Typic Ustipsamment Research Articles

EFFECT OF MODES AND LEVELS OF MOLYBDENUM APPLICATION ON GRAIN YIELD PROTEIN CONTENT AND NODULATION OF CHICKPEA GROWN ON LOAMY SAND SOIL

A field experiment was laid out during three consecutive years of 1997–98 to 1999–2000 on loamy sand soil (typic ustipsamment) of the state of Rajasthan in India in rabi season to investigate the effect of modes of application and different levels of molybdenum (Mo) on grain yield, protein content and number of nodules per plant of chickpea (Cicer arietinum L.; Variety RSG-44). Doses applied were: 0.5, 1.0 and 1.5 kg Mo ha−1 as ammonium molybdate for soil application, and 1.75, 3.5 and 5.25 g sodium molybdate kg−1 seed for seed treatment. The six treatments with one control were replicated thrice in a randomized block design. The physico-chemical characteristics of the soil were: pH-8.1, EC 0.11 dsm−1 and OC 0.12%. Available N, P and K were 158, 20 and 216 kg ha−1, respectively. The Mo status of soil was 0.06 ppm. The three years' pooled data revealed that application of Mo either by soil application or through seed treatment, significantly increased the grain yield of chickpea. Soil application of 1.0 kg Mo ha−1 and seed treatment with 3.5 g sodium molybdate kg−1 seed increased the grain yield by 13.13% and 16.76% over the yields (24.4 and 24.5 q ha−1, respectively) at lower doses while it was at par with yields at higher doses of Mo. Protein content of grain, number of nodules per plant of chickpea and available nitrogen in soil also increased with increasing doses of Mo under both the modes of application.

Organic C, N and P in size fractions of virgin and cultivated soils of the semi-arid pampa of Argentina

Nutrient and organic carbon (OC) losses are important components of the soil degradation processes produced by continuous agriculture. It was hypothesized that coarse textured soils will be more affected by cultivation than fine textured ones. The purpose of this study was to evaluate the status of OC, total nitrogen (Nt), and three phosphorous fractions (total inorganic, Pi; organic, Po; and available, Pa) in different textured virgin (under Prosopis caldenia forest) and cultivated soils of the semi-arid pampa of Argentina. Three virgin and non-fertilized cultivated soil pairs, representative from soils of the region, were selected for this study: two fine sandy loam Entic Haplustolls and a sandy Typic Ustipsamment. The element content of each soil was analysed from the <0·1-mm to 0·1–2-mm sized aggregates. Results indicated that cultivation decreased the OC, Po and Pi contents in fine aggregates of the fine textured soils, and in coarse aggregates of the coarse textured soil. Plant absorption and wind erosion were probably the main processes which decreased element contents in both textural soil types. It was speculated that in the sandy soil the elements lost from fine sized aggregates were restored by the break down of the weak coarse aggregates produced by tillage. The C/N ratios showed mostly small changes due to cultivation, indicating that no changes of organic matter quality occurred. Only the sandy soil showed C/N increases in the fine sized aggregates and decreases in the coarse sized aggregates. The C/Po quotients were not changed by cultivation, indicating that the qualitative composition of P organic compounds remained unchanged. Large OC decreases and Pa increases after cultivation detected in one of the fine textured soil were apparently linked to the occurrence of natural fires.

Effect of mixing black clay soil and organic amendment on properties of coarse-textured soil and rice yield

In Tamil Nadu, rice is grown on coarse-textured soils across a significant area with marginal yields. To improve soil, water, and nutrient retention and to enhance rice yields, a field experiment was conducted during the wet seasons of 1996-97 and 1997-98 (October-January), with each season trial done in one of two adjacent fields. Treatments used were different incorporation levels of black clay soil (0, 20, 40, 60, 80, and 100 t ha -1 ), with or without 25 t raw coir pith ha -1 , replicated thrice in a randomized block design. The black clay soil and coir pith were mixed with the puddled soil up to 20 cm depth by trampling and leveling before transplanting. At the beginning of the experiment, soil in control plots had comparable properties such as contents of clay, silt, organic carbon, total N, P, K, Ca, and Mg, available N, P, K, and exchangeable Ca and Mg, electrical conductivity (EC), pH, and cation exchange capacity (CEC) as the soil in the rest of the field. Rice varieties IR60 and ADT36 (parentage: local variety, Triveni/ IR20) were grown in the first and second croppings, respectively. Grain and straw yield were recorded. Neither field supported any crop other than the wet-season rice crop under study. The soil was coarse-textured throughout the solum of 2 m and was classified as a coarse loamy, kaolinitic, nonacid, isomegathermic Typic Ustipsamment.

WIND EROSION IN LOESS SOILS OF THE SEMIARID ARGENTINIAN PAMPAS

This study is the first effort to measure wind erosion in the field in South America. Wind erosion of two bare soils, a loamy sand surface Typic Ustipsamment and a sandy loam surface Entic Haplustoll of the Semiarid Argentinian Pampas, were measured in the field during wind storms that started on June 16 (mean wind speed = 14 km/h; storm duration 103 h) and June 30 (mean wind speed = 21.4 km/h; storm duration 25 h) of 1995. Measurements were made with dust samplers placed at heights of 0.135, 0.54, and 1.47 m within a 1-ha field. Mass flux (amount of eroded material within a given time) was larger in the Ustipsamment soils than in the Haplustoll soils in both storms. A maximum amount of transported dust was found within the limits of the studied field (100 x 100 m 2 ) during the June 16 wind storm and outside the studied field during the June 30 wind storm. This was attributed to the variation in wind direction on June 16. The total amount of material eroded from the field during each storm reached 1.82 mt ha -1 in the Ustipsamment and 0.29 mt ha -1 in the Haplustoll on June 16 and 0.98 mt ha -1 in the Ustipsamment and 0.75 mt ha -1 in the Haplustoll on June 30. Wind velocity was high enough to erode the loosened Ustipsamment but not the better structured Haplustoll on June 16. On June 30, wind velocity was high enough to erode both soils, but a shorter storm duration did not allow the erosion of large amounts of soil.

Long-Term Maize, Sorghum, and Millet Monoculture Effects on an Argentina Typic Ustipsamment

Maize, sorghum, and millet monoculture effects on soil properties of a Typic Ustip samment in the semiarid pampa of Argentina were evaluated after 27 years in a plot experiment. A permanent Eragrostis curvula pasture was used as a reference. Millet was the most destructive crop to the soil because it decreased dry aggregate stability by 10%, soil organic matter (OM) by 30%, extractable K by 20%, available P by 44%, inorganic P by 11%, available Fe by 20%, available Zn more than 90%, available Cu by 30%, and available Mn by 26%, and it increased wet aggregate instability by 75%. Grain sorghum was less destructive to the soil than millet because it only decreased OM by 30% and extractable K by 24%. All studied crops decreased the cation exchange capacity of the soil between 20 and 30%, the pH values, and the concentration of soil extractable Mg2+by 38 to 63%. Soil extractable Ca2+ was decreased 30% by the Eragrostis pasture and 40% by maize. The negative effect of millet and grain sorghum on OM was attributed to a low coverage of the soil with plant residues left by these crops as well as the long exposition of the bare soil during temperate and wet periods. Decreases of soil nutrient contents were attributed to plant uptake in all cases, except the Zn concentrations, which were related to variations on soil pH and phosphate concentrations. It was concluded that maize, the most commonly cultivated crop in the region studied, did not affect physical and chemical soil properties to a large extent. Conversely, millet had the most negative effect on physical and chemical properties of the soil.

Seedbank Characteristics of a Nebraska Sandhills Prairie

Evaluating seedbank ecology is critical for understanding plant community development and successional patterns and for identifying factors regulating population dynamics. The relationships among seedbank composition, seedbank depth, seed dormancy, and vegetative expression were evaluated for a range site on a Valentine fine sand soil (mixed, mesic Typic Ustipsamments) in the Sandhii Prairie. Twenty soil samples were collected at each of 2 depths (0 to 515 to 20 cm) in early June 1990 and 1991 from 12 macroplots (32 X 32 m) representing 3 range condition classes. A seed extraction and germination trial was conducted to determine the diversity, size, and germinability of the persistent seedbank. Seedling emergence was counted in a greenhouse, with and without a 1Cday prechilling(3 to 5°C) stratification treatment, to characterize seedbank dormancy. Fourteen grass species, 17 forb species, and Schweinitz flatsedge (Cyperus schweinitzii Torr.) were identified in the seed hank. Two additional genera (Carex and Euphorbia) also occurred in the seedbank. Only 10 species occurred in 8 or more macroplots in both years. Aboveground botanical composition was not correlated with (P > 0.10) seedbank species composition. More germinable seeds occurred in the 0 to 5 cm depth (P < 0.01) than the 15 to 20 cm depth. Also, the species diversity and seed number were greater in the shallower depth. Germination percentage was low for all types of vegetation. Lambsquarters (Chenopodiutn album L.) and annual eriogonum (Eriogonum annuum Nutt.) had the largest seedbanks, but germination was less than 6 % . Sand dropseed [Sporobolus cryptandrus (Torr.) Gray] and sand lovegrass [Eragrostis trichodes (Nutt.) Wood] were the most abundant perennial grasses and accounted for about 60% of the germinated seeds. Prechilling increased seedling emergence of grasses (P < O.Ol), forbs (P < O.Ol), and grass-like species (P < 0.01). Perennial grasses emerged first, forbs later, and grasslike species exhibited a bimodal emergence pattern. Based on germination percentage and emergence data, sand dropseed has the potential to colonize openings in the Sandbills prairie, possibly to the exclusion of many annuals occurring in the seedbank.

Irrigation of sunflower ( Helianthus annuus) in relation to tillage and mulching

For sustainable sunflower production in semi-arid sub-tropical regions, it is essential to increase its water use efficiency. Field studies were conducted for three years on deep alluvial loamy sand (Typic Ustipsamment) and sandy loam (Typic Ustochrept) soils at Punjab Agricultural University, Ludhiana, India, to evaluate the interactive effects of three irrigation regimes (irrigation water to net open pan evaporation ratios, I 1, I 2, I 3) on sunflower yield in relation to tillage (conventional tillage, CT, and deep-tillage, DT) and mulching (no mulch, M 0, and residue mulch, M 1). Both deep tillage and mulch significantly increased crop yield irrespective of soil type and year. Increase in mean achene yield across soils during three years with DT over CT varied between 10 and 16% and that with mulch over no mulch by 8 to 17%. Deep tillage and/or mulching helped the crop in efficient utilization of water by increasing leaf area index (LAI) and the depth and density of rooting. Irrigation and tillage interacted for their effects on yield on loamy sand, as the crop responded to higher level of irrigation with CT than with DT. On loamy sand, mean achene yield increased with increase in water supply up to IW/PE = 1.5 in a dry year and upto IW/PE = 1.2 in relatively wetter years. On sandy loam, mean yield response to irrigations was observed upto IW/PE = 1.0 in all the three years. Regression analysis of relative yield against water supply during the three years on both the soils, showed that for 80% relative yield the crop required 105 cm water in CTM 0, 90 cm in CTM or DTM 0 and only 80 cm in DTM. The study suggests that deep tillage or straw mulch may be used to achieve higher water use efficiency in sunflower on coarse textured soils in semi-arid, sub-tropical regions.

Millet yield as affected by tractor traffic in a sandy loam soil in Borno State, Nigeria

The effect of traffic on the production of pearl millet ( Pennisetum americanum (L.) Leeke) was investigated in a sandy loam soil (Typic Ustipsamment) of Borno State, Nigeria. A randomized complete block design was used with treatments of 0, 5, 10, 15, and 20 passes of a tractor with 31.0 kPa contact pressure. The soil dry bulk density, penetration resistance, and air permeability for each applied load were measured from the soil surface to a depth of 0.20 m and the yield from each treatment was determined. Dry bulk density and penetration resistance increased with an increase in the number of tractor passes, while air permeability decreased with increases in the number of tractor passes. Head weight increased with increases in the number of tractor passes up to 15 passes, and then decreased. Plant moisture content and stem diameter increased with increases in the number of tractor passes. Statistical models were used to predict head weight in terms of the number of tractor passes, contact pressure, air permeability, and soil parameters; with air permeability giving the best prediction.

Tillage responses of wheat in relation to irrigation regimes and nitrogen rates on an alluvial sand in a semi-arid subtropical climate

A 3 year field study was conducted to evaluate the effects of conventional tillage (CT, uniform soil disruption to 10 cm depth) and deep tillage (DT, sub-soiling to 40–45 cm depth with passes of a single tine chisel 35–40 cm apart, followed by CT) in combination with frequent small and infrequent large irrigation applications and a range of N fertilizer rates on root growth, water and nutrient use, and yield of wheat. The trial with tillage and irrigation combinations in main plots and N rates in sub-plots was performed on an alluvial sand (Typic Ustipsamment) in north-west India. Deep tillage decreased bulk density and soil strength (measured in the first year of experiment) in the tilled zone and increased the depth and density of rooting. Frequent and small irrigations also enhanced root growth during the dry year. In both of these cases, there were significant increases in dry matter accumulation and grain yield of wheat. At 160 kg N ha −1, deep tillage and infrequent large irrigation increased mean grain yield by 1.0 Mg ha −1 over 2.7 Mg ha −1 obtained with conventional tillage and infrequent large irrigations. The corresponding increase of yield in conventional tillage with frequent small irrigations was 0.7 Mg ha −1. A combination of deep tillage and frequent small irrigations increased yield by 2.3 Mg ha −1. These results suggest that for higher wheat yields and input use efficiencies on alluvial sands, deep tillage should be combined with frequent small irrigations.

Calibration of a water uptake simulation model under varying soil moisture regime and nitrogen level for wheat crop

Crop production is directly related to the time-depth status of soil water which is often predicted with the help of a simulation model avoiding time-consuming deterministic procedures. In the present study, the accuracy of a mathematical simulation model has been tested by comparing the simulated profile water content with its measured counterpart in a field experiment conducted with winter wheat on a sandy loam soil (Typic Ustipsamment). Wheat crop was grown under two soil water regimes, monitored by applying irrigation at 1.2 (wet, W) and 0.6 (dry, D) ratios of irrigation water to cumulative pan evaporation and at two levels of nitrogen: high, (120 kg ha −1, N) and low (60 kg ha −1, N). The calibration studies indicated high dependency of the simulation model on the depth of rooting used as an input parameter. The matching between simulated and measured profile water content was better when penetration depth of wheat roots was less than 0.6 m. Predictability of the model was found to be high under wet soil moisture regime and at low level of fertilizer nitrogen.

Tillage, mulch and irrigation effects on corn ( Zea mays L.) in relation to evaporative demand

The effects of deep tillage, straw mulching, and irrigation on corn ( Zea mays L.) yield on a loamy sand (mixed, hyperthermic, Typic Ustipsamment) were studied for early (high evaporativity) and normally sown (relatively low evaporativity) crop for 3 years in a semi-arid sub-tropical monsoon region at Punjab Agricultural University, Ludhiana, India. Treatments included all combinations of two tillage systems (conventional tillage — harrowing the soil to a 10-cm depth; deep tillage — chiselling 40 cm deep, 35–40 cm apart), two irrigation regimes (75 mm irrigation when net open pan evaporation accumulated to 75 mm or 50 mm), and two straw mulch rates (0 and 6 Mg ha −1). Deep tillage significantly reduced soil strength (cone index) and caused deeper and denser rooting than conventional tillage, more so in the dry season and with the infrequent irrigation regime than in the wet season and frequent irrigation regime. Mulch also improved rooting by influencing the hydrothermal regime of the soil. Better rooting with deep tillage and/or mulch helped the crop to extract stored soil water more efficiently, which was reflected in a favourable plant water status (indicated by canopy temperature). Averaged across years, irrigation, and mulch, deep tillage increased grain yield by 1.6 Mg ha −1 for the early season and 0.5 Mg ha −1 for the normal season crop over the yield of 2.0 Mg ha −1 achieved with conventional tillage regardless of season. Yield increase with mulching was also greater for the early season crop. Crop response to deep tillage and mulching was generally linked to the interplay between water supply (rain + irrigation) and demand (seasonal evaporativity) during the growing season. Increasing irrigation frequency increased crop yield when evaporativity exceeded rainfall early in the growing season. The results show that higher corn yields on coarse-textured soils in these regions may be achieved by advancing the seeding time and by using a proper combination of deep tillage, mulch, and irrigation.

Soil‐landscape relationships in Siwalik Hills of the semiarid tract of Punjab, India

Remotely sensed satellite data of IRS‐lB‐LISS‐1 have been analyzed to delineate five different geomorphic surfaces in the Siwalik hills in a semiarid tract of the Punjab state in northwest India. Soils from unstable geomorphic surfaces (shoulder, toeslope, and rivulet) showed A‐C profiles, while soils developed on relatively stable geomorphic surfaces (backslope and footslope) had a well‐developed cambic horizon and showed A‐Bw‐C profile development. Topography, along with the nature of parent material and time, was found to be responsible for the pedogenic differences in the soils developed on different landscapes. The eroded soils from shoulder and toeslope were classified as Typic Ustorthents, and the coarse‐textured soils from rivulet as Typic Ustipsamments. The moderately developed soils from backslope and footslope were classified as Typic Ustochrepts. This study established a well‐defined relationship between geomorphic surfaces and development of soils. Concatenation of soils on these geomorphic surfaces was the result of surface and subsurface movement of materials.

Mobility of aniline, benzoic acid, and toluene in four soils and correlation with soil properties

Soil properties and retention mechanisms affecting the relative mobility of aniline, benzoic acid, and toluene in Cecil sandy loam (clayey, kaolinitic, thermic Typic Hapludults), Holdredge silt loam (fine-silty, mixed, mesic Typic Argiustolls), Sharpsburg silty clay loam (fine, montmorillonitic, mesic Typic Argiudolls), and Valentine fine sand (mixed, mesic Typic Ustipsamments) were delineated in laboratory studies. The effect of the synthetic organic compounds (SOCs) was also determined on effective organic campounds (SOCs) was also determined on effective cation exchange capacity (ECEC) of the soils. Benzoic acid was most mobile of the SOCs but was retained in the Cecil soil by hydrogen bonds to Fe oxides. Toluene was least mobile and probably was hydrophobically sorbed to all soils. Aniline was electrostatically retained in protonated form to organic and inorganic exchange sites of the soils and reduced the ECEC of aniline-treated Holdredge and Sharpsburg soils.

Soil resource mapping using IRS-1A-LISS II digital data—A case study of Kandi area adjacent to Chandigarh-India

Abstract Soil survey provides information on soils, their spatial distribution and their areal extent for proper land use planning and agro-technology transfer. Remote sensing has emerged as a potential modern tool which can be utilised as a cost eiTective means of small-scale soil mapping. In the present study, different soilscape units (physiography-cum-soil association units) were identified following a supervised classification based on a maximum likelihood classifier using IRS (Indian Remote Sensing Satellite) 1A-LISS-II digital data. Six soilscape units, namely hills, valleys, moderate and severe eroded piedmonts, alluvial plain and river terraces were identified and delineated digitally. The overall classification accuracy of the digital soil map is 92 per cent. Major soils (subgroup levels) encountered in various soilscape units are-Typic/Lithic Ustorthents; Typic/Udic Ustochrepts; Typic Haplustalfs; Typic Ustipsamments and Typic Ustifluvents. The pedogenetic clues for the development of these soi...

Pedogenesis in relation to physiography in semiarid and arid tracts of Punjab, India

Abstract Morphological, physical, and chemical characteristics of soils developed in different physiographic units in the Punjab state (northwest India) revealed three distinct stages of pedogenic development: A‐C, A‐(Bw)‐C, and A‐Bt‐C profiles. The young and stratified soils from unstable landforms (sandbars, rivulets, floodplains, and foothills) representing newer alluvium are classified as Typic Ustipsamments or Typic Ustifluvents. The severely eroded and shallow soils of foothills are classified as Typic Ustorthents. The soils developed on relatively stable landforms (alluvial terraces, old channel fill, and interdunal areas) show development of cambic or structural B horizon and are classified as Ustochreptic Camborthids, Typic Ustochrepts, and Aquic Ustochrepts, depending on the prevailing climatic and drainage conditions. Contrary to the above, the soils formed on old alluvial terraces show the development of argillic (Bt) horizons. These soils are classified as Typic Haplustalfs. Genesis of these ...

Nitrogen Leaching Losses from Irrigated Orchardgrass on Sandy Soils

AbstractIrrigated pasture may provide an alternative forage source for livestock producers in Nebraska's Sandhills. As with any heavily fertilized crop, there is a significant potential for groundwater contamination by nitrate nitrogen (NO3‐N) leached from the crop root zone. A 3‐yr experiment was conducted in West Central Nebraska to evaluate water and nitrate (NO−3) leaching losses from irrigated orchardgrass (Dactylis glomerata L.) seeded on a Valentine fine sand (Typic Ustipsamments). Three irrigation levels (slight deficit, slight excess, and excess) and four N amounts (0, 112, 224, and 336 kg−1) were applied. Deep percolation and NO−3 leaching were measured with Duke‐Haise trough‐type extractors. All irrigation treatments had more deep percolation than expected, as the crop coefficient used for irrigation scheduling proved to be too large. The deficit irrigation treatment served as a “close management” treatment since percolation was minimal and yield was not reduced by water stress. During the first 2 yr of operation, in‐season percolation losses averaged 7, 28, and 47 cm yr−1 for low, medium, and high irrigation levels, respectively. Total in‐season NO3‐N leaching loss for the same period ranged from 6 to 228 kg ha−1, depending on N and irrigation amount. Winter and early spring N leaching losses, as estimated by soil sampling, were a significant part of total N loss. Under reduced inseason drainage and an N rate commensurate with 80 to 85% of maximum production, a minimum annual N leaching loss of 35 kg ha−1 can be expected. Greater losses are probable under average water and N applications and average management skills.

Soil-Physiography relationship in Mahanadi Delta (Part) using Landsat Imagery

Visual Interpretation of Landsat Imagery (TM-FCC) on 1∶250,000 scale covering 2410 sq km in a part of Mahandi Delta, Kataka district, Orissa was carried out for delineating the physiographic units. The major physiographic units identified and delineated were ‘Delta plain’ and ‘Coastal plain’. These units were further subdivided on the basis of image elements. The abstraction level attained was ‘Family’ based on Soil Taxonomy. The soils of the beach were classified as Typic Ustipsamments; old coastal plain as fine, Typic Haplaquept and coarse loamy Aquic Ustifluvent; Tidal flat as fine Typic Haplaquept and fine loamy Aquic Ustifluvent; mud flat as fine Typic Haplaquept; Levee-plain complex as Typic Ustipsamment and fine loamy Typic Ustorthent; old Delta plain as fine Udic Ustochrept and Aeric Haplaquept and recent delta plain as fine loamy and coarse loamy Typic Ustorthent. The soils are mixed in mineralogy and Isohyperthermic in temperature regime.

Defoliation Effects on Production and Morphological Development of Little Bluestem

Response of key warm-season grasses to time, frequency, and duration of defoliation is needed to develop grazing systems for the Nebraska Sandhills. A 3- year (1986 to 1988) study was conducted on a Valentine fine sand (mixed, mesic Typic Ustipsamments) at the Gudmundsen Sandhills Laboratory near Whitman, Nebraska, to determine the effect of defoliation on little bluestem [Schu 2 defoliations on 10 June and 10 Aug.; and 3 defoliations on 10 June, 10 July, and 10 Aug. Control plants were huvested only at the end of the growing season (October). All plots receiving summer defoliation were harvested in October to obtain aftermath yield. Treatments were initiated in 1986,1987, and 1988 and the effects of l,2, and 3 years of defoliation on dry matter (DM) yield, bud and tiller numbers, and tiller weight were measured. Experimental design was a split block with 4 plants as replications. In the first yeu of treatment annual DM yield from control plants was 2 times greater than that from all defoliated plants, but bud and tiller numbers were similar. In the second year of treatment, all treatments reduced annual DM yield and morphological development below that of the control if precipitation was subnonnal, but not if precipitation was above normal. In the third year of defoliation, with above-nonnd precipitation, single June or July defoliations produced DM yields and morphological development similar to that of the control, but single August or multiple defoliations generally reduced yield md development. Little bluestem may not persist if exposed to multiple, close defolitions during the growing season.

Plant growth response to applied k on coarse‐textured feldspathic soils

Abstract An experiment was conducted to determine the influence of continuous cropping and K fertilization on plants grown on coarse‐textured soils high in feldspars. The A and C horizons of Elsmere (sandy, mixed, mesic Aquic Haplustoll), Valentine (mixed, mesic Typic Ustipsamment) and Sharpsburg (fine, montmorillonitic, mesic Typic Arguidoll) soils were continuously cropped in the greenhouse with annual ryegrass (Lolium multiflorum Lam.). Four K treatments (0, 18.5, 37.5 and 75.0 mg K/kg soil) were applied before planting. At approximately 4 week intervals, above ground plant tissue was harvested and analyzed for K content for a total of 12 cuttings. Potassium deficiency symptoms (marginal necrosis, spotting) eventually appeared in plants grown on all but the A horizon of the Sharpsburg soil. Continuous cropping decreased plant K concentration, averaged across all treatments, from 38 to 10 g/kg dry matter. Potassium fertilization increased K concentration in plant dry matter on the soils initially low in...

Use of staining and inhibitors to separate fungal and bacterial activity in soil

The relative contribution of two major soil microbial groups, fungi and bacteria, to soil respiration was investigated because of their importance in decomposition and nutrient cycling in agroecosystems. The bactericide streptomycin and the fungicide cycloheximide were applied singly and in combination in two glucose-amended (5 g kg −1 soil) and texturally differing agricultural soils, a Valentine sand (Typic Ustipsamment) and a Sharpsburg silty clay loam (Typic Argiudoll). Soils receiving only glucose served as controls. Total and metabolically-active fungal and bacterial microscopic counts were made at 1, 3 and 10 days after amendment. CO 2 evolution was measured for 24 h before each sampling for the purpose of relating soil respiration to specific microbial metabolic activity. Intracellular reduction of iodonitrotetrazolium to formazan and accumulation of fluorescein from fluorescein diacetate were used as indicators of metabolically-active bacteria and fungi, respectively. Production of new biomass in controls and fluctuations in CO 2 evolution were primarily associated with bacterial activity on the first day, indicating an advantage of bacteria over fungi in initial glucose metabolism. Fungal activity was associated with CO 2 production at later sampling times. Reduced respiration, as a result of biocide treatment, occurred only on the first day whereas nontarget or indirect effects of both inhibitors were apparent at later times. Fungal activity rose two to five times above the level of the glucose-amended control on day 3 in streptomycin-treated soils, and bacterial activity was stimulated in the cycloheximide treatment of the Sharpsburg soil on day 10. The effectiveness of streptomycin inhibition on total and active bacterial densities was greater in the Sharpsburg silty clay loam than in the Valentine sand. There was no reduction of total hyphal length due to biocide treatment, and fungal activity with cycloheximide did not differ significantly from that of the control. For our experimental conditions the use of biocides alone did not effectively differentiate between bacterial and fungal activity. Selective staining of metabolically-active microorganisms, however, may offer promise in achieving this goal and appears useful in understanding the importance of bacteria and fungi to nutrient cycling in soil ecosystems.