Abstracts

Babu, R.C., Nguyen, B.D., et al. 2003, 'Genetic Analysis of Drought Resistance in Rice by Molecular Markers: Association between Secondary Traits and Field Performance', Crop Science, vol. 43, pp. 1457-1469.

Drought stress is the major constraint to rice (Oryza sativa L.) production and yield stability in rainfed ecosystems. Identifying genomic regions contributing to drought resistance will help develop rice cultivars suitable for rainfed regions through molecular marker assisted breeding. Quantitative trait loci (QTLs) linked to plant water stress indicators, phenology and production traits under irrigated and drought stress conditions were mapped by means of a doubled-haploid (DH) population of 154 rice lines from the cross CT9993-5-10-1-M/IR62266-42-6-2. The DH lines were subjected to water stress before anthesis in three field experiments at two locations. The DH lines showed significant variation for plant water stress indicators, phenology, plant biomass, yield and yield components under irrigated control and water stress. A total of 47 QTLs were identified for various plant water stress indicators, phenology, and production traits under control and water stress conditions in the field, which individually explained 5 to 59% of the phenotype variation. A region was identified on chromosome 4 that harbored major QTLs for plant height, grain yield, and number of grains per panicle under drought stress. By comparing the coincidence of QTLs with specific traits, we also genetically dissected the nature of association of root traits and capacity for osmotic adjustment with rice production under drought. Root traits had positive correlations with yield and yield components under drought stress. This study demonstrated that the region RG939-RG476-RG214 on chromosome 4 identified for root-related drought resistance component QTLs also had pleiotropic effects on yield traits under stress. Consistent QTLs for drought resistance traits and yield under stress were detected and might be useful for marker-assisted selection for rainfed rice improvement.

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Drury, C.F., Tan, C.S., et al. 2003, 'Impacts of Zone Tillage and Red Clover on Corn Performance and Soil Physical Quality', Soil Science Society of America Journal, vol. 67, pp. 867-877.

Despite extensive research, reduced corn (Zea mays L.) performance is still encountered using conservation tillage on fine-textured soils in cool humid temperate climates. These problems are intensified when corn is planted into residue from a previous crop such as winter wheat (Triticum aestivum L.). The objective of this 4-yr study was to determine the influence of fall zone tillage (ZT), no tillage (NT), and conventional moldboard plow tillage (CT) (fall plowing) on corn performance and soil physical quality under a winter wheat–corn–soybean (Glycine max L. Merr.) rotation with and without red clover (Trifolium pratense L.) (RC) underseeded in the wheat phase of the rotation. A randomized complete block design (3 x 2 factorial, 4 replicates) was established on three adjacent fields in the fall of 1996 on a Brookston clay loam soil (fine loamy, mixed, mesic, Typic Argia-quoll) at Woodslee, ON Canada, and measurements were collected during 1997 to 2000. Over both wet and dry growing seasons from 1998-2000, zone tillage following underseeded RC produced average corn grain yields (7.23 Mg ha^-1) that were within 1% of those obtained using conventional tillage (7.33 Mg ha^-1), and 36% higher than those obtained using no tillage and RC (5.33 Mg ha^-1). Zone tillage also improved soil quality as evidenced by generally lower soil strength than no tillage, and near-surface soil physical quality parameters that were equivalent to, or more favorable than, those of the other treatments. It was concluded that corn production using zone tillage and RC underseeding is a viable option in Brookston clay loam soil, as it retains much of the soil quality benefit of conventional tillage but still achieves most of the yield benefit of conventional moldboard plow tillage.

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Fesha, I.G., Shaw, J.N., et al. 2002, 'Land Use Effects on Soil Quality Parameters for Identical Soil Taxa', in Making Conservation Tillage Conventional: Building a Future on 25 Years of Research. Proceedings of the 25th Annual Southern Conservation Tillage Conference for Sustainable Agriculture. Auburn, AL 24-26 June 2002. Special Report no. 1., ed^eds E. van Santen, Alabama Agric. Expt. Stn. and Auburn University, AL 36849. USA., pp. 233-238

Near-surface or use-dependent soil properties are relatively dynamic and can change over a few years time. These manageable, use-dependent properties are critical to soil quality. Past studies have documented land use effects on near-surface soil properties without ensuring soil taxa were identical. Our objective was to evaluate soil quality differences due to land use in taxonomically identical soils. Research sites were located at the Sand Mountain Research Center (SMRC) and E.V. Smith Research Center (EVS) of the Alabama Agricultural Experiment Stations. Soils were classified as fine-loamy, siliceous, subactive thermic Typic Hapludults at SMRC and coarse-loamy, siliceous, subactive, thermic Typic Paleudults at EVS. Experiments were conducted in long term conventional and conservation tillage plots, pastureland, and woodland areas. Investigated parameters included: bulk density (Db), water stable aggregates (WSA), saturated hydraulic conductivity (Ksat), soil water retention (SWR), soil strength, water dispersible clay (WDC), soil organic carbon (SOC), total nitrogen (TN), and soil microbial biomass C. Results at SMRC indicated that the conventional tillage system had lower values of WSA, SWR, SOC, TN, and soil microbial biomass C as compared to the other systems. At SMRC, WSA in the conventional tillage system were 28, 25, and 24% lower than pastureland, woodland, and the conservation tillage system, respectively. Similarly, SWR in the conventional tillage system was 19, 23, and 11% lower than pastureland, woodland, and the conservation tillage system, respectively. Pastureland had higher WSA, Db, and soil strength. Woodland had the highest SOC, TN, microbial biomass C, and Ksat. At EVS, the conventional and no-tillage systems had lower WSA, WDC, and microbial biomass C and higher Db and SWR compared to woodland. Pastureland had higher SWR, SOC, TN, and soil microbial biomass C than woodland. The conservation tillage system had higher WSA, SWR, TOC, TN, and microbial biomass C and lower Ksat, and WDC compared to the conventional tillage system. At EVS, WSA in the conventional tillage system were 14, 26, and 12% lower than pastureland, woodland, and the conservation tillage system, respectively. In addition, the woodland had lower values of SOC and TN compared to the pastureland and conservation tillage systems. Our data at EVS suggests that loblolly pine (Pinus teada L.) plantation management did not improve soil quality relative to croplands. In general, the aggregate of data suggested that intensive soil cultivation resulted in reduced soil quality at both sites. Our data showed differences in near-surface soil properties that resulted from land use systems in taxonomically similar soils. Variation in near-surface properties resulting from land use suggests further work is needed to enhance soil map unit interpretations. KEYWORDS: Soil quality, land use, soil taxa, use-depedent soil properties, soil.

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Gomez, A., Powers, R.F., et al. 2002, 'Soil Compaction Effects on Growth of Young Ponderosa Pine Following Litter Removal in California’s Sierra Nevada', Soil Science Society of America Journal, vol. 66, pp. 1334-1343.

Increased use of heavy equipment and more frequent entry into forest stands has increased the potential for soil compaction and decreased productivity. We examined compaction and tree growth relationships on three California soils of contrasting textures (clayey, loamy, and sandy loam) on plots from which the organic soil horizon had been removed. Compacted and noncompacted treatments were compared. Changes in bulk density (D_b), soil strength, and total porosity, measured during the growing season, were greatest in the 15- to 30-cm depth at all sites. Bulk density increases were greatest in the loamy soil (30%) and least in the sandy loam (23%). Total porosity decrease in the upper 45 cm averaged 20, 9, and 13% for the clay, loam, and sandy loam textures, respectively. In the 30- to 45-cm soil depth, compacted soils reached critical water potentials (< 1.5 MPa) 50 d sooner in the loam and 67 d sooner in the clay. In the sandy loam, compaction extended the period of plant-available water for 86 and 48 d in the 1- to 15- and 15- to 30-cm soil depths. Midday stem water stress was greater for trees in compacted plots of loamy and clayey textures, but less on sandy loam. Soil compaction did not reduce tree growth universally in these 3- to 8-yr-old plantations. Effects were detrimental, insignificant, and beneficial for clayey, loamy, and sandy loam soils, respectively. Results show that compaction effects depend strongly on soil texture and soil water regime. Soil physical values, per se, are not always reliable criteria for evaluation.

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Miller, R. and Anderson, H. 2002, 'Soil compaction: concerns, claims and evidence', in Small Diameter Timber: Resource Management, Manufacturing, and Markets proceedings from conference held February 25-27, 2002 in Spokane, Washington., ed^eds D.M. Baumgartner, L.R. Johnson and E.J. DePuit, Washington State University Cooperative Extension, Pullman, WA, pp. 97-106

Soil resistance to penetration was measured in ten 7- to 27-acre operational units in overstocked mixed-conifer stands at the Fritz Timber Sale in Northeast Washington. Different combinations of felling and yarding equipment were used to thin eight of these units; no combination was replicated. Two other units remained nonharvested controls. Using a recording penetrometer, resistance was measured to the 33-cm depth (13 inches) at ten stations on 5–17 100-foot long, randomly oriented transects in each unit. Ground-based harvesting equipment operated on and off designated trails. Although trails occupied 6– 57% of the harvested units, total area of strong compaction on these trails varied greatly (0–42%). Consequences of soil compaction for tree performance at this sale area are unknown. In fact, consequences of soil disturbance for trees have seldom been measured in the Northwest. At the relatively few places where trees were measured, response to compaction ranged from mostly negative through none to positive. Therefore, current claims about dire consequences of compaction for long-term site productivity must be based largely on limited sampling, assumptions about the consequences of compaction for tree performance, and speculation. We assert that uncertainty about the consequences of compaction and other forms of soil disturbance will remain until long-term tree performance is correctly measured over a wide range of regional soils and climatic.

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Miller, R.E., Hazard, J., et al., 2001, Precision, Accuracy, and Efficiency of Four Tools for Measuring Soil Bulk Density or StrengthPacific Northwest Research Station General Technical Report PNW-RP-532 Portland, ORUnited States Department of Agriculture Forest Service pp 16 pp.

Monitoring soil compaction is time consuming. A desire for speed and lower costs, however, must be balanced with the appropriate precision and accuracy required of the monitoring task. We compared three core samplers and a cone penetrometer for measuring soil compaction after clearcut harvest on a stone-free and a stony soil. Precision (i.e., consistency) of each tool at depths of 0-10, 10-20, and 20-30 cm was determined from two adjacent samples at 21 or more sampling points in each harvested location. Because one bulk density (D_b) sampler provided a continuous sample of each decimeter depth, it was designated as the standard; thereby, the relative accuracy and bias of the two shorter core samplers could be calculated. Both shorter samplers overestimated D_b as determined by the standard. At least 15 penetrometer samples could be taken and processed in the time required for three D_b samples to the same 30-cm depth. Precision of measurements taken by the cone penetrometer, however, was clearly less than that with any of the D_b samplers. Based on time requirements and precision of each tool, we examined the efficiency of double sampling (using a combination of penetrometer and core sampler) for estimating D_b. Results from the stone-free soil indicated an advantage in both precision and efficiency in applying double-sampling theory to estimate Db rather than sampling exclusively by the more time-consuming core samplers.

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Niewenhuis, P., Lales, J.S., et al. 2002, Soil Moisture Dynamics During Drought in a Simulated Rainfed Lowland Environment, 17th World Congress of Soil Science: Confronting New Realities in the 21st Century, Thailand. 14-21 August 2002 pp. Paper No. 2335.

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Sanchez, F.G., Carter, E.A., et al. 2000, 'Soil Carbon and Soil Physical Properties Response to Incorporating Mulched Forest Slash', New Zealand Journal of Forestry Research, vol. 30, no. 1/2, pp. 150-168.

A study was installed in the Lower Coastal Plain near Washington, North Carolina, to test the hypothesis that incorporating organic matter in the form ofcomminuted forest slash would increase soil carbon and nutrient pools and alter soil physical properties to favour pine growth. Two sites were selected, an organic and a mineral site, to compare the treatment effects on the different soil types. The mulching treatments included a surface broadcast mulch, a surface strip mulch, and a strip mulch and till. On the mineral site, the three treatments resulted in general decreases in soil bulk density, gravimetric soil water content, and soil strength. Soil carbon and nitrogen increased for all the treatments on the mineral site, with some significant differences between the treatments. The broadcast mulch and bed treatment resulted in an almost 100% increase in soil carbon and nitrogen. On the organic site, the treatments did not have a significant effect on soil physical properties or soil carbon and nitrogen. There was a consistent decrease in soil carbon and nitrogen on this site but these changes were not significantly different from those in the control treatment.

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Seixas, F. and McDonald, T. 1997, 'Soil Compaction Effects of Forwarding and its Relationship with 6- and 8-wheel Drive Machines', Forest Products Journal, vol. 47, no. 11/12, pp. 46-52.

A study was done to determine the impact, if any, of a range of drive train options on the soil compaction effects of forwarders. The purpose of the study was to evaluate the cost of optional forwarder equipment versus its ability to reduce detrimental soil physical property changes. Tests were done on forwarders equipped with wide and narrow tires, rear steel tracks, and 6 or 8 tires. The configurations differed, at the extremes, by a factor of about 2 in expected ground pressure. Despite that, results showed little difference in bulk density, soil strength, rut formation, or porosity changes (pre- vs. post-traffic) between any of the tested options. The implication was that, for the moisture conditions encountered in the study, the use of the tested options did not alter soil compaction impacts substantially. A drop in macroporosity was observed, however, which may have been evidence that traffic affected soil structure without compacting it by a detectable amount.

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Sparrow, L. and Cotching, W., 2000, Pyrethrum Paddocks – What makes them good for subsequent cropping? Publication No. 00/27 Project No.TAR-3A Canberra, ACTRural Industries Research and Development Corporation pp

Concerns exist about the long term capacity of soils in north west Tasmania to support intensive horticulture. Pyrethrum, because it is a perennial crop, offers the soil relief from cultivation and a chance for the soil to repair. A number of pyrethrum growers in NW Tasmania have reported that when they plough pyrethrum paddocks in preparation for a subsequent crop, the soil is easier to work than in paddocks following other crops. Some also consider that the subsequent crop grows better than in a paddock which had not come out of pyrethrum. This study sought to find out whether these benefits could be measured by a change in one or more soil properties, whether there was any evidence for better growth of subsequent crops, and whether other pyrethrum farmers agreed with the views expressed above.
Eight pairs of paddocks were studied, each pair comprising one paddock recently out of pyrethrum, the other never having grown that crop. The soil on all paddocks was a red ferrosol, the most commonly used soil for pyrethrum in Tasmania. A range of soil properties were assessed, and the yields of crops, either potatoes or green peas, growing in the paddocks were also measured. Paddocks were selected so that both paddocks in each pair were growing the same crop and were close to each other.
There were no significant differences in yield due to the prior presence of pyrethrum. The only significant differences in soil properties measured were penetration resistance, liquid limit and earthworm numbers. The most significant soil difference was that ex-pyrethrum paddocks had lower resistance to penetration in the top soil, supporting the growers’ views that these paddocks are easier to cultivate. However, the fact that yields were not affected suggests that any benefit of this change is small compared to other influences on crop yield such as plant density, and management of water, weeds, fertilisers, pests and diseases. Earthworm numbers in ex-pyrethrum paddocks were significantly less than in other paddocks, which is consistent with our earlier observations in paddocks still growing pyrethrum. It seems that 1 year is not long enough for worms to return to such paddocks. Further study is needed to determine if earthworms naturally recolonise ex-pyrethrum paddocks or if re-introduction is necessary and desirable. Growers were divided in their views about the benefits of pyrethrum for yield of subsequent crops, and were mostly unsure how long the soil benefits lasted.
Our conclusion is that cropping pyrethrum offers little significant benefit in rejuvenating soil attributes on red ferrosols, which is consistent with the knowledge that these soils have no capacity for self-repair and that pyrethrum plants do not have vigorous, fibrous root systems.

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Vetsch, J.A. and Randall, G.W. 2002, 'Corn Production as Affected by Tillage System and Starter Fertilizer', Agronomy Journal, vol. 94, pp. 532-540.

Potential agronomic and soil conservation benefits of modified no-till (NT) systems make them appealing for corn (Zea mays L.) production in the northern Corn Belt where adoption of NT has been limited due to yield reductions on these colder soils. A 4-yr (1997–2000) experiment was conducted on a high P– and K–testing Port Byron silt loam (fine silty, mixed, mesic typic Hapludoll) to determine the effects of four tillage systems [no-till (NT), Rawson zone till (ZT), fall strip till (ST), and conventional tillage practice (CT)] on corn production and cone index (CI; penetrometer resistance) in continuous corn and corn following soybean [Glycine max (L.) Merr.]. Eight treatments, four tillage systems (main plots) with starter fertilizer at rates of 0 and 168 kg ha^-1 of a 9–10–24, were arranged in a split-plot design with four replicates. Surface residue coverage after planting was maintained at high levels (>40%) with NT, ZT, and ST, whereas coverage averaged only 25% with the CT practice. Cone index during the period of early plant growth was significantly less for the ZT and ST systems compared with the NT and CT systems, but CI did not exceed 1.3 MPa. Four-year average yields of continuous corn grain ranked according to tillage were CT > ZT = ST > NT. A significant tillage X year interaction indicated equal yields for CT and NT in the first 2 yr but 1.0 to 1.2 Mg ha^-1 less with NT in the last 2 yr. Tillage system did not significantly affect corn grain yields following soybean when averaged across years. Starter fertilizer increased yields by 0.5 Mg ha^-1 on this high-testing soil for all tillage systems in both crop rotations. Surface residue and corn yields following corn and soybean can be optimized using modified NT systems (ZT and ST) and starter fertilizer in these well-drained, loess soils.

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