Non-cultivated Soils Research Articles

Effects of Soil Physical Structure on Solute Transport in a Weathered Tropical Soil

AbstractEffects of soil structure on solute transport were studied in a clayey, well‐aggregated Oxic Dystropept under grass and secondary forest at La Selva, Costa Rica. Both fine pores (<0.1 µm) and coarse pores (>30 µm) are abundant, as indicated by a water content of 0.37 m3 m−3 at −1500 kPa matric potential, the shape of the moisture release curve, and an initial infiltration rate (at field capacity) averaging 3900 mm hr−1. Field application of Rhodamine B dye without ponding (simulating heavy rainfall) showed preferential flow along decayed‐root channels, animal burrows, cracks, and other macropores. Dye application to intact cores under conditions of ponded steady‐state flow gave a good correlation between flow rate and total stained area (p <0.01 under forest; p < 0.05 under grass). Solute (CaCl2) breakthrough occurred very rapidly, often after < 0.1 pore volumes had percolated; however, relative concentration of the effluent did not exceed 0.95 even after five pore volumes had percolated. These results indicate that most water flows between aggregates or through macropores (as preferential or channelized flow), even when the fine pores are not fully saturated, and in effect bypasses the fine pore space. When solution inflow was interrupted after ∼1.8 pore volumes, then resumed after 10 min pause, relative concentration of the effluent dropped by 10 to 40%, then rose again. This indicates that solute diffused slowly into the aggregates. Taken together the results suggest that this soil strongly resists leaching. Preferential water flow may serve to prevent nutrient loss from the matrix of all highly aggregated soils and of all noncultivated soils in which animal activity and turnover of woody roots create abundant macropores.

Rhizobium inoculation of Calopogonium caeruleum

The shade-tolerant cover legume Calopogonium caeruleum is promiscuous in its nodulating habits. In sand culture, symbiotic effectiveness of the strains tested was variable; 6 strains of rhizobia markedly improved shoot yields and 20 increased shoot N content. In pot experiments using cultivated and non-cultivated soils, inoculation gave no significant increase in shoot yields. When grown under rubber in plantation conditions at four localities, shoot dry matter yields, N content and nodulation also were not different from uninoculated plants when sampled for up to 2 yr after planting. This occurred despite the low numbers (< 10 g −1 soil) of native rhizobia at some sites and an appreciable establishment (> 70% recovery in nodules) by the inoculant strains.

Occurrence, distribution and seasonal periodicity of some aquatic fungi of Sat-Tal (Nainital), India

The occurrence of 23 species of aquatic fungi belonging to Blastocladiales, Saprolegniales, Lagenidiales and Peronosporales in three lakes and their surrounding cultivated and non-cultivated soils of Sat-Tal area have been studied. The species were found to be different in their habitat and temperature range.

THE OCCURRENCE OF BLUE-GREEN ALGAE IN SILT LOAMS OF WHITMAN COUNTY, WASHINGTON

The occurrence of blue-green algae in cultivated and noncultivated soils in Whitman County, Washington, was studied over a 12-month period. Nostoc and Anabaena were found in the soils, Nostoc being ubiquitous. Microbial enumeration was by the most-probable-number method. Moisture and temperature were recorded on each sampling date, while climatic and agronomic events were noted and chemical properties estimated for four soil series. The infrequent occurrence and low densities of blue-green algae in the soils make improbable any assumption that nitrogen input by blue-green algae is significant in this region. Rapid loss of surface soil moisture, seasonal climatic fluctuations, slightly acid soils, and agricultural practices were probably the major reasons why greater numbers and diversity of blue-green algae were not observed on cultivated soils, while uncultivated soils supported more kinds and numbers.

LES EFFETS DE LA MISE EN CULTURE ET DE LA PRAIRIE PROLONGEE SUR LE CARBONE, L'AZOTE ET LA STRUCTURE DE QUELQUES SOLS DU QUEBEC

The effects of cultivation (cultivated vs. non-cultivated soils) and the age of cultivated meadows (from 5 to 25 yr) on the evolution of carbon, nitrogen and soil structure were studied on some Quebec soils. The soil series used were Beaurivage, Charlevoix, Greensboro and Kamouraska which are important agricultural soils for Eastern Quebec. The air- and water-stability of soil aggregates were used to characterize the soil structure. As a result of cultivation, the Kamouraska soil lost 33% of the carbon and 8% of the nitrogen originally present in the virgin soil, while the decrease in the water-stable aggregates was 84%. Charlevoix and Greensboro soils showed losses varying from 30 to 35% for carbon and from 21 to 31% for nitrogen while the water-stable aggregates decreased by 50%. Under continuous meadow for 25 yr, the Kamouraska soil showed an increase of up to 36% for carbon and 64% for nitrogen whereas the Beaurivage soil did not show much variation. Such a cultural practice improved the soil structure mainly in the Kamouraska soil, as a result of the increase not only in carbon content but likely in the root biomass with time.

Pyrimidine Decomposition in Cultivated and Non-cultivated Soils

Oxidation of cytosine and uracil was studied and the number of bacteria capable of utilizing these substrates as a single source of electrons and nitrogen was estimated. Four cultivated and two virgin soils were compared. The Warburg technique was used for measurement of oxygen consumption and the decrease of substrate concentration was determined by chromatography and spectrophotometry. Both substrates were oxidized to a greater extent in the cultivated soils. A correlation was found between the oxidation of substrates and the number of specific bacteria. Added substrates could not be detected in these soils after one mole of oxygen had been used per mole of substrate. Wir studierten die Cytosin- und Uraziloxydation und die zahlenmäßigen Veränderungen der Bakterien, die diese Substrate als alleinige Elektronenquelle auszunutzen fähig sind. Wir haben vier bearbeitete und zwei jungfräuliche Böden verglichen. Für die Messung des Sauerstoffverbrauches haben wir die Warburg-Technik angewandt. Der Substratschwund wurde mit Hilfe von Chromatographie und Spektrophotometrie ermittelt. Beide Substrate wurden stärker in den Kulturböden als in den jungfräulichen oxydiert. Zwischen Substratoxydation und Zahl der spezifischen Bakterien ergab sich eine Korrelation. Nach einem Verbrauch von 1 Mol Sauerstoff pro 1 Mol Substrat konnte dieses nicht mehr im Boden nachgewiesen werden.

QUANTITATIVE AND QUALITATIVE COMPARISONS OF FUSARIUM POPULATIONS IN CULTIVATED FIELDS AND NONCULTIVATED PARENT SOILS

In soils of the Salinas watershed Fusarium solani and Fusarium tricinctum were found only in the cultivated soils. Propagules of Fusarium oxysporum were numerous and varied in the cultivated fields but were relatively scarce and existed essentially as a single clone in the noncultivated soils. In the Castroville watershed both F. solani and F. oxysporum were recovered from noncultivated soils fairly frequently.The 'Gibbosum' cultivar of Fusarhim roseum, the most frequently isolated fusarium from field soils, was less common in the noncultivated soils.Other fusaria, such as Fusarium episphaeria and some cultivars of F. roseum, were about as numerous in the noncultivated as in the cultivated soils. The cultivation of these soils markedly affected the makeup of the fusarium populations in them.