Extended Dry Periods Research Articles

SOIL GENESIS AND MORPHOLOGY OF A MONTANE MEADOW IN THE NORTHERN SIERRA NEVADA RANGE

Given the importance of riparian areas in the western United States, knowledge about the spatial distribution, properties, and genesis of these soils is surprisingly limited. In conjunction with an interdisciplinary study of the impacts of grazing on soils and vegetation, we characterized three pedons along a hydrologic gradient on a montane meadow of the northern Sierra Nevada range. Radiocarbon dating of charcoal indicates that meadow pedogenesis began approximately 3600 years B.P., after a catastrophic valley erosional event. Since that time, nearly 1 meter of soil has accumulated over a basal glaciolacustrine unit. Critical factors and processes influencing soil genesis and morphology include: seasonal variation in soil redox status, frigid soil temperatures, additions of volcanic tephra, wildfires, and polygenesis related to Holocene climatic, hydrologic, and vegetation changes. Argillans are present on ped faces of certain soil horizons, which suggests extended dry periods at which time clay pervection occurred. Clay mineralogy is disjunct; surface horizons are dominated by kaolinite and underlying horizons by smectite. The high clay content of such youthful soils suggests rapid primary mineral weathering. Charcoal-containing strata attest to frequent wildfires during the Holocene epoch. The spatial complexity of soil patterns and their properties infers that these riparian areas are dynamic, and their character may have been shaped by previous climatic patterns.

SOIL GENESIS AND MORPHOLOGY OF A MONTANE MEADOW IN THE NORTHERN SIERRA NEVADA RANGE

Given the importance of riparian areas in the western United States, knowledge about the spatial distribution, properties, and genesis of these soils is surprisingly limited. In conjunction with an interdisciplinary study of the impacts of grazing on soils and vegetation, we characterized three pedons along a hydrologic gradient on a montane meadow of the northern Sierra Nevada range. Radiocarbon dating of charcoal indicates that meadow pedogenesis began approximately 3600 years B.P., after a catastrophic valley erosional event. Since that time, nearly 1 meter of soil has accumulated over a basal glaciolacustrine unit. Critical factors and processes influencing soil genesis and morphology include: seasonal variation in soil redox status, frigid soil temperatures, additions of volcanic tephra, wildfires, and polygenesis related to Holocene climatic, hydrologic, and vegetation changes. Argillans are present on ped faces of certain soil horizons, which suggests extended dry periods at which time clay pervection occurred. Clay mineralogy is disjunct; surface horizons are dominated by kaolinite and underlying horizons by smectite. The high clay content of such youthful soils suggests rapid primary mineral weathering. Charcoal-containing strata attest to frequent wildfires during the Holocene epoch. The spatial complexity of soil patterns and their properties infers that these riparian areas are dynamic, and their character may have been shaped by previous climatic patterns.

Moisture Sensor‐Controlled Irrigation for Maintaining Bermudagrass Turf1

AbstractThe feasibility of tensiometer soil moisture sensing devices for scheduling bermudagrass (Cynodon dactylon× C. transvaalensis) turf irrigation and their impact on N fertilization practices under sub‐tropical conditions was assessed. Irrigation water savings of 42 to 95% were obtained in sensor controlled plots over conventionally irrigated plots. The greatest benefit of the sensor system was achieved during periods of frequent but unpredictable rainfall by eliminating unnecessary irrigations. Application of a wetting agent was necessary during extended dry periods to prevent localized dry spots when irrigation was limited by the sensor system to an as needed basis. Reduced irrigation by the sensor system resulted in better turf appearance and equal effectiveness of water‐soluble and slow‐release N sources.

Developing a potato irrigation scheduling program—the Maine situation

The future of irrigation in Maine appears to be still in question. Maine farmers will probably continue to face extended periods of dry conditions yearly. One such period has already been experienced in Maine during the 1983 growing season, as only 0.88 of an inch of rainfall was received in June. During such extended dry periods, the number of inquiries concerning irrigation increases. Once adequate rainfall is received, however, such inquiries stop. Yet each year, it is learned that an additional irrigation system or two is installed in Aroostook County.

Basidiocarp development in Gloeophyllum (Lenzites) saepiarium in the natural environment

Basidiocarp development in Gloeophyllum saepiarium begins with the emergence of vegetative hyphae from the wood, their exposure to the relatively severe, fluctuating conditions of light and moisture, and their loss of direct contact with the substratum. In response to these changes the hyphae become organized into hyphal strands composed of generative hyphae and skeletal hyphae. Hyphal strands direct the growth of the advancing margin and are involved in the development of tomentum, context, and hymenophore. Their marked sensitivity to light and humidity accounts for the presence of growth zones in the basidiocarp. Atmospheric humidity is considered to be the factor of primary importance in influencing the growth, differentiation, and orientation of the hyphae in the perennial basidiocarp during the growing season. The close association of skeletal and generative hyphae allows the fruit body to withstand the extended dry periods characteristic of its xeric habitat, and to develop over a long period of time.

Soil Profile Gravel Layers: I. Effect on Water Storage, Distribution, and Evaporation

AbstractSoil water distribution and evaporation following water application were affected by a gravel layer placed on or 5, 15, or 25 cm below the soil surface. Soil above gravel retained more water than soil at similar depths in uniform columns. Evaporation from soil with gravel on the surface or at 5 cm was slower than from the check, while evaporation from soil with gravel at 15 or 25 cm generally was more rapid than from the check.The water content of soil near the surface of field plots was markedly influenced by rainfall or duration of rain‐free periods. For the entire soil mass sampled, gravel on or at 5 cm below the surface increased the water content of plots as compared with both the check plots and treatments with gravel at 15 or 25 cm during periods of relatively frequent precipitation (spring and early summer). All treatments, however, permitted considerable water losses during extended dry periods (late summer, fall, and winter).

Yield comparisons of thirty-eight introductions of Glycine javanica in swards in three environments

Thirty-eight introductions of Glycine javanica were established in swards with an associate grass at Lawes and Kumbia in south-eastern Queensland and at 'Lansdown' near Woodstock in northern Queensland. The introductions showed highly significant differences in annual yield and total yield of dry matter. At Lawes there were also significant differences in ease and vigour of establishment, in nitrogen content, and in seasonal yield distribution. Late maturing introductions grew better late in the season when early and mid-season maturity types were either flowering or had flowered. At 'Lansdown' all the introductions tolerated a dry season of 27 weeks in 1965, but failed to survive a dry season of 36 weeks in 1966. At Lawes, the most promising introductions in terms of high yield and strong stolon development in each maturity type were, Tinaroo (late), C.P.I. 26433 (mid-season), Cooper (early), and C.P.I. 27835 (early). At 'Lansdown' C.P.I. 25423 (early) and C.P.I. 25918 (very early) appeared most tolerant of extended dry periods. At Lawes, swards of Cooper (C.P.I. 25702) and green panic grass (Panicum maximum var trichoglume) yielded 7,000 to 8,000 lb of dry matter an acre with a legume content of 50 to 56 per cent in their third, fourth, and fifth seasons. In these swards the dry matter production and legume content showed no signs of declining after the third season.