Soil Science Project Topics

Evaluation of the Macro-nutrient Status of the Current Field Practical Training (305) Experimental Farmsite

Evaluation of the Macro-nutrient Status of the Current Field Practical Training (305) Experimental Farmsite




The main objective of this research study is basically to evaluate the macronutrient status of the Current Field Practical Training (305) Experimental Farm site soils of the University of Benin (Ugbowo Campus) in Benin City, Edo state in Nigeria. To achieve the main objective; these are the following specific objectives;

  1. Evaluate the macro-nutrients status of the soils on the farm site in the study area.
  2. Ascertain what macro-nutrients is suppose to be sufficient or low for plant growth, survival and optimal yield in the study area.
  3. Quantify the fertility of the soil in the study area.




The macronutrients are essential elements that comprise between 0.1 – 1.0 % of a plant.  They generally are important to the structural molecules of a plant, including carbohydrates, proteins, chlorophyll, cell walls, DNA, RNA, sugar phosphates and phospholipids.

Essential elements used by plants in relatively large amounts for plant growth are called macronutrients. The major macronutrients are nitrogen (N), phosphorous (P), and potassium (K). Calcium (Ca), magnesium (Mg), and sulfur (S) are also macronutrients. All six nutrients are important constituents in soil that promote plant growth. Concentrations of these macronutrients in the soil are generally determined before the site is disturbed in order to complete a site reclamation plan. Knowing the initial macronutrient concentrations of the soil before disturbance can allow reclamationists to ensure that the same concentrations of macronutrients are in the soil after reclamation for revegetation purposes.


Primary (macro) nutrients are nitrogen, phosphorus, and potassium. They are the most frequently required in a crop fertilization program. Also, they are need in the greatest total quantity by plants as fertilizer.

2.2.1    NITROGEN

Nitrogen is important for growth because it is a major part of all amino acids, which are the building blocks of all proteins, including the enzymes, which control virtually all biological processes. A good supply of nitrogen stimulates root growth and development, as well as the uptake of other nutrients. Plants deficient in nitrogen tend to have a pale yellowish green color (chlorosis), have a stunted appearance, and develop thin, spindly stems (Brady and Weil, 1999).


Phosphorus (P) is an essential element classified as a macronutrient because of the relatively large amounts of P required by plants. Phosphorus is one of the three nutrients generally added to soils in fertilizers. One of the main roles of P in living organisms is in the transfer of energy. Organic compounds that contain P are used to transfer energy from one reaction to drive another reaction within cells. The term available phosphorus refers to the inorganic form occurring in soil solution which is almost exclusively ‘Orthophosphate’. This Orthophosphate occurs in several forms and combinations. The phosphate contributions in soil are governed by hydrogenous equilibria in which it takes part. This can be represented as,

Phosphorus absorbed in soil phase ⇌ P in soil solution ⇌ Precipitated P

The phosphorus absorbed by plants from soil comes from the soil solution in which it exists as an inorganic Orthophosphate ion H2PO4, HPO42- and PO43-. The most accessible ion is H2PO4. Adequate P availability for plants stimulates early plant growth and hastens maturity. The quality of phosphorus accessible to the plants is influenced by a series of soil properties. Phosphorous enhances many aspects of plant physiology, including the fundamental processes of photosynthesis, nitrogen fixation, flowering, fruiting (including seed production), and maturation. Root growth, particularly development of lateral roots and fibrous rootlets, is encouraged by phosphorous. Phosphorous uptake by plants is about one-tenth that of nitrogen and one-twentieth that of potassium. According to Tisdale et al (1997), about 50% of phosphorus is found in organic form and decomposition of organic matter produces humus which forms complex with Al and Fe and protect the P fixation.  Its deficiency is generally not as easy to recognize in plants as are deficiencies in many other nutrients. A phosphorous-deficient plant is usually stunted, thin-stemmed, and spindly, but its foliage is often dark, almost bluish, green. Thus, unless much larger, healthy plants are present to make a comparison, phosphorous-deficient plants often seem quite normal in appearance. In severe cases, phosphorous deficiency can cause yellowing and senescence of leaves (Brady and Weil, 1999).




The study was conducted at the Soil Science Field Practical Farm site behind the Faculty of Agriculture, University of Benin. The land is the experimental farm with a gently sloping landscape of about 40. The vegetation of the area includes some vegetable arable crops such as cassava (Manihot utilissima), yam (Dioscorea spp), some vegetable such as pumpkin (Telfaria occidentalis) and grasses (Pernisetum purperum) and citrus. The arable land has been cultivated over the years for about 12-15 years with crops like maize (Zea maize) okra (Abelmiscus esculeutus), bitter leaf (Vernonia amygdaline). Located in the rainforest savanna ecological zone of Nigeria, the land measures an area of 2877.6m2.

3.2       STUDY AREA

The study area covers the current 305 Field Practical Training Farm site of the Faculty of Agriculture, University of Benin (Ugbowo), Benin City in Nigeria.  Five locations on the sparse vegetation namely; Mimosa pudica, banana plantation, pineapple plantation, sugar cane plantation and Elephant grass were selected for the study. Five soil samples were collected and five different composite samples (0-15 cm) for the five locations each were bulked into five. Soil samples were air dried, processed to pass through 2 mm sieve mesh and analyzed for pH, EC, OC and chemical properties of macronutrients as per standard methods (Chopra and Kanwar, 2005). Organic carbon, available nitrogen (0.32% alkaline KMnO4) c phosphorus (0.5M NaHCO3), potassium (1 N neutral ammonium acetate extractable),sodium and calcium by Flame Photometer and sulphur (turbidimetric method) were determined following the methods described by Page et al., (1982). The simple correlation analysis of data was computed in relation to available nutrient contents with chemical properties of the soils under study.



The basic reason for a soil test/analysis is to accurately determine the available nutrient status of the soil and to clearly indicate to the farmer the seriousness of any deficiency. The analysis was used to determine the true value of the soil under investigation. For this reason, the chemical properties are discussed below.  The soil characteristics studied are those require for the evaluation of the macro-nutrient status of the soils in the study area, the results are given below in Table 1.


The soil is a chemical entity. All the materials there are chemical substances. Soils are composed of solid, liquid and gas; soluble and insoluble; organic as well as inorganic substances. There are ions and compounds, salts, acids, bases, minerals, and rock fragments. There are also colloids which are very active chemically. Soil pH is probably the most commonly measured soil chemical property and is also one of the more informative. One of the most important chemical characteristics of a soil is its pH which shows whether a soil is acidic, neutral or basic and it has a lot to do with solubility of various compounds; the relative bonding of ions to various exchange sites and the activities of various microorganisms. It is important to note that soil pH ranges are particularly in formative because it is a determinant factor in determining the solubility of the elements which tends to equilibrate with a solid phase and the solubility of the oxides of Fe and Al are directly dependant on the hydroxyl ion (OH-) concentration and increases as pH decreases.




Growing concerns about environmental pollution by excessive use of fertilizers have led to increasing needs to monitor soil nutrients required for crop growth. Traditionally, such measurements have been carried out in a central laboratory, involving time-consuming sampling, transportation and storage steps. On-site monitoring of N, P, and K nutrients is preferable due to the potential for a higher density of measurements at a relatively low cost, allowing more efficient mapping of soil nutrient variability for variable–rate nutrient management.

Over the years, there has been a continuous cropping on the experimental farm, based on this fact, the nutrient status of the top soil has been altered following the result from the chemical analysis and therefore is of great concern to both the famer. Owing to the fact that the farm is located on a rainforest zone, some of the elements may have been leached due to heavy downpour (erosion). However, the low pH has reduced the activities of N-fixing bacteria, microbial activities in the soil.

From the chemical analysis carried out, it can be concluded that some correlation existed between the soils irrespective of the different soil samples and results showed that the land is not alive.

5.2 Conclusion

Considering the critical limit of macronutrients, the recorded macronutrients N, Ca and K are low and high in P (20.2mg/kg).The results indicated that the soil properties pH, EC, and OC are the main characteristics playing major role in controlling the availability of macronutrients. These factors could be manipulated in order to combat any present or future deficiencies of macronutrients in these soils.

The results also show that the soils are low in nutrient status. Therefore, a careful management of the soil chemical properties through studies of fertilizer trial soil and plant analysis, nutrient deficiency symptoms, soil water relation and studies of other cultural practices like cover cropping and intercropping are required in order to maximize the productivity of the soils and to ensure that the desirable soil characteristics are maintained over a long period of time.


The experimental plots should be left to fallow more for a period of 2-4years for the soil to regain lost nutrient thereby increasing soil productivity and microbial activities.

  • Organic manure should be incorporated into the soil to boost the nitrogen availability.
  • Fertilizers especially nitrogen sources should be applied in splits to reduce the amount of nitrogen being leached from the soil.
  • No-till farming should be employed on the land so as to reduce adverse effect of inter-rill erosion.
  • There should be a reduction in the use of NPK fertilizers on the experimental farm.
  • Cover crops should also be planted on the feed to ensure that the farm restores its lost nutrients.


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