EFFECT OF FUMIGATION, FERTILIZATION, AND VARIOUS OTHER SOIL TREATMENTS ON GROWTH OF ORANGE SEEDLINGS IN OLD CITRUS SOILS

Abstract

A study was made to determine whether reduced growth of citrus in old or 2d or 3d planting groves could be demonstrated with citrus seedlings in old citrus soils in the greenhouse, and if so, to determine possible causes and methods of control. Sour and sweet orange seedlings grown in 3-gallon pots made approx. 50-175% more growth in noncitrus soil, that is, soil which had never been cropped to citrus, than in soil from adjacent areas which had supported citrus trees for 40-70 yrs. Seedlings in old citrus soil did not respond to applications of P, K, Mg, Cu, B, Zn, or Mn. Soil fumigation prior to planting usually controlled root rotting and the citrus root nematode (Tylenchulus semipenetrans) and markedly stimulated growth of orange seedlings in old citrus soil. In most noncitrus soils growth was only slightly increased or decreased by fumigation. Although applicationsof soil fumigants markedly stimulated growth of orange seedlings in old citrus soils it did not increase growth to a point comparable to that of plants in noncitrus soil. It appears evident that 8729-8741 HORTICULTURE [Vol. 23] 922 microbial factors are at least partly responsible for reduced growth of trees in old citrus soils, however, other factors, such as the presence of some toxic material, may also be involved.