Plant-available Nitrogen Research Articles

Deodorant compositions containing antibacterial zeolite and silicones

Livestock manure is a major contributor to ammonia and greenhouse gas emissions and treatment technologies such as slurry acidification can be used to reduce both. In this study, life cycle assessment was used to compare impact potentials of slurry acidification at either the pig housing or the field application stage with conventional slurry management. Furthermore, the effects of differences in environmental regulations concerning nitrogen application limits were analysed. The impact categories analysed were terrestrial eutrophication potential, climate change potential, marine eutrophication potential and toxicity potential. Slurry acidification reduced the terrestrial eutrophication potential by 71% for in-house acidification and by 30% for field acidification. Changes in regulatory plant-available nitrogen application limits resulted in changes in climate change potential and marine eutrophication potential, with lower limits favouring in-house acidification. Acidification can substantially reduce the environmental impacts of animal slurry, but the effect depends on the context of the regulatory regime.

Treedyn3 forest simulation model

The treedyn3 forest simulation model is a process model of tree growth, carbon and nitrogen dynamics in a single-species, even-aged forest stand. It is based on the treedyn model. Major changes include the computation of sun angle and radiation as a function of latitude and day of the year, the closed-form integration of canopy production as a function of day and hour, the introduction of tree number, height, and diameter as separate state variables, and different growth strategies, mortalities, and resulting self-thinning as function of crowding competition. The tree/soil system is described by a set of nonlinear ordinary differential equations for the state variables: tree number, base diameter, tree height, wood biomass, nitrogen in wood, leaf mass, fine root mass, fruit biomass, assimilate, carbon and nitrogen in litter, carbon and nitrogen in soil organic matter, and plant-available nitrogen. The model includes explicit formulations of all relevant ecophysiological processes such as: computation of radiation as a function of seasonal time, daytime and cloudiness, light attenuation in the canopy, and canopy photosynthesis as function of latitude, seasonal time, and daytime, respiration of all parts, assimilate allocation, increment formation, nitrogen fixation, mineralization, humification and leaching, forest management (thinning, felling, litter removal, fertilization etc.), temperature effects on respiration and decomposition, and environmental effects (pollution damage to photosynthesis, leaves, and fine roots). Only ecophysiological parameters which can be either directly measured or estimated with reasonable certainty are used. treedyn3 is a generic process model which requires species- and site-specific parametrization. It can be applied to deciduous and coniferous forests under tropical, as well as temperate or boreal conditions. The paper presents a full documentation of the mathematical model as well as representative simulation results for spruce and acacia.

Analytical model of stemwood growth in relation to nitrogen supply.

We derived a simplified version of a previously published process-based model of forest productivity and used it to gain information about the dependence of stemwood growth on nitrogen supply. The simplifications we made led to the following general expression for stemwood carbon (c(w)) as a function of stand age (t), which shows explicitly the main factors involved: c(w)(t) = eta(w)G*/ micro (w)(1 - lambdae(- micro (w)t) - micro (w)e(-lambdat)/lambda - micro (w)), where eta(w) is the fraction of total carbon production (G) allocated to stemwood, G* is the equilibrium value of G at canopy closure, lambda describes the rate at which G approaches G*, and micro (w) is the combined specific rate of stemwood maintenance respiration and senescence. According to this equation, which describes a sigmoidal growth curve, c(w) is zero initially and asymptotically approaches eta(w)G*/ micro (w) with the rate of approach dependent on lambda and micro (w). We used this result to derive corresponding expressions for the maximum mean annual stem-wood volume increment (Y) and optimal rotation length (T). By calculating the quantities G* and lambda (which characterize the variation of carbon production with stand age) as functions of the supply rate of plant-available nitrogen (U(o)), we estimated the responses of Y and T to changes in U(o). For a plausible set of parameter values, as U(o) increased from 50 to 150 kg N ha(-1) year(-1), Y increased approximately linearly from 8 to 25 m(3) ha(-1) year(-1) (mainly as a result of increasing G*), whereas T decreased from 21 to 18 years (due to increasing lambda). The sensitivity of Y and T to other model parameters was also investigated. The analytical model provides a useful basis for examining the effects of changes in climate and nutrient supply on sustainable forest productivity, and may also help in interpreting the behavior of more complex process-based models of forest growth.

Rooting Characteristics and Nitrogen Utilisation of Brussels Sprouts and Leeks

ABSTRACT Under field conditions a crop of Brussels sprouts (Brassica oleracea, var. gemmifera) usually utilises the plant-available nitrogen better than leeks (Alliumporrum L.). To investigate the role of the root system in nitrogen utilisation, the two crops were grown in the Wageningen Rhizolab, a new rhizotron facility. Large differences in rooting pattern were observed. Leeks had a relatively shallow rooting system with maximum root growth at a depth of 15 to 20 cm and a low rooting intensity. The rooting pattern of Brussels sprouts could explore the soil profile to a depth of one metre in a very short period. Large differences in nitrogen uptake pattern also showed up between the crops. Brussels sprouts depleted the entire rooted profile of nitrogen in a relatively short period (June to mid-August) whereas in leeks the nitrogen uptake was greatest in the second part of the season. The implications of these rooting and nitrogen uptake patterns for fertilisation management strategies to minimise N loss...

Amino Acid Absorption by Arctic Plants: Implications for Plant Nutrition and Nitrogen Cycling

Recent studies of nitrogen (N) cycling in arctic tundra have indicated that inorganic N supplied to plants by mineralization is not sufficient to meet the annual requirement of N by many tundra species. Whereas N mineralization is slow in tundra soils and concentrations of inorganic N are low, these soils have large stocks of both structural and soluble organic N. In light of these observations, kinetics of absorption of three amino acids (glycine, aspartic acid, and glutamic acid) were measured in dominant vascular plant species of the four major ecosystems types in arctic Alaska and compared with concentrations of free amino acids in soils. Absorption rates were measured on roots using 14C—labeled substrates. Concentrations of free amino acids in soil were measured on water—extracted samples by high pressure liquid chromatography. All species had higher capacity (Vmax) for ammonium uptake (measured using methylamine as an ammonium analogue) than for any amino acid. However, at concentrations observed in the field, uptake rates estimated for amino acids were similar to (glycine) or less than (aspartic and glutamic acids) that for ammonium. On the basis of these comparisons, uptake rates of the three amino acids together may account for between 10 and 82% of the total N uptake in the field, depending on species and community. Deciduous shrubs had higher uptake rates than the more slowly growing evergreen shrubs, suggesting that new growth created a sink that strongly influenced capacity for amino acid uptake. In general, ectomycorrhizal species had higher amino acid uptake than did non—mycorrhizal species. In species that were sampled from more than one community, amino acid uptake rates were highest in the community where a given amino acid was most abundant in the soil. The results indicate that, in arctic tundra, plants short—circuit the mineralization step of decomposition by directly absorbing amino acids. This implies that in the organic soils of these tundra systems (1) inorganic nitrogen is an inadequate measure of plant—available soil nitrogen, (2) mineralization rates underestimate nitrogen supply rates to plants, (3) the large differences among species in capacities to absorb different forms of N provide ample basis for niche differentiation of what was previously considered a single resource, and (4) by short—circuiting N mineralization, plants accelerate N turnover and effectively exert greater control over N cycling than has been previously recognized.

Nitrogen effects on rhizosphere processes of range grasses from different successional seres

Nitrogen and rhizosphere microorganism effects on nitrogen and carbon dynamics of Sitanion hystrix (early successional species), Stipa comata and Poa secundu which are (mid-successional species), and Agropyron spicatum (late successional species) were evaluated in a growth chamber study. Rhizosphere inocula resulted in increased nitrogen in both root and shoot tissue, and also of water-extractable carbon in the rhizosphere. Plant species, rhizosphere inocula and nitrogen level showed a three-way significant interaction for total and plant-available nitrogen. Rhizosphere microbe presence resulted in higher plant-available nitrogen in the rhizosphere of S. hystrix and less with A. spicatum, suggesting nitrogen immobilization with the later successional grass. Higher nitrogen resulted in decreased active bacteria in the rhizosphere of all plants tested, and decreased fungal hyphal lengths in the rhizosphere of the later successional P. secunda and A. spicutum. Exudate carbon in the rhizosphere of the late successional species A. spicatum, was more recalcitrant, which also may contribute to nitrogen immobilization. These differential responses of early- and late-successional grasses may be important factors contributing to plant succession.

A model analysis of the influence of root and foliage allocation on forest production and competition between trees.

A general model was constructed relating forest growth to nitrogen uptake and the partitioning of biomass among leaves, fine roots and woody tissues. The model was used to assess the influence of the allocation pattern on stand wood production, individual tree growth and nutrient cycling for even-aged conifer stands with adequate water, but suboptimal nitrogen. Stand wood production was maximized by quite low allocation to roots for specified amounts of plant-available nitrogen. However, the wood production of the individual was maximized by higher allocation to roots, because large root systems enhanced the ability of individuals to compete for nutrients. The optimal fine root allocation for a competing individual was less than 5% of total production for adequate nitrogen, but rose to 30% as nitrogen became more limiting, in general agreement with observed allocation patterns for fertilized versus non-fertilized forests. The high allocation to roots predicted for competitors may also enhance long-term productivity by decreasing nutrient losses from the ecosystem. Although collective, short-term stand wood production could be increased by shifting growth from roots to stems, this strategy may increase nutrient losses, ultimately decreasing productivity.

Soil and Plant Nitrogen Availability Tests for Corn following Alfalfa

Economic and environmental incentives to accurately predict corn (Zea mays L.) N requirements emphasize the need to accurately credit N supplied to first-year corn from a previous alfalfa (Medicago sativa L.) crop. A 4-yr study (24 site-yr) was conducted to evaluate the use of preplant and pre-sidedress soil and basal stalk nitrate tests and an end-of-season stalk nitrate test to assess N availability to first-year corn following alfalfa. Pre-sidedress soil and basal stalk samples were obtained when corn was 6 to 12 in. tall and analyzed for nitrate. Grain yield was not significantly increased by applied N at any location during the study [...]

Long-term effects of conservation practices on the nitrogen fertility of a soil cropped annually to wheat

Sustainable farming in the semi-arid interior of South Africa requires the adoption of conservation practices to maintain and, if possible, increase soil fertility. The effects of some such practices on the nitrogen fertility of a hydromorphic sandy clay loam soil were examined in a field trial at Bethlehem, in the eastern Orange Free State. Soil from selected plots was analysed, after this trial had been run for 11 and 12 years, for organic carbon and total nitrogen to use as measures of soil organic matter, and for residual inorganic and mineralizable nitrogen to use as measures of plant-available nitrogen. The trial includes 36 treatments, namely, all combinations of straw burning (burnt or unburnt), three primary cultivation methods (ploughing, stubble mulch or no cultivation), two weed control methods (mechanical or chemical) and three levels of nitrogen fertilization (20, 30 or 40 kg N ha−1). The 30 kg N ha−1 level was selected, reducing the number of treatments to 12. Similar measurements were made...

Fallow management, soil water, plant-available soil nitrogen and grain sorghum production in south west Queensland

The effects of tillage frequency (conventional, reduced and zero), primary tillage implement (disc, blade and chisel plough), stubble management (retention and removal), gypsum application, and paraplowing were examined with respect to soil water storage, soil nitrate accumulation, crop establishment, crop growth, grain yield and grain nitrogen content for 4 successive sorghum crops on a sodic, texture-contrast soil in south west Queensland. Retention of sorghum stubble (v. removal) produced an increase in mean yield of sorghum grain of 393 kg/ha, due to increased soil water extraction and increased water use efficiency by the following crop. The highest mean yield occurred after reduced blade tillage with stubble retained. Zero tillage with stubble removed gave the lowest mean grain yield. Zero tillage always had the lowest quantity of soil nitrate-nitrogen at sowing. In one fallow, increased aggressiveness of primary tillage (disc v. blade plough) increased the quantity of nitrate-nitrogen in the top 60 cm of soil at sowing. These effects on available soil nitrogen did not result in corresponding differences in grain nitrogen content. Results indicate that for optimum fallow management on this texture-contrast soil in south west Queensland, sorghum residues should be retained, tillage frequency should be reduced, but not to zero, blade ploughing should be preferred to discing, and gypsum application should not be practised.

Following practices, soil water storage, plant-available soil nitrogen accumulation and wheat performance in South West Queensland

The effects of tillage frequency (conventional, reduced and zero), primary tillage implement (disc, blade and chisel plough), stubble management (retention and removal), gypsum application and paraplowing were examined with respect to soil water storage, soil nitrate accumulation, seedling establishment, crop growth, yield and grain protein content for four successive years of wheat, grown on a sodic, duplex soil in South West Queensland, Australia. Stubble retention generally resulted in more soil water at sowing but less at harvest, compared with stubble removal. This led to higher grain yields in dry growing seasons and has implications for reducing runoff. Zero tillage with stubble removal had the lowest mean water storage and, in dry growing seasons, the lowest grain yield. This indicates that when stubble is absent or lacking, some tillage is needed, probably to break surface seals and increase surface roughness. Zero tillage with stubble retention accumulated the most soil water but the least soil nitrate. Consequently this treatment outyielded all others in the driest growing season but was outyielded by almost all others in the wettest. Increased frequency and aggressiveness of tillage, and stubble removal, increased the amount of soil NO 3-N at 0–60 cm. There were no significant ( P<0.05) tillage×stubble interactions. In the wettest growing season, wheat grain yields reflected the different levels of NO 3-N in the soil. In the other three years, grain protein contents reflected these levels. Both zero tillage and stubble retention reduced the efficiency of water use, probably because both also reduced nitrogen supply. So despite high yields from zero tillage with stubble retention in the dry growing seasons, the full yield potential of this treatment with respect toits water supply was not realized. Gypsum application at 5 t ha −1 had no commercially useful effect on establishment or grain yield and is not recommended. Similarly, paraplowing had no effect on yield. Reduced or zero tillage is recommended, provided that stubble is present and nitrogen supply is adequate.

Simulation of forest stand dynamics, using real-structure process models

The dynamic richness of forest ecosystem response to climate, management and pollution stress cannot be adequately described by traditional descriptive growth-and-yield simulators, but requires sufficiently detailed models of the underlying eco-physiological processes and their structural interactions (real-structure models). Two such models are described, and representative results presented. The generic real-structure model TREEDYN describes stand growth, and its carbon and nitrogen dynamics in interaction with corresponding soil processes, using ten nonlinear differential equations. The state variables are: leaf, fine-root, wood, fruit, and assimilate biomass; carbon and nitrogen in litter and soil organic matter; and plant-available nitrogen. The model has been applied to both a broadleaf tree ( Acacia auriculiformis) under tropical conditions, and to a coniferous tree ( Picea abies) under European conditions. The real-structure model SPRUCOM simulates Norway-spruce stand growth, including the light-competition-induced self-thinning process, using 30 non-linear differential equations for each of four tree competition classes. The state variables in this case are: needles (7 classes); corewood; sapwood (18 rings); branches; coarse roots; fine roots; and assimilate. The model has been used, in particular, for the study of stand production as a function of air pollution affecting leaf efficiency and/or fine-root turnover. Both models employ a full description of light attenuation and photosynthetic production in the canopy. The models are parameterized by species-and region-specific real-system parameters; no time-series data are required for this purpose. For more efficient computation in management tools, a condensation of complex models to simpler models may be required, while maintaining structural, behavioral, empirical, and application validity. Work on this aspect is briefly reported.

Plant Response to Herbivory and Belowground Nitrogen Cycling

Plant responses to herbivory and links to belowground nitrogen cycling were investigated at Wind Cave National Park, South Dakota. Laboratory estimates of net nitrogen mineralization were highest in soils from the more altered areas of prairie dog colonies (Cynomys ludovicianus) and lowest in the adjacent, lightly grazed, uncolonized grassland. The ratio of CO2: net nitrogen mineralized, as index of immobilization, was highest in the uncolonized grassland and lowest in the altered core areas. Soil moisture was an important modifier of in situ field estimates of net nitrogen mineralization. Root biomass, an important carbon source for decomposers in perennial grasslands, was lowest in the altered core area and highest in the adjacent uncolonised grassland. Decreased nitrogen immobilization and increased net nitrogen mineralization in the laboratory incubations likely resulted from decreased root carbon inputs in grazed areas, which limited carbon availability to decomposers. Such increases in plant—available nitrogen may partially explain the frequently reported grazing—induced increases in shoot nitrogen concentrations. These studies suggest that carbon allocation to roots is a key link determining nitrogen—cycling responses to herbivory.

Generic simulation model of forest growth, carbon and nitrogen dynamics, and application to tropical acacia and european spruce

Abstract In order to provide accurate assessments of forest stand development even in the absence of long-term growth and yield observations (as may be the case in developing countries and for less well-known species), a generic dynamic (cybernetic) simulation model has been developed representing tree growth, and carbon and nitrogen dynamics in a single-species, even-aged forest stand. The tree/soil system is described by a set of nonlinear ordinary differential equations for the state variables: wood, leaf, fine root, fruit biomass; assimilate; carbon and nitrogen in litter; carbon and nitrogen in soil organic matter; and plant-available nitrogen. All parameters are measurable ecophysiological quantities (no statistical parameter estimation). The model includes explicit formulations of all relevant ecophysiological processes such as: temporal and spatial light distribution and photosynthesis in the canopy; respiration of all parts; assimilate allocation; increment formation; nitrogen fixation, mineralization, humification and leaching; forest management (thinning, felling, litter removal, fertilization, etc.); and environmental effects (air pollution and insect damage). Application of the model requires specification of 38 tree-specific and 15 region-specific parameters (obtainable - except for root data - from simple field estimates or laboratory measurements not requiring time-series studies), 10 initial conditions for the state variables and 13 scenario parameters (e.g. nitrogen input, maximum nitrogen-fixing rate, litter removal, thinning and cutting schedule, pollution damage to photosynthesis, leaves, or fine roots, time and severity of insect calamity). The simulation model has been applied successfully to study stand growth behavior under different conditions of soil quality, forest management, and pollution and insect damage for broadleaf trees in a tropical climate ( Acacia auriculaeformis ) Cunn. ex Benth. in South China) and coniferous trees in a temperate climate ( Picea abies (L.) Karst. in Central Europe). Despite the difference of species and climate, the model provides accurate representations of stand development under various conditions in both cases, yielding good agreement with standard yield tables (for spruce).

Effects of available soil N and rates of inoculation on nitrogen fixation by irrigated soybeans and evaluation of δ15N methods for measurement

Nitrogen fixation by irrigated soybeans (Glycine max (L.) Merr. cv. Forrest) was studied in a field experiment on a grey clay soil at Trangie, N.S.W. during the summer of 1985-86. Cropping with oats during the previous winter diminished the concentration of plant-available nitrogen in the soil from 37.6 to 18.5 mg N kg-1 and induced differences in the natural abundance of 15N (S15N) in this nitrogen. Four rates of liquid inoculation with Bradyrhizobium japonicum strain CB 1809, interacted with soil nitrogen to produce a wide range of nodulation of the soybeans. The following main effects on growth and N2 fixation resulted: (a) Initially, growth and accumulation of plant nitrogen was lower in pre-cropped than in prefallowed soil but N2 fixation was higher. (b) Nitrogen fixation during seed development was high in pre-cropped soil and greatest at the highest rate of inoculation. It resulted in high yields of seed (3.5 t ha-1 with 100 times the normal inoculation) with significantly higher concentration of seed nitrogen than from plants grown in prefallowed soil. (c) With increasing rates of inoculation on the pre-fallowed soil, more uniform nodulation was associated with smaller variances in most of the parameters studied. Other findings included further validation of the S15N method of calculating the proportion (p) of plant nitrogen derived from N2 fixation, with good agreement between treatment effects based on such estimates and those based on the relative concentrations of ureides in vacuum-extracted xylem sap. The values of p from S15N measurements on shoot nitrogen were affected little by inclusion of root nitrogen, and similar values were obtained when uninoculated, unnodulated Forrest soybeans, a nonnodulating genotype (non-nod Clark 63) or extractable mineral nitrogen of soil were used to estimate the S15N of plant N assimilated from soil. More dry matter (flowers, young pods and older leaves) containing more nitrogen (23-26 kg N ha-1) fell from the canopy of plants during seed maturation on pre-fallowed soil (high nitrogen) than on pre-cropped soil (13-15 kg N ha-1). Several correlations between the various quantities measured were noted and are discussed. It is concluded that growing winter cereals on land newly broken from pasture, coupled with high rates of inoculation of the following soybeans, may be a profitable way of diminishing plant-available soil nitrogen, thus maximizing the contribution of nitrogen from N2 fixation with benefits in seed yield and protein content.

The natural abundance of 15N in an irrigated soybean crop and its use for the calculation of nitrogen fixation

In a field experiment at Leeton, N.S.W., Chaffey soybeans were grown with irrigation at various plant spacings and with various inoc~ilation treatments and two pre-planting soil treatments. Uninoculated plants were almost completely non-nodulated. Measurements of the natural abundance of 15N (S15N) in the total nitrogen of the plants were made at all stages of growth and in the grain at harvest. The 6lSN in all nodulated treatments declined progressively with time in comparison with un-nodulated plants, due to the incorporation of atmospheric N2 of lower 15N concentration than the soil nitrogen. This enabled calculation of the proportions of plant-nitrogen obtained from the soil and by symbiotic N2-fixation. The main findings were as follows: There was a gradient of S15N in plant-available nitrogen across the experimental area. Therefore, treatments were compared by using the nearest non-nodulated plot for the estimate of S15N in plantavailable soil nitrogen. Despite large differences in plant size due to plant spacing, S15N in mature nonnodulated plants did not differ significantly, indicating that the natural abundance of 15N in plantavailable soil nitrogen was uniform in root zones of different sizes. In well-nodulated plants, the proportion (p) of shoot nitrogen derived from N2-fixation increased with time, reaching approximately 70% and 90% in previously fallowed and previously cropped soil respectively, during a period of rapid growth between 78 and 98 d&amp; after planting. The fixed N, in the best-nodulated treatments at (114 days) was 143 and 244 kg N ha-1 respectively for previously fallowed and previously cropped soil. There were consistent trends for increased N2 fixation with increased inoculation rates. In non-nodulated plants, nitrogen recovered in the grain represented most of that present in the shoots at maturity. In well-nodulated treatments, grain nitrogen, although similar in S15N to that of shoots + fruits, represented only 47 and 59% of the 406 and 348 kg N ha-1 present at maturity in shoots + fruits from previously fallowed and previously cropped soils respectively. After harvesting more than 3 t ha-1 of grain, the nitrogen balance in the previously cropped soil, if all of the residual nitrogen in the soybeans could have been retained in the soil, was positive. In the previously fallowed soil there could have been a net depletion of soil nitrogen.

ASSESSMENT OF AGRISPON, A MICROBIAL SOIL SUPPLEMENT, ON CEREAL PRODUCTION

Agrispon has been promoted in Western Canada as a soil supplement that provides plant-available nitrogen via undefined catalytic as well as microbial processes. Testing was undertaken in a controlled environment and under field conditions, to substantiate claims made by manufacturers and promoters that this product enhances germination and availability of nitrogen to plants. Characterization of the microbial composition of this product was also undertaken. Germination of Neepawa hard red spring wheat (Triticum aestivum L.) was not influenced in a greenhouse study. Growth chamber studies did not show any beneficial effect of Agrispon on total dry matter, grain yield or protein content of Neepawa wheat. Field studies with Canuck hard red spring wheat gave similar results to those obtained in the growth chamber i. e., no benefit in grain yield or protein content of Agrispon-treated plants. Analysis of soil samples taken at the end of the experiment also revealed no treatment effect of Agrispon or N fertilizer on available NO−3-N or NH4+-N levels. Microbiological determinations revealed relatively low populations of common soil organisms.Key words: Agrispon, Nitro/Max, soil supplement, bacterial population, fertilizer

Microbial transformations of some particulate pollution deposits in soils — A source of plant-available nitrogen and sulphur

Atmospheric pollution deposits, largely consisting of soot, were removed from sycamore leaves growing downwind of a coking plant, and added to soil. Increases in plant available S-ions (S2O32−; S4O62− and SO42−) and N (NH4+ and NO3−) occurred due to the action of soil microorganisms on the deposits. Although the detrimental effects of air pollution on plant growth have been previously emphasised, supply of nutrients resulting from the microbial transformation of particulate pollutants may prove important to the growth of pollution-resistant plant communities.