TITLE:
Rice Hull Mulch Affects Germination of Bittercress and Creeping Woodsorrel in Container Plant Culture
AUTHORS:
James E. Altland, Jennifer K. Boldt, Charles C. Krause
KEYWORDS:
Mulch Depth, Light, PAR, Seed Placement, Nonchemical Weed Control
JOURNAL NAME:
American Journal of Plant Sciences,
Vol.7 No.16,
November
28,
2016
ABSTRACT: Mulches are commonly used to control weeds in container nursery crops, especially
in sites where preemergence herbicides are either not labeled or potentially phytotoxic
to the crop. Parboiled rice hulls have been shown to provide effective weed
control when applied 1.25 to 2.5 cm deep over the container substrate surface. The
objective of this research was to determine if weed seed placement, above or below
the mulch layer, affects flexuous bittercress or creeping woodsorrel establishment.
Seeds of both species were placed either above or below rice hull mulch layers 0, 0.6,
1.3, or 2.5 cm deep in nursery containers with a 80 pine bark: 20 sphagnum peat
moss substrate. Establishment of both weeds decreased with increasing mulch depth.
Establishment of both species was generally greater from beneath the mulch compared
to when seed were applied above the mulch. Light penetration through varying
depths of rice hulls was determined with a spectroradiometer. Photosynthetically active
radiation (PAR) decreased exponentially with increasing rice hull depth, and was
less than 1 μmol·m-2·s-1 beneath depths greater than 1 cm. Germination of both species
was determined in Petri dishes placed beneath varying densities of shade cloth.
Flexuous bittercress germination responded quadratically to decreasing light level,
but still germinated (13%) in complete darkness after 3 weeks. Creeping woodsorrel
germination was not affected by light level and was high (92%) after 3 weeks. The
role of light exclusion by rice hulls as a mechanism for controlling buried weed seed
is discussed. Water retention immediately after irrigation, and for 24 hr following irrigation,
was determined for a 2.5 cm layer of rice hulls, sphagnum peat moss, and
pine bark. Rice hulls retained less water, and dried more quickly than peat moss or
pine bark. The volumetric water content of the rice hull layer is less than 0.20
cm·cm-1 and what has been shown necessary for plant growth. Lack of water availability
in the rice hull layer is discussed as the primary mechanism of control of weed
seed above the mulch layer.