Wet Clay Soil Research Articles

Clays as Micro-Electrodes in Environmental Detoxification

AbstractIn-situ reduction of contamination in soil and groundwater is an ongoing challenge that often requires a multi-pronged approach for effective and efficient clean-up. Spontaneous or assisted electrochemical reactions that break down certain pollutants held on clay surfaces can render natural clays a unique and powerful ally in environmental mitigation of contaminated soils. Application of a low-level DC electric field (mV/cm) has been shown to facilitate transformation of some compounds and ionic species through redox reactions in addition to transporting them through the pores in wet clay soils. Results from previous tests suggest that the natural electrochemical processes that promote pollutant sloughing or chemical breakdown can be enhanced for targeted treatment by applying low-level electric field to the contaminated soil with clay content. The central idea of this hypothesis is that clay, due to its surface charge and electrostatic interaction with adjacent pore fluid, acts as a “micro-electrode” through the diffused double layer (DDL) interactions when subjected to an external electric field. This hypothesis, proven viable, may unlock potential ability of natural clays to generate beneficial reactions for detoxification of contaminated sub-surfaces. Evidence from past laboratory experiments accompanied by a proposed electrical model of clay behaving as a micro-electrode are presented in this paper. The laboratory experiment results support the proposed electrical model.

Land–atmosphere coupling exacerbates the moisture-associated heterogeneous impacts of compound extreme events on maize yield in China

Compound climate events are major threats to crop production under climate change. However, the heterogeneity in the impact of compound events on crop yield and its drivers remain poorly understood. Herein, we used empirical approach to evaluate the impact of compound hot–dry (HD) and cold–wet (CW) events on maize yield in China at the county level from 1990 to 2016, with a special focus on the spatial heterogeneity. Our findings indicate comparable impact of extremely compound CW events (−12.8 ± 3.6%) on maize yield loss to extremely compound HD events (−11.3 ± 2.1%). The spatial pattern of compound HD and CW events impacts on maize yield was dominantly associated with moisture regime, followed by management practices and soil properties. Specifically, drier counties and counties with less fraction of clay soil and organic carbon tend to experience greater yield loss due to compound HD events, and wet condition, excessive fertilizer, clay soil and rich organic carbon aggravate the maize yield loss due to compound CW events. Moreover, the land–atmosphere coupling exacerbated the heterogeneous yield impact through divergent heat transfer. In drier regions, the greater proportion of sensible heat creates a positive feedback between drier land and hotter atmosphere. In contrast, the greater proportion of latent heat in wetter regions results in a positive feedback between wetter land and colder atmosphere. Our results highlighted a critical element to explore in further studies focused on the land–atmosphere coupling in agricultural risk under climate change.

Innovative no-till seeding technology improves yield and nitrogen use efficiency while reducing environmental pressure in wheat after rice harvesting

Optimizing tillage and seeding strategies is important for increasing crop productivity and nitrogen use efficiency (NUE) while reducing environmental impact. A newly developed innovative no-till seeding (INtS) technology was shown to effectively enhance seeding quality and increase wheat yield in wet clay soil after puddled rice harvest in the Yangtze River Basin (YRB) of China. However, comprehensive assessments of the yield, NUE, and eco-environmental benefits of INtS technology have not been performed. The present study conducted a consecutive three-year field experiment combining field plots and microplots with the 15N tracer method using two wheat seeding technologies (INtS and typical rotary-till seeding (TRtS) technology) and three nitrogen (N) application rates (0, 90, and 180 kg ha−1). The study evaluated the yield, NUE, fate of fertilizer/straw N, N budgets, and environmental footprints of wheat production after rice harvesting. The results showed that compared with TRtS, the average yield, N uptake and NUE of wheat under INtS technology increased by 27.2%, 28.9%, and 31.9%, respectively. By tracing the multi-seasonal fate of 15N-labeled fertilizer/straw N in soil-crop systems, it was found that 43.8% and 6.0% of fertilizer N and rice straw N applied in the first wheat growing season were recovered by wheat plants in the same season under INtS technology, which significantly decreased to 29.0% and 4.1% for TRtS technology. Over the five growing seasons, the cumulative recoveries of fertilizer and straw N for INtS technology were 26.2% and 15.6% higher, while the total fertilizer and straw N losses were 20.6% and 20.0% lower than those for TRtS technology, respectively. Over 50% of straw N remained in the soil after the fifth growing season, while only 14.5–23.6% of fertilizer N remained. In addition, INtS technology significantly reduced the fertilizer/straw N losses when applied in the subsequent rice growing season. Unlike TRtS technology, INtS could maintain a low-level soil N balance (2.1 kg N ha−1 for N180) and generate less soil surface N surplus in the wheat growing season. On average, INtS significantly reduced the carbon footprint and N footprint in the wheat growing season by 26.8% and 19.1%, respectively. In conclusion, INtS technology can significantly improve crop production and agricultural sustainability while minimizing negative environmental impacts for wheat production after rice cultivation in the YRB of China and other areas of the world with similar field conditions.

Early sowing increases nitrogen use efficiency of sunflower in wet clay soils

AbstractEarly sowing increases yield potential of sunflower on wet, saline clay soils but the effects on nitrogen (N) requirements have not been determined. In a 2‐year study on a drainable field with wet, saline clay soils in southwestern coastal Bangladesh, we investigated nitrogen use efficiency (NUE) and yield responses to N rates (0, 60, 90, 120, 150, 180 and 210 kg ha−1) for zero‐till sunflower cv. Hysun‐33 sown from November 30 (early) to December 30 (late). Early sowing produced highest seed yield (3.59 ton ha−1) and oil yield (1400 kg ha−1) at 150 kg N ha−1. Delayed sowing (December 15–December 30) reduced seed and oil yields by 4%–15% and 7%–18%, respectively. In late sowing, crops suffered from multiple stresses (soil–water deficit, salinity, and heat), which decreased yields. The N fertilizer requirement in late sowing was higher (180 kg ha−1) to achieve maximum yield, yet the yield was lower than from earlier sowing. Compared with nil N supply, the rates of 60–150 kg N ha−1 increased seed and oil yields of the early‐sown sunflower by 1.3–3.3 times and 1.2–2.9 times, respectively, whereas the rates of 180–210 kg N ha−1 decreased seed and oil yields by 2%–5% and 7%–14%, respectively. Higher net profit (US$764) was also achieved from earlier sowing with 150 kg N ha−1. We conclude that under wet and saline clay soils, higher sunflower yield in early sowing is attributable to lower stress that increased NUE and decreased N requirement.

Heat exchange modeling between the air flow and the metro ventilation shaft lining in the conditions of St. Petersburg, Russia

Icing of the injection layer in underground tunnels and ventilation shafts leads to wear, destruction of supporting structures and flooding. In St. Petersburg the air temperature in winter can drop to -25 ° C, what can lead to these phenomena in the subway facilities. The article presents the modeling results of a viscous three-dimensional air flow, heat and mass transfer of a metro ventilation shaft in the Ansys CFX program. A numerical model of the ventilation shaft and the surrounding soil consisting of five layers has been developed: air; foam glass concrete; prefabricated cast-iron tubing lining; injection layer; soil massif. The parameters of the computational grid and the boundary conditions of the problem are specified. Two models of the ventilation shaft with an axial length of 1 m and 10 m were built. Temperature plots are constructed for three tasks, where the injection layer consists of water, wet clay soil and average between water and wet clay soil. The choice of overall thermal and technical characteristics of the thermal insulation material during the reconstruction of the existing ventilation shafts in three different sealing space conditions is confirmed.

Analysis and Simulation of Wheel-Track High Clearance Chassis of Rape Windrower

The middle and lower reaches of the Yangtze River are the main production area of rapeseed. Small windrowers with two tracks are adopted in this area, which have lower efficiency. With the advancement of large-scale rape planting, medium and large windrowers are urgently needed; however, most medium and large windrowers are wheeled machines which have poor adaptability to sticky soil in rice–rape rotation areas. Therefore, a wheel-track high clearance chassis for rape windrower was developed. Theoretical analysis and simulation of the main performance of this chassis were investigated. Mathematical models of the relationship between the chassis eccentricity and running resistance, uphill and downhill angle and the height of obstacle were established. Then, three-dimensional modeling and dynamic simulations of a wheel-track high clearance chassis of a rape windrower in wet clay soil were carried out based on Pro/E and RecurDyn software. The simulation results indicated that when the chassis ran on flat hard road at the same speed, eccentricity had little effect on average walking speed; the coefficient variation of speed decreased with the increase of eccentricity, while the driving torque and its coefficient variation decreased first and then increased. The minimum driving torque and the coefficient variations were obtained when the eccentricities were 1484 mm and 1584 mm. Field experiments were carried out on two kinds of ground. The results showed that on flat hard road, the speed of the wheel-track high clearance rape windrower was 0~20.22 km/h, the minimum turning radius was 5.965 m; on rice stubble field with 38.7% water content, the working speed was 0~9.12 km/h, the minimum turning radius was 6.498 m, and the climbing angle was over 20°. All parameters of the wheel-track high clearance chassis met the design specifications, and the working efficiency increased over 100% compared with the existing two-tracked rape windrower. A new kind of rape windrower for the middle and lower reaches of the Yangtze River was provided.

Development and performance evaluation of a wet-resistant strip-till seeder for sowing wheat following rice

Seedling establishment is critical for grain yield and net benefits of wheat in wet clay soil after puddled rice harvest in the Yangtze River basin (YRB) of China. A wet-resistant rotary strip-till seeder (WR seeder) was developed to drill seeds in zero tillage (ZT) conditions with complete rice residue mulching. The rotary blades adopted were medium radius C type blades creating a 50–60 mm wide and 30–50 mm deep furrow for seed placement. The pressing roller, usually used in the traditional wheat seeders, has been replaced by two ground wheels covered in rubber to reduce the mud adhesion. Moreover, a stainless-steel chain was installed behind the machine for better seed covering with soil. Based on three-year long field comparisons with the traditional deep tillage seeder (DT seeder) and a rototiller disc-type seeder with shallow tillage (SHT seeder), the six-row WR seeder significantly enhanced seedling establishment, and reduced energy consumption by 51.3% and 24.5%, respectively. The WR seeder also conserved the topsoil moisture. Over three years, the WR seeder produced similar grain yield to the SHT seeder, but 3.1% more than the DT seeder. Moreover, the net profit with WR seeder increased by 39.4% and 0.9% compared to the DT and SHT seeders, respectively. Furthermore, comparisons across the YRB also confirmed the positive effects of the WR seeder on grain yield and economic benefits over the conventional seeding practices. Thus, it was demonstrated that the improved seeder is an optimal option to enhance the RW system productivity in the YRB. • A strip-till seeder was developed for wheat sowing in wet clay fields. • Yield superiority and energy efficiency with the improved seeder were demonstrated. • The wheat yield increase resulted from the large increase in fertile spikes. • Effective residue management enhances the seeder performance.

Analysis of Adhesion between Wet Clay Soil and Rotary Tillage Part in Paddy Field Based on Discrete Element Method

To analyze the process of wet clay soil adhering to the rotary tillage part during rotary tillage in paddy field, simulation tests were carried out based on the discrete element method (DEM) in this study. The Plackett-Burman (PB) test was applied to obtain simulation parameters that significantly affected the soil adhesion mass. The Box-Behnken design (BBD) based on the principle of response surface method (RSM) was used to establish a regression model between significant parameters and soil adhesion mass. The soil adhesion mass obtained from the actual soil bin test as the response value was brought into the regression model. The optimal simulation parameters were obtained: the particle-particle coefficient of rolling friction, the particle-geometry coefficient of static friction, and the particle-particle JKR (Johnson-Kendall-Roberts) surface energy were 0.09, 0.81, and 61.55 J·m−2, respectively. The reliability of the parameters was verified by comparing the soil adhesion mass obtained under the optimal simulation parameters with the actual test value, and the relative error was 1.84%. Analysis of the rotary tillage showed that soil adhesion was mainly concentrated in the sidelong section of the rotary blade. The maximum number of upper soil particles adhering to the rotary tillage part was 2605 compared to the middle soil and lower soil layers. The longer the distance the rotary tillage part was operated in the soil for, the more soil particles would adhere to it. This study can provide a reference for the rational selection of simulation parameters for rotary tillage and the analysis of soil adhesion process in rotary tillage.

Optimal design and setting of rotary strip-tiller blades to intensify dry season cropping in Asian wet clay soil conditions

Fine-textured clayey soils dominate Asian rice fields that are kept either fallow or cultivated with non-rice crops after harvest of monsoon rice. Use of seeding machinery compatible with the principles of conservation agriculture on such soils, however, has not been promising. Under these conditions – which predominate the population and poverty dense areas of coastal South Asia – such machinery fails to open a furrow or throws excessive soil out of the tilled furrow during strip-till seeding. This results in a poor seed coverage at planting jeopardizing crop establishment. In response, this soil bin study investigated strip-tillage blade designs and settings to optimize rotary strip-till system for wet clay soil conditions common in South Asian rice fields. Three designs of C type rotary blade (conventional, medium and straight) and two blade settings (four and six blades per row; 50 and 100 mm cutting widths) were tested at three blade operating depths (50, 75, and 100 mm) using a tillage test rig and a soil bin, and a high-speed camera to understand the processes of soil cutting, throwing, backfilling, and creation of furrow seedbed. The soil bin soil consisted of a wet sandy-clay-loam soil with a moisture content of 28.2% (85% of field capacity) and was compacted to the bulk density of 1440 kg m−3. Using the test rig, rotary speed of the blades was maintained at 480 rpm and forward speed at 0.4 m s−1. At four blades per row setting, all blades created high amounts of optimum clods (1–20 mm size). The conventional and medium blades threw too much soil out of the strip-tilled furrow while the straight blade created adequate backfill at 75 and 100 mm operating depths. At 6 blades per row setting, all blades produced high amounts of backfill at any depths, but the straight blade also produced the highest amounts of optimum clods and a uniform furrow. Considering machine and energy costs, blade performance, and the necessity of minimizing soil disturbance in strip-tillage, our study indicates that the use of straight blades (four blades per row) operated at a depth of 75 or 100 mm are more ideal. These specifications are likely to enhance strip-tillage stand establishment in fine-textured soils with high moisture contents, though further work is needed under actual field conditions to confirm suitability of the proposed strip-till system for crop establishment in currently fallowed as well as the intensively cropped lands of Asia.

Variation in the yield of sunflower (Helianthus annuus L.) due to differing tillage systems is associated with variation in solute potential of the soil solution in a salt-affected coastal region of the Ganges Delta

Intensification of crop production in the coastal zones of the mega-deltas of Asia by dry season cropping requires timely crop establishment to mitigate the adverse effects of waterlogging, drought, salinity and poor soil structure. In the salt-affected coastal zone of the Ganges Delta, the best method of mechanized cultivation for the timely establishment of non-rice dry season crops on poorly structured, wet clay soils is unknown. Two field experiments were conducted to evaluate the effects of tillage systems with different levels of soil disturbance on the establishment, growth and yield of sunflower, and on soil physical and chemical properties. In 2016-17, five tillage treatments were tested: zero tillage (ZT), narrow strip tillage (NST), bed planting (BP), single pass shallow tillage (SPST) and double pass shallow tillage (DP); in 2017-18, four tillage types were tested: NST, wide strip tillage (WST), BP and SPST. Intensive soil disturbance (BP, DP and SPST) maintained higher soil water content in the surface soil (0–15 cm depth) than less disturbance (ZT, NST and WST) in both years. Tillage treatments had no effect on soil salinity (EC1:5) in 2016-17, but in 2017-18 BP significantly reduced the soil salinity relative to NST throughout the season. Highest yields (19 % and 10 % improvements in 2016-17 and 2017-18 respectively) were associated with tillage treatments with greatest soil disturbance, the BP and DP treatments in 2016-17, and the SPST treatment in 2017-18. These effects were mostly due to increases in soil water content and solute potential in surface soil layers. We conclude that for a wet-clay soil, heavy soil disturbance, such as with BP has the potential to increase the yield of sunflower by increasing soil water supply, decreasing soil salinity and maintaining a higher solute potential in the upper soil layers.

The shear strength alteration on clay soil considering the plasticity index and the percentage of fine aggregates in tropical climate regions

Seasonal changes in tropical regions could cause variations of soil water content, especially in clay soil. Furthermore, there is a significance difference in shear strength between wet and dry clay soil which depends on the plasticity index and the percentage of fine aggregates. Laboratory experiments were conducted to investigate the effect of the plasticity index and the percentage of fine aggregates in clay soil on soil shear strength changes due to water content variation. Soil samples were obtained from five locations in Surabaya City, Indonesia. The soil characteristics were tested in a laboratory to obtain the initial water content, Atterberg limits, specific gravity, and soil size distribution. The next stage was drying the soil samples. Each one was stored at room temperature to reach the determined soil weight. The shear strength of the soil in initial and drying conditions was determined by an unconfined compression test. The results indicated that the lower the moisture contents of soil, the greater the shear strength of soil, and vice versa. Soil shear strength changes up to 52 times within the range of 36% to 72% of moisture content The results also show that the value of shear strength variation depends on the plasticity index and the percentage of fine aggregate.

Frogs seek hypoxic microhabitats that accentuate metabolic depression during dormancy.

Many animals occupy microhabitats during dormancy where they may encounter hypoxic conditions (e.g. subterranean burrows). We used the green-striped burrowing frog (Cyclorana alboguttata) to test the hypothesis that animals seek hypoxic microhabitats that accentuate metabolic depression during dormancy. We first measured the partial pressure of oxygen (PO2 ) within artificial cavities excavated in wet clay soil, which simulated C. alboguttata underground aestivation chambers, and recorded hypoxic conditions (PO2 as low as 8.9 kPa). Using custom-built tunnels that maintained a longitudinal PO2 gradient (hypoxic to normoxic), we then examined the PO2 preference of C. alboguttata in response to drying habitat conditions. In support of our hypothesis, we found that C. alboguttata chose to spend a greater proportion of time at the hypoxic end of the PO2 gradient compared with the normoxic end. To determine whether hypoxia accentuates metabolic depression in C. alboguttata, we exposed frogs to normoxia (21.0 kPa) or hypoxia (10.5 kPa) for 7 weeks during the transition from an active to an aestivating state. We found that hypoxia exposure accelerated the onset of metabolic depression in C. alboguttata by 2 weeks. Furthermore, we found that frogs exposed to hypoxia exhibited a 66% reduction in O2 consumption after 7 weeks compared with active frogs in normoxia, whereas frogs exposed to normoxia reduced O2 consumption by only 51%. Overall, our findings indicate that some animals may seek microhabitats to maximally depress metabolic rate during dormancy, and that microhabitat O2 availability can have significant implications for energy metabolism.

Ground penetrating radar (GPR) detects fine roots of agricultural crops in the field

Ground penetrating radar (GPR) as a non-invasive technique is widely used in coarse root detection. However, the applicability of the technique to detect fine roots of agricultural crops is unknown. The objective of this study was to assess the feasibility of utilizing GPR to detect fine roots in the field. This study was conducted in four locations with different soil types and soil moisture conditions in Texas. Several varieties of winter wheat and energy cane were scanned with GPR (1600 MHz). Soil cores were collected immediately after scanning to measure root parameters. Using an image analysis software, four pixel indices with or without intensity threshold were used to assess the relationships between GPR signal and root parameters. There were significant relations between GPR indices and root parameters depending on soil conditions. The accuracy of root estimation was higher in wet clay soils than in dry sandy soils. Estimated root parameters from GPR had lower variation than measured roots. Average GPR pixel intensity without intensity threshold may be better to reflect root information than pixel indices with intensity threshold. This study demonstrates that GPR has the potential to predict bulk root biomass and diameter in winter wheat and energy cane.

Experimental Investigation of Rapid Stabilization of Soft Clay Soils Using Chemical Admixtures

The rapid treatment of soft soil foundation is one of the main ways to solve problems associated with road construction. This study was conducted to determine the most effective stabilizer to increase the strength of wet and soft clay soils within 72 hours for rapid road construction. Extra admixtures are added to accelerate the reactions of cement and improve the stabilization effect. Using the unconfined compressive strength test (UCS), the effectiveness of admixtures was compared with that of a common cement-based binder. The results show that the addition of extra admixtures could rapidly improve the early strength of cement stabilized soils.

The Biological Flora of Coastal Dunes and Wetlands:Solidago sempervirensL. andSolidago sempervirensL. subsp.mexicana(L.) Semple

ABSTRACT Lonard, R.I.; Judd, F.W., and Stalter, R., 2015. The biological flora of coastal dunes and wetlands: Solidago sempervirens L. and Solidago sempervirens L. subsp. mexicana (L.) Semple. Solidago sempervirens L. and Solidago sempervirens L. subsp. mexicana (L.) Semple are New World humid continental, temperate, subtropical, and tropical maritime taxa. Both taxa are long-lived perennials that occur in wet mineral sands and clay soils. Reproduction is primarily vegetative in stable sites. However, achene/seed production is prolific, and seed viability is high in either stable or disturbed sites. Also known as seaside goldenrod, both taxa occur in conditions ranging from freshwater to salinity conditions of 40 parts per thousand. Seeds and seedlings do not tolerate excessive burial, but high levels of sand deposition are associated with plant vigor in mature clones. Optimal growth for both taxa occurs in habitats with increasing distance from the water table.

A Study of Ground Water Potential for Sustainable Development in Igbo-Ora, Oyo State, Nigeria

The entire system of Opeki Dam serving the Igbo-Ora Community of Oyo State is spent. Rainfall, rivers, ponds and swamps are seasonal and grossly inadequate. There are quests for alternative sources of supply. The objective of this paper is to ascertain the reliability of ground water as an alternative source in Igb – Ora, Oyo State of Nigeria. Electrical Resistivity method of Geophysical investigation was adopted using Rectified Resistivity Meter (RRM) Model. Readings were taken of the earth resistance by sending fairly large current I(µ A) into the ground. Data were collected from three locations: Igbole, Saganun, and Isale-Oba. A typical geo-electric section showing the thickness, depth, and lithography reveals that topmost is sandy clay soil (1m), followed by wet clay soil (2.1-3.1m); and at a depth of about 8.7m is the unsaturated weathered basement rock which is about 5.6m thick. Saturated weathered basement rock is about 11.3m thick and it is 20.0m deep on the average. The average resistivity within the first 1m is 120.3Ωm and it is 156.1Ωm to a depth of 20.0m. The groundwater potential may be feasible at the sounded points with average groundwater yield: An overburden unit depth of about 25m (on the average and total drill depth of between 35 and 38m). For sustainable water, the hole must be properly cased to a stable earth unit below the overburden unit.

Modeling of Urea Release from Briquettes Using Semi infinite and Shrinking Core Models

Briquetted urea is commonly used in wet agricultural soils since it has potential to reduce loss of urea occuring in the fields by various mechanisms. In the present study, commercially available uncoated urea briquettes were subjected to release in wet loam and wet silty clay soils, both maintained at 40% moisture, measured on dry basis. Adapted semi infinite model and developed shrinking core model predictions were compared with the experimentally determined concentration profiles and unreleased quantity of urea, respectively. Semi infinite model developed with the assumption of unchanging briquette size did not match well with experimental results. However, shrinking core model predicted the unreleased urea contents in briquettes reasonably well.

The vicissitudes of vivianite as pigment and corrosion product

Vivianite, hydrated ferrous phosphate, Fe2+ 3(PO 4)2˙8H2O, can be formed in the soil under reducing conditions. It occurs in wet clay soils, in the presence of a source of phosphate ions such as decomposing bone, and in the absence of sulphur compounds. As an iron corrosion product it sometimes preserves iron finds in excellent condition. When exposed to air, it undergoes oxidation to Fe3+ -containing species, which cause a shift in colour from pale blue to darker blue or blue-green. Vivianite has also been used as a pigment, and the number of published occurrences has been increasing steadily over the last few years. It can discolour, a problem encountered in both Romanesque wall paintings and seventeenth-century Dutch paintings. The occurrence of vivianite as a pigment is sufficiently rare to provide information on dating and provenance. All published occurrences of the pigment to date are reviewed.

Tree Nutrition and Forest Fertilization of Pine Plantations in the Southern United States

Abstract The growth of many pine plantations in the southern United States is limited by soil nutrient availability. Therefore, forest fertilization is a common silvicultural practice throughout the South. Approximately 1.2 million ac of pine plantations were fertilized in 2004. In the last 10 years, considerable advances have been made in identifying the ecophysiological basis for stand growth and the response to fertilizer additions. Nitrogen (N) and phosphorus (P) are the nutrients that most commonly limit growth of southern pine. On wet clay soils in the lower Coastal Plain and on some well-drained soil in the upper Coastal Plain, severe P deficiencies exist. On these soils, P fertilization with 25–50 lb of P per acre at the time of planting produces a large and sustained growth response, on the order of 50 ft3 ac−1 yr−1 (1.5 tn ac−1 yr−1) throughout the rotation. On most other soils in the South, chronic deficiencies of both N and P exist. On these sites, soil nutrient availability often is adequate early in the rotation when tree demand is small. However, around the time of crown closure, N and P frequently become limiting. Fertilization with both N and P in these intermediate aged stands typically increases growth for 8–10 years. The growth response to a combination of 25 lb of P per acre plus 200 lb of N per acre averages around 55 ft3 ac−1 yr−1 (1.6 tn ac−1 yr−1) for an 8-year period. The amount of leaf area in the stand is the main factor determining the current growth rate of the stand and the potential growth response after fertilization. When stand leaf area index is less than 3.5, light capture by the stand is restricted and growth is negatively affected. In many of these stands, fertilization will increase leaf area because of increased soil nutrient availability and thus increase growth. The financial return after fertilization depends on the growth response that occurs, the cost of the fertilizer treatment, and the stumpage value of the timber produced. Using a growth response of 55 ft3 ac−1 yr−1 over 8 years, a fertilizer cost of $90 ac−1, and stumpage values from the first quarter of 2006, the internal rate of return from midrotation fertilization of a loblolly pine plantation with N and P would be approximately 16%.

Comparative Performance of Some Bullock Drawn Puddlers

Four different bullock drawn puddlers were tested under wet sandy clay loam soil conditions and the comparative performance was evaluated from mechanical, ergonomical and economical aspects. From the results it was found that the improved rotary puddler gave better performance than others tested. The puddling index, draft requirement, vibration level and energy expenditure rate were 67.9%, 42.3 kg, 0.910 RMS/acc. mls2 and 5.02 k cal/min respectively. The work load was graded as moderately heavy. The cost of operation for two passes was calculated to be Rs.224.00/ha.