Grain Legumes and Green Manures for Soil Fertility in ... - cimmyt

RESPONSE OF BEAN (PHASEOLUS VULGARIS, L.) CUL TIVARS TO
INOCULATION AND NITROGEN FERTILIZER IN ZAMBIA
FRIDAY SIKOMBE, OBED I LUNGU, KALALUKA MUNYINDA and MASAUSO SAKALA
Abstract
University of Zambia, Department of Soil Science, Lusaka,
and Mount Makulu Research Station, Chilanga, Zambia
Bean is an important component of the diet of people of Zambia, and many farm households grow it for subsistence and
barter in their communities. However, grain yields are low, typically 500 to 700 kg ha- 1 with local cultivars and without
supplemental nitrogen fertilizer application. Many soil and plant factors have been investigated to explain these low
yields, but there is still limited information on the contribution of soil fertility, variety and inoculation to improvement
in bean Yi.elds. A field study was conducted to evaluate the response of bean cultivars to applied nitrogen fertilizer and
to inoculation with native and introduced rhizobium strains. The experiment was set up as a 5 x 5 factorial design comprising
25 treatment combinations of five common bean cultivars and five nitrogen sources (3 strains and 2 nitrogen
fertilizer levels). The treatments were replicated four times and arranged in a randomized complete block design at
Mount Makulu Central Research Station, Chilanga, Zambia . The data collected included nodule count, dry nodule
weight, dYlJ shoot weight, total nitrogen content in shoots and grain weight. The amount of nitrogen fixed by the inoculated
crop was estimated by the difference method, using wheat as the non-fixing control crop. The results show that a
combination of some strains with some cultivars tested is as effective as applying nitrogen fertilizer to the crop. An effective
strain such as T AL1383 increased grain yield by 38.2% with some cultivars compared to the average grain yield
of the other four strains with other cultivars. The local strain isolated from nodules of common beans grown locally was
comparable to introduced strains in Mbala and Lundazi cultivars. The reduction in biological nitrogen fixation (BNF)
by inorganic nitrogen application was more with the Lundazi cultivar than other cultivars. The native rhizobia strains
at the trial site were as effective as the introduced strains. This study has shown that optimization of the effect of inoculation
lies in identifying and matching bean cultivar to Rhizobium strain. Therefore, because of strain/cultivar specificity,
it may be advisable to develop a broad-spectrum inoculum for use with bean cultivars in Zambia .
Key words: Nz-fixation, N fertilization, rhizobium strains, common bean
Introduction
Beans are produced for both domestic consumption
and sale in Zambia. Some bean leaves are consumed
as a vegetable, and only cultivars with palatable
leaves are consumed; other cultivars have tough
textured leaves. The major production areas in this
country are the high rainfall areas of Northern,
Northwestern, Luapliia Provinces and medium to
high rainfall areas of Eastern and Central Provinces.
In other provinces, production of beans is on a small
scale.
Most farmers prefer to grow local cultivars for their
colour and taste. However, average grain yields of
local cultivars are exceptionally low (500 -700 kg
ha- I ) even under commercial production (Annual
Report, 1978). Beans experience a deficient in nitrogen,
which results in poor yields (Lupwayi and
Mkandawire, 1996).
To improve bean yields, in the absence of effective
rhizobia, it is recommended to apply nitrogen fertilizer.
However, most resource-poor small-scale
farmers are unable to afford N fertilizers. The
cheaper option, therefore, is to exploit Biological
Nitrogen Fixation (BNF) through inoculation with
Rhizobia, and use bean genotypes that respond well
to inoculation. Llipwayi and Mkandawire (1996)
made similar observations to other researchers, that
inoculation with some strains of rhizobia increased
yield in common beans.
Some factors may cause failure of applied inoculum
to increase grain yield. According to Weiser et al.
(1985), soil pH, low phosphorus, high levels of exchangeable
aluminium and manganese, poor nutritional
status, and water stress may limit nodulation
and nitrogen fixation. Further, high levels of applied
N or soil N can inhibit nodulation (Munyinda,
personal communication). Nodulation and N2 fixation
is also influenced by climatic factors such as
light (Antoninew and Sprent, 1978), temperature
(Rennie and Kemp, 1981) and cultural aspects such
as planting density (Graham and Rosas, 1978).
In Zambia, very little research work has been conducted
on the inoculation of common bean. A great
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