Effects of soil temperature in winter on growth of seedlings of some citrus rootstocks

Abstract

1. To know the effects of winter soil temperature on the growth of citrus trees in sloping citrus groves where the soil temperature is generally several degrees in centigrade higher than that of flat land, the growth of potted seedlings of sour orange, trifoliate orange and Yuzu (Citrus Junos) was observed under the different treatments of soil temperature during winter. The fresh weight and N, P, K contents were measured of the top and root of excavated seedlings.
2. The higher soil temperature promotes the bud sprouting about 10 days in spring.
3. The later shoot growth of evergreen sour orange as well as initial growth was much larger in high soil temperature than in low soil temperature, but the difference of shoot growth of deciduous trifoliate orange between the treatments was decreased and almost disappeared by the middle of April.
4. The fresh weight of sour orange seedlings was also significantly larger in high soil temperature than in low one, but no difference was found for the trifoliate orange. The assimilation of sour orange leaves or the absorption by root during winter, which might be promoted by some-what higher soil temperature during winter, seems to be very effective for the later growth of the shoot especially for the evergreen fruit trees.
5. There was no definite difference in N, P, K concentration of shoots or roots between treatments. But the thickness of roots during winter or much growth of shoot and root until later season in higher temperature plots shows the active absorption by roots in warm soil during winter in such as sloping orchards or groves.