Cm Layer Of Soil Research Articles

Conversion from Conventional to No Tillage Alters Thermal Stability of Organic Matter in Soil Aggregates

The quantity and stability of soil organic matter (SOM) associated with soil aggregates are affected by tillage management, which can be characterized potentially using the technique of thermal analysis. In this study, we evaluated the concentration and thermal stability of SOM occulted with various aggregate classes under no-tillage (NT) and moldboard plow (MP) treatments using thermogravimetry (TG) and differential scanning calorimetry (DSC). Soil samples were collected 10 yr after tillage experiment was started. The results showed that conversion from MP to NT significantly increased SOM concentration and the proportion of large macro-aggregates (>2 mm) in the 0- to 5-cm soil layer. For all aggregate classes the derivatives of thermogravimetry curves (DTG) had three weight loss peaks near 100, 350, and 500°C, and one endothermic peak and three exothermic peaks in the DSC curves. No differences in ignition temperature, peak position, and ending temperature of SOM combustion were observed between tillage treatments and among the soil layers. For both tillage systems, the proportion of thermal labile SOM (weight loss in 200–400°C accounting for that in 200–550°C, Exo1/Exotot) and energy densities (ED) of SOM (energy release per unit SOM) declined with decreasing aggregate size in the 0- to 20-cm soil layer. Moreover, TG-T50 (the temperature resulting in 50% of SOM loss) correlated negatively to aggregate size, but DSC-T50 (the temperature at which 50% of energy resulting from organic matter combustion release) correlated positively to aggregate size. Compared with MP management, NT management improved quantity but decreased thermal stability of SOM in aggregates in the 0- to 5-cm layer, which was indicated by the greater weight loss at combustion, higher Exo1/Exotot ratio, greater energy densities and lower TG-T50. No tillage also led to increased stratification ratios of thermal labile and thermal recalcitrant SOM.

Nitrate leaching of winter wheat grown in lysimeters as affected by fertilizers and irrigation on the North China Plain

Proper application of nitrogen (N) fertilizers and irrigation management are important production practices that can reduce nitrate leaching into groundwater and improve the N use efficiency (NUE). A lysimeter/rain shelter facility was used to study effects of the rate of N fertilization, type of N fertilizer, and irrigation level on key aspects of winter wheat production over three growing seasons (response variables were nitrate transport, N leaching, and NUE). Results indicated that nitrate concentration in the soil profile and N leaching increased with the rate of N fertilization. At the end of the third season, nitrate concentration in the top 0–75 cm layer of soil was higher with manure treatment while urea treatments resulted in higher concentrations in the 100–200 cm layer. With normal irrigation, 3.4 to 15.3% of N from applied fertilizer was leached from the soil, yet no leaching occurred under a stress irrigation treatment. The manure treatment experienced less N leaching than the urea treatment in all cases except for the 180 kg N ha−1 rate in 2011–2012 (season 3). In terms of grain yield (GY), dry matter (DM) or NUE parameters, values for the manure treatment were lower than for the urea treatment in 2009–2010 (season 1), yet were otherwise higher for urea treatment in season 3. GY and crop nitrogen uptake (NU) were elevated when the rate of N fertilizer increased, while the NUE decreased; GY, DM, and NU increased with the amount of irrigation. Data indicated that reduced rates of N fertilization combined with increased manure application and proper irrigation management can lower nitrate levels in the subsoil and reduce potential N leaching into groundwater.

湖南省森林土壤有机碳密度及碳库储量的动态

Soil organic carbon( SOC) represents a large component of the global carbon cycle,and the SOC pool varies in forest ecosystems depending on species composition,growth stage and management practice. In order to accurately evaluate SOC distribution and dynamics in forests in Hunan Province of China, we reviewed, assembled and analyzed acomprehensive data package collected from(1) published estimates of SOC contents in various forested soil profiles( a total of 277 soil profiles in the province) in the past 15 years( from 2000 to 2014),(2) four times of forest inventory data from1983 to 2009 in Hunan' s forests,( 3) long-term field measurements in the Key National Observation Station of Central South University of Forestry and Technology in Huitong County,Hunan Province of China over the past 15 years(2000—2014) and(4) field surveys of 59 soil profiles taken from ten typical forest types in the province during the period of 2008 to 2014. All forests in the province were classified into four categories of timber-forests,economic-forests,bamboo-forests and shrub-forests. The timber-forests were further divided into eight major forest types based on the species composition of the forest stands. The results showed that the arithmetic average of SOC contents ranged from 9. 53 to 22. 86 g / kg in the four main forest categories,of which the shrub-forests had the highest SOC content. The differences of SOC mainly occurred in the 0—40 cm of soil layer among the studied forest groups. SOC density was in the range of 95. 44—181. 30 t C / hm2 in the 0—80 cm soil layer,with an average of 137. 15 t C / hm2 in the examined forests. The differences of SOC density among the forest groups declined with the increase of soil depth,and the effect of forest types on variation of SOC density was gradually weakened with the increasing soil depth. From 1983 to 2009,SOC pool( 0—80 cm soil depth) increases in Hunan's timber-forests with a net increase of 414. 86 × 106 t C and the area weighted average of SOC density increased 10.98 t C / hm2 in the studied timber-forested soils( 0—80 cm soil depth) as well. The difference of SOC pool gradually increased with aged stands of timber-forests,mainly occurring in Chinese fir( Cunninghamia lanceolata) forests,Masson Pine( Pinus massoniana) forests and broad-leaved forests. Among the forest types,natural forest accounted for a large percentage( 50%) of the total SOC storage in Hunan's forests. But the proportion of SOC in plantation forests increased as the plantation areas gradually increased in the studied province. Economic-forests,shrub-forests and bamboo-forests made different contributions to the total SOC pool( 0—80 cm soil depth) in Hunan' s forests,depending upon planting areas,cultivate systems and management practices. The changes in SOC pool in studied forests were closely associated with the alteration of forested area,convention of forest types and land use changes. These changes in terms of forested area and forest type were related to the formation and implementation of forestry policies in local,province and national levels. Our study suggested that human activities would influence SOC pool in forest ecosystems in regional scale through altering forested area and forest types.

Geochemistry and spatial variability of metal(loid) concentrations in soils of the state of Minas Gerais, Brazil

Since 2009 a policy has been implemented in Brazil to establish the natural concentrations of potentially toxic substances in soil for each state. Historically a ‘mining state’, Minas Gerais established a Quality Reference Value for metal(loid)s for all of the soils in the state. To successfully establish these values it is important to study the spatial geochemical diversity for the state. In this context, the objectives of this work are: (1) to evaluate the natural concentrations of metal(loid)s in pristine Minas Gerais soils and (2) to interpret the spatial variability in concentration of these elements. The 0–20cm layer of soils was sampled for 697 georeferenced sites including the main geological materials and soil groups. Soil properties were analyzed according to methodologies suitable for Brazilian soils. The concentration of metal(loid)s was determined by acid extraction according to EPA 3051A. Descriptive statistics, Pearson correlation and spatial variability analyses were performed. The dominance of acidic pH and low CEC values reflects the pervasive deep acid weathering. The variability of metal(loid) concentrations for soils of the state may be attributed to geological diversity and different pedogenesis. Correlation and spatial analysis indicated that the Fe concentration is strongly associated with metal(loid) concentrations in topsoil. According to the spatial geochemical diversity of the state, a k-means cluster analysis was performed which identified four clusters. A significant difference in the mean values of metal(loid) concentrations between the clusters confirmed that the single Quality Reference Value established does not represent the geochemical diversity of soils in Minas Gerais.

Morphology and phylogenetic position of the oxytrichid ciliates, Urosoma salmastra (Dragesco and Dragesco-Kernéis, 1986) Berger, 1999 and U. karinae sinense nov. sspec. (Ciliophora, Hypotrichia)

The morphology and infraciliature of two hypotrichous ciliates, Urosoma salmastra and U. karinae sinense nov. sspec., were investigated for populations collected from the surface of intertidal gravel in the Huguang Mangrove Forest, Zhanjiang, China and the upper 10cm layer of soil in the Sangke Grass Land in the southern part of Gansu Province, China, respectively. Urosoma salmastra is characterized by its elongate-elliptical body with no tail-like structure; two macronuclear nodules; cortical granules colourless, less than 1μm across, and arranged in short rows; adoral zone occupying 25% of body length in vivo; paroral conspicuously short and located in front of endoral. Urosoma karinae sinense nov. sspec. is characterized by its elongate-elliptical body with no tail; 2–4 macronuclear nodules; cortical granules colourless, less than 1μm across, and arranged in short rows; adoral zone occupying 30% of body length in vivo; paroral shorter than, and located ahead of endoral. Phylogenetic analyses based on SSU rRNA gene sequence data suggest a close relationship between U. salmastra, U. karinae sinense nov. sspec. and Oxytricha granulifera within the Oxytrichinae assemblage.

Soil organic carbon estimation with topographic properties in artificial grassland using a state-space modeling approach

She, D., Xuemei, G., Jingru, S., Timm, L. C. and Hu, W. 2014. Soil organic carbon estimation with topographic properties in artificial grassland using a state-space modeling approach. Can. J. Soil Sci. 94: 503–514. Knowledge of the distribution of soil organic carbon (SOC) in artificial grasslands in semiarid areas is helpful in optimizing management for soil fertility recovery and carbon sequestration. Accurate estimation of SOC with easy-to-obtain topographic properties can save considerable labor and cost as well as protect the grassland from being disturbed by intensive soil sampling. In our study, a total of 113 sampling points were setup within a patch of artificial grassland in a small catchment located in the north Loess Plateau of China. State-space modeling and traditional linear regression were used to estimate the localized variation of SOC in the 0- to 20-cm surface soil layer using five selected topographic properties (elevation, slope, aspect, plan curvature, and surface soil roughness). Soil surface roughness and plan curvature were identified as the most effective variables for SOC estimation in state-space models. Soil surface roughness and plan curvature explained 92.5% and 84.5% of the total variation of SOC, respectively. The best state-space model was the one using both plan curvature and surface soil roughness, explaining 94.5% of the total variation of SOC, whereas the best linear regression model could only explain 15.9% of the total variation of SOC. The results indicate that all the derived state-space models performed better than the equivalent linear regression models. Our study provides an insight into the possibility of accurate estimation of SOC only using one or two easy-to-obtain topographic properties with state-space modeling approach.

Study of Effects of Different Fertigation Modes on Soil Profile Nitrogen Distribution and Rice Yield

Field experiments were conducted for controlled and mid-gathering irrigation mode in Nanjing, Jiangsu Province, focusing on the effect analysis of this mode with different fertilizations on profile soil total nitrogen and alkali-hydrolyzale nitrogen distributions and rice yield compared with the conventional irrigation mode. Results obtained showed that both total nitrogen and alkali-hydrolyzale nitrogen in soil profile were decreased with the increase of soil depth. Fast decrement of total nitrogen was found from surface 0-20 cm of soil layer and it reached the plateau below 40 cm of soil layer. Under the same fertilizer application, both total nitrogen and alkali-hydrolyzale nitrogen in surface soil layer were lower under controlled and mid-gathering irrigation mode which reduced the loss risks of runoff and leaching of soil and fertilizer nitrogen. Controlled and mid-gathering irrigation reduced water comsumption and N pollutant discharge without significant changes in rice yield compared with conventional irrigation. Conjunction of organic and inorganic fertilizers significantly improved the rice yield and utilization rate of nitrogen.

Soil organic carbon stocks in the Yunnan Plateau, southwest China: spatial variations and environmental controls

Greater increases in temperature are expected in high mountain regions than the global average making mountain soils a potentially vulnerable component of the global carbon cycle. Little is known about the spatial distribution and environmental factors controlling soil carbon in mountainous regions. This study analyzed the spatial patterns of soil organic carbon (SOC) density in mountainous regions and evaluated the impact of various environmental factors on SOC density. This study focused on Yunnan Province, a typical high-elevation, mountainous region in southwest China. A soil database was constructed based on 684 soil profiles documenting 12 environmental factors. Significant differences in SOC density among the upper and subsoil layers were found. Forestland and grassland SOC density were significantly higher than that of cropland. The widely distributed forestland in Yunnan Province had a higher SOC storage capacity than non-forested areas. The forests of the northwestern mountainous region had higher SOC densities than those of the agricultural areas of the southeastern plateau region. Environmental factors affected SOC density more strongly in forestland than grassland and cropland, and those factors were better correlated to the 0–20 cm layer of soils than the 20–100 cm layer. Elevation is the major controlling factor controlling SOC density for the three land uses. Correlating topography to SOC density proved difficult. SOC densities were highest when annual temperatures ranged from 0–2 °C. SOC density decreased with increased precipitation up to 800 mm per year and then remained constant. The SOC density increased with elevation up to 4,000 m then decreased. The results indicate that both the local land use development plans and regional climatic change scenarios may result in a decrease in SOC storage in this region and increase the CO2 flux into the atmosphere. In consideration of the high sensitivity of the regional response to global warming, effective ecological compensation mechanisms and active forest protection should be undertaken in this region.

Baseline map of organic carbon in Australian soil to support national carbon accounting and monitoring under climate change.

We can effectively monitor soil condition—and develop sound policies to offset the emissions of greenhouse gases—only with accurate data from which to define baselines. Currently, estimates of soil organic C for countries or continents are either unavailable or largely uncertain because they are derived from sparse data, with large gaps over many areas of the Earth. Here, we derive spatially explicit estimates, and their uncertainty, of the distribution and stock of organic C in the soil of Australia. We assembled and harmonized data from several sources to produce the most comprehensive set of data on the current stock of organic C in soil of the continent. Using them, we have produced a fine spatial resolution baseline map of organic C at the continental scale. We describe how we made it by combining the bootstrap, a decision tree with piecewise regression on environmental variables and geostatistical modelling of residuals. Values of stock were predicted at the nodes of a 3-arc-sec (approximately 90 m) grid and mapped together with their uncertainties. We then calculated baselines of soil organic C storage over the whole of Australia, its states and territories, and regions that define bioclimatic zones, vegetation classes and land use. The average amount of organic C in Australian topsoil is estimated to be 29.7 t ha−1 with 95% confidence limits of 22.6 and 37.9 t ha−1. The total stock of organic C in the 0–30 cm layer of soil for the continent is 24.97 Gt with 95% confidence limits of 19.04 and 31.83 Gt. This represents approximately 3.5% of the total stock in the upper 30 cm of soil worldwide. Australia occupies 5.2% of the global land area, so the total organic C stock of Australian soil makes an important contribution to the global carbon cycle, and it provides a significant potential for sequestration. As the most reliable approximation of the stock of organic C in Australian soil in 2010, our estimates have important applications. They could support Australia's National Carbon Accounting System, help guide the formulation of policy around carbon offset schemes, improve Australia's carbon balances, serve to direct future sampling for inventory, guide the design of monitoring networks and provide a benchmark against which to assess the impact of changes in land cover, land management and climate on the stock of C in Australia. In this way, these estimates would help us to develop strategies to adapt and mitigate the effects of climate change.

Geostatistical analyses of spatial distribution and origin of soil nutrients in long-term wastewater-irrigated area in Beijing, China

The purpose of this study was to investigate the current status of soil fertility in the long-term wastewater-irrigated agricultural areas of Beiyechang District in the suburb of Beijing. A total of 103 soil samples from the top 20 cm of soil layer were collected and analyzed for macro- and micronutrient elements. The mean values of these elements were: total nitrogen (TN), 0.08 ± 0.02%; available nitrogen (AN), 60.34 ± 10.08 mg/kg; available phosphorus (AP), 19.59 ± 9.75 mg/kg; available potassium (AK), 84.22 ± 19.66 mg/kg; and availabilities of trace elements (B, Cu, Fe, Mn, Mo, and Zn), 0.29 ± 0.12, 1.44 ± 0.34, 8.97 ± 2.05, 5.44 ± 0.95, 0.27 ± 0.16, 1.16 ± 0.42 mg/kg, respectively. Compared with other similar areas, the overall soil nutrient content in the study area was still at a low level after nearly 30 years of wastewater irrigation. The organic matter content of wastewater-irrigated soils has significant impact on the accumulation of nutrient elements in these soils. Geostatistical analyses suggested that the spatial distribution of TN and AP was on account of agricultural practices, such as wastewater irrigation and fertilizer use. The availability of P, Mo, Cu and Zn may be due to the joint effect of soil parent material and wastewater irrigation. The availability of K, Fe and Mn was attributed to soil parent material. A significant availability of some elements occurred around sewage outfalls in the irrigation area and water canals, where the wastewater could be easily lifted. The knowledge of spatial distribution and sources of soil nutrients in such areas is the basis for undertaking appropriate farming and irrigation activities with rationalized utilization of treated wastewater.

Changes in the properties of soils in a solonetz soil complex thirty years after reclamation

The long-term (30 year) dynamics of a solonetz soil complex composed of solonetzic light chestnut soils and chestnut solonetzes under standard conditions and with the application of agromeliorative measures are considered. When the standard zonal agricultural practice is used, the soils of the solonetzic complex have unfavorable agrophysical, chemical, and physicochemical properties and low productivity. After 30 years of the standard three-level tillage of the soils to a depth of 40–45 cm, the productivity of the biogeocenosis decreased. Thirty years after a single rotary-milling subsoil treatment of the 20- to 45-cm soil layer using a milling tool FS-1.3, there were no morphological features pointing to the restoration of the solonetzic process. The humus content in the 0-to 20-cm and 20-to 40-cm soil layers was 2.3 and 1.7%, respectively; the content of adsorbed Na+ in the 20-to 30-cm layer was 11.6% of the total exchange capacity, or 38% lower than its content in the reference soil. The additional yield reached 30–70% and more of that obtained with the standard agricultural technology used during the whole period under investigation. The method of systems biogeotechnology (systems bio-geo engineering) is proposed as a method for the preventive control of soil evolution and the maintenance of the stability and high productivity of the soil cover.

Organic carbon stocks and erosion in the soils of Guangdong, South China

Soil organic carbon (SOC) storage and erosion in South China at the regional scale in the past decades remains far from being understood. This paper calculated the SOC density, storage and erosion in 14 soil classes in Guangdong Province, South China, based on statistical data from the soil survey and soil erosion survey of Guangdong, which was performed in the 1990s. The purpose of this study is to understand the relationships between soil classes and SOC erosion at the regional scale. The results indicated that the SOC density in the soils of Guangdong varied from 12.7 to 144.9 Mg ha−1 over the entire profile and from 12.6 to 68.4 Mg ha−1 in the top 20-cm soil layer. The average area-weighted SOC density in the topsoil (0–20 cm) and the entire profile was 32 ± 3 and 86 ± 4 Mg ha−1, respectively. The total SOC storage was 1.27 ± 0.06 Pg, with 35.6 % (0.46 ± 0.04 Pg) located in the topsoil. The average area-weighted strength of the SOC erosion in the 1990s was 20.6 ± 0.8 Mg km−2 year−1. The results indicated that SOC erosion was strongly related to soil class.

Effects of nitrogen management on root morphology and zinc translocation from root to shoot of winter wheat in the field

Nitrogen (N) nutrition is a critical factor in root uptake and deposition of zinc (Zn) into wheat grain. However, little is known about how the root system in the soil profile responds to various N supplies under field conditions. A two-year field experiment was conducted to investigate the temporal and spatial distributions of winter wheat roots and relationships between root morphological traits and root Zn uptake with different N supplies. Results showed that an increasing N supply improved root length density (RL), surface area (RSA) and root dry weight (DW), thereafter, resulting in an increased root Zn uptake. For example, root Zn uptake significantly and positively correlated with RL, RSA and root DW at jointing (r=0.608*, 0.540* and 0.785***, respectively) and flowering (r=0.611*, 0.602* and 0.876***, respectively) stages. Furthermore, substantial root DW (80–92%) and root Zn uptake (85–96%) were mainly recovered from the upper 30cm of soil layer irrespective of N supply, showing a good spatial matching. The increased ratios of shoot-to-root Zn concentration and shoot-to-total Zn content with the increasing N supply indicate improving N supply promotes the root-to-shoot Zn transport and increases shoot Zn nutrition. Shoot Zn content was positively correlated with final grain yield and grain Zn concentration. Thus, a combination of optimum N supply with breeding for a better root system could be a promising approach to improve root uptake and accumulation of Zn in grain to maintain relatively higher grain Zn for human nutrition.

Organic Amendments to a Wheat Crop Alter Soil Aggregation and Labile Carbon on the Loess Plateau, China

The Loess Plateau in China is one of the most severely eroded areas in the world. Understanding the characteristics of soil aggregation and the distribution of soil organic carbon (SOC) in aggregates on the plateau is essential for improving regional soil quality. A 2-year study was conducted in a wheat cropping system on the plateau to investigate short-term responses of soil aggregation measured via water stability and total as well as labile SOC (permanganate-oxidizable C [POXC]) fractions to organic amendments (low-, medium-, and high-level maize stalks, stalk composts, and cattle manure) combined with inorganic fertilization (nitrogen/phosphorous/potassium [NPK]). Compared with NPK fertilization, combined organic amendments enhanced soil aggregate stability mostly for 5-to 0.5-mm size classes. Among the treatments, high-level maize stalk plus NPK was associated with the greatest water stability of all aggregates and lowest aggregate deterioration rate (11.3%), followed by cattle manure plus NPK (21.2%). In the 0- to 20-cm soil layer, the SOC content had no significant changes among treatments, whereas the POXC content was significantly higher in the organically amended treatments (especially cattle manure plus NPK, 108.6 %) than in the NPK treatment (P< 0.05). In most aggregate size classes, the SOC content had no significant differences between the organically amended and NPK treatments, whereas the POXC content was significantly higher in the former than in the latter (P< 0.05). There were significant positive relations between the proportions of water-stable aggregates and POXC content (P< 0.05). Application of high-level maize stalk or manure plus NPK was effective for improving soil structure and SOC sequestration of the loess soil.

In Situ Monitoring of Soil Bulk Density with a Thermo-TDR Sensor

Monitoring spatial and temporal dynamics of soil bulk density (ρb) can be challenging, and ideally soil ρb measurements should be continuous in situ. The thermo-time domain reflectometry (TDR) technique is emerging as a useful technique for measuring soil ρb, with the advantages of being automated, rapid, and minimally destructive. The objective of this study is to evaluate the effectiveness of the thermo-TDR technique for monitoring the temporal dynamics of soil ρb under field conditions. Thermo-TDR sensors were installed at two experimental sites with different soil textures, silt loam and sandy loam, to monitor soil ρb continuously in the 0- to 10- and 10- to 20-cm soil layers. The results showed that the thermo-TDR ρb in general agreed with gravimetric ρb from the core method, and the differences between the two methods were within 8%. Compared with the core method, the thermo-TDR technique had the advantage of capturing the in situ ρb changes over time with minimal soil disturbance. We conclude that the thermo-TDR sensors can be used effectively to continuously monitor soil ρb under field conditions.

Comparative study on methods for computing soil heat storage and energy balance in arid and semi-arid areas

Observations collected in the Badan Jaran desert hinterland and edge during 19–23 August 2009 and in the Jinta Oasis during 12–16 June 2005 are used to assess three methods for calculating the heat storage of the 5–20-cm soil layer. The methods evaluated include the harmonic method, the conduction-convection method, and the temperature integral method. Soil heat storage calculated using the harmonic method provides the closest match with measured values. The conduction-convection method underestimates nighttime soil heat storage. The temperature integral method best captures fluctuations in soil heat storage on sub-diurnal timescales, but overestimates the amplitude and peak values of the diurnal cycle. The relative performance of each method varies with the underlying land surface. The land surface energy balance is evaluated using observations of soil heat flux at 5-cm depth and estimates of ground heat flux adjusted to account for soil heat storage. The energy balance closure rate increases and energy balance is improved when the ground heat flux is adjusted to account for soil heat storage. The results achieved using the harmonic and temperature integral methods are superior to those achieved using the conduction-convection method.

Density-Dependent Growth and Production of Nile Tilapia (Oreochromis niloticus) Fingerlings Relative to Phytoplankton and Periphyton Biomass

The growth, production and survival of Nile tilapia Oreochromis niloticus, with an average individual weight of 0.2 g were used to determine the density-dependent growth and production relative to phytoplankton and periphyton biomass in periphyton-based aquaculture. The trial was conducted in 10 m2 concrete tanks for a 56 day period. A 10 cm layer of soil was placed at the bottom of each tank. To act as substrates for periphyton, bamboo poles with an approximate submerged surface area of 50% to that of the total tank surface area were vertically posted in the tank bottom. A weekly fertilizer dose of urea and triple superphosphate at a rate of 28 kg N and 7 kg P/ha/week was added. Four stocking densities in triplicate were used: 5, 10, 20, and 40 fish/m2 (50, 100, 200, and 400 fish/tank). The results indicated that the carrying capacity of periphyton-based tanks for Nile tilapia was 293 g/m2 in a 56-day culture period. The relationships between gross yields of tilapia (y) and periphyton dry matter (x), or chlorophyll a (x) were described as y = 353.2483-109.1809x, R2 = 0.5646, P = 0.005, y = 125.5916 + 0.9698x, R2 = 0.5841, P = 0.004. Provision of substrates at 50% of total tank surface area was sufficient for periphyton production in nutrient-rich aquaculture ponds where grazing rate and fish density in the system are balanced.DOI: http://dx.doi.org/10.3126/on.v11i2.9646 Our Nature 2013, 11(2): 105-115

Protected Nursery Aided Popularization of Jehlum – A High Yielding Rice Variety to Enhance Productivity and Profitability under Mid Altitude Temperate Conditions of Kashmir Valley

Temperature fluctuations and lower night temperature during April and May not only pose great threat to paddy nurseries but also results in slow growth of seedlings, which delays rice transplanting in temperate Kashmir valley. The farmers of mid altitude alleviations grow traditional varieties like K-332 and Kohsar, which have low yield potential. Jhelum, a high yielding rice cultivar famous for yield potential and quality in the planes of valley is now occupying maximum area under mid altitude temperate conditions. The adaption of Modified Protected nursery, to save nursery from climatic vagaries and to simultaneously provide robust and healthy seedlings in a short period, ensures early transplanting and boost the yield potential of the variety in mid altitudes. In view of this-on-farm trials on modified protected nursery (Improved practice) verses open nursery (Farmers’ practice) were conducted at Farmers’ field. In modified protected nursery the medium consisted of a 20–25 cm layer of soil, sand, organic manure and ash mixed in the ratio of 2:2:1:1, which was laid on polythene sheet. Nursery was kept covered with polythene during cloudy/rainy days and also during night hours particularly for initial 10–15 days after sowing. Seedlings under protected nursery technique were healthy and robust and ready for transplanting 8–10 days earlier compared to farmers’ practice. Yield attributes and grain yield improved appreciably in improved practice over farmers’ practice. Panicles/m2(387), grains/panicle (85) and 1000 gain weight (22.9g) were higher in protected practice as compared to farmers’ practice. Grain yield was more (61.7q/ha) in the improved practice. An increase in the grain yield to the tune of 12 per cent with wet profit (Rs.61,240/ha) and B:C ratio (2.4:1) was recorded in the improved practice of modified protected nursery as against net returns of Rs. 53,580/ha and B: C ratio (2.1:1) in farmers’ practice.

Examination of Vertical Distribution of Fine Root Biomass in a Tropical Moist Forest of the Central Amazon, Brazil

Fine roots are an important component of the carbon flow of forests. Soil properties in tropical forest (terra firme forest) of the Central Amazon differ substantially along topography, and the biomass and vertical distribution of fine roots may also differ accordingly. Information on the vertical distribution of fine roots is essential to obtain unbiased estimates of fine root biomass. Accordingly, we examined fine root biomass and its vertical pattern along the gradient of topography in a typical terra firme forest in this region. The regressions on the cumulative fine root biomass along soil depth (at 5 cm intervals from 0-40 cm in depth) revealed significantly different vertical distribution of fine root biomass among three topographic habitats (lower-slope valley called baixio, mid-slope, and upper-slope plateau). A shallower rooting pattern was observed in the plateau than the other habitats, while fine root biomass was larger in the baixio than the plateau – a difference likely attributable to the soil physical properties than the aboveground stand structures among the sites. More than 74 and 93% of the fine root biomass was estimated to be distributed within the upper 20- and 40-cm soil layers, respectively. Our results suggested that a shallow sampling depth, which is common in fine root research in the Amazon, would be reasonable, though we should examine the consistency of our results in different regions.

Productivity of Marandu grass as a function of liming and phosphate fertilization in a Typic Hapludult from Amazonia

Little information is available concerning liming and phosphate fertilization for grassland maintenance in Amazonia. The dry-weight yield of Brachiaria brizantha was assessed over three harvest periods as a function of top-dressing with lime and phosphorus. The experimental design consisted of fully randomized blocks with four replicates arranged in subdivided plots according to the sampling season (plots), phosphorus application rate (0, 30 and 60 kg ha–1 P2O5) (subplots) and presence or absence of liming (sub-subplots). The grass was harvested by cutting 25 cm above the soil level, and the 0- to 5-, 5- to 10-, 10- to 20- and 20- to 40-cm soil layers were sampled 3, 9 and 13 months after liming. Top-dressing with phosphorus and lime had no effect on the dry-weight yield, nutrient uptake or crude-protein percentage of the Brachiaria brizantha shoots. However, phosphorus and lime treatment reduced the soil acidity and increased the calcium, magnesium and phosphorus levels in the upper soil layers.