Uppermost Soil Layer (uppermost + soil_layer)

Distribution by Scientific Domains

Selected Abstracts

Biological soil properties in a long-term tillage trial in Germany

Sebastian Ulrich
Abstract After 37 years of different soil-tillage treatments in a long-term field experiment in Germany, a number of biological soil characteristics was measured. The field trial comprised six major treatments with different implements and various depths. In this paper, results from a comparison of long-term use of a plow (to 25,cm depth), a chisel plow (to 15,cm depth), and no-tillage are presented. The biological soil characteristics measured include the soil-organic-carbon (SOC) content, microbial biomass, enzyme activities, and the abundance and biomass of earthworms. Long-term use of a chisel plow and no-tillage increased the organic-C content in the uppermost soil layer (0,10,cm) compared with the plow treatment. The microbial biomass and the enzyme activities arginine-ammonification, ,-glucosidase, and catalase decreased with depth in all treatments. Arginine-ammonification and catalase were higher in the plow treatment in soil layers 10 to 30,cm. Additionally, the chisel plow caused an increase in number and biomass of earthworms compared to both other tillage treatments. Differences in earthworm numbers and biomass between plowing and no-tillage were not statistically significant. [source]

Effects of decreasing soil water content on seminal lateral roots of young maize plants


Abstract Soil micropores that contain water at or below field capacity cannot be invaded by seminal or first-order lateral roots of maize plants because their root diameters are larger than 10 ,m. Hence, at soil-water levels below field capacity plant roots must establish a new pore system by displacement of soil particles in order to access soil water. We investigated how decreasing soil water content (SWC) influences growth and morphology of the root system of young maize plants. Plants were grown in rhizotrons 40,cm wide, 50,cm high, and approximately 0.7,cm thick. Five SWC treatments were established by addition of increasing amounts of water to soil and thorough mixing before filling the rhizotrons. No water was added to treatments 1,4 throughout the experiment. Treatment 5 was watered frequently throughout the experiment to serve as a control. Seminal-root length and SWC in soil layers 0,10, 10,20, 20,30, 30,40, and 40,50,cm were measured at intervals of 2,3 d on scanner images by image analysis. At 15 d after planting, for treatments 1,4 shoot dry weight and total root length were directly related to the amount of water added to the soil, and for treatments 4 and 5, total root length and shoot dry weights were similar. Length of seminal roots visible at the transparent surface of the rhizotron for all treatments was highest in the uppermost soil layer and decreased with distance from the soil surface. For all layers, seminal-root elongation rate was at maximum above a SWC of 0.17,cm3,cm,3, corresponding to a matric potential of ,30 kPa. With decreasing SWC, elongation rate decreased, and 20% of maximum seminal root elongation rate was observed below SWC of 0.05,cm3,cm,3. After destructive harvest for treatment 1,4, number of (root-) tips per unit length of seminal root was found uninfluenced over the range of initial SWC from 0.10 to 0.26,cm3,cm,3. However, initial SWC close to the permanent wilting point strongly increased number of tips. Average root length of first-order lateral (FOL) roots increased as initial SWC increased, and the highest length was found for the frequently watered treatment 5. The results of the study suggest that the ability to produce new FOL roots across a wide range of SWC may give maize an adaptive advantage, because FOL root growth can rapidly adapt to changing soil moisture conditions. [source]

Effects of soil bulk density on seminal and lateral roots of young maize plants (Zea mays L.)

Rolf O. Kuchenbuch
Abstract It is well established that increasing soil bulk density (SBD) above some threshold value reduces plant root growth and thus may reduce water and nutrient acquisition. However, formation and elongation of maize seminal roots and first order lateral (FOL) roots in various soil layers under the influence of SBD has not been documented. Two studies were conducted on a loamy sand soil at SBD ranging from 1.25 g,cm,3 to 1.66 g,cm,3. Rhizotrons with a soil layer 7 mm thick were used and pre-germinated plants were grown for 15 days. Over the range of SBD tested, the shoot growth was not influenced whereas total root length was reduced by 30,% with increasing SBD. Absolute growth rate of seminal roots was highest in the top soil layer and decreased with increasing distance from the surface. Increasing SBD amplified this effect by 20,% and 50,% for the top soil layer and lower soil layers, respectively. At the end of the experiment, total seminal roots attributed to approximately 15,% of the total plant root length. Increasing SBD reduced seminal root growth in the lowest soil layer only, whereas FOL root length decreased with SBD in all but the uppermost soil layer. For FOL, there was a positive interaction of SBD with distance from the soil surface. Both, increasing SBD and soil depth reduced root length by a reduction of number of FOL roots formed while the length of individual FOL roots was not influenced. Hence, increasing SBD may reduce spatial access to nutrients and water by (i) reducing seminal root development in deeper soil layers, aggravated by (ii) the reduction of the number of FOL roots that originate from these seminal roots. Einfluss der Bodendichte auf Seminal- und Lateralwurzeln von jungen Maispflanzen (Zea mays L.) Es ist bekannt, dass zunehmende Bodendichte (SBD) oberhalb eines Grenzwertes das Wurzelwachstum von Pflanzen und die Wasser- und Nährstoffaufnahme reduziert. Bildung und Wachstum der Seminal- und der Lateralwurzeln erster Ordnung (FOL) von Mais in Bodenschichten verschiedenen Abstands von der Bodenoberfläche unter dem Einfluss verschiedener Bodendichten wurde bisher nicht beschrieben. Zwei unabhängige Versuche wurden mit einem lehmigen Sandboden durchgeführt. Vorgekeimte Maiskörner wurden in Rhizotrone mit einer etwa 7,mm dicken Bodenschicht eingesetzt, die Bodendichten lagen im Mittel der Rhizotrone zwischen 1,25 g,cm,3 und 1,66 g,cm,3. Die Versuchsdauer betrug 15 Tage. Über den Bereich der geprüften SBD wurde das Sprosswachstum nicht beeinflusst, während die Gesamtwurzellänge mit zunehmender SBD um bis zu 30,% abnahm. Die absolute Wachstumsrate der Seminalwurzeln war in der obersten Bodenschicht am höchsten und nahm mit zunehmendem Abstand von der Bodenoberfläche ab. Seminalwurzeln trugen zu ca. 15,% zur Gesamtwurzellänge bei. Zunehmende SBD reduzierte das Wachstum der Seminalwurzeln nur in der untersten Bodenschicht. Demgegenüber wurden die Längen der FOL in allen außer der obersten Schicht bei zunehmender SBD verringert. Bei den FOL wurde eine positive Interaktion zwischen SBD und Abstand von der Bodenoberfläche festgestellt. Sowohl zunehmende SBD als auch zunehmende Tiefe reduzierte die Wurzellänge durch eine Verringerung der Anzahl an FOL, während deren Länge nicht beeinflusst wurde. Folglich kann zunehmende SBD die räumliche Zugänglichkeit zu Wasser und Nährstoffen für die Pflanzen dadurch beeinflussen, dass (i) die Entwicklung von Seminalwurzeln in tieferen Bodenschichten reduziert wird und dass dieser Effekt verstärkt wird durch (ii) die verringerte Bildung von FOL an Seminalwurzeln. [source]

The fate of seeds in Mediterranean soil seed banks in relation to their traits

Juan Traba
Abstract Question: Is there any change in seed density and species richness in Mediterranean surface soil banks during summer? Are there any relationships between these summer variations and seed traits (weight, length and shape), without and with controlling the phylogenetic effect? Location: Central Spain. Methods: Samples of the surface soil seed bank were collected in two Mediterranean systems, grassland and scrubland, at two points in the year: immediately after the summer production peak and immediately prior to the autumn germination peak. We used Canonical Correspondence Analysis ordination to check for changes in floristic composition and ANOVAs to check for changes in seed density and species richness between summer and autumn samples. We used multiple regression analysis to analyse the relationship between summer variations in soil seed density and form traits, with and without controlling phylogenetic relations. Results: Soil seed density dropped significantly during the summer in the two systems (28% in grasslands, repeated measures ANOVA test; F = 58.19, P < 0.01; 72% in scrublands, repeated measures ANOVA test; F = 75.67, P < 0.001). Species richness, however, only dropped significantly in the scrubland (32%; repeated measures ANOVA test; F = 9.17, P < 0.05). Variation in the floristic composition of the shallow banks was only significant in the scrubland. Changes in shallow bank density were related significantly to seed morphology features, with greater drops in species with heavier seeds in grasslands and species with longer seeds in scrubland. Conclusions: Our results show a substantial loss of seeds in the uppermost soil layer during the summer period between the point of peak production and the autumn germination peak. This drop was clearer in the scrubland than in the grassland. Longer and/or heavier seeds underwent the greatest declines in density at the end of summer, indicating a more intense effect of post-dispersal predation on large-seeded species. [source]