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Abstract
Mature Marsh seedless grapefruit trees on Sour orange stock planted in a loamy soil were subjected to three levels of nitrogen fertilization with and without phosphate or chicken manure added. The details of the experimental plan and tree responses during the five-year experimental period will be described elsewhere. Briefly, the phosphate and manure treatments resulted in a significant increase in yield and in improved fruit quality. As far as the leaf composition is concerned, the phosphate and manure treatments caused an increase in the P and a decrease in the N content of the leaves, thus producing a completely inverse relationship between leaf N concentration and the yield of the corresponding trees. This situation served as an opportunity to test—under orchard. conditions—the validity of NaR (nitrate reductase) assay in leaves as a measure for some “active fraction” of leaf nitrogen and as a parameter for tree productivity. The use of the NaR assay has been suggested for the determination of N requirements of citrus trees (1).
Abstract
The presence of tristeza in Israel has prompted an interest in inarching citrus trees grafted on sour orange (C. aurantium L.) or Palestine sweet lime (C. limettoides Tan.) rootstocks. Tests conducted since 1976 at several locations in Israel have shown that: a) Swingle citrumelo (C.P.B. 4475) [C. paradisi Macf. × P. trifoliata (L.) Raf.] outperforms other rootstocks when used for inarching citrus trees; b) Swingle inarches of small diameters grow faster than those of large diameter; c) inarches on young trees grow faster than those on older trees; and d) the effect of Swingle citrumelo, C. volkameriana, and, to a lesser extent, of sour orange on ‘Shamouti’ fruit quality are similar to their effect when used as rootstocks.
Little is known about the effect of growth temperature on Aster (Compositae, Asteraceae) flower development. In this study, we report on this effect for two aster lines, `Suntana' and `Sungal'. Growth temperature had a dramatic effect on the duration of flower development, ranging from 22 days for plants growing at 29 °C up to 32 days for plants grown at 17 °C. Flower longevity was ≈40% shorter under the higher temperature for both lines. Growth temperature also affected flowerhead form: `Suntana' flowerhead diameter was 20% larger at 17 °C than at 29 °C. The number of `Sungal' florets per flowerhead was four times greater at the lower temperature. Shading (30%) under temperature-controlled conditions had no effect on any of the parameters measured. For plants grown outdoors, our results suggest that shading plants may increase quality by reducing the growth temperature.