Field and greenhouse experiments were conducted at the University of Nigeria, Nsukka, in 2011, to examine the effects of lime, poultry manure and NPK 15-15-15 on the soil nutrient content and yield of maize. The experiment was first carried out in the greenhouse and later evaluated in the field. The experimental designs used were 6 x 4 factorial in completely randomized design (CRD) and randomized complete block design (RCBD) for the greenhouse and field experiments respectively. Two factors were considered in the experiments. Factor A: different fertilizer rates and their combinations viz: T1 (200 kgha-1NPK + 6 tha-1 PM), T2 (300 kgha-1NPK + 4 tha-1 PM), T3 (400 kgha-1NPK + 2 tha-1 PM), T4 (400 kgha-1NPK only), T5 (8 tha-1 PM only), T6 (Control; no fertilizer application). Factor B: liming levels: pH 6.0, pH 6.5, pH 7.0 and pH 5.5 (control). Maize plant was used as a test crop. In the greenhouse trial, among the six treatments applied, T5 (8 tha-1 PM only) had significant (P < 0.05) effect on soil available P, soil pH, cation exchange capacity and exchangeable magnesium but not on other parameters measured. For the field evaluation, treatment T1 had significant (P < 0.05) effect only on soil aggregate stability but not on mean weight diameter (MWD), aggregate stability (AS), bulk density, total porosity and hydraulic conductivity. Also this treatment had significant (P < 0.05) effect on the soil nutrient contents than other treatments applied. This was similar to that obtained from the greenhouse trial. Soil limed to pH 7.0 significantly (P < 0.05) decreased the soil acidity and increased the exchangeable calcium. A combination of NPK and poultry manure at various rates had better effects than either sole application of NPK or poultry manure on maize parameters measured namely: plant height, leaf number, leaf area index, tasselling number, cob weight, chaff weight, and dry matter. Similarly, liming the soil to different pH levels had significant (P < 0.05) effect on maize plant performance. The highest plant physiological parameters were obtained from the soil limed to pH 7.0 while soil limed to pH 6.0 gave the least plant parameters. The order of performance was as follows: soil limed to pH 7.0 > pH 5.5 (control) > pH 6.5 > pH6.0 in plant parameters namely plant height, cob weight, tasselling number, and seed weight. From the study, soil of pH 5.5 with the application of 200 kgha-1 NPK + 6 tha-1 or 8 tha-1 PM only is recommended for maize production.
Soil fertility decline is one of the acute problems facing farmers in the world and Nigeria in particular. The constraints to food security and widespread poverty, as they affect development and livelihoods, are well known even in Sub-Saharan region of Africa (SSA), where population growth at 3% supersedes agricultural production rate of 2% per annum (Bationo et. al, 2006). Although the causes of food insecurity and poverty are numerous, the decline in soil fertility with resultant decreasing crop yields is severally highlighted and stressed (Sanchez et. al, 1997; Smaling et. al, 1997; Bationo et. al, 2006).
In Nigeria, the practice of shifting cultivation which was one of the effective methods of overcoming the problem of poor crop yield due to decline in soil fertility has virtually disappeared. This could be linked to the increasing population explosion and the stiff competition for land space by other land uses (Hati et. al, 2005). According to Ayoub (1994), population explosion added to the increased continuous farming on the available land by farmers who often do not add adequate soil nutrient supplements (organic and inorganic fertilizers) to beef up soil fertility and increase yield.
Makinde et. al, (2001) reviewed that decline in soil fertility is a fundamental impediment to agricultural growth and food production. According to them, crop production in the past relied on shifting cultivation to maintain the fertility and productivity of the soil through organic matter build up during a long fallow period. This practice enabled farmers to produce substantial crop yield over a period even without adding external inputs. Okalebo et. al, (2009) observed that decreases in available nitrogen and phosphorous are among the most severe nutrient problems in the tropics.
To cope with these problems, there has been an increase in the use of inorganic fertilizer mostly ammonium sulphate ((NH4)2SO4) fertilizer. The continuous use of the mineral fertilizers resulted to increase in acidity of such soils. Researchers have shown that pH decline occurs more rapidly in continuously cropped lands and soils tend to acidify over time particularly when large application of ammonium-based fertilizers and urea-based fertilizers, [Co(NH2)2] are used.
Soil acidity is a major problem in crop production in the tropics. This is especially so in more than 90% of soils in the agroecological zones in Nigeria (Enwezor et. al, 1990). The problems of soil acidity are very prevalent in southeastern Nigeria where coarse sedimentary parent materials had undergone earlier cycles of weathering before deposition (FDALR, 1990).
According to Ohiri and Ano (1989) the acidic nature of the soils in Southeast Nigeria are due to their parent materials, leaching and degradation in soil physical properties. In acid soils, there are problems of both plant nutrient deficiencies and toxicity of three elements (Aluminum, Manganese, and Hydrogen). Plant growth, especially root growth, in acid soils is retarded by toxicity of Al, Mn, and H. The degree of toxicity depends upon how high the concentration of soluble or exchangeable Al3+ is and how low the pH is (Crawford et. al, 2008).
Soil acidity can also reduce the availability of phosphorous by forming insoluble compounds when combined with Fe and Al oxide at pH < 5.0. Thus, due to the increased acidity of the soil, inorganic phosphorous applied to the soil becomes fixed or immobilized (Tinker and Nye, 2000). Chude et. al, (2004) reported that soil acidity is one of the major constraints to crop production in humid tropical region. This according to them, it is due to the usual accompanying effects of aluminum and manganese toxicity and nutrient deficiencies and their consequential effects on crop growth and yield. Soils with pH <5.5 have high exchangeable aluminium and outright toxicity to most crops (Carver and Ownby, 1995). According to Atiwag (1992), the way of improving crop output from such soils include application of nitrogenous and phosphatic fertilizers, liming and addition of organic manure.
Soil acidity can affect plant growth directly and indirectly by affecting the plant-availability of nutrients, levels of phytotoxic elements, microbial activity, and other soil properties. Soils may become acidic in the long term as a result of several natural processes. In the short term, however, soil acidity develops mainly due to application of N fertilizers, primarily those having high concentrations of ammonium or urea because nitrification releases hydrogen (H) ions. To make soils less acid, it is a common practice to apply a material that contains calcium and/or magnesium oxides or carbonates.
Liming has long been recognized as an important way of ameliorating soil acidity. Soils are limed to reduce the harmful effects of low pH, aluminium and manganese toxicity by adding calcium and magnesium to the soil. The amount of lime needed to achieve certain pH depends on the pH of the soil and its buffering capacity which is related to the C.E.C of the soil. Lime applied to acid soils raises the pH of soils, resulting in enhanced availability of nutrients, such as P, Ca, Mg, Mo etc. and improved crop yields (Nekesa, 2007; Kisinyo et. al, 2009).
According to Osodeke (2000), women used lime as a source of soil amendment to improve the fertility of their farms and also as liming material to reduce the acidity of the soil. Lime is an additional purchase for farmers; who seek good return for their investment by using a product that is fast-acting and which has benefits for both crop yield and soil properties. Farmers appreciate the important value of lime and manure application but they seldom apply them at the recommended rates and at the appropriate time because of the high cost, lack of credit facilities, inefficient distribution and poor delivery system (Ayoub, 1994).
Most of the results of the field trials across the ecological zones of the country have clearly brought out the fact that neither organic fertilizer nor the mineral NPK fertilizer alone can achieve the desired soil fertility level needed for optimum crop production. The use of both inorganic and organic fertilizers often results in improving efficiency of nutrients and water use (Onwueme and Sinha, 1991). Onwuka (2008) reported better performance of organic –inorganic fertilizer combination than either farmyard or inorganic fertilizers.
The main objective of this work was to evaluate the effect of lime and different combining levels of organic and inorganic fertilizer on soil physicochemical properties and maize yield.
The specific objectives were to determine:
- the effect of different levels of poultry manure combined with NPK fertilizer and lime on some physicochemical properties of the soil
ii. the lime rate(s) required for optimum maize performance in an Ultisol, Southeastern Nigeria. the effect of poultry manure, NPK fertilizer and their combination on maize performance.