Yield and Nitrogen Use Efficiency of Maize (Zea mays L.) Following the Application of Various Nitrogen Sources under Rainfed Conditions in the Bono Region of Ghana

Maize (Zea mays L.) accounts for more than 50% of the total cereal production, making it an essential cereal crop in Africa (Partey et al., 2018). After wheat and rice, maize is the third most valuable crop (Ofori and Kyei-Baffour, 2006). Ragasa et al., (2013) reported that production of maize in Sub-Sahara Africa is mainly for food consumption making it an important crop for food security. In Ghana, maize cultivation is mainly done under rainfed conditions in almost all the agro-ecological zones by smallholder farmers (Ofori and Kyei-Baffour 2006). The average yield of maize is estimated to be 1.9 t ha^-1 (FAO, 2015). According to Rockstrom et al., (2010), rainfed maize cultivation contribute to 75% of agriculture in areas where the crop is the main source of food and livelihood for the people.
 
Ofori and Kyei-Baffour (2006) stated that the difference in maize yield is as a result of environmental conditions under which it is grown, the genetic composition of the hybrid and the degree of pest infestation. However, soil nutrient depletion through poor soil fertility management accounts for poor yield of crops such as maize (Ojobor et al., 2021). In addition, yield of maize is affected by deficient recharge of essential nutrients including nitrogen and phosphorus (FAO, 2007). Nutrient uptake in plants are hindered by improper soil fertility management resulting in lower nitrogen use efficiency (NUE) in crops. Therefore, utilization of organic and inorganic fertilizers has been detected to have the ability to better growth and yield of maize (Kalyanasundaram and Augustine, 2021; Almaz et al., 2017) which brings about an improvement in the nutrient level of the soil and high amount of residues that can be incorporated into the soil to enhance its fertility (Campbell et al., 2001). Although the use of nitrogen is increasing worldwide, NUE for maize is about 30% in agricultural production (Cassman et al., 2002). According to Fageria et al., (2015), enhancing NUE is an essential way for not only contributing to increment in crop yield but also help to reduce crop production cost and environmental pollution. Therefore, this research aimed at determining the responsiveness of maize yield and nitrogen use efficiency to different nitrogen sources.
 

The experiment was conducted during the major and minor rainy seasons of 2019 at the Demonstration Farm of the School of Agriculture and Technology, UENR, Dormaa-Ahenkro Campus from April to December 2019. The trial was laid out in a randomized complete block design with five treatments replicated three times. The treatments were NPK 15-15-15, Urea, Poultry manure, ½ NPK 15-15-15 + ½ Poultry manure (NPKM) and Control (No fertilizer). The soil initial physical and chemical analyses were carried out following standard procedures as described by Motsara and Roy (2008) (Table 1). Samzal Sima (maize variety) was sourced from Savannah Agricultural Institute, Tamale. Sowing of seeds for the major and minor rainy seasons was carried out on 4^th April and 4^th September 2019 respectively at a spacing of 75cm between rows and 25cm within rows at a rate of one seed per stand. The recommended rates of applications per hectare in Ghana is 90:60:60 kg N:P₂O₅:K₂O (Tetteh et al., 2008).


 
The poultry manure was applied two weeks before planting. The application of the inorganic fertilizers was done using the split method. The first (60 kg N ha^-1) and second application (30 kg N ha^-1) were done two and six weeks after sowing as side placement respectively. The application rates of the treatments used were NPK 15-15-15 at (90:60:60 kg ha^-1 N:P:K), Urea (90 kg ha^-1) Poultry manure (4.2 ton ha-¹) and combination of ½ NPK 15-15-15 and ½ poultry manure. During the cropping season, pesticide (Deviance) with the active ingredient emamectin benzoate was used to control fall army worm. The nitrogen concentration was determined using the Carbon Nitrogen Sulphur analyzer machine. Phosphorus and potassium were obtained using the wet digestion method (Mehlich, 1984). The procedure involved in developing the P colour was the use of paranitrophenol and ammonia (Bray and Kurtz, 1945) and read using spectrophotometer. The N, P and K uptakes were estimated by multiplying the biomass weight by the corresponding N, P and K total concentration.
 
Data were collected on the yield and yield components (ear length, ear diameter, kernel number, 1000 grain weight, grain yield), harvest index, biomass, NUE and nutrients uptake. NUE, Partial factor productivity, Agronomic efficiency nitrogen, Recovery efficiency nitrogen and Nitrogen harvest index were obtained using the formulae described by Dobermann (2007). Data collected were subjected toanalysis of variance using the GenStat Statistical package (Version 11.1). Mean separation was carried out using the least significant difference at p=0.05.
 

Yield and yield components
 
All the yield and yield components, except 1000-grain weight in the major rainy season and grain yields during the minor rainy season, were not significantly affected (P>0.05) by fertilizer application for both seasons (Table 2). The greater grain yield (5551 kg ha^-1) and biomass yield (14296 kg ha^-1) were produced by the NPKM treatment during the major season. This confirms the observation that the integrated use of organic and inorganic fertilizers improves soil fertility and also enhance maize yield as likened to the sole application of organic or inorganic fertilizer (Mahmood et al. 2017).



The yield of all treatments were significantly higher than the yield of the control during the minor season (Table 2). However, there was a reduction of yields in the minor rainy season as compared to the major season. This reduction might be due to variations in climatic conditions such as rainfall. In line with this, reduction of 40% to 60% yields of maize in the dry season compared to yields in the rainy season due to low rainfall was reported by Sogbedji et al., (2006). However, the greatest grain yield (3507 kg ha^-1) was recorded by the NPK 15-15-15 treatment whilst the lowest grain (2838 kg ha^-1) yield was recorded by the control. This could be attributed to the presence of the inorganic nutrients which is readily available and accessible to plants for growth and development. In a similar study by Arije et al., (2018), the highest yield of maize was recorded by the NPK 15-15-15 treatment and the lowest maize yield was recorded by the control.
 
Nitrogen use efficiency
 
Better yield of crops and a reduction in plant nutrient loss can be greatly achieved in crop production when there is an improvement in plant nitrogen use efficiency (Cassman et al., 2002). From the results, Partial Factor Productivity was higher in the NPKM treatment (61.68 kg ha^-1) and NPK 15-15-15 treatment (38.96 kg ha^-1) for major and minor rainy seasons respectively (Table 3). This resulted from the high performance of the two treatments with regards to grain yields. Except for NPKM which recorded a positive agronomic efficiency nitrogen (AEN) (2.8 kg ha^-1), all the other treatments recorded negative mean values for AEN during the major rainy season. This was as a result of the higher performance of the control plot than the fertilized plots with respect to grain yield. The plot treated with urea recorded the highest recovery efficiency nitrogen (1.62 and 1.08 kg ha^-1) for the major and minor seasons respectively.


 
The performance of urea is a reflection of the results for plant nitrogen uptake where it had the highest nitrogen uptake for both seasons. However, it can be said that urea recovered more nitrogen than the other treatments. Barbieri et al., (2008) stated that one beneficial way of improving NUE of maize is the increase its recovery efficiency. Nitrogen harvest index shows the efficiency of plants to utilize the accumulated nitrogen in the grains (Fageria, 2014). For the major season, the control treatment recorded the highest nitrogen harvest index (0.179) but it did not differ significantly from the fertilized treatments. The fertilized treatments did not significantly (P>0.05) affect nitrogen harvest index. This could be due to the partitioning of the total nitrogen to the vegetative parts of the crop. However, significant differences were recorded during the minor season. Similar results were recorded by Belete et al., (2018) on nitrogen fertilizers on different varieties of bread wheat.
 
Nutrients uptake
 
The most limiting nutrient to maize yield is nitrogen (Stevens et al., 2005), however, inorganic sources of nitrogen are readily available for plant use but organic sources of nitrogen such as manure has to undergo a mineralization procedure which is controlled by soil microbes, moisture level and quantity of nitrogen and carbon in the manure (Nyiranneza et al., 2009). From the results, it was observed that urea treatment absorbed more plant nitrogen as compared to the other treatment during both seasons. This is a characteristic of urea being an inorganic fertilizer which is readily available for plant use. Gutser et al., (2005) reported that higher plant nitrogen uptake by inorganic fertilizers than organic fertilizers could be as a result of the slow release of plant nutrients by organic fertilizers due to their higher C/N ratio because C/N ratio plays an important role in mineralization and nutrientrelease during decomposition. 
 
Our results differ with the findings of Songo (2017) who observed higher nitrogen uptake by the combination of manure and mineral fertilizer. Similar results were recorded by Chikowo et al., (2004). Statistically, observing the results for both seasons, nitrogen uptakes were higher in the inorganic treatments than the organic treatment (Table 4). This could be attributed to the fast release of nitrogen to plants by inorganic amendments than organic amendments. The N and P uptake in the major season was higher for all the treatments as compared to the minor season. Moreover, poultry manure recorded the highest phosphorus (327.3 kg ha^-1) and potassium (918 kg ha^-1) uptake while urea and NPK 15-15-15 recorded the lowest phosphorus (246.5 kg ha^-1) and potassium (585.8 kg ha^-1) uptake respectively for the major season. This could be attributed to the influence of poultry manure through its decomposition, microbial activities and chemical properties of the soil (Ylivainio et al., 2008). The performance of the poultry manure is in line with the findings of Pinto et al., (2012) who stated that there is a high concentration of phosphorus and potassium in manure obtain from poultry production. Also, poultry manure enhances the chemical and physical properties of the soil, hence increasing the concentration and uptake of plant nutrients. However, this is dependent on the quantity of manure applied (Hou et al., 2012).



 

Significant (P>0.05) differences were not recorded among the treatment means except for 1000 grain weight for the major rainy season and grain yield, nitrogen uptake and nitrogen harvest index for the minor rainy season. Combined application of NPK 15-15-15 and poultry manure produced higher results with respect to grain yield, yield component, partial factor productivity and agronomic efficiency nitrogen, than the other treatments. Application of urea resulted in higher nitrogen uptake and poultry manure recorded the highest phosphorus and potassium uptake by the plant. Further research should be conducted at the experimental site for long term. This will enable the researcher to know the actual effects of the fertilizer treatments on the crop.
 

We are grateful to the technical support from Shadrack Asomah and the Laboratory Technicians at University of Ghana Soil Science Department for their assistance.
 

None.