Typic Haplustept Research Articles

Effect of induced defoliation in pigeonpea, farmyard manure and sulphitation pressmud on soil organic carbon fractions, mineral nitrogen and crop yields in a pigeonpea–wheat cropping system

Soils of the Indo-Gangetic Plain (IGP) region are inherently low in organic matter and N contents, hence studying changes in these parameters consequent to nutrient management practices is of great significance with the viewpoint of sustaining agricultural productivity. We, therefore, studied the effects of fertilizer NPK applied alone or in combination with organic inputs of varying nature and composition on soil organic carbon (SOC) fractions and mineral-N under the pigeonpea (Cajanus cajan L. Millsp.)–wheat (Triticum aestivum L.) cropping system on a Typic Haplustept at the Indian Agricultural Research Institute, New Delhi. The organic inputs included farmyard manure (FYM), sulphitation pressmud (SPM), and induced defoliation (ID) imposed by foliar spray of urea solution (10%, w/v) on pigeonpea at physiological maturity. The total organic carbon (TOC) and its different fractions, and mineral-N (NH4-N and NO3-N) in 0–15cm soil layer increased significantly with conjoint use of fertilizers and organics compared with fertilizers alone, but the extent of increase differed in accordance with the nature of organic inputs. Compared with fertilizer NPK, IPNS involving FYM or SPM brought greater increase in Walkley-Black C (WBC), particulate organic C (POC) and TOC, whereas the magnitude of increase in microbial biomass C (MBC) and labile C (LBC) over NPK was greater under ID treatments. Contribution of WBC, MBC and LBC towards TOC across the treatments was in the range of 17–22%, 1.0–1.8% and 6.7–11.8%, respectively. Fractionation of oxidizable organic C into different lability pools helped detecting even smaller changes in SOC due to nutrient management. Different SOC fractions were significantly correlated with each other, and also with mineral-N and crop yields. Grain yields of pigeonpea and wheat were significantly (p<0.05) greater in the treatments that received FYM, SPM or ID along with NPK, compared to sole NPK treatments. Yields with organics (FYM or SPM) alone were, however, invariably smaller than those obtained with fertilizer NPK.

Characterization and Classification of Soils on an Agricultural landscape in Dingyadi District, Sokoto State, Nigeria

A semi-detailed fixed grid soil survey of Dingyadi District was conducted in order to obtain comprehensive soil data for characterization and classification. Three soil mapping units TLL1, TUP2 and TUP3 were identified on the basis of land forms and surface texture. Morphological properties of the soil reveal that soil unit TLL1 is deep, imperfectly drained and generally loamy sand in texture. TUP2 was well drained with deep rooting zone and texture varies from loamy sand on the surface to sandy clay loam in the subsoil. Soil unit TUP3 has an impermeable layer at less than 50 cm depth with generally gravelly sand texture. Physical properties of the soils indicate a relative high bulk density and low porosity. Mean equilibrium infiltration rates (MEIR) (cmhr-1) for soil units TLL1, TUP2 and TUP3 were 20, 40 and 32 respectively. The dominant exchangeable bases were calcium and magnesium with the soils having high base saturation. The soils were neutral to slightly alkaline in reaction. Organic matter, available P, total N and CEC contents of the soils were generally low. According to USDA Soil Taxonomy System, soil units TLL1, TUP 2, and TUP 3 were classified as Typic Endoaqualfs, Typic Haplustepts and Lithic Ustorthents, respectively and correlate with Haplic Luvisols, Argic Lixisols and Ruptic Cambisols in WRB system of Classification.

English

A pot culture experiment was conducted to investigate the effect of pesticides &ndash; 2,4-D (herbicide), endosulfan (insecticide) and dithane M-45 (fungicide) at their field application rates (1.0, 2.0 and 1.5 kg a.i ha-1), respectively, on the available Diethyl Triamine Pentacetic acid (DTPA) extractable copper (Cu), manganese (Mn) and zinc (Zn) along with the population of viable bacteria and fungi in new alluvial soil (Typic&nbsp;haplustepts). The results reveal that as compared to control, 2,4-D effectuated a significant increase in the population of total bacteria (up to 21.1%) and fungi (33.7%) besides available Cu (21.7%) and Zn(119.4%) during later stages and Mn (8.7%) almost throughout the incubation period though there was significant progressive immobilization of Cu (17.7%) during initial stages. Endosulfan, contrarily caused significant reduction of total bacteria (up to 18.4%), fungi (13.1%) and immobilization of Zn (42.1%) during later stages, Cu (10.3%) in the intermediary stage and Mn (64.7%) almost&nbsp; throughout. Dithane M-45, however, resulted in a significant increase in available Cu (13.2%) and Mn (3.38%) in the intermediary stage in spite of inducing detrimental influence on fungi (18.7%) and immobilization of Zn (12.9%) during intermediary stage and Mn in early (3.0%) and late stages (6.7%) of incubation. Among the pesticides used in the investigation, the performance of herbicide (2,4-D) was encouraging in almost every aspect. &nbsp; Key words:&nbsp;Pesticide, DTPA extractable Cu, Mn and Zn, viable bacteria and fungi

The effect of urease and nitrification inhibitors on ammonia and nitrous oxide emissions from simulated urine patches in pastoral system: A two-year study

This field study evaluated the effects of applying a combination of urease (UI) and nitrification inhibitors (NI) on ammonia (NH3) and nitrous oxide (N2O) emission from urine patches, using zeolite, single superphosphate (SSP) and urea fertilizer as a carrier. The trial was conducted on a Typic Haplustepts silt loam soil, near Lincoln, Canterbury, New Zealand during 2009–11. The treatments in 2009 included: a control (no urine or inhibitor), urine alone at 600kgNha−1, and urine with either double inhibitor (DI) a mixture (1:7 ratio w/w) of UI (N-(n-butyl) thiophosphoric triamide (nBTPT — trade name Agrotain®) and NI, dicyandiamide (DCD) or DCD alone at 10kgha−1 using zeolite and SSP as carriers. In 2010 trials, both zeolite and urea were used as carriers for DI and DCD. DI-zeolite and DI-urea were equally effective and reduced the average NH3 losses from applied urine over two years by 34.6% in autumn and 40% in spring respectively. The nBTPT in DI-SSP was decomposed by the free acid produced during its dissolution and therefore increased NH3 emission as does DCD alone. DCD consistently increased NH3 emissions by 39% and 15.6% in autumn and spring respectively. Spring application resulted in NH3–N losses of 16.9% as a percentage of the total N applied compared to 8.4% in autumn. Over the two years, the DI reduced N2O emissions by 53% in autumn and 46% in spring over urine alone treatment; the equivalent reductions for DCD were 42% and 39% for autumn and spring, respectively. These results suggest that applying DI in autumn and spring using zeolite or urea carrier five days prior to grazing has the most potential to reduce NH3 and N2O losses from specific urination event than using DCD alone; and therefore warrants further research to improve its longevity.

Variables of Microbial Response in Natural Soil Aggregates for Soil Characterization in Different Fluvial Land Shapes

The main objective of this study was to determine changes in microbial response in natural soil aggregates for soil characterization in different fluvial land shapes. This study was carried out in fluvial lands formed on accumulated sediment depositions carried by Kızılırmak River. The majority soils of the study area were classified as Typic Ustifluvent and Typic Haplustept in Soil Taxonomy. It was found that macroaggregates (especially >6300 μm and 2000–4750 μm diameters) of all soil samples were higher than microaggregate of soils. In addition, it was determined that the Corg content varies between 0.41–0.91% in soil samples. Cmic content was also found higher level in aggregates involved <250 and 250–425 μm diameters as compared to other aggregate size classes. Moreover, we detected that Corg:Cmic ratio was much higher in macroaggregates than in microaggregate fractions. BR levels were also greater in macroaggregates of >6,300, 4,750–6,300 and 2,000–4,750 μm than in the other macroaggregates sizes and microaggregates. Consequently, macroaggregates have relatively more Corg level than the Corg level in microaggregates, even if the absolute values of Cmic were the lower. This study thus evidenced contrasting microbial habitats and their response in different soil aggregate size formed in various developed soils.

Soil phosphorus fractions in a typic haplustept as influenced by organic sources after soyabean (Glycine max L.) – wheat (Triticum aestivum) cropping sequence in semi arid condition

Rock phosphate enriched biogas slurry, pressmud and farm yard manure alone and in combination with DAP in different ratios (1:3, 1:1 and 3:1) were evaluated in field with soybean-wheat cropping sequence at the IARI, New Delhi on a sandy loam soil. Soil samples (0–15 cm) after the harvest of wheat were taken to examine the residual effect of various treatments on available, inorganic and organic P pools in soil. Application of manure showed significant increase in available P over control. Among the fractions of phosphorus Fe-P, Ca-P and organic P fractions in soil remained almost unaltered while Saloid-P and Al-P fractions were increased in comparison to their initial concentration noted before sourcing the soybean. The extent of increase was more at higher rates of P application to soybean. Application of rock phosphate enriched biogas slurry in the ratio of 1:1 and 3:1 of DAP and manure on P2O5 basis gave the highest increase in the P fractions of soil. Therefore, a change in different inorganic and organic P fraction in soil can be influenced by the manipulation of sources and levels of phosphorus.

Ameliorative effect of potassium sulphate on the growth and chemical composition of wheat (Triticum aestivum L.) in salt-affected soils

Abstract Potassium (K) and sodium (Na) coexist on the soil exchange complex and soil solution. Both cations may exert antagonistic or synergistic effects on mutual absorption and translocation within plants, particularly under saline and saline-sodic field conditions. This study investigated the role of K in alleviating the adverse effects of Na on wheat [ Triticum aestivum (L), Iquilab-91] grown at two fields sites varying in salinity. The soils were moderately calcareous, weakly structured, mixed hyperthermic Typic Haplustepts. Site 1 was silty clay loam saline-sodic soil (ECe = 4.23-9.45 dS m -1 ) irrigated with groundwater with an EC iw value of 5.0 dSm -1 ; Site 2 was clay loam saline soil (ECe = 3.2-5.0 dS m -1 ) irrigated with groundwater with an ECiw of 2.4 dS m . Both sites were treated with 0, 50 and 100 kg K ha -1 applied as K 2 SO 4 (41% K) fertilizer. Significant increases of 14 and 30% in grain yield were measured at both sites, and 35 and 54% increase in dry matter yields were observed in clay loam soil with the application of 50 and 100 kg K ha

Soil development and microbial functional diversity: Proposal for a methodological approach

The aim of the work was to propose a new methodological approach that relates soil microbial functional diversity to soil development under different moisture regimes. As soil evolution proceeds through an increasing niche separation we expect a link between functional diversity and soil development. Shannon's (H') and Gini (D) diversity indices were calculated using eight enzyme activities (β-cellobiohydrolase, N-acetyl-β-glucosaminidase, β-glucosidase, α-glucosidase, acid phosphatase, arylsulfatase, xylosidase and butyrate esterase) in order to assess functional diversity at different scales, from soil horizons (α-diversity) to soil profiles (β-diversity) under different moisture regime (γ-diversity) and belonging to different taxonomic levels. In addition, the ratio of acid phosphatase to chitinase was calculated as a potential index of soil development. Eight soil profiles were selected: four in Northwestern Italian Alps or Northern Apennines with Udic soil moisture regimes (Typic Haplocryod, Mollic Haplocryept, Lithic Dystrudept, Lithic Cryorthent) and four in Northeastern Italy where in two cases the water table near the soil surface strongly affects the Ustic soil moisture regime, and intrazonal Aquic regime or Aquic conditions develop (Typic Haplustept, Typic Ustipsamment, Aquic Ustipsamment, Typic Psammaquent). D ranged from 50 to 95%, while the H' ranged from 3 to 2.4 in Lithic Cryorthent and Typic Psammaquent, respectively. Under Udic moisture regime an inverse relationship between soil profile development and the diversity index was observed. However the lowest the diversity in the profile, the highest the variability of the values obtained within horizons in the soil profile suggesting a link between differentiation of soil horizons and biochemical properties. The Aquic conditions interfere in establishing the relationship between soil profile development and the microbial functional diversity since H' and D increased in Typic Psammaquent with respect to Typic Haplustept (H' from 2.4 to 2.6 and D from 52.2 to 60.4). Finally, the phosphatase/chitinase ratio was related to soil development since the lowest values were obtained in the upper horizons of Typic Haplustept, Typic and Aquic Ustipsamment (from 2.0 to 4.0), while the highest values were obtained in deep horizons of Typic Haplocryod and Lithic Dystrudept (e.g. 39.2 in Bs2 and 28.0 in Bw1). In conclusion, microbial functional diversity assessed using Shannon or Gini diversity indices and phosphatase/chitinase ratio measured at different scales from soil horizons to soil profiles under different moisture regime and belonging to different taxonomic levels, may represent a new approach to establish the interrelationship between pedogenetic processes, soil development and soil microbial functions.

Terrain Characterization for Soil Resource Mapping Using IRS-P6 Data and GIS - A Case Study From Basaltic Terrain of Central India

In the present study, landforms and soils have been characterized in Borgaon Manju watershed of basaltic terrain located in Akola district, Maharashtra, Central India. Terrain characterization using Shuttle Radar Topography Mission (SRTM) elevation data (90 m) and IRS-P6 LISS IV data in conjunction with adequate field surveys shows nine distinct landforms. Soil resource inventory shows fourteen soil series in the study area. Soils formed on gently sloping (3–8 %) subdued plateau are very shallow (23 cm), moderately well drained, moderate (15–40 %) surface stoniness, severely eroded, clayey and slightly alkaline in reaction, whereas, the soils formed on level to nearly level (0–1 %) slope in the main valley are very deep (>150 cm), well drained, very slight (<3 %) surface stoniness, moderately eroded with clayey surface and moderately alkaline in reaction. Soils in the watershed are grouped into Lithic Ustorthents, Vertic Haplustepts, Calcic Haplustepts, Typic Haplustepts, Typic Haplusterts and Sodic Calciusterts. The study demonstrates that the analysis of SRTM elevation data and IRS P6–IV data in Geographic Information System (GIS) with adequate field surveys helps in characterization of landforms and soils in analysis of landscape-soil relationship.

PHYTOREMEDIATION OF ARSENIC CONTAMINATED SOIL BY PTERIS VITTATA L. I. INFLUENCE OF PHOSPHATIC FERTILIZERS AND REPEATED HARVESTS

A greenhouse experiment was conducted to evaluate the effectiveness of diammonium phosphate (DAP), single superphosphate (SSP) and two growing cycles on arsenic removal by Chinese Brake Fern (Pteris vittata L.) from an arsenic contaminated Typic Haplustept of the Indian state of West Bengal. After harvest of Pteris vittata the total, Olsen's extractable and other five soil arsenic fractions were determined. The total biomass yield of P. vittata ranged from 10.7 to 16.2 g pot−1 in first growing cycle and from 7.53 to 11.57 g pot−1 in second growing cycle. The frond arsenic concentrations ranged from 990 to 1374 mg kg−1 in first growing cycle and from 875 to 1371 mg kg−1 in second growing cycle. DAP was most efficient in enhancing biomass yield, frond and root arsenic concentrations and total arsenic removal from soil. After first growing cycle, P. vittata reduced soil arsenic by 10 to 20%, while after two growing cycles Pteris reduced it by 18 to 34%. Among the different arsenic fractions, Fe-bound arsenic dominated over other fractions. Two successive harvests with DAP as the phosphate fertilizer emerged as the promising management strategy for amelioration of arsenic contaminated soil of West Bengal through phyotoextraction by P. vittata.

How application timings of urease and nitrification inhibitors affect N losses from urine patches in pastoral system

In intensively dairy-grazed pastoral systems, urine patches are the major source of nitrogen (N) losses via gaseous emissions of ammonia (NH3) and nitrous oxide (N2O) and nitrate (NO3−) leaching. Minimizing these N losses can therefore enable substantial economic and environmental gains. However, the current practice like the blanket application of nitrification inhibitor (NI) such as dicyandiamide (DCD) in suspension form after grazing is not effective at reducing these N losses. The objective of this study was to identify the best time to apply a combination of urease (UI) and NI inhibitors to reduce these N losses from urine patches. A field experiment on Typic Haplustepts silt loam soil, near Lincoln, Canterbury, New Zealand was conducted. The treatments included: a control (no urine or inhibitor), urine alone at 600kgNha−1, and urine with either double inhibitor (DI) in solid form which consists of a mixture (1:7 ratio w/w) of UI (N-(n-butyl) thiophosphoric triamide (nBTPT-trade name Agrotain®) and DCD or DCD alone at 10kgha−1 in suspension form. The DI or DCD was applied to undisturbed lysimeters/field plots 10 and 5 days prior to, the same day, and 5 days after urine application in autumn (May 2008) and again to new lysimeters and field plots in spring (September 2008). Overall there were 10 treatments: control, urine alone and urine with DI or DCD applied at the time of urine application, 5 days before or after urine application and 10 days before urine application. After these treatment applications in 2 seasons, soil ammonium (NH4+) and NO3− concentrations, soil pH, gaseous emissions of NH3 and N2O, and NO3− leaching were monitored for different period of time and pasture growth and N uptake were measured over a year. The DI applied 5 days prior to urine application was more effective in reducing the 3N losses of NH3 volatilization, N2O emissions and NO3− leaching than its corresponding or DCD treatment applied 5 days after urine application. The DI applied 5 days prior to urine application significantly reduced soil NH4+ and NO3− production from applied urine and thus exhibited a minimal increase in soil pH compared with urine alone or with DCD treatments for 4–6 weeks during the two seasons. DCD consistently increased NH3 volatilization when applied 5 or 10 days prior to or concurrently with urine, however it decreased N2O emissions compared to urine alone in both seasons. Applying DI 5 days prior to urine application not only decreased N2O emissions as much as DCD did, it also significantly decreased NH3 volatilization by 38% in autumn and 28% in spring compared to urine alone. Applying DCD or DI in autumn was more effective than spring applications probably because of the lower soil temperature (<10°C) in autumn. Compared to urine alone, DI and DCD applied 5 days prior to urine application in autumn significantly reduced NO3− leaching by 58% and 43%, respectively since the leaching events occurred during the time when these inhibitors were effective (1–2 weeks for nBTPT and 4–6 weeks for DCD). Neither the DI nor DCD had any such significant effect on NO3− leaching losses after their spring application because the leaching events occurred 3–5 months after inhibitor application, which was beyond the time that these inhibitors could be effective. Pasture productivity was only significantly increased by the DI after autumn application, but no significant trend was observed after spring application. These results suggest that DI applied in solid form prior to grazing has the most potential to reduce the 3 key N losses in grazed pastoral system; and it therefore warrants further research to improve its longevity to control N losses for a longer period.

Bed planted rice–wheat rotation at differential soil moisture regimes on soil hydro-physical properties, root growth, nitrogen uptake, and system productivity

Along with most widely practiced resources conserving technology zero-tillage wheat after rice, adoption of permanent beds for rice–wheat rotation is also gaining popularity. Since relatively a new approach particularly for dry-seeded rice and permanent beds for wheat, very little information is known about permanent beds on soil properties, nutrient (N) use efficiency, and system productivity. A field experiment was carried out in a Typic Haplustept soil of New Delhi, India to study the effect of permanent beds on soil hydro-physical properties, root growth, nitrogen uptake, and system productivity of irrigated rice–wheat rotation. Results revealed that direct-seeded rice followed by wheat on permanent beds irrigated at different soil water tensions (field capacity, 20 and 40 kPa) reflected a significant variation in soil hydro-physical properties, reduced total nitrogen uptake, contribution by different plant parts, and N use efficiency compared to wheat after flooded transplanted rice system. Rice root weight density at flowering was also significantly low at 0–15 cm depth but higher at 15–60 cm depth in dry-seeded rice on beds. System productivity of rice–wheat rotation was 25–33% lower in permanent beds compared to flooded transplanted system. For wider acceptability of permanent beds as a promising resource conserving technology, system productivity needs to be improved.

Soil application of dinitroaniline and arylphenoxy propionic herbicides influences the activities of phosphate-solubilizing microorganisms in soil

An experiment was conducted under laboratory conditions to investigate the effect of two systemic herbicides, viz. pendimethalin (a dinitroaniline) and quizalofop (an arylphenoxy propionic acid) at their recommended field application rates (1.0 kg and 50 g active ingredient per hectare, respectively), either separately or in a combination, on growth and activities of phosphate-solubilizing microorganisms in relation to their effects on biochemical transformations and availability of organic carbon, total and available phosphorus in a Typic Haplustept soil of West Bengal, India. Application of herbicides, in general, significantly stimulated the growth and activities of phosphate-solubilizing microorganisms which increased microbial biomass resulting in higher accumulation of oxidizable organic carbon, total and available phosphorus in soil as compared to untreated control. The combined application of both the herbicides highly stimulated the proliferations of phosphate-solubilizing microorganisms, while pendimethalin alone significantly accentuated phosphate-solubilizing capacities 36.4% as compared to untreated control and retained highest amount of total phosphorus due to greater microbial activities in soil. The separate application of quizalofop also manifested an induced effect on the proliferations of phosphate-solubilizing microorganisms and accounted significant amounts of organic carbon and available phosphorus in the soil system. The results of the present study thus indicated that the cited herbicides at their field application rates can be safely used to eradicate weeds in the crop fields.

A New Systematic Technique for Optimum Fertilizer Treatment in Fertilizer Response Experiments

Experiments were carried out to optimize the nutrients for hybrid maize through nutrient sorption study and green house experiment during 2007- 2008 at Tamil Nadu Agricultural University, Coimbatore. A systematic procedure for optimum nutrient treatment (ONT) as the basis for formulating the treatment structure for field experiments for fertilizer response studies was tested in the present investigation in two soil series belonging to Mayamankuruchi (Typic Haplustepts and Madukkur (Udic Haplustalfs). Nutrient sorption studies were conducted in these soils for P, K, S, Zn, Fe, Cu, Mn and B. The critical level of nutrients for these soils were fixed prescribed by Portch and Hunter. The sorption curves were used to formulate Optimum Nutrient Treatment (ONT). The validity of these ONTs was verified in a green house experiment using the same soil. The two experimental soils were found to deficient in N, P, K and Zn, and their optimum amounts varied between the soils. The optimum nutrients for hybrid maize var. COHM5 were formulated for these two soil series from this study.

Effect of pendimethalin and quizalofop on N2-fixing bacteria in relation to availability of nitrogen in a Typic Haplustept soil of West Bengal, India

An experiment was conducted under laboratory conditions to investigate the effect of two systemic herbicides viz., pendimethalin and quizalofop, at their recommended field rates (1.0 kg and 50 g active ingredient ha(- 1), respectively) on the growth and activities of non-symbiotic N(2)-fixing bacteria in relation to mineralization and availability of nitrogen in a Typic Haplustept soil. Both the herbicides, either singly or in a combination, stimulated the growth and activities of N(2)-fixing bacteria resulting in higher mineralization and availability of nitrogen in soil. The single application of quizalofop increased the proliferation of aerobic non-symbiotic N(2)-fixing bacteria to the highest extent while that of pendimethalin exerted maximum stimulation to their N(2)-fixing capacity in soil. Both the herbicides, either alone or in a combination, did not have any significant difference in the stimulation of total nitrogen content and availability of exchangeable NH(4)(+) while the solubility of NO(3)(-) was highly manifested when the herbicides were applied separately in soil.

Impact of elevated CO 2 on utilization of soil moisture and associated soil biophysical parameters in pigeon pea ( Cajanus cajan L.)

An experiment was conducted with two genotypes of pigeon pea ( Cajanus cajan L.) grown in an alluvial sandy loam soil (belonging to Holambi series, a mixed hyperthermic family of typic Haplustept) in open top chambers (OTCs) installed in the field. The objective was to find out the effect of elevated CO 2 (580 ppm) on soil moisture changes, crop water use, root growth characteristics and status of active carbon pools in soil. Soil temperatures at 9:00 and 16:00 h were similar till 94 days after sowing (DAS), and were marginally less thereafter in the CO 2 chambers. Profile moisture content was consistently lower in CO 2 chambers, indicating greater water use by the crop. An exponential relationship was obtained between crop biomass and its water use. Greater biomass led to higher water use efficiency by the crop, though genotypic differences were evident only in pod yields. Root characters at two growth stages (72 and 110 DAS) showed a significant increase in its weight density, length density and surface area at 0–15 and 15–30 cm layers for plants grown under elevated CO 2. Significantly higher amount of roots with smaller diameter (<0.1 mm) under elevated CO 2 possibly contributed in greater soil moisture absorption. There was no appreciable change in the soil physical properties (bulk density, hydraulic conductivity and mean weight diameter); but different active carbon pools (oxidizable, carbohydrate, labile, microbial biomass and total) in the soil increased significantly due to CO 2 exposure. Dehydrogenase and FDA hydrolysis enzymes also increased substantially and were found to have a highly positive correlation with all C fractions indicating the role of active carbon pools in stimulating microbial population, leading to better biological activity in soil near the root zone under CO 2 enrichment.

Characterizing soils of Delbo Wegene watershed, Wolaita Zone, Southern Ethiopia for planning appropriate land management.

The soils of the Delbo Wegene watershed of Southern Ethiopia were characterized along toposequence for the development of land management plan for sustainable soil management practices. Four pedons along toposequence were studied. Delbo Wegene watershed is located between 06°52’ 45.9’’ and 06°53’34.8’’ N latitude and between 37°48’ 10.5’’ and 37°48’42.4’’E longitude, with altitude ranging from 2100 to 2300 m.a.s.l. The soils were generally dark reddish brown to very dark brown and very deep (> 150 cm). The overall friable consistency, low bulk density (1.0 to 1.26 gm/cm3), sub angular to angular blocky structure, high total porosity (53 to 61%) indicated that the soils have good physical condition for plant growth. The soils were slightly (pH: 5.8) to moderately acidic (pH: 6.4). Organic carbon content, available micronutrients and cation exchangeable capacity of the soils decrease with soil depth. However, exchangeable cations increase with increasing soils depth. Available phosphorus content of the soils ranged from very low to high. However, available Cu content of the soils were marginal to deficient. The upper and middle pedons with argilic subsurface horizons were classified as Typic Paleustults (Soil Survey Staff, 1999). These soils correlate with Cutanic Luvisols (WRB, 2006). The lower and toe slope pedons with mollic epepedon and cambic subsurface horizon were classified as Typic Haplustepts. These soils correlate with Haplic Cambisols (WRB, 2006). The result indicated that the distribution and properties of the soils vary along the toposequence in the watershed. Key words: Soil characteristics, soil classification, Delbo-Wegene watershed

Urea hydrolysis and lateral and vertical movement in the soil: effects of urease inhibitor and irrigation

A glasshouse-based study was conducted to investigate the effect of urease inhibitor N-(n-butyl) thiophosphoric triamide (‘Agrotain’) and irrigation on urea hydrolysis and its movement in a Typic Haplustept silt loam soil (in 72 repacked soil cores). Half (36) of these cores were adjusted to soil moisture contents of 80% field capacity (FC) and the remaining 36 cores to 50% FC. Granular urea with or without Agrotain was applied at a rate equivalent to 100 kg N ha−1. There were three replicates to these two sets of soil cores. After 1 day of treatment application, soil cores of the 50% FC were adjusted to 80% FC by applying surface irrigation. Twelve pots were destructively sampled at each day after 1, 2, 3, 4, 7 and 10 days of treatment application to determine urea hydrolysis and its lateral and vertical movement in different soil layers. Agrotain-treated urea delayed urea hydrolysis during the first 7 days after its application. This delay in urea hydrolysis caused by Agrotain enabled added urea, which is uncharged, to move away from the surface soil layer to the sub-surface soil layer both vertically and laterally. In contrast, most urea hydrolysed to soil NH4+ within 2 days of its application. Irrigation after 1 day resulted in further urea movement both laterally and vertically from the surface soil layer (0–10 mm) to the sub-soil layer (30–50 mm) in Agrotain-treated urea. These results suggest that Agrotain delayed urea hydrolysis and allowed more time for rainfall or irrigation to move added urea from the surface layer to sub-soil layers where it is likely to make good contact with plant roots. This distribution of urea in the rooting zone has the potential to enhance N use efficiency and minimize N losses associated with ammonia volatilization from surface-applied urea.

Elevated CO2 reduces rate of decomposition of rice and wheat residues in soil

The production and quality of belowground roots and plant are likely to be affected by the increase in atmospheric CO2 level with subsequent changes in their decomposition rates in soil. However, the quality of residues has received very little attention, particularly in rice and wheat residues. The present experiment was laid out to study the decomposition of residues of rice (R) and wheat (W) grown in a Typic Haplustept soil under ambient (A) and elevated (E) CO2 conditions maintained in a phytotron. The decomposition of RA and WA was carried out in ambient atmospheric CO2 conditions, while that of RE and WE was done in elevated CO2 condition. Ambient CO2 grown rice and wheat residues were found to decompose at a faster rate compared to the corresponding elevated CO2 grown residues. The amount of residues left over after 150 days of decomposition was comparatively higher in the elevated CO2 grown residues indicating their slow rate of decomposition. However, ambient and elevated CO2 grown wheat residues did not differ significantly with respect to the amount remaining at later stages of decomposition. The RA and RE decomposed to 81% and 77% of their initial amount after 150 days of decomposition, while WA and WE decomposed to 73% and 71% of their initial amounts, while the C loss from RA, RE, WA and WE were 83%, 79%, 76% and 73%, respectively. Ambient atmospheric CO2 grown residues exhibiting narrow C:N ratios decomposed to a faster rate than the elevated CO2 grown residues. Overall, total organic carbon (TOC) content was significantly higher in WA treated soil than in WE treated soil. Net N mineralization (Nmin), microbial biomass carbon (MBC) and Nmin:MBC were greater in soil amended with ambient CO2 grown residues than in elevated CO2 grown residues. Rice residues as compared to wheat residues decomposed at a faster rate thereby releasing higher amount of N in soil. In near future the residues produced under higher concentration of atmospheric CO2 need to be handled carefully as these are decomposed with difficulty due to wide C:N ratios. This has direct implications on N cycling in soil and therefore N fertilization needs to be modified when crop residues are incorporated in soil for optimum crop production. Though lower decomposability of elevated CO2 grown residues might cause more C sequestration in soil, N limitation might adversely affect the plant C sequestration in future.

Caracterização de solos em uma topoclimossequência no maciço de triunfo - sertão de pernambuco

Os brejos de altitude nordestinos constituem uma disjunção da mata atlântica, formando ilhas de floresta úmida em plena região semiárida, tendo uma condição climática bastante atípica, favorecida pela ocorrência de chuvas orográficas, com precipitação pluvial que pode atingir valores superiores a 1.200 mm por ano. No Estado de Pernambuco, a maioria dos estudos em brejos de altitude abrange os aspectos botânicos e faunísticos, sendo, portanto, importante a realização de estudos para caracterização dos recursos edáficos. Com intuito de estudar os solos de brejos de altitude no Sertão Pernambucano e avaliar a influência dos diversos fatores pedogenéticos na sua formação e evolução, foi feita a caracterização morfológica, física, química e mineralógica de três perfis no maciço de Triunfo, em diferentes altitudes, localizados nos municípios de Serra Talhada (P1), Santa Cruz da Baixa Verde (P2) e Triunfo (P3), formando uma topoclimossequência. Os perfis estudados apresentam características morfológicas similares, relacionadas com o pequeno grau de desenvolvimento pedogenético, principalmente nos perfis P3 (Triunfo) e P2 (Santa Cruz), classificados, respectivamente, como Cambissolo Háplico Tb Eutrófico latossólico e Cambissolo Háplico Tb Eutrófico típico. O perfil P1 (Serra Talhada), localizado no sopé, apresentou menor teor de argila e acentuado gradiente textural, resultante de descontinuidade litológica, sendo classificado como Argissolo Vermelho-Amarelo distrófico abrúptico (cambissólico). Todos os solos deste estudo são oriundos de rochas sieníticas, sendo, pelo menos em parte, influenciados pelo transporte e pela deposição de materiais oriundos da parte superior do relevo. O perfil de Triunfo, em local mais úmido, apresentou o maior grau de desenvolvimento em relação aos demais. O clima, atuando principalmente pela variação de umidade, não foi, entretanto, o único fator de formação responsável pela diferenciação dos solos ao longo da topoclimossequência, devendo-se ressaltar, também, a influência do material de origem e do relevo.