ESTIMATING RELATIVE ERROR IN NEMATODE NUMBERS FROM SINGLE SOIL SAMPLES COMPOSED OF MULTIPLE CORES

  • 1 January 1982
    • journal article
    • research article
    • Vol. 14  (4) , 522-529
Abstract
Spatial distributions of several species of plant-parasitic nematodes were determined in each of 3 fallow vegetable fields and in smaller subunits of those fields. Goodness of fit to each of several theoretical distributions was tested by means of an .CHI.2 test. Distributions for most species showed good agreement with a negative binomial model. An exception occurred with Criconemella sp., which showed a better fit to the Neyman Type A distribution. For nematodes distributed according to the negative binomial model, the number of cores per composite sample needed to achieve specified relative errors was calculated. For a given nematode species, such as Quinisulcius acutus (Allen) Siddiqi or Meloidogyne incognita (Kofoid and White) Chitwood, the k values for the negative binomial distribution increased as field size decreased, with the result that fewer cores were needed to achieve the same level of precision in a smaller field. Best results were achieved when the single sample was used to estimate populations in fields of 0.25-0.45 ha in size. When using only a single composite sample to estimate mixed populations of the nematodes studied here in a field of that size, .apprx. 22 cores/composite sample would be needed to estimate all population means within a SE-to-mean ratio of 25%. Considerably more cores were needed to maintain a given level of precision in fields of 1.0 ha or greater, and it may be necessary to subdivide larger units (.apprx. 1.5 ha and up) for accurate sampling.