Fate of 15N-fertilizers in the soil-plant system of a forage rotation under conservation and plough tillage.

The long-term effect of conventional plough tillage (PT) and conservation minimum tillage (MT) on soil N (0-5, 5-15, 15-30, 30-45 and 45-60 cm), recovery efficiency of 15N-fertilizer (REN), plant N concentration and N exported with crops was evaluated during two years in a 14-year-old ryegrass-maize forage rotation. Adjacent PT (n=9) and MT (n=9) plots were randomly assigned in triplicate to three treatments to which 15NH4 15NO3 (10 atom % 15N) was applied in one of the three first fertilizations (15NOctober-, 15NMarch- and 15NMay-fertilizer), the others being done with unlabelled N. Plant N concentration (% N) was affected (p ryegrass-2 (1.9 ± 0.4%) > maize-2 (1.4 ± 0.1 %) > maize-1 (1.1 ± 0.2 %)] and the crop-tillage interaction (22 % of variance explained). Jointly considering all data, more 15N-fertilizer was recovered in the MT (25 ± 4 %) than in the PT soil profile (19 ± 6 %) at the end of the experiment whereas the N exported with the crops was unaffected by the tillage system and varied from 5-6 % (15NOctober-fertilizer) to 45-49% (15NMarchfertilizer) and 52-53 % (15NMay-fertilizer; despite only three instead of four subsequent crops were studied).The 15N unaccounted for in the case of 15NOctober-fertilizer (72 ± 5 %) was more than twice that in 15NMarch- (34 ± 7 %) and 15NMay-fertilizer (25 ± 14 %). Considering soil, site and weather conditions, denitrification and nitrate leaching during the ryegrass-1 crop were the most likely processes explaining the high losses of the 15NOctober-fertilizer. Results suggested a higher initial immobilization of the applied 15N in the soil organic matter (SOM) of MT, that reduces 15N availability to the first crop, followed by an increase of the residual availability of the fertilizer 15N to the subsequent 2-3 crops.Peer reviewe

Relationships among main soil properties and three N availability indices.

A biological (aerobic incubation for 3 and 6 weeks) and a chemical method [successive extractions with cold 0.1 (H1-N) and 0.5 M HCl (H2-N)] were applied to 21 soils to determine: a) the potentially mineralizable-N; b) the most useful soil variables for predicting soil N availability; and c) their usefulness for predicting N uptake by a greenhouse wheat crop. At t=3, both net N mineralized (NNM) and net N mineralization rate (NNMR) were correlated: a) positively with SOM- and CEC-related variables; and b) positively with soil δ 15N and negatively with soil pH, suggesting that Nmineralization, dominated by nitrification, is associated with NO3 --N losses and soil acidification. At t=6, all previously discussed variables were important for NNM, but not for NNMR, mainly controlled by the available-P content. The importance of H1-N increased with N2-inputs and decreased with NO3 - losses and soil-N. Relationships of H1-N and H2-N with soil CEC and texture showed the strong relations among nutrients content, biological activity and N mineralization, as well as the recalcitrance of clay-bounded SOM. Soil total-N correlations with wheat-N in absolute amount (positive) and as percentage of soil-N (negative) showed an important supply of available-N by N-rich soils, despite their slow N turnover. The best regression models for wheat-N always included 1-2 main available nutrients. The percentage of soil N exported to plant biomass was negatively correlated with noncrystalline Al compounds and soil δ 15N. Mineralized-N and wheat-N pools did not share many correlations with soil properties and seemed to come from different sources; consequently, the former pool, which only explained a quarter of wheat-N variance, was not more useful than soil total-N for predicting it. Only a positive correlation with soil total-N was shared by wheat-N and hydrolysable-N, highlighting that the latter N pools are mainly unrelated. Nevertheless, half of wheat-N variation was explained by its negative relationship with the percentage of soil-N as (H1+H2)-N; a possible explanation is that chemically labile N is also biologically labile, being cumulated because of a limiting factor for microbial N mineralization or plant growth and emerging as a good predictor for wheat-N uptake.Peer reviewe

Effects of fire and three fire-fighting chemicals on main soil properties, plant nutrient content and vegetation growth and cover after 10 years.

The study addresses a knowledge-gap in the long-term ecological consequences of fire and fire-fighting chemicals. Ten years after a prescribed fire and the application of three fire-fighting chemicals, their effects on the soil-plant system were evaluated. Five treatments were established: unburnt soils (US) and burnt soils treated with water alone (BS), foaming agent (BS+Fo), Firesorb (BS+Fi) and ammonium polyphosphate (BS+Ap). Soils (0-2 cm depth) and foliar material of shrubs (Erica umbellata, Pterospartum tridentatum and Ulex micranthus) and trees (Pinus pinaster) were analysed for total N, 15N, and soil-available and plant total macronutrients and trace elements. Soil pH, NH4 +-N and NO3 --N; pine basal diameter and height; and shrub cover and height were also measured. Compared with US plots, burnt soils had less nitrates and more Mo. Although differences were not always significant, BS+Ap had the highest levels of soil available P, Na and Al. Plants from BS+Ap plots had higher values of 15N (P. pinaster and E. umbellata), P (all species), Na (P. tridentatum and U. micranthus) and Mg (E. umbellata and P. tridentatum) than other treatments; while K in plants from BS+Ap plots was the highest among treatments for P. pinaster and the lowest for the shrubs. Pines in US plots were higher and wider than in burnt treatments, except for BS+Ap, where the tallest and widest trees were found, although half of them were either death (the second highest mortality after BS+Fi) or had a distorted trunk. BS+Ap was the treatment with strongest effects on plants, showing E. umbellata the lowest coverage and height, P. tridentatum the highest coverage, U. micranthus one of the lowest coverages and being the only treatment where Genista triacanthos was absent. Consequently, it is concluded that both fire and ammonium polyphosphate application had significant effects on the soil-plant system after 10 years.Peer reviewe

Soil C and N dynamics in a Mediterranean oak woodland with shrub encroachment.

Background and aims Intensive land use has led to degradation and abandonment of Portuguese oak woodlands, and subsequent shrub encroachment may have altered the spatial heterogeneity of soil C and N pools. The aim of this study was to evaluate the effects of shrub invasion on soil C and N dynamics in an oak woodland in Southern Portugal.Peer reviewe

Extinguishment Agents

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Soil organic N dynamics and stand quality in Pinus radiata pinewoods of the temperate humid region.

Soil organic-N dynamics, its controlling factors and its relationships with stand quality were studied in the 0-15 cm soil layer of 24 pinewoods with contrasting age, productivity and parent material (granite; acid schists), searching for N variables useful to predict stand growth and site quality. No significant differences were found between young and old stands for any of the N variables considered, nor two- or three-order interactions among stand age, site quality and parent material. The soil total-N content, which was correlated positively with the Al oxides content [a soil organic matter (SOM) stabilizing agent], did not vary significantly according to parent material, but it was lower (P # 0.02) in stands with high than with low site index (2.68 ± 1.11 and 3.97 ± 1.13 g N kg-1 soil, respectively). The soil δ 15N ranged from +3.5 to +6.5 d, without significant differences among stand groups, and it was negatively correlated with water holding capacity, exchangeable bases, Al oxides and N content, suggesting that: i) N losses by NO3 - leaching are the most important controlling factor of δ 15N in these temperate humid region soils; and ii) soil N richness is related with limited N losses, which discriminate against 15N. At any incubation time, no significant differences were found in soil inorganic-N content among stand groups (7.78 ± 4.57, 39.33 ± 16.20 and 67.80 ± 26.50 mg N kg-1 soil at 0, 42 and 84 d, respectively). During the incubation, the relative importance of the ammonification decreased and that of the nitrification increased. The net N mineralization rate (NNMR, in % of organic N) was significantly higher in granite than in schists soils at both 42 d (1.24 ± 0.34 and 0.75 ± 0.37%, respectively) and 84 d (2.18 ± 0.56 and 1.53 ± 0.66%, respectively). In high quality pinewoods, the NNMR at 42 d and 84 d (1.16 ± 0.45 and 2.12 ± 0.79%, respectively) were significantly higher than in low quality stands (0.83 ± 0.35 and 1.59 ± 0.45%, respectively). This result, together with those on soil total-N and inorganic-N supply, suggests that soil N dynamics in low and high quality stands is different: in the former there is a bigger N pool with a slower turnover, whereas in the latter there is a smaller N pool with a faster turnover, both factors being nearly compensated, making similar the soil available N supply. After 42 and 84 d of incubation, the NNMR and the nitrification rate were higher in the coarse textured soils, likely due to the low physical and chemical protection of their SOM; both rates were positively correlated with available P, exchangeable K+ and CEC base saturation, suggesting strong relationships among the availabilities of the main plant nutrients, and they increased with SOM quality (low C-to-N ratio). The strong negative correlation of site index with soil total-N (r= - 0.707; P # 0.005), and its positive correlations with NNMR after 42 and 84 d of incubation, suggested that site quality and potential productivity are closely related to soil organic-N dynamics. Half of the site index variation in the stands studied could be predicted with a cheap and easy analysis of soil N content, the prediction being slightly improved if soil δ 15N is included and, more significantly, by including N mineralization measurements.This research was framed within the European Regional Development Fund (EU)-CICYT programme. The isotopic ratio mass spectrometer was partly financed by the European Regional Development Fund (EU).Peer reviewe

Efectos dos eucaliptos sobre os ecosistemas ibéricos: unha revisión

To establish the position and demands of the Galician Society of Natural History (SGHN, Sociedade Galega de Historia Natural) regarding eucalypt plantations, a bibliographic search was done on the allelopathy and invasivity of Eucalyptus, as well as on their effects on water, biodiversity, wildfires and soils. The search was done in the scientific publications included in the “Journal Citation Reports” with the keywords “eucalyptus” and “eucalypte(s)”, without time frame but, with a few exceptions, geographically restricted to the Iberian Peninsula. From the results obtained, SGHN considers that Eucalyptus globulus, and by appliyng the precautionary principle the other species of the genus, should be included in the Spanish catalog of invasive alien species. Moreover, SGHN also considers that Galician government must: a) forbid new Eucalyptus plantations; b) eradicate eucalyptes from all public domains; c) require the logging of all illegal Eucalyptus stands; d) promote eucalypte removal from the private properties within natural protected areas; and e) schedule a progressive reduction of the surface covered by Eucalyptus spp. to warrant their eradication within a realistic deadline.Para fixar a posición e as peticións da Sociedade Galega de Historia Natural (SGHN) en relación coas plantacións de eucaliptos, realizouse unha revisión bibliográfica sobre a súa alelopatía e invasividade, así como sobre os seus efectos na auga, a biodiversidade, os incendios e os solos. A búsqueda fíxose nas publicacións científicas incluidas no “Journal Citation Reports” coas palabras chave “eucalyptus” e “eucalypte(s)”, sen límite temporal pero, agás excepcións, restrinxida ao ámbito da Península Ibérica. En base aos resultados obtidos, SGHN considera que Eucalyptus globulus, e polo criterio de precaución as restantes especies do xénero, deberían incluirse no catálogo español de especies invasoras. SGHN considera asimesmo que se deberían: a) prohibir novas plantacións de eucaliptos en toda Galicia; b) eliminar os eucaliptos en todos os terreos de propiedade pública; c) eliminar todas as plantacións de eucaliptos feitas sen axustarse á normativa legal vixente; d) incentivar a eliminación de todos os eucaliptos nos espazos naturais protexidos; e) planificar unha redución progresiva das plantacións de eucalipto para garantir a súa erradicación nun horizonte temporal realista

Effects of biotic and abiotic factors on 15N in young Pinus radiata

In a 12-year-old Pinus radiata plantation, three dominant and three suppressed trees removed by thinning were randomly selected, and needles, annual rings from basal stem disks and bark were collected and analysed to study the relationships of climate, tree age, dominance and growth with tree 15N. The high foliar-N concentration (1.35-2.73 % N, dw) suggested that N was not limiting tree growth, therefore allowing plants to fractionate versus 15N, leading to differences in 15N among trees. Most wood 15Nair values were below the 15Nair natural abundance in the dominant pines (-2.43 to +1.69 ‰) and above it in the suppressed trees (+0.73 to +3.35 ‰), likely due to the access of dominants to exogenous N sources with lower 15Nair than those of suppressed. However, no dominance effect was detected in 15Nair of bark and needles that decreased in the order: buds (+1.20 to +2.44 ‰) > needles 1-year (-0.27 to +1.43 ‰) > needles 2-years (-0.97 to +0.41 ‰) > bark (-1.18 to +0.15 ‰). Compared with the soil N in the 0-15 cm layer (15Nair= +4.8 ‰), all plant material was 15N-depleted. Results suggest that seedlings and foliar buds have a less efficient system for N conservation and recycling, with higher losses. The linear regression models showed that both biotic (dominance and tree age) and abiotic factors (temperature in spring-summer and annual precipitation) are needed to explain the wood 15Nair satisfactorily.Peer reviewe

Short -and medium- term effects on fire and fire fighting chemicals on soil micronutrient availability.

The impact of fire and three fire-fighting chemicals (FFC) on soil micronutrient availability was evaluated 1, 90 and 365 days after a prescribed fire. Five treatments were considered: unburnt soil (US) and burnt soil with 2 l m-2 of water (BS) or water with foaming agent Auxquímica RFC-88 at 1% (BS+Fo), Firesorb at 1.5% (BS+Fi) and FR-Cross ammonium polyphosphate at 20% (BS+Ap). Prefire contents of available micronutrient were homogeneous among plots and high (Fe, Zn) or insufficient (Co, Cu, Mn) for plant nutrition. At t=1 day, Fe availability decreased greatly in burnt treatments, with significant differences in BS+Fi (-50%) and BS+Ap (-75%), contrasting with Fe richness of the ammonium polyphosphate. The fire induced a significant increase (9-16x) of available Mn in burnt treatments that lasted for at least three months; the FFC effect on soil available Mn was imperceptible, despite the noticeable amounts of Mn they supplied (especially Firesorb and ammonium polyphosphate). In burnt soils, the Fe/Mn ratio also decreased strongly (92-99%) and significantly till t=90 days. A high increase was also found, at t=1 day, for the available Zn in all burnt treatments and, although the ammonium polyphosphate provided more Zn than the Firesorb, the increment was only significant in BS+Fi plots (+100%). Neither fire nor FFC effects on soil Cu availability were found. The slight increase of Co availability in BS, BS+Fo and BS+Ap at t=1 day was followed by a transient decrease in all burnt treatments at t=90 days. Except the Mn and the Fe/Mn ratio in BS+Ap, which remained significantly higher and lower, respectively, the indices of available micronutrients at t=365 days in all burnt soils were similar to the pre-fire levels.This research was supported by the Spanish Ministery of Education and Science through the project number AGL2001-1242-C04-01.Peer reviewe

Short- and medium-term effects of three fire fighting chemicals on the properties of a burnt soil

Final version of the paper available at: http://www.sciencedirect.com/science/journal/00489697The impact of three fire fighting chemicals (FFC) on 11 chemical soil properties and on soil recovery (0–2 cm depth) was evaluated 1, 30, 90 and 365 days after a prescribed fire. Five treatments were considered: unburnt soil (US) and burnt soil with 2 l m−2 of water alone (BS) or mixed with the foaming agent Auxquímica RFC-88 at 1% (BS + Fo), Firesorb at 1.5% (BS + Fi) and FR Cross ammonium polyphosphate at 20% (BS + Ap). At t = 1 day, soil pH increases in the order US < BS ≤ BS + Fo, BS + Fi < BS + Ap, which was most likely due to the accumulation of ashes, the reduction of organic acids and the cations supplied by FFC. In all burnt treatments, soil pH remained significantly higher than in US up until t = 90 days. SOM richness remained similar and constant until t = 90 days in all plots, but, probably due to fire-triggered erosion, at t = 365 days it was significantly lower in BS + Ap (C, N), BS and BS + Fo (C) than in US. Immediately after the fire, soil δ15N decreased in all burnt soils (significatively in BS + Ap) due to the inputs of 15N depleted ashes from leguminous vegetation. Compared with US, soil δ15N increased significantly in all burnt plots between t = 90 days (30 days in BS + Ap) and t = 365 days, suggesting a medium-term fire-triggered increment of N outputs (15N depleted). As is habitually the case, there was a transient post-fire increase of NH4+–N levels (significative for BS + FFC plots) that lasted for 30 (BS, BS + Fo and BS + Fi) to 90 days (BS + Ap). The high initial NH4+–N levels in BS + Ap (200× that of US; 9–18× those of BS, BS + Fo and BS + Fi), and its persistence can delay the post-fire vegetation recovery due to the toxicity of NH4+ to seeds and seedlings. NO3–N levels changed significantly only in BS + Ap between t = 30 and t = 90 days due to the nitrification of its large NH4+–N pool. Except in BS + Ap, whose soil P levels were 70–140× (t = 1 days) and 10–20× (t = 365 days) higher than in the other treatments, available P content in BS and BS + FFC was not significatively higher than in US. The concentrations of available cations in BS and BS + FFC were higher (not always significatively, except for K) than in US until t = 90 days, likely due to ashes- and FFC-derived cations. Contrarily to divalent cations, monovalent cations (more soluble and easily leached) decreased slowly until t = 90 days.This research was supported by the Spanish Ministery of Education and Science through the project number AGL2001-1242-C04-01. The participation of A. Couto in this research was supported by a CSIC-Xunta de Galicia fellowship. The isotopic ratio mass spectrometer was partly financed by the European Regional Development Fund (EU).Peer reviewe