Due to high cost and scarcity of chemical fertilizers, it has become necessary to source for agro-industrial wastes which could be used as manure for crops in tropical countries. In recent times that researchers were focused on the potential of these wastes as soil improvers and sources of nutrients. The wastes which have been proved as effective organic fertilizers include animal wastes, wood ash, rice husks, mill and brewery wastes, sawdust and other crop wastes.
Studies into use of sawdust ash which are left as wastes at sawmills, carpenter sheds and furniture factories as plant nutrient sources have not received attention. Odedina et al. (2003) found that sawdust ash at 2 to 8 t ha-1 increased yield of pepper (Capsicum annum) and tomato (Lycopersicon esculentum) significantly and also increased soil nutrients and plant N, P, K, Ca and Mg contents.
This work studied the effect of sawdust ash on soil and leaf nutrient contents, growth and yield components of cowpea in Southwest Nigeria.
MATERIALS AND METHODS
Field trials were conducted in Southwest Nigeria between August 2002 and 2003 at Akure and Ado-Ekiti respectively. Akure (7°16N, 5°15E) and Ado-Ekiti (7°31N, 7°49E) sites are in the rainforest zone. The Akure soil is Oxic Tropuldalt United State Depertment of Agriculture (USDA) while Ado-Ekiti soil is Sandy Arsenic Haphistalf. The sites were manually cleared. There were six sawdust as (0, 2, 4, 6, 8 and 10 t ha-1) treatments applied to soil grown to cowpea 1T84/716 obtained from International Institute of Tropical Agriculture (IITA), Ibadan, Nigeria. The treatments were replicated three times using a randomized complete block design. Each plot was 25 m2 with cowpea spaced at 0.60x0.30 m at one plant per stand. Ash was applied in ring form after two weeks after planting. Manual weeding was done thrice.
Thirty plants were randomly selected on each plot for data collection. Air-dried pods were harvested between 7th to 9th weeks after planting and number and weight of pods taken. Grains were extracted and weighed and grain weights were converted to per hectare.
Pre-planting surface (0-15 cm) soil samples collected over each site were
bulked for analysis. At completion of harvest 9 weeks after planting, samples
were also collected from treatment plots. The samples were air-dried and 2 mm
sieved. Particle size distribution by hydrometer method was done. The pH in
soil-CaCl2 (1:1) was determined using glass calomed electrode pH
meter. Total N was evaluated by micro-kjeldahl approach. Organic Matter (OM)
was determined by Walkey-Black Oxidation method and available P by Bray 1 extraction
was evaluated by molybdenum blue calorimetery. Exchangeable K, Ca and Mg were
extracted using ammonium acetate, K was determined using flame photometer and
Ca and Mg by atomic absorption spectrometer Tel and Hagarty (1984).
Leaf and Sawdust Analysis
Cowpea leaf samples collected per plot at mid-flowering were air-dried,
ground and ashed at 500°C for 2 h. Ash was dissolved in HCl to extract nutrients.
Nitrogen was determined using Kjeldahl approach, P by molybdenum blue colorimetry,
K by flame photometer and Ca Mg by atomic absorption spectrometer (Tel and Hagarty,
1984). Sawdust ash was also dissolved in HCl analyzed as for leaf.
Cowpea growth, yield data, soil analysis and leaf analysis data collected
in 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
Pre-planting soil analysis data are shown in Table 1. 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 soil chemical properties influenced by application of sawdust ash are shown in Table 2. Sawdust increased soil pH, OM, N, P, Ca and Mg. The values of these properties tended to increased with amount of ash. High positive correlations of 0.95, 0.95, 0.93, 0.95, 0.96, 0.91 and 0.98 were recorded for relationship between amount of ash and mean soil pH, OM, total N, P, K, Ca and Mg, respectively. Owolabi et al. (2003) and Odedina et al. (2003) had found that different types of ash enhanced soil pH and nutrient availability in soils of Southwest Nigeria. The increase in soil pH and cations associated with application of sawdust ash affirms that ash had liming effect. Other workers (Obi and Ekperigin, 2001) have successfully tried ash as a liming material.
Analysis of sawdust ash used in this work showed the values of 2.52 N, 12.8 P, 0.89 k, 8.64 Ca, 0.92 Mg, 0.67, 0.26, 0.73, 0.08 and 0.06 g kg-1, respectively. The material is relatively high in P. The increase in soil nutrient contents as a result of application of sawdust ash implies that the component nutrients were mineralized to be made available in soil and subsequently for crop uptake.
|| Pre-planting soil analysis for Akure and ado-ekiti, southwest
|| Effect of sawdust ash on leaf nutrient content of cowpea
at Akure in 2002 (a) and 2003 (b)
Table 3 shows data on leaf nutrient composition of cowpea in response to sawdust ash treatments. Ash treatments increased leaf N, P, K, Ca and Mg contents. Among the ash treatments (0, 2, 4, 6 and 8 t ha-1), the 8 t ha-1 ash gave higher leaf N, P, K, Ca and Mg contents at the two sites under consideration. The values dropped at 10 t ha-1 ash relative to 8 t ha-1 ash. This could be due to very high soil pH (well exceeding 7.0) recorded for 10 t ha-1 ash. The high pH would have adversely affected uptake of some nutrients including micronutrients such as B, Cu, Fe (Obi and Akinsola, 1995) and reduce root growth. For cowpea, Obi and Ekperigin (2001) recommended liming to 5.5. Also, excessive Ca in soil due to 10 t ha-1 ash and might have led to fixation and reduced availability of P (Table 2). This should have adversely affected cowpea whose grain yield and growth depended on availability of P (Adetuyi, 1984). Generally, sawdust ash at 4 (t ha-1) and above significantly (p>0.05) enhanced nutrient status of cowpea.
Table 4 shows data on yield components of cowpea. Sawdust ash treatments increased number and weight of pods relative to control (0 t ha-1). The 4, 6, 8 and 10 t ha-1 ash increased pod weight and grain yield but 2 t ha-1 ash did not. As in case of leaf N, P, K, Ca and Mg contents, the 8 t ha-1 ash gave highest values of yield components of Cowpea. It is suggested that the availability of these nutrients dictated the performance of cowpea.
The yield parameters were significantly (p>0.05) increased by sawdust ash at 6, 8 and 10 t ha-1. The increases in grain yield adduced to 4, 6, 8 and 10 t ha-1 ash at Akure were 23, 64, 107 and 84%, respectively. The values for Ado-Ekiti were 10, 60, 95 and 50%. Across the locations, they were 17, 63, 102 and 68%. In their trial on tomato, Odedina et al. (2003) also found that 8 t ha-1 sawdust ash most increased yield (77%).
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; Van Reuler and Janseen, 1996) that ash derived from plant sources served as liming material and increased nutrient uptake and yield of crops such as tomato, rice and vegetables.
Correlation coefficients between mean leaf N, P, K, Ca and Mg and cowpea pod weight were 0.76, 0.89, 0.95, 0.91 and 0.93, respectively. These values ascertain that increased availability of N, P, K, Ca and Mg enhanced cowpea yield. The correlations between sawdust level and leaf N, P, K, Ca and Mg contents of cowpea were 0.79, 0.76, 0.96, 0.86 and 0.76, respectively. These show that sawdust ash increased uptake of nutrients by cowpea. The correlations between sawdust ash level and number of pods and pod weight were 0.94 and 0.91, respectively. Hence, sawdust ash application and resultant increased availability of N, P, K, Ca and Mg positively influenced yield of cowpea.
Sawdust ash was an effective liming material and source of soil organic matter N, P, K, Ca and Mg. Its use as manure for cowpea significantly improved leaf N, P, K, Ca and Mg contents of cowpea, pod and grain yield on slightly acidic soils of Southwest Nigeria. The 8 t ha-1 treatment most enhanced cowpea nutrient content and yield.