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S.S. Snapp and C. Shennan

Roots respond first to edaphic stresses, yet little is known about root response to stress in mature, soil-grown plants. We investigated the effects of salinity and phytophthora root rot on root growth and senescence in tomato (Lycopersicon esculentum Mill.). Using minirhizotron- and rhizotron-based methodologies, we quantified intraspecific differences in root-system response to salinity and inoculation. Genotype susceptibility to salt-induced disease was related to root vulnerability to salt. `UC82B' was vulnerable to infection by Phytophthora parasitica when subjected to salt stress and produced thinner roots and ≈50% higher root-senescence rates compared to the phytophthora root rot-resistant `CX8303'. Root growth at the peripheral regions of the `CX8303' root system was inhibited by salinity, but otherwise root dynamics were not affected by salinity or inoculation. Overall, roots from the central root system and roots from the periphery responded differently to salt stress. Monitoring the diameters of new initiated roots indicated the vulnerability of a stressed root system to disease and early senescence.

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J.P. Mitchell, D.M. May, and C. Shennan

Field studies were conducted in 1992 and 1993 to assess the effects of irrigation with saline drainage water on processing-tomato fruit yields and quality constituents. Saline water (ECiw = 7 dS/m) was used for 66% of the seasonal irrigation requirements in 1992 and 82% in 1993. Yields of tomatoes irrigated with saline water were maintained relative to nonsaline irrigation in 1992, but were decreased by 33% in 1993. Juice Brix and Bostwick consistency were generally improved by irrigation with saline water. pH was unaffected by irrigation treatment, and titratable acidity, an estimate of citric acid content, was increased only in 1993. Calculated quantities for various marketable processed product yields reflect the dominant influence of fresh fruit yield that masked, to a large extent, whatever quality enhancements that may have derived from saline irrigation. The substantial tomato yield reduction that occurred in the second year of this study in plots irrigated with saline drainage water, the gradual surface accumulation of boron, as well as the significant salt buildup in lower portions of the crop root zone following drainage water irrigations demonstrate definitive limitations to the reuse approach and restrict options for the crops that can be grown in this system and the frequency of saline drainage reuse.

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J.P. Mitchell, C. Shennan, D. Peters, and R.O. Miller

Sustainable alternatives for saline drainage water management in areas such as California's San Joaquin Valley are needed. Previous work has demonstrated the short-term potential for reuse of saline drainage water for irrigation in this area. Results from our 6-year cyclic drainage reuse study, however, indicate that soil structural problems may occur which can greatly reduce stand establishment and crop yields in periodically salinized soils. To prevent these problems, we are evaluating the effectiveness of winter cover crop incorporation and gypsum applications relative to conventional fallows, for improving/maintaining soil physical properties and crop productivity in cyclically salinized soils. Six winter cover crop/fallow treatments have been imposed upon a rotation of tomatoes, tomatoes and cotton as summer crops. By monitoring water use, relevant soil physical and chemical properties as well as crop performance during the course of this 3-year rotation study, we are assessing the potential benefits and constraints of using winter cover crops in drainage water reuse systems.

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J.P. Mitchell, C. Shennan, S.R. Grattan, and D.M. May

Effects of deficit irrigation and irrigation with saline drainage water on processing tomato (Lycopersicon esculentum Mill, cv. UC82B) yields, fruit quality, and fruit tissue constituents were investigated in two field experiments. Deficit irrigation reduced fruit water accumulation and fresh fruit yield, but increased fruit soluble solids levels and' led to higher concentrations of hexoses, citric acid, and potassium. Irrigation with saline water had no effect on total fresh fruit yield or hexose concentration, but slightly reduced fruit water content, which contributed to increased inorganic ion concentrations. Fruit set and marketable soluble solids (marketable red fruit yield × percent soluble solids) were generally unaffected by either irrigation practice. Water deficit and salinity increased starch concentration during early fruit development, but, at maturity, concentrations were reduced to < 1%, regardless of treatment. Higher fruit acid concentrations resulted from water deficit irrigation and from irrigation with saline water relative to the control in one year out of two. These results support the contention that deficit irrigation and irrigation with saline drainage water may be feasible crop water management options for producing high quality field-grown processing tomatoes without major yield reductions. Appropriate long-term strategies are needed to deal with the potential hazards of periodic increases in soil salinity associated with use of saline drainage water for irrigation.

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Laurie E. Drinkwater, Deborah K. Letourneau, Fekede Workneh, Marita Cantwell, Ariena H.C. van Bruggen, and Carol Shennan

Twenty commercial tomato production systems were compared in a multidisciplinary on farm study. The aim was to determine if organic (ORG) and conventional (CNV) systems differed in terms of agronomic criteria or indicators of underlying ecological characteristics. Field level measures of inputs, yields, fruit quality, arthropod abundance and management operations were made. Also, multiple samples within each field were taken to measure soil chemical and physical properties, root pathogen populations, disease incidence, and pest damage levels for multivariate analysis. Management effects on agronomic criteria (yield, fruit quality, pest damage) were small, whereas differences in soil N pools, microbial activity, pathogen populations and arthropod communities between ORG and CNV sites were sufficiently robust to be distinguished from site to site variation. Relationships between management, crop productivity and fruit quality will be discussed.