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Accueil du site Doctorat États-Unis 1985 Relationship between observations in mini-rhizotrons and true root length density

Titre : ** Relationship between observations in mini-rhizotrons and true root length density **

Auteur : ** Upchurch, Dan Royce **

Université de soutenance : ** Texas Tech University **

Grade : ** Doctor of Philosophy (PhD) 1985 **

**Résumé **

This project has resulted in the development of two models which
can be applied to the mini-rhizotron technique for root observations.
The models are based on probabilistic assumptions concerning root growth
directions in the soil. The models apply to the average number of roots
which intersect the wall of several tubes buried in the soil, and not to
individual observation tubes. The usefulness of the mini-rhizotron
technique has been expanded to include indications of the orientation of
the root system through the ratio hypothesis. The conversion of root
counts to root length density (RLD) has been given a mathematical basis,
with few assumptions. The primary disadvantage of the system is the
number of samples required.

By determining the ratio of the number of roots which intersect the
top to the number which intersect the bottom, the model predicts the
direction of deviation from a random orientation. Observations made on
the wall of a trench confirmed the horizontal orientation of a cotton
root system and the existence of upward growth which had been predicted
by the model from observations in mini-rhizotrons.

A model, relating the number of root intersections on a mini-rhizotron
to the bulk soil RLD, predicted a linear relationship. The average
length to associate with each intersection was determined assuming that
root growth was affected only after an intersection occurred, that roots
can be represented by straight line segments, and that root growth
direction followed some probability density function. The assumption
that roots can be represented by straight lines can be removed if the
tortuousity of the path of root growth is known. The length can be
weighted by the probability of root growth in that direction, if it is
known.

The correlation coefficient between RLD determined by applying the
model to mini-rhizotron observations and that from soil cores was low
but significant at the 99% level, when all treatments and angles were
considered. The correlation was largest, 0.70, in the dryland treatment
at the 30 installation angle. The higher correlation in the dryland
treatment may have resulted from of the reestablishment of the
natural soil structure at the interface as the soil dried.
The statistical properties of the mini-rhizotron system emphasize
the need for a large sample size. The number of samples required to
detect specific differences in RLD is large for both soil cores and
mini-rhizotrons when the difference is small. The decision about the
number of tubes to install will be affected by the reported variance,
the magnitude of the expected RLD, the difference in RLD which is important
to the project, and the resources of the project. The variance
of the mini-rhizotron was larger than soil cores in this project, but in
another project reported in the literature this result was reversed.

**Mots clés :** Roots (Botany) ; Cotton – Growth ; Plant-soil relationships

Page publiée le 20 juin 2013, mise à jour le 27 décembre 2016