NITROGEN MANAGEMENT OPTIONS FOR IRRIGATED AND RAIN-FED RICE (Oryza sativa L.) VARIETIES IN SUDAN SAVANNA OF NIGERIA

ABSTRACT

Rice is one of the main staple food crops and its demand is rapidly increasing in West Africa, hence there is need to increase its production at lower production costs through adequate N management with appropriate varieties.Nitrogen (N) management is one of the key inputs in rice production, especially in the savanna soils which is usually associated with widespread N deficiency. The focus of this research was to evaluate the performance of rice under different N fertilizer management options. Field experiments were conducted in 2012 and 2013 at the research farm of the Institute for Agricultural Research, Talata Mafara (irrigated) and Kadawa (rain-fed). The treatment combinations included two granular forms of N as Urea Super Granule (USG) and Granular Urea (GU) at different rates [0, 45.1, 72.2, 117.3 kg N/ha and a rate based on leaf colour chart (LCC)] with three varieties of rice (FARO 55, FARO 57 and FARO 52) as the test crops. The experimental design was Randomized Complete Block Design (RCBD) and replicated thrice. The second phase of the study involved the use of Quantitative Evaluation of the Fertility of Tropical Soils (QUEFTS) model to simulate rice performance as a decision support tool for site-specific fertilizer recommendation in the study areas. Crop growth attributes generally increased with increased N application for both USG and GU, but with delay in days to heading. Application of USG at 117.3 kg N/ha significantly (p<0.01) increased yield and yield attributes, except for grain-, phosphorus- and potassium- harvest indices where application of GU based on LCC gave the highest values. Interaction between N management and varieties indicated that application of USG at 117.3 kg N/ha on FARO 52 resulted in significant rice yield increase.Paddy yield was highly and positively correlated with total biomass (r= 0.883**), straw yield (0.733**), dry matter (0.351**), plant height (0.158**) and N uptake (0.701**); but weak and non-significant negative relationship existed between soil pH (- 0.021) and available P (- 0.055). The indigenous soil nutrients supplies (INS, IPS and IKS) were 25.26 –94.50 kg N ha-1, 5.78 – 28.84 kg P ha-1and 47.48 – 156.30 kg K ha-1with fertilizer recovery fractions of 0.25 – 0.61, 0.09 – 0.48 and 0.27 – 0.69 for N, P and K respectively at both locations. The recommended fertilizer dosage modeled by QUEFTS were 104 – 140 kg N ha- 1, 69 – 94 kg P ha-1 and 23 – 46 kg K ha-1for dry season (Talata Mafara) and 92 – 130 kg N ha-1, 34 – 56 kg P ha-1 and 10 – 19 kg K ha-1 for wet season (Kadawa). It was higher than the conventional „blanket fertilizer‟ rate recommended over the years. The model also recommends higher N with lower K for FARO 55, but lower K for FARO 57 and FARO 52; thereby advocating for site specific nutrient management (SSNM) through the use of different fertilizer combinations for different soil conditions. Field validation of the QUEFTS model showed a good agreement between observed and simulated yields (R2 = 0.85, RSME = 0.93, RSMEn =< 30% and d-stat = 0.71), thus confirming better performance of QUEFTS in the rice ecosystem under different nitrogen regimes. Partial economic analysis of rice production at both locations revealed that application of USG at 117.3 kg N/ha with FARO 52 gave the highest gross margin of ₦237,907.22k/ha and a profit of ₦2.81k per naira invested. Results obtained from this study revealed that FARO 52 using USG had better paddy yields and highest NUE.Further studies are also required to establish the appropriate use of leaf colour chart in the study areas.

CHAPTER ONE

Rice (Oryza sativa L.) is the main food crop of an estimated 40% of the world‟s

population (Liu, 2013; FAO, 2008). The World‟s more than three billion people

depend on rice as their staple food and the demand for rice is rapidly increasing in

West Africa (FAO, 2003). Manypeople in the major rice consuming countries are

living at sub‐optimal nutritional levels, there is need to increase rice productionby

as much as 70% in order to raise nutritional levels to satisfy current dietary needs

(Greenland, 1997).Annually, about 5 million metric tons of rice is consumed in

Nigeria and over 80% is imported costing the country a humongous amount of

money (Onu et al., 2015).Local productionis low and efforts to increase production

are hindered by high input costs, low prices for riceespecially under rain-fed conditions. Fertilizer nitrogen (N) has become one of the key inputs in food production and despite numerous research investigations; our understanding of N management for rice grown under diverse agro-ecological situations is still inadequate. Cereals

including rice, wheat and maize, accounts for more than half of the total fertilizer N used in the world. Research has also shown that about 50 – 70 % more cereal grain will be required by 2050 to feed over 9 billion world population (Yadvinde-Singh et al., 2011) and this will further increase demand for fertilizer N at greater magnitude