Effect of Poultry Manure Rates on Soil Acidity in an Ultisol

MATERIALS AND METHODS

Soil AnalysisThe soil used in this study was an ultisol characterized by deep porous red soils derived from sandy deposits in the coastal plain, collected from the Federal University of Technology Teaching and Research Farm Owerri during the 2001 cropping season.

Before application of poultry manure, bulked soil samples were collected randomly from the experimental site using a soil auger, from a depth of 0-15 cm (top soil) and 15-30 cm (sub soil) for determination of soil physical and chemical properties, including the soil acidity status. The collected soil samples were air-dried in the laboratory, ground and sieved using a 2 mm mesh size sieve pan. The particle size fraction was determined by the hydrometer method of Bouyoucos (1951), using sodium hexa-metaphosphate as a dispersant The soil pH was determined in distilled water and in KCI on a ratio of 1::2.5 soil/solution using the pH meter. The soil acidity status was also determined after application of poultry manure in 2001.

Organic carbon contents of the soil was ascertained using 2 g sample and by the dichromate wet oxidation method of Walkley and Black as outlined by Jackson (1969). The total nitrogen content of the soil was determined using the modified macro-Kjedahl method (Jackson, 1969) by crushing and sieving soil samples through a 0.5 mm mesh. The Bray-No. 2 method was used to extract available phosphorus while exchangeable cations were determined on extracts obtained after leaching samples with IN neutral ammonium acetate solution (Bray and Kurtz, 1945). Exchangeable potassium and sodium contents were estimated by the flame photometer while calcium and magnesium contents were determined by the versenate titration method. Effective cation exchange capacity was obtained by summation of exchangeable cations and acidity (IITA, 1979). The exchangeable acidity was determined by IN KCI extraction procedure as outlined by Mclean (1965). The percent base saturation was determined by expressing the sum of the exchangeable cations as a percentage of the ECEC values. The soil physical and chemical properties were also analysed after application of poultry manure using the methods outlined above after 21 days incubation period.

Analysis of the Poultry Manure
Samples of the cured poultry manure were collected randomly from the bulk, air-dried in the laboratory under room temperature for 3 days. The determination of the chemical nutrient contails was done as described above for the soil. Results are shown in Table 1. Analysis of variance was performed according to the General Linear Model procedure in Statistical Analysis System SAS (1998). Means were separated using the least significant differences at the 5% level of probability.

Table 1:	Chemical properties of the poultry manure used in the experiment

Incorporation of the Poultry Manure
The four poultry manure rates namely 0, 8, 16 and 24 kg plot^-1, respectively were weighed out using a weighing balance and applied manually by broadcasting uniformly on experiential plots of 4x4 m and tilled into a depth of 0.30 cm using the garden fork. For control plots, no poultry manure was applied. The post-soil physical and chemical analysis was carried out after 21 days of applying poultry manure. The experimental design was the Randomized Complete Block Design with three replications.

RESULTS AND DISCUSSION

The soil physical and chemical properties before application of poultry manure are shown in Table 2. The soil pH in water was 4.7 (top soil) and 4.8 (subsoil) while the soil pH in KCI was 4.6 (top soil) and 4.5 (sub soil) which indicates high soil acidity. The low ECEC of less than 10 meq/100 g soil) and low base saturation suggest the dominance of 1:1 clays and high level of aluminium. Generally, the low soil organic carbon, total nitrogen and organic matter contents indicates poor soil fertility. The soil is of sandy loam textural class, thus confirming similar observations by Jungerius (1964), Ofomata (1975) and Ononiwu (1990). Table 3 shows the soil physical and chemical properties after poultry manure applications. Results indicated that there are significant differences (p = 0.05) in the soil pH among the various treatments and control.

Statistical analysis indicated that the soil pH in water and in KCl were significantly (p = 0.0001) affected by application of poultry manure.

The 15 t ha^-1 poultry manure rate significantly (p = 0.0001) reduced soil pH from 4.14±0.09 (control) to 5.80±0.23 (pH in water) and from 3.62±0.13 to 5.73±0.18 (pH in KCl), respectively. The 5 t ha^-1 did not significantly (p = 0.0001) reduce soil pH, however the 10 t ha^-1 poultry manure significantly (p = 0.0001) reduced soil pH from 4.14±0.09 (control) to 5.20±0.19 (pH in KCl). This increase in soil pH with increased poultry manure rate of application as observed in this study agrees with Pitram and Singh (1993), who reported an increase in soil pH with the application of poultry manure. The mechanism responsible for this increase in soil pH was due to ion exchange reactions which occur when terminal OH¯ of Al or Fe²⁺ hydroxyl oxides are replaced by organic anions which are decomposition products of the manure such as malate, citrate and tartrate (Besho and Bell, 1992; Van et al., 1996; Pocknee and Summer, 1997; Hue and Amiens, 1989).

Table 2:	Soil physical and chemical properties before poultry manure application

Table 3:	Physico-chemical properties of the soil after poultry manure application

The ability of organic manure to increase soil pH was due to the presence of basic cations contained in the poultry manure. Natsher and Schwetnmann (1991) reported that such basic cations are released upon microbial decarboxylyation. It may thus be recommended that use of 15 t ha^-1 poultry manure will reduce soil acidity to near neutrality in an ultisol to enhance nutrient availability and uptake by crops.