A common chemical extractant for estimating plant-available zinc in different soil types (peaty,red and alluvial)

Summary Relative efficiency of five chemical extractants for the extraction of available Zn in four different soils and its uptake by rice seedlings was studied in a pot culture experiment. The Zn extracted by dithizone-ammonium acetate showed a significant relationship with plant uptake whereas the values for other extractants except NH₄OAc (pH4.8) did not approach the level of significance. Among the soil properties studied, pH and CaCO₃ correlated negatively and organic matter and CEC positively with Zn uptake by rice plants.Contribution from the Soil Science and Agricultural Chemistry Dept., Banaras Hindu University, Varanasi-221005, India.Lecturer and Research Scholar of the Soil Science and Agricultural Chemistry Department, respectively.Lecturer and Research Scholar of the Soil Science and Agricultural Chemistry Department, respectively.     

Nitrogen-tillage-residue management

Summary NCSWAP (nitrogen and carbon cycling in soil, water and plant) is a simulation model of the soil-crop-water system which integrates water flow dynamics, crop growth, N transformations, tillage and residue effects, soil temperature, and solute transport. A small plot field study was initiated in May of 1980 to determine the effects of N rate (2 or 20 g N/m²), tillage (rototill or no-till), and residue management system (residue return or noresidue) on soil parameters, and maize (Zea mays L.) production.Significant differences due to treatments (N rate, tillage, and residue) were not detected in 1981 for the measured soil-plant parameters including soil moisture, yield, and N uptake. Therefore, two representative treatment combinations (N rates of 2 or 20 g N/m²-tilled-no residue) characterized the field research data. Calculated and observed data sets were compared for several parameters including: (1) soluble NO₃–N, (2) N leaching losses (3) plant total-N and¹⁵N, (4) root growth, (5) soil moisture, and (6) fertilizer efficiency.The objectives of this study were to initiate the validation process of the model NCSWAP, and to illustrate how NCSWAP can be used as a research tool to infer operational characteristics of the N cycle.Contribution of the Soil and Water Management Research Unit, USDA-ARS, and the Department of Soil Science, University of Minnesota, St. Paul, MN 55108. Minn Agric. Exp. Sta., Sci. J., Ser. Paper 13907.Senior Laboratory Technician; Research Chemist, USDA-ARS and Professor; Professor of Soil Microbiology; and Soil Scientist, USDA-ARS and Assistant Professor; all Department of Soil Science, University of Minnesota, respectively. Inquiries about NCSWAP should be sent to J. A. E. Molina.     

Biological nitrogen fixation (BNF): Commonly asked questions and answers

J.P. Roskoski was formerly with the NifTAL Project, Department of Agronomy and Soil Science, College of Tropical Agriculture and Human Resources, University of Hawaii, Hawaii, USA     

Influence of iron on the uptake of phosphorus by maize

Summary Experiments were carried out with maize in solution culture at three different iron levels at each of which P solubilities were varied through a relatively wide range (upto 80 per cent). Studies were made of the interactions between iron and phosphorus in their effects upon the dry matter production, iron and phosphorus uptake. The results revealed that iron above 5 mg per litre adversely affected the growth as well as P uptake. At higher P solubility levels, translocation of iron from the roots to the shoots was reduced, indicating an internal inactivation of iron by the phosphorus. Assistant Professor, Department of Soil Science, Tamil Nadu Agricultural University Coimbatore 641003 South India Professor and Head of Institut fur Pflanzenern?hrung, Weihenstephan 805 Freising, W. Germany Professor and Head of Institut fur Pflanzenern?hrung, Weihenstephan 805 Freising, W. Germany     

长期定位施肥与地膜覆盖对土壤肥力和生物学性质的影响

采集沈阳农业大学棕壤定位实验站(1987年设置)的土样,测定土壤pH、有机碳、全氮、碱解氮、速效磷、速效钾、微生物生物量碳、氮和BIOLOG碳源利用,结合地上部分生物量,系统分析了长期施肥与地膜覆盖对土壤肥力指标和微生物学性质的影响.结果表明,传统栽培条件下,土壤微生物群落平均吸光度(AWCD)与土壤有机碳含量、速效磷和有效钾显著相关(p<0 01),表明施肥通过影响有机碳和速效磷、钾含量影响微生物功能.在覆膜栽培条件下,AWCD与土壤pH和土壤碳氮比显著相关(p<0.01),表明覆膜通过影响土壤pH和土壤碳氮比影响微生物功能.覆膜引起玉米生育期的变化,影响有效碳的投入,从而直接影响土壤微生物功能.与相应的传统栽培相比,覆膜栽培后土壤pH的变化对微生物群落结构有一致影响.     

Three independent genetic systems that control initiation of a fungal fruiting body

Summary The initiation of monokaryotic fruiting in the basidiomycetous fungus Schizophyllum commune has been observed to occur spontaneously, in response to biochemical substances, and following mechanical injury. The responses to these three stimuli are genetically separable and under polygenic control.Paper #2259 from the Laboratory of Genetics, University of Wisconsin, Madison, Wisconsin 53706Supported in part by the College of Agriculture and Life Science, University of Wisconsin and NIH Predoctoral Training Grant #GM 07133 to the Laboratory of Genetics, University of WisconsinSupported in part by the College of Agriculture and Life Sciences, University of Wisconsin and by grant PCM77-05581 from the National Science Foundation     

Molecular nitrogen content in a submerged rice field

Summary The amount of nitrogen gas, oxygen, hydrogen, and methane in soil samples from a submerged rice field was determined using the modified Koyama's apparatus and gas chromatography. Soils planted to rice had significantly larger amounts of nitrogen gas than unplanted soils. The amount of N₂ in a field soil increased after transplanting and reached a maximum at tillering. The amount of N₂ in unplanted submerged soils did not increase significantly during the same period. Visiting Scientist at the Institute, Professor of Soil Science, Tokyo University. Visiting Scientist at the Institute, Professor of Soil Science, Tokyo University.     

A study of soil nitrogen organic fractions and correlation with yield response of Sudan-sorghum hybrid grass on Quebec soils

Summary Acid-hydrolysable organic nitrogen fractions were determined before and after two crops of Sudan-sorghum hybrid grass grown in a growth chamber on twenty Quebec soils. The relationship between the organic nitrogen fractions and yield response to N fertilizer and N uptake was examined by correlation methods and compared with corresponding relations obtained using incubation and boiling water extraction methods as indices of soil N availability. Mean contributions to total N lost during growth of the two crops were: hydrolysable NH ₄ ⁺ -N−19%, amino acid N−16% and hexosamine N−2%. The amino acid N, hydrolysable NH ₄ ⁺ -N and total hydrolysable N were significantly correlated with percent yield, log percent yield decrement and N uptake. Better correlations were obtained with the incubation and boiling water extraction methods than with the organic-N fractions. Contribution from Department of Soil Science, Macdonald College of McGill University.     

Fine structure of vascular and epidermal plastids of the mature maize leaf

Summary In addition to the highly differentiated lamellar chloroplasts and bundle sheath plastids, the normal mature maize leaf contains six relatively less differentiated but distinctive minor types of plastid associated with vascular and epidermal tissues.Paper No. 1547 from the Laboratory of Genetics, University of Wisconsin, Madison, Wisconsin 53706.     

不同土壤类型和肥力玉米地土壤养分根际效应研究

采集吉林省玉米植株及土壤样品,研究不同土壤类型和肥力,玉米不同品种和生育时期土壤－植物系统根际养分动态变化及植物吸收的相互关系,结果表明,玉米地土壤ＮＨ＾＋４－Ｎ、ＮＯ＾－３－Ｎ在根际富集,其变化主要与化肥供应有关,高肥力土壤根际有效磷亏缺,种植密度越大,根际亏缺率超大;低肥力土壤则有效磷在根际略高。高肥力土壤有效钾较高,根际有效钾富集也更明显,茎叶、根对养分的吸收量顺序为：Ｎ     

Changes in soil organic matter and phosphorus fractions under planted fallows and a crop rotation system on a Colombian volcanic-ash soil

Acquisition of soil and fertiliser phosphorus (P) by crops depends on soil and plant properties. Soil processes determining P availability to plants are P solubility/sorption, P transport, root/soil contact and mineralisation/immobilisation. Plants have evolved properties contributing to a more efficient use of plant-available soil P and to mobilise P from less available soil P fractions. Agronomic measures may affect P availability to crops through the modification of soil properties or through direct quantitative and qualitative crop impact on soil P dynamics. Among the agronomic measures, the application of organic matter such as green manure and crop residues to maintain or increase soil organic matter content and to enhance soil biological activity, and the incorporation into the cropping system of P-mobilising plant species are particularly beneficial.Our experimental activities have concentrated on the characterisation of the P mobilising capacity of different leguminous grain and cover crops, and their effect on P availability to less P-efficient cereals grown in mixed culture and in rotation. Fractionation of P in the rhizosphere soil revealed the capacity of some legumes to better use P from sparingly soluble soil P fractions than maize. Field experiments conducted on 2 sites in the Northern Guinea Savannah of Nigeria and accompanying green-house pot experiments revealed a positive rotational effect of P-efficient cover crops on maize growth and grain yield with and without the return of crop residues. This could unequivocally be attributed to a better P supply to maize, especially on strongly P-fixing soil. However, the residual effect was small compared to the application of water-soluble P fertiliser. This clearly indicates the need for a maintenance application of fertiliser P in addition to the agronomic measures for sustainable crop production.     

Effect of the fumigant dazomet on the development of mycorrhizae and growth of nursery stock

Summary The harmful effect of the fumigant Dazomet (DMTT, Mylone 50 D) on the development of mycorrhiza-forming fungi and accompanying growth of nursery stock is usually due to an inadequate pre-seeding detoxification period and/or a prolonged occurrence during this period of temperatures below 10°C. The eradication of the symbionts is occasionally caused by the lateral movement of water causing local high concentrations of the toxic chemical. A low supply of soil organic matter greatly aggravates the vulnerability of the mycorrhiza-formers to damages by the eradicant. During the past many years, a critical demycorrhization of stock in Wisconsin nurseries was observed predominantly in soils with organic matter content of less than 1.5% in the 15-cm surface layer.Research supported by the College of Agricultural and Life Sciences, Univ. of Wisconsin, Madison, and the Wisconsin in Department of Natural Resources.     

Effects of antitranspirants on distribution and utilization of photosynthate in Pinus resinosa seedlings

When 3-year-old Pinus resinosa Ait. seedlings were exposed to C¹⁴O₂ 24 hours after application of Aqua Gro, CS 6432, or Wilt Pruf antitranspirants, more activity was recovered from treated seedlings than from control seedlings 1 day after exposure to C¹⁴O₂. However, less activity was recovered when seedlings were exposed to C¹⁴O₂ 11 days after treatment with any antitranspirant except Clear Spray. Clear Spray, Folicote, and Keykote reduced accumulation of photosynthate, but their effects diminished with time. They also reduced the rate of loss of currently produced photosynthate, with the utilization effect most pronounced in Folicote-treated seedlings. All antitranspirants tested, except Aqua Gro and CS 6432, initially reduced the rate of conversion of labelled photosynthates into ethanol-insoluble components when treated seedlings were exposed to C¹⁴O₂ 24 hours after antitranspirant application. More labelled ethanol-insoluble components were recovered from antitranspirant-treated seedlings than from controls 14 days after exposure of seedlings to C¹⁴O₂. The type of spray, time between antitranspirant application and exposure to C¹⁴O₂, as well as the time between exposure and seedling harvest, had significant effects on C¹⁴ assimilation and redistribution of soluble and insoluble assimilates in various plant parts. Many of the observed effects may not have been directly due to the antitranspirants alone but may have been secondary effects caused by antitranspirant-induced changes in photosynthesis and plant water balance. Research supported by the College of Agricultural and Life Sciences, University of Wisconsin, Madison. The cooperation of Professor D. M. Adams and the Wisconsin Department of Natural Resources is acknowledged. Research supported by the College of Agricultural and Life Sciences, University of Wisconsin, Madison. The cooperation of Professor D. M. Adams and the Wisconsin Department of Natural Resources is acknowledged.     

不同促腐条件下秸秆还田对土壤微生物量碳氮磷动态变化的影响

通过2年田间定位试验,研究了冀东地区小麦 玉米轮作制度下,不同促腐条件下玉米秸秆配施化肥直接还田对土壤微生物量C、N、P动态变化的影响,并讨论了其与土壤养分和酶活性的关系.结果表明,秸秆配施化肥并调节其C/N条件下,施用促腐剂处理作物各生育期土壤微生物量C、N、P均表现出高于未施用处理的趋势,并使微生物量N、P达到高峰期的时间提前,对土壤养分调控效果较好.土壤微生物量C、N、P与土壤酶活性在作物各生育期均表现为显著和极显著正相关关系,但与土壤碱解氮、有效磷的相关性受到施肥制度和作物生长的强烈影响.     

东北玉米带农田土壤磷素分布特征

对东北玉米带农田土壤全磷及有机磷在0～100 cm剖面中的垂直分布及纬向分异的研究结果表明：海伦、哈尔滨、公主岭和大石桥点的土壤全磷含量随深度增加而下降,0～40 cm土层全磷含量显著高于40～100 cm土层（P<0.01）;德惠、昌图和沈阳点40～60 cm土层土壤全磷含量相对较低,但各土层之间差异不大;0～20 cm土层有机磷含量显著高于20 cm以下各土层(P<0.05).土壤全磷和有机磷含量随着纬度的升高而显著增加(P<0.05),气候条件和土壤类型的差异可能是导致土壤磷素纬向分布差异的主要原因.土壤全磷和有机磷含量与土壤有机碳呈极显著正相关 (P<0.01),说明东北玉米带农田有机质含量是影响土壤磷素含量和分布的主要因素之一.     

A dynamical systems perspective on vegetation theory

A dynamical systems perspective is employed to develop a simple conceptual model of vegetation and environment as coupled dynamical systems. The conceptual model characterizes the influence of environment on vegetation, the effect of vegetation on the environment, and the subsequent response of vegetation to the modified environment. Vegetation and environmental dynamics are modeled as trajectories in complementary state spaces, with the trajectories jointly determined by the position of a given site in both spaces. The vegetation and environment state spaces are coupled by the physiological requirements of the component species and the modification of environment by vegetation. From a dynamical systems perspective, current vegetation theory and analyses overemphasize environmental determination of vegetation composition and neglect the effects of vegetation on environment. A dynamical systems perspective is capable of synthesizing previous concepts of vegetation; the continuum and community type concepts are possible consequences of site specific differences in vegetation metabolism and environmental plasticity.I would like to acknowledge the helpful comments and criticisms of Drs G. Cottam, J. D. Aber, T. F. H. Allen, R. P. McIntosh, C. G. Lorimer, and anonymous reviewers.I would like to thank the University of Wisconsin, Madison for a fellowship which supported this research. This paper is dedicated with great respect and gratitude to Professor G. Cottam on the occasion of his retirement from the University of Wisconsin.     

玉米 线辣椒套作系统中土壤养分与根际土壤微生物、酶活性的关系

采用玉米单作、线辣椒单作、玉米-线辣椒套作3种栽培模式,并在玉米-线辣椒套作的种间根部设3种不同隔离处理（膜隔、网隔和无隔）,研究了玉米-线辣椒套作系统中土壤生物因子与土壤养分的关系．结果表明：玉米-线辣椒套作具有明显优势;与两作物单作和玉米-线辣椒套作种间根区膜隔处理相比,玉米-线辣椒根区无隔和网隔处理复合群体中两作物根际土壤酶活性、微生物数量、土壤养分均显著提高;除有效镁与真菌种群数量、过氧化氢酶活性呈负相关外,其余速效养分与各生物因子均呈显著或极显著正相关．通径分析表明,该系统中促进有机质累积的主要生物因素是脲酶、过氧化氢酶、细菌和蛋白酶,蔗糖酶是影响碱解氮的最主要因子,脲酶是影响有效磷的最主要因子,细菌是影响有效钾的最主要因子,碱性磷酸酶、真菌只是选择性地对有机质的累积和氮、磷、钾有效养分的形成起作用,放线菌对土壤养分的直接作用系数为负,对土壤养分形成的作用较小．     

Temporal variations in some plant and soil P pools in two pasture soils of widely different P fertility status

Temporal variations in plant production, plant P and some soil P (and N) pools were followed over 21 months in two New Zealand pasture soils of widely different P fertility status. Plant growth rates, and herbage composition at the high-fertility site, were closely linked to soil water use, with growth rates falling when soil water deficits exceeded 60 mm. Herbage P concentrations reflected P fertility, and varied with season, being generally higher in winter and lower in summer. A similar temporal pattern was also observed for labile organic P (NaHCO₃-extractable P₀) in both soils. In the low-fertility soil in spring, net mineralization was especially strong, but from early winter net immobilization occurred. Surprisingly, Olsen P also changed temporally in the high-fertility soil. The microbial biomass remained fairly constant throughout the year, whereas the P content of the biomass varied seasonally. Although microbial biomass was not a useful index of soil fertility, highest microbial P₀ contents coincided with periods of maximum labile P₀ mineralization, when herbage production was also at a peak. Net N-mineralization in the low-fertility soil, in contrast to the high-fertility soil, was low but varied seasonally, under standardised incubation conditions. Soil P and N dynamics were apparently synchronised in the low-fertility soil through soil microbial processes, with mineral N being negatively correlated with microbial P₀ in samples collected two months later. The results of this investigation suggest that the demands of rapid and sustained pasture growth in spring and early summer can best be met by maximising the build-up of organic matter during the preceding autumn and winter. This practice could help to alleviate the common problem of feed shortage in North Island hill country pastures in late winter-early spring.     

Acidification of a kaolinitic Alfisol under continuous cropping with nitrogen fertilization in West Africa

Increased use of N fertilizer and more intensive cropping due to the rising food demand in the tropics requires design and evaluation of sustainable cropping systems with minimum soil acidification. The objectives of this study were to quantify acidification of an Oxic Kandiustalf with different types of N fertilizer in two cropping systems under no-tillage and its effect on crop performance. Chemical soil properties in continuous maize (Zea mays L.) and maize-cowpea (Vigna unguiculata (L.) Walp) rotation were determined with three N sources (urea (UA), ammonium sulfate (AS) and calcium ammonium nitrate (CAN)) in Nigeria, West Africa, during five years. Chemical soil properties were related to grain yield and diagnostic plant nutrient concentrations. For the three N sources, the rate of decline in soil pH in maize-cowpea rotation was 57±7.5% of that in continuous maize, where double the amount of N fertilizer was applied. The rate of soil acidification during the five years was greater for AS than for UA or CAN in continuous maize, and not different for UA and CAN in both cropping systems. With AS, soil pH decreased from 5.8 to 4.5 during five years of continuous maize cropping. Exchangeable acidity increased with N fertilization, but did not reach levels limiting maize or cowpea growth. Return of residues to the soil surface may have reduced soluble and exchangeable Al levels by providing a source of organic ligands. Soil solution Mn concentrations increased with N fertilization to levels likely detrimental for crop growth. Symptoms of Mn toxicity were observed on cowpea leaves where AS was applied to the preceding maize crop, but not on maize plants. Soil acidification caused significant reductions in exchangeable Ca and effective CEC. Main season maize yield with N fertilization was lower with AS than with UA or CAN, but not different between UA and CAN during the six years of cropping. The lower maize grain yield with AS than with the other N sources was attributed to lower pH and a greater extractable Mn concentration with AS. When kaolinitic Alfisols are used for continuous maize cropping, even under no-tillage with crop residues returned as mulch, the soil may become acidifed to pH values of 5.0 and below after a few years. The no-till cereal-legume rotation with judicial use of urea or CAN as N sources for the cereal crop is a more suitable system for these poorly buffered, kaolinitic soils than continuous maize cropping. The use of AS as N source should be avoided. H Marschner Section editor     

The Effects of Crop Rotation and Nitrogen Fertilization on Soil Chemical and Microbial Properties in a Guinea Savanna Alfisol of Nigeria

The impacts of crop rotation and inorganic nitrogen fertilization on soil microbial biomass C (SMBC) and N (SMBN) and water-soluble organic C (WSOC) were studied in a Guinea savanna Alfisol of Nigeria. In 2001, fields of grain legumes (soybean and cowpea), herbaceous legume (Centrosema pascuorum) and a natural fallow were established. In 2002, maize was planted with N fertilizer rates of 0, 20, 40 and 60 kg N ha⁻¹ in a split-plot arrangement fitted to a randomized complete block design with legumes and fallow as main plots and N fertilizer levels as subplots. Surface soil samples were taken at 4 weeks after planting and tasselling stage of the maize. Inorganic N fertilization had no significant (P>0.05) effect on SMBC, SMBN and WSOC, while crop rotation significantly (P<0.0001) affected both SMBC and WSOC. These results demonstrate that crop rotation do not necessarily influence the gross soil microbial biomass, but may affect physiologically distinct subcomponent of the microbial biomass. The soils under the various rotations had a predominance of fungi community as indicated by their wide biomass C/N ratio ranging from 9.2 to 20.9 suggesting fungi to be mainly responsible for decomposition in these soils. Soil microbial biomass and WSOC showed significant (P<0.05) correlation with both soil pH and organic carbon but no relationship with total N. Based on these results, it appears that the soil pH and organic carbon determined the flux of the soil microbial biomass and amount of WSOC in these soils.