Abstract:

Dry beans (JPhaseolus vulgaris L.) are major legume crops and an
important source of protein in Uganda. Their production is constrained by
low soil fertility and weed competition. Field experiment was carried out
at Thompson Farm (Freeville Farm), Cornell University in 1995 and
1996, and at Namulonge Agricultural and Animal Production Research
Institute (NAARI) in Uganda in the 1997A and B seasons. The goal was
to determine the effect of competition between beans and weeds
(Galinsoga parviflora Cav., Bidens pilosa L. and Solanum nigrum L.) on
bean and weed nutrient uptake and bean yield under low soil fertility.
Low levels of nutrients (NPK, OPK, NOK, NPO and OOO) were
broadcast applied at 50, 50 and 60 kg N, P and K ha1, respectively. These
were combined with bean-weed treatments in a split-plot design with
nutrients as the main plots and bean-weed combinations as the sub-plots.
Results indicate that high bean dry matter was recorded under full
nutrients and under P and N deficit conditions. High weed dry matter was
observed in the presence of N and P. Beans are better accumulators of N
and the weeds are better accumulators of P, K, Ca and Mg. Bean yield
was high under P deficit condition resulting in high total revenue and net
profit. Galinsoga parviflora caused 33-42%; S. nigrum 29% and B. pilosa
THE INTERACTION OF WEEDS AND DRY BEANS (JPHASEOLUS
VULGARIS L.) UNDER VARIED SOIL FERTILITY CONDITIONS,
AND THE ECOLOGY OF WEEDS IN DRY BEAN FIELDS IN
Michael A. Ugen, Ph.D.
Cornell University 1999
I
46-50% yield reduction in beans. Beans are likely to be competitive with
weeds under P deficit condition and weeds are likely to be very
competitive with beans in the presence of N and P.
A screenhouse experiment under NPK, NPO and NOK nutrients
indicated that high shoot and root relative growth rates, and high root
elongation and growth rates of the weeds contribute to their
competitiveness especially with adequate N and P. Beans are more
competitive with weeds under P deficit conditions due to early
emergence, erect growth for a longer time, and more root volume
compared to the weeds. This is likely to contribute to better growth and
yield of beans under P deficit condition.
A survey was also carried out in Uganda on farmers’ fields to
determine the relationship between weeds and soil chemical and physical
characteristics and cropping system-related factors. Both soil factors and
cropping systems affected weed abundance. It was noted that B. pilosa
abundance was positively related to soil P and N while G. parviflora was
positively associated with soil Ca and pH. Both weeds were widely
distributed and were reported by farmers to cause yield losses to beans of
over 30%.