Effect of dimethylarsenic acid (DMAA) on growth,tissue arsenic,and photosynthesis of rice plants

The effect of dimethylarsenic acid (DMAA) applied to the root on arsenic (As) uptake and concentration, net photosynthesis (Pn), and growth parameters of rice (Oryza sativa L. cv. ‘Mercury') plants was studied. The experiment consisted of four treatments (0, 0.2, 0.8, and 1.6 mg As/L) with four replications in a completely randomized design. The DMAA was applied in nutrient solution as its sodium salt. The solution culture was changed every four days to avoid changes in the As chemical form. Arsenic uptake and concentration in shoot and root increased upon increased DMAA concentration in solution. Upon uptake, DMAA was readily translocated to the shoot. At the two higher rates of DMAA application (0.8 and 1.6 mg As/L), Pn and photosynthetic capacity were significantly decreased in response to tissue As concentration. Leaf area and dry matter production were also significantly reduced at the two higher rates of DMAA. At the lower rate (0.2 mg As/L) of DMAA application, there was no significant reduction in Pn or growth. Dimethylarsenic acid application did not affect nutrient allocation within the rice plant at concentration levels used in this study.     

Irrigation scheduling in a mature peach orchard using tensiometers and dendrometers

Three trickle irrigation schedules, two of which were scheduled according to soil water potential ( soil) (tensiometer method) and daily stem contraction (DSC) (dendrometer method) respectively and the other one was a schedule of restricted water supply, were applied to a mature peach orchard.The annual water application based on soil was greater than that based on DSC. However, tree growth, fruit size and leaf water potential (leaf) on the trees in the dendrometer scheduling plot did not differ from those in the tensiometer scheduling plot while the premature fruit drop and fruit bud initiation were greatly different. The restricted water supply treatment limited significantly both tree and fruit growth. In addition, the lower leaf was observed on the trees in this plot.Further study shows that use of the dendrometer method for scheduling irrigation satisfies the water needs of the plant and that the tensiometer method is less accurate.Abbreviations leaf leaf water potential - soil soil water potential - DSC daily stem contraction - LVDT linear variable displacement transducer - PET potential evapotranspiration     

The effect of disturbance by Phellinus weirii on decomposition and nutrient mineralization in a Tsuga mertensiana forest

Summary Microbial biomass in the upper 7 cm of soil and needle decomposition on the forest floor were measured seasonally for 10 months in a mountain hemlock (Tsuga mertensiana) old-growth forest and in a regrowth forest after Phellinus weirii, a root-rot pathogen infection, had caused disturbance. The microbial biomass was higher in the old-growth forest soil than in the regrowth forest soil. However, T. mertensiana needle decomposition rates were higher in the regrowth than in the old-growth forest. Total N, Ca, Fe, Cu, and Zn concentrations in needles increased during the 1st year of decomposition in both the old and the regrowth forests, but P, K, Mg, Mn, and B concentrations decreased. N, P, K, Mg, Cu, and Zn concentrations were lower in regrowth than in old-growth decomposing needles. During mineralization, needles in the regrowth forests released more N, P, and K as a result of higher needle decomposition rates. Our results suggest that higher needle decomposition rates increased the mineralization of N, P, and K, which may lead to increased soil fertility and faster tree growth rates in the regrowth forest.     

Influence of a vesicular-arbuscular mycorrhizal fungus on the competitive ability of Bradyrhizobium spp. for nodulation of cowpea Vigna unguiculata (L.) Walp in non-sterilized soil

Summary We examined the influence of a vesicular-arbuscular (VAM) fungus (Glomus pallidum Hall) on the competitive ability of introduced and native Bradyrhizobium strains to nodulate cowpeas [Vigna unguiculata (L) Walp]. Our experiments in non-sterilized soil revealed that in the presence of VAM fungus, introduced Bradyrhizobium spp. strains become more competitive than native rhizobia. For example, strain JRC29 occupied 59.2% of the total nodules when inoculated alone, but this figure increased to 71.2% when JRC29 was used in dual inoculations with VAM fungus. A similar pattern of enhanced competitiveness for nodule formation was observed with the two other strains in the presence of the VAM fungus. Our results suggest that the competitiveness of rhizobia can be enhanced by co-inoculating with a selected strain of a VAM fungus.     

Presence and dispersal of infective Frankia in peat and meadow soils in Sweden

Summary Use of the N₂-fixing grey alder, Alnus incana (L.) Moench, as a short-rotation crop for energy production is currently being explored. To evaluate the need for inoculation of alders, the distribution of infective propagules of Frankia in the soil at potential sites for alder plantations was examined. Uninoculated grey alder seedlings were grown in three types of soil. Frequent nodulation was found in a meadow soil which had been free from actinorhizal plants for nearly 60 years, but the alder seedlings failed to nodulate in peat soil from two different bog sites. One of these bogs had been exploited for peat and the surface layer of the peat had been removed, so that the soil samples were taken from deep layers of the peat. At the other site, an area of cultivated peat, there were no infective propagules of Frankia in plots without alders; the infective Frankia was present in plots only where it had been introduced by inoculated alders. There was no detectable air-borne dispersal of Frankia. Instead, water movement might account for the dispersal of Frankia in peat. Although the apparent absence of Frankia in these peat soils necessitates inoculation of alder seedlings before planting out, this makes it possible to introduce and maintain Frankia strains with selected beneficial characteristics, since there is no competition from an indigenous Frankia flora.     

Buckwheat (Fagopyrum esculentum Moench) Potential to Contribute Solubilized Soil Phosphorus to Subsequent Crops

Reports supporting folklore beliefs that buckwheat (BW) can significantly contribute solubilized phosphorus (P) from sparingly soluble soil P to subsequent crops remain anecdotal. To quantify P solubilized by BW from five inorganic and three organic pools in a Fargo silty clay, spring wheat (Triticum aestivum L.) (WHT) was grown as a reference crop to compare P mineralized and P uptake in a complete randomized design. Following fractionation and analysis, P changes between pools indicated solubilization from recalcitrant to less recalcitrant P pools. Calcium-bound P contributed the most P (72% of inorganic pool) to the available fraction, and P uptake by BW (40 kg ha^?1) was significantly greater than wheat (16 kg ha^?1) from the inorganic pools, whereas WHT uptake was significantly greater (P < 0.05) from the organic pool. Following harvest, more P was found in available P pools after BW compared to WHT, suggesting potential solubilization of P to subsequent crops compared with WHT.     

Microbial Dynamics,Root Colonization,and Nutrient Availability as Influenced by Inoculation of Liquid Bioinoculants in Cultivars of Apple Seedlings

The present study investigates the performance of recommended doses of chemical fertilizer (RDF) and locally isolated strains of Azotobacter, Azospirillum, and arbuscular mycorrhizal fungi (AMF) inoculated either solely or in combination with seedlings of Red Delicious and Lal Ambri cultivars. The RDF (T₇) treatment recorded significantly greater vegetative growth and leaf nitrogen (N), phosphorus (P), and potassium (K) contents over multi-inoculation of Azotobacter + Azospirillum + AMF (T₆) but root colonization and microbial counts decreased significantly. Inoculation of Azotobacter + Azospirillum + AMF (T₆) was superior over sole and dual inoculation with respect to vegetative growth and nutrient contents in leaves and soil but had significant greater counts of Azotobacter, Azospirillum, and Pseudomonas than RDF. Greatest root colonization (34.0 and 35.1%) was recorded in Azotobacter + Azospirillum + AMF (T₆) followed by AMF (T₄) treatment (29.3 and 32.0%) in Red Delicious and Lal Ambri seedlings, respectively. Overall, it can be inferred that multiinoculation of synergistically interacting bioinoculants may be helpful in the establishment of healthy organic apple orchards.     

Evolution of dinitrogen and nitrous oxide from the soil to the atmosphere through rice plants

Summary It is commonly assumed that a large fraction of fertilizer N applied to a rice (Oryza sativa L.) field is lost from the soil-water-plant system as a result of denitrification. Direct evidence to support this view, however, is limited. The few direct field, denitrification gas measurements that have been made indicate less N loss than that determined by ¹⁵N balance after the growing season. One explanation for this discrepancy is that the N₂ produced during denitrification in a flooded soil remains trapped in the soil system and does not evolve to the atmosphere until the soil dries or is otherwise disturbed. It seems likely, however, that N₂ produced in the soil uses the rice plants as a conduit to the atmosphere, as does methane. Methane evolution from a rice field has been demonstrated to occur almost exclusively through the rice plants themselves. A field study in Cuttack, India, and a greenhouse study in Fort Collins, Colorado, were conducted to determine the influence of rice plants on the transport of N₂ and N₂O from the soil to the atmosphere. In these studies, plots were fertilized with 75 or 99 atom % ¹⁵N-urea and ¹⁵N techniques were used to monitor the daily evolution of N₂ and N₂O. At weekly intervals the amount of N₂+N₂O trapped in the flooded soil and the total-N and fertilized-N content of the soil and plants were measured in the greenhouse plots. Direct measurement of N₂+N₂O emission from field and greenhouse plots indicated that the young rice plant facilitates the efflux of N₂ and N₂O from the soil to the atmosphere. Little N gas was trapped in the rice-planted soils while large quantities were trapped in the unplanted soils. N losses due to denitrification accounted for only up to 10% of the loss of added N in planted soils in the field or greenhouse. The major losses of fertilizer N from both the field and greenhouse soils appear to have been the result of NH₃ volatilization.     

Shortcut Approach Alternative to the Step‐by‐Step Conventional Soil Phosphorus Fractionation Method

Abstract

In an attempt to characterize the phosphorus (P)–supplying capacity of a soil and to understand the dynamics of soil P, a procedure was followed whereby consecutive extraction procedures were carried out on a soil sample, first by dialysis membrane tubes filled with hydrous ferric oxide (DMT‐HFO), followed by subsequent P fractionation procedure. However, this combined method is lengthy and time‐consuming, and an approach to shorten these P desorption studies in soils was important. The major objective of this article, therefore, was to present a shortcut method as an alternative approach to the combined fractionation method. Comparison of the sum of DMT‐HFO‐P_i, sodium bicarbonate (NaHCO₃)‐P_i, sodium hydroxide (NaOH)‐P_i, D/hydrochloric acid (HCl)‐P_i, and C/HCl‐P_i extracted by a conventional step‐by‐step method with the sum of DMT‐HFO‐P_i and a single D/HCl‐P_i extraction as a shortcut approach for all extraction periods resulted in a very strong and significant correlations. Both these methods were correlated with maize grain yield, and it was found to be highly significant. This study revealed that this shortcut approach could be a simplified and economically viable option to study the P dynamics of soils especially for soils where the P pool acting as a source in replenishing the labile portion of P is already identified.