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Jeb S. Fields, William C. Fonteno, Brian E. Jackson, Joshua L. Heitman, and James S. Owen Jr.

Pine tree substrates (PTSs) may provide growers with sustainable substrate component options. Improved processing of PTS components has provided new materials with little scientific evaluation or understanding of their hydrophysical behavior and properties. Moisture retention characteristics were developed for two PTSs and four traditional greenhouse components: sphagnum peat, coconut coir, perlite, pine bark, shredded-pine-wood (SPW), and pine-wood-chips (PWC). Mixtures of peat containing 10%, 20%, 30%, 40%, and 50% of perlite, SPW, or PWC were also characterized. Hydrophysical properties were measured, allowing for comparison of the PTS components to the more traditional substrate components (peat, coir, perlite, and pine bark). The SPW was constructed to retain water similarly to peat and pine bark, whereas the PWC was made to increase drainage like perlite. Shredded pine wood had higher total porosity and more easily available water than did PWC components. Total porosities of SPW and PWC were similar to pine bark and coir; air space and drainage were higher than peat and coir because of the lower percentage of fine particles in the PTS components. The two PTS components had a greater influence on water drainage and retention dynamics than did perlite when amended with peat as an aggregate. Water release patterns of SPW or PWC components at low tensions were lower than peat and greater than pine bark; drainage was similar to perlite at higher tensions. Equilibrium capacity variable models predicted similar physical properties (and trends) across multiple container sizes for peat mixes amended with perlite, SPW, or PWC. The impact of PWC on drainage and aeration was similar to perlite in all containers, but these effects were greater in smaller containers.

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Ian Merwin and Warren C. Stiles

Eight vegetation management systems (VMS) were evaluated over four years in a newly planted apple site. VMS treatments included pre- and post-emergence herbicide strips, a close-mowed sodgrass, a growth-suppressed (maleic-hydrazide) sodgrass, a crownvetch “living mulch,” clean cultivation, and straw mulch. Soil moisture supply was highest under the straw mulch and lowest under crownvetch, and varied inversely with groundcover biomass. Leaf N was deficient in tress in both sodgrass VMS, and increased by the lequme “living mulch” only after four years. Leaf Cu was lowest, and appeared to limit tree growth in VMS with prolonged soil moisture deficits. No significant differences were observed in leaf transpiration over a broad range (10 to 700 kPa) of soil matric tension. Cumulative trunk crosssectional area was greatest in straw-mulched trees and least in sodgrass and crownvetch VMS. The optimal soil matric tension for nutrient uptake and tree growth appeared to be 175 to 200 kPa in this orchard. Increasing the width of glyphosate herbicide strips from 1.5 to 2.5 m in tree rows did not improve tree growth, nutritional status or fruit yield.

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T.K. Hartz

Drip-irrigation scheduling techniques for fresh-market tomato (Lycopersicon esculentum Mill.) production were compared in three growing seasons (1989-91). Three regimes were evaluated: EPK [reference evapotranspiration (ETo, corrected Penman) × programmed crop coefficients], ECC (ET0 × a crop coefficient based on estimated percent canopy coverage), and SMD (irrigation at 20% available soil moisture depletion). EPK coefficients ranged from 0.2 (crop establishment) to 1.1 (full canopy development). Percent canopy coverage was estimated from average canopy width ÷ row width. Irrigation in the SMD treatment was initiated at -24 kPa soil matric tension, with recharge limited to 80% of daily ET0. The EPK and ECC regimes gave similar fresh fruit yields and size distributions in all years. With the EPK scheduling technique, there was no difference in crop response between daily irrigation and irrigation three times per week. In all seasons, ECC scheduling resulted in less total water applied than EPK scheduling and averaged 76% of seasonal ET0 vs. 86% for EPK. Irrigating at 20% SMD required an average of only 64% of seasonal ET0; marketable yield was equal to the other scheduling techniques in 1989 and 1991, but showed a modest yield reduction in 1990. Using an SMD regime to schedule early season irrigation and an ECC system to guide application from mid-season to harvest may be the most appropriate approach for maximizing water-use efficiency and crop productivity.

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S.M. Scheiber and Richard C. Beeson, Jr

lowest within the control treatment (data not shown). Varying effects on yield have been reported in response to deficit irrigations. Smajstrla and Locascio (1996) found tomato ( Solanum lycopersicum ) yield declined as soil matric tension increased