results) appears to be related to that of the iron (Fe) signal. Signals of ³¹P‐NMR spectra are attributable to inorganic orthophosphate, and orthophosphate monoesters and diesters. No important differences between horizons were observed. Apparently in this soil, P are mainly associated with iron oxides and organic matter. The organic P forms were not readily subjected to mineralization.     

Moderately resistant phosphorus forms in subtropical ultisol of Argentina

Abstract

The efficiency of phosphorus (P) fertilization may be improved through knowledge of soil P fraction changes with time. This study examined: i) the distribution of P fractions according to Hedley's fractionation scheme and ii) the sequential changes in soil organic P (OP) and inorganic P (IP) in a typical Kandihumult, under favorable conditions for mineralization and under depletion conditions, with and without P fertilization. Soil P fractions considered were IP‐resin, IP‐ and OP‐bicarbonate, and IP‐ and OP‐hydroxide. The soil is characterized by the predominance of moderately resistant P, in organic and inorganic fractions. In the presence of favorable conditions for mineralization, a substantial decrease in moderately resistant organic P was observed, enhanced even more by fertilizer incorporation. The decrease of total extracted P (TPe) before depletion situations was mainly produced in the moderately resistant fraction, that registered a decrease of 23% (of this value 65% were due to OP). The main fate of the fertilization, in both situations (active mineralization as well as depletion) was moderately resistant inorganic phosphate.     

Phosphorus speciation and colloidal phosphorus responses to short-term cessation of fertilization in a lime concretion black soil

Long-term excessive application of mineral fertilizer has led to soil acidification and phosphorus(P) accumulation, increasing the risk of P loss and environmental pollution, and cessation of fertilization is widely considered as a cost-effective management strategy to relieve this situation; however, how such cessation influences P speciation and concentrations in a bulk soil and colloidal fractions and whether decreasing P concentration might maintain soil fertility remain unclear. In this stu...     

Inorganic orthophosphate for diagnosing the phosphorus status of wheat plants

Winter wheat (Triticum aestivum L) was grown to the 6‐leaf stage hydroponically under wide‐ranging conditions of phosphorus (P) supply. Tissue concentrations of inorganic orthophosphate (Pi) were measured in different plant parts and related to growth. The Pi was extracted from microwave‐dried plant material which is an effective and practical way of preserving Pi at levels close to those prevailing in fresh tissue. Extremely deficient wheat contained low levels of “metabolic”; Pi (1.4 mM), while wheat abundantly supplied with P accumulated Pi to concentrations of 40 mM without adverse effects on growth. The main effect of P on shoot growth was to increase the number and weight of tillers. The maximum weight of different organs was attained with different internal Pi concentrations. Critical leaf Pi (last fully expanded main‐shoot leaf) and critical whole shoot Pi for maximum whole shoot growth were 2.8 mM (0.043%) and 2.6 mM (0.040%), respectively. The Pi in mature main‐shoot leaves was closely related to whole shoot Pi. The diagnosis of plant nutrient status using P “storage pool”; concentrations is discussed.     

不同种类解磷微生物的溶磷效果及其磷酸酶活性的变化

比较了不同种类的微生物菌株对不同种类难溶性磷酸盐及磷矿粉的溶解能力。结果发现,细菌、酵母、霉菌在解磷方面均有一定作用,发挥着不同优势。磷酸钙、磷酸铝、磷酸铁等难溶性磷酸盐容易被酵母菌、霉菌溶解,而磷矿粉容易被巨大芽孢杆菌溶解,显示不同微生物与不同磷源的亲和溶解能力不同。不同种类磷酸盐或磷矿粉对微生物磷酸酶活力的影响不同,贫磷条件可以促进酸性和碱性磷酸酶活性的增加     

Slurry injection with nitrification inhibitor in maize: Plant phosphorus,zinc, and manganese status

Slurry injection below the maize (Zea mays L.) row may substitute a mineral nitrogen (N) phosphorus (P) starter fertilizer (MSF) and thus reduce nutrient surpluses in regions with intensive livestock husbandry. We investigated the plant P, zinc (Zn), and manganese (Mn) status compared to the current farm practice. In 2014 and 2015 field trials were conducted to evaluate plant nutrient status at different growth stages. Besides an unfertilized control, two slurry injection treatments (±nitrification inhibitor (NI)) were compared to slurry broadcast application plus MSF. In both experiments NI addition significantly increased nutrient concentrations during early growth (6-leaf 2015: +33% P, +25% Zn, +39% Mn). Under P deficiency due to cold weather conditions broadcast application showed higher P uptake until 6-leaf (36–58%), while it was lower at 8- (32%) and 10-leaf (19%) stage compared to slurry injection (+NI). Zn availability was enhanced for slurry injection (+NI) during early growth and Zn and Mn uptakes were higher at harvest. Slurry injection decreased P balances by 10–14 kg P ha^?1, while Zn and Mn balances were excessive independent of treatments. Slurry injection (+NI) can substitute a MSF without affecting early growth and enhances the Zn and Mn status. This new fertilizing strategy enables farmers to reduce P surpluses.     

Growth Behavior,Nutrient Harvest Index,and Soil Fertility in Okra-Pea Cropping System as Influenced by AM Fungi,Applied Phosphorus,and Irrigation Regimes in Himalayan Acidic Alfisol

The impact of arbuscular mycorrhizal fungi (AMF), inorganic phosphorus (P), and irrigation regimes was studied in an okra (Abelmoschus esculentus)–pea (Pisum sativum) cropping system in an acidic Alfisol. Experimentation was carried out at Palampur, India, in a randomized bock design (RBD), replicated three times with fourteen treatments comprising AM fungi (Glomus mosseae), inorganic phosphorus (50, 75, and 100% soil-test-based recommended P dose), irrigation regimes (at 40 and 80% available water capacity), generalized recommended NPK and irrigations (GRD), and farmers’ practice. Effects of AM fungi on plant height, leaf area index (LAI), and dry-matter accumulation (DMA) were nominal at early crop growth stage, i.e., 50 DAS (days after sowing). However, at 100 DAS, AMF imbedded treatments led to higher plant height (4%), LAI (3%), and DMA (6%) in okra, whereas in pea the magnitude of increase in these parameters following AMF inoculation was 6, 5, and 8%, respectively, over non-AMF counterparts. AMF + 75% soil-test-based P dose at either of these irrigation regimes gave statistically similar yields in both okra and pea as that obtained under 100% soil-test-based P dose at either of two irrigation regimes, thus indicating an economy of about 25% in soil-test-based P dose. Regarding nutrient harvest index in okra and pea, statistically similar values were registered with most nutrients under both AMF inoculated and non-AMF counterparts. In the case of okra, P harvest index was registered less by 3% with AMF inoculation; however, its magnitude increased by 3% in pea following AMF inoculation compared to non-AMF counterparts at similar levels of P and irrigation. At completion of two cycles of okra-pea system, AMF imbedded treatments did not alter available soil nutrient status significantly in comparison to non-AMF counterparts. Overall, current study suggests that practice of AMF inoculation has great potential in enhancing growth parameters for better productivity, fertilizer-P economy, and nutrient harvest efficiency in okra-pea production system in Himalayan acidic Alfisol.     

EFFECT OF DIFFERENT PHOSPHORUS SOURCES ON THE GROWTH,YIELD, ENERGY CONTENT AND PHOSPHORUS UTILIZATION EFFICIENCY IN MAIZE AT RAWALAKOT AZAD JAMMU AND KASHMIR,PAKISTAN

Effect of poultry manure (PM) and four inorganic phosphorus (P) fertilizers sources, i.e., diammonium phosphate (DAP), single super phosphate (SSP), nitrophos (NP) and triple super phosphate (TSP) on crop production and P utilization efficiency (PUE) of maize was studied. Both inorganic P fertilizers and PM applied alone or combined in 50:50 proportions at equivalent rate of 90 kg P₂O₅ ha^?1. Results indicated that inorganic P sources with PM significantly increased plant height, leaf area and chlorophyll content. Average values showed that combined application of inorganic P with PM increased grain yield by 19 and 41% over inorganic P and PM alone, respectively. Similarly, increase in P-uptake due to the combined application of inorganic P + PM was 17% compared to sole inorganic P. Phosphorus utilization efficiency of inorganic P was increased with PM and the highest PUE was recorded in DAP + PM. Generally, combination of DAP + PM proved superior over the remaining P fertilizers.     

Aging effects of organic and inorganic fertilizers on phosphorus fractionation in a calcareous sandy loam soil

In most arid and semiarid soils, naturally occurring phosphorus(P) is a major yield-limiting plant nutrient. In this study, to investigate the effects of organic(OP) and inorganic P(IP) sources on P fractionation, a calcareous sandy loam alkaline soil was fertilized with OP and IP fertilizers at low(80 mg P kg~(-1) soil) and high(160 mg P kg~(-1) soil) application rates. Three combinations of OP and IP(i.e., 75% OP + 25% IP, 50% OP + 50% IP, and 25% OP + 75% IP) were applied at low and high application rates,respectively, followed by soil aging for 21 d. Soil samples were collected after 1, 2, 3, 7, and 21 d and subjected to sequential extraction to analyze soluble and exchangeable, Fe-and Al-bound, Ca-bound, and residual P fractions. The soluble and exchangeable P fraction significantly increased up to 24.3%, whereas the Ca-bound fraction decreased up to 40.7% in the soils receiving 75% OP + 25% IP and 50% OP + 50% IP, respectively, compared with the control(receiving no P fertilizer). However, the transformation of P fractions was influenced by aging time. Addition of P sources caused instant changes in different P fractions, which then tended to decline with aging time. Change in soil p H was the limiting factor in controlling P availability. At high application rate, the OP source significantly increased soil P availability compared with the IP source with soil aging. Depending on P fractionation, a proper combination of OP and IP fertilizers, as long-term slow and instant P-releasing sources for plant uptake, respectively, may be a sustainable strategy to meet crop P requirements in the arid and semiarid soils.     

适应玉米的溶磷细菌筛选及其对玉米生长的影响

从石灰性土壤中分离获得4株高效溶磷细菌X5、X6、Z4和Z8,研究其生物学特征,探索其单独及复合的溶磷促生潜能。研究发现菌株X5、X6、Z4和Z8均可以利用玉米根系分泌物作碳源生长。菌株X6和Z4均能产生吲哚乙酸(IAA)和铁载体,菌株Z8可产生IAA不产生铁载体,菌株X5可产生铁载体不产生IAA。盆栽试验结果表明,接种单一溶磷菌及4株菌复合处理均可促进玉米生长,但复合菌群的溶磷促生效果显著高于单一菌株。通过16S r RNA基因序列分析研究菌株的分类地位,初步鉴定X5、X6、Z4、Z8分别为荧光假单孢菌(Pseudomonas fluorescens)、草假单胞菌(Pseudomonas poae)、巨大芽孢杆菌(Bacillus megaterium)和枯草芽孢杆菌(Bacillus subtilis)。     

施加粪肥对潮土有机磷形态转化的影响

施加粪肥是提高土壤肥力的重要措施,为了解粪肥磷在潮土中的化学行为,通过室内培养试验,采用NaOH-EDTA 浸提和 31P 核磁共振技术分析比较了鸡粪、牛粪及施肥后土壤中的磷形态及含量,并研究了施肥对潮土有效磷的影响。结果表明,粪肥磷主要以无机态形式存在,2 种粪肥的有机磷形态及含量有明显不同,肌醇六磷酸在鸡粪中的含量明显高于牛粪。粪肥施加到潮土后丰富了土壤有机磷的形态。随时间延长,潮土中各形态磷发生相互转化,以肌醇六磷酸为主的正磷酸单酯含量明显降低,核酸等正磷酸双酯显著升高。鸡粪处理的土壤有效磷含量逐渐升高,牛粪处理则表现出相反的趋势。施加粪肥后,土壤有效磷呈现不同的变化规律可能是无机磷在土壤中固定或沉淀,有机磷矿化和无机磷被微生物固持这三方面综合作用的结果。     

Changes in net ecosystem production associated with forest fire in taiga ecosystems,near Yakutsk,Russia

Abstract

The effect of sucrose on the growth of rice plants under gnotobiotic conditions was studied at test tube scale in vinyl isolators under weak or strong light. Under weak light (500 lux) the growth of rice plants on agar medium containing only inorganic nutrients during the 20 days after transplanting stopped at 3rd leaf stage, whereas plants on agar medium containing inorganic nutrient plus 2% sucrose grew to 5th or 6th leaf stage. Under strong light (1.5 × 10⁴ lux) the stage of tillering was promoted by supplying sucrose. The growth of rice plants in pot-hydroculture under weak light had the same tendency as that obtained in test tube culture under weak light.

Considering the concentration of inorganic elements in rice shoots, it seems most likely that the uptake of inorganic elements. especially phosphorus and potassium, was enhanced by the supplements of 2% sucrose under weak light. An increase of calcium and manganese uptake was observed in plants grown in medium containing 2% sucrose compared with that of plants grown in inorganic medium alone under strong light. The uptake of inorganic elements from medium containing inorganic nutrients plus 2% sucrose depended chiefly on light energy under strong light in the phytotron used.     

Loss of phosphorus from soil in semi-arid northern Tanzania as a result of cropping: evidence from sequential extraction and 31P-NMR spectroscopy

In semi‐arid northern Tanzania, the native woodland is being rapidly cleared and replaced by low input agriculture. This has resulted in pronounced environmental degradation, and in particular loss of phosphorus (P) from the soil. We have used sequential extraction and ³¹P‐NMR to investigate the effects of land use changes, i.e. native woodland, degraded woodland, cultivation for 3 and 15 years and homestead fields where manure was applied, on the amount and structural composition of P in this soil. Clearing and continuous cultivation reduced both organic and inorganic P in the soil. The difference in the amount of organic P from the bulk soil of the fields cultivated for 3 and 15 years was not statistically significant (P < 0.05), suggesting that most of the depletion in organic P occurred during the first 3 years of cultivation. By contrast, in the homesteads, there was much organic and inorganic P in the soil. The ³¹P‐NMR revealed that cultivation resulted in a 53% depletion of orthophosphate diester P, whereas only a 30% and 39% reduction of orthophosphate monoester P was found in the bulk soil after 3 and 15 years of cultivation, respectively. These results concur with the suggestion that diester P constitutes more easily mineralizable forms of organic P in soil than does monoester P. Our ³¹P‐NMR also showed that 70% of the inorganic orthophosphate P was depleted from the coarse and fine sand separates as a result of cultivation. The influence of clearing and subsequent cropping on the amount and forms of P was more pronounced in the coarse and fine sand than in the silt and clay, stressing the importance of particle size and chemical properties such as organic matter and oxides in the availability of P in this soil. Our results show that the current low input agricultural practice is not sustainable, and that practices must be developed to combat the ongoing degradation of the soil. A combined use of available organic materials such as animal manure with the judicious use of inorganic fertilizers can replenish the soil's fertility.