Abstracts

Burton, A.J., Pregitzer, K.S., et al. 1998, 'Drought Reduces Root Respiration in Sugar Maple Forests', Ecological Applications, vol. 8, no. 3, pp. 771-778.

Soil moisture deficits can reduce root respiration, but the effects have yet to be quantified at the stand level or included in models of forest carbon budgets. We studied fine-root (≤1.0 mm diameter) respiration in four sugar maple forests for three growing seasons in order to assess the combined effects of temperature, N concentration, and soil moisture on respiration rates. Fine-root respiration at the four sites was exponentially related to soil temperature and linearly related to root N concentration and soil moisture availability. Most of the variability in respiration rates was explained by temperature. Differences in soil moisture availability explained temporal variation within sites in respiration rate at a given temperature, whereas differences among sites in respiration rates resulted from site-specific differences in fine-root N concentration. Periodic moisture deficits during 1995 and 1996 were sufficient to cause declines of up to 17% in total growing-season root respiration at affected sites. Estimated reductions in respiration of up to 0.8 Mg C/ha during dry years were equivalent to a significant portion of annual aboveground woody biomass C increment, arguing for the inclusion of soil moisture availability as a predictor of root respiration when modeling C allocation in forest ecosystems.

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Hubbert, K.R., L., B.J., et al. 2001, 'Roles of Weathered Bedrock and Soil in Seasonal Water Relations of Pinus Jeffreyi and Arctostaphylos patula', Canadian Journal of Forest Research, vol. 31, pp. 1947-1957.

In the southern Sierra Nevada, California, relatively thin soils overlie granitic bedrock that is weathered to depths of several metres. The weathered granitic bedrock is porous and has a plant-available water capacity of 0.124 m³ m^-3, compared with 0.196 m³ m^-3 for the overlying soil. Roots confined within the bedrock joint fractures access this rock-held water, especially during late summer when overlying soils are dry. We sought to determine seasonal soil and bedrock water changes in a Jeffrey pine (Pinus jeffreyi Grev & Balf.) plantation and to examine concurrent effects on the water relations of Jeffrey pine and greenleaf manzanita (Arctostaphykis patula Greene). In 1996, plant-available water in the 75 cm thick soil was depleted by late June, with soil water potential (ψsoil) was still > -2.2 MPa. Thus, the bedrock, not the soil, supplied water to plants for the remainder of the dry season. Higher values of, and smaller fluctuations in, seasonal predawn pressure potential (ψpredawn) for Jeffrey pine indicated that it is deeply rooted, whereas active roots of greenleaf mananita were interpreted to be mostly within the upper 100 cm. The extra rooting volume supplied by weathered bedrock is especially important to pine relative to manzanita.

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Lof, M. 2000, 'Establishment and Growth in Seedlings of Fagus sylvatica and Quercus robur: Influence of Interference from Herbaceous Vegetation', Canadian Journal of Forest Research, vol. 30, no. 6, pp. 855-864.

The interference from natural vegetation on the establishement and growth in Fagus sylvatica L. and Quercus robur L. was studied on an open site starting from bare soil. Four treatments were applied: herbicide, herbicide plus fertilization, mowing, and untreated control. Seedlings of beech and oak were spring planted side-by-side in two subsequent years and monitored through the 1995, 1996 and 1997 growing seasons. Interference had a strong negative inglude on the seedling shoot dry mass, leaf area, relative diameter growth, leaf nitrogen concentration and leag water potential and conductance. Oak had a shorter period of transplanting shock, a higher relative growth rate during interference from vegetation, and deeper roots than beech, which intially may need more intense site preparation. Neither fertilization compared with vegetation control only, nor mowing compared with untreated control, influenced seedling growth. Low soil water potential had a strong influence on seedling growth, although the competing vegetation at the same time reduced light, soil temperature, and the soil nitrogen concentration.

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Stenitzer, E. and Gassner, L. 2005, 'Assessment of the effect of Groundwater Lowering on the Capillary Rise in a Sandy Soil', in Monitoring and Modelling the Properties of Soil as a Porous Medium, eds W.M. Skierucha and R.T. Walczak, Institute of Agrophysics PAS, Lublin, pp. 179-187

Importance of capillary conductivity in assessing the effect of lowering groundwater depth on the water supply of grassland by capillary rise is demonstrated applying the model SIMWASER using data on soil water regime and grass growth from field experiments in the Drau valley in Carinthia/Austria.

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Stenitzer, E. and Gassner, L. 2005, 'In Situ Estimation of Deep Percolation in a Dry Area by Concurrent Measurements of Soil Water Content and Soil Water Potential', in Monitoring and Modelling the Properties of Soil as a Porous Medium, eds W.M. Skierucha and R.T. Walczak, Institute of Agrophysics PAS, Lublin, pp. 188-195

For sustainable groundwater management, groundwater extraction must be kept below natural groundwater recharge. Quantification of natural groundwater recharge may be assessed either locally from groundwater fluctuations or for the whole catchment area by analysing low water discharge of its outlet. In many cases groundwater fluctuations may be influenced by massive but unknown water extraction and do not reflect natural conditions, and results of analysing low water discharge will not be representative to the area of interest within the whole catchment basin. Physically based simulation models could help to overcome such shortcomings, being able to predict unknown natural ground water recharge from well-known weather-, soil- and cropping- data. Such models have to be validated using measured deep percolation, either from lysimeters or from indirect flux measurements as described in this paper.

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Timlin, D.J., Pachepsky, Y., et al. 2001, 'Water Budget Approach to Quantify Corn Grain Yields Under Variable Rooting Depths', Soil Science Society of America Journal, vol. 65, pp. 1219-1226.

This study investigated the relationships between corn (Zea mays L.) grain yield and weather over a range of soil rooting depths with and without irrigation. The purpose was to test if variability of corn grain yield over a range of soil rooting depths could be reduced if water is supplied via irrigation. An additional goal was to test a simple water balance simulation model which calculates a seasonal moisture stress index based on relative evapotranspiration deficits. Such a water budget model could be used to estimate variations in corn grain yields as a function of spatial differences in soil depth and available water holding capacity in site specific agriculture. Corn grain yields were measured over a 3-yr period from 70 plots at the Cornell University Robert Musgrave Research Farm at Aurora, NY, USA. Soil depths ranged from 0.2 to 1 m. During one year of the study, paired irrigated and non irrigated plots were placed at locations that had varying soil rooting depths. Irrigation resulted in significant increases in grain yield with the greatest response occurring on the soils with less than 0.5 m of rooting depth. Yields under irrigation were similar at all soil depths suggesting that, as soil depth decreased on these soils, water was the major limiting factor. The water budget model gave satisfactory estimates of grain yields as a function of soil depth and available water capacity and appears to be a useful tool to estimate corn grain yield as a function of soil depth and available water. The estimated potential yields can be used as a guide for site specific soil management given variations in available water holding capacity that affect potential soil productivity.

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Ulery, A., Stewart, S., et al. 2000, 'Vacuum method for field installation of pipes and casings in sandy soils', Soil Science, vol. 165, no. 3, pp. 269-273.

Soil moisture-monitoring equipment is difficult to install in poorly consolidated sand or sediments using hand tools because the loose material tends to collapse. The technique described herein uses a 5.5-hp wet/dry vacuum cleaner, powered by a portable gasoline generator, to remove the soil while an operator pushes a conductor pipe or casing into the profile. After initiating the hole using a hand bucket auger, an open-ended metal pipe or polyvinyl chloride (PVC) casing is inserted vertically into the shallow hole. A smaller tube, or stinger, attached to a wet/dry vacuum is inserted into the pipe to extract loose material while downward pressure is applied on the pipe. Once the casing is installed, instrumentation such as lysimeters, gypsum blocks, or tensiometers can be placed at the desired depth and backfilled with native soil. The casing is then raised and the soil allowed to collapse around the equipment, or the pipe can be left in place for neutron probe access. Measurements of soil water content after an infiltration experiment demonstrated uniform downward movement with minimal preferential flow or soil disturbance as a result of the vacuum installation of gypsum blocks and a neutron access tube.

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