Abstract:
The performance of crops are generally hindered by weeds, but some Leguminous Weeds (LW)
such as Sesbania spp. have been reported to serve as Green Manure (GM) in the production of
vegetables, including Amaranthus cruentus (Ac). While some LW do not nodulate, limiting their
potential as GM, Indigofera hirsuta (Ih), a LW, nodulates and can serve as GM but its use on Ac
has not been adequately documented in Nigeria. Therefore, the aim of this work was to determine
the GM potential of Ih on Ac performance, and to study its bioecology in Ibadan, Nigeria.
Floristic enumeration was carried out at Teaching and Research Farm, University of Ibadan, during
Wet Season (WS) and Dry Season (DS). Quadrats (0.5m2) were laid 15 times, using X-Y
coordinate random sampling technique, to determine Relative Importance Value-RIV (%) and
Shannon-Wiener index (H´). Seeds (20 each) of Ih, scarified with concentrated H2SO4 (analar
grade) for 10 (T1), 20 (T2), 30 (T3), 40 (T4), 50 (T5) and 60 (T6) minutes and un-scarified seeds
(T7=control) were placed in Petri dishes. The treatments were arranged in a completely randomised
design replicated four times and Germination Percentage (GP-%) was determined at day seven.
Seeds from T1 were stored in envelope at room temperature to determine storability after
scarification and GP was evaluated monthly for eight months. Field experiment was carried out to
evaluate the GM potential of Ih. Seeds from T1 were sown for 4, 6, 8 and 10 weeks in 1 m2 plots,
arranged in randomised complete block design in triplicates. The shoots were cut into pieces,
incorporated into the soil and allowed to decompose for three weeks before sowing seeds of Ac.
Plant Height-PH (cm), Stem Diameter-SD (cm), Leaf Area-LA (cm2) and Fresh Weight-FW (kg) of
Ac were determined using standard procedures. Data were analysed using descriptive statistics and
ANOVA at α0.05.
Twenty weed species were encountered in WS and 14 in DS. The RIV was highest for Tridax
procumbens in WS=19.02 and DS=29.03, lowest for both Sida acuta and Talinum fructicosum in
WS=0.62 and DS=1.67, respectively. Indigofera hirsuta had 6.87 (WS) and 13.96 (DS). The H´ of
2.11 (WS) was higher than 1.98 (DS). The GP ranged from 96.3 in T1 to 2.5 in T7. Seeds stored for
one to four months had similar GP with range 83.0 to 95.0 and significantly higher than those
stored for five to eight months with range 15.0 to 73.5. Incorporation of 8-week GM increased PH,
SD, LA and FW of Ac with 59.53±1.33, 0.90±0.00, 88.73±4.35 and 1.73±0.04 compared with
45.87±0.80, 0.67±0.03, 51.28±1.24 and 0.77±0.05 recorded for 4-week GM, respectively. This
could be adduced to production of high number of effective nodules by Ih at eight weeks. The
control plot had the least PH:40.83±0.54, SD:0.60±0.00, LA:43.95±2.59 and FW:0.55±0.03.
All the weed species, including Indigofera hirsuta, were randomly distributed in both seasons.
Seeds treated with concentrated H2SO4 maintained high germination and short viability duration.
Performance of Amaranthus cruentus was superior in plots incorporated with Indigofera hirsuta.
