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991.
992.
Jose Maria da Silva Paulo Cezar Rezende Fontes Carla do Carmo Milagres July Anne Amaral de Abreu 《Journal of plant nutrition》2020,43(18):2833-2843
Abstract Adequate plant nutrition is important to reduce costs and increase the crop yield. This study tried to verify the influence of Nitrogen (N) on plant biomass production and the yield of bell pepper grown in SLAB; quantify the N use efficiency (NUE), and to quantify the residual N concentration in the substrate after the end of the crop cycle. The experiment was carried out in a protected environment. Pepper seedlings were transplanted to SLAB bags containing 40?dm3 of substrate. The treatments consisted of six N rates (0, 1.5, 3.0, 4.5, 6.0, and 7.5?g plant?1) split into 10 fortnightly applications, in a randomized block design with four replications. The fruit yield was evaluated throughout the experiment and after the final harvest, the dry mass of leaves, stem, and root of the plant, the N content and accumulated, the residual nitrate and ammonium in the substrate, and the NUE were evaluated. The rate of 5.51?g plant?1 of N, corresponding to 355.5?kg ha?1, provided the maximum yield of commercial fruits of 1.57?kg plant?1 or 101.2 t ha?1. With increasing N rate, the residual nitrate concentration in the substrate increased and the NUE decreased. 相似文献
993.
Tiago Miqueloto Cauby de Medeiros Neto Clovis David Medeiros Martins Rodrigo Amorim Barbosa Sila Carneiro Da Silva André Fischer Sbrissia 《Acta Agriculturae Scandinavica, Section B - Plant Soil Science》2020,70(3):208-214
ABSTRACTThe aim of this study was to evaluate the defoliation patterns of individual tillers, efficiency of herbage utilisation, and forage production in continuously stocked Brachiaria humidicola cv. Comum swards during periods of the year of restricted pasture growth. The experiment was conducted at the Embrapa, Campo Grande-MS, Brazil, from April to October 2012. Treatments consisted of two grazing management strategies, defined by two ranges of sward height (10–15 and 20–25 cm) managed under continuous and variable stocking rates. The experiment was conducted as a completely randomised block design with three replications. During periods of resource constraints, grazing management strategies based on ‘steady state’ sward heights did not alter defoliation patterns, herbage utilisation efficiency (HUE), and forage production in Brachiaria humidicola swards under a continuous stocking method. A direct implication of our results is that grazing management strategies during the driest and coldest periods of the year in the tropics should be developed based on the conditions most suitable for better promoting faster pasture recovery and a return to production in the following spring; it is unlikely that any grazing management strategy would be successful in increasing herbage production and/or HUE in periods of restricted pasture growth. 相似文献
994.
Andreas B. Wolff Maria Sidirelli Constantinos Paradellis Kiriakos Kotzabasis 《Biology and Fertility of Soils》1995,20(4):249-252
The relationship between soil acidity and polyamine (putrescine, spermidine, spermine) concentrations in roots was evaluated and compared to (1) nodule numbers in common beans and (2) tannin concentrations in roots. Six Phaseolus vulgaris cultivars were grown in pots in a greenhouse in soil at pH 4.5 or 5.5 and inoculated with Rhizobium leguminosarum bv. phaseoli strains. At pH 4.5 nodule numbers were strongly reduced but polyamine concentrations were 50% higher than at pH 5.5. At both pH levels putrescine and spermidine were the dominant polyamines, while the concentration of spermine was less than half of the other two. There was also a cultivar effect on the polyamine concentration, but this was much less pronounced than the pH effect. By 22 days after planting the uninoculated control plants had about 13% lower levels of polyamines than the inoculated plants. The concentrations of putrescine, spermidine, and spermine were negatively correlated with nodule numbers, but positively correlated with the root tannin content. There were no significant correlations with either root or plant dry weight. 相似文献
995.
W. de Vries E. E. J. M. Leeters C. M. A. Hendriks 《Water, air, and soil pollution》1995,85(3):1063-1068
Effects of elevated S and N deposition on the solution chemistry of Dutch forest soils are mainly manifested by increased concentrations of Al associated with increased concentrations of SO4 and NO4. Presumed critical Al/base cation ratios are often exceeded below 20 cm soil depth. There is also evidence that elevated N deposion during the last decades affected the forest nutrient status and caused large changes in forest vegetation. About half of the Dutch forests have absolute shortage of P and relative Mg deficiencies compared to foliar N contents. Evidence from field studies of a relationship between soil acidification and nutrient imbalances in the soil and the foliage on one hand and the vitality of forests on the other hand is, however, lacking. 相似文献
996.
Quantifying the most important mechanisms of acid buffering in carbonate-free soils From the release of cations from the soil matrix during pH-stat-titrations, characteristic values for assessing buffer rates were derived separately for single elements. Recorded buffer reactions became almost exclusively apparent in the release of Al and Fe, however the contribution of Fe to the total turnover only amounted to 1–3%. The release of each element and of DOC in the course of time was due to the overlapping of two first-order reactions, respectively. In the fast initial reaction all measured elements were released at nearly the same velocity, whereas in the 2nd, slower reaction the rate of Al-release corresponded to that of DOC but was at least seven times higher than that of Fe. Correlations between the maxima of release and soil chemical properties revealed a dominating contribution of organically bound Al (Alp) to proton buffering. It is assumed that also the amount of Fe released is originating in organic complexes. 相似文献
997.
998.
Colin Southwell David Borchers Charles G. M. Paxton Louise Burt William de la Mare 《Journal of Agricultural, Biological & Environmental Statistics》2007,12(1):41-54
We use line transect detection functions together with generalized linear and additive models to estimate detection probability
when detection on the line (“g(0)”) may not be certain. The methods provide a flexible way of modeling detection probability
for independent observer surveys, and for investigating the effects of explanatory variables. Analysis of data from an aerial
survey of pack-ice seals produced g(0) estimates substantially below 1 for some observers (it varied from 0.80 to 0.98), demonstrated a fairly complex dependence
of detection probability on covariates, and showed negative correlation between observers’ search width and their g(0). In addition to illustrating the utility of generalized additive models for capturing the effect of covariates on detection
probability, the analysis suggests that detection functions may be sufficiently variable that use of g(0) correction factors obtained from other surveys would be inadvisable. We recommend that estimation of g(0) be considered for all aerial surveys; if g(0) is found to be very close to 1, estimation from subsequent surveys under the assumption that it is 1 may be reasonable,
but without any estimation of g(0), the assumption that it is 1 is a matter of faith. 相似文献
999.
Ulrich?F?rstnerEmail author Susanne?Heise René?Schwartz Bernhard?Westrich Wolfgang?Ahlf 《Journal of Soils and Sediments》2004,4(4):247-260
Background, Aims, and Scope
Data from the Elbe River and its tributaries indicate, despite extensive improvement in water quality during the last 15 years, that the respective sediment situation of many priority pollutants has not reached an acceptable level. For the coming decades, risks for downstream sites and stakeholders will persist, mainly due to secondary sources originating from historical pollution of soils and sediments in the catchment area. In practice, a catchment-wide assessment of historical contaminated soil and sediment should apply a three-step approach: (i) Identification of substances of concern (s.o.c.) and their classification into ’hazard classes of compounds’; (ii) identification of areas of concern (a.o.c.) and their classification into ‘hazard classes of sites’; (iii) identification of areas of risk (a.o.r.) and their assessment relative to each other with regard to the probability of polluting the sediments in the downstream reaches. The conversion of this concept has to consider the underlying philosophy of the EU Water Framework Directive, particularly with respect to the analysis and monitoring of priority substances in solid matrices. However, major deficiencies are still in the assessment and prognosis of resuspension processes, and potential approaches to fill this gap are described both in theory and from examples of the Elbe River. 相似文献1000.
Carbon assimilation and allocation were studied in a tundra ecosystem in northern Scandinavia. Seasonal variation in the below-ground carbon allocation to dissolved organic carbon (DOC), coarse-, fine-, and hair roots was investigated using in situ 14C pulse-labelling, adding 2-3 MBq 14CO2 dm−2 to the above-ground vegetation. Combining the allocation data with regression models of the seasonal carbon flux made it possible to estimate a temporally explicit ecosystem carbon allocation budget.The ecosystem was a net source of CO2, losing on average 0.97 g C m−2 d−1 to the atmosphere, with little variation through the season. There was, however, significant temporal variation in partitioning of recently assimilated carbon. Allocation to below-ground compartments over 32 days following labelling increased from 18% in June to 55% in September. Above-ground allocation showed the opposite trend. Hair roots and DOC were strong sinks in the autumn. Transport of newly assimilated carbon occurred rapidly throughout the season, 14C appearing in all sampled pools within 4 h of labelling.The seasonal variation in carbon partitioning observed in this study has implications for the residence time of assimilated carbon in the ecosystem. A relatively greater allocation to rapidly decomposing pools, such as hair roots and DOC, would tend to reduce incorporation into woody tissue, increasing the overall rate of carbon cycling and decreasing ecosystem storage. The results of this study will be of value for building and validating mechanistic models of ecosystem carbon flow in tundra and subarctic ecosystems. 相似文献