Increase In Filtration Rate Research Articles

Grassland development in tropical and subtropical southern China

China’s 79 million ha of tropical and subtropical grasslands represent a significant national forage resource with a potential for further development for sustainable livestock production. The species rich original forest vegetation has been converted through natural and human activities to secondary forest, grassland and agricultural land. The grasslands which include savannah, shrubland, coppice forest and arable land sown with exotic legumes and grasses are expected to become China’s third largest livestock production zone. Despite degradation the grasslands retain a high level of biodiversity which has been preserved in germplasm depositories with on-going collection expeditions throughout south China. Productivity of natural grasses is moderate (<5 t DM/ha) but can be increased significantly by augmenting with Stylosanthes and other introduced legumes adapted to the infertile or acidic soils and seasonal rainfall. Stylosanthes species which is used for grazing, green chop or leaf-meal production, as well as a cover crop in orchards, plantations and forest are successful because they are simple to establish and deliver immediate profits to farmers through improved livestock production or sale of forage for leaf meal manufacture. On-going plant breeding programs are delivering new higher yielding legume and grass cultivars with disease resistance and acid soil tolerance. They are expanding selection priorities to address environmental concerns (e.g. soil acidifying legumes) and to meet the needs of new integrated production systems. Introduced legumes and grasses have provided benefits to the environment through improved soil fertility, reduced soil erosion, increased infiltration rates and reduced weed invasion. Experts believe that the southern tropical and subtropical grasslands still have the capacity to safely increase production and contribute significantly to the improvement of the regional ecosystem. However, this can only be achieved if current programs on germplasm preservation, breeding new cultivars and developing management systems for integrated production systems need to be balanced with work precision livestock management and promotion of monitoring individual animal performance to achieve improved livestock production efficiency.

Quantifying heterogeneity in variably fractured sedimentary rock using a hydrostructural domain

Characterizing permeability at a regional scale where fracture distributions are heterogeneous can be aided by defining hydrostructural domains. A hydrostructural domain approach is applied to a fracture data set for Mayne Island, one of the Gulf Islands in British Columbia, Canada. Fracture domains were defined using changes in fracture intensity, and are represented and modeled using a stochastic, discrete fracture-network approach. Models that statistically honor field data were constructed for representative stations for three hydraulically distinct, hydrostructural domains: “highly” fractured, interbedded mudstone and sandstone (IBMS-SS) ( 1.0-m spacing), and fault and fracture zones (FZ). The highly fractured IBMS-SS and FZ domains have a greater potential porosity compared to the LFSS domain due largely to greater fracture intensities. The two highly fractured domains (IBMS-SS and FZ) have an average permeability, on the order of 10 −13 m 2 , due to enhanced fracture-network connectivity. In contrast, the LFSS domain has an average permeability of 10 −14 m 2 . The possibility of increased infiltration rates within FZ domains, coupled with a high-storage potential relative to the other domains suggests that fault zones with similar characteristics are likely zones of recharge. As a result, these recharge zones have an increased capacity to store and transmit infiltrated water throughout the interconnected fracture network. This study demonstrates that hydrostructural domain modeling provides a good foundation upon which to simulate flow and transport in regional groundwater resource studies.

Challenges in Dewatering of Indian Medium Coking Coals: Case Studies with Chemical Reagents

At the West Bokaro Washery of Tata Steel, India, the coarse coal is dewatered in a vibrating basket centrifuge and fine clean coal is dewatered in a screen bowl centrifuge. Due to the higher amount of fine fraction (0.038 mm) treated in the flotation circuit of the washery (about 9% of ROM), the moisture content of the clean coal fines is high. A polyacrylate surfactant reduced the fine coal moisture content by 8% and it was found to be the best among the various reagents tested in the laboratory. The chemical was found very effective for dewatering the coarse clean coal. Laboratory and plant trials showed that through treating only the coarse clean coal by the surfactant, the moisture in the composite clean coal could be reduced from 12.0% to 9.8%. The optimum dosage of the reagent was 0.24 kg/t dry coal. Laboratory-scale filtration using coagulant and surfactant increased filtration rate of centrifuge centrate. Also, the final moisture content was found to be 10% less than that obtained without addition of any reagents. For improving the clarity of thickener overflow, anionic polyacrylate based flocculant was found better than present plant flocculant based on polyamide. The optimum dosage of the recommended flocculant was 0.012–0.016 kg/t of dry fine coal.

Erosion rates and nutrient losses affected by composted cattle manure application in vineyard soils of NE Spain

Land preparation for mechanisation in vineyards of the Anoia–Alt Penedès region, NE Spain, has required major soil movements, which has enormous environmental implications not only due to changes in the landscape morphology but also due to soil degradation. The resulting cultivated soils are very poor in organic matter and highly susceptible to erosion, which reduces the possibilities of water intake as most of the rain is lost as runoff. In order to improve soil conditions, the application of organic wastes has been generalised in the area, not only before plantation but also every 3–4 years at rates of 30–50 Mg ha − 1 mixed in the upper 30 cm. These organic materials are important sources of nutrients (N and P) and other elements, which could reduce further fertilisation cost. However, due to the high susceptibility to sealing of these soils, erosion rates are relatively high, so a higher nutrient concentration on the soil surface increases non-point pollution sources due to runoff. The aim of this study is to analyse the influence of applied composted cattle manure on infiltration, runoff and soil losses and on nutrients transported by runoff in vineyards of the Alt Penedès–Anoia region, NE Spain. In the two plots selected for the analysis, composted cattle manure had been applied in alternate rows 1 year previous to the study. In each plot soil surface samples (0–25 cm) were taken and compared to those of plots without manure application. The study was carried out at laboratory scale using simulated rainfall. Infiltration rates were calculated from the difference between rainfall intensity and runoff rates, and the sediment and total nitrogen and phosphorus were measured for each simulation. In addition, the influence of compost was investigated in the field under natural rainfall conditions by analysing the nutrient concentration in runoff samples collected in the field (in the same plots) after seven rainfall events, which amount different total precipitation and had different erosive character. Compost application increases infiltration rates by up to 26% and also increases the time when runoff starts. Sediment concentration in runoff was lower in treated (13.4 on average mg L − 1 ) than in untreated soils (ranging from 16.8 to 23.4 mg L − 1 ). However, the higher nutrient concentration in soils produces a higher mobilisation of N (7–17 mg L − 1 in untreated soils and 20–26 mg L − 1 in treated soils) and P (6–7 mg L − 1 in untreated soils and 13–19 mg L − 1 in treated soils). A major part of the P mobilised was attached to soil particles (about 90% on average) and only 10% was dissolved. Under natural conditions, higher nutrient concentrations were always recorded in treated vs. untreated soils in both plots, and the total amount of N and P mobilised by runoff was higher in treated soils, although without significant differences. Nutrient concentrations in runoff depend on rainfall erosivity but the average value in treated soils was twice that in untreated soils for both plots.

Effect of tillage, fertilizer and green manure cropping on soil quality at an abandoned brick making site

Soils at abandoned brick production sites are inherently low in fertility and have poor physical conditions. In order to develop efficient soil management practices for rapid restoration of these seriously degraded soils, a field experiment was conducted on an abandoned brick production site in Shaoxing county, Zhejiang province, southeast China. Amelioration methods, including tillage, fertilization and green manure (GM) cropping, were compared for their effects on improving selected soil quality indicators. Both fertilization and tillage improved chemical, biological and physical properties of the soils. Deep tillage significantly decreased soil bulk density and significantly increased infiltration rate. Use of organic manure and chemical fertilization increased soil nutrients and microbial biomass. Application of organic manure significantly increased levels of organic C and N and the formation of water-stable aggregates, as compared with application of chemical fertilizers. Deep tillage combined with application of organic manure and green manure cropping was the most efficient method for increasing quality of the soil.

Alternative practices for sediment and nutrient loss control on livestock farms in northeast Iowa

A number of structural and managerial practices were evaluated to determine their environmental and economic effectiveness on animal feeding operations in the upper Maquoketa river watershed in northeast Iowa. Economic and environmental model simulations were performed over a 30-year time horizon for each of these practices using extensive data collected from the study area. Results from model simulations indicate that while most of the practices (including terraces, no till farming, contouring, and in-field contour buffers) would reduce sediment and sediment-bound nutrient losses significantly, they have very little benefit on soluble nitrogen and phosphorus losses. This is primarily because the increased infiltration rates resulting from those practices leads to greater losses of subsurface and return flow in the heavily tile-drained watershed. Nonetheless, when these practices are combined with judicious commercial fertilizer use, appreciable reductions in soluble nutrient losses are also indicated, and improvements in sediment loss are maintained. Terraces are indicated to provide the greatest sediment loss reduction (over 60% reduction) at the watershed level, relative to the status quo. Accordingly, installed terraces also lead to the highest simulated reductions in organic nitrogen and organic phosphorus (over 70%). Predicted reductions in sediment for most of the other practices ranged from almost 30% to about 45%. Corresponding reductions in simulated organic nitrogen and organic phosphorus losses range from about 35% to almost 50%. Economic model simulations also show varied impacts. In general, costs of sediment reducing practices range from about $6 per hectare of implemented area with contouring to almost $65 per hectare when terraces are installed on high-slope cropland. Terraces also indicated the greatest sediment loss reduction. On the other hand, judicious commercial fertilizer use is indicated to offset these costs by as much as roughly $50 per hectare. The study indicates that programs that offer producers some flexibility in choosing practice combinations may lead to the best outcomes.

Soil Water Extraction with a Suction Cup: Results of Numerical Simulations

Porous cups are widely used to extract soil water for monitoring solute transport. However, it is not yet clear how the suction cup influences the matric potential in the surrounding soil and which part of the soil is sampled. This research was designed to numerically evaluate the activity domain, the extraction domain, and sampling area of a suction cup under constant infiltration. A finite‐element model (HYDRUS‐2D) was used to simulate the effect of various applied suctions at two infiltration rates on the water status in three soils (clay loam, sandy clay, and sand). Particle tracking was used to track the streamlines that define the sampling area and extraction domain of the suction cup. In general, the activity domain, the extraction domain, and sampling area of the suction cup depend primarily on the soil hydraulic parameters and the upper boundary, and secondarily on the applied suction. Results showed that the activity domain, the extraction domain, and the sampling area are largest for highest ambient hydraulic conductivities. The activity domain and the sampling area also decrease with increasing infiltration rates. Further, the activity domain of the suction cup depends strongly on the duration of water extraction. Soil heterogeneity seems to play a minor role with respect to the activity domain and sampling area of the cup.

Abkhandari (Aquifer management): a green path to the sustainable development of marginal Drylands

Recurrent droughts and occasional floods are the facts of life in drylands. The presence of innumerable societies in deserts is the living proof that even the extremely dry environments are livable; the secret is how to adapt to the situation. Floodwater management, the most important art of sedentarized desert dwellers, is the secret of living with deserts. Floodwater irrigation alone, or in combination with the artificial recharge of groundwater (ARG), has sustained the Persians for millennia. The scientists at the Kowsar Floodwater Spreading and Aquifer Management Research, Training and Extension Station in the Gareh Bygone Plain have been working since January 1983 to revive this ancient art and upgrade it to the level of science. A summary of important findings is provided as follows: Debris cones and coarse alluvial fans are the best places for the ARG as they provide the potential aquifer for groundwater storage. The recharged water may be used for irrigation on the lower lying, fine alluvium; Flood is not a proverbial curse but a blessing in disguise, and the turbid floodwater is the best resource for the sustainable development of drylands; Translocation of fine clay minerals eventually makes the vadose zone impermeable. Planting deep-rooted, drought-resistent trees and shrubs, and introducing sowbugs (Hemilepistus shirazi Schuttz) are reliable methods to increase infiltration rate and the saturated bydraulic conductivity of the ARG systems; The moving sand stabilization is best achieved by spreading turbid floodwater onto them. Establishing of living windbreaks and planting of fodder trees and shrubs turn a sand menace into a verdant pasture; The 10 year average of native forage yield in the ARG systems has been 445 kg·ha−1·year−1 as o:osed to 92 kg·ha−1·year−1 for the control. At 4×4 m2 spacing,Atriplex lentiformis (Torr.) Wats. can annually yield 1500 kg ha−1 of dry matter and su:ort 3 heads of sheep; The stem- and fuel wood yield of 18 year oldEucalyptus camaldulensis Dehnh. in the ARG system have been 4,684 and 781 kg·ha−1·year−1, respectively. The mean annual carbon sequestration of this tree has been 2.975 tons per ha; Up to 80% of the diverted floodwaters reach the unconfined aquifer. As evaporation practically wastes large volumes of water in surface reservoirs, storing water underground is logical in deserts; The high evaporation rate, the large sediment load, the environmental hazards, the undesirable social costs, the long time needed for the different phases of study, and the very large price tag make dam building the mosthydro-illogical choice in deserts where the ARG is practicable; Each 5.5 ha of the irrigated farm provides income for a family of 7.64 member and 0.38 employment o:ortunities for a farm hand. On average, 4-ha of an ARG system provides one full time job for irrigation farmers. The benefit: cost ratio for this project is 22; The number of wells in the area affected by the ARG activities has increased 10-fold to 130 wells, the irrigated area has increased 8-fold to 1,193 ha, and 345 job o:ortunities have been created in 4 villages that surround the Station.

Irrigation and soil management strategies for using saline-sodic water in a cotton–wheat rotation

Consequent to population growth and high living standards in several arid and semi-arid regions, competition for freshwater among different water-use sectors is expected to increase vis-à-vis its decreased allocation to irrigation. Non-conventional water resources, such as saline and/or sodic drainage and groundwater represent complementary supply to narrow the gap between freshwater availability and demand. We carried out a 3-year field study in the Indus Plains of Pakistan to evaluate different irrigation and soil management strategies for using saline-sodic water to grow cotton ( Gossypium hirsutum L.) and wheat ( Triticum aestivum L.) on a sandy loam soil (EC e = 1.31–1.76 dS m −1, pH s = 8.47–8.61, SAR = 5.50–7.41, infiltration rate = 0.6–0.8 cm h −1, ρ b = 1.56–1.61 Mg m −3). The treatments were: (1) irrigation with freshwater from a nearby canal (FW); (2) irrigation with saline-sodic water (EC = 3.32 dS m −1, SAR = 16.29, SAR adj = 18.24, RSC = 5.25 mmol c L −1) (SSW); (3) cyclic use of fresh and saline-sodic water through alternate irrigations (FW − SSW); (4) Soil application of farm manure at 25 Mg ha −1 year −1 and irrigation with saline-sodic water (FM + SSW); and (5) soil application of gypsum equivalent to gypsum requirement of saline-sodic water and irrigation with the same water (G + SSW). The seed yield of first cotton crop was not significantly affected by different treatments. The yields of subsequent wheat and cotton crops were lower in the SSW than other treatments, indicating negative impacts of saline-sodic water when used in the absence of a soil or irrigation management approach. The treatments using saline-sodic water did increase soil EC e and SAR levels, but this increase was only significant in SSW treatment. Irrigation with saline-sodic water together with amendments significantly increased infiltration rate than SSW alone, where bulk density was increased. The net benefit was the maximum from FW − SSW treatment followed by FW, G + SSW, FM + SSW and SSW.

Filtration rate dependence of hyaluronan reflection by joint-to-lymph barrier: evidence for concentration polarisation.

Hyaluronan (HA), a component of synovial fluid, buffers fluid loss from joints. To explain this, a quantitative theory for HA concentration polarisation at a partially sieving synovial lining was developed. The theory predicts a fall in HA reflected fraction R with increased filtration rate. To test this, knees of anaesthetised rabbits were infused with HA and fluorescein-dextran (FD) at constant trans-synovial filtration rates of 6-89 microl min(-1). Samples of femoral lymph, mixed intra-articular fluid and subsynovial fluid after >/= 3 h were analysed by high-performance liquid chromatography. R was calculated as (1 - downstream/upstream concentration), using [FD] to adjust for joint lymph dilution in femoral lymph. Intra-articular HA concentration after >/= 3 h, 0.47 +/- 0.02 mg ml(-1) (mean +/-s.e.m., n= 31), exceeded the infusate concentration, 0.20 mg ml(-1), while subsynovial and lymph [HA] were reduced relative to [FD]. The changes in [HA] demonstrated synovial molecular sieving of HA. R from cavity to lymph (R(lymph)) fell monotonically from 0.93 at 6 microl min(-1) to 0.14 at 89 microl min(-1) (P < 0.0001, regression analysis, n= 33). R values calculated from the intra-articular HA accumulation (R(asp)) or the low subsynovial concentrations (R(syn)) were similar negative functions of filtration rate. R for lymphatic capillary endothelium (R(endo)), calculated from lymph/subsynovial concentration ratios, was effectively zero (-0.03 +/- 0.18, n= 21), confirming that synovium, not initial lymphatic endothelium, is the reflection site. Logarithmic linearisation of the results evaluated the synovial HA reflection coefficient as 0.91. In conclusion, the existence of concentration polarisation during joint fluid drainage was supported by the demonstration of a negative relation between filtration rate and R(lymph), R(asp) and R(syn).

Effects of intensive monocropping of bananas on properties of volcanic soils in the uplands of the French West Indies

Abstract. On the volcanic soils of the uplands of the French West Indies, banana monocropping has been practised since about 1980, mostly with large inputs of chemicals and replanting every three to five years after ploughing. However, in Guadeloupe less intensive cropping systems with only few added chemicals are still being used. The effects of the intensive practices on the physical, chemical and biological attributes of soils were evaluated on 34 farmed fields, which were selected to include the diverse soils and management practices found in the uplands of South Basse‐Terre. Management was classified into four groups to differentiate effects of fertilizers, nematicides and tillage over at least 10 years. The population of the parasitic nematode Radopholus similis was, on average, greater 3 months after the application of nematicides. Thus, the use of nematicides increases the dependency of yield on nematicides. Ploughing decreased soil organic matter in the 0–10 cm layer as well as microbial respiration and earthworm biomass, but increased banana root infestation by R. similis. Ploughing was also associated with a change in soil structure, as revealed by the decrease in soil water content at −1 kPa potential and the increased infiltration rate of water into the 0–10 cm layer. The use of fertilizers has advantages for the maintenance or increase of soil reserves of K. However, due to the decreasing of negative electrical charges in the lower layers of andosols, where pH remains low, the majority of the cations supplied by fertilizers, mainly potassium, are prone to leaching.

Atrazine distribution measured in soil and leachate following infiltration conditions

Atrazine transport through packed 10 cm soil columns representative of the 0–10 cm soil horizon was observed by measuring the atrazine recovery in the total leachate volume, and upper and lower soil layers following infiltration of 7.5 cm water using a mechanical vacuum extractor (MVE). Measured recoveries were analyzed to understand the influence of infiltration rate and delay time on atrazine transport and distribution in the column. Four time periods (0.28, 0.8, 1.8, and 5.5 h) representing very high to moderate infiltration rates (26.8, 9.4, 4.2, and 1.4 cm/h) were used. Replicate soil columns were tested immediately and following a 2-d delay after atrazine application. Results indicate atrazine recovery in leachate was independent of infiltration rate, but significantly lower for infiltration following a 2-d delay. Atrazine distribution in the 0–1 and 9–10 cm soil layers was affected by both infiltration rate and delay. These results are in contrast with previous field and laboratory studies that suggest that atrazine recovery in the leachate increases with increasing infiltration rate. It appears that the difference in atrazine recovery measured using the MVE and other leaching experiments using intact soil cores from this field site and the rain simulation equipment probably illustrates the effect of infiltrating water interacting with the atrazine present on the soil surface. This work suggests that atrazine mobilization from the soil surface is also dependent on interactions of the infiltrating water with the soil surface, in addition to the rate of infiltration through the surface soil.

Effect of cultural practices on soil properties, moisture conservation and grain yield of winter sorghum ( Sorghum bicolar L. Moench) in semi-arid tropics of India

A field experiment was laid out during winter seasons of 1994–1995 and 1995–1996 on deep black clayey soils (Vertisols) at Regional Research Station, Bijapur, in the northern dry zone of Karnataka State (Zone 3) of south India to evaluate the effect of cultural practices on soil moisture conservation, soil properties, root growth and yield of sorghum ( Sorghum bicolar L. Moench). Lay out of plots with in situ moisture conservation practices reduced bulk density, increased infiltration rate, porosity, improved root growth and grain yield of winter sorghum. Conservation and availability of higher amount of moisture and nutrients during various stages of crop growth with moisture conservation practices resulted in better crop growth with higher amount of dry matter production and its translocation to ear in winter sorghum. Compartmental bunding and ridges and furrows increased the grain yield by 22.8 and 25.6% (mean of 1994–1995 and 1995–1996), respectively, over flat bed with similar trend observed during 1994–1995 and 1995–1996. Among organic sources, incorporation of Leucaena loppings improved soil physico-chemical properties, conserved higher amount of moisture and increased winter sorghum yield to a greater extent than farmyard manure and vermicompost. Average grain yield (1994–1995 and 1995–1996) of winter sorghum increased by 11.7% with Leucaena application as compared to vermicompost. Grain yield increased significantly by 20% with application of 25 kg N ha −1 and further increase in nitrogen dose up to 50 kg ha −1, increased the grain yield by 30.5% in the pooled data.

Leguminous trees for the restoration of degraded sodic wasteland in eastern Uttar Pradesh, India

AbstractThe study was carried out in sodic lands of Sultanpur District, Uttar Pradesh, India. The barren soils and the soils supporting 3‐, 6‐ and 9‐year‐old plantations of Prosopis juliflora (Swartz) D.C. and Dalbergia sissoo Roxb. Ex. D.C. plantations were examined to assess the rate and extent of changes undergone by physical and chemical properties of the soil. The study brought out that these species indicated the process of soil rehabilitation from the early stages of growth and the extent of rehabilitation increased with the age of the plantation. P. juliflora was found to be more efficient in reclaiming the soil in comparison to D. sissoo. The decline in soil pH and exchangeable sodium percentage (ESP) indicates the desodification and enrichment with organic C, N, P and K indicates improvement in nutrient status of the soil. After 9 years of planting the surface soil was completely desodified as indicated by pH (&lt;8ċ5), ESP (&lt;15) and sodium adsorption ration (&lt;15). A significant increase in organic C, exchangeable Ca2+ and Mg2+ and decrease in exchangeable Na+ reveals that the nutrient status is attaining suitable balance. The physical attributes of the soil also underwent improvement in terms of increase in porosity, water‐holding capacity, field capacity and decline in bulk density. The flocculation of dispersed soil surface and improvement in soil structure was indicated by increased infiltration rate (cm h−1) and soil permeability (cm2). Copyright © 2003 John Wiley &amp; Sons, Ltd.

Rehabilitation of degraded sodic lands during a decade of Dalbergia sissoo plantation in Sultanpur District of Uttar Pradesh, India

AbstractThe ameliorative effect of Dalbergia sissoo, planted on sodic land at Sultanpur (26° 10′–26° 40′N, 81° 45′–82° 30′E), India, in a tropical environment, was studied at 3, 6 and 9 years of age. The soil properties of the sites improved significantly, showing marked reduction in pH, electrical conductivity (EC) and exchangeable sodium percentage (ESP) and an increase in organic carbon, nitrogen and availability of nutrients in the soil. The significant reduction in Na ion was found in all the age groups. Results showed an improvement in the soil moisture regime due to increased infiltration rate (cm hr−1), soil permeability (cm2), water‐holding capacity, field capacity and pore space whereas, the bulk density decreased significantly after successive years of planting. The effect on soil attributes was confined to surface soil in the young plantation and deeper in older plantation. Therefore, the study clearly indicated that the sodic soil could be desodified by growing D. sissoo plantations on these degraded sites. Copyright © 2002 John Wiley &amp; Sons, Ltd.

Analysis of water movement in paddy rice fields (I) experimental studies

For the purpose of increasing the amount of ground water recharge, we investigated the hydraulic characteristics of water infiltration in a flooded paddy rice field in Ten-Chung, Chung-Hwa county, Taiwan. Experimental results based on mini-tensiometers and double ring infiltrometer measurements indicated that the least permeable layer occurred at the interface of the puddled topsoil and non-puddled subsoil. The average thickness of this layer was about 7.5 cm and saturated hydraulic conductivity ranged from 0.034 to 0.083 cm/day. Vertical infiltration flow was saturated within the plow sole layer and became unsaturated in the subsoil below the plow sole layer. The hydraulic conductivity of the subsoil, 20–30 times greater than that of the plow sole layer, revealed that the subsoil was more permeable than the plow sole layer. In situ measurements also demonstrated that breakage of the plow sole layer increased infiltration rate by a factor of 3.7. Increasing ponded water depth from 6 to 16 cm increased infiltration 1.5 fold. It is suggested that using the fallow paddy rice fields without puddling is a feasible way to enhance groundwater recharge, but for cultivated paddy rice fields, breaking the plow sole needs further study in terms of its recoverability and because of the potential contamination of the shallow aquifer by agrochemicals. The experimental data can be applied in numerical simulation models to quantify detailed water movement mechanisms and accurately estimate the amount of ground water recharge in paddy rice fields.

Effect of Compactions on Infiltration Characteristics of Soil

The field research was conducted at Sindh Agriculture University Tandojam, Pakistan. The treatments were soil compactions (uncompacted, 5 and 10 times compacted soil) and their effect on water infiltration rate in silt loam soils. It was observed that infiltration rate was higher during initial irrigation application, but, gradually reduced and became constant when the soil was saturated. The bulk density of uncompacted, 5 and 10 times compacted soils was recorded as 1.13 to 1.20, 1.19 to 1.29 and 1.19 to 1.32 g/cc, respectively at 0 to 90 cm soil profile. The infiltration rate was higher (17.10 mm/hr) in the uncompacted soil compared to those 5 and 10 times compacted soils (13.89 and 9.78 mm/hr.) respectively. The increased infiltration rate in the uncompacted soil was mainly due to soil porous medium having low bulk density values.

Tillage and legume mulching effects on moisture conservation and productivity of rainfed maize (Zea mays)wheat (Triticum aestivum) cropping system

A field experiment was conducted at Selakui, Dehradun from 2001 to 2004 to study the effect of tillage, viz. con- ventional tillage (CT) and minimum tillage (MT); and weed-control practices, viz. chemical and mechanical weed- ing along with legume mulching, viz. in situ grown sunnhemp (Crotalaria juncea L.) and subabul [Leucaena leucocephala (Lam.) de Wit] on soil moisture conservation, crop productivity and soil health in maize (Zea mays (Triticum aestivum L. emend Fiori &amp; Paol.) cropping system. CT gave higher grain yield of maize (+0.11 to O. 17 t/ha), but wheat performed equally well under CT (2.48 tiha) and MT conditions (2.36 t/ha). Chemical weeding with herbicides (alachlor in maize and isoproturon in wheat) resulted in 7.8 and 9.9% higher yield of maize and wheat, respectively over mechanical weeding. Beneficial effect of live mulching with sunnhemp or Leucaena was similar (12.314.7%), while their combined application increased the maize yield by 19.1% over no mulching. Further, enhanced soil moisture conservation due to mulching at maize harvest led to greater productiv- ity of wheat by 16.1% with sunnhemp or Leucaena, and 27.0% with sunnhemp + Leucaena. Nitrogen uptake of maize and wheat increased significantly with chemical weeding and legume mulching, but tillage practices made no effect on wheat while in maize it was lower under MT. Wheat gave 45 times more net retums than maize, and the net B : C ratio of the system was &gt; .O with chemical weeding and legume mulching. Tillage and weed-control practices made no effect on organic C and total N status of soil but legume mulching improved these parameters and reduced bulk density associated with increased infiltration rate. It was concluded that CT along with legume mulching in maize and MT in wheat, and chemical weeding of both the crops was beneficial for improving moisture and nutrient conservation, and achieving higher productivity and profitability of maizewheat cropping system un- der Doon valley conditions.

Integrated use of crop residues and fertilizers for sustainability of potato (Solanum tuberosum) based cropping systems in Bihar

A field experiment was conducted at Patna for 4 years (2002-03 to 2005-06) on a fixed site to study the effect of crop residues(CR) recycling along with 2 levels of recommended dose of NPK fertilizers (RDF) i.e. RDF and 125% RDF in two potato ( Solanum tuberosum L.) based cropping systems [potato-onion ( Allium cepa L.)-rice ( Or yza sativa L.) and potato-wheat ( Tr iticum aestivum L. emend. Fiori &amp; Paol)-rice]. Incorporation of CR has im- proved the mean rice equivalent yields of system by 7.86% as compared to their removal (24.15 t/ha). Incorpora- tion of CR decreased the bulk density and increased infiltration rate, water holding capacity, microbial population, soil fertility than the initial values as compared to no residue treatment after four years of study. Increasing levels of RDF also increased the yield but did not show any significant effect on soil physico-chemical properties. Incor- poration of residues along with RDF improved the crop productivity in both the cropping systems and was at par with 125% RDF. The residue incorporation with NPK fertilizer resulted in the highest yield, nutrient uptake, im- proved residual soil fertility and soil microorganism status and ultimately high benefit: cost ratio.

Water Ponding Depths Affect Temporal Infiltration Rates in a Water‐Repellent Sand

Water‐repellent soils exhibit a positive water entry pressure head, hp The effects of imposing differing water pressure head values, by using differing water ponding depths, h0, on infiltration into water‐repellent soils was investigated. A sand, with particulate size between 0.05 and 2.0 mm, was treated with two concentrations of octadecylamine to create a sand with hp values of 8.4 and 3.5 cm. The hydraulic conductivity, K, of the water‐repellent sands increased with increasing values of h0 The K of the treated sand was equal to K of untreated sand when the ratio h0/hp was ≈3.1 for each treated sand. The infiltration rate increased with increased time for lower h0 values, but decreased with increased time for higher h0 values. The transition from increasing to decreasing infiltration rates with time occurred when h0/hp was approximately equal to 2.6. The infiltration rate behavior of an aqueous ethanol solution was consistent with theoretical relationships based on liquid surface tension. A positive hydraulic head was created at the interface of an overlying wettable and underlying water‐repellent layer that affected the infiltration rate consistent with the effects of h0 on a nonlayered water‐repellent sand. The following mechanism is proposed to explain the increase in infiltration rate with time. In water‐repellent materials, positive hydraulic heads can be created within the profile during infiltration, which can increase as the depth to the wetting front increases. The higher hydraulic head induces an increase in hydraulic conductivity, which contributes to increased infiltration rate. Alternatively, if the depth of ponded water is sufficient to cause a hydraulic conductivity equal to that of the wettable material, the infiltration rate behavior is the same as traditionally observed for wettable soils.