Heterogeneous distribution of phosphorus and potassium in soil influences wheat growth and nutrient uptake

Heterogeneous distribution of mineral nutrients in soil profiles is a norm in agricultural lands, but its influence on nutrient uptake and crop growth is poorly documented. In this study, we examined the effects of varying phosphorus (P) and potassium (K) distribution on plant growth and nutrient uptake by wheat (Triticum aestivum L.) grown in a layered or split soil culture in glasshouse conditions. In the layered pot system the upper soil was supplied with P and either kept watered or allowed to dry or left P-deficient but watered, whereas the lower soil was watered and fertilised with K. Greater reductions in shoot growth, root length and dry weight in the upper soil layer occurred in −P/wet than in +P/dry upper soil treatment. Shoot P concentration and total P content were reduced by P deficiency but not by upper soil drying. Genotypic responses showed that K-efficient cv. Nyabing grew better and took up more P and K than K-inefficient cv. Gutha in well-watered condition, but the differences decreased when the upper soil layer was dry. In the split-root system, shoot dry weight and shoot P and K contents were similar when P and K were applied together in one compartment or separated into two compartments. In comparison, root growth was stimulated and plants took up more P and K in the treatment with the two nutrients supplied together compared with the treatment in which the two nutrients were separated. Roots proliferated in the compartment applied with either P or K at the expense of root growth in the adjoining compartment with neither P nor K. Heterogeneous nutrient distribution has a direct decreasing effect on root growth in deficient patches, and nutrient redistribution within the plant is unlikely to meet the demand of roots grown in such patches.     

Availability of iron,manganese, zinc and phosphorus in submerged sodic soil as affected by amendments during the growth period of rice crop

Summary Effect of amendments, gypsum (12.5 tonnes/ha), farmyard manure (30 tonnes/ha), rice husk (30 tonnes/ha) and also no amendment (control) on the availability of native Fe, Mn and P and applied Zn in a highly sodic soil during the growth period of rice crop under submerged conditions was studied in a field experiment. Soil samples were collected at 0, 30, 60 and 90 days of crop growth. Results showed that extractable Fe (1N NH₄OAC pH 3) and Mn (1N NH₄OAC pH 7) increased with submergence upto 60 days of crop growth but thereafter remained either constant or declined slightly. Application of farmyard manure and rice husk resulted in marked improvement of these elements over gypsum and control. Increases in extractable Mn (water soluble plus exchangeable) as a result of submergence and crop growth under different amendments were accompanied by corresponding decreases in easily reducible Mn content of the soil. Application of 40 kg zinc sulphate per hectare to rice crop could substantially raise the available Zn status (DTPA extractable) of the soil in gypsum and farmyard manure treated plots while the increase was only marginal in rice husk and control plots indicating greater fixation of applied Zn. Available P (0.5M NaHCO₃ pH 8.5) behaved quite differently and decreased in the following order with crop growth: gypsum>rice husk>farmyard manure>control.     

Arbuscular mycorrhizal fungi contribute to phosphorus uptake by wheat grown in a phosphorus-fixing soil even in the absence of positive growth responses

We used 32P to quantify the contribution of an arbuscular mycorrhizal (AM) fungus (Glomus intraradices) to phosphorus (P) uptake by wheat (Triticum aestivum), grown in compartmented pots. The soil was from a major cereal-growing area, the Eyre Peninsula, South Australia; it was highly calcareous and P-fixing. Fertilizer P was added to soil at 20 mg kg(-1), as solid or liquid. Two extraction methods were used to estimate plant-available P. Fungal colonization was well established at harvest (36 d). Application of P decreased both colonization and hyphal length density in soil, with small differences between different P fertilizers. Plants showed large positive responses in terms of growth or total P uptake to all P additions, and showed no positive (or even negative) responses to AM colonization, regardless of P application. 32P was detected only in AM plants, and we calculated that over 50% of P uptake by plants was absorbed via AM fungi, even when P was added. The results add to the growing body of knowledge that 'nonresponsive' AM plants have a functional AM pathway for P transfer to the plant; it should not be ignored in breeding plants for root traits designed to improve P uptake.     

Soil potassium mobility and uptake by corn under differential soil moisture regimes

This study examined the effects of soil moisture on soil K mobility, dynamics of soil K, soil K fixation, plant growth and K uptake. A pot experiment, with and without corn (Zea maysL.), was conducted over a 16-d duration using a Yolo silt loam treated with two soil moisture regimes, i.e. constant moisture vs. wetting–drying (W–D) cycles. Soil K dynamics were determined using both ion exchange resin and direct extraction of soil solution. Soil K mobility increased significantly with soil moisture content (θ_v) and there was a positive curvilinear relationship between θ_v and effective diffusion coefficient (D_e), suggesting that more K⁺ can diffuse to the plant roots at sufficient soil moistures. Increase in D_e could be attributed to the decrease of impedance factor. During W–D cycles, soil solution K concentration increased as soil solution volume decreased, but soil solution K and NH₄ ⁺-extractable K pools decreased. In the constant moisture regime, available K pools decreased over the 16-d duration, but to a lesser extent than in W–D regime. The W–D cycles significantly enhanced K fixation and reduced available K pools in the soil in contrast to the constant moisture regime. Potassium fixation by the soil showed a biphasic pattern under the W–D regime, with a rapid fixation within the first 2 d after re-wetting, followed by a slower fixation. In the soil with constant moisture, K fixation was rapid during the first 8 h after wetting the soil, and then proceeded so slowly that no significant K fixation was observed after 4 d. The W–D cycles decreased root and shoot growth and K uptake by corn compared to constant moisture condition. Our results support the hypothesis that W–D cycles enhance soil K fixation, reduce soil K mobility and plant growth, and therefore reduce plant K⁺ uptake. This revised version was published online in June 2006 with corrections to the Cover Date.     

Quantifying uptake rate of potassium from soil in a long-term grass rotation experiment

Soil-plant potassium (K) dynamics were studied using a long-term field experiment in order to evaluate the plant performance and K delivering capacity of the soil parent material. Rye grass (Lolium perenne L.) based rotations on a loamy sand derived from granitic bedrock were studied over 30 years with two K-fertilisation regimes, nil (K0) and 65 kg K ha^?1?yr^?1. Mineralogical and chemical methods were combined to identify and quantify soil K resources including the partitioning of K between minerals. Two or three cuts were taken annually and herbage yield and composition together with exchangeable soil K were analysed. Herbage yield declined with time and significantly reduced when the K concentrations approached 1%. The grass K concentration also declined over time and stabilized at around 0.5–0.7% (dw) in K0 in all cuts. Input-output mass balances showed an accumulated net K off-take (deficit) of 1,100 kg ha^?1, i.e. 35 kg ha^?1?yr^?1. With an exchangeable K pool of 100 kg ha^?1 (in the rooting zone 0–40 cm) this indicated a substantial release of K from mineral sources, most probably biotite and hydrobiotite. Assuming a similar net off-take was continued then this particular mineralogical K source would be depleted within two centuries. The study illustrates the strength of combining long-term field experimental data with state of the art quantitative mineralogical methods in order to assess site-specific resources which can form a basis to evaluate the sustainability of different management practices.     

Changes in soil phosphorus fractions in a calcareous paddy soil under intensive rice cropping

We conducted a 4-year field experiment on a calcareous paddy soil in Zhejiang province of China to measure the changes in chemically extracted soil P fractions in an irrigated double-cropping rice system. Treatments included four fertilizer combinations (unfertilized control, NK, NP, and NPK) as main-plots and two rice cultivar types (inbred vs. hybrid rice) as sub-plots. Total plant P uptake and grain yield of rice declined in all treatments over time. Severe P-deficiency and significant rice yield losses began in treatments without P application after the second rice crop. Compared to inbred rice, hybrid rice increased grain yield (+18%), N uptake (+11%) and K uptake (+27%) but there was no significant difference in total plant P uptake. Recovery efficiencies of fertilizer-P averaged 31–32% in both cultivars. In treatments without P application, the P mass balance was negative (−6 to −8 kg P ha⁻¹ crop⁻¹) and phosphorus was drawn down in all inorganic P fractions, including resin, alkali- (NaHCO₃-Pi and NaOH-Pi) and acid-soluble P fractions (dilute HCl-P, concentrated HCl-P, residual-P). Only small amounts were removed from organic P fractions, 1–3 mg P kg⁻¹ year⁻¹ from NaHCO₃-Po and none from NaOH-Po. In treatments with fertilizer-P addition, the P mass balance was positive (+8 to 10 kg P ha⁻¹ crop⁻¹), soil P declined at a slower rate in inorganic P fractions and it increased (+51%) in the residual-P fraction. Hybrid rice generally caused greater depletion of inorganic soil P fractions than inbred rice, but there was no difference among cultivars in their effect on NaHCO₃-Po and NaOH-Po. Positive correlations (r = 0.63–0.81, P < 0.001) were observed between all inorganic P fractions (except residual-P) and total P uptake by rice. Our results suggest that rice plants draw P from a continuum of chemically extracted fractions that are assumed to have widely differing plant P availability. Regular P additions are required to maintain the effective soil P supply and differences between inbred and hybrid rice should be taken into account in P management strategies.     

长期施肥对石灰性土壤磷素肥力的影响 Ⅰ.有机质、全磷和速效磷

在陕西关中黄土区连续23年进行了不同施肥、小麦玉米轮作定位试验,研究了0～100cm土层土壤有机质、全磷、速效磷含量变化.结果表明,长期单施化肥或有机肥与化肥且配施均可增加耕层(0～20cm)土壤有机质含量.长期施用厩肥并配施化肥处理对土壤总磷库及无机磷库、速效磷的贡献大于玉米秸秆处理.长期单施化肥可增加土壤全磷、无机磷和速效磷含量,增加幅度低于厩肥和休闲处理,与秸秆处理对全磷、速效磷含量的影响效应相近.23年的不同施肥处理,与无肥处理相比,其理土壤磷素增量在0～100cm土壤剖面中的分布特点是:全磷增量剖面分布可为3层———耕层(0～20cm)为显著累积层,20～60cm土层为微增-亏损层,60～100cm土层为轻度累积层.速效磷增量剖面分布趋势与全磷增量分布趋势基本相同,仅在60～100cm土层累积较弱.     

酸性土壤上肥田萝卜和小麦对低品位磷矿粉的吸收差异

根据对肥田萝卜和小麦生长于不同P处理下的网膜分隔三室及二室模拟栽培系统的试验,分析了肥田萝卜和小麦对酸性土壤上低品位磷矿粉不同处理的吸收效果。结果表明,肥田萝卜对磷矿粉的吸收受到根系活动范围的限制,它可以有效利用施在根室区的低品位磷矿粉,干物重增加幅度达233%,比对照有极显着的提高;不论根室区是否施磷矿粉,肥田萝卜对于施在外室区(与根室区用网膜相隔)的低品位磷矿粉都具有微弱的利用能力,认为这是少量渗入到外室的根分泌的有机酸的活化作用。不过肥田萝卜对这一部分P的利用量不足以显着提高植株的干物重;小麦对于施在根室或外室区的低品位磷矿粉均不能有效利用.     

Relationships between soil potassium supply characteristics based on soil solution concentration and buffer power and field responses of winter wheat and maize

The relationship between soil K supply, characterised by the soil solution K concentration and the soil K buffer power, and plant K status was investigated for field grown crops. The study was carried out in 15 K fertilisation trials with maize and wheat covering a wide range of agricultural soils and K level. Soil K buffer power was obtained through sorption–desorption curves. For each trial the critical K concentration in the soil solution was deduced from the relationship between the K concentration in the soil solution and the K concentration in shoot tissue water, which was considered as a relevant indicator of the plant K status. At sufficient K levels, the maximal K concentration in the shoot tissue water of maize (145 mM) was lower than that of wheat (175 mM) but the percentages of the critical K concentration in plant tissue water to this maximal K concentration were similar for the two plant species with an average of 75%. The critical K concentration in the soil solution varied between soils. However, a close correlation was found between the critical K concentration in soil solution and the inverse of the soil buffer power at this concentration (r ²=0.981) or the inverse of the square of buffer power (r ²=0.989). On a wide range of soils and field conditions, these two indicators were more able to account for K availability and plant response than exchangeable K content or K saturation ratio of the CEC.     

Isolation and characterization of a motile hydrogenotrophic methanogen from rice paddy field soil in Japan

A hydrogenotrophic motile methanogen was isolated from flooded Japanese paddy field soil. Anaerobic incubation of the paddy soil on H(2)-CO(2) at 20 degrees C led to the enrichment of symmetrically curved motile autofluorescent rods. The methanogenic strain TM20-1 isolated from the culture was halotolerant and utilized H(2)-CO(2), 2-propanol-CO(2), or formate as a sole methanogenic substrate. Based on the 16S rRNA gene sequence similarity (94.8%) with Methanospirillum hungateii, and on the physiological and phenotypic characteristics, TM20-1 was suggested to be a newly identified species belonging to the genus Methanospirillum. This is the first report of isolation of the genus Methanospirillum strain from a rice paddy field.     

Methanogenic symbionts of anaerobic ciliates and their contribution to methanogenesis in an anoxic rice field soil

Methanogenesis in rice field soils starts soon after flooding while potentially competing processes like reduction of sulphate and iron take place. Early methanogenesis is mainly driven by hydrogen, while later in the season acetate tends to become more important. Anaerobic ciliates are abundant during this period, and their endosymbionts use hydrogen produced by the ciliates to reduce carbon dioxide to methane. These endosymbiotic methanogens are protected from the competition for substrates with other bacteria that may control methanogenesis outside the protozoan cells. Thus, we focussed on early methanogenesis and on the potential contribution from ciliates and their endosymbionts. Only ciliates of the genus Metopus were found to harbour methanogens, as identified by the F(420)-fluorescence of the endosymbionts. We followed the population dynamics of the ciliates with time, and calculated the ratio of symbiotic methane production to overall methanogenesis. Symbiotic methane production was calculated from the species-specific numbers of methanogenic endosymbionts times the cell-specific methane production of the symbionts. According to this calculation, the symbionts' contribution to overall methane production was only 6.4% at the beginning and decreased with time. In a second experiment, colchicine and cycloheximide were used to inhibit all eukaryotes, comparing the remaining methane production rate to a control without inhibitors. In the inhibition experiment, the contribution from symbionts decreased from 40% to 6% during the first days after flooding, and dropped to near zero within 2 weeks. However, nearly all methane produced from H(2)/CO(2) could be attributed to the ciliates' symbionts between days 5 and 10 after flooding. Both experiments showed that the contribution of methanogenic symbionts to overall methane production is a transient phenomenon, restricted to the first 2 weeks.     

Effect of lime and phosphorus applications on concentrations of available nutrients and on P,Al and Mn uptake by two pasture legumes in an acid soil

Summary Effects of increasing rates of lime and phosphorus addition on concentrations of available nutrients in soil and on P, Al and Mn uptake by two pasture legumes, lotus (Lotus pedunculatus Cav.) and white clover (Trifolium repens L.), were studied in a pot experiment using a highly leached acid (pH 4.2) soil.Liming resulted in an increase in exchangeable Ca and thus in percentage base saturation, with concomitant decreases in levels of exchangeable Al, Fe and Mn. The relationship between exchangeable Ca and Al was linear and negative with a gradient of almost unity. Liming had no consistent effect on measured CEC values. Increasing lime rates significantly reduced concentrations of Mg, K and Na in saturation paste extracts but had no effect on exchangeable Mg, K and Na levels.With increasing lime additions, available phosphate indicesviz water soluble, resin-, Morgan-and Williams-extractable all decreased significantly, Truog-extractable was unaffected, while Brayextractable generally increased. Fractionation revealed that lime additions caused a decrease in easily soluble, Fe-bound and to a lesser extent Ca-bound phosphate fractions, had no effect on reductant soluble phosphate, but resulted in an increase in the Al-bound fraction. P uptake and yield of both legumes increased with lime and P additions.Correlations between available phosphate indices and yield of both legumes were weak or nonsignificant. However, high, significant positive correlation coefficients were found between available phosphate and plant uptake of P. Indices of available Al and Mn were not generally significantly correlated with plant uptake of Al or Mn but significant negative correlations were found between available Al and Mn and yield of both species.     

长期施磷对黄壤旱地磷库变化及地表径流中磷浓度的影响

对贵州黄壤旱地进行采样以及盆栽试验,探索黄壤旱地磷库的变化及其对地表径流磷量的影响。结果表明,长期施磷后黄壤旱地无机磷占全磷的比例逐渐增高,Al-P、Fc-P和Ca-P积累的顺序为Fe-P>Al-P>Ca-P。长期施磷后黄壤旱地的有效磷和藻类可利用的总磷也不断积累,高磷（Olsen-P>25mg·kg^-1)旱地藻类可利用的总磷与Al-P、Fe-P和Ca-P的相关系数分别为0.859、0.903和0.650,Fc-P对藻类可利用磷量的影响起着最重要的作用。在模拟雨强为63.2mm·h^-1下,降雨30min后,低磷黄壤旱地（Olsen-P为4.62-15.9mg·kg^-1)径流中磷酸根磷含量仅为2.81-4.17μg·L^-1,生物有效性磷含量为0.723-0.876mg·L^-1;高磷黄壤旱地（Olsen-P)为29.4-59.2mg·kg^-1)径流中磷酸根磷含量达到0.026-0.714mg·L^-1,生物有效性磷含量增加到0.996-1.281mg·L^-1;高磷黄壤旱地地表径流磷量能加速水体富营养化的产生。     

长期定位施肥对保护地土壤供钾特性的影响

研究了16年定位施肥条件下,不同施肥方式对蔬菜保护地土壤中有效钾含量与土壤供钾特性的影响。结果表明:土壤全钾含量保持在较高水平22.43～26.92g.kg-1;与不施有机肥处理相比,长期施用有机肥后土壤全钾含量有所下降(单施磷肥处理除外),但不同的化肥单施或配施对土壤全钾含量影响不大;长期单施或化学肥料配施土壤的供钾强度和钾素有效率都不高,但施用有机肥明显提高了土壤有效钾含量及土壤的供钾能力,其中,长期单施化学钾肥土壤中有效钾含量为195.60mg.kg-1,单施有机肥处理为460.14mg.kg-1,而化学钾肥与有机肥配施后增长为621.06mg.kg-1;土壤供钾强度和钾素有效率在施用有机肥后也大幅度提高。     

长期施肥对麦田大型土壤动物群落结构的影响

于2007、2008年春季在中国科学院封丘农业生态实验站,研究长期定位施肥对麦田大型土壤动物群落结构的影响。调查共获得大型土壤动物3068头,隶属8纲,19目,28科。不同施肥处理条件下土壤动物类群数差异显著(F=2.51, P＜0.05, df=55),个体数差异极显著(F=8.99, P＜0.01, df=55)。结果显示,大型土壤动物的类群数和个体数在有机肥和营养均衡条件下较高,缺磷条件下较低。土壤动物多样性指数(H')以有机肥和营养均衡条件下显著高于营养不均衡和不施肥处理(P＜0.05)。主成分分析结果显示,第一主成分贡献值47.14%,第二主成分贡献值30.10%。经线性检验第一主成分与土壤动物个体数(y=0.335x-2.163,R²=0.51)和类群数(y=0.042x-1.25,R²=0.67)均呈线性关系。总之,长期施用有机肥和营养均衡大型土壤动物群落构成相似。土壤有机质和磷含量是影响土壤动物群落构主要生态因子。     

施钾量和施钾时期对小麦氮素和钾素吸收利用的影响

利用¹⁵N示踪技术,研究了施钾量和施钾时期对高产小麦氮素和钾素吸收利用的影响.结果表明： 0～20 cm土层土壤速效钾含量为118.5 mg·kg^-1时,一次性基施钾肥未提高植株的氮、钾积累量;速效钾含量为79.0 mg·kg^-1时,施钾显著提高了植株的氮、钾积累量.采用分期施钾时（1/2基施、1/2拔节期追施）,随施钾量增加,小麦吸收的肥料氮和土壤氮量及追施氮肥在土壤中的残留量均增加,肥料氮的损失量降低.分期施钾显著提高了植株的氮、钾积累量、吸收效率和生产效率,当施钾量为135 kg·hm^-2时,与一次性施钾相比,分期施钾促进了植株对追肥氮和土壤氮的吸收,提高了追施氮肥在土壤中的残留量.结果还表明：施钾提高了小麦的籽粒产量、蛋白质含量和湿面筋含量;分期施钾处理优于一次性施钾处理,以K45+45（45 kg·hm^-2基施、45 kg·hm^-2拔节期追施）处理最优.过多施钾使小麦产量和品质趋于降低.     

The PDI genes of wheat and their syntenic relationship to the esp2 locus of rice

The storage protein polymers in the endosperm, stabilised by disulphide bonds, determine a number of processing qualities of wheat dough. The enzyme protein disulphide isomerase (PDI), involved in the formation of disulphide bonds, is strongly suggested to play a role in the formation of wheat storage protein bodies. Reports of the rice mutant esp2 exhibiting aberrant storage protein deposition in conjunction with a lack of PDI expression provided strong indications of a direct role for PDI in storage protein deposition. The potential significance of wheat PDI prompted the present studies into exploring any orthology between wheat PDI genes and rice PDI and esp2 loci. By designing allele-specific (AS)-polymerase chain reaction (PCR) markers, two of the three wheat PDI genes could be genetically mapped to group 4 chromosomes and showed close association with GERMIN genes. Physical mapping led to localisation of wheat PDI genes to chromosomal “bins” on the proximal section of chromosome 4AL and distal sections of 4BS and 4DS. Identification of the putative PDI gene of rice and its comparison to the esp2 locus revealed that they were present at similar positions on the short arm of chromosome 11. Analysis of a large section of the PDI-containing section of rice chromosome 11S revealed a number of putative orthologues from The Institute for Genomic Research Triticum aestivum Gene Index database, of which five had been mapped, each localising to group 4 chromosomes, many in good agreement with our mapping results. The results strongly suggest a close linkage between the esp2 marker and the PDI gene of rice and an orthology between the PDI loci of rice and wheat and predict quantitative-trait loci involved in storage protein deposition at the PDI loci.     

太湖地区稻田氮肥吸收及其利用的研究

The effects of different amounts and kinds of nitrogen fertilizer on rice yield and its nitrogen uptake and utiliza-tion were studied on a main paddy soil (Wushan soil) of Taihu area. The results indicated that the optimal amount of nitrogen fertilizer was about 180 kg N· hm^-2 for rice production. Applying ammonium sulfate was better than applying urea for increasing rice yield. The efficiency of nitrogen fertilizer in this experiment was about 41.8-48.5%, and its loss was 22.8-38.1% .     

Potassium and phosphorus uptake by corn genotypes grown in the field as influenced by root characteristics

Summary Root parameters of three corn (Zea mays L.) genotypes influencing P and K uptake were investigated in solution culture and field experiments. The data for these parameters were used to simulate P and K uptake by plants grown in the field using the Claassen-Barber model⁵. Root characteristics for ion influx, maximum rate of influx,Imax; Michaelis-Menten constant,Km; and minimum concentration of solution below which no further net influx occurs,Cmin were determined in solution culture. These kinetic parameters varied 2 to 3 fold among genotypes. Variations among genotypes were different for K than for P.Three corn genotypes were grown in the field and harvested 47, 54 and 68 days after emergence. Yield and root surface per plant increased about 3 fold during this time. At 47 days, 2/3 of the total root surface was in the top soil whereas 3 weeks later, it was less than 50%. Genotypes differed in distribution of roots between the topsoil and subsoil as well as in root surface per unit of shoot.K uptake predicted by the Claassen-Barber model was 2 to 3 times the observed. The overprediction could be related to high root density (length of root per unit soil volume) which indicated that competition between roots occurred that was not considered in the simulation model. The predicted P uptake (y) was correlated (r=0.91) to observed uptake (x) byy=0.98+0.67x, indicating underprediction of P uptake. The presence of root hairs may have been the cause of the underprediction. The calculated contribution of the subsoil to the observed uptake was 10% for K and 1% in the case of P. It was concluded that the plant parameters used to simulate nutrient uptake were rated accurately when allowance was made for root competition and presence of root hairs.Journal Paper No. 7608. Purdue University, Agric. Exp. Station, West Lafayette, IN 47907. Contribution from the Department of Agronomy. This research was supported in part by the Tennessee Valley Authority and the Deutsche Forschungsgemeinschaft.     

Transformation and movement of zinc in an alkali soil and their influence on the yield and uptake of zinc by rice and wheat crops

Summary In the summer of 1980, a field experiment was started to evaluate the direct and residual effect of applied zinc (as zinc sulphate) on the yield and chemical composition of rice and wheat grown as crops in sequence, on an alkali soil. The treatments comprised six rates of zinc 0, 2.25, 4.5, 9.0, 18.0 and 27.0 kg ha⁻¹ applied either only once to the first crop, or repeated to each successive crop in a split plot design with 4 replications. Gypsum at 14 t ha⁻¹, was applied uniformly to all plots. The results show that with respect to increase of yield and available zinc content of soil, an application of 2.25 kg ha⁻¹ zinc frequently to each crop was better than a single high dose. A major portion of the applied zinc accumulated in the 0 to 10 cm soil layer; the movement of zinc to lower layers was negligible. Zinc applications increased the concentration of exchangeable < complexed < amorphous sesquixoides-bound zinc > crystalline sesquioxide-bound zinc fractions. Amorphous sesquixoides bound the major portion of the applied zinc compared to other fractions. Exchangeable and amorphous sesquioxide-bound zinc fractions contributed significantly more to zinc uptake by rice, than the other fractions. DTPA extracted zinc more readily from exchangeable and complexed fractions than from sesquioxides. Application of zinc increased the DTPA extractable zinc and hence zinc uptake by plants.