Soil Type Interactions Research Articles

HASIL TANAMAN PADI (Oryza sativa L Var. Inpari) AKIBAT PUPUK BIOSLURRY DAN PEMBENAH TANAH PADA TIGA JENIS TANAH

The impact of soil fertility degradation is the continuous use of inorganic fertilizers, which caused soil organic matter and rice production degradation. The study was conducted to obtain the optimal dose of bioslurry fertilizer for rice growth and production in andosol, regosol, and aluvial soil types without or with soil amendment. The experiment used split split plot with Completely Randomized Design and three replication. The main plot is soil type, L1:Andosol, L2:mediterranean, and L3:aluvial. The subplots is soil amendment, R1:without amendment, and R2:with amendment. The sub subplots used is bioslurry fertilizer, P1:125kgN/ha, P2:1,5 x 125kgN/ha, and P3: 2 x 125kgN/ha. The results showed that interaction of soil amendment and bioslurry dose had a significant (P<0.05) on the growth and production of Inpari rice. The interaction of soil type and amendment showed significance (P<0.05) in plant height, number of tillers, parameters with highest result at aluvial soil with amendment. The interaction of amendment and bioslurry showed significance (P<0.05) on fresh weight and dry weight of grain parameter with highest result at dose of 2 x 125kgN/ha with amendment. The interaction between soil type, amendment, and bioslurry show significance (P<0.05) at weight of 1000 seeds, and production with ameliorant parameters with highest result in aluvial soil types with 2 x 125kgN/ha dose. Alluvial soil with amendment and bioslurry 2 x 125 kg N/ha dose gave the highest rice production yield of 15,94 t/ha. Keywords: amendment , bioslurry, rice, soil type

Native tree seedling growth and physiology responds to variable soil conditions of urban natural areas

Soils in urban natural areas can be highly variable due to legacies of land use change that include excavation of existing soils and dumping of construction debris or other anthropogenic materials. As cities undertake large‐scale tree planting efforts to sustain and increase forest cover, understanding how urban soil quality influences native tree seedling survival and performance is important. In a greenhouse setting we examined growth and physiology of native silver maple (Acer saccharinum), black birch (Betula lenta), red oak (Quercus rubra), and Canadian serviceberry (Amalanchier canadensis) seedlings planted in soils collected from locations across New York, NY, U.S.A. The soils were collected from areas currently undergoing forest restoration, representing a range of soil nutrient quality and anthropogenic disturbance. We measured seedling survival, height growth, leaf chlorosis, and chlorophyll fluorescence for two growing seasons, after which seedlings were harvested to assess biomass allocation and foliar chemistry. Selected variables were standardized and combined to create a seedling stress index. Overall, seedlings performed best in the least disturbed urban soils and had the poorest performance in the more highly disturbed, nutrient‐poor urban soil types and a greenhouse mix. Species × soil type interactions on physiological responses indicate that tree species may not respond to urban soil conditions consistently. Consequently, matching native tree species to soil type could help optimize establishment and growth of urban forest restoration projects. Seedling stress scores from the first growing season were correlated with second year height growth for three of four species, illustrating their utility for managers.

Interaction studies between geotextile and fill material

As the growth in geotechnical science, there are a lot of new innovations that are used for solving geotechnical problems. One of those innovations is geotextile.This geotextile is often used in earth fill as reinforcement with function to increase the shear strength of existing fill and related with the interaction between geotextile and fill material. Based on this fact, this research is conducted to know the interaction of soil type to geotextile. The result of the research shows that all of the tested soil shear strength parameter comparison are below 1 (0.23; 0.29; 0.24 for C of clay comparison), (0.65; 0.77; 0.98 for ϕ of clay comparison), (0.53; 0.66; 0.67 for ϕ of sand comparison), and (0.53; 0.66; 0.67 for ϕ of coarse aggregate comparison). So it could be concluded that the shear strength of fill material and geotextile material is lower than the shear strength of fill material without geotextile.

Functional Phenology of a Texas Post Oak Savanna from a CHRIS PROBA Time Series

Remnant midwestern oak savannas in the USA have been altered by fire suppression and the encroachment of woody evergreen trees and shrubs. The Gus Engeling Wildlife Management Area (GEWMA) near Palestine, Texas represents a relatively intact southern example of thickening and evergreen encroachment in oak savannas. In this study, 18 images from the CHRIS/PROBA (Compact High-Resolution Imaging Spectrometer/Project for On-Board Autonomy) sensor were acquired between June 2009 and October 2010 and used to explore variation in canopy dynamics among deciduous and evergreen trees and shrubs, and savanna grassland in seasonal leaf-on and leaf-off conditions. Nadir CHRIS images from the 11 useable dates were processed to surface reflectance and a selection of vegetation indices (VIs) sensitive to pigments, photosynthetic efficiency, and canopy water content were calculated. An analysis of temporal VI phenology was undertaken using a fishnet polygon at 90 m resolution incorporating tree densities from a classified aerial photo and soil type polygons. The results showed that the major differences in spectral phenology were associated with deciduous tree density, the density of evergreen trees and shrubs—especially during deciduous leaf-off periods—broad vegetation types, and soil type interactions with elevation. The VIs were sensitive to high densities of evergreens during the leaf-off period and indicative of a photosynthetic advantage over deciduous trees. The largest differences in VI profiles were associated with high and low tree density, and soil types with the lowest and highest available soil water. The study showed how time series of hyperspectral data could be used to monitor the relative abundance and vigor of desirable and less desirable species in conservation lands.

Potential impact of biochar types and microbial inoculants on growth of onion plant in differently textured and phosphorus limited soils

Non-renewable phosphorus (P) resources are intensively declining and recyclable P is high in demand for agricultural sector. Biochar as a renewable source of P and its physicochemical properties may improve the nutrients condition in the soil for plant availability. This study was designed to evaluate the interaction of biochar with soil microbes in differently textured and P-limited soils for P availability, root colonization and nutrient uptake by plants. Onion plants were grown in two differently textured soils with two types of biochar, with or without P application, three microbially inoculated treatments and uninoculated control. Plants were grown for 65 days and root-shoot biomass, nutrient concentration and mycorrhizal root colonization were analyzed. The WinRhizo was used to evaluate root attributes such as length, surface area and volume of roots. Biochar addition enhanced the nutrient uptake and plant biomass in the presence of P and microbial inoculants. Root colonization was notably increased in biochar + mycorrhizal inoculated plants. Biochar and soil type interactions may develop a unique behavior of nutrient uptake, root colonization, plant growth and root attributes. Biochar in combination with microbial inoculants could be considered a potentially renewable source of P fertilizer.

Emergence and establishment of native and non-native species in soils of remnant and converted highland grasslands – southern Brazil

Abstract Native grasslands in the Campos de Cima da Serra, Brazil, are being converted at speed for exotic tree plantations and cropland. The impact of modified and novel soil conditions on the establishment of native grassland species is unknown; establishment of non-native species, deliberately or accidentally introduced, could be favoured. In a common garden composed of fully randomized replicate samples of soils collected from remnant grassland, former cropland and pine plantations, we tested emergence and establishment of five cold-season species: Native low-tussock grass Piptochaetium montevidense (Spreng.) Parodi; native legume Trifolium riograndense Burkart; naturalized low-tussock grass Vulpia bromoides (L.) Gray; low-tussock grass Holcus lanatus L., cultivated and naturalized in Brazil; and a cultivar of non-native Trifolium repens. Other than expected, soil type and species*soil type interactions had no significant effect on seedling emergence after 132 days in the field. Species effect on seedling emergence, however, was highly significant. Vulpia bromoides emergence was significantly highest in all soil types. Holcus lanatus and Trifolium riograndense both achieved second highest emergence rates and did not differ significantly from each other. Lowest overall emergence rates were found in the non-native clover cultivar. Lab germination tests failed for Piptochaetium, although it showed reasonable emergence in the field. Good performance of the native clover is encouraging for future grassland restoration, but the value of highly germinable Vulpia as a forage remains to be tested. Holcus tolerates a wide range of soil conditions and its life history traits may promote naturalization, or even invasiveness. Native grasslands of the region should be monitored for this species. Studies like these, but set up on a larger geographical scale and with a wider array of native species, will be essential in developing ecological restoration methods for southern Brazilian grasslands.

Variability in Urban Soils Influences the Health and Growth of Native Tree Seedlings

Reforesting degraded urban landscapes is important due to the many benefits urban forests provide. Urban soils are highly variable, yet little is known about how this variability in urban soils influences tree seedling performance and survival. We conducted a greenhouse study to assess health, growth, and survival of four native tree species growing in native glacial till, coal ash, urban fill, and sandy clean fill soils collected from urban forest restoration sites in New York City. Using a multifactorial design, nine replicates of silver maple (Acer saccharinum), black birch (Betula lenta), red oak (Quercus rubra), and Canadian serviceberry (Amelanchier canadensis) were planted in four urban soil types and one greenhouse mix. We hypothesized that: 1) urban soil type would influence growth, health, and survivorship; 2) each tree species would respond differentially to each soil type; and 3) seedling stress and mortality would be higher for soils with more anthropogenic disturbance. After one growing season, we found that seedlings were less healthy and grew less in soils with a history of greater anthropogenic disturbance. Seedling mortality was low (< 3% overall) except for red oak seedlings in urban fill soil from one location. These results demonstrate that urban soil conditions can impact tree growth and health while supporting high survivorship. Species × soil type interaction for height growth and stress indicate that native tree species may not respond to urban soil conditions consistently. Consequently, matching tree species to soil type could help optimize establishment and growth of urban forest restoration projects.

Effect of soil type, organic matter content, bulk density and saturation on clubroot severity and biofungicide efficacy

Growth room experiments were conducted to assess the interaction of soil type, biofungicides, soil compaction and pathotype/host on infection and symptom development caused byPlasmodiophora brassicae, the cause of clubroot onBrassicaspp. In two initial experiments, four soil types (peat soil, mineral soil, non‐calcareous sand, soil‐less mix), two biofungicides (Bacillus subtilis,Clonostachys rosea), and two pathotypes (3 and 6, Williams’ differential set) were assessed. Differences in clubroot severity associated with soil type were unexpectedly small and variable. Prestop (C. rosea) was often more effective than Serenade (B. subtilis) at reducing clubroot levels on peat and mineral soils, but less effective than Serenade on sand. Inoculation with pathotype 3 often resulted in a slightly higher mean severity than pathotype 6. The interaction of soil type × biofungicide was similar on both canola (B. napus) and Shanghai pak choy (B. rapasubsp.chinensis), whether the soil was kept saturated or allowed to drain after inoculation. The impact of soil type on biofungicide efficacy might explain, in part, why biofungicides are more effective in one location than another. The observation that clubroot severity in soil‐less mix was affected by compaction led to an investigation of soil bulk density. Severity was higher in soil‐less mix that was more compacted than in the initial experiments, and was lower in peat and mineral soils when soil bulk density was reduced by adding soil‐less mix. In this study, soil bulk density had a larger impact on clubroot than soil type, organic matter or pathotype.

Quantifying Sugarcane Cultivar Genetic Gains in the Midlands Region of South Africa

Analyzing genetic gains of sugarcane cultivars provides a measure of performance for plant breeding programs. Previous studies in several countries showed yield of up to 150% in the last 50 yr. The objective of this study was to determine the genetic gains for cane yield, percent estimated recoverable crystal (ERC%) cane and sugar yield of cultivars grown in the humic and sandy soils of the Midlands region in South Africa. Data were derived from the final stage of cultivar testing. There was 0.40 Mg ha−1 yr−1 cane yield genetic gain in humic soils and 0.38 Mg ha−1 yr−1 in sandy soils. Sugar yield genetic gains were 0.051 Mg ha−1 yr−1 in humic soils and 0.047 Mg ha−1 sandy soils. Genetic gains by sequence of release ranged from 1.70 to 2.45 Mg ha−1 cultivar−1 for cane yield and 0.23 to 0.27 Mg ha−1 cultivar−1 for sugar yield. Recently released cultivars produced genetic gains equivalent to 9 to 28% in cane and sugar yield. There were no genetic gains for ERC% cane. Significant cultivar × soil type interaction indicated that certain cultivars were not adapted to both soil types. Cultivars released after 2000 produced genetic gains equivalent to more than 14% increase in cane and sugar yield compared to older cultivars. Replanting 70% of current hectarage to newer and higher yielding cultivars will increase grower cane and sugar yield by 5 to 17%.

Can pH amendments in grazed pastures help reduce N2O emissions from denitrification? – The effects of liming and urine addition on the completion of denitrification in fluvial and volcanic soils

Soil pH plays a critical role in determining the overall rate of several important processes in the agricultural nitrogen cycle. During denitrification, the activity of nitrous oxide reductase (N2O-R) is reduced at low pH. This effect has led to suggestions that soil pH adjustment via liming to enhance the activity of this enzyme might be a viable agricultural greenhouse gas mitigation strategy by enhancing the reduction of N2O in the soil to climatically inert N2. We assessed the effect of liming on the apparent activity of N2O-R by measuring the denitrification end products, N2O and N2, in a series of short-term anaerobic incubations. We compared a weakly-buffered fluvial soil and a well-buffered, volcanic soil under different incubation temperatures and in the presence or absence of a ∼600 kg ha−1 cow urine-N amendment. Our results indicated that the liming effect was heavily modulated by soil type, temperature, and urine amendment. Liming (at rates of 1.5 and 3.0 t ha−1 for the volcanic soil and at rates of 5 and 10 t ha−1 for the fluvial soil) caused pH increases of between 0.43 and 1.25 pH units. The highest reductions in N2O in the fluvial soil occurred when the 1.5 t ha−1 rate was used in the fluvial soils under urine addition and at the higher temperature. The combined flux of N2O + N2 did not change with liming. However, an interaction of soil type and urine amendment caused large differences in the partitioning of the denitrification end-products between N2O and N2 – an effect that overwhelmed the relatively modest effects of liming. When the soils were amended with urine-N, the resulting denitrification gases from the volcanic soil were mostly in the form of N2O (60–77%), whereas in the fluvial soil the denitrification products were mostly in the form of N2 and a much smaller portion were in the form of N2O (11–45%). Nevertheless, we found liming-induced enhancements of N2O-R of 15–20% (P < 0.05) in urine-amended, fluvial soil. We suggest some possible mechanisms that would explain such large differences in the N2O/(N2O + N2) product ratio.

Effect of pyrolysis temperatures on stability and priming effects of C3 and C4 biochars applied to two different soils

Biochar (BC) is a recalcitrant soil amendment that is being used for long-term carbon sequestration while also enhancing soil fertility. In an effort to better understand the interaction of soil type and biochar type, Mollisol (Minnesota) and Ultisol (Georgia) were incubated with biochars prepared from C3 (rice hull and wheat straw) and C4 (maize stover and switch grass) crop residues at 400°C and 600°C and the stability of biochar was studied by CO2 evolution measurements for 60 days. The C3 and C4 biochars were applied to the Ultisol and Mollisol samples which had a long term history of cropping with C4 and C3 crops, respectively. Overall the total and fixed C content of biochar increased, while the N content decreased with increase in pyrolysis temperature from 400°C to 600°C, thus increasing the C:N of the biochar. The volatile matter component of biochar decreased significantly at the higher pyrolysis temperature. In the Mollisol, the wheat straw biochar prepared (WSBC) at 600°C was more stable than the rice hull biochar (RHBC). However, in the Ultisol, RHBC was more stable than the WSBC. Corn stover biochar (CSBC) prepared at 600°C showed greater stability in both the Mollisol and Ultisol. The WSBC and CSBC prepared at 600°C which showed negative priming of native soil organic matter (SOM) had greater potential for long term carbon sequestration in soil. The δ13C signatures of the CO2 evolved on the 2nd day matched δ13C signatures of biochar confirming the contribution of biochar. On days 9 and 20 the δ13C signatures matched that of control soil indicating very little or no contribution of biochar to CO2 evolution. In spite of significant changes in pH and EC of soil biochar mixtures, these parameters had no effect on C mineralization. Nonlinear regression model confirms that the decomposition rate constant was higher in the 400°C biochar than in the 600°C biochar. Corn biochar prepared at 600°C could be useful for enhancing carbon storage in both the Mollisol and Ultisol. Soil organic matter level might have controlled the direction and magnitude of priming effect.

Modelling fine root biomass of boreal tree stands using site and stand variables

Quantification of fine root biomass is needed for estimating the role of roots as carbon (C) stores and sources of C input into the soil, as well as for modelling of forest nutrient cycling. Due to the laborious nature of root biomass determinations, there is a need to develop indirect methods that would allow fine root biomass to be estimated using data on easily measurable stand and site variables. We developed models for estimating tree fine root (diameter⩽2mm) biomass of boreal forests by compiling data from 95 Finnish forest stands (55 on upland soils and 40 on drained peatlands). Stand basal area predicted fine root biomass (R2-adj.=0.35, p<0.001) better than any other stand variable alone. A model that included stand basal area, dominant tree species group [birch/other], soil type [upland soil/drained peatland], temperature sum and the interaction of soil type and temperature sum accounted for 46% of the variation in fine root biomass. Stand basal area, the C:N ratio of the organic layer or upper 0–20cm peat layer and the dominant tree species group together explained 45% of the variation in fine root biomass. Temperature sum correlated with fine root biomass in opposite ways in upland soils and in drained peatlands: fine root biomass increased with decreasing temperature sum in upland soil sites, whereas in peatlands fine root biomass decreased as the temperature sum decreased. Although the models were based on a large dataset representing well the variation in stand age, basal area, site fertility and climatic conditions in northern European boreal forests, half of the variation in fine root biomass remained unexplained. More comprehensive fine root biomass sampling in relation to spatial and temporal variation in the forthcoming studies, for example in connection with monitoring campaigns, and additional predictors such as soil texture, successional stage and the fine root biomass of ground vegetation might improve the predictive power of fine root biomass models.

Plant-available water and integral energy for Medicago sativa and Bromus tomentellus in texturally different soils

Soil water availability is very crucial for pasture plants because their growth solely depends on the soil water storage. While plant-available water (PAW) is successfully related to plant growth, it is the energy required per unit mass of water, integrated over the PAW range, named the integral energy (EI) that determines how easily plants can take up water from the soil. The soil water retention function was integrated over the PAW range to calculate the EI. PAW and EI were determined for Medicago sativa (alfalfa, a legume) and Bromus tomentellus (a grass) species in five texturally different soils of semi-steppe rangeland in central Zagros, western Iran. The PAW was calculated as the difference between field capacity and permanent wilting point (nominal h of 15,000 hPa or actual h obtained from PWP value determined in greenhouse). EI values were calculated for the nominal and actual PAW values. M. sativa PAW and EI values were more than those from B. tomentellus, indicating that M. sativa was able to tolerate higher soil matric suctions at similar conditions. Results showed predicting EI only from basic soil properties is not accurate. PAW and EI are dependent on plant species and soil type interactions, and environmental compatibility.

Soil quality evaluation under different land management practices

Sustainable agricultural production requires prudent management backed by reliable information that accurately elucidates the complex relationships between land management practices and soil quality trends. Therefore, this study investigates the influence of management on soil properties acquired at different depths, and yields, at five different field sites within Ohio, USA. The principal management systems considered were no till with or without manure and cover crops, natural vegetation (NV) or forest, and conventional tillage (CT) defined as farms with surface residue cover (<30 %). Analyses of variance (ANOVA), correlation analyses, stepwise regression, and the principal component analyses (PCA) were used to elucidate and model the link between four different management practices and the soil physical and chemical properties. The ANOVA results indicate that the available water capacity and electrical conductivity (EC) were the major variables affected by management. In contrast, soil pH, bulk density (ρ b), porosity, soil organic carbon (SOC), and total nitrogen (TN), were invariable with management, yet only pH and EC did not significantly vary with the interaction of soil type and management effects. In comparison, the PCA results suggest that SOC, TN, porosity, ρ b, and EC were the major determining factors controlling yield variability. Interestingly, the derived models revealed that the highest yields, notably 10 and 2.7 Mg ha−1 for corn (Zea mays L.) and soybean (Glycine max (L.) Merr.) occurred in soils under CT management. Quantifying the nexus between soil properties and management choices as demonstrated in this study, can provide critical insight for sustainable agricultural production.

Soil pH controls nitrification and carbon substrate utilization more than urea or charcoal in some highly acidic soils

Understanding the mechanism and key controlling factors of nitrification in highly acidic soils is important from both ecological and environmental perspectives. Many acid soils are also characterized by vegetation that produces polyphenolic and terpene compounds that inhibit microbial activity. We investigated the potentially ameliorative effects of lime, charcoal, and urea additions on soil nitrification and carbon substrate utilization (using the MicroResp method). Four soils were studied from widely different environments but with similar pH and inputs of phytochemicals to determine the relative effects of these potentially controlling factors. The addition of charcoal had no significant effect on net nitrification, but charcoal significantly increased soil basal respiration and altered C substrate utilization in the two Scottish soils. Urea greatly increased nitrification in both the Chinese soils, but there was no effect of urea on nitrification in the two Scottish soils. Lime application increased nitrification in all the soils except for the Chinese mixed forest soil. Multivariate analysis of the C source utilization data revealed that lime altered C substrate utilization more than urea or charcoal in these highly acidic soils. Our results suggest that acid-tolerant nitrifiers do exist in these soils and have potential for high activity, and pH (lime addition) and N-substrate (urea) most often increased nitrification. However, no single factor controlled nitrification in every soil, suggesting an interaction between abiotic and nitrifier community composition as a result of land use and soil type interactions.

Characterisation of land types and agro-ecological conditions for production of Jatropha as a feedstock for biofuels in Zimbabwe

There is increasing interest in Zimbabwe in developing a biofuels industry based on the production of biodiesel using Jatropha as the main feedstock. This has led to the introduction of Jatropha as a commercial energy crop in the country. There are plans to grow 1220 km(2) of Jatropha which will supply about 365,000 t of seed. This will provide about 110 dam(3) of biodiesel required to achieve a blending level of 10% with petro-diesel. The availability and suitability of land for the production of Jatropha cannot be taken for granted, particularly given the fact that the concept and practice of production of feed-stocks for biofuels remain contested on the threat they pose to food security. Determining the land that is potentially available for biofuels is a non-trivial task. A multiplicity of factors needs to be considered. It is important to determine the spatial extent of areas with suitable growth conditions for Jatropha. The interaction of soil type and land use is an important interface in agriculture. Added to this is the need to balance food, fodder and fuel supply in land use planning. This paper attempts to assess the availability and suitability of various land types as well as agro-ecological conditions for the production of Jatropha in Zimbabwe. (C) 2011 Elsevier Ltd. All rights reserved.

Effect of Soil Type and Moisture Availability on the Foraging Behavior of the Formosan Subterranean Termite (Isoptera: Rhinotermitidae)

This study examined the influence of soil type and moisture availability on termite foraging behavior. Physical properties of the soil affected both tunneling behavior and shelter tube construction. Termites tunneled through sand faster than top soil and clay. In containers with top soil and clay, termites built shelter tubes on the sides of the containers. In containers with sand, termites built shelter tubes directly into the air and covered the sides of the container with a layer of sand. The interaction of soil type and moisture availability affected termite movement, feeding, and survival. In assays with moist soils, termites were more likely to aggregate in top soil over potting soil and peat moss. However, termites were more likely to move into containers with dry peat moss and potting soil than containers with dry sand and clay. Termites were also significantly more likely to move into containers with dry potting soil than dry top soil. In the assay with dry soils, termite mortality was high even though termites were able to travel freely between moist sand and dry soil, possibly due to desiccation caused by contact with dry soil. Evaporation from potting soil and peat moss resulted in significant mortality, whereas termites were able to retain enough moisture in top soil, sand, and clay to survive for 25 d. The interaction of soil type and moisture availability influences the distribution of foraging termites in microhabitats.

Quantification of 3-D soil macropore networks in different soil types and land uses using computed tomography

Summary The importance of soil macropores as preferential pathways for water, air, and chemical movement in different soils has long been recognized. However, quantification of complex macropore structures and their relationships to soil types and land uses remains elusive. The objectives of this study were to (1) quantify 3-D macropore networks in intact soil columns using an improved approach and (2) investigate the effects of soil type and land use on soil macropore characteristics. Two soils with contrasting textures and structures (Hagerstown silt loam and Morrison sand) from two land uses (row crop and pasture) were investigated. Intact soil columns, 102 mm in diameter and about 350 mm in length, were taken for each soil type-land use combination. The soil columns were scanned using X-ray computed tomography at a voxel resolution of 0.234 mm × 0.234 mm × 2.000 mm. After reconstruction, characteristics of macropore networks were quantified, including continuous macroporosity change along depth, macropore size distribution, network density, surface area, length density, length distribution, mean hydraulic radius, tortuosity, inclination (angle), and connectivity (path number and node density). The approach we developed provided an improved quantification of complex 3-D macropore networks. The analysis of variance indicated that soil type, land use, and their interaction significantly influenced macroporosity, network density, surface area, length density, node density, and mean angle. The interaction of soil type and land use also influenced mean tortuosity and hydraulic radius. Within the same soil type, the soils under pasture land use had greater macroporosity, length density, and node density than that under row crop, especially in the subsoil. This was due to greater organic matter content and more biota activities in the pasture. Within the same land use, the Morrison sand displayed lower overall macroporosity than the Hagerstown silt loam because of weaker structure and higher amount of rock fragments in the Morrison soil and thus less suited for biota activities. The results from this study provide improved quantitative evaluation of a suite of soil macropore features that have significant implications for non-equilibrium flow prediction and chemical transport modeling in field soils.

Allelopathic, Autotoxic, and Hormetic Effects of Postharvest Sugarcane Residue

With green sugarcane (interspecific hybrids of Saccharum spp.) harvesting, 6 to 24 Mg ha−1 of postharvest residue is deposited on the field surface covering the sugarcane stubble that must reemerge for several ratoon crops. The objectives of this research were to: (i) determine if postharvest residue possesses allelopathic, autotoxic, and hormetic properties; (ii) determine the interaction of soil type with possible autotoxic effects; and (iii) identify a reliable indicator species. Extract concentrations consisted of 0, 0.1, 10, 25, and 100% of the original solution of a 1:28 tissue to water extract. The higher concentrations of residue extracts exhibited autotoxicity by delaying early leaf development. The lower extract concentration of 10% increased sugarcane bud germination by 45% compared with the control, indicating hormetic effects. Allelopathic activity on tall morninglory (Ipomoea hederacea Jacq.) was more pronounced on a light soil; germination and radical length were reduced by all concentrations by an average of 42% and 8 mm, respectively, compared with the control. Seedling dry weights were reduced by an average of 10 mg by the 10, 25, and 100% extract concentrations relative to the control. On the heavy soil, only the 100% concentration reduced radical length and weight by 5 mm and 4 mg, respectively, relative to the control. Extract effects on oat (Avena nuda L.), rye (Secale cereale L.), and tomato (Lycopersicon esculentum Mill.) showed poor correlation with effects on sugarcane. Chemical analysis by gas chromatography/mass spectrotometry indicated the extract contained benzoic acid. Further studies are needed to establish the impact of benzoic acid in natural settings.

SPATIAL CLUSTERS OF SUBSURFACE DRAINAGE WATER NO3-N LEACHING LOSSES

Grouping of nitrate-nitrogen (NO 3 -N) leaching losses from agricultural fields into spatial clusters can help determine the cause/effect relationships for their occurrence. This study was designed to investigate the spatial relationships of low, medium, and high NO 3 -N leaching losses clusters with soil and landscape attributes using cluster and discriminant analysis and the map overlay capability of a geographical information system (GIS). Field measured data of a six-year (1993 through 1998) study on NO 3 -N leaching losses from 36 experimental fields at the Iowa State University's northeastern research center near Nashua, Iowa, were normalized on an annual basis to compare over the years. The cluster analysis resulted in the formation of three clusters based on the satisfactory evaluation criteria of pseudo-F statistic, cubic clustering criterion, and R 2 values. The discriminant analysis, carried out on the basis of clusters, identified elevation and subsurface drainage as the factors that contributed significantly (p < 0.01) in discriminating among these clusters. The verification of discriminant functions developed on these factors predicted the cluster membership for all the groups with an overall accuracy of 86 percent. The map overlay analyses of GIS showed that spatial occurrence of the clusters transporting high NO 3 -N leaching losses was affected by the interaction of soil type and elevation levels.