Cowpea (Vigna unguiculata (L.) walp.) is the most important pulse crop in the savanna regions of West and Central Africa, where it is also an important vegetable a valuable source of fodder (Brink et al., 2006). Soils in areas of Southern Nigeria are acidic due to the nature of the parent material, heavy leaching and weathering. In addition to acidity, the soils suffer from nutrient deficiency (Owolabi et al., 2003). Although, cowpea derives a significant amount of the nitrogen requirements from the atmosphere and may leave 75-150 kg ha-1 in the soils for the benefit of succeeding crop (Brink et al., 2006). However, cowpea requires phosphorus for nodulation and root growth. Incorporation of 25 kg ha-1 is required for phosphorus and potassium deficient soils. Lime and chemical fertilizers are scarce and when seen are not affordable because of the high cost. Therefore, there is that need to investigate into the use of available domestic and agricultural waste that could serve as lime and fertilizer (Obi and Ekperigin, 2001).
Pod ash is known to contain an appreciable phosphorus and potassium (Odedina et al., 2003). Ojeniyi et al. (2001) found that yield of vegetable crops and nutrient content were improved by wood ash manure in trials conducted in Southwest Nigeria. Also, ash derived from burnt vegetation is known to reduce soil acidity, increase availability of cationic nutrients and improve yield of millet in Zambia (Araki, 1993).
The experiments being reported were conducted to study effect of wood ash manure treatments on nutrient status, growth and yield of cowpea.
MATERIALS AND METHODS
Field experiment was conducted at Akure (7°16N, 5°15E) in the rainforest
zone of Southwest Nigeria on a loamy sand soil, skeletal, Kaolinitic palenstalf
(USDA soil taxonomy).
Two trials were conducted on manually cleared land using early maturing IT
84/716 cowpea variety obtained from International Institute of Tropical Agriculture,
Ibadan, Nigeria between August and November, 2001 and 2002. Six levels of sawdust
ash namely: 0, 2, 4, 6, 8 and 10 t ha-1 were replicated three lines
on single plants spaced at 60x30 cm, each of the 18 plots being treatments were
25 m2. At 2 weeks after planting, sawdust ash was applied by ring
method. Manual weeding was done 3 times and novacron was sprayed against insects
6 weeks after planting.
Ten plants were selected on each of the 18 plots for data collection in each trial. At 9 weeks after ash application, plant height, number of branches and leaves were determined. Matured pods were harvested between 7 to 9 weeks after ash manure application, and the number of pods, pod weight, weight of 100 grains and grain yield per hectare basis were evaluated.
Surface (0-15 cm) soil samples collected on plot basis by anger in October
were bulked, air-dried and 2 mm sieved for chemical analysis. The pH is 1.2
soil-CaCl2 medium, total N by micro-kjeldahl method, available P
by molybdenum blue colorimetry after Bray-1 extraction were determined. The
exchangeable K, Ca and Mg were extracted using ammonium acetate, K was determined
on flame photometer, and Ca and Mg by atomic absorption spectrometry (Tel and
Analysis of Sawdust Ash
Two grammes of sawdust ash were used for analysis. The N was determined
by kjeldahl method, while determination of other nutrients (available P, exchangeable
K, Ca, Mg, Na, Fe, Mn, Cu and Zn) was done using the wet digestion method based
on 25-5-5 nitric-sulphuric and perchloric acids, respectively (Carter, 1993).
The K, Ca, Na were read on flame photometer, while the Mg and micronutrients
were read on atomic absorption spectrophotometer. The P content was developed
into colouration with vanaclo-molybdenum solution and read on spectronic 20
at 442 Um (Moyin-Jesu, 2003).
Cowpea leaf samples collected at 50% flowering were air-dried, ground and
ashed at 450°C for 6 h in muffle furnace. The nutrients in the ash was extracted
with water. The N was determined by micro-kjeldahl method and P by vanado-molybdate
colorimetry. The K and Ca were read on flamephotometer using appropriate element
filters, while Mg was determined on atomic adsorption spectrophotometer.
Cowpea growth, yield data, soil analysis and leaf analysis data collected
on sawdust ash treatment and replicate basis were subjected to analysis of variance
and their means compared using least significant difference at 5% level of probability.
RESULTS AND DISCUSSION
Table 1 shows value of chemical analysis of sawdust ash.
The surface (0-15 cm) soil had 74.6% sand, 13.4% silt, 12% clay, pH (CaCl2)
of 5.5, Organic Matter (OM) 1.3%, total N 0.06%, available P 6.2 mg kg-1,
exchangeable K 1.4 cmol kg-1, Ca 0.81 cmol kg-1 and Mg
3.1 cmol kg-1 (Table 2). The values of pH, exchangeable
K, Ca and Mg are suitable but the OM and available p-values were inadequate
(Kparmwang et al., 2004).
The mean soil pH (CaCl2) recorded for 0, 2, 4, 6, 8 and 10 t ha-1
ash treatments for experiment 1 and 2 are 5.5, 6.6, 6.6, 7.0, 7.2 and 7.2, respectively
(Table 3 and 4). Therefore soil alkalinity
increased with the amount of sawdust ash, indicating increasing supply of cations
(K, Ca and Mg). The high soil pH of between 5.5 to 7.0 are suitable for crops
in soils of Southwest Nigeria (Obi and Ekperigin, 2000).
||Chemical analysis of sawdust ash
||Pre-planting soil analysis for the experiments
||Effect of sawdust ash manure on soil composition (2001)
|NS: Not Significant
||Effect of sawdust ash on soil composition (2002)
|NS: Not Significant
Ash treatments increased leaf N, P, K, Ca and Mg contents. Among the ash treatments
(0, 2, 4, 6, 8 and 10 t ha-1), the 8 t ha-1 ash gave higher
leaf N, P, K, Ca and Mg contents at the two experiments under consideration
(Table 5). The values dropped at 10 t ha-1 ash
relative 8 t ha-1 ash. This could be due to very high soil pH (>7.0)
recorded for 10 t ha-1 ash. The high pH could have adversely affected
uptake of some nutrients micronutrients such as B, Cu, Fe (Obi and Ekperigin,
2001) and reduce root growth. Also, excessive Ca in soil due to 10 t ha-1
ash might have led to fixation and reduced availability of P. Cowpea grain yield
and growth depends on the availability of P (Brink et al., 2006).
The effect of ash treatments on the plant height and number of branches were
significant (p>0.05) as the 2, 4 and 6 t ha-1 ash significantly
increased plant height and number of branches (Table 6).
||Effect of sawdust ash on leaf nutrient content of cowpea
|nd: Not detected
||Effect of sawdust ash manure on growth parameters of cowpea
nine weeks after application
|NS: Not Significant
Also, there were increases in the number of leaves with the increasing rates
of ash treatment application. It is ascertained that increased uptake of N,
P, K, Ca and Mg due to application of sawdust ash to soil led to increased growth
All sawdust ash (2, 4, 6, 8 and 10 t ha-1) treatments increased
number of pods, pod weight and weight of 100 grains (Table 7).
As in case of leaf N, P, Ca and Mg contents, the 8 t ha-1 gave the
highest values of yield components of cowpea. The positive response of cowpea
to sawdust ash is consistent with earlier findings (Obi and Ekperigin, 2001;
Ojeniyi and Adejobi, 2002; Odedina et al., 2003).
Findings from this research show that sawdust ash increased growth, yield components and the grain yield of cowpea.
Sawdust ash could be utilized as source of nutrients especially P and K in cowpea production. Its use would enhance growth and yield. Sawdust ash through a lining material is also good source of organic matter, N, P, K, Ca and Mg. Cowpea pod and grain yield were significantly improved by sawdust ash application. The 8 t ha-1 treatment most enhanced cowpea nutrient and yield.