Thesis Abstract

Abstract
In the Nigerian savanna, sorghum is a vital cereal crop that plays a significant role in food security and economic stability. However, the productivity of sorghum is often limited by low soil fertility, particularly nitrogen deficiency. Inorganic fertilizers have been widely used to enhance crop yields, but there is a need to optimize their application to improve sorghum production and nitrogen use efficiencies in this region. This research project aimed to investigate the effects of optimized inorganic fertilizer application on sorghum yield and nitrogen use efficiencies in the Nigerian savanna. A field experiment was conducted over two growing seasons to evaluate the impact of different fertilizer rates and application methods on sorghum growth, yield, and nitrogen uptake. The treatments included varying levels of nitrogen fertilizer applied at planting and top-dressed at different growth stages. The experimental design was a randomized complete block design with three replications. The results revealed that optimized inorganic fertilizer application significantly influenced sorghum growth and yield parameters. The sorghum plants treated with the recommended fertilizer rate exhibited improved plant height, leaf area, and biomass production compared to the control and suboptimal fertilizer treatments. Furthermore, the application of nitrogen fertilizer at critical growth stages such as tillering and flowering resulted in higher grain yields and nitrogen use efficiencies. Nitrogen use efficiency indicators, such as agronomic efficiency and recovery efficiency, were markedly higher in sorghum plants that received optimized fertilizer treatments. The findings suggest that proper timing and dosage of inorganic nitrogen fertilizer application are crucial for enhancing sorghum productivity and nitrogen utilization in the Nigerian savanna. Moreover, the study highlights the importance of site-specific fertilizer recommendations to maximize crop yields while minimizing environmental impacts. In conclusion, optimized inorganic fertilizer application significantly enhances sorghum yield and nitrogen use efficiencies in the Nigerian savanna. By fine-tuning fertilizer rates and application methods, farmers can improve sorghum production sustainably while ensuring efficient use of nitrogen resources. This research provides valuable insights for developing nutrient management strategies tailored to the specific needs of sorghum cultivation in the region.

Thesis Overview

1.0 INTRODUCTION

Sorghum (Sorghum bicolar (L.) Moench) is an important staple food grain among many smallholder farmers of the Nigerian savanna (Ofor et al., 2009). It occupies about 44% of the total land area devoted to cereals in Nigeria (Ajeibe et al., 2010). The land area put into cultivation of sorghum in Nigeria is 6.7 million hectares (FMARD, 2012b).

Decline in yield has been identified as major constraint to sorghum production. Average yield is estimated at 0.6-1.7 tons per hectare against potential yield of 4.0-5.0 tons per hectare of sorghum (FMARD, 2012b). The yield gap is attributed to poor inherent soil fertility and low fertilizer use. (Vanlauwe and Giller, 2006). Smallholder farmers apply little to no fertilizer to their land due to socioeconomic factors including timely access to fertilizer (SSA-CP, 2005). Improper types of fertilizers, ineffective extension system and inappropriate fertilizer recommendation which limit the efficiency of fertilizer use reduce farmer‟s income and increase poverty and food insecurity in the Northern Guinea Savanna of Nigeria (SSA-CP, 2005).

Nitrogen use efficiency (NUE) is important in developing fertilizer recommendations for profitability and environmental sustainability (Kaizzi et al., 2012). Low nitrogen use efficiency in crop production is due to excess application of N. Deficiency of phosphorus (P) and other essential nutrients limit crop growth due to biotic and abiotic factors (Bekuda et al., 2007; Kaizzi et al., 2012). Several attempts to provide fertilizer recommendations tosmallholder farmers often lead to inappropriate fertilizer rates that lower the NUE of crops.

1.1 Justification of the Study

Current fertilizer recommendations are aimed at maximizing yield rather than profit. The fertilizer rate needed to maximize net returns is a function of fertilizer cost relative to grain prices as the fertilizer prices increase relative to the prices, the economic optimal rate (EOR) is expected to decrease. Therefore, they need to maximize net returns for a given amount of money they have to invest in fertilizer which can be maximized by identifying the right combinations of nutrient, and application rate that will give highest value to cost ratio (VCR).

1.3 Objective of the Study

The general objective of this study was to provide recommendations for optimizing crop yield and profit from fertilizer use for financially constraint and small holder sorghum farmers in the northern guinea savanna zone of Nigeria. The specific objectives are:

• To evaluate the yield response of sorghum to N, P and potassium (K) at the selected sites in the Northern Guinea Savanna of Nigeria.

• To determine the economically optimal nutrient rate for N, P and K and the corresponding value to cost ratio (VCR) at different fertilizer cost to grain price ratio.

• To determine the N use efficiency (NUE) of sorghum at the selected sites in the Northern Guinea Savanna of Nigeria.