CC BY
119
EFFECTS OF RUMEN DIGESTA ON THE PHYSICO - CHEMICAL PROPERTIES OF SOILS IN NSUKKA, SOUTHEASTERN NIGERIA
Edeh I.G., Igwe C.A., Ezeaku P.I.
University of Nigeria, Nsukka, Nigeria E-mail: [email protected], [email protected], [email protected]
ABSTRACT
In tropical and subtropical areas, the importance of organic manure in improving soil physico-chemical properties and crop production for food security cannot be overemphasized. A study was conducted during 2012/2013 crop years to investigate the effects of rumen digesta on the physical and chemical properties of soils in Nsukka, Enugu state Nigeria. The soil samples collected from Opi, Nsukka were treated to four rates of rumen digesta (viz. 0, 50, 100, and 150 gkg" soils). Physical and chemical properties of the soil were determined pre and post-experiment. The results obtained revealed that rumen digesta significantly (p = 0.05) increased the mean weight diameter (0.49 to 1.75mm), aggregate stability (54.7% to 75.3%), soil pH (3.8 to 7.8), total nitrogen (0.01% to 0.02%), exchangeable sodium and potassium (0.22 to 4.39cmolkg" for Na+ and 0.30cmolkg" to 4.31 for K+), CEC (7.2 to 14.9cmolkg") and organic matter content (0.97% to 4.29%). It had no significant effect on the texture, micro-aggregate (measured as dispersion ratio), exchangeable calcium and magnesium content of the soils. The study found significant reduction in the exchangeable aluminum (1.5 to 0.0cmolkg") and hydrogen content (3.7 to 2.2cmolkg") of the soils. It recommended that farmers can improve the physical and chemical properties of soils by using rumen digesta as an alternative liming material.
KEY WORDS
Rumen digesta, soil properties, evaluation, rural land, Nsukka-Nigeria.
The use of organic manures (especially ruminant dung, poultry droppings, household refuse and effluents) for crop production is an age long agricultural practice among the subsistence farming communities in West African sub region (Lombin et al., 1991). In many developing countries like Nigeria, the likelihood of obtaining enough synthetic fertilizers to meet the food crop requirement of the teeming farming population is remote. The ever-increasing demand for food has intensified the quest for more production per unit area and for an increase in land under arable cultivation. Farmers in the tropics and the subtropics have been forced to eliminate fallow periods and rely on synthetic fertilizers. These practices (reduction in fallow periods and increased use of synthetic fertilizers) have lead to the increment in land degradation and decline of crop productivity. Odu and Mba (1991) stated that inorganic fertilizer supply nutrients alone, while organic manure not only supply nutrient elements through microbial activities but also help in improving the soil physico-chemical properties. The inventory of urban and industrial wastes in Nigeria, as compiled by Sridar (2006) showed that millions of tons of industrial, domestic and animal wastes so produced annually in the country are not effectively utilized whereas these wastes can be utilized effectively for agriculture.
Evidences indicate that by judicious application of these wastes in agricultural field one could maintain a high level of soil fertility. Investigations on the possible use of organic waste to improve the productivity of soils have been carried out (Agbim, 1981; Omaliko & Agbim, 1983; Mbagwu 1985; Omaliko 1985).
The use of organic wastes as biofertilizers has necessitated many studies aimed at evaluating the fertilizing value of these organic waste products (poultry dropping, cow dung, and sewage sludge and swine wastes) to ascertain their potentials in improving soil fertility. However there is little information available about the effect of rumen digesta on the physical and chemical properties of soils in the study area. Rumen digesta are wastes water from an abattoir gotten from the paunch content (Rumen) of ruminant animals, they are part of organic wastes or manures. A total of 194kg of solid (rumen/stomach) waste is generated
daily in Nsukka abattoir (Nwanta et al., 2010), therefore it will be beneficial to study its effect on the physical and chemical properties of soils. The objective of the study therefore, was to determine the effects of rumen digesta on the physico-chemical properties of soils from Opi in Nsukka local government area (L.G.A) in Enugu state.
MATERIALS AND METHOD
Study Area. The experiment was carried out at the Green house of the Faculty of Agriculture, University of Nigeria, Nsukka. The soil sample was collected from Opi while the rumen digesta was collected from Ikpa abattoir in Nsukka, Enugu State. Nsukka location falls within latitude 06052N and longitude 07024E with an altitude of approximately 400m above sea level. Generally the climate of Nsukka is characterized by mean annual total rainfall of about 1600mm and mean annual evapotranspiration (ET) of about 1560mm. the ET, however exceeds total rainfall in most months of the year (Igwe, 2004). Rainfall distribution is characteristically biomodal, with peaks during July and October. The entire wet season lasts from April to October, whereas dry season lasts from November to March. During the wet season, there is a soil moisture recline of 104mm and a moisture surplus of about 260mm which depletes to an average deficit of about 650mm in the dry season (Mbagwu, 1987). Temperature is uniformly high throughout the year, with mean minimum and maximum annual values of 21oc and 31oc respectively. Rarely does it exceed 35oc during the hottest months (Asadu, 1990; Obi and Salako, 1995).
Grassland vegetation is predominant in the study location which according to Mbagwu (1991) is within the forest-savanna transition vegetation zone. The area has an ustic soil moisture regime and the soil around are characterized as being well drained with very low total exchangeable base, cation exchange capacity(CEC) and base saturation (Asadu, 1990). The soil is deep coarse textured and low in organic matter with perennial leaching problem (Igwe 2004). The soils mostly belong to the order of ultisol and vertisol.
Sample Collection. From farmers' farm field (0.05km2) at Opi in Nsukka LGA of Enugu State, auger samples were collected at a depth of 0 - 30cm from randomly selected positions. The samples were bulked to get composite samples and transported to the green house. The soil samples were air dried and sieved through a 2mm mess and stored in 12 plastic containers (1564 cm3) before amendments were applied. The rumen digesta was collected from the paunch content of cattles, from Ikpa-Nsukka abattoir, Enugu state and air dried.
Experimental Design. 1kg of soil was measured into plastic containers and treated with the waste at the rates of 0, 50, 100, and 150g. Experimental design was completely randomized design (CRD) and treatments were replicated 3 times resulting to a total of 12 samples. The treated soil samples were kept moist with distilled water (200ml daily) during the 5 weeks duration of the experiment. The soil samples were analyzed for physical and chemical properties before and after amendment, while the rumen digesta was analyzed for its chemical properties before application.
Laboratory Studies. The laboratory analysis was conducted at the Soil Science laboratory, Faculty of Agriculture, University of Nigeria, Nsukka. The physical properties analysed were as follows; Particle size distribution was determined using the hydrometer method (Bouyoucos 1962), Dispersion ratio, Clay dispersion ratio and the water stable aggregate of the soil which was determined by wet - sieving method of Kemper and Rosenau (1986). Aggregate stability was calculated as thus;
weight of stable aggregate-weight of sand. ^ ^qq weight of sample-weight of sand
Chemical properties analysed were; Soil pH was determined using glass electrode pH meter in water in the ratio of 1:2.5 (Maclean, 1982), organic carbon content was determined by wet dichromate acid oxidation method (Nelson and Sommers 1982), and Organic matter was obtained by multiplying organic carbon by a factor of 1.724. Total nitrogen was
determined by using kjeldahl apparatus (Bremner and Mulvaney 1982), Exchangeable base by ammonium acetate leaching and exchangeable acidity by titration (MaClean, 1982). The effective cation exchangeable capacity (ECEC) was determined by summation of exchangeable bases and exchangeable acidity.
Statistical analysis. All data collected were statistically analyzed using Genstat 9.2 edition. A t-test was used to verify whether there were statistically significant differences (LSD0.05) according to Steel and Torrie (1980).
RESULTS AND DISCUSSION
The chemical properties of the rumen digesta are shown in Table 1. The pH is 8.0 (alkaline in character).
Table 1 - Chemical properties of rumen digesta (RD)
Parameter Value
pH H2O 8.0
OC % 28.15
TN % 0.023
Na+ cmol/kg 24.21
K+ cmol/kg 28.68
Ca2+ cmol/kg 3.2
Mg2+ cmol/kg 4.6
Al3+ cmol/kg 0.00
H+ cmol/kg 33.46
OC = organic carbon, TN = total nitrogen.
The physical and chemical properties of the soil before application of rumen digesta are shown in Table 2. The soil has sandy clay loam texture. The percentage water dispersible (WD) clay and silt is 10%. Chemically, the soil is highly acidic (pH 3.1) with low percentage organic carbon (0.54%) and total nitrogen contents (0.11%). Generally the values of exchangeable cations (Ca2+, Mg2+, K+ and Na+) are low according to Mbagwu (1992).
Table 2 - Initial soil analysis
Parameters Value
Physicalnproperties Clay (%) 20
Silt (%) 4
T.sand (%) 76
Textural Class Sandy Clay Loam
WD Clay (%) 10
WD Silt (%) 10
DR 0.77
CDR 0.5
MWD (mm) 0.47
AS (%) 53
Chemical properties pH 3.1
OC (%) 0.54
OM (%) 0.93
TN (%) 0.011
Na+ (cmol/kg) 0.22
K+(cmol/kg) 0.39
Ca2+(cmol/kg) 1.2
Mg2+(cmol/kg) 2.4
Al3+(cmol/kg) 0.8
H+(cmol/kg) 4.4
CEC(cmol/kg) 6.4
T. sand = total sand, WD clay = water dispersible clay, WD silt = water dispersible silt, DR = Dispersion ratio, CDR = clay dispersion ratio, MWD = mean weight diameter, AS = aggregate stability, OC = organic carbon, OM = organic matter, TN = total nitrogen and CEC = cation exchange capacity.
Physical Properties. The results of the soil particle size distribution (PSD) at different rates of rumen digesta application are presented in Table 3. There were no significant differences (p=0.05) between the %clay, %silt, and %total sand content and textural class of the treated soils and the untreated soils.
Table 3 - Particle size distribution of the soils of Opi-Nsukka
LRD Clay -► Silt % T. Sand <- Textural Class
0 20 4 76 Sandy clay loam
50 21 5 74 Sandy clay loam
100 20 6 74 Sandy clay loam
150 19 5 76 Sandy clay loam
LSD0.05 n.s n.s n.s
LRD = level of rumen digesta application and T. sand = total sand.
The texture of the soils was determined before and after treatment with rumen digesta. From the results obtained in Table 3, rumen digesta had no effect on the texture of the soil this could be due to the fact that texture is believed to be a fixed property. The entire soils had sandy clay loam texture.
The water-dispersible particle size distribution, dispersion ratio and clay dispersion ratio at different rates of rumen digesta application are presented in Table 4. There were no significant differences (p=0.05) in the water-dispersible clay, water-dispersible silt, dispersion ratio and clay dispersion ratio of the treated soils and the untreated soils.
Table 4 - Water-dispersible particle size distribution of the soils of Opi-Nsukka
LRD WD Clay% WD Silt % DR CDR
0 9 12 0.76 0.45
50 10 8 0.75 0.5
100 13 8 0.84 0.93
150 14 6 0.84 1.0
L.S.D0.05 1.960 3.075 0.0395 0.1874
LRD = level of rumen digesta application, WD clay = water dispersible clay, WD silt = water dispersible silt, DR = Dispersion ratio, CDR = clay dispersion ratio.
In Table 4, there was no significant difference between the DR of the treated soils and the untreated soils. The DR of the soil was 0.76 while that of the treated soils ranges 0.75 to 0.84. This is similar to the result gotten by Mbah and Onweramadu (2009) which state that additions of soil organic amendments failed to significantly improve micro-aggregate (measured as dispersion ratio).
The soil weight at >2mm, 2-1mm, 1-0.5mm, 0.5-0.25mm and <0.25mm, mean weight diameter and aggregate stability at different rates of rumen digesta application are presented in Table 5. Positive significant differences (p=0.05) in the weights of the soil, MWD and AS were recorded due to the application of rumen digesta. The variables increased as the rate of rumen digesta applied increased.
Table 5 - Percent water-stable aggregates, mean-weight diameter (MWD) and aggregate stability
of the soils of Opi-Nsukka
LRD >2 2-1 1-0.5 0.5-0.25 <0.25 MWD AS %
0 0.28 6.15 25.19 33.61 34.77 0.49 54.7
50 7.98 15.29 28.25 25.59 22.89 0.84 69.3
100 26.55 18.65 18.53 16.77 19.49 1.40 72.7
150 34.26 13.99 14.49 12.79 20.24 1.75 75.3
LSD0.05 8.60 4.875 3.919 3.764 6.99 0.2816 6.54
LRD = level of rumen digesta application, MWD = mean weight diameter, AS = aggregate stability.
Table 5 shows the Water-stable aggregate, mean-weight diameter and aggregate stability. There was significant differences (p=0.05) between the mean weight diameter (MWD) of the treated soils and the untreated soils. Rumen digesta significantly increased the mean weight diameter as the LRD increased. MWD value obtained in 150gkg-soil LRD was significantly higher than the control by 27.4%.
There was significant differences (p=0.05) between the aggregate stability (AS) of the treated soils and the untreated soils. Rumen digesta significantly increased the aggregate stability of the soils as the LRD increased. The AS of the untreated soil was 54% while the mean of the treated soils were 72.4% (range: 69.3 to 75.3%). This could be due to the binding power of organic matter on soil particles to form stable aggregates. This is in accordance with the research findings by Chaney and Swift, (2006); El hadj et al, (2013); Nwite, (2013); Mbah and Onweremadu, (2009).
Chemical Properties. The soil pH in water, exchangeable bases (Ca, Mg, K, and Na), exchangeable acidity (Al and H), ECEC, total nitrogen, and organic matter at different rate of rumen digesta application are presented in Fig 1. As the rate of rumen digesta application increased the soil pH, exchangeable sodium (Na), exchangeable potassium (K), effective cation exchange capacity (ECEC), and organic matter content increased while the exchangeable acidity decreased.
From Fig 1 it was recorded that untreated soil had high soil acidity (pH = 3.8) while application at 50g rumen digesta produced less acidic condition. At 150 LRD, soil pH appreciated by 15.4% relative to LRD at 50g, due to significant (p=0.05) increase in exchangeable cation contents in the soil colloidal complex. Low pH of 3.8 and 6.6 obtained in LRD 0 and 50g might be associated to loss of exchangeable bases resulting from displacement reactions in the soil colloidal complex. Soil acidity has been blamed on excessive rainfall that necessitated eluviations and leeching losses of cations under field conditions. The rise in pH of the treated soils above 6 may have effect on the nutrient availability in the soil, because this is the pH range for maximum nutrient availability in the soils (Brady and Weil 2005). The improvement of soil pH in the treated soils confirms the liming effect of rumen digesta. Similar reports on the liming effect of organic materials were shown by Duruigbo et al., (2006), Anon and Ubochi, (2007), Okonkwo et al., (2009), Osemwota, 2010 and Ekpe, 2013.
Organic matter content of the untreated soil was 0.97% for untreated soils and ranged from 2.38% to 4.29% for treated soils Fig. 1. The organic matter content was highest in soils with treatment level of 150g/kg soil of rumen digesta. There were significant differences (p = 0.05) between the organic matter contents of untreated and treated soils. The increase in organic matter of the treated soils can be attributed to the increase in organic carbon and mineralization of the rumen digesta. This finding is in agreement with that of NRCS (1996) and Ekpe (2013) which noted that applying animal manure increases the supply of organic matter in the soil.
The total nitrogen content of the untreated soil was 0.010% but ranges from 0.014 to 0.020 for treated soils. The highest nitrogen content of treated soils of 0.020% was obtained from the application of 150g/kg soil of rumen digesta. This was significantly different (p=0.05) from the total nitrogen obtained from the control. Total nitrogen obtained from 150gkg-soil LRD was higher than that of 100gkg-soil, 50gkg-soil and 0gkg-soil LRD by 10%, 30% and 50% respectively (Table 6). This might have resulted from the incorporation of rumen digesta to the soil and agrees with the findings of Awodun (2008) and Okonkwo et al., (2009) who noted that mineralization of organic wastes results in the release of organic bound nutrients in the soil notably N.P.K. However, there were no significant differences between the total nitrogen obtained from the applications of 50, 100 g/kg soil rumen digesta and the control. Rumen digesta appeared to have influenced the total nitrogen content of the treated soils. A substantial amount of the nitrogen may have been lost through volatilization because of the pungent smell that was emanating from the waste (Prasad and De Datta 1979).
10 8 6 4 2 0
pH
LRD
pH
-1-1-1
0 50 100 150
Organic Matter (%)
OM %
n-1-1-1
0 50 100 150
LRD
Total Nitrogen (%)
0,025 0,02 0,015 0,01 % 0,005 0
T
N
TN %
n-1-1-1-1
0 50 100150
LRD
Exchangeable Bases (cmolkg-)
50 100 150 LRD
4
3
Na+
2
K+
1
Ca2+ 0
Mg2+
Exchangeable Acidity (cmol/kg-)
n-1—I I
0 50 100 150
Al3+ H+
LRD
0
Effective Cation Exchange Capacity (cmolkg-)
LRD
Figure 1 - Effect of rumen digesta on the organic matter content, total nitrogen, exchangeable bases,
exchangeable acidity and cation exchange capacity
All exchangeable cations (Ca2+, Mg2+, K+ and Na+) had significant (p=0.05) increases in the soil with increase in treatment application (Fig 1), a suggestion that amendments had effect on the measured soil parameters. Exchangeable K+ increased by 93.0% in LRD 150 relative to LRD 0g. the values from LRD 50g to 150g were higher than the critical values of
0.16 to 0.20cmolkg" for crop production in the subtropical area (Isirima et al., 2003 as cited in Ezeaku, 2011). Findings are in agreement with what was reported by Osemwota, (2010). The concentrations of the exchangeable cations in the treated soils improved, this shows that rumen digesta improved the exchangeable bases content in the soil. The increase in values may be as a result of increased soil pH which invariably has a liming effect on the soil and agrees with NRCS, (1998) which noted that increase in soil pH increases the availability of exchangeable bases. Increases in exchangeable bases due to application of organic residues have also been reported by Mbagwu (1992).
The untreated soil contained 1.5 cmol/kg of Al3+ but after amendment the Al content was significantly reduced to 0.0cmol/kg. The H+ content of the untreated soil was significantly different from the H+ content of the treated soils. Rumen digesta significantly reduced the H+ content of the soils. The H+ content of the untreated soils was 3.7cmol/kg, while that of the untreated soils were between 2.2 and 2.3cmol/kg. This also may have accounted for the increase in soil pH and reduction in acidity level. This result is in accordance with other works where organic manure reduced the Al3+ and H+ content of the soil (Agboola and Odeyemi 1975; Charreau, 1975; Nwite et al, 2012; Enueke et al, 2013).
Effective cation exchange capacity contents in the treated soils were significantly different (p=0.05) from that of the untreated soils. The content of ECEC, in the controls was 7.2cmol/kg while in the treated soils it varied from 11.1 to 14.9cmol/kg (Fig. 1). Therefore it could be said that rumen digesta significantly increased the ECEC of the soils. This result is similar to other reports that showed that organic matter increases the ECEC of the soil, examples of such works were those conducted by Egawa (1975), Nwite (2012) and Asadu and Nweke (1999). This also is in agreement with NRCS (1996) which noted that organic matter retains nutrients by providing cation and anion exchange capacities. For the soils of the tropics, values of ECEC between 6 to 8cmolkg" is regarded as low, 8 to 11cmolkg" as medium and >12cmolkg" as high (Enwezor et al., 1990 in Ezeaku, 2011). Based on these limits the amount of ECEC obtained in LRD 0 (control) and LRD 50g was low and medium respectively. The values obtained at LRD 100 and 150g were high (Fig. 1), indicating no response to N, P and K fertilization for the crops in tropical area (Ezeaku, 2011).
CONCLUSION
Results of the study revealed that rumen digesta significantly increased the mean weight diameter (MWD), aggregate stability (AS), soil pH, total nitrogen (TN), exchangeable sodium (Na), exchangeable potassium (K), effective cation exchange capacity (ECEC) and organic matter content. It had no significant effect on the texture, exchangeable calcium (Ca) and exchangeable magnesium (Mg) content of the soils. Finally it significantly reduced the exchangeable aluminum (Al) and hydrogen (H) content of the soils.
Rumen digesta are sources of organic manure, therefore for better sustainability of the soil and crop productivity 100g of rumen digesta/kg soil is recommended to improve the physic-chemical properties of the soils of Opi since it gave the best result and also at rates more than this the soil pH will increase to a level where the soil will become alkaline/ saline which will have a negative effect on both the soil and the crop productivity. This study recommend the use of rumen digesta as a form of liming material but with caution to avoid making the soil alkaline.
REFERENCES
1. Agbim, N.N. (1981). Potentials of cassava peels as a soil amendment. Corn growth, J. environmental qual 14.3:411-415.
2. Agboola, A.A. and Odeyemi, O. (1972). The effect of land use on the soil organic matter, exchangeable K, Available phosphorus and soil pH in the rainforest zone of western Nigeria. Nigeria Agricultural Journal. 2: 161-168.
3. Anon, A.O. and Ubochi, C.I. (2007). Neutralization of soil acidity by animal manures. Mechanism of reactions, African Journal of Biotechnology 6(4): 364-368.
4. Asadu, C.L.A. and Nweke, F.I. (1999). Soils of arable crop fields in sub- Saharan Africa: Focus on cassava growing areas. Collaborative study of cassava in Africa. Working paper No. 18, IITA, Ibadan Nigeria.
5. Awodun, M.A. (2008). Effects of nitrogen released from rumen digesta and cow dung on soil and leaf nutrient content of Gboma (Solanum. Macrcapon .L) Journal of Applied Biosciences. 7: 202-206.
6. Bouyoucos, G. J. (1962). Hydrometer method for making particle size analysis of soils. Soil Science Society of America Proceedings. 26: 464-465.
7. Brady, N. C. and Weil, R. R. (2005). The nature and properties of soils, 13th ed. Delhi: Pearson Education.
8. Bremner, J. M. and Mulvaney, C. S. (1982). Nitrogen. In A. I. Page, R. H. Miller, & D. R. Keeney (Eds.), Method of soil analysis, part 2, Agron. Monogr. 9, 2nd ed. Madison: ASA. pp. 159-165)
9. Chaney, K. and Swift, R.S. (2006). The influence of organic matter on aggregate stability in some british soils. European Journal of Soil Science. Vol. 35 (2):223-230
10. Duruigbo, C.J., Obiefuna, J.C., Onweremmadu, E.U., Ogbede, K.O., Ihejirika, G.F. and Obilo, O.P. (2006). Effects of poultry manure rates on soil acidity in an ultisol. In: Proceedings of Agricultural Society of Nigeria Annual Conference, Umudike.
11. Ekpe, I.I. (2013). Effect of Fresh Rumen Digesta on Soil Chemical Properties and Yield of Cucumber (Cucumis sativus) In Abakaliki Southeast Nigeria. International Journal of Food, Agriculture and Veterinary Sciences. Vol. 3 (2): 110-117
12. El hadj, B., Saad, A.H. and Aziz, L. (2013). Short-term effect of organic residue incorporation on soil aggregate stability along gradient in salinity in the lower Cheliff plain (Algeria). African Journal of Agricultural research. Vol. 8 (19): 2144-2152
13. Enueke, E.C., Ojeifo I.M. and Nnaji, G.U. (2013). Residual effects of organic manure and inorganic fertilizer on maize grain weight and soil properties in Asaba area of Delta state. International Journal of Advanced Biological Research. Vol. 3(3): 433-442.
14. Ezeaku, P.I. (2011). Soil quality as influenced by landuse and management in the southern guinea savanna of Nigeria. Nig. J. of Soil and Env. Res. 9:1-11
15. Kemper, W.D. and Rosenau, R.C. (1986). Aggregate stability and size distribution. In: Method of Soil Analysis. Part 1. Physical and Mineralogical Methods, Soil Science Society of American Agronomy Monograph No. 9, 2nd ed., pp. 425-440.
16. Lombin, C.G., Adepetu, J.A. and Ayotade, K.A. (1991). Complementary use of organic manure and inorganic fertilizers in arable crop production. Proceedings of a national organic fertilizer seminar, Kaduna Nigeria. Pp 146-162
17. Maclean, E.O. (1982). Soil pH and Line requirements. In: edited by Page et al.,, Methods of soil Analasysis part II, American Society of Agronomy 9 Madison WIUSA. Pp 199-234.
18. Mbagwu, J.S.C. (1985), Subsoil productivity of an ultisol in Nigeria as influenced by organic waste and inorganic fertilizers amendments. Soil science 140: 436-441.
19. Mbagwu, J.S.C. (1992). Improving the productivity of a degraded ultisols in Nigeria using organic and inorganic amendments, Part 2: chemical properties and maize yield Biores. Technol 42: 149-154.
20. Mbah, C.N. and Onweremadu, E.U. (2009). Effect of organic and mineral fertilizer inputs on soil and maize grain yield in an acid ultisol in Abakaliki-south eastern Nigeria. American-eurasian Journal of agronomy 2(1): 07-12.
21. Nelson, D. W. and Sommers, L. S. (1982). Total carbon In A. I. Page, R. H. Miller, & D. R. Keeney (Eds.), Method of soil analysis, part 2, Agron Monogr 9, 2nd ed. Madison: ASA. pp. 539-579.
22. NRCS (1996). Soil Quality Indicators: Organic matter, soil quality information sheet.
23. NRCS (1998). Soil quality indicators: pH, soil Quality information sheet.
24. Nwanta, J.A., Onunkwo, J. and Ezenduka, E. (2010). Analysis of Nsukka metropolitan abattoir solid waste and its bacterial contents in South Estearn Nigeria: Public Health implications. Archives of Environmental & Occupational Health, 65(1): 21-26.
25. Nwite, J.C., Essien, B.A., Amaele, M.U., Obalum, S.E., Keke, C.I. and Igwe, C.A. (2012). Supplementary use of poultry droopings and rice-husk waste as organic amendments in southeastern Nigeria. 1: soil chemical properties and maize yield. Libyan Agriculture Research Center Journal International. 3(2): 90-97.
26. Nwite, J.N. (2013). Effect of different rates of poultry manure on soil properties and grain yield of maize at Abakaliki Ebonyi state, Nigeria. Crop Science Society of Nigeria book of abstracts. Pp140
27. Odu, C.T.I. and Mba, C.C. (1991). Microbiological consideration for maximizing nutrient availability through organic fertilization. Proceedings of a national organic fertilizer seminar, Kaduna Nigeria. Pp 67-80.
28. Okonkwo, B.C.N., Okoro, I.K., Chukwu, G.O., Okonkwo, J.C. and Olojede, O.A. (2009). Agronomic potentials of defatted Palm kernel Cake in sweet potato production on typic paleudult. Proceedings of the 43rd Annual Conference of Agricultural Society of Nigeria, Abuja. Pp 56-59.
29. Omaliko, C.P.E. (1985). Dung decomposition and its effect on the soil component of a grass land ecosystem. Tropical Ecology. 25: 214-220
30. Omaliko, C.P.E. and Agbim, N.N. (1983). Forage corn response to rice mill waste and fertilizer. J. Environmental Qual 12: 320-324.
31. Prasad, R. and De Datta, S. U. (1979). Increasing fertilizer nitrogen efficiency in wet land rice. Rice Research Institute. Report, Manila, Philippines. pp. 465-484
32. Sridar, M.K.C. (2006). Solid waste management in the 21st century in Nigeria. In proceeding of the fourth annual conference of senate on the Nigerian environment organized at port harcourt by senate committee on environment and ecology, National assembly, July 5-7 Abuja. Pp 1-11
33. Steel, R.D. and Torrie, J.H. (1980). Principles and procedures of ststistics. A Biometric Approach. 2nd edition. McGraw Hill Book Coy, In, N.Y. U.S.A., 663ppt xxi.
