ABSTRACT

This experiment was conducted at experimental field of Faculty of Agriculture, University of Benin, Benin-City, during 2014 growing season. A 3x4 factorial experiment in randomized complete block design with 3 replications was used to study effect of defoliation and NPK fertilizer on yields of maize. Factors were three defoliation levels, No defoliation (D0), defoliation above ear (D1), defoliation below ear including the ear leaves (D2) and four fertilizer rates (0, 300, 400 and 500 kg/ha). Parameters measured were ear diameter, No. of harvested ear, ear weight, ear length, cob diameter, No. of kernel row/ ear, No. of kernel row, 100 seed weight, grain yield, % germination ( laboratory and field ), radical length, shoot length and Ogi yield. The results showed that defoliation had significant effect on ear diameter, ear weight, number of kernel per ear, grain yield, seedling dry weight and “Ogi” yield. Defoliation reduced ear weight (D1 26% and D2 14.68%), grain yield (D1 26.79% and D2 13.32 % ) and Ogi (D1 26.78% and D2 9.93 %). NPK application showed significant effect on ear length, ear weight, number of kernel, grain yields and “Ogi” yield. Defoliation effect was more severe on plants defoliated above the ear. This suggest that top leaves should not be defoliated as above leaves transferred more of their assimilates to the ear. Fertilizer application failed to ameliorate the effect of the imposed defoliation.

CHAPTER ONE

INTRODUCTION

Maize (Zea mays L.) is a member of the grass family (Poaceae). It originated from South and Central America. It was introduced to West Africa by the Portuguese in the 17th century. In the world agricultural economy, maize is one of the important crop as it has higher yield potential than any other cereals and it is often referred to as “miracle” crop or the “queen” of cereals (Iken and Amusa, 2004). Maize is grown both as food for man and feed for animal. Maize can be consumed maize as a starchy base in a wide variety of porridges, pastes, grits and beer. Green maize (fresh on the cob) is eaten parched, baked, roasted or boiled and plays an important role in filling the hunger gap after the dry season (Agbato, 2003). Many agro-based industries depend on maize as raw material for their production (Iken and Amusa, 2004). 

Photosynthesis is one of the important biochemical processes which take place in chloroplast of leaves. It is the ability of green leaves only to utilize the energy of light to produce carbon containing organic material from stable inorganic matter by photosynthesis process. Photosynthesis efficiency depends on light interception by canopy of leaves which is strongly influenced by size, angle and orientation of leaf area (Erbas and Baydar, 2000). One of the most important factors affecting yield and its components is assimilate availability and allocation to reproductive structures, which is primarily determined by leaf area, photosynthetic activity and the number of competing sinks (Mauney et al., 1978). The reduction in the photosynthetic activity of a plant due to loss in leaf area could result in yield loss. The loss in yield varies depending on the variety, stage of growth of the crop and the intensity of leaf loss.

Defoliation, or leaf damage, such as that associated with hailstorm, frost, wind, disease crop protection chemicals vegetation eating animal and insects, can influence pollination and subsequent grain production (Hassan, 2012). Defoliation treatments decreases assimilate availability during grain filling leading to low productivity (Mauney et al., 1978). Grain yield is strongly depended on leaf area index, (LAI), leaf area duration (LAD) and leaves efficiency for absorption of solar radiation for photosynthesis process (Mouhamed and Ouda, 2006). Defoliation reduced crop yield due to reduced photosynthetic capacity leading to reduced production of assimilate (Erbas and Baydar, 2000). Luzuriaga et al. (2006) reported that in Sinapis arvensis, addition of nitrogen to maternal environment reduced germination rate of seeds. In other research, seed germination percentage reduced due to increasing maternal nutrient and light levels (Galloway, 2001). In Vicia sativa, seeds produced by plants in different defoliation treatments had similar germination percentage and germination time (Koptur et al., 1996). Maturity in maize was significantly affected by defoliation treatments and soluble-solid content in the stem reduced quickly after leaf removal (Tollenaar and Daynard, 1987).

Adequate fertilizer application can go a long way to ameliorate the effect of leaves defoliation on the crop production. Plants showed responses to growth and yield in soils treated with fertilizers (FAO,2004).

The role of fertilizer application should be emphasized in development of crops in Nigeria (FAO, 2004). Maize requires a lot of nutrient for proper growth and yield. Generally, an application of 15:15:15 compound fertilizer at the rate of 300 kgha-1 should be made at sowing time and at 6 weeks after sowing (Agboola, 1982; Agbato, 2003). 

The objectives of this study are:

To evaluate the effect of defoliation on yield of maize. 

To determine the effect of NPK fertilizer on defoliated maize.