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Five Texas orchards were selected in Spring 1993 in commercial pecan counties for testing three types of soil aeration equipment. Mechanical aeration spikes were either 20 or 46 cm long, and a pneumatic spike was 20 cm long. The mechanical spikes are on a rolling cylinder that can be manufactured in sufficient lengths to fit the tree spacing in different orchards. The pneumatic probe is manually inserted into the soil so that a quick burst of 130-psi air can be delivered to effect soil profile fracturing. The fourth replicated treatment was an nontreated control. There were no differences in trunk diameter increases and yield in 1993 between May-applied replicated treatments. The May treatments and November measurements will continue for two more years to allow for differences in soil aeration to influence growth and yield. Shoot growth measurements will be taken in Spring 1995. Irrigation water has penetrated the soil under aerated trees more readily than in nonaerated controls.

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Abstract

Root regeneration from root cuttings of both difficult-to-transplant Pistacia chinensis and moderately easy-to-transplant Liquidambar styraciflua was studied in a sphagnum peat medium varying from 0-100% Ca saturation and from 0-50% air filled porosity. Maximum root regeneration of Pistacia root cuttings was obtained at 75% Ca saturation and 30% and 40% air filled porosity, whereas Liquidambar root cuttings regenerated roots best at 25% Ca saturation and at 20% to 40% air filled porosity. Indolebutyric acid applied to the root cuttings greatly increased root-regenerating potential of Pistacia root cuttings but did not affect the optimum Ca and aeration requirement(s). Similarly, indolebutyric acid treatment greatly promoted the root-regeneration potential of Liquidambar root cuttings. Satisfactory root-regenerating conditions of both Ca saturation and air filled porosity for Liquidambar root cuttings were a little broadened by indolebutyric acid (IBA) application.

Pistacia bare root seedlings also required high levels of Ca saturation and aeration for optimum root regeneration. Considerably greater numbers of roots were regenerated in peat having 75% Ca saturation and 20% air filled porosity than in peat having 0% Ca saturation and 5% air filled porosity. Root regeneration was not improved by increasing only the air filled porosity when Ca was low.

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The use of drip irrigation in orchards is increasing worldwide. Water shortage, prevention of ground water contamination, and improved production are the main reasons for this increase. The combination of partial wetting of the soil and control of the water penetration depth considerably increases the efficiency of irrigation. Recent technological improvements permit maintenance of a constant volume of irrigated soil in which gradients of soil water matric potentials and mineral concentrations exist from the irrigation point to the margins of the wetted zone. Because water and mineral uptake is a function of soil matric potential and mineral concentration, respectively, optimal uptake rates by certain portions of the root system always exist along these gradients for any given environmental conditions. Gradients of air concentration act similarly and permit maintenance of high water availability without any interference with root aeration. Due to the relative ability of the roots to exchange water, minerals, and, possibly, oxygen, the entire root system functions more efficiently compared to root systems under conventional irrigation methods. Physiological root restriction effects induce the formation of a large number of small roots with frequent branching. Consequently, the relative surface area for water and mineral absorption is increased several-fold, and the increased number of root tips that are known to be involved in production of hormones (such as gibberelins and cytokinins) is significant. Evidence for enhanced fruit bud formation under conditions of root restriction is presented here. Water treatment and filtration technology has improved, and clogging of surface or buried drip systems now can be minimized, which also increases the suitable range of water quality for use in drip systems.

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Soil physical amendment (soil mixing) is a widespread horticultural practice. Unfortunately, it is often done with little understanding of the principles involved or the physical effects produced. Three simple demonstrations are described which have proved helpful in explaining the physical effects of soil amendment in classroom and extension presentations. These exercises use simple volume measurements and require commonly available supplies including containers, a volume measure, a sieve, plastic sheets, and media components such as soil and sand. The differences between component and mixture water retention are used to demonstrate the effect of amendment on porosity, water retention, and aeration. Some sample results and discussion questions are included.

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In the Spring and Summer 1997, severe die back of `Pinot Gris' and `Chambourcin' grape (Vitis vinifera) vines was observed by aerial surveillance in a commercial vineyard adjacent to Lake Erie. Vines grown over the tile lines grew well during 1997-99 following the excessively wet year of 1996. This was not the case for vines that were located betweentile lines. It was postulated that by digging and refilling the trench to insert the tile that either soil compaction or soil pH had been altered and could be responsible for the vine performance. Measurements indicated that these factors were not altered enough to explain the growth differences between vines growing over tile lines and those vines growing between tile lines. It appears that soil oxygen was improved by tiling and likely made the difference in cane dieback during the excessively wet year of 1996. By 1999, vines over tile and between tile had similar yields, and the pattern was no longer visible from the air. This study showed that heavy clay soils with naturally poor internal drainage caused cane dieback and poor growth of vines, especially in very wet years. Thus, it appears prudent on soils of this type, tile drainage is beneficial and spacing of lateral tile lines needs to be closer than 40 ft (12 m) in plateau silt loam soils to adequately protect vines from wet years.

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controlled with fungicides unless the Fe deficiency is first corrected. The most common cause of Fe deficiency in palms is poor soil aeration, with related factors that reduce root surface area, or metabolic rate such as root rot diseases and deep planting

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, phytoavailability of specific nutrients such as Fe is often inadequate due to several factors. However, pedological and crop genetic factors are responsible for low Fe bioavailability resulting in crop Fe deficiency. Soil pH, nutrient interactions, soil aeration

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Soil compaction is considered to be a major factor in the loss of grass in established turf plantings. Associated with the onset of soil compaction is a decrease in soil aeration (1), a reduction in gaseous exchange, and reduced water infiltration rates (2, 6, 7). Attempts to increase turf vigor and putting green resiliency by applying higher rates of fertilizer and by increased irrigation have often accentuated long-standing problems of diseases, poor root development, and low water infiltration rates (3,7). Frequent but light irrigations may also contribute to a buildup of harmful salt concentrations in compacted soils (5, 8).

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Flooding damage causes millions of dollars in losses to horticultural crops every year. Plantings established on sites with poor drainage and/or an impervious soil layer may flood periodically after heavy rainfall or excessive irrigation. Planting sites with lowlying areas or where site preparation is inadequate for drainage of excess water add to the problem. Poor soil aeration associated with flooding may induce numerous soil and plant changes that adversely affect plant survival, growth, development, and yield. Organic and inorganic soil toxins may accumulate in flooded soils, adversely affecting plant metabolism and physiology.

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There has been recent speculation in trade journals that landscape fabrics, while doing a excellent job of weed control, may have a detrimental effect upon ornamental plant growth. A study is in progress to investigate the manner in which applied landscape fabric affects soil aeration, soil temperature, and water infiltration rate over a period of 18 months. The experimental design is a split-plot with main plots identified as composted or non-composted areas. Within each main plot, the design is a randomized complete block with four blocks and three treatments per block (control, organic mulch, landscape fabric + organic mulch). Each plot has been planted with herbaceous perennials so as to allow analysis of treatment effects upon plant growth. Re-dox potential is measured on a weekly and infiltration rate is measured on a biweekly basis. Soil temperature within plots is monitored on a continuous basis. Preliminary results suggest that landscape fabrics have a detrimental effect on soil aeration and that this likely has a adverse effect upon plant growth. An attempt will be made in this study to contrast any adverse effects of landscape fabric use with the obvious benefits offered by increased weed control.

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