John L. Neal

Soil pH and phosphatase activity

Abstract Approximately twenty years before this study, a site that consisted of a mixed oak forest was harvested, cleared, and divided into three treatment areas consisting of approximately 20 acres each. The three areas were planted to oak (forest), grass (grassland) and corn (agricultural) respectively. The influence of pH on the rate of phosphatase activity was determined over a broad range of soil pH in soil sampled from each treatment area. Phosphomonoesterase activities were measured at a pH of 2 through 12 and phosphodiesterase activities determined at a pH of 4 through 12. In the forest soil only a acid phosphomonoesterase was detected whose pH optima was maximal at the measured soil pH of 4.9. A neutral phosphomonoesterase was found in the grassland soil, pH 6.6, with a broad pH optima ranging from 4.6 to 7.0, while the detection of an acid phosphatase and a alkaline phosphatase, with a pH optima of 4.8 and 11.0 respectively, was found associated with the agriculture soil with a measured pH of 7....

Phosphatase activity in arctic tundra soils disturbed by vehicles

Abstract Increased productivity and improved nutrient status of plants in arctic tundra soils disturbed by vehicles has been attributed to increased availability of P that may be related to mineralization of organic P by soil phosphatase enzymes. Phosphomonoesterase and phosphodiesterase activities were examined in disturbed and undisturbed organic arctic soils collected from two sites: a wet site approaching water saturation and a drier, well drained site. Only acid phosphomoesterase activity was detected, while an acid to neutral phosphodiesterase was found. Phosphonaonoesterase activity was 20- to 30-fold greater in wet tundra soil than in corresponding drier soil and phosphodiesterase activity was 25- and 35-times greater in soils from the wet site than in soils from the dry site. Vehicle disturbance of the wet tundra soil ecosystem caused a significant decrease in phosphomonoestcrasc and phosphodiesterase activities. In contrast, enzyme activities were not significantly affected by vehicle disturbance in soils from the drier site. The results show that maximal enzyme activity occurs at the pH of the natural ecosystem. Based upon the amount of enzyme activity, our results support the conclusion than phosphatases may play a significant role in the nutrient cycling process of P in arctic tundra soils. However, the potential for increased P availability in soils disturbed by vehicles could not be attributed to increased soil phosphatase activity.

Abiontic enzymes in arctic soils: changes in sulphatase activity following vehicle disturbance

SummaryThe effect of vehicle perturbation on sulphatase enzyme activity in arctic tundra soils was examined. Sulphatase activity was significantly less in disturbed (vehicle track) than that adjacent undisturbed tundra soils. Soil moisture and water movement appeared to be major controlling factors. The results of the study suggest that biochemical mineralization of organic sulphur in disturbed tundra soils is controlled by nutrient influx associated with water movement, altering sulphatase activity to a level consistent with the need for, as well as the supply of, the mineralized element.

Abiontic enzymes in arctic soils: Influence of predominant vegetation upon phosphomonoesterase and sulphatase activity

Abstract The level of phosphomonoesterase and sulphatase enzyme activity in Arctic soils subjected to an environmental gradient established by snow patch water melt was examined. Within the environmental gradient, distinct zones of vegetation had been established and could be delineated on the basis of dominant plant growth form. Phosphomonoesterase and sulphatase activity levels were not only influenced by the presence of the plant, but also by the dominant vegetation. The levels of activity for each abiontic enzyme differed with respect to vegetative zone. Although soil moisture and water movement could be implicated as influencing the level of enzyme activity within the environmental gradient, their exact role was not apparent. Various factors associated with water movement and soil moisture level and their possible influence upon phosphomonoesterase and sulphatase activity levels are discussed. In comparison to Virginia temperate soils dominated by single physiognomic vegetation, the levels of phospho...

Delayed inoculation and starter nitrogen for enhancing early growth and nitrogen status ofLespedeza cuneata

SummaryTwo growth chamber experiments were conducted to determine the response ofLespedeza cuneata (Dumont) G. Don. (sericea lespedeza) to delayed inoculation and low levels of nitrogen fertilization. Nitrogen was supplied either as NH4+ or as NO3− in solution. At 0.5 and 5.0 ppm nitrogen early growth and N2(C2H2) fixation was inhibited by NH4+ and promoted by NO3−. Inoculation at seeding did not negatively affect growth prior to the onset of N2(C2H2) fixation. Delayed inoculation until the trifoliate stage thus did not increase growth or N2 fixation during the first 40 days of growth. After 40 days, specific nitrogenase activity was highest for plants inoculated at the first trifoliate stage of growth. In contrast, growth and total shoot nitrogen accumulation were higher in plants inoculated at planting. The experimental results suggest that delaying inoculation is not a useful technique for improving early growth ofL. cuneata for surface mine reclamation.

Field evaluation of starter N and delayed inoculation ofLespedeza cuneata grown in minesoil

A field study was conducted on freshly reclaimed surface-mined area to determine response of sericea lespedeza (Lespedeza cuneata [Dumont] G. Don.) to delayed rhizobial inoculation. Soybeans (Glycine max L.) were used as a control legume. Plots were inoculated with spray applications of rhizobial suspensions at seeding, cotyledon stage or second trifoliate leaf stage, or not inoculated. Starter N at 0, 10 or 20 kg ha−1 was applied preplant in a factorial arrangement with inoculation timings.G. max. was grown for 92 days andL. cuneata for 121 days.Starter N increased plant growth and total shoot N in both species. However, % shoot N was found to increase only inL. cuneata. Delaying inoculation had no significant effect upon total shoot N or % shoot N accumulation inL. cuneata. Inoculation ofG. max at planting produced greater plant growth and N accumulation than delayed inoculation treatments. Application of inoculum as a surface spray appeared to be an effective method for delayed inoculation as evidenced by nodule formation. Lack of increased plant growth, regardless of time of inoculation, suggests that delayed inoculation does not improve establishment and growth ofL. cuneata in minesoil.

Evaluation of rhizobial strains nodulating lespedeza cuneata for improving n input into minesoil revegetation systems

Abstract This study was designed to identify strains of Bradyrhizobium sp. (lespedeza) which could improve the plant performance and N status of Lespedeza cuneata (Dumont) G. Don (sericea lespedeza). Based upon preliminary screening for nodulation capability and acetylene reducing activity (ARA), six strains of rhizobia were chosen to be evaluated in the greenhouse for plant growth effects and N2‐fixing ability. The L. cuneata symbiosis with two strains, VPI 142 and VPI 163, resulted in the greatest plant growth, total N accumulation, and highest nodule nitrogenase activity (acetylene reduction activity). The high correlation (significant at the 1% level) of shoot dry weight with root dry weight (r = .94), nodule dry weight (r = .92), total shoot N (r = .98), total root N (r = .92), as related to nitrogenase activity of the nodule mass (r = .71), indicates that plant dry weight could be used as an easily determined measurement for screening isolates to be used with L. cuneata. The identification of effici...

The effect of delayed inoculation on nitrogen fixation by Phaseolus vulgaris L. Grown in minesoil

Abstract The influence of delayed inoculation on N2(C2H2)‐fixation by Phaseolus vulgaris L. grown in minesoil is described. Fertilizer treatments included in the study were 0, 25, 50, and 100 kg N/ha applied at 21 days or at seeding. A peat culture of Rhizobium phaseoli was inoculated at 21 days or at seeding. Nitrogenase activity was determined by reduction of C2H2 to C2H4, at 7, 21, 35, and 49 days. Nitrogenase activity was related to N‐fertilizer rate and treatment sequence. Addition of 25 kg N/ha significantly stimulated N2(C2H2)‐ fixation while greater rates of N‐fertilizer decreased the rate of Ng(C2H2)‐fixation. The results of this study suggest that addition of 25 kg N/ha at time of seeding, followed by inoculation with R. phaseoli after legume growth has been established (21 days) results in an initial greater amount of N2(C2H2)‐fixation.

Nodulation and nitrogen fixation of Phaseolus vulgaris L. grown in minesoil as affected by soil compaction and N fertilization

Abstract The objectives of this growth chamber study were to assess the influence of three soil compaction levels, as determined by bulk density, and four N fertilizer treatments on growth, nodulation and N2 fixation of P. vulgaris in minesoils. Shoot and root growth was severely retarded and nodulation essentially absent in N unfertilized, uninoculated (control) plants. With inoculated plants, root and shoot mass increased and nodule mass decreased as bulk density was decreased from 1.55 g/cm3 (unamended) to 1.40 g/cm3 (amended with 50% by volume sand). Root and shoot mass increased as N fertilizer rates increased from 0 to 100 kg N/ha. Nodule mass increased at 25 kg N/ha, but higher N rates decreased nodule mass compared to unfertilized plants. There was no significant correlation between bulk density and N2 fixation, as measured by the acetylene reduction assay. In general, N2(C2H2) fixation was the greatest at 35 days from seeding; however, at 21 days, unfertilized plants showed high N2(C2H2) fixation...

Influence of temperature on nonenzymatic hydrolysis of P‐nitrophenyl phosphate in soil

Abstract Nonenzymatic hydrolysis of the substrate, p‐nitrophenylphos‐phate used for detection of phosphomonesterase activity in soil, was found to occur. The nonenzymatic hydrolysis of the substrate was temperature dependent; the higher the assay temperature, the greater the amount of hydrolysis. Modifications of the method for determining soil phosphomonesterase are suggested in order to alleviate potential overestimation of phosphomonoesterase activity in soil.