Tropical Ferralsol Research Articles

Soil Fertility, Physiological Traits, and Fruit Quality of Morinda citrifolia as Influenced by Agroecological Management Practices in a Tropical Ferralsol

Soil Fertility, Physiological Traits, and Fruit Quality of Morinda citrifolia as Influenced by Agroecological Management Practices in a Tropical Ferralsol

Nitrogen fertilization and liming increased CO2 and N2O emissions from tropical ferralsols, but not from a vertisol

AbstractThe application of nitrogen (N) fertilizers and liming (CaCO3) to improve soil quality and crop productivity are regarded as effective and important agricultural practices. However, they may increase greenhouse gas (GHG) emissions. There is limited information on the GHG emissions of tropical soils, specifically when liming is combined with N fertilization. We therefore conducted a full factorial laboratory incubation experiment to investigate how N fertilizer (0 kg N ha−1, 12.5 kg N ha−1 and 50 kg N ha−1) and liming (target pH = 6.5) affect GHG emissions and soil N availability. We focussed on three common acidic soils (two ferralsols and one vertisol) from Lake Victoria (Kenya). After 8 weeks, the most significant increase in cumulative carbon dioxide (CO2) and nitrous oxide (N2O) fluxes compared with the unfertilized control was found for the two ferralsols in the N + lime treatment, with five to six times higher CO2 fluxes than the control. The δ13C signature of soil‐emitted CO2 revealed that for the ferralsols, liming (i.e. the addition of CaCO3) was the dominant source of CO2, followed by urea (N fertilization), whereas no significant effect of liming or of N fertilization on CO2 flux was found for the vertisol. In addition, the N2O fluxes were most significantly increased by the high N + lime treatment in the two ferralsols, with four times and 13 times greater N2O flux than that of the control. No treatment effects on N2O fluxes were observed for the vertisol. Liming in combination with N fertilization significantly increased the final nitrate content by 14.5%–39% compared with N fertilization alone in all treatment combinations and soils. We conclude that consideration should be given to the GHG budgets of agricultural ferralsols since liming is associated with high liming‐induced CO2 and N2O emissions. Therefore, nature‐based and sustainable sources should be explored as an alternative to liming in order to manage the pH and the associated fertility of acidic tropical soils.

Implications of ecological parameters on earthworm diversity and abundance in southwestern Nigeria

A survey on the diversity and abundance of earthworms in southwestern Nigeria was carried out. Earthworm and soil samples were collected from thirty different locations within the sub-region. Earthworms were identified and soil samples were analysed for mineral and metal loads, using standard procedures. Taxonomic analysis of collected earthworm samples revealed 24 species belonging to eight families namely Moniligastridae, Megascolecidae, Acanthodrilidae, Octochaetidae, Ocnerodrilidae, Eudrilidae and Almidae. These include some genera and species that are reported for the first time from Nigeria. Analysis of earthworm biomass showed that Libyodrilus violaceus had the highest biomass (104.4g/m2) while Hyperiodrilus africanus had the highest density (160 worms/m2). Earthworm biomass correlated negatively but significantly with pH (p<0.01). Analysis of earthworm abundance in relation to soil types indicates that E. eugeniae was present in all seven soil types studied, while only Alma millsoni and H. lagosensis can be used as indicators of ferruginous tropical soils and red-yellow ferralsols. Earthworms from this study revealed affinity for various combinations of sand and loam soils. The present results revealed a decline in earthworm abundance when compared with previous works. This work revealed the need to harness the habitat factors, which support earthworm abundance for use in both earthworm and soil conservation efforts.

Erratum zu: Wirkung von Phosphor und arbuskulären Mykorrhizapilzen (AMF) auf Wachstum und Produktivität von Mais (Zea mays L.) in einem tropischen Ferralsol

Erratum zu: Wirkung von Phosphor und arbuskulären Mykorrhizapilzen (AMF) auf Wachstum und Produktivität von Mais (Zea mays L.) in einem tropischen Ferralsol

Relative Suitability of Phosphorus Extraction Procedures for F Tropical Ferralsol

Purpose: To evaluate the predictive capacity common procedures for soil P extraction and testing in laboratories in the region.
 Materials and Methods: A pot study with treatments viz. soil phosphorus extraction methods (Bray I, Bray II and Mehlich 3), and six P application rates (0, 20, 40, 60, 80 and 100 kg P ha-1). Maize (Zea mays L.) variety Longe IV was the test crop. A Ferralsol from northwestern Uganda (West Nile) was used in this study.
 Results and Conclusion: Mehlich 3 correlated most with plant P uptake by presenting the highest correlation coefficient with plant P content (r = 0.254) and a number of leaves per plant (r = 0.733). A strong positive correlation existed between Bray I and Mehlich 3 extractable P values (r = 0.975), suggesting lack of a marked difference between them; implying that either of the two procedures could be applied for soil P extraction in Ferralsols. However, Mehlich 3, being a multi-nutrient extractant, was recommended as the most suitable for P extraction for the Ferralsol used in this study.

Multiple-nutrient limitation of upland rainfed rice in ferralsols: a greenhouse nutrient-omission trial

To optimize the nutrient management of upland rice production on tropical ferralsols, a greenhouse experiment was established using the multi-nutrient omission approach. A reciprocal soil origin-rice cultivar transplant experiment was also conducted to better understand the relative contributions of the soil origin and the rice cultivar in rice nutrient limitation. We tested the deficiency of seven major and secondary nutrients [nitrogen (N), phosphorus (P), potassium (K), sulfur (S), calcium (Ca), magnesium (Mg), and silicon (Si)] and a solution of six micronutrients (B, Mn, Cu, Co, Na, Mo) likely to limit the growth of two upland rice cultivars, Chhomrong Dan and Nerica 4, on two Ferralsols from the highlands of Madagascar. We found severe multiple nutrient deficiencies. For both cultivars, P, Ca, N, Mg omission significantly depressed the shoot and root dry biomass and their amounts in plant tissues. However, the main limiting nutrients were not the same in both soils. We conclude that the multinutrient deficiencies observed for rice growth in the Ferralsols are site-specific, even though P limitation appears to be in common, and requires a holistic consideration of the mineral fertility, including micronutrients.

Tropical forest structure and understorey determine subsurface flow through biopores formed by plant roots

Erosion and mass wasting processes on mountain slopes can benefit from or be adversely affected by the presence of biopores formed by plant root systems or soil fauna. The relationship between biopores and subsurface flow during rainstorms is poorly understood. Here, we examined the link between subsurface flow and biopores formed through different processes, including soil faunal activity and abundance of fine and coarse roots. As the distribution of biopores is influenced by the type of vegetation present, we investigated the effect of plant diversity (forest with or without understorey vegetation) on the pattern of water infiltration throughout the soil. We hypothesized that increased species diversity would enhance the extension of subsurface flow because biopores would be distributed throughout the soil profile and that more coarse roots would create large biopores, increasing subsurface flow. In situ experiments were conducted on hillslopes with plantations of rubber trees (Hevea brasiliensis) growing on terraces, or with secondary mixed forests, in the tropical zone of Yunnan province, China. Three sites with Ferralsol soils and different vegetation types were examined: (1) plantation with no understorey; (2) clear-cut plantation with understorey; and (3) secondary mixed forest with understorey. Irrigation experiments with Brilliant Blue FCF dyed water were performed upslope of trees at each site and staining patterns resulting from infiltrated dyed water were examined at two different scales. After dye irrigation, soil was removed in 1.0 × 0.8 m slices starting 1 m downslope and soil profiles were photographed for subsequent mapping of dyed areas in the profile (macroscale). Each profile was then divided into a 0.1 × 0.1 m grid (microscale) and burrows formed by macrofauna and fine and coarse root densities were measured. At the macroscale, the greatest lateral extension in subsurface flow occurred in the natural forest and the least in the rubber tree plantation with no understorey vegetation. At the microscale, and in all types of vegetation, fine roots significantly increased the incidence of subsurface flow compared to coarse roots and macrofauna activity. We conclude that in tropical Ferralsols, fine roots, and hence understorey vegetation, play a positive role in promoting subsurface flow and therefore reducing water erosion and mass wasting processes. Thus, planting mixtures that include a diversity of species and strata could significantly improve soil conservation.

How do methane rates vary with soil moisture and compaction, N compound and rate, and dung addition in a tropical soil?

Soil moisture and compaction, and source of N and bovine urine can reduce methane (CH4) rates from agricultural soils. However, the magnitude of the effect is unknown in tropical soil under different conditions, as well as the potential of different urine-N concentration, volume, and sources of N in such an effect. This study aimed to investigate the effects of different soil conditions (moist, dry, compacted, moist-dung, moist-dung-compacted), N concentration in urine (2.5, 5.0, 10.0, and 15.0g N L-1), volume of urine (25, 50, 100, and 200mlkg-1 dry soil), and source of N (ammonium, nitrate, and urea) on CH4 emissions. A tropical Ferralsol soil from marandu-grass pasture was incubated during 106days and the CH4 concentration determined by gas chromatography. The CH4 rates varied significantly according to the soil conditions when manipulated the urine-N (p < 0.01) and averaged 0.75, - 0.50, 1.14, 6.23, and 8.17μg C-CH4 m-2h-1for the moist, dry, compacted, moist-dung, and moist-dung-compacted soil, respectively, and, not responded to the level of N (p = 0.73) averaging 2.57μg C-CH4 m-2h-1. When evaluated, the volumes of urine cumulative CH4 averages were - 0.52, - 1.24, - 0.88, 14.48, and 18.56μg C-CH4 m-2h-1 for the moist, dry, compacted, moist-dung, and moist-dung-compacted, respectively. Soils were affected by soil treatments (p < 0.001) but not by urine volumes (p = 0.30). The source of N did not influence the CH4 rates (p = 0.1) averaging 0.88, - 1.26, and - 1.19μg C-CH4 m-2h-1 respectively, for urea, nitrate, and ammonium. The CH4 fluxes in tropical Ferralsols are controlled by the soil characteristics and dung addition.

Rapid and irreversible sorption behavior of 7Be assessed to evaluate its use as a catchment sediment tracer

Beryllium-7 (7Be) has been used as a sediment tracer to evaluate soil redistribution rates at hillslopes and as a tool to estimate sediment residence time in river systems. A key assumption for the use of 7Be as a sediment tracer is the rapid and irreversible sorption of 7Be upon contact with the soil particles. However, recent studies have raised questions about the validity of these assumptions. Seven soil types were selected to assess the adsorption rate of 7Be on the soil particles, subsequently an extraction experiment was performed to assess the rate of desorption. Next, different treatments were applied to assess the impact of soil pH, fertilizer, humic acid and organic matter on the adsorption of Be. Finally, the influence of regularly occurring cations present on the soil complex on the adsorption of Be on pure clay minerals was evaluated. The adsorption rate experiment showed a rapid and nearly complete sorption of Be for Luvisols and Cambisols under agriculture. For a temperate climate Stagnosol under forest and two highly weathered tropical Ferralsols sorption of Be was less rapid and less complete. This may result in an incomplete adsorption of 7Be on these three soils when runoff initiates, which could lead to an overestimation of erosion rates and sediment residence time. Additional observations were made during the extraction experiment, showing a significant loss of Be from the forest Stagnosol and a stable binding of Be to the arable soils. Of the different treatments applied, only pH showed to be of influence. Finally, Ca2+ and NH4+ on the soil complex had only a limited effect on the adsorption of Be, while Al3+ in combination with a low pH inhibits the adsorption of Be on the exchange complex of the pure clay minerals. All these findings more rigorously support the use of 7Be as a soil redistribution tracer in arable soils in a temperate climate at a hillslope scale. The use of 7Be in highly weathered Ferralsols or forest rich environments should be limited to avoid overestimations of erosion rates. The spatially extended use of 7Be to evaluate residence times of sediments should be avoided in catchments with rapid changing environmental parameters as they might influence the sorption behavior of 7Be.

Effects of soil type and rainfall intensity on sheet erosion processes and sediment characteristics along the climatic gradient in central-south China

Soil erosion poses a major threat to the sustainability of natural ecosystems. The main objective of this study was to investigate the effects of soil type and rainfall intensity on sheet erosion processes (hydrological, erosional processes and sediment characteristics) from temperate to tropical climate. Field plot experiments were conducted under pre-wetted bare fallow condition for five soil types (two Luvisols, an Alisol, an Acrisol and a Ferralsol) with heavy textures (silty clay loam, silty clay and clay) derived separately from loess deposits, quaternary red clays and basalt in central-south China. Rainfall simulations were performed at two rainfall intensities (45 and 90mmh−1) and lasted one hour after runoff generation. Runoff coefficient, sediment concentration, sediment yield rate and sediment effective size distribution were determined at 3-min intervals. Runoff temporal variations were similar at the high rainfall intensity, but exhibited a remarkable difference at the low rainfall intensity among soil types except for tropical Ferralsol. Illite was positively correlated with runoff coefficient (p<0.05). Rainfall intensity significantly contributed to the erosional process (p<0.001). Sediment concentration and yield rate were the smallest for the tropical Ferralsol and sediment concentration was the largest for the temperate Luvisol. The regimes (transport and detachment) limiting erosion varied under the interaction of rainfall characteristics (intensity and duration) and soil types, with amorphous iron oxides and bulk density jointly enhancing soil resistance to erosive forces (Adj-R2>88%, p<0.001). Sediment size was dominated by <0.1mm size fraction for the Luvisols and bimodally distributed with the peaks at <0.1mm and 1–0.5mm size for the other soil types. Exchangeable sodium decreased sediment size while rainfall intensity and clay content increased it (Adj-R2=96%, p<0.01). These results allow to better understand the climate effect on erosion processes at the spatial-temporal scale from the perspective of soil properties.

Impact of plant root functional traits and associated mycorrhizas on the aggregate stability of a tropical Ferralsol

In many tropical regions, such as New Caledonia, soil erosion from anthropogenic activities and subsequent ecological restoration are major issues that require detailed soil and vegetation data for the production of management plans. To determine if some plant species are more useful for stabilizing soil aggregates and thus reducing erodibility, we examined three species endemic to New Caledonia, and measured how root traits and associated mycorrhizas and fungi influenced Ferralsol aggregate stability (MWD). The three species are hosts to different types of mycorrhizas and were: (i) the sedge Costularia arundinacea (Sol. Ex Vahl) Kük., an AMF (arbuscular mycorrhizal fungi) host, (ii) the shrub Tristaniopsis glauca Brongn. & Gris and (iii) the tree Arillastrum gummiferum (Pancher ex Brongn. & Gris) Baill., both of the latter are ectomycorrhizal fungi (ECM) hosts. Fungal abundance, aggregate stability, soil organic carbon (SOC), iron (Fe) and aluminium (Al) sesquioxides were measured in the soil beneath 20 individuals for each species, as well as in 20 control samples of bare soil. Root functional traits including root mass density (RMD), root length density (RLD) and percentage of fine roots were measured on all individuals. Results showed that plant species can significantly influence soil aggregate stability. MWD was greater in soil beneath Costularia characterized by high RMD, RLD, percentage of fine roots and fungal abundance, while MWD in the rhizosphere of Tristaniopsis and Arillastrum was similar to that of bare soil. Fe and Al were very high in all soil samples and are suspected of masking the influence of roots, fungi and SOC on MWD at the scale of isolated ECM-hosts. Therefore, MWD alone would not be a relevant predictor of restoration on such soil and further investigations should be carried out to identify a set of predictors useful for indicating the restoration of degraded soils on ultramafic substrates.

N2O emissions from urine-treated tropical soil: Effects of soil moisture and compaction, urine composition, and dung addition

Increasing attention is being paid to the importance of N2O emissions due to livestock activities in tropical countries. Understanding the key variables driving N2O emission could help minimize impacts of N2O release and improve the accuracy of N2O inventories. We aimed to investigate the effects of soil moisture, soil compaction, urine composition, urine volume, and dung addition on N2O emissions from a urine-treated tropical Ferralsol under controlled conditions. Manipulated soil conditions (e.g., moisture content, compaction, and dung addition) affected N2O emissions when varying quantities of urine-N (p=0.02) were applied (urine volumes remained equal) and when varying urine volumes (p=0.04) were applied (quantities of urine-N remained equal). When the amount of urine-N applied was varied, the estimated N2O emission factor (EF) was 3.14±0.70%, 2.29±1.25%, 3.90±0.64%, 4.73±0.88%, and 6.62±1.10% for moist soil, dry soil, compacted soil, plus dung, and plus dung and compacted soil treatments, respectively. While varying the volume of urine, the estimated N2O EF was 4.96±1.66%, 4.27±1.42%, 3.99±1.19%, 6.50±0.35%, and 7.37±0.76% for moist, dry soil, compacted soil, plus dung, and plus dung and compacted soils treatments, respectively. The urine-N concentration influenced N2O emissions (p=0.02) [which decreased linearly (p=0.062)] as well the volume of urine (p<0.01) [which increased linearly (p<0.01)]. The chemical form of the applied urine-N (urea, nitrate, or ammonium) did not affect N2O emissions and the emissions factor averaged 1.40±0.38%. N2O production was affected by the KCl concentration in the urine (p<0.01), and the effect was curvilinear. The key driving factor affecting N2O emissions was soil moisture content. The N2O response varied when the urine volume differed (in both moist and dry soil conditions), and with the addition of dung.

Benefits of biochar, compost and biochar–compost for soil quality, maize yield and greenhouse gas emissions in a tropical agricultural soil

Soil quality decline represents a significant constraint on the productivity and sustainability of agriculture in the tropics. In this study, the influence of biochar, compost and mixtures of the two on soil fertility, maize yield and greenhouse gas (GHG) emissions was investigated in a tropical Ferralsol. The treatments were: 1) control with business as usual fertilizer (F); 2) 10tha−1 biochar (B)+F; 3) 25tha−1 compost (Com)+F; 4) 2.5tha−1 B+25tha−1 Com mixed on site+F; and 5) 25tha−1 co-composted biochar–compost (COMBI)+F. Total aboveground biomass and maize yield were significantly improved relative to the control for all organic amendments, with increases in grain yield between 10 and 29%. Some plant parameters such as leaf chlorophyll were significantly increased by the organic treatments. Significant differences were observed among treatments for the δ15N and δ13C contents of kernels. Soil physicochemical properties including soil water content (SWC), total soil organic carbon (SOC), total nitrogen (N), available phosphorus (P), nitrate-nitrogen (NO3−N), ammonium-nitrogen (NH4+-N), exchangeable cations and cation exchange capacity (CEC) were significantly increased by the organic amendments. Maize grain yield was correlated positively with total biomass, leaf chlorophyll, foliar N and P content, SOC and SWC. Emissions of CO2 and N2O were higher from the organic-amended soils than from the fertilizer-only control. However, N2O emissions generally decreased over time for all treatments and emission from the biochar was lower compared to other treatments. Our study concludes that the biochar and biochar–compost-based soil management approaches can improve SOC, soil nutrient status and SWC, and maize yield and may help mitigate greenhouse gas emissions in certain systems.

Biochar and biochar-compost as soil amendments: Effects on peanut yield, soil properties and greenhouse gas emissions in tropical North Queensland, Australia

This study investigated the effects of biochar and compost, applied individually or together, on soil fertility, peanut yield and greenhouse gas (GHG) emissions on a Ferralsol in north Queensland, Australia. The treatments were (1) inorganic fertilizer only (F) as a control; (2) 10tha−1 biochar+F (B+F); (3) 25t compost+F (Com+F)ha−1; (4) 2.5t Bha−1+25t Comha−1 mixed on site+F; and (5) 25tha−1 co-composted biochar-compost+F (COMBI+F). Application of B and COMBI increased seed yield by 23% and 24%, respectively. Biochar, compost and their mixtures significantly improved plant nutrient availability and use, which appeared critical in improving peanut performance. Soil organic carbon (SOC) increased from 0.93% (F only) to 1.25% (B amended), soil water content (SWC) from 18% (F only) to over 23% (B amended) and CEC from 8.9cmol(+)/kg (F only) to over 10.3cmol(+)/kg (organic amended). Peanut yield was significantly positively correlated with leaf chlorophyll content, nodulation number (NN), leaf nutrient concentration, SOC and SWC for the organic amendments. Fluxes of CO2 were highest for the F treatment and lowest for the COMBI treatment, whereas N2O flux was highest for the F treatment and all organic amended plots reduced N2O flux relative to the control. Principal component analysis indicates that 24 out of 30 characters in the first principal component (PRIN1) individually contributed substantial effects to the total variation between the treatments. Our study concludes that applications of B, Com, B+Com or COMBI have strong potential to, over time, improve SOC, SWC, soil nutrient status, peanut yield and abate GHG fluxes on tropical Ferralsols.

Shift in C and N humification during legume litter decomposition in an acid tropical Ferralsol

Several long-term studies on tropical soils have shown that legume residue incorporation increases soil nitrogen (N) sequestration more than that of carbon (C), resulting in a fall in the C/N ratio. This study was designed to assess the short-term effect of legume litter addition on N supply and the long-term effect on soil organic matter (SOM) formation and soil C/N decrease. The long-term effect was evaluated in a 2-year mesocosm experiment with high and frequent organic inputs from two types of legume litter with different C/N ratios, using stable isotope techniques. The short-term effect of litter was analysed using four different litters in 3-month laboratory incubations. A model of litter decomposition was used to describe C and N kinetics in the laboratory experiment and to verify whether the long-term effect of litter may be predicted from short-term incubations. The results of the mesocosm experiment confirmed that legume inputs increased soil organic N (mean +21%) more than organic C (mean +15%) (P = 0.05). Although no differences between litters were observed for C dynamics, N sequestration (14% and 28%) and the final soil C/N (12.0 and 10.8) varied with litter C/N (34.4 and 16.1, respectively). The laboratory experiment and model outputs confirmed these findings and indicated that the higher N sequestration was due to a change in the parameters describing humification of C and N coming from litter. This change depended on litter quality and was greater for litters with low C/N—C humification 0.66 g C g–1 C and N humification 0.76 g N g–1 N for litter C/N 16.1. Carbon and N sequestration were greater in the laboratory experiment, due to a higher mineralisation of the new SOM derived from litter in the mesocosm experiment—32% and 15% for the mesocosm and the laboratory experiments, respectively. Our results indicated that the decrease in soil C/N and the rapid mineralisation of new SOM should be considered in models of litter decomposition to respond correctly to the long- and the short-term effects of legume litter inputs in tropical soils.

Effects of Tillage and Crop Residue Application on Soybean Nitrogen Fixation in a Tropical Ferralsol

This study was aimed at quantifying soybean (Glycine max) nitrogen fixation under reduced tillage (RT) and conventional tillage (CT) in a tropical Ferralsol of the sub-humid zone of western Kenya, using the isotope 15N dilution method. Crop residue (CR) management was a superimposed treatment in soybean-maize rotation and intercropping systems. This study quantified N in abscised soybean leaves. Soybean-N derived from the atmosphere (%NDfA) ranged between 41–65%; it was higher (P &lt; 0.05) in RT (55.6%) than in CT (46.6%). Total fixed-N under ‘RT + CR’ was more than in the other treatments by at least 55% in intercropping and 34% in rotation system. Nitrogen fixed in soybean aboveground parts was 26–48 kg N ha−1 with intercropping and 53–82 kg N ha−1 with rotation. Seasonal litter fall contained about 15 kg N ha−1, with 54% NDfA. Annual nitrogen balances with soybean and maize grain removed were better in RT (−9 to −32 kg N ha−1) than in CT (−40 to −60 kg N ha−1). Application of P increased nodule weight (P &lt; 0.05) by 3 to 16 times over the control. Soybean residues should be returned to the field after harvest to reduce soil N mining. We conclude that ‘RT + CR’ increases biological nitrogen fixation in soybean, over CT, and that phosphorus application is needed for better soybean nodulation in western Kenya.

Effect of the endogeic earthworm Pontoscolex corethrurus on the microbial structure and activity related to CO 2 and N 2O fluxes from a tropical soil (Madagascar)

The objective of this laboratory study was to determine the influence of a tropical endogeic earthworm, Pontoscolex corethrurus, on CO 2 and N 2O fluxes from a tropical Ferralsol and microorganisms potentially involved in these gases emissions. CO 2 and N 2O fluxes were measured during 35 days from soil mesocosms with and without earthworms. At the end of the incubation, 7% of soil was egested as cast in the earthworm treatment. Then, casts which may be aged from few hours to 35 days old were isolated from non-ingested soil. Different descriptive parameters (activity, density, and structure) of the microbial communities were investigated in the control, the non-ingested soils, and the casts. Quantitative PCR of denitrification genes encoding the nitrite ( nirK) and nitrous oxide ( nosZ) reductases was used to study denitrifier density in the earthworm casts. The presence of P. corethrurus induced a significant increase in CO 2 emissions but did not affect N 2O fluxes when measured at mesocosm level. Despite the absence of significant differences in C and N contents between soils and casts, the near infra-red spectra analysis clearly underlined a specific organic signature for the casts. Fungal and bacterial biomass significantly decreased (∼2-fold) in casts compared to parent soil, but the fungal-to-bacterial ratio was not modified by the earthworm casting activity. Data suggested that bacterial communities, especially denitrifiers, were modified in casts. The relative abundance of nirK and nosZ genes increased in the casts while the genetic structures of total bacteria and denitrifying communities were slightly modified in the casts. This study highlighted the importance of earthworm casts as a specific soil habitat where a subset of soil functional bacterial communities (such as denitrifiers) found favourable condition for their growth. However the effect of P. corethrurus was less evident when up-scaling from casts to mesocosm level.

Land Application of Wastewater in Brazil - A scientific challenge: Chemical Characterization of Soil at Populina, São Paulo State (9 pp)

Background, Aims and Scope The rapid increase of wastewater worldwide and the consequently urgently needed treatment measures towards disposal purposes has led to an expansion of alternative treatment methods. Besides conventional and cost intensive systems, domestic wastewater treatment by overland flow process represents an effective and low-cost alternative. However, in addition to beneficial elements in wastewaters, there is a release of other elements of the Periodic Table into the environment, which can be considered as potentially toxic. This requires a reliable chemical characterization of the wastewater element composition as well as the soils onto which it will be applied. This paper aims at presenting the chemical fingerprint methodology to characterize concentrations of a large set of elements in a tropical ferralsol in order to provide information concerning chemical modifications after long-term application of wastewater by overland flow process. The results are also used to estimate environmental implications according to guiding values for soils in Sao Paulo State.

Iron nutrition in plants: A world overview

Abstract Fe‐deficiency chlorosis has been recognized since 1844 (Gris) and was the first plant nutrient deficiency to be investigated. It is a reflection of the continuing importance of iron nutrition problems in major crops worldwide that anybody interested in any aspect of plant nutrition cannot but be aware of them, whether as Fe‐deficiency or Fe‐toxicity. This paper does not purport to be a review, but rather attempts to sketch in the dimensions of the problem. Iron, as the element, is seldom deficient as it comprises 4.2% of the earth's crust, the fourth most abundant element, and commonly occurs as 2–6% Fe203 in temperate soils, increasing to as much as 60% Fe2O3 for certain tropical Ferralsols (Bould, 1963). Therefore, iron deficiency and toxicity are functions of the whole soil system and its effect on the availability of iron to the plant, and an understanding of this is essential to an appreciation of the problems.