OPTIMIZED INORGANIC FERTILIZER APPLICATION ON SORGHUM YIELD AND NITROGEN USE EFFICIENCIES IN THE NIGERIAN SAVANNA

ABSTRACT
Sorghum (sorghum bicolor (L.) Moench) is an important staple food grain that is grown among smallholder farmers. The yield is low due to inherent low soil fertility because resource poor farmers apply little to no fertilizer to their land due to economic and social factors. The objective of the study was to provide recommendations for optimizing yield and profit from fertilizer use for financially constrained and smallholder sorghum farmers. The treatments consisted of five levels of inorganic N fertilizer (0, 30, 60, 90 and 120 kg N ha^-1), four levels of inorganic P fertilizer (0, 7.5, 15 and 22.5 kg P ha^-1) and four levels of inorganic K fertilizer (0, 10, 20 and 30 kg K ha^-1) and with some diagnostic nutrients. The experiments were laid out in a randomized complete block design (RCBD) replicated three times on-station and fifteen times on-farm. The experiment was carried out in 2015 on smallholder farms in Unguwar Chida, (Zamfara state), Zarewa (Kano state) and IAR experimental farm at Samaru, Kaduna state of Nigerian northern Guinea savanna.Result showed that application of 60 kg N ha^-1,15 kg P ha^-1 and 10 kg K ha^-1 gave the highest grain yield (2567.3 kg ha^-1) at Samaru, 120 kg N ha^-1 and 22.5 kg P ha^-1 had the highest grain yield
 
(2432.1 kg ha^-1) at Unguwar Chida, and 30 kg N ha^-1 and 15 kg P ha^-1 obtained highest grain yield (2181.6 kg ha^-1) at Zarewa. The economically optimal nitrogen rate (EONR) means were 52 to 34 kg N ha^-1 in Unguwar Chida, 45 to 26 kg N ha^-1 in Zarewa and 40 to 2 kg N ha^-1 at Samaru with the fertilizer cost to grain price ratios (CPs) of 2 to 6 across the locations. Mean economically optimal phosphorus rate (EOPR) were 21 to 10 kg P ha^-1 at Unguwar Chida, 20 to 14 kg P ha^-1 and 7 to 5 kg P ha^-1 in Samaru. Agronomic use efficiency decreased with increasing nitrogen rates and were 11.50, 31.10 and 10.08 kg kg^-1 respectively at EONR. Partial factor productivity decreased with increasing nitrogen rate and were 57.91, 65.95 and 61.19 kg ha^-1, respectively at EONR. The optimized fertilizer recommendation per hectare for the sites studied were 78 kg N and16 kg P at Unguwar Chida, 51 kg N and 49 kg P, at Zarewa, and 72 kg N, 23 kg P at Samaru. The use of inorganic fertilizer by smallholder farmers in these regions based on this study was very profitable. Therefore, favourable formulated fertilizers blends and policies that will make available straight fertilizers and these blends available to smallholder farmer should be developed.
CHAPTER ONE
 
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 to smallholder 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:

1. To evaluate the yield response of sorghum to N, P and potassium (K) at the selected sites in the Northern Guinea Savanna of Nigeria.
2. 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.
3. To determine the N use efficiency (NUE) of sorghum at the selected sites in the Northern Guinea Savanna of Nigeria.