Medium-textured Soils Research Articles

Electrokinetic retention, migration and remediation of nitrates in silty loam soil under hydraulic gradients

Contamination of groundwater by nitrates leaching from intensive agricultural and livestock operations have become a major concern for surrounding communities that use groundwater as their water supply. High levels of nitrate in drinking water poses a significant risk to human health, i.e., methaemoglobinaemia (“blue baby” syndrome). The traditional pump-and-treat method is ineffective in medium to fine-textured agricultural soils due to the low hydraulic conductivity. This paper presents the results of a laboratory experiment investigating the feasibility of using electrokinetic treatment in retaining, accumulating, moving and remediating nitrates in a silty loam soil under hydraulic gradients. A hydraulic gradient of 1.25 was applied to the horizontal soil columns to simulate a groundwater movement system. The study was performed in two stages. During the first stage of the experiment, the anode located at the inflow end of the columns was able to retard the movement of nitrates even under a hydraulic gradient of 1.25. After 15 days of flow, the effluent nitrate concentration in the control column rose to 90 mg l −1 while no nitrates were detected in the effluent from columns subjected to the electrokinetic treatment. After 15 days, the polarity of the electrodes was switched and this second stage lasted another 20 days. The cathode near the inflow end promoted the conversion of nitrates entering the column to other forms. The anode near the outflow end promoted the migration and accumulation of negatively charged nitrate ions towards the outflow end. By the 12th day, the nitrate concentrations in the electrokinetically treated columns were brought down to <5 mg NO 3-N l −1. Electrokinetic treatment retarded nitrate movement against a hydraulic gradient of 1.25 and effectively restored a medium-textured soil contaminated with NO 3-N. The NO 2-N level remained below 1 mg l −1 throughout the experiment. The hydraulic conductivity varied between 1.0E–7 and 3.6E–7 m s −1. The current requirement varied between 3 and 6 mA.

Processing Tomato and Weed Response to Flufenacet plus Metribuzin

Field experiments were conducted in 1998, 1999, and 2000 at two locations (Harrow and Ridgetown) in southwestern Ontario to determine the biologically effective rates (I90) of a commercial formulation of flufenacet plus metribuzin for weed control and processing tomato tolerance. At the proposed label use rate, flufenacet plus metribuzin provided excellent (≥90%) early-season (22 to 29 d after planting) control of velvetleaf, good (80 to 89%) control of barnyardgrass and redroot pigweed, and fair (60 to 79%) control of common lambsquarters. Flufenacet plus metribuzin provided fair late-season (59 to 97 d after planting) control of redroot pigweed and common lambsquarters and poor (≤59%) control of barnyardgrass and velvetleaf. At Harrow and Ridgetown, I90values for early-season weed control ranged from 70 to 1,300 g ai/ha and 50 to 1,900 g ai/ha, respectively. Flufenacet plus metribuzin provided poor weed control at Ridgetown. This result was not attributable to higher weed density or particular weed species but may have been caused by lack of rainfall and too low application rates for the medium-textured soil type. It is estimated that flufenacet plus metribuzin at 1,400 g/ha can control green foxtail season-long, whereas barnyardgrass and common lambsquarters would require 1,900 g/ha. Season-long control of velvetleaf and redroot pigweed would require application rates of 3,200 and 7,100 g/ha, respectively. Only slight early-season crop injury was observed, which was not reflected in yields. Optimum yields of tomatoes were obtained at Harrow at rates lower or slightly higher than the registered rates for corn and soybean. Tomato yields were higher at Harrow than at Ridgetown, which may have been due to differences in soil texture. Tomatoes grown in a medium-textured (Ridgetown) soil appeared to be less competitive against weeds than those grown in a coarse-textured soil (Harrow).

Effects of soil and climatic conditions on the variation in some ryegrass seed crops

Site specific data for ryegrass seed crops has been obtained from two precision agriculture projects in Canterbury. Using yield maps and proximal sensors, the temporal and spatial variability within and between crops was quantified. In general, the best ryegrass seed yields were on the medium textured soils within a paddock. The lightest textured parts of a paddock could yield as well or better than these areas, particularly in seasons with cool springs, and in average to dry seasons provided irrigation was optimal. In contrast, heavier textured soils only yielded as well as medium textured soils if they were not overly wet (or cool) early in the season and in very dry years, when irrigation could not meet crop water demands, or in dryland situations. When irrigation was altered on perennial ryegrass by restricting moisture in November, there was greater reduction in seed yield in the lighter textured areas compared to the medium textured areas of a paddock. Extra nitrogen applied in late October improved yields in the medium textured part of the paddock but had a slight negative effect in the lighter areas of the paddock. In a trial using the plant growth regulator, Moddus, application was only beneficial in the medium textured parts of the paddock. Interpretation of ryegrass seed yield maps can be confounded by crop management decisions such as grazing, irrigation and harvest conditions. Late harvesting decreased seed yield so that the effects of soil texture and moisture were less evident. Farmers without this technology can use soil maps, aerial photographs and observation to identify areas of potential difference within a paddock. Targeting soil sampling, plant dry matter, soil moisture and perhaps nutrient analysis to major areas of difference can be useful in developing a zonal management system. Keywords: crop management, precision agriculture, ryegrass seed crops, seed yield maps

Use of N-(n-butyl)thiophosphoric triamide (NBPT) to increase safety of seed-placed urea

Current guidelines for safe seedrow placement of urea N in the western Canadian prairies are based on texture, seedbed utilization and soil moisture conditions at the time of seeding. However, if N requirement is high, not all fertilizer N requirements can be met as excess urea N in the seedrow may result in plant stand reduction, delay in maturity and/or lead to yield loss. This study investigated the use of the urease inhibitor N-(n-butyl)thiophosphoric triamide (NBPT) as a means of increasing the safety of seedrow applied urea. Four experiments consisting of 39 trials were carried out over 3 yr to ascertain whether current guidelines could be modified through the use of NBPT. The experiments were carried out on loam to clay loam soils and barley, canola and wheat were sown with seedrow spacing and seed spread to produce seedbed utilization of approximately 10%. A safe N rate in this study was defined as the one that resulted in less than 15% reduction in the stand density of plants and no delay in maturity. There was no damage from seed-placement of N when the site received 5 to 10 mm of precipitation within 48 h of seeding. Treatment of urea with NBPT resulted in a significant improvement in stand density in two out of every three (20 of the 31) trials, where a significant reduction of stand density due to N application was observed. There were no cases where an increase in seedling damage was observed as a result of NBPT treatment of urea. Treatment of urea with NBPT resulted in an overall reduction in days to maturity with greater benefit at higher N rates of seed row placed N. However, there was a yield benefit as a result of NBPT application in only eight of the trials. Average guidelines for urea seedrow placement for barley, canola and wheat grown on medium textured soils with 10% seedbed utilization can be increased by 30, 20 and 15 kg N ha-1, respectively, when urea is treated with NBPT. Key words: Stand density, maturity, yield, barley, canola, wheat

Effect of saline water on oil yield and quality of a high oleic sunflower ( Helianthus annuus L.) hybrid

Sunflower is a species moderately tolerant to salt stress and is currently cultivated in dry areas where salinity can be a threat. The effect of salt stress on achene yield has been investigated, but no information exists about its effect on the oil fatty acid composition. The aim of this paper was to evaluate the changes in oil yield and fatty acid composition in a high oleic hybrid submitted to different salinity levels of irrigation water. Furthermore, since the addition of a leaching fraction to the irrigation volume may be relevant to prevent excessive soil salinization, a water regime equal to 1.5 maximum evapotranspiration (1.5 ETc) was compared with the restoration of evapotranspiration (1 ETc). A pot experiment was carried out in a greenhouse with a high oleic sunflower hybrid (Platon) grown on a loam soil under two irrigation regimes with five salinity levels of irrigation water (0.6, 3, 6, 9 and 12 dS m −1). At harvesting, seed production, oil yield and fatty acid composition were determined. The percent seed yield decrease per unit increase of irrigation water electrical conductivity (ECw) was higher for 1 ETc (7%) than for 1.5 ETc (5.8%). Oil yield showed a significant decrease from 38.3 to 3.4 g per head on increasing salt stress and a marked increase of about 50% with the higher irrigation volume. Under our experimental conditions with a medium textured soil, this result confirms the importance of leaching to limit salt accumulation along the soil profile, thus reducing seed and oil yield drop under salt stress. Concerning fatty acid oil composition, under all the adopted experimental conditions, both oleic and linoleic acid accounted together for 90% of total fatty acid concentration, while stearic and palmitic acid were about 4%. No great differences were observed in fatty acid composition between the two irrigation regimes. With the higher irrigation volume, only a slight decrease in linoleic and gadoleic acid and an increase in arachidic acid were observed. The only significant differences among saline treatments were observed for oleic and linoleic acid. Oleic acid showed an increase from 82.8% in the control to 86.8% at the highest salinity treatment. Inversely, for linoleic acid a progressive decrease from 6.9 to 2.8% with increasing salinity level was observed. These results will be discussed in the light of a possible inhibition of oleate desaturase occurring under salt stress.

Estimativa do risco de sodificação de solos de Pernambuco pelo uso de águas salinas

Com o objetivo de se avaliar o risco de sodificação em solos irrigados com águas de diferentes condutividades elétricas (CE) e relações de adsorção de sódio (RAS), realizou-se um ensaio como permeâmetros de coluna vertical e carga constante. Os tratamentos corresponderam a nove amostras de solo e soluções percolantes com três CE (175, 500 e 1.500 mS cm-1) e seis RAS (de 0 a 30 para solos arenosos, de 0 a 25 para solos de textura média e de 0 a 15 para solos de textura argilosa). Inicialmente, realizou-se o ajuste da relação Na:Ca no complexo de troca catiônico dos solos, utilizando-se soluções na concentração de 50 mmol c L-1, nos níveis de RAS descritos; em seguida, iniciou-se a passagem das soluções de diferentes CE porém mesma RAS até escoamento permanente quando, então, os permeâmetros foram desmontados e as amostras analisadas. Determinaram-se o sódio trocável e a capacidade de troca de cátions das amostras e se calculou a relação de sódio trocável (RST) e a percentagem de sódio trocável (PST). Foram ajustadas equações relacionando-se a RST e a PST do solo com a CE e a RAS das soluções percolantes, em que o incremento da CE e da RAS elevou a RST e a PST dos solos. Os resultados demonstram que a correta avaliação dos riscos de sodificação deve levar em consideração as propriedades do solo e a qualidade da água.

Condutividade hidráulica de solos de Pernambuco em resposta à condutividade elétrica e RAS da água de irrigação

Objetivando-se avaliar a condutividade hidráulica em solos irrigados com águas de diferentes condutividades elétricas (CE) e relações de adsorção de sódio (RAS) realizaram-se ensaios em permeâmetros de coluna vertical e carga constante. Os tratamentos corresponderam a nove solos, três CE (175, 500 e 1.500 miS cm-1) e seis RAS (de 0 a 30 para solos arenosos, de 0 a 25 para solos de textura média e de 0 a 15 para solos de textura argilosa). De início, realizou-se o ajuste da relação Na:Ca no complexo de troca catiônico dos solos, utilizando-se soluções na concentração de 50 mmol c L-1, nos níveis de RAS descritos; depois, determinou-se a condutividade hidráulica em meio saturado (K0) e se calculou a condutividade hidráulica relativa (K0R), atribuindo-se o valor de 100% à máxima K0 média de cada solo. Os valores de K0R foram relacionados com a CE e a RAS dos tratamentos impostos, ajustando-se superfícies de resposta. As correlações entre K0 e a percentagem de sódio trocável (PST) indicaram relação inversa entre as duas variáveis, na maioria dos solos estudados. O incremento da RAS levou à diminuição da K0R. Não foi possível se fixar um único valor de PST no estabelecimento de um limite para solos sódicos, devendo esta característica ser associada à CE da água de irrigação e a outras propriedades do solo, como textura e mineralogia.

Rice-wheat productivity and nutrient status in a lantana- (Lantana spp.) amended soil

Imbalanced and inadequate use of chemical fertilizers is responsible for low rice- (Oryza sativa L.) wheat (Triticum aestivum L.) productivity in many resource-poor farmers' fields. Wheat yields in post-rice soils are also constrained due to soil conditions created by puddling in rice, especially in fine to medium textured soils. Organic amendments are known to improve soil productivity under rice-wheat cropping by way of improving physical conditions and nutrient status of the soil, but their availability is restricted. There is a need to identify locally available and cost-effective organic materials, which have minimal alternate uses as fodder and fuel. We evaluated lantana (Lantana spp. L.) residues, a fast-growing weed in nearby wastelands, as a potential soil organic amendment. Yield trends, and soil and crop nutrient status in a 12-year rice-wheat experiment at Palampur, India, involving four levels (0, 10, 20, and 30 Mg ha-1 year-1 fresh mass) of lantana addition were investigated. Chopped lantana was incorporated into soil 10–15 days before puddling. Lantana additions at 10, 20 and 30 Mg ha-1 increased rice yields on average by 18%, 23% and 30%, wheat yields by 11%, 14% and 20%, and total system productivity (rice + wheat) by 15%, 20% and 26% over controls, respectively, and at the same time saved NPK fertilizer. Linear regression analyses over 12 years did not show any change in yield trends of rice and wheat at P =0.05. Continuous cultivation of rice-wheat significantly increased total C, labile C, and other C indices of soils. Total N, Olsen's P, and NH4OAc-extractable K in the lantana-amended plots were higher than in the controls. Nutrient concentrations in crop biomass, however, remained generally unaffected by lantana treatments. Results suggest that lantana residues, which improved the nutrient status of soil and system yield, have the potential for resource conservation and sustaining rice-wheat productivity.

Organic matter fractions and soil fertility under the influence of liming, vermicompost and cattle manure

This work evaluates effects of cattle manure vermicompost in association with liming on soil fertility indexes. The experiment was carried out in greenhouse conditions, in pots containing samples of a Typic Hapludox, medium-textured soil. Five levels of vermicompost (equivalent to 0, 28, 42, 56, and 70 t ha-1, dry weight) and five liming levels (to raise base saturation to 20, 30, 40, 50, and 60%) were combined in a factorial scheme and samples were incubated for 180 days. Samples of the same soil received the equivalent to 70 t ha-1 of the cattle manure used to produce the vermicompost, and the same lime rates. Cattle manure was better than vermicompost to supply K and Mg. Small differences in P supply were observed between the manures. The vermicompost increased the levels of Ca, pH, organic matter (OM) and CEC more than the manure. C-humic acids decreased and C-humin increased with vermicompost application. With liming, C-humic acids decreased, but the total content of OM was not affected.

A Comparison of Presettlement and Present-day Forests in Northeastern Lower Michigan

General Land Office survey records of 1838–1846 were used to reconstruct the pre-European settlement vegetation along a soil moisture gradient in the Huron National Forest of northeastern lower Michigan. These data were compared to current forest data. Jack pine (Pinus banksiana), red pine (P. resinosa) and white pine (P. strobus) dominated fire-prone presettlement dry and dry-mesic sites on coarse-textured soils of glacial outwash plains and moraines. Hemlock (Tsuga canadensis), beech (Fagus grandifolia), sugar maple (Acer saccharum) and white pine were most important on presettlement mesic sites on medium-textured soils of moraines and kame and kettle topography. Presettlement wet-mesic sites were dominated by hemlock, white pine and aspen (Populus spp.). White cedar (Thuja occidentalis) and tamarack (Larix laricina) dominated presettlement wet sites on organic soils of outwash plains. Important presettlement forest types included: jack pine (41%), mixed conifer–northern hardwood (22%), lowland conifer (15%) and mixed pine (14%).Tree species composition has substantially changed on dry-mesic to wet-mesic sites over the last 150 y. White pine and hemlock have significantly declined in abundance. Oak (Quercus spp.), sugar maple and aspen currently dominate dry-mesic to wet-mesic sites. Important current forest types include: jack pine (32%), aspen–white birch (Betula papyrifera; 16%), oak (16%) and northern hardwood (8%). Today's forests have smaller trees and higher tree densities than forests in the presettlement era. Widespread logging, altered fire regimes and other anthropogenic disturbances since European settlement have interacted with physical factors to produce today's forests.

Ephemeral gully erosion in northwestern Spain

This study aimed to describe types of ephemeral gullies and to determine their origin, evolution and importance as sediment sources in A Coruña province (northwest Spain). Ephemeral gullies and/or rills have been measured in a representative sample of medium-textured soils, most prone to crusting, developed over basic schist. This sample consisted of 11 small sites, ranging from 0.63 to 7.34 ha. A case study of concentrated (rill+gully) erosion in a 0.47-ha catchment with coarse-textured soils developed over granite was also reported. The mean slope of the sites studied ranged from 6.1% to 16.8%. Main periods when soil surface was poorly covered were late spring (maize seedbeds) and late autumn–early winter (grassland and winter cereal seedbeds). Case studies where fields were left bare in winter were also investigated. Soil incision and channel formation were observed even with relatively low rainfall intensities when the soil surface was sealed, but also after a single short intense rainfall event on recently tilled surfaces. Concentrated erosion took place mainly on seedbeds and newly tilled soils in late spring and by autumn or early winter, but gullies also appeared in other seasons when the soil surface was left bare. In most of the cases studied, ephemeral gully erosion caused significant soil losses, ranging between 2 and 5 m 3/ha for a single season to locally, over 25 m 3/ha. Gully development was significantly affected by agricultural operations, such as lineal elements often acting as initial axes of concentrated erosion. Main gullies tended to reappear at the same position.

SW—Soil and Water: Estimation of Manning Roughness Coefficient for Bare and Vegetated Furrow Irrigation

The manning roughness coefficient n is one of the parameters in designing furrow irrigation. Its appropriate selection is important for efficient water application in field. In this research, the Manning roughness coefficient in ordinary and every other furrow irrigations with different inflow rates (0·4, 0·8, 1·1 l s −1) and furrow slopes (0·2 and 0·4%) at various growth stages of wheat with different crop vegetation covers were determined on a clay loam soil. The calculation was based on the volume balance equation in the form of a differential equation that was solved with the forward finite difference (method I) and the secondary backward finite difference (method II) procedures. Comparison of the results obtained from these two methods showed that method I resulted in lower values of n than method II. So, the mean of the values for n from the two methods were used for the medium texture soil of the present study. There was no difference between the values of n in ordinary and every-other furrow irrigations. The results also indicated that at the first irrigation, the values of n were high (0·07–0·121), but at the second and third irrigations, the values of n decreased by about 60–70%. However, after the third irrigation, the seedling emergence of wheat resulted in increasing the values of n. The minimum and maximum values of n which belonged to the third and seventh irrigations were 0·047 and 0·136, respectively. Finally, two equations were proposed for the estimation of the roughness coefficient for bare and vegetated furrows according to the number of irrigations (up to three before seedling emergence), inflow rates and percentage of vegetation covers.

Model-based assessment of water balance components under different cropping systems in north-west India

Water balance components were assessed under main cropping systems of the Punjab state in north-west India with a simplified model using long-term weather data. Ten years’ average annual evapotranspiration (ET) was maximum in sugarcane (136 cm) followed by cotton–wheat (125 cm), rice–wheat (92 cm) and maize–wheat (86 cm) cropping system on a medium textured soil. However, on a coarse textured soil, ET was less by 6–11 cm under different cropping systems. Soil water evaporation ( E) constituted the major proportion of the annual water loss during establishment and senescence periods of the cropping cycles and intervening bare periods. Water loss by deep drainage in rice (68.2 cm) was more by 2.4 times than in maize, by 3.1 times than in cotton and by 3.3 times than in sugarcane. Irrigation water required to meet ET and drainage was maximum in rice–wheat (106.8 cm) followed by sugarcane (85.5 cm), cotton–wheat (81.6 cm) and maize–wheat system (61.2 cm). Straw mulching in maize, cotton and sugarcane decreased irrigation requirement further by reducing unproductive E losses. Thus, maize–wheat or cotton–wheat cropping systems having low irrigation requirement can be an appropriate alternative to rice–wheat system for maintaining balanced hydrology in the state.

Feasible suppression technique of methane emission from paddy soil by iron amendment

A revolving furnace slag (RFS), which is a by-product of the steel industry, and a spent disposable portable body warmer (PBW), which harnessed the heat of iron oxidation reaction, were used as iron materials. Portions of 4 kg of Coarse and Medium Textured Gley soil were placed into plastic pots (3 L). RFS was added to the pots at the rate of 0 (control), 10, 20, 40, 100 ton ha−1, while PBW was added at 10 ton ha−1 only. Methane flux from the potted soil with rice plants and Eh were measured during cropping seasons in 1999 and 2000. In the 1999 experiment, the RFS treatments showed lower Eh values compared with the control, especially at the early period of cultivation, although the RFS was applied to maintain the soil oxidative. The rapid decrease in Eh under high application of RFS may be due to the high pH of the RFS (pH (RFS:H2O = 1:2.5) was 12.2). However, total methane emission during the cultivation period significantly decreased, about 10%, when 10–40 ton ha−1 of RFS and 10 ton ha−1 of PBW were applied. The grain yield was significantly increased, about 30%, when 40 or 100 ton ha−1 of RFS was applied. This was also partly due to the release of inorganic nutrients from RFS and also from soil. The latter, due to effect of the alkaline RFS on soil. In the 2000 experiment, the pots with soils from 1999 were used without further application of iron materials. The influence of high application of RFS on soil Eh disappeared, compared with 1999. Total methane emission significantly decreased, about 35%, at 20 ton ha−1 of RFS. However, the increase of grain yield caused by RFS in 1999 was diminished, compared with 1999. Production activity of both methane and carbon dioxide at the RFS treatments were decreased, while methane oxidizing activity was increased. The decrease in total methane emission may be attributed to not only inhibition of methane production but also enhanced methane oxidation. In conclusion, methane emission from paddy soil could be suppressed, over two cropping seasons by single application of RFS without loosing grain yield.

Straw management and tillage effects on soil water storage under field conditions

Abstract. A two year field study was conducted to evaluate the effects of straw management and tillage on the soil profile (1.5m) water storage, nature of the moisture profile, infiltration and sorptivity as influenced by rainfall, evaporativity (E0) and soil texture. The straw mulch treatment stored more moisture under low E0 rainy conditions in three coarse to medium textured soils. Straw incorporation treatment was better under low E0 rain free conditions, as well as under high E0 rainy conditions in the two coarser textured soils. In the coarsest textured soil, tillage and straw mulching were not effective in maintaining greater soil water storage under high E0 because of the very open nature of the soil. The soil moisture profiles showed a sharper increase in water content below the tilled layer in the tillage and straw‐ incorporation treatments than the untreated and straw mulch treatments. Tillage and straw incorporation treatments increased the sorptivity of the soil compared with untreated and straw mulch treatments respectively. The results of this study suggest that when selecting a suitable soil water conservation practice to increase water storage in the soil profile, information on soil texture and weather (rain and evaporativity) must be considered.

In Search of a Sustainable Cropping System for the Semiarid Canadian Prairies

ABSTRACT Producers in the semiarid Canadian prairies have begun to extend and diversify their cropping systems. These newer cropping systems are often considered to be more sustainable. We examine the agronomic, environmental, and economic effects of reducing summerfallow use and including grain lentil (Lens culinaris Medikus) in rotation with spring wheat (Triticum aestivum L.). Data from a long-term crop rotation experiment conducted on a medium texture soil at Swift Current, Saskatchewan were analyzed. Four cropping systems were evaluated over the 1979 to 1997 period; namely, fallow-wheat (F-W), fallow-wheat-wheat (F-W-W), continuous wheat (W), and wheat-lentil (W-L). Nitrate leaching below the 120 cm rooting depth of wheat was lower under continuously cropped systems than under fallow-based rotations, and was lowest overall for W-L. Wheat, whether grown on fallow or stubble, used almost all of the available water in the 0–120 cm depth soil profile, but lentil extracted about 1.5 cm less water than wheat. On average, wheat yield was unaffected by inclusion of lentil in the rotation; however, grain protein content was higher in 11 of 18 years. The incidence of leaf spotting diseases in wheat was lowest for wheat grown after lentil and highest for wheat grown on fallow. Soil quality (soil organic carbon, mineralizable N and C, light fraction organic C, and water stable aggregates) increased with cropping intensity in the order of W-L ≥ W > F-W-W > F-W. Although inputs of non-renewable energy and CO2 emissions were higher for the continuous compared to fallow-based rotations, including lentil in the rotation lowered the energy requirements for N fertilizer and provided an overall 19% reduction in CO2 emissions. The economics favored the W-L system whenever lentil price was above $350 t−1. The level of financial risk was lowest for F-W and F-W-W, intermediate for W-L, and highest for W. Our findings confirm the recent changes in land use practices being adopted by producers, and clearly show that extending and diversifying crop rotations by reducing fallow and including pulse crops in the rotation will improve the overall sustainability of agricultural production in this semiarid region.

Restoring organic matter in a cultivated, semiarid soil using crested wheatgrass

Planting of cultivated land with perennial forages may increase C sequestration in soil organic matter and contribute to atmospheric CO2 mitigation strategies. However, little is known of the effectiveness of introduced grasses in restoring organic C in cultivated soils of the Canadian prairies. Our objective was to evaluate the C sequestration potential of crested wheatgrass (CWG) (Agropyron cristatum L. Gaertn.), a widely introduced, early-season grass. In 1995 and 1996, we measured soil CO2 fluxes, C inputs in plant material and total soil C under CWG and a fallow-wheat (Triticum aestivum L.)-wheat rotation (F-W-W). These were two of the treatments in a replicated crop rotation experiment initiated in 1987 in southwestern Saskatchewan on a medium-textured soil that had previously been under long-term wheat production. Average to above-average growing season (1 May to 31 July) precipitation in 1995–1996 resulted in annual inputs of C in wheat residues of 3000–4500 kg ha−1. Growth of CWG, which was hayed and removed, was relatively poor in both years, but especially in 1995 when dry matter yield was only 1300 kg ha−1. For the 1988–1996 period, there was a strong correlation (R2 = 0.81; P &lt; 0.001) between CWG yield and precipitation received in May, showing the importance of early spring rains determining CWG yield and C inputs to the soil. Carbon inputs under CWG (1200 kg ha−1 in 1995 and 2400 kg ha−1 in 1996) were less than under wheat but CO2-C emissions were similar under CWG and wheat. Soil C measurements in fall 1996 confirmed that CWG did not gain C relative to the F-W-W rotation. Although failure of CWG soil to store more C than cultivated soil may be partly because weather conditions during the experiment were more favourable for wheat than CWG, our results cast doubt on the ability of CWG to restore C stocks in prairie soils degraded by long-term cropping. Key words: Carbon sequestation, carbon dioxide emissions, wheat, crested wheatgrass, fallow

Wheel traffic impact on soil conditions as influenced by tillage system in Central Anatolia

The increased limiting effects of soil compaction on Central Anatolian soils in the recent years demonstrate the need for a detailed analysis of tillage system impacts. This study was undertaken to ascertain the effects of seven different tillage systems and subsequent wheel traffic on the physical and mechanical properties of typical Central Anatolian medium textured clay loam soil (Cambisol), south of Ankara, Turkey. Both tillage and field traffic influenced soil bulk density, porosity, air voids and strength significantly except the insignificant effect of traffic on moisture content. Traffic affected the soil properties mostly down to 20 cm. However, no excessive compaction was detected in 0–20 cm soil depth. The increases of bulk density following wheel traffic varied between 10–20% at 0–5 cm and 6–12% at 10–15 cm depth. In additions, traffic increased the penetration resistance by 30–74% at 0–10 cm and 7–33% at 10–20 cm. Less wheel traffic-induced effects were found on chisel tilled plots, compared to ploughed plots. Soil stress during wheel passage was highly correlated with soil strength. Also, both tillage and traffic-induced differences were observed in mean soil aggregate sizes, especially for mouldboard ploughed plots. The obtained data imply that chisel+cultivator-tooth harrow combination provides more desirable soil conditions for resisting further soil compaction.

Improvement in Field Texture Accuracy for Sustainable Agriculture

ABSTRACT The improvement in field texture accuracy of 100 soil samples from contrasting parent materials–Coastal Plain Sands (33), Basement Complex (27), and Flood Plain (40)–were studied for sustainable agriculture. The results of improvement in field texture accuracy of the soil scientists used in the study were similar in both years. Absolute accuracy in the subsequent year (A2) increased over the previous year (A1) in descending order: Flood Plain (23%) > Coastal Plain (20%) > Basement Complex (8%). Relative accuracy was highly significant (r = 0.68–0.86, P < 0.001) irrespective of the period of determination (A1 or A2) and the parent material used. Time of determining field texture also reduced considerably in the subsequent year (A2) and for each successive rounds of determination. Reduction in time of soil texture determination per sample (seconds) follows descending order: Basement Complex (4.2) > Flood Plain (2.4) > Coastal Plain (1.2). It was noticed that medium texture soil require less time of determination by feel than heavy or light soils. Wherever heavy and light soils are more accurately determined by feel than medium textured soil. For sustainable agriculture in the global South, Relative Accuracy (cv(%) 4–9) is more reliable and pragmatic for most soil management practices than Absolute Accuracy (cv(%) 7–38).

Comportamento erosivo de um sistema pedológico de Umuarama, noroeste do estado do Paraná

O município de Umuarama, noroeste do estado do Paraná, apresenta solos de textura arenosa e média, associados aos arenitos da Formação Caiuá do Cretáceo Superior. Além da fragilidade natural desses solos, o desmatamento, o uso e a ocupação generalizados contribuíram para a intensificação dos processos erosivos. Uma vertente próxima à área urbana foi escolhida para estudo em toposseqüência, visando à caracterização pedológica macro e micromorfológica, acompanhada de caracterização físico-hídrica dos horizontes pedológicos. Os dados permitiram chegar a algumas conclusões importantes, quanto ao comportamento dos materiais, dos fluxos hídricos e quanto à dinâmica erosiva dos solos, bem como permitiram distinguir os setores inferiores da vertente como os de maior risco à erosão linear.