Abstract:

Little research has been done on spring-sown cover crops for vegetable
production in the northern temperate and tropical regions. Results obtained from
studying spring-sown cover crops can be extrapolated to tropical situations as in
both cases the cover crops have a limited period (1% to 2 months) to accumulate
above-ground biomass prior to being killed for mulch. Cover crops suppress
weeds through competition, physical suppression, and production of
allelochemicals, and primary crops may be equally affected. There is a need to
research cover crops for specific regions and crops.
Pure and biculture stands of rye (Secale cereale L.) and field pea (Pisum
sativum L.) were established and killed for mulch by mowing in spring 1996, and
undercutting in 1997 and 1998. Their effect on weed and tomato (Lycopersicon
esculentum Mill.) growth were compared to a weedy check, a tilled and unwas
buried 1 cm deep in rye, pea, and weeded control plots to test its potential in
trapping allelochemicals, and to determine if the cover crops produced any
growth inhibiting compounds. Four tropical species, siratro (Macroptilium
atropurpureum), lablab bean (Lablab purpureas), velvet bean (Mucuna prunens),
and soybean (Glycine max) were tested in greenhouse studies for their weed
weeded check, and a tilled, conventionally weeded check. Activated charcoal
control potential and effect on tomato growth and yield. Weeds were suppressed in treatments with higher rye ratios and high cover crop biomass. Yields of
tomato in the bicultures with 1:1 and 1:3 rye to pea ratios when undercut in 1997
were as high as 50 MT. ha’1. These bicultures also suppressed weeds before
mowing or undercutting by as much as 90% compared to the weedy check and
yielded more than 4 MT. ha.-1 of above-ground biomass. Extracts from the
activated charcoal buried in rye and pea plots suppressed lettuce seed
germination at the highest concentration compared to those from the weeded check and fresh activated charcoal. Siratro and soybean accumulated above ground biomass faster than lablab and velvet bean, significantly suppressing
weeds both before and after kill. Tomato fruit yields in siratro and soybean
mulches were higher than those from tomato plants grown in lablab and velvet
bean mulches.