Nitrous oxide and methane fluxes from organic soils under agriculture

Trace gas fluxes of N₂O and CH₄ were measured weekly over 12 months on cultivated peaty soils in southern Germany using a closed chamber technique. The aim was to quantify the effects of management intensity and of soil and climatic factors on the seasonal variation and the total annual exchange rates of these gases between the soil and the atmosphere. The four experimental sites had been drained for many decades and used as meadows (fertilized and unfertilized) and arable land (fertilized and unfertilized), respectively. Total annual N₂O-N losses amounted to 4.2, 15.6, 19.8 and 56.4 kg ha^–1 year^–1 for the fertilized meadow, the fertilized field, the unfertilized meadow and the unfertilized field, respectively. Emission of N₂O occurred mainly in the winter when the groundwater level was high. At all sites maximum emission rates were induced by frost. The largest annual N₂O emission by far occurred from the unfertilized field where the soil pH was low (4.0). At this site 71% of the seasonal variation of N₂O emission rates could be explained by changes in the groundwater level and soil nitrate content. A significant relationship between N₂O emission rates and these factors was also obtained for the other sites, which had a soil pH between 5.1 and 5.8, though the relation was weak (R² = 15–27%). All sites were net sinks for atmospheric methane. Up to 78% of the seasonal variation in CH₄ flux rates could be explained by changes in the groundwater level. The total annual CH₄-C uptake was significantly affected by agricultural land use with greater CH₄ consumption occurring on the meadows (1043 and 833 g ha^–1) and less on the cultivated fields (209 and 213 g ha^–1).     

Decomposition of fine roots of Pinus kesiya and turnover of organic matter, N and P of coarse and fine pine roots and herbaceous roots and rhizomes in subtropical pine forest stands of different ages

Organic matter accumulation, N and P concentrations of fine (<2 mm diameter) and coarse (2-10 mm) roots of Pinus kesiya and fine roots and rhizomes of ground vegetation, and decomposition of P. kesiya fine roots (<2 mm diameter) were studied in 6-, 15- and 23-year-old P. kesiya forest stands at Shillong, the capital of Meghalaya, India. The mean annual dry weight of P. kesiya fine roots did not vary significantly between the stands, but the coarse root mass increased significantly from the 6- to 23-year-old stand. However, herbaceous fine roots and rhizomes showed a reverse trend. Live roots (biomass) showed a higher N and P concentration than the necromass (dead root mass). Nutrient concentrations were greater in the fine roots compared to coarse roots. N and P accumulation was maximum in the 6-year-old stand and minimum in the 15-year-old stand. P. kesiya fine roots decomposed in a three-phased manner in all the stands. The first phase, lasting about 30 days, was characterised by a slow rate of weight loss. This was followed by a rapid phase of weight loss up to 90 days, with an average weight loss of 7.7 mg day^-1, and the third phase showed a slow decay pattern (1.2 mg day^-1). The weight loss pattern showed a strong seasonal trend; a faster rate of decay in the warm-humid period and a slow rate of decay in the dry-cold period. Nitrogen and P concentration in the decomposing root litter showed a marked decrease and/or increase during decomposition. The study reveals that in the 6-year-old pine stand the roots of herbaceous plants play a more significant role in maintaining the organic matter, N and P status of the soil, while in the older stands pine roots assumed greater significance.     

Decomposition of roots and shoots of perennial grasses and annual barley—separately or in two residue mixes

Little is known about the decomposition rates of shoot and root residues of perennial grasses. This knowledge is important to estimate the carbon sequestration potential of the grasses. An incubation experiment was carried out in a sandy clay loam with shoot and root residues of three native perennial grasses (Wallaby grass, Stipa sp. and Kangaroo grass) and the annual grass barley either separately or in mixtures of two residues. Respiration rate was measured over 18 days, and microbial C and available N were measured on days 0 and 18. Decomposition was lower for roots than for shoots and lower for residues of perennial grasses than for barley. Cumulative respiration was positively correlated with water-soluble C in the residues but not with residue C/N. In the mixtures, the measured cumulative respiration was higher than the expected value in five of the nine mixes usually where the differences in cumulative respiration between the individual residues were relatively small. Lower than expected cumulative respiration were found in two of the mixtures in which barley shoots (high cumulative respiration) were mixed with residues with low cumulative respiration. There was a negative correlation between the change in microbial biomass C concentration from day 0 to day 18 and cumulative respiration on day 18. In the amended soils, the available N concentration decreased from day 0 to day 18. It is concluded that the low decomposition rate of perennial grasses residues should favour C sequestration, but that mixing residues of similar decomposition rate may accelerate their decomposition.     

Degradation of hemicellulose, cellulose and lignin in decomposing spruce needle litter in relation to N

Decomposing needles from a Norway spruce forest in southern Sweden were studied for 559 days under laboratory conditions. Falling needles were collected in control (Co) plots and plots that had received 100 kg N ha⁻¹ yr⁻¹ as (NH₄)₂SO₄ for 9 years under field conditions. One of the aims was to determine whether the previously documented low decomposition rate of the N fertilized (NS) needles could be explained by a lower degradation degree of lignin. The lignin content was studied using the alkaline CuO oxidation method, the Klason lignin method and CPMAS ¹³C NMR spectroscopy. The amounts of cellulose and hemicellulose were also determined.The fertilized needle litters initially decomposed faster than the unfertilized, but later this reaction reversed, so that at the end the mass loss was 45% initial C in the control and 35% initial C in NS. Klason lignin decreased with time in both treatments and overall, the change of Klason lignin mirrored the litter mass loss. No major difference as regards the decomposition of hemicellulose occurred between the treatments, whereas significantly lower concentrations of cellulose were found in NS needles throughout the incubation. The CuO derived compounds (VSC) were somewhat lower in NS needles throughout the decomposition time. Initially, VSC increased slightly in both treatments, which contradicts the Klason lignin data. There was a weak positive relationship (p>0.05) between VSC and Klason lignin. Both vanillyls compounds (V) and cinnamyl compounds (Ci) increased slightly during decomposition, whereas syringyl compounds (S) vanished entirely. The lignin degradation degree, i.e. the acid-to-aldehyde ratio of the vanillyl compounds expressed as (Ac/Al)_v, showed no significant effect of treatment. The ¹³C NMR analyses of the combined samples showed increased content of aromatic C with increasing decomposition time. The carbohydrate content (O-alkyl C) was lower in the fertilized needle litter throughout the incubation time. The alkyl C content tended to increase with decomposition time and N fertilization. The alkyl C/O-alkyl C ratios increased in both treatments during the incubation. The NMR results were not tested statistically.In conclusion, no major difference concerning lignin degradation could be found between the unfertilized and N fertilized needle litter. Thus, the study contradicts the hypothesis that higher amounts of N reduce lignin degradation. The reduced biological activity is probably due to direct N effects on the microorganisms and their decomposing ability.     

Changes in chemical composition of Pinus sylvestris needle litter during decomposition along a European coniferous forest climatic transect

The objective of this investigation was to assess the changes in chemical composition (lignin, cellulose, hemicelluloses, non-structural compounds, N, and ash) of decomposing litter. Standard Pinus sylvestris needle litter, originating from southern Sweden, was incubated in litterbags at 15 sites selected from the Netherlands to south Spain. The changes in chemical composition of this litter were determined using near infrared reflectance spectroscopy. The hypothesis was that standard (chemically uniform) litter decomposing under a range of climates would show different dynamics of accumulation and loss of C-fractions, N, and ash, relative to mass loss. It was shown that, for a given mass-loss value (10, 20, 30, 40, or 50%), the proportion of lignin, cellulose, hemicelluloses, non-structural compounds, N, and ash in the decomposing pine needles differed between sites. Lignin concentration in the litter residue at 50% mass loss ranged from approximately 26 to 43%, cellulose from 19 to 27%, hemicelluloses from 7 to 11%, non-structural compounds from 19 to 25%, N from 0.7 to 1.3%, and ash content from 1.4 to 10.1%. Lignin concentrations showed the highest range of variation. Lignin concentrations during decomposition were positively related to moisture factors as significant correlations were found with actual evapotranspiration and were improved in multiple regressions by the mean annual precipitation or the water surplus. Cellulose was degraded further at sites with high precipitation whereas hemicellulose degradation was related to temperature. This leads to the conclusion that the remaining organic matter produced by standard litter decomposition within the studied climatic range of variations tended to be more recalcitrant under wet and warm climatic conditions than under cold or dry climate.     

Litterfall, litter decomposition and nutrient release patterns in four native tree species raised on coal mine spoil at Singrauli, India

 Litterfall, leaf litter decomposition and N and P release were studied in four tree species (Dalbergia sissoo, Azadirachta indica, Pongamia pinnata and Shorea robusta) planted on a mine spoil habitat. Annual litterfall varied from 1220 kg ha^–1 in the S. robusta stand to 3620 kg ha^–1 in the A. indica stand. The fast-growing species A. indica and D. sissoo exhibited higher litter production in comparison to the other two slow-growing species. The total N returned to the soil through litterfall ranged from 8.6 kg ha^–1 year^–1 in the S. robusta stand to 36.5 kg ha^–1 year^–1 in the D. sissoo stand. The annual percent leaf litter mass loss was distinctly greater in A. indica (73%) and D. sissoo (69%) in comparison to P. pinatta (59%) and S. robusta (47%). The mean relative decomposition rates of leaf litter material were maximum in the rainy season and minimum in summer. Rainfall and its associated variables exhibited greater control over litter docomposition than temperature. Lignin and water-soluble compounds were better predictors of annual mass loss rates accounting for 90% variability. Mass loss was positively correlated with N and P mineralization rates. Lignin was the best predictor of annual N and P mineralization rates. Nutrient release pattern differed; constant release occurred in A. indica, initial release followed by delayed immobilization and release occurred in D. sissoo and P. pinnata, and initial immobilization followed by gradual release was noticed in S. robusta. A. indica and D. sissoo, showing high litterfall and rapid litter decomposition rate, hold promise for the rehabilitation of nutrient-poor coal mine spoils. On the other hand, S. robusta with less litterfall and a slow decomposition rate may prove disadvantageous. Received: 10 March 1998     

Water points and their influence on grazing resources in central northern Namibia

Debate among scientists about ecological dynamics and appropriate management of semi‐arid rangelands has led to a challenge of received wisdoms of range management and pastoral development in dryland Africa. In our study, we investigated impacts of grazing on grass composition around permanent water points along a pipeline and around a traditional hand‐dug well in an important grazing area in central northern Namibia. Grass species abundance and selected environmental variables sampled along transects radiating out from these water points were analysed using Canonical Correspondence Analysis (CCA). Significant grazing‐induced changes, manifested by palatable perennial grasses being replaced by less palatable annual grasses, were identified around water points along the pipeline. There annual grasses Schmidtia kalihariensis and Aristida stipioides dominate the vegetation as far as 5 km from the water points. No significant grazing‐induced changes in grass composition were observed around the hand‐dug well. Private ownership leading to stronger control of access to traditional wells compared to the open access water points along the pipeline seems to be a key factor preventing overutilisation of grazing resources around the former. Copyright © 2007 John Wiley & Sons, Ltd.     

Litter decomposition and nutrient release in relation to atmospheric deposition of S and N in a dry tropical region

Temporal and spatial variations in litterfall, leaf litter decomposition and nutrient release were quantified along an air pollution gradient around an industrial area in a dry tropical region of India. Significant differences were found in litterfall between the sites. Litter decomposition rates also significantly varied among the study sites. Litter decomposition was faster at sites away from the industrial region with coal-fired power plants. The concentrations of N and P increased, whereas that of Ca and SO₄-S decreased in decomposing litter over time. The nutrient release pattern was also modified by atmospheric deposition. Concentrations of SO₂ and NO₂ were negatively correlated with relative mass loss. Turnover time of nutrients, except SO₄-S in decomposing litter was maximal at the site receiving highest atmospheric depositions. The study documents that industrial emissions significantly modified nutrient cycling in adjacent terrestrial ecosystems.     

多年生杂草入侵一年生草地后土壤呼吸和凋落物分解增加

Exotic plant invasions may alter ecosystem carbon processes, especially when native plants are displaced by plants of a different functional group. Forb invasions into grasslands are common, yet little is known about how they impact carbon cycling. We conducted a field study over 2 years from April 2010 to March 2012 in China to examine changes in soil respiration (R_soil) following invasion of exotic perennial forb species (Alternanthera philoxeroides or Solidago canadensis) into an annual grassland dominated by a native annual graminoid (Eragrostis pilosa). Measurements of R_soil were taken once a week in stands of the native annual graminoidor one of the forb species using static chamber-gas chromatograph method. Aboveground litterfall of each of the three focal species was collected biweekly and litter decomposition rates were measured in a 6-month litterbag experiment. The monthly average and annual cumulative R_soil increased following invasion by either forb species. The increasesin cumulative R_soil were smaller with invasion of Solidago (36%) than Alternanthera(65%). Both invasive forbs were associated with higher litter quantity and quality (e.g., C:N ratio) than the native annual graminoid. Compared to the native annual graminoid, the invasive forbs Alternanthera (155%) and Solidago (361%) produced larger amountsof more rapidly decomposing litter, with the litter decay constant k being 3.8, 2.0 and 1.0 for Alternanthera, Solidago and Eragrostis, respectively. Functional groups of the invasive plants and the native plants they replacedappear to be useful predictors of directions of changes in R_soil, but the magnitude of changes in Rsoilseems to be sensitive to variations in invader functional traits.     

Subsurface drip irrigation and urea phosphate fertigation for vegetables on calcareous soils

Drip irrigation lines installed at 5 cm (shallow) or 15 cm (deep) below the soil surface and furrow irrigation were compared for vegetables grown on calcareous desert soils. Urea phosphate (UP) fertilizer (17–44–0) was injected twice in the drip irrigation lines during the growing season. Yields were compared to preplant fertilized and unfertilized furrows. Fall cabbage (Brassica oleracea var. capitata L.) gave comparable yields under the different irrigation treatments with the drip treatments using half the water used by the furrow treatment. Cabbage yield increased in all fertilized treatments as compared to the unfertilized furrow. Petiole P and NO₃‐N concentrations were higher from the drip than from the furrow treatments. Zucchini squash (Cucurbita pepo L.) had the highest yields under deep drip and fertilized furrow treatments, with the deep drip using half the water and P rate used by the furrow treatment. The deep drip increased squash yield by 34% over the shallow drip. The unfertilized furrow gave the lowest yield. Leaf tissue concentrations of P and NO₃‐N were comparable under deep drip and fertilized furrow treatments and were higher than the concentrations achieved from shallow drip and unfertilized furrow treatments.     

Influence of ectomycorrhizal mat soils on lignin and cellulose degradation

Summary The ectomycorrhizal fungus Hysterangium setchellii (Fisher) forms extensive hyphal mats at the soillitter interface with the roots of the host tree Douglas fir Pseudotsuga menziesii [(Mirb.) Franco]. Microbial biomass, and lignin and cellulose decomposition rates were measured seasonally for 1 year, using ¹⁴C techniques in ectomycorrhizal mat soils and adjacent non-mat soils in a second-growth Douglas fir forest. The microbial biomass and cellulose degradation rates were 3–6 times higher in ectomycorrhizal mat soils than in adjacent nonmat soils. Lignin degradation rates were higher in ectomycorrhizal mat soils than adjacent non-mat soils. Our data suggest that the ectomycorrhizal fungus H. setchellii provides a microenvironment with increased microbiological activity which results in faster lignin and cellulose decomposition.     

Effect of potassium phosphate fertilization on production and emission of methane and its C-stable isotope composition in rice microcosms

Rice fields are an important source for atmospheric CH₄, but the effects of fertilization are not well known. We studied the turnover of CH₄ in rice soil microcosms without and with addition of potassium phosphate. Height and tiller number of rice plants were higher in the fertilized than in the unfertilized microcosms. Emission rates of CH₄ were also higher, but porewater concentrations of CH₄ were lower. The δ¹³C values of the emitted CH₄ and of the CH₄ in the porewater were both 2-6% higher in the fertilized microcosms than in the control. Potassium phosphate did not affect rate and isotopic signature of CH₄ production in anoxic soil slurries. On the other hand, roots retrieved from fertilized microcosms at the end of incubation exhibited slightly higher CH₄ production rates and slightly higher CH₄-δ¹³C values compared to roots from unfertilized plants. Addition of potassium phosphate to excised rice roots generally inhibited CH₄ production and resulted in increasingly lower δ¹³C values of the produced CH₄. Fractionation of ¹³C during plant ventilation (i.e. δ¹³C in pore water CH₄ versus CH₄ emitted) was larger in the fertilized microcosms than in the control. Besides plant ventilation, this difference may also have been caused by CH₄ oxidation in the rhizosphere. However, calculation from the isotopic data showed that less than 27% of the produced CH₄ was oxidized. Collectively, our results indicate that potassium phosphate fertilization stimulated CH₄ emission by enhancing root methanogenesis, plant ventilation and/or CH₄ oxidation, resulting in residence times of CH₄ in the porewater in the order of hours.     

Tree species effects on microbial respiration from decomposing leaf and fine root litter

Tree species have an impact on decomposition processes of woody litter, but the effects of different tree species on microbial heterotrophic respiration derived from decomposing litter are still unclear. Here we used leaf and fine root litter of six tree species differing in chemical and morphological traits in a temperate forest and elucidated the effects of tree species on the relationships between litter-derived microbial respiration rates and decomposition rates and morphological traits, including specific leaf area (cm² g⁻¹) and specific root length (m g⁻¹) of litter at the same site. Litterbags set in forest soil were sequentially collected five times over the course of 18 months. During litter decomposition, microbial respiration from leaf and fine root litter differed among the six tree species. Temporal changes in the remaining mass and morphology (specific leaf area and specific root length) were observed, and the magnitude of these changes differed among species. Positive correlations were observed between respiration and mass loss or morphology across species. These results revealed that litter mass loss and morphological dynamics during decomposition jointly enhanced microbial respiration, and these carbon-based litter traits explained species differences in decomposition of leaves and fine roots. In conclusion, tree species influenced the magnitude and direction of microbial respiration during leaf/fine root litter decomposition. Tree species also affected the relationship between microbial respiration and litter decomposition through direct effects of litter traits and indirect effects mediated by regulation of heterotroph requirements.     

Influence of nitrogen on leaf chlorophyll content and photosynthesis of ‘Golden Delicious’ apple

Abstract

The aim of the present study was to estimate the influence of different rates of soil-applied nitrogen on leaf N and chlorophyll content and photosynthesis in ‘Golden Delicious’ apple trees. Three different treatments were included: the trees were either fertilized with 80 kg N ha^?1 (N-80), 250 kg N ha^?1 (N-250) or left unfertilized (CON). Fertilization increased leaf nitrogen content, with a more prominent effect in high N application level treatment. In all treatments, a slight seasonal decrease in leaf nitrogen content was observed. N-250 treatment resulted in higher chlorophyll content; a similar effect was found late in the season for N-80 treatment. Measurements of A-C _i curves, performed on spur leaves, revealed a higher CO₂ saturated photosynthetic rate in N-250 trees compared with low application level fertilized or unfertilized trees. No effect of N fertilization on carboxylation efficiency was found, as revealed by comparisons of the initial slopes of A-C _i curves. The lack of positive effect is rather surprising, since the leaf N content was efficiently increased with application of fertilizer. Obviously, the existing pool of leaf nitrogen in non-fertilized trees does not limit Rubisco activity and efficiency.     

Perennial plant species from semiarid gypsum soils support higher AMF diversity in roots than the annual Bromus rubens

The arbuscular mycorrhizal fungi (AMF) communities composition regulate plant interactions and determine the structure of plant communities. In this study we analysed the diversity of AMF in the roots of two perennial gypsophyte plant species, Herniaria fruticosa and Senecio auricula, and an annual herbaceous species, Bromus rubens, growing in a gypsum soil from a semiarid area. The objective was to determine whether perennial and annual host plants support different AMF communities in their roots. The roots were analysed by nested PCR, cloning, sequencing of the ribosomal DNA small subunit region and phylogenetic analysis. Twenty AMF sequence types, belonging to the Glomus group A, Glomus group B, Diversisporaceae, Acaulosporaceae, Archaeosporaceae and Paraglomeraceae, were identified. Both gypsophyte perennial species, H. fruticosa and S. auricula had different compositions of the AMF community and higher diversity than B. rubens. This annual plant species shared the full composition of its AMF community with both perennial plant species. Seasonal variations in the colonisation of AM fungi could explain the observed differences in AMF community composition, but this is still a working hypothesis that requires the analysis of further data obtained from a higher number of both annual and perennial plant species in order to be fully tested.     

Nitrate leaching loss under annual and perennial pastures with and without lime on a duplex (texture contrast) soil in humid southeastern Australia

Mineral N accumulates in autumn under pastures in southeastern Australia and is at risk of leaching as nitrate during winter. Nitrate leaching loss and soil mineral N concentrations were measured under pastures grazed by sheep on a duplex (texture contrast) soil in southern New South Wales from 1994 to 1996. Legume (Trifolium subterraneum)‐based pastures contained either annual grass (Lolium rigidum) or perennial grasses (Phalaris aquatica and Dactylis glomerata), and had a control (soil pH 4.1 in 0.01 m CaCl₂) or lime treatment (pH 5.5). One of the four replicates was monitored for surface runoff and subsurface flow (the top of the B horizon), and solution NO₃^– concentrations. The soil contained more mineral N in autumn (64–133 kg N ha^?1 to 120 cm) than in spring (51–96 kg N ha^?1), with NO₃^– comprising 70–77%. No NO₃^– leached in 1994 (475 mm rainfall). In 1995 (697 mm rainfall) and 1996 (666 mm rainfall), the solution at 20 cm depth and subsurface flow contained 20–50 mg N l^?1 as NO₃^– initially but < 1 mg N l^?1 by spring. Nitrate‐N concentrations at 120 cm ranged between 2 and 22 mg N l^?1 during winter. Losses of NO₃^– were small in surface runoff (0–2 kg N ha^?1 year^?1). In 1995, 9–19 kg N ha^?1 was lost in subsurface flow. Deep drainage losses were 3–12 kg N ha^?1 in 1995 and 4–10 kg N ha^?1 in 1996, with the most loss occurring under limed annual pasture. Averaged over 3 years, N losses were 9 and 15 kg N ha^?1 year^?1 under control and limed annual pastures, respectively, and 6 and 8 kg N ha^?1 year^?1 under control and limed perennial pastures. Nitrate losses in the wet year of 1995 were 22, 33, 13 and 19 kg N ha^?1 under the four respective pastures. The increased loss of N caused by liming was of a similar amount to the decreased N loss by maintaining perennial pasture as distinct from an annual pasture.     

Exploitation of Annual and Perennial Herbaceous Species for the Rehabilitation of a Sand Quarry in a Mediterranean Environment

Commercial seeds are widely used for re‐vegetation interventions in Mediterranean areas. These seeds mostly consist of species and varieties of non‐local provenance. The current practice relies mainly on forage or turf and fast growing species, even if it is often inefficient. Twenty‐two local populations or commercial varieties of annual and perennial species belonging to the botanical families Leguminosae, Graminaceae and Compositae were evaluated in a 4‐year field experiment in order to investigate their potential in terms of establishment and persistence in the re‐vegetation of an inactive sand quarry. Native species showed better performances than commercial varieties and encouraged further actions for the valorisation of local plant biodiversity. Among legumes, the best adapted species was the perennial Lotus cytisoides that showed high persistence in combination with other positive traits. A few annual species, that is, Melilotus indica, Trifolium subterraneum and Ornithopus sativus performed well and persisted until the end of the experiment. Among perennial grasses, Cynodon dactylon survived to drought and low soil nutrients. Both native annual grasses Lolium rigidum and Aegilops geniculata performed very well during the first 2 years of experiments. Both forbs, the perennial Cichorium intybus and the annual Chrysanthemum coronarium did not guarantee a satisfactory persistence. Some native species were evidenced, which may play an important role in the re‐vegetation of sand quarries and have good potential to be further characterized before introduction in the seed market. Copyright © 2013 John Wiley & Sons, Ltd.     

西红柿对聚烯烃控释肥这种新的施肥方法的反应

The response of tomato （Lycopersicon esculentum） plants basically fertilized with 0.3 g N per plant of compound fertilizer with a N：P2O5：K2O ratio of 20：10：20 to sticks of polyolefin-coated fertilizer （POCF） （LongT0 with a N：P2Os：K2O ratio of 14：12：14） applied 23 d after transplanting was investigated using rooting boxes in the greenhouse. The results at 26 and 40 d after stick fertilizer treatment showed that the use of the stick fertilizer greatly increased the production of many new fine roots from the tomato plants. Compared to the unfertilized control, root length and root length density in the stick fertilizer treatment increased by 3.6-6.7 fold. In the soil zones near the stick fertilizer, root weight and root mass density were also significantly higher for the stick fertilizer treatment. Additionally, the use of the stick fertilizer increased the N, P and K concentrations in the leaves and stems of the tomato plants. The new fine roots growing near the stick fertilizer not only absorbed more nutrients and translocated them to the shoots, but also contained more nutrients within themselves. The soil ammonium and nitrate N data showed that N released from the stick fertilizer played a major role in inducing the production of new fine roots. These results indicated that stick fertilizer could be used as an alternative to the co-situs application technique to change and control the root distribution of crops as well as to increase the potential capacity of roots for water and nutrient absorption.     

Suppression of decomposition of 14C-labelled plant roots in the presence of living roots of maize and perennial ryegrass

The rates of decomposition of barley roots labelled with ¹⁴C were investigated in soil planted with maize or perennial ryegrass and in fallow controls. Evolution of ¹⁴CO₂ was significantly less from the planted soils than from fallow controls. Roots of maize and ryegrass appeared to compete substantially with soil microbes for ¹⁴C-labelled materials. Simple competitive effects were, however, insufficient to explain all of the observed effects of root growth on soil organic matter decomposition. There was no indication that the detrimental effects of maize roots on aggregate stability could be associated with increased degradation of native soil organic materials; the broader significance of the results is also discussed.     

Determination of water-soluble and total extractable polyphenolics in biomass, necromass and decomposing plant material using near-infrared reflectance spectroscopy (NIRS)

Near infrared reflectance spectroscopy (NIRS) was used to predict the water-soluble and total extractable polyphenolics of plant material. Different life forms (forbs, grasses, shrubs, giant rosettes), organs (leaves, stems, roots) and decomposition stages (biomass, necromass and decomposing plant material) were studied. Prediction was good, with a R² in validation ranging from 0.91 to 0.93 and in prediction from 0.88 to 0.94. Various standard error ratios were used to assess the quality of the models, which are generally very good, being the model for predicting the water-soluble polyphenolics in the decomposing plant material the slightly less good. Because it is a cheap and rapid method, it would allow to perform a large screening for studies concerning (i) polyphenolics control on decomposition process and (ii) phenolics implication in herbivory.