Yield andGrowthResponse ofMaize (Zeamays L.) to Varietal and Nitrogen Application in the Guinea Savanna Agro-Ecology of Ghana

Background and Objective. Maize is one of the oldest cultivated crops. It is the third most important cereal after wheat and rice globally. Compared to all other cereals, maize has the highest average yield per unit area. (e objective of the research was to evaluate maize varietal response to different nitrogen fertilizer rates. Materials and Methods. (e treatment consisted of two factors, namely six varieties of maize and four levels of nitrogen application rates. (ese were arranged in 6× 4 factorial combinations and laid out using randomized complete block design (RCBD) with three replications. (e data collected were subjected to combined analysis for variation in factorial experiments in RCBD using Genstat statistical package edition 18. (e means were separated using Duncan’s multiple range test at a 5% probability level. Results. (e study revealed that varieties, such as IWD-C3-SYN-F2 and OBATAMPA, produced the highest grain yield and growth parameters (agronomic traits) relative to other varieties. (e maximum grain yield and biomass production also occurred at the nitrogen application rates of 90 and 120 kgN/ha. Conclusion. Varieties, such as IWD-C3-SYN-F2 and OBATAMPA, and N rate of 90 kgN/ha are, therefore, recommended to be used for maize production by the resource-poor farmers in the Guinea Savanna Agro-Ecology of Ghana.


Introduction
Maize or corn (Zea mays L.) is a plant belonging to the tribe Maydeae of the grass family Graminae (Poaceae). It is a native of Southern Mexico [1]. Maize is a versatile crop grown over a range of agroclimatic zones [2]. e genus Zea (Zela) was derived from an old Greek name for food grass. e genus Zea consists of four species of which Zea mays L. is economically important. e other Zea species, referred to as teosintes, are largely wild grasses native to Mexico and Central America [2]. e number of chromosomes in Zea mays is 2n � 20. Maize is a tall, determinate, and monoecious plant. e plant has separate staminate and pistillate flowers on the same plant. It is an annual C 4 plant varying in height from 1 to 4 m [3]. Maize is generally a protandrous plant, i.e., the maize flower matures earlier than the female.
According to [4], maize ranks third globally in the area and total production after wheat and rice. Maize remains an essential cereal crop and is a polyvalent seed. A large percentage of maize produced in Africa is utilized for household consumption even though it is progressively used for feeding animals [5]. In Northern Ghana, maize stovers are used as fuelwood [6], and for several decades, maize has been used as an industrial raw material from which products, such as cornflakes, oil, jam, alcohol, and paper are produced. e current area planted to maize in Ghana stands at approximately 1 million ha. e per capita consumption of maize in Ghana is estimated at 44 kg/person/year, and the national demand is forecast to grow at approximately 1.83% per annum [7]. It is an important cereal produced in all five agroecological zones of Ghana. ese include forest, Guinea savanna, coastal savanna, transitional zone, and Sudan savanna [8]. e Guinea and Sudan savannas, however, have the highest potential for increased maize production and productivity because of high solar radiation, low night temperatures, and low incidence of diseases [6]. Maize is one of the country's major food security crops. It also remains Ghana's most consumed cereal crop with surging production since 1965 [9]. Maize is largely the utmost prudent cereal crop in Ghana, and it is cultivated largely by rural and peri-urban farm families and resource-poor smallholder farmers [10]. It is extensively eaten nationwide and is Ghana's second most essential staple food after cassava [11]. e maize crop, however, has a minimum stress tolerance among the three main cereal crops [12].
Maize production in Ghana is bedeviled with problems of soil degradation, low soil nutrient levels (particularly nitrogen and phosphorus), inappropriate fertilizer application, leaching of soil minerals, and bush burning. It has been the major cause of the low yield of maize in the guinea savanna agroecology of Ghana [13]. e average maize grain yield is approximately 1.7 tons/ha as against an estimated achievable yield of approximately 6.0 tons/ha [14] as a result of low nitrogen and phosphorus levels in the soil, inappropriate fertilizer application, drought, and Striga infestation [15]. Nitrogen is an essential part of chlorophyll [16] and also forms a significant unit of many enzymes, nucleic acids, and proteins. erefore, the deficiency or overapplication of nitrogen affects maize yields negatively [17]. An optimal nitrogen application enhances the protein content aside from the resultant significant increase in the yield of the maize crops [18]. Nitrogen deficiency stems from low crop development, which reduces the crop yield, leaf area, leaf number, and photosynthetic rate. To boost the productivity of the maize crop, various nitrogen fertilizer application regimes need to be critically examined to determine the optimum N application rate for increased maize grain production. e objective of the study was to examine the varietal response of maize to different nitrogen fertilizer application rates.

Experimental Area.
e studies were conducted at Nyankpala in the Northern Region of Ghana during the 2016 and 2017 cropping seasons. e experimental site has tree and weed species, such as Neem tree (Azadirachta indica), Shea tree (Vitellaria paradoxa), Dawadawa tree (Parkia biglobosa), Teak (Tectona grandis), Broom weed (Sida acuta), Spear grass (Imperata cylindrica), Pigweed (Boehevia difusa), and Andropogon gayanus [19]. e soil in the area is of the Nyankpala series and is mainly made up of sand and loam. Rainfall, temperature, and relative humidity distribution in the area during the field studies were as shown in Tables 1-3. e rainfall, temperature, and relative humidity data were taken at the agrometeorological station of the CSIR-Savanna Agricultural Research Institute.

Soil Analysis.
Before planting, the soil samples were arbitrarily collected from four different cores from 0 cm to15 cm for the determination of soil physical and chemical properties using a soil auger. e results from soil analysis indicated that the soils at the experimental site were largely Sandy loam and classified as Ferric Acrisol, equivalent to Typic Haplustult in the USDA soil classification system. e soil pH was 6.5 with very low nitrogen and organic matter content. e result of the initial soil analysis is presented in Table 4.

Land Preparation, Planting, and Experimental Design.
e experiments were conducted at the experimental field of the CSIR-Savanna Agricultural Research Institute (SARI) at Nyankplala in the Northern Region of Ghana. In each of the experimental year, the land was prepared by ploughing, after which all debris was removed. Land demarcation was done using lining and pegs. e prepared land was leveled using a hoe before the seeds of the genotypes were planted. Six maize varieties obtained from the Savanna Agricultural Research Institute (SARI) of the Council for Scientific and Industrial Research (CSIR) were screened under four nitrogen fertilizer application rates for improved grain yield, yield components, and other growth/agronomic characteristics during the 2016 and 2017 cropping seasons under field experimental conditions. e treatment consisted of two factors, namely six varieties of maize and four levels of nitrogen application rates.
e six varieties used for the study were TZE-W-DT-STR-C4, IWD-C3-SYN-F2, GH120 DYF/D POP, OBA-TAMPA, DT-STR-W-C2, and COMP 1 SYN. e four nitrogen rates used for the study were 0 kg N/ha, 60 kg N/ha, 90 kg N/ha, and 120 kg N/ha. ese were arranged in 6 × 4 factorial combinations and laid out using randomized complete block design (RCBD) with three replications. e control plants (0 kg/ha N) did not receive nitrogen fertilizer. e furrows between the blocks/replications were 1.5 m, while a 1 m space was left in between the plots. A plot size of 6 m × 4 m was used with a planting distance of 75 cm × 40 cm. Planting was done in July 2016 and 2017. ree seeds per hill were planted and later thinned out to two per hill after germination. e plant populations for all plots were 66,666 plants/ha.

Effect of Variety on Growth Parameters
3.1.1. Leaf, Shoot, and Biomass Production. e data for the two seasons were combined and analyzed, and the results indicated that the variety GH120 DYF/D POP produced the lowest number of 11 leaves, while OBATAMPA produced the highest number of 14 leaves (Table 5). ere were significant differences (p < 0.05) between OBATAMPA and GH120 DYF/D POP with respect to leaf production (Table 6). COMP 1 SYN recorded the highest plant height of 181 cm whilst TZE-W-DT-STR-C4 recorded the least plant height of 121 cm. ere was a significant difference (p < 0.05) between COMP 1 SYN and TZE-W-DT-STR-C4 for shoot production. e total biomass production was the highest in OBATAMPA (13,500 kg/ha). However, this was not significantly different (p > 0.05) from that of COMP 1 SYN, which recorded a biomass of 13,000 kg/ha.

Silk Production and Physiological Maturity.
e variety COMP 1 SYN took a maximum of 68 days for silk production whilst DT-STR-W-C2 took a minimum of 59 days to produce silk (Table 5). ere was a significant difference (p < 0.05) in terms of the number of days for silk production between the varieties COMP 1 SYN and DT-STR-W-C2 (Table 6). COMP 1 SYN took a maximum of 93 days to attain physiological maturity, and this was significantly different from all the other five varieties with respect to days to physiological maturity.

Effect of Variety on Grain Yield and 100-Grain Weight.
OBATAMPA recorded the highest grain yield of 3.6 tons/ha under all N application rates (Table 5). e yield was, however, not significantly different (p > 0.05) from that of IWD-C3-SYN-F2 (3.5 tons/ha) ( Table 6). e variety GH120 DYF/D POP produced the lowest grain yield of 2.5 tons/ha. For grain weight, OBATAMPA recorded the highest of 45 g, however, this was not significantly different (p > 0.05) from that of IWD-C3-SYN-F2 (39 g) and TZE-W-DT-STR-C4 (39 g).

Effect of Nitrogen Rate on Growth Parameters
3.3.1. Leaf, Shoot, And Biomass Production. All the varieties applied with 90 kg/ha N recorded an average of 13 leaves, whilst the varieties applied with 0 kg/ha N recorded the lowest of 10 leaves (Figure 1). ere were no significant differences (p > 0.05) between the 90 kg/ha N application rate and the other application rates (60 and 120 kg/ha N) with respect to leaf production (Table 6). e control plants applied with 0 kg/ha N recorded the lowest biomass yield of 7500 kg/ha, whilst the varieties applied with 120 kg/ha N recorded the highest biomass yield (15,000 kg/ha) (Figure 2). ere were significant differences (p < 0.05) between the plants applied with 120 kg/ha N rate and 0 and 60 kg/ha N rate (Table 6) with respect to biomass production. However, the biomass production was significantly similar among the plants applied with 120 and 90 kg/ ha N.

Silk Production and Physiological Maturity.
e control plants applied with 0 kg/ha N recorded the highest number of days (65 days) for 50% silking, whilst the varieties applied with 120 kg/ha N recorded the lowest of 58 days for silking ( Figure 3). ere were significant differences (p < 0.05) between the plants applied with 120 kg/ha N application rate and those applied with 0, 60, and 90 kg/ha N application rates with respect to the days to silk production ( Table 6). e varieties applied with 90 kg/ha N took a maximum of 85 days to attain physiological maturity. However, this was not significantly different (p > 0.05) from the days taken to attain physiological maturity by the plants applied with N rates of 0 and 120 kg/ha (Figure 4).

Grain Production per Cob.
All the varieties applied with 120 kg/ha N recorded a maximum of 500 grains per cob, whilst the varieties applied with 0 kg/ha N recorded a minimum of 310 grains per cob ( Figure 5). ere were no significant differences (p > 0.05) between the 120 kg/ha N application rate and the other application rates of 60 and 90 kg/ha N with respect to grain production per cob (Table 6).

Grain Yield.
e plants applied with 120 kg/ha N recorded the highest grain yield of 4 tons/ha, whilst the control plants applied with 0 kg/ha N recorded the lowest grain yield of 1.3 tons/ha ( Figure 6). ere were, however, no significant differences (p > 0.05) between the 120 kg/ha N and 90 kg/ha N application rates with respect to grain production ( Table 6).

Discussion
From the study, the varieties applied with 90 kg/ha N were not significantly different from 0 to 120 kg/ha with respect to the days taken to attain physiological maturity. It might occur as a result of the ineffective utilization of nitrogen by the plants that received 120 kg/ha N. e erratic rainfall distribution and the amount of rainfall could have considerably influenced the response of maize to nitrogen application. It is because the rain might have caused the runoff and leaching of applied nitrogen. 4 Advances in Agriculture Maize nitrogen use efficiency is estimated globally to be 33% because of the loss of N fertilizer from leaching below the root zone, denitrification, and soil-and plant-derived volatilization [20]. e inherent genetic factors could have also caused the uniformity of days to attain physiological maturity among the maize varieties. is observation confirms the findings of [21], who reported that maize varieties have a specific growth cycle. Chouhan et al. [22] also mentioned that genetic variability in growth and development exists among different maize cultivars, contributing to the differences in the observed days to 50% physiological maturity.
Silking and physiological maturity were earlier among DT-STR-W-C2, TZE-W-DT-STR-C4, and GH120 DYF/D POP but delayed among Comp 1 SYN and OBATAMPA for all nitrogen application rates. It is possible that DT-STR-W-C2, TZE-W-DT-STR-C4, and GH120 DYF/D POP had a relatively high nitrogen use efficiency relative to the other varieties, resulting in an earlier production of silk. is result is supported by that of Khan et al. [23] but contravenes that    Advances in Agriculture of Hassan et al. [24], who revealed that maize cultivars had significant differences in the days to 50% silking and physiological maturity. e variation in maturity periods could be a result of genetic and environmental factors. e studies of [25] and Bationo et al. [26] revealed that the growth, development, and maturity of maize are directly related to the number of nutrients that are made available to the plant during its growth period. Air-dried grain yield was the highest among OBATAMPA and IWD-C3-SYN-F2 but lowest among GH120 DYF/D POP. e observed increase in yield with increasing N rates is in agreement with the finding of Singh et al. [27], who observed that a moderate absorption of nitrogen by the maize plants tends to increase its net returns. e differences in the yield of different varieties may be attributed to the existence of differences in the cultivars in terms of their reactions to external factors and utilization of soil and water resources, which also have a significant effect on the yield and other agromorphological parameters [28].
Reference [29] observed the genetic variability in the growth and development among different cultivars of maize. e highest number of leaves was recorded by OBATAMPA, however, it was not significantly different from that of TZE-W-DT-STR-C4. It may be attributed to the inherent ability of these varieties to generate more leaves. However, GH120 DYF/D POP produced the least number of leaves. e variation in leaf production could have been because of the differences in response to different rates of N application. e variation in leaf appearance could also be a result of the crop's inherent ability to efficiently utilize soil resources.
Reference [30] also reported that increasing the nitrogen fertilizer rate from 0 kg N/ha to 250 kg N/ha significantly increased leaf production in the maize plants. IWD-C3-SYN-F2 and OBATAMPA produced the highest biomass, however, it was not statistically different (p > 0.05) from that of COMP 1 SYN. e lowest biomass production was recorded by GH120 DYF/D POP. Reference [31] observed a significant disparity in the genotypes with respect to biomass production. e insignificant differences in the maximum grains per cob of the varieties are in contrast to the findings of Akmal et al. [31,32], who observed significant differences in varieties with respect to the yield and other agromorphological traits. Generally, all treatments at N > 0 kg/ha significantly produced more grains per cob than the control. e findings are partly in agreement with those of Maqsood et al. [33] and Sharar et al. [34], who observed that the number of grains per cob varied with different varieties.
In general, it was observed from the field data that the grain yield and yield components produced are related to the variation in N rates. All the varieties applied with 120 kg/ha N recorded a relatively higher grain yield and several grains per cob as compared to the yields produced at 0, 60, and 90 kg/ha N. [35] reported that increasing the N levels   significantly increased the grain yield, days to 50% silk emergence, percent grain moisture content at harvest, and 1000-seed weight, however, it negatively impacted the ear acceptability rating and percent total lodging. Nitrogen is a vital plant nutrient and a major yield-determining factor required for maize production [36]. Reference [37] reported that the nitrogen fertilizer levels are significant for grain yield, days to mid-silking, days to mid-anthesis, anthesis-silking interval, plant height, ear height, open tip, cob aspects, dry stover weight, cob length, and grain depth at nitrogen levels of 0, 45, and 90 kg N/ha. It may be because of adequate nitrogen in combination with P and K, which greatly influenced the vegetative growth of the plant. e observed trend in cob weight confirms the results of [28], who observed significant differences in the cob weight among different genotypes at different N rates. Differences arise as a result of the difference in the genetic composition of the cultivars that also influence their responses to the external environment. On the contrary, Akmal et al. [32] observed no significant differences in cob weight for different varieties. Different N levels also produced significant differences in the empty cob weight. e results are supported by the findings of Hassan et al. [24], who reported that the grains per cob increased with the increasing levels of NPK fertilizers. e highest number of grains per cob was recorded at 120 kg/ha N across all the six genotypes used in the study.

Conclusion and Recommendations
e study was conducted to examine the varietal response of maize to different nitrogen fertilizer application rates. From the results and discussion of the experiment, the following conclusions were deduced: e varieties OBATAMPA and IWD-C3-SYN-F2 produced the best results with respect to grain yield, total biomass, leaf, and shoot production. All the varieties applied with 120 and 90 kg/ha N recorded relatively higher grain yield and growth parameters as compared to 0 and 60 kg/ha N. e cultivation of OBATAMPA and IWD-C3-SYN-F2 will result in an increased grain yield. e application of 90 kg/ha N will also result in increased grain production.

Data Availability
e data used to generate the results in this manuscript is not available.

Additional Points
is study discovered that the type of maize variety and nitrogen fertilizer rate used by the farmers for production influence the maize grain yield in the Savannah Agroecology of Ghana. e use of low-yielding varieties, coupled with an inappropriate nitrogen application rate is the major cause of the continuous low yield of maize in Northern Ghana. rough this study, the researcher had discovered that the use of varieties, such as OBATAMPA and IWD-C3-SYN-F2, and the application of 90 kg ha −1 N will result in increased maize productivity in Northern Ghana.

Conflicts of Interest
e author has declared no conflicts of interest.