CHAPTER ONE
INTRODUCTION
1.1 Background Information
Too much overuse of inorganic fertilizer has led to low soil pH which reduces the availability of essential nutrients to the plants (Mokaya 2016, Singh et al., 2015; Cheng-Wei Liu et al., 2014). This results in low rates of decomposition of organic matter. It also leads to depletion of micronutrients leading to the production of food of low quality nutritionally (Rashid et al., 2016; Brar et al., 2015). Unless the problem is addressed, the soil will eventually become unproductive. The organic matter is a necessity to increase buffering capacity of the soil and also releases nutrients to the plant. The soil pH is increased by liming, which is an expensive exercise and does not add fertility to the soil. There is a need for an alternative method to the application of inorganic fertilizers and liming materials.
The increased human population has not only increased overuse of the land but also has resulted in low yields leading to encroachment of forest cover, which, in turn, leads to reduced rainfall (Liu et al., 2017; Kitula et al., 2015). Therefore, there is need to look for an alternative to inorganic fertilizers that can also increase the forest cover.
The application of mineral fertilizers alone in rehabilitating degraded soils have yielded limited success in farming even when they are available and affordable to farmers (Schröder et al., 2018; Goulding et al., 2016). Organic nitrogen and phosphorus owing to their biogenic origin (Kiyoshi et al., 2017; Kopytko et al., 2017) have the virtue of being released slowly and steadily (Kopytko et al., 2017) to meet the nitrogen demand of crops at all stages of growth. This is opposed to nitrogen in soluble mineral fertilizers is released rather fast and that a part of it may be lost through leaching especially if the rate of release transcends plant uptake. Duong (2013) and Masunga et al. (2015) noted that composts made from organic wastes supply plant nutrients in a slow pattern. When applied in farms, they increase soil organic matter and slowly release organic nutrients as well as preventing luxury consumption (Bley et al., 2017). While examining the suitability of corn-cob compost on plants in acid red soil, Mutezo (2013) reported that composts are suitable in mitigating adverse effects that result harvest loss due to acidity. Successful application of organic manures has prompted more research to be conducted in order to come up with the organic nutrient sources to supplement or even be superior the expensive mineral fertilizer formulations used in crop production. This study therefore wants to investigate the effect of a combination of inorganic fertilizers and organic manure (composted rice straw) on soil health and tomato yield.
1.2 Problem Statement and Justification
Continuous cultivation of diminishing farms to feed the growing population has resulted in soil degradation and consequently a rise in use of inorganic fertilizers to increase crop yield. Inorganic fertilizers tend to change soil pH if applied for a long period since they are acidic in nature (Goulding et al., 2016). The lowering of soil pH has negative effect on the growth of the plants and soil organisms and, therefore, reduces expected yields. This is because the acid deposition leads to leaching of essential nutrients such as potassium (Duan et al., 2016; Goulding et al., 2016). The inorganic fertilizers are expensive and hence out of reach to most rural farmers, majority of whom are women. In addition inorganic fertilizers are not always available, especially subsidized ones which results in late planting and thus poor yields. Studies of composted rice straw have been shown to increase soil pH and crop biomass possibly due to availability of nutrients (Wiklund, 2017; Carter et al., 2013).
Research Objectives
1.3. 1 General Objective
To investigate the effects of a combination of composted rice straw and inorganic fertilizer on soil health and tomato yield
1.3.2 Specific objectives
- To determine the effect of composted rice straw and inorganic fertilizer on soil health.
- To investigate the effects of the leaf extracts of Composted rice straw and inorganic fertilizer on the yield of tomatoes.
- To determine the effect of Composted rice straw and inorganic fertilizer on nitrogen, phosphorus and potassium levels in the soil.
1.4 Hypotheses
- There is decrease in acidity in the soils treated with Composted rice straw and inorganic fertilizer.
- There is significant effect on the growth rate and productivity of tomatoes due to treatments with Composted rice straw and inorganic fertilizer.
1.5 Significance of the Study
This study sought to know if a combination of composted rice straw can be substituted for fertilizer. A positive result will enable poor farmers to improve tomatoes growth rate and boosts its nutritional value thus generating income.
1.6 Scope of the study
This study is focused on examining the effect of a combined application of composted rice straw and inorganic fertilizer on soil health and tomatoes yield. The study will be limited to the confines of the University of Port Harcourt, all experiments will be conducted within the premises of the University.
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