Interaction effect of sulphur and phosphorus on growth and nutrient content of moong (Phaseolus aureus L.)

Summary Sulphur-phosphorus interaction has been studied in a greenhouse experiment on a soil, deficient both in S and P with moong (Phaseolus aureus) as the test crop. The treatments were in the factorial combination of five levels of S and P (0, 5, 10, 20 and 40 ppm) applied as CaSO₄. 2H₂O and Ca(H₂PO₄)₂. H₂O respectively. A uniform treatment of N and K was made. The yield of vegetative tissues and grains increased with the application of S and P individually but decreased when S and P were applied in different combinations. Sulphur application increased S content but decreased P content in straw as well as in grains. Total P content increased with applied P and decreased with S application. Applied sulphur increased and phosphorus decreased the protein content in moong grains. Changes in N:S ratio in interaction was found to exist between S and P on the yield, grain quality, concentration and total removal of sulphur and phosphorus by Moong crop The antagonistic effect of sulphur and phosphorus fertilizer on the uptake and utilization of each other was more conspicuous when they were applied together. re]19760106     

Lead-induced tissue fatty acid alterations and lipid peroxidation

Previous work showed that dietary lead (Pb) increases the relative concentration of arachidonic acid (20∶4) as a percentage of total fatty acids, and decreases the relative proportion of linoleic acid (18∶2) to arachidonic acid (18∶2/20∶4) in chick liver, serum, and erythrocyte membranes. The present investigation was undertaken to examine the time-course and magnitude of the fatty acid alterations with increasing dietary Pb levels. We also examined the effects of Pb on the fatty acid composition and lipid peroxide content of hepatic subcellular organelles. In Exp. 1, chicks were fed diets containing 0, 62.5, 125, 250, 500, or 1000 ppm added Pb (as Pb acetate trihydrate) from 1 to 21 d of age. After 21 d, no growth effects were observed; however, Pb lowered the 18∶2/20∶4 ratio and increased 20∶4 concentration in total liver and serum lipids, and in total hepatic phospholipids in a dose-dependent manner. Hepatic mitochondrial membrane fatty acids were not altered, nor was there any increase in hepatic lipid peroxidation. In Exp. 2, chicks were fed diets containing 0, 500, 1000, or 2000 ppm added Pb from 1 to 21 or 22 d of age. Pb depressed growth in a dose-dependent manner. In addition, Pb lowered the 18∶2/20∶4 ratio and increased 20∶4 concentration in total liver lipids and in hepatic mitochondrial and microsomal membranes in a dose-dependent manner. Total hepatic lipid peroxidation was increased over control values by 1000 ppm Pb, and hepatic microsomal lipid peroxidation was increased by dietary Pb levels of 1000 and 2000 ppm. In Exp. 3, body weight, hepatic microsomal lipid peroxidation, and fatty acid composition were determined in 4-, 9-, 14-, 18-, and 23-d-old chicks fed 0 or 1500 ppm added Pb. Body weights of Pb-treated chicks were significantly lower than those of control chicks by day 18. Microsomal 20∶4 concentration and peroxidation increased, and the 18∶2/20∶4 ratio decreased with age in both groups, but the changes were of greater magnitude in the Pb-treated chicks. The results suggest that some of the manifestations of Pb toxicity may be a reflection of increased concentration of 20∶4 in specific membranes. Further, since the Pb-induced alterations in fatty acid composition were noted in the absence of any growth depression, we propose that fatty acid composition is more sensitive than growth rate to the presence of lead in the diet.     

Effects of fertigation scheme on N uptake and N use efficiency in cotton

While fertigation can increase fertilizer use efficiency, there is an uncertainly as to whether the fertilizer should be introduced at the beginning of the irrigation or at the end, or introduced during irrigation. Our objective was to determine the effect of different fertigation schemes on nitrogen (N) uptake and N use efficiency (NUE) in cotton plants. A pot experiment was conducted under greenhouse conditions in year 2004 and 2005. According to the application timing of nitrogen (N) fertilizer solution and water (W) involved in an irrigation cycle, four nitrogen fertigation schemes [nitrogen applied at the beginning of the irrigation cycle (N–W), nitrogen applied at the end of the irrigation cycle (W–N), nitrogen applied in the middle of the irrigation cycle (W–N–W) and nitrogen applied throughout the irrigation cycle (N&W)] were employed in a completely randomized design with four replications. Cotton was grown in plastic containers with a volume of 84 l, which were filled with a clay loam soil and fertilized with 6.4 g of N per pot as unlabeled and ¹⁵N-labeled urea for 2004 and 2005, respectively. Plant total dry matter (DM) and N content in N–W was significantly higher than in N&W in both seasons, but these were not consistent for W–N and W–N–W treatments. In year 2005, a significantly higher nitrogen derived from fertilizer (NDFF) for the whole plant was found in W–N and N–W than that in W–N–W and N&W. Fertigation scheme had a consistent effect on total NUE: N–W had the highest NUE for the whole plant, but this was not significantly different from W–N. Treatments W–N and W–N–W had similar total NUE, and N&W had the lowest total NUE. After harvesting, the total residual fertilizer N in the soil was highest in W–N, lowest in N–W, but this was not significantly different from N&W and W–N–W treatments. Total residual NO₃–N in the soil in N&W and W–N treatments was 20.7 and 21.2% higher than that in N–W, respectively. The total ¹⁵N recovery was not statistically significant between the four fertigation schemes. In this study, the fertigation scheme N–W (nitrogen applied at the beginning of an irrigation cycle) increased DM accumulation, N uptake and NUE of cotton. This study indicates that Nitrogen application at the beginning of an irrigation cycle has an advantage on N uptake and NUE of cotton. Therefore, NUE could be enhanced by optimizing fertilization schemes with drip irrigation.     

Response of irrigated wheat to residual and fertilizer nitrogen

Summary A cotton and a wheat experiment were conducted in sequence to evaluate the effect of residual and fertilizer N on wheat with a water table fluctuating between 65 and 125 cm. Cotton treatments, replicated four times, consisted of 3 irrigation treatments as main plots and 6 N levels as subplots (0, 25, 50, 75, 100, 125 kg N/ha). After cotton the plots were planted to wheat and each subplot was divided into two equal sub-subplots. One received N at a rate similar to that previously applied to cotton and the other sub-subplot was left without N application for evaluating the residual effect. Determination of N forms in the soil before wheat indicated that NO₃-N content of the top 25 cm increased from 4.4 to 16.3 ppm as N applied to cotton increased from 0 to 125 kg/ha. On the other hand, mineralizable-N was greater in the control than in the fertilized treatments, suggesting a priming effect on the mineralization of soil N. The residual effect on wheat was related to mineralizable-N rather than to NO₃-N as grain yield was higher for the control than for the residual fertilizer N treatments. The yield was also higher for the more frequent than for the less frequent irrigation treatments, which may be attributed to increase in mineralization with soil water content. Wheat response to N application was significant. But high N levels accompanied by frequent irrigation enhanced lodging with subsequent reduction in yield. Measuring N uptake by grain and straw indicated 37% recovery of fertilizer N. It was concluded that under the prevailing conditions of high water table wheat response was largely dependent on the applied fertilizer due to insignificant residual N availability.     

氮和钙交互作用对番茄氮素吸收的影响

以沈阳草甸土为栽培基质,采用二次D-饱和最优设计,进行番茄N、Ca两因素效应的盆栽试验,结果表明,在本试验条件下,番茄茎、叶、果实中氮素含量随生育期的进展而下降,氮肥对番茄果实中NO3^--N含量影响呈直线正效应,但各处理番茄果实中NO3^--N含量均不超过可生食标准．适量施用钙肥有利于控制果实中NO3^--N含量,氮肥对番茄植株地上部分和果实中N含量影响均符合报酬递减律．氮肥和钙肥对番茄N素积累符合报酬递减律;番茄从开花期到果实膨大期属N素最大效应期．番茄叶片硝酸还原酶活性受氮素影响较大．N、Ca配合施用,有利于提高番茄叶片硝酸还原酶活性,钙素可降低硝酸还原酶活性,土壤中NO3^--N含量和电导率EC值均随氮肥施用增加而提高。     

Biomass and mineral element responses of a Serengeti short-grass species to nitrogen supply and defoliation: compensation requires a critical [N]

Large mammalian herbivores in grassland ecosystems influence plant growth dynamics in many ways, including the removal of plant biomass and the return of nutrients to the soil. A 10-week growth chamber experiment examined the responses of Sporobolus kentrophyllus from the heavily grazed short-grass plains of Serengeti National Park, Tanzania, to simulated grazing and varying nitrogen nutrition. Plants were subjected to two clipping treatments (clipped and unclipped) and five nitrogen levels (weekly applications at levels equivalent to 0, 1, 5, 10, and 40 g N m⁻²), the highest being equivalent to a urine hit. Tiller and stolon production were measured weekly. Total biomass at harvest was partitioned by plant organ and analyzed for nitrogen and mineral element composition. Tiller and stolon production reached a peak at 3–5 weeks in unclipped plants, then declined drastically, but tiller number increased continually in clipped plants; this differential effect was enhanced at higher N levels. Total plant production increased substantially with N supply, was dominated by aboveground production, and was similar in clipped and unclipped plants, except at high nitrogen levels where clipped plants produced more. Much of the standing biomass of unclipped plants was standing dead and stem; most of the standing biomass of clipped plants was live leaf with clipped plants having significantly more leaf than unclipped plants. However, leaf nitrogen was stimulated by clipping only in plants receiving levels of N application above 1 g N m⁻² which corresponded to a tissue concentration of 2.5% N. Leaf N concentration was lower in unclipped plants and increased with level of N. Aboveground N and mineral concentrations were consistently greater than belowground levels and while clipping commonly promoted aboveground concentrations, it generally diminished those belowground. In general, clipped plants exhibited increased leaf elemental concentrations of K, P, and Mg. Concentrations of B, Ca, K, Mg, and Zn increased with the level of N. No evidence was found that the much greater growth associated with higher N levels diminished the concentration of any other nutrient and that clipping coupled with N fertilization increased the total mineral content available in leaf tissue. The results suggest that plants can (1) compensate for leaf removal, but only when N is above a critical point (tissue [N] 2.8%) and (2) grazing coupled with N fertilization can increase the quality and quantity of tissue available for herbivore removal. Received: 25 August 1997 / Accepted: 14 April 1998     

Evaluation of N2-fixation and nitrogen economy of a maize/cowpea intercrop system using15N dilution methods

Yields of above ground biomass and total N were determined in summer-grown maize and cowpea as sole crops or intercrops, with or without supplementary N fertilizer (25 kg N ha⁻¹, urea) at an irrigated site in Waroona, Western Australia over the period 1982–1985. Good agreement was obtained between estimates of N₂ fixation of sole or intercrop cowpea (1984/85 season) based on the¹⁵N natural abundance and¹⁵N fertilizer dilution techniques, both in the field and in a glasshouse pot study. Field-grown cowpea was estimated to have received 53–69% of its N supply from N₂-fixation, with N₂-fixation onlyslightly affected by intercropping or N fertilizer application. Proportional reliance on N₂-fixation of cowpea in glasshouse culture was lower (36–66%) than in the field study and more affected by applied N. Budgets for N were drawn up for the field intercrops, based on above-ground seed yields, return of crop residues, inputs of fixed N and fertilizer N. No account was taken of possible losses of N through volatilization, denitrification and leaching or gains of N in the soil from root biomass. N₂-fixation was estimated tobe 59 kg N ha⁻¹ in the plots receiving no fertilizer N, and 73 kg N ha⁻¹ in plots receiving 25 kg N ha⁻¹ as urea. Comparable fixation by sole cowpea was higher (87 and 82 kg N ha⁻¹ respectively) but this advantage was outweighed by greater land use efficiency by the intercrop than sole crops.     

Selecting appropriate forms of nitrogen fertilizer to enhance soil arsenic removal by Pteris vittata: a new approach in phytoremediation

Certain plant species have been shown to vigorously accumulate some metals from soil, and thus represent promising and effective remediation alternatives. In order to select the optimum forms of nitrogen (N) fertilizers for the arsenic (As) hyperaccumulator, Pteris vittata L., to maximize As extraction, five forms of N were added individually to different treatments to study the effect of N forms on As uptake of the plants under soil culture in a greenhouse. Although shoot As concentration tended to decrease and As translocation from root to shoot was inhibited, overall As accumulation was greater due to higher biomass when N fertilizer was added. Arsenic accumulation in plants with N fertilization was 100-300% more than in the plants without N fertilization. There were obvious differences in plant biomass and As accumulation among the N forms, i.e., NH4HCO3, (NH4)2S04, Ca(NO3)2, KNO3, urea. The total As accumulation in the plants grown in As-supplied soil, under different forms of N fertilizer, decreased as NH4HCO3>(NH4)2S04 > urea > Ca(NO3)2 >KNO3>CK. The plants treated with N and As accumulated up to 5.3-7.97 mg As/pot and removed 3.7-5.5% As from the soils, compared to approximately 2.3% of As removal in the control. NH4+ -N was apparently more effective than other N fertilizers in stimulating As removal when soil was supplied with As at initiation. No significant differences in available As were found among different forms of N fertilizer after phytoremediation. It is concluded that NH4+ -N was the preferable fertilizer for P. vittata to maximize As removal.     

Urease activity in soils

Summary The availability of Ca from different levels of gypsum and calcium carbonate in a non-saline sodic soil has been investigated. Different levels of tagged gypsum (Ca⁴⁵SO₄.2H₂O) and calcium carbonate (Ca⁴⁵CO₃) (i.e. 0, 25, 50, 75, and 100 per cent of gypsum requirement) were mixed thoroughly in 3.5 Kg of a non-saline alkali soil (ESP, 48.4; ECe, 2.68 millimhos/cm). Dhaincha (Sesbania aculeata) — a legume and barley (Hordeum vulgare L.) — a cereal were taken as test crops. Increasing levels of gypsum caused a gradual increase in the yield of dry matter, content of Ca and K in the plant tops and Ca:Na and (Ca+Mg):(Na+K) ratios in both the crops. Application of calcium carbonate caused a slight increase in the dry matter yield, content of Ca and Mg and Ca:Na and (Ca+Mg):(Na+K) ratios in barley, however, in case of dhaincha there was no such effect. Gypsum application caused a gradual decrease in the content of Na and P in both the crops. Total uptake of Ca, Mg, K, N and P per pot increased in response to gypsum application. The effect of calcium carbonate application on the total uptake of these elements was much smaller on dhaincha, but in barley there was some increasing trend.Increasing application of tagged gypsum and calcium carbonate caused a gradual increase in the concentration and per cent contribution of source Ca in both the crops, although, the rate of increase was considerably more in dhaincha. The availability of Ca from applied gypsum was considerably more than that from applied calcium carbonate. Efficiency of dhaincha to utilize Ca from applied sources was considerably more (i.e. about five times) than that of barley     

Uptake by wheat plants and turnover within soil fractions of residual N from leguminous plant material and inorganic fertilizer

Summary The availability and turnover in different soil fractions of residual N from leguminous plant material and inorganic fertilizer was studied in a pot culture experiment using wheat as a test crop. Plants utilized 64% of the residual fertilizer N and 20% of the residual legume N. 50–60% of the N taken up by plants was recovered in grain and 4–8% in roots. After harvesting wheat up to 35% and 38% of the residual legume N and fertilizer N, respectively was found in humic compounds. A loss of humus N derived from legume and fertilizer was found during wheat growth but the unlabelled N increased in this fraction. Biomass contained 6% and 8% of the residual legume and fertilizer N, respectively when both were available. The mineralizable component contained upto 28% of both the residual legume and residual fertilizer N. Only a small percentage of the soil N (3–4%) was observed in biomass whereas the mineralizable component accounted for 7–14% of the soil N. In this fraction legume derived N increased during wheat growth whereas unlabelled N increased in both the mineralizable component and microbial biomass. Some loss of N occurred from residual legume and fertilizer N. Nevertheless, a positive total N balance was observed and was attributed to the addition of unlabelled N in the soil-plant system by N₂ fixation. The gain in N was equivalent to about 38% of the plant available N in the soil amended with leguminous material. The additional N was concentrated mainly in the mineralizable fraction and microbial biomass, although some addition was also noted in humus fractions.     

Effect of phosphorus and zinc on nodulation and nitrogen fixation in chickpea (Cicer arietinum L.)

A green house study was conducted on the effect of P and Zn on nodulation and N fixation in chickpea (Cicer arietinum L.) in a loamy sand (Typic Torripsamments) using treatment combinations of five levels of P (0, 25, 50, 100 and 250 ppm), and six levels of Zn (0, 5, 10, 20, 40 and 100 ppm). The number, dry matter and leghaemoglobin content of nodules, and amount of N fixed generally increased with Zn alone upto 19 ppm and P alone upto 50 ppm, and decreased with their higher levels. Application of 25 to 50 ppm P and 5 to 10 ppm Zn counteracted to a greater extent the adverse effect of 40 and 100 ppm Zn, and 250 ppm P, resp. Maximum nodulation and N fixation (91 to 145% over zero P and Zn, at maturity) was recorded with 25 to 50 ppm P applied along with 5 to 10 ppm Zn. At 64 days, depletion in soil-N was noted, particularly when P was applied, whereas at maturity there was a gain in soil-N, ranging from 10.5 to 44.5 kg/2×10⁶ kg soil depending upon P and Zn treatments. The increase in nodulation and N fixation with balanced P and Zn nutrition might be attributed to an increase in leghaemoglobin, and K and Fe concentration in nodules, and increased plant growth, resulting into enhanced activity of N fixing organisms. The results showed that balanced P and Zn nutrition is essential not only for plant growth but also for maximum activity of Rhizobium for N fixation. Work done at Harvana Agricultural University, Hissar, India.     

The influence of zinc and sulphur deficiency on oil-filling in peanut (Arachis hypogaea L.) kernels

In the developing peanut (Arachis hypogaea L.) kernels, the period between 15 and 35 days after podding (DAP) was identified as the active period of oil-filling. The period of active oil-filling was associated with a decrease in the starch, soluble sugars and proteins so as to make available the energy and carbon skeleton for the synthesis of oil. The oil content in the mature kernels decreased by 11, 12 and 25 per cent with Zn, S and Zn+S deficiency, respectively. In addition, proteins and starch content decreased significantly while that of soluble sugars increased slightly. The activity of malate dehydrogenase and glucose-6-phosphate dehydrogenase also decreased due to Zn as well as S deficiency. The deficiency treatments resulted in a decrease in phospholipids, free fatty acids and triacylglycerols in mature kernels. Further the proportion of 16∶0 and 18∶2 decreased while that of 18∶1 increased in developing kernels.     

Effects of N-serve on soybeans and soil nitrogen transformations

Summary Plant dry weight, total N, and total Ca was increased at 0.1 and 1 ppm N-serve. At greater 10 ppm the plants showed visual symptoms of a stunted growth, stem elongation, flowers, and pods failed to form or were aborted, young leaves were curled, and roots were club shaped with many branches. These symptoms were increasingly evident with increasing N-serve application rates. The reason was attributed to an auxin effect. Dry wt and total N in the plant was less than the control at the higher N-serve applications. There was little effect on nitrogenase activity at less than 10 ppm N-serve. Nodulation tended to increase at 0.1 and 1 ppm N-serve.Nitrification was inhibited up to 104 days at 20 ppm N-serve. The soil pH of the high N-serve rates was decreased at 104 days probably due to nitrification. Generally there were little detectable differences among treatments in soil organic N. The average soil organic N from 0 to 104 days decreased by 0.01%. Average increase in total N within each pot at harvest was equivalent to about 138 kg N/ha.     

Comparison of isotope techniques and non-nodulating isolines to study the effect of ammonium fertilization on dinitrogen fixation in soybean,Glycine max

Summary Two experiments were carried out with two nodulating and non-nodulating soybean isolines, with three different levels of N as (¹⁵NH₄)₂SO₄ at the equivalent of 0, 25 and 50 kg N/ha. In the first experiment three seeds were sown in each pot and the plants harvested at 35, 55 and 75 days. In the second experiment only one seed was sown per pot and harvested at 75 days.Isotope dilution technique and in certain cases natural isotope variation (¹⁵N) was used to determine directly the origin of nitrogen in the plant, whether from soil, fertilizer or biological N₂-fixation. The use of nodulating and non-nodulating isolines enabled comparison with the classical method of estimating N₂-fixation by difference from total plant N. Results at the 75 day harvest were similar for either method, but at the earlier harvests, particularly at 35 days, the total-N method was inadequate. The isotope method appeared more sensitive while the total-N method suffered from greater variability with correspondingly high standard errors and significant differences.It was found that by the 35 and 55 day harvests hardly any N₂-fixation had taken place, plant nitrogen being almost entirely derived from soil or fertilizer N. Plants in competition used up soil fertilizer N more rapidly, thus stimulating symbiotic nitrogen fixation. When only one plant was grown in each pot it had a greater proportion of N derived from soil or fertilizer, and less N derived from fixation. In general the¹⁵N data showed that only about 25% of the applied fertilizer N was absorbed by the plant.The nodulating isoline absorbed more N than the non-nodulating plants. This suggests a possible synergistic effect of N₂-fixation on N derived from other sources, giving an increase in total-N content of nudulated plants. The N derived from N₂-fixation was scarcely detectable in the roots but appeared to be translocated almost entirely to shoots and pods.With 25 kg N/ha the greater proportion of the nitrogen in the pods was derived from N₂-fixation. Even with 50 kg N/ha the nitrogen in the pods derived from fixation remained high, that being derived from fertilizer being less than 15%. About 80% of the nitrogen in the nodules was due to fixation.In the present experiment the application of 25 kg N/ha appeared sufficient to give maximum N absorption by both isolines. At this level symbiotic fixation by Rhizobium remained high in nodulating plants, while the proportion of total N due to fixation was reduced with 50 kg N/ha.UNDP/IAEA Project BRA 78/006.     

Growth Responses of Tomato Plants in Non-aerated Water Culture to Foliar Sprays of Gibberellic Acid and Benzyladenine

Tomato plants were grown to the five-six leaf stage in aeratedwater culture and aeration then discontinued. Foliar spraysof gibberellic acid (G), N⁶ benzyladenine (B), and ammoniumnitrate (N) were applied for periods up to 7 days and the plantsharvested on the eighth day. A mixture of 2·5 ppm G,5·0 ppm B, and 280 ppm N increased growth of the wholeplant and this was attributable almost entirely to G and B.In the leaf, both increased water content (B>G) and dry weight.G, but not B, increased leaf area; B, but not G, increased freshweight leaf/unit area. In the stem, G increased dry weight andheight; B reduced height but increased diameter and water content.Inclusion of O·I ppm indol-3yl-acetic acid in the mixturewas ineffective. The percentage increase in growth of non-aerated plants withG+B+N was greater with non-acrated than with aerated plantsfor weight of whole plant and leaf area, but not for stem height.Growth of non-aerated plants could not be increased by increasingthe volume of the nutrient solution, by ‘aerating’with nitrogen, or by applying minerals in foliar sprays.     

Microbial contributions to the increased nitrogen mineralization after air-drying of soils

The amounts of mineral-nitrogen (NH₄−N+NO₃−N) extracted by 2MKCL and the net amounts of N mineralized (δ Min-N) during a 10-day incubation of field-moist soils, air-dried then rewetted samples, and chloroform-fumigated samples, were measured in a range of 20 topsoils from grasslands. Air-drying generally increased extractable-N and the δ Min-N of the remoistened soils, but decreased the Min-N flush after fumigation. The C∶N ratios (CO₂−C production: net Min-N production) over 10 days decreased significantly from an average of 25 to 12 after initial air-drying, suggesting that substrates of low C∶N ratio, such as microbial cells, were contributiong to the extra N mineralized after the air-drying treatment. A procedure to quantify the contribution from microbial-N to the increased δ Min-N after air-drying was only partially successful, but indicated a large proportion of this increase was derived from microbial cells killed by desccation.     

土壤盐渍化对尿素与磷酸脲氨挥发的影响

氨挥发是肥料氮素损失的重要途径之一,肥料类型、土壤类型、肥料用量以及土壤全盐量均影响氨挥发损失率及挥发特征。本文采用通气法测定了磷酸脲和尿素两种肥料六个施肥量处理分别施入六个不同盐渍化程度（1.7、9.9、16.4、23.2、29.1、37.9 g/kg）的土壤后氨挥发累积状况和动力学特性,以及土壤氨挥发累积量与土壤电导值之间的相关性。结果表明：（1）在土壤总盐介于1.66 -37.9 g/kg的范围内,随着土壤含盐量增加,尿素与磷酸脲处理的氨挥发累积量显著增加;土壤含盐量对氨挥发速率有显著的促进作用。（2）各处理二次线性函数拟合的二项式系数a均为负值,表明：在不同盐渍化条件下肥料的挥发速率是随着时间增长而降低的;一次线性函数和Elovich 方程的斜率a随土壤含盐量增加而增大,表明：土壤盐渍化将加剧土壤的氨挥发速率。（3）土壤氨挥发累积量与电导值拟合结果符合logistic方程（︱R︱分别为0.9732,0.9815,0.965,0.9182,0.9817,0.9971︱R︱>r0.01=0.9172, n=6）,氨挥发累积量随土壤电导值呈“S”型增长。     

Accumulation, Partitioning and Redistribution of Dry Matter and Mineral Nutrients in Ixia flexuosa L., with Special Reference to its Cormaceous Habit

The seasonal dynamics of uptake, partitioning and redistributionof dry matter, N, P, K, S, Ca, Mg, Na, Cl, Fe, Zn, Mn and Cuby the cormaceous plant Ixia flexuosa were studied in pot cultureat Perth, Western Australia. Dry matter and P, N, K, Zn andCu were redistributed from the mother corm with about 90 percent net efficiency: there was no net redistribution of Ca,Na, Fe or Mn. The efficiency of redistribution from the leafyshoot to fruits and the new season's corm was 80 per cent forN and P, 24–49 per cent for K, Cu and Zn, and 0–15per cent for Na, Fe, Ca, Mn, Cl, Mg, S and dry matter. Redistributionfrom the mother corm and vegetative organs could have suppliedthe replacement corm, cormlets and fruits with 32–53 percent of their S, K, P, N, Cu and Zn, and 11–25 per centof their Ca, Cl, Mn, Mg and dry matter. The mature replacementcorm had over 60 per cent of the plant's N and P, 25–50per cent of its dry matter, Zn, Cu, Mg, K and Cl, but less than20 per cent of its Ca, Na, Fe and Mn. Each plant produced anaverage of 12 cormlets; these had 35 per cent of the dry matterand 23–47 per cent of the amount of a particular nutrientin the new season's corms. Fruits had less than 16 per centof the dry matter and each mineral in the mature plant. Ratesof mineral intake by Ixia were much lower than reported forcrop plants, and may be related to the long growing season ofthe species. Ixia polystachya L., corm, nutrition, mineral nutrients, nutrient redistribution     

Effects of sulphur nutrition on growth and nitrogen fixation of pea (Pisum sativum L.)

A S-deficient soil was used in pot experiments to investigate the effects of S addition on growth and N₂-fixation in pea (Pisum sativum L.). Addition of 100 mg S pot⁻¹ increased seed yield by more than 2-fold. Numbers of pods formed were the most sensitive yield component affected by S deficiency. Sulphur addition also increased the concentration of N in leaves and stems, and the total content of N in the shoots. The amounts of N fixed by pea were determined at four growth stages from stem elongation to maturity, using the ¹⁵N dilution technique. Sulphur addition doubled the amount of N fixed at all growth stages. In contrast, leaf chlorophyll content and shoot dry weight were increased significantly by S addition only after the flowering and pod fill stage, respectively. Pea roots were found to have high concentrations of S, reaching approximately 10 mg g⁻¹ dry weight and being 2.6–4.4 times the S concentration in the shoots under S-sufficient conditions. These results suggest that roots/nodules of pea have a high demand for S, and that N₂-fixation is very sensitive to S deficiency. The effects of S deficiency on pea growth were likely to be caused by the shortage of N, due to decreased N₂-fixation. This revised version was published online in June 2006 with corrections to the Cover Date.     

不同水肥因子与AM真菌对黄芩生长和营养成分的交互效应

利用盆栽接种试验,探讨不同水肥条件下AM真菌双网无梗囊霉Acaulospora bireticulata对黄芩生长、养分含量和次生代谢产物的影响,为黄芩水肥合理施用提供理论依据。结果表明,不同水肥条件下,AM真菌能与黄芩根系形成良好共生关系,接种AM真菌能显著提高黄芩根系菌根侵染率和生物量,水分和施肥处理对菌根侵染率和黄芩生长具有显著交互作用。不同水肥条件下,接种AM真菌提高了植株保护酶活性和叶片渗透调节物质含量,降低了脯氨酸和丙二醛含量;显著增加了黄芩苷和N、P、K、Ca、Mg、Fe和Zn含量,降低了Mn和Cu含量。N和P含量随施肥量增加而提高,其余矿质元素在施肥量N 0.383 g、P 0.564 g、K 0.251 g时含量最高,说明AM真菌能够促进宿主植物根系对水分和矿质元素的吸收和利用,提高水分和肥料利用率,具有明显的节水节肥作用,其中50%相对含水量,施肥量N 0.383 g、P 0.564 g、K 0.251 g时,接种AM真菌的促生效应最佳。