Date of Award

Winter 1988

Project Type

Dissertation

Program or Major

Plant Science

Degree Name

Doctor of Philosophy

First Advisor

James E Pollard

Abstract

In cool temperature climates where plant growth may be limited by short growing seasons and low temperature stress rowcovers are being used to increase production of fruit and vegetable crops. Two field experiments were conducted to investigate how floating rowcovers applied during autumn, winter and spring affect plant growth and development. The first experiment, 1985-86, examined mineral nutrient and biomass partitioning in a short-day cultivar, 'Sparkle', and a day-neutral cultivar, 'Fern', in rowcovered and nonrowcovered plants in autumn. The second experiment, 1986-87 examined carbon, nitrogen and biomass partitioning over time in autumn and in spring and development of yield components for the short-day cultivar 'Earliglow' in response to an autumn rowcover plus a short-term winter mulch and to no rowcover in autumn plus a long-term winter mulch.

In 1985-86 a rowcover in autumn extended the fall growing season by approximately three weeks increasing degree days (base 5$\sp\circ$C) by 63.5. For 'Sparkle', percents nonstructural carbohydrate and nitrogen in plants were lower and biomass in the canopy was higher under rowcovers than for controls. Differences in mineral nutrients were minor. For 'Fern' the only difference between treatments was a slightly higher photosynthetic rate for rowcovered plants.

Time course studies in 1986-87 indicated that rowcovers in autumn sustained the plant canopy, increased soluble sugar content in leaves and delayed development of leaf morphology typical of plants in rest, but had no effect on partitioning of carbon, nitrogen and biomass in other plant organs. In spring plants in the rowcover plus short-term mulch treatment began growth earlier, had higher levels of metabolizable carbon and a lower percent nitrogen than leaves on control plants. The major effect of the rowcovers plus short-term mulch treatment compared to the no rowcover plus long-term mulch treatment was to increase branch crown mass and earliness of flower emergence. It is concluded that use of rowcovers in autumn and winter plus early removal of winter mulch can significantly enhance development of yield components by sustaining plant growth during autumn and spring.

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