Yield Response of Maize to Irrigation and Nitrogen Fertilization

The world population is growing day by day. It is expected to reach up to 7.4 billion by 2025. Undernourishment is affecting 850 million people around the world (FAO, 2010). Under this circumstance, food security has been identified as a major concern by different countries especially the underdeveloped countries to contribute to its socio economic stabilization as well as development (Kashem and Faroque, 2011). But the agricultural production is under severe strain to satisfy the food demand due to limited resource and energy, climate change, soil degradation and higher reliance on certain crops. To accomplish the food goal, production per unit area must be raised while resources are well utilized. Maize (Zea mays) is a fast-growing, high-yielding cereal crop that has the potential to alleviate global cereal crop shortages. It is the third most significant grain crop in the world pertaining to the grass family Poaceae (Djaman et al., 2018). Maize is produced for human and animal sustenance all over the world. This crop is consumed as a main diet by many people in Mexico, Central and South America and parts of Africa whereas in Europe and the rest of North America it is popular for animal feed. Because of its C4 pathway, it has a high rate of photosynthetic activity, resulting in higher grain yield and biomass potential. Maize grain is a rich source of starch, protein, oil, fiber and minerals (Reddy and Reddy, 2003). Some researchers considered maize as more nutritious than rice in terms of protein, phosphorus and carotene content. Various food items viz. soup, corn flakes, khichuri, bhutta polao etc. can be prepared from maize. Maize flour alone or in combination with flour from other cereals and pulses is also used to make bread, mixed parota, pulse puri and other foods. In fact, it can be utilized in the same way as rice and wheat. So, Maize production in the country can be a significant source of food and nutrition for the country’s growing population.
       
Irrigation and fertilizers are two of the most important inputs for higher crop productivity. Irrigation and fertilization have contributed to the advancements of soil fertility, crop productivity and food security as it affects the farm environment by altering soil water and nutrient content (Godfray et al., 2010). As a high-yielding crop, maize requires adequate soil moisture in the root zone for proper growth and development. Maize is typically planted during the dry season. The moisture level of the soil declines gradually over the dry season. Lack of water induces water deficit condition in soil and plant system. Moisture stress causes maize plant to delay tasseling and silking, as well as limits vegetative development and production of yield (Abrecht and Carberry, 1993; Singh et al., 2007). Additional irrigation is necessary during dry season for proper crop performance. Inappropriate irrigation scheduling can lead to both water wastage and decrease in crop production which ultimately results in energy loss and low returns to the farmers. So, proper irrigation planning is required for the most effective use of available water in improving maize yield.
       
Nitrogen (N) is a vital nutrient and plays important role in the improvement of crop production. It is an integral component of many plant structures and processes, both internal and external (Szulc et al., 2016). Maize is a nitro-positive crop which necessitates a greater amount of nitrogen for its economic production (Adhikary et al., 2020). But nitrogenous fertilizers can be raised to a certain point before losing it via leaching, runoff, volatilization and other means that plants cannot use. Thus the non-judicial use of nitrogenous fertilizers causes environmental pollution and increases farmers cost of production. To reduce nitrogen losses while also increasing crop output and farm income, an appropriate level of nitrogen fertilizer is compulsory.
       
World’s demand for maize is growing day by day because of its excellent nutritive values and ability to minimize reliance on rice and wheat. The high productivity of maize can be achieved under the most favourable irrigation practices with applying the needed nutrients in right amounts and at the right times. Until recent, Very limited researches are available relating to coupling effect of irrigation and nitrogen application on maize yield. Therefore, an attempt has been made to evaluate the effect of irrigation and nitrogen on the performance of maize with the goal of establishing an irrigation schedule and nitrogen dose that will result in the highest possible maize yield.
 

The experiment was conducted at the research field under department of Soil Science of Bangabandhu Sheikh Mujibur Rahman Agricultural University, Gazipur, Bangladesh, during November 2018 to April 2019. The country receives about 2500 mm of rainfall on average each year which occurs mostly during the monsoon (June to October). There is little or no rain during dry season but it is uncertain and unpredictable.  The examined area belongs to AEZ 28 known as Madhupur tract and corresponds to the order Inceptisols under Salna series, characterized by Shallow Red Brown Terrace soil having bulk density (1.41 g cm^-3), porosity (47.4%), field capacity (30.1%), pH value about 5.8, organic carbon (0.62%), total nitrogen (0.072%), available phosphorus (10.22 mg kg^-1), available sulphur (12.01 mg kg) and exchangeable potassium [0.15 cmol (+) kg^-1].  
       
The effect of two factors was evaluated in the study. Factor A consisted of four irrigation schedules (irrigation at 20%, 40%, 60% and 80% available water) and factor B consisted of three nitrogen doses [75%, 100% and 125% of recommended dose (RD) as per fertilizer recommendation guide (FRG). The treatments were settled down in a randomized complete block design (RCBD) with three replications.
       
A high yielding maize variety BARI Hybrid Maize-9 was used as test crop in the experiment. A plot size of 3 m×2 m was constructed after preparing the land. The amounts of N, P, K and S were applied in various doses as urea, triple super phosphate (TSP), muriate of potash (MoP) and Gypsum depending on the treatment requirements. One third of the N and full amount of all other nutrients were applied at final land preparation before sowing. The remaining two third of N was top-dressed at knee height and tassel emergence. Two seeds at each hill were sown at a spacing of 75×25 cm on 5 December 2018. Intercultural activities were performed as per needed. The soil was moistened by ten light irrigations up to 40 days following emergence to encourage improved germination and establishment of seedlings. After that irrigation water was applied according to the treatment plan to bring the soil moisture up to field Capacity and rooting depth of the crop.
       
Soil available water for plant was calculated using following formula:
 
Available water= Field capacity-Wilting point
 
Irrigation requirement was calculated as follows:  
Where,
IR= Irrigation requirement (cm).
MFC= Soil moisture (%) at field capacity.
MBI= Soil moisture (%) before irrigation.
ρb= Soil bulk density  (g cm^-3).
D= Rooting depth (cm).
     
The crops were harvested when around 50-60% of the cobs turned into straw color. Four plants were randomly marked for data collection. Number of cobs per plant, cob length and cob diameter were recorded at the time of each harvest and the average value of four plants was treated as one replication. Dry matter yield was estimated after drying the plants as whole plot basis. Cob yield and grain yield per plot was converted to ton per hectare.
       
Water use efficiency of maize was calculated from total dry matter and grain yield by using following formula:
      
       The data on different parameters were statistically analyzed using Statistix 10 software. The difference between the treatment means were adjudged by Duncan’s multiple range test (DMRT) according to Gomez and Gomez (1984).
 

Effect of irrigation on yield and yield components of maize
 
The varying degrees of irrigation had offered significant impact on maize yield attributes like cobs per plant, cob length, cob diameter, cob yield, grain yield and dry matter yield (Table 1). Treatment I₃ resulted the maximum cobs per plant (1.11) followed by I₄ and I₂ treatment (1.08 and 1.00 respectively). The highest cob length (21.29 cm) and cob diameter (4.72 cm) was also found with I₄ treatment and the lowest (20.38 and 4.52 cm respectively) was with I1 treatment. Different levels of moisture contributed significantly to cob yield (t ha^-1), grain yield (t ha^-1) and dry matter yield (t ha^-1) of maize. I4 treatment produced significantly increased cob yield (13.93 t ha^-1), grain yield (7.86 t ha^-1) and dry matter yield (8.01 t ha^-1) whereas the decreased results (11.11 t ha^-1, 6.48 t ha^-1 and 4.60 t ha^_-1 respectively) were found with I1 treatment. The study signified that enhancement in irrigation levels provided positive impact on plant growth and development. Increased soil moisture level led to conducive environment for plant growth through boosting plant nutrient availability, photosynthetic activity and metabolic rates which in turn improves plant yield. Our research results are in accordance with the findings of Kidist (2013) and Akbar (2003).


 
Effect of nitrogen on yield and yield components of maize
 
The effect of different levels of nitrogen application on yield and yield components of maize was found significant except number of cobs per plant (Table 2). However, number of cobs per plant was increased with increased level of nitrogen application. The size of maize cobs was also varied significantly while N₂ treatment produced largest cob length (21.15 cm) and cob diameter (4.70 cm) which was statistically identical with N₃ treatment (20.95 and 4.69 cm respectively).  The highest cob yield (13.22 t ha^-1), grain yield (7.44 t ha^-1) and dry matter yield (7.37 t ha^-1) was also obtained with N₂ treatment followed by N₃ treatment (12.27, 7.36 and 7.30 t ha^-1 respectively) simply with no statistical variation between two treatments compared to N₁ treatment. The results reveal that the nitrogen requirement of maize to get optimum yield under Salna soil series can be satisfied by applying nitrogen according to 100% RD. Application of lower amount of N produced unacceptable yield of maize. The optimal rate of N promotes photosynthetic processes as well as net assimilation rate, resulting in increased yield of maize. On the other hand, higher dose of N could not give higher yield because N is particularly reactive and volatile in soils, it is vulnerable to losses through volatilization, denitrification, leaching and surface runoff. These findings were similar with other studies depicted by Hou et al. (2012) and Halvorson et al. (2006).


 
Interaction effect of irrigation and nitrogen on yield and yield components of maize
 
Significant interactive response had been exhibited by yield and different yield attributes of maize to varying degrees of irrigation and nitrogen excluding number of cobs per plant shown in Table 3. However, the interaction effect was found significant on cob length (cm) and cob diameter (cm). I₄N₂ treatment showed highest cob length (22.01 cm) and cob diameter (4.83 cm) which was statistically similar to treatments I₃N₃ and I₄N₃ for cob length and I₄N₃, I₃N₃, I₃N₂, I₂N₃ and I₂N₂ for cob diameter. The maximum cob yield (16.89 t ha^-1), grain yield (9.19 t ha^-1) and dry matter yield (10.15 t ha^-1) was found with I₄N₂ treatment which was statistically identical to I₃N₃. On the other hand, the minimum cob yield (10.67 t ha^-1), grain yield (6.07 t ha^-1) and dry matter yield (3.86 t ha^-1) was observed with I₁N₁ treatment. It can be ascertained from the study that proper water application with nitrogen dose is indispensable to ensure proper yield of maize as optimum moisture level and nitrogen supply favours the growth and development of the crop. Similar results were pointed out by Paolo and Rinaldi, (2008).


 
Interaction effect of irrigation and nitrogen on the primary nutrient contents of maize
 
Maize grains were analysed to evaluate the interaction effect of irrigation and nitrogen treatments on primary nutrient contents exposed in Fig 1. The primary nutrient contents of maize grain showed remarkable variation with the variation of applied irrigation and nitrogen. The highest grain N (0.87%) was attained from I₄N² which did not differ statistically from I₃N₁, I₃N₂, I₃N₃ treatment. Treatment I₄N₂ also resulted in the highest level of P (0.20%) which was in the same statistical category as I₃N₃ treatment (0.19%). Similar trends also recorded for K content of grain where K content was highest with treatment I₄N₂ (0.26%). As compared to other treatments, I₁N₁ treatment produced lowest values for N (0.29%), P (0.06%) and K (0.16%) content of maize grain. As a result of the current research, it can be revealed that nutrient mineralization, availability to the root zone and assimilation by plants are aided by adequate supply of water and nitrogenous fertilizer which eventually improve maize grain quality. These findings agree with that of Li et al. 2020 findings.


 
Interaction effect of irrigation and nitrogen on water use efficiency of maize
 
The data conveyed on the interaction effect of irrigation and nitrogen on water use efficiency of maize was presented in Fig 2. Water use efficiency of maize was estimated based on total dry matter and grain yield. The maximum water use efficiency for total dry matter (24.67 kg ha^-1 mm^-1) was generated from treatment I₃N₃ and the minimum (15.13 kg ha^-1 mm^-1) was from treatment I₃N₁. Treatment I₁N₂ produced highest water use efficiency (23.59 kg ha^_-1 mm^-1) for grain yield and the lowest was recorded from I₄N₁ (15.13 kg ha^-1 mm^-1). According to the study, crops’ water use efficiency was increased under moderate irrigation and high nitrogen application. However, excessive irrigation and insufficient nitrogen application caused reduction in water use efficiency of crops due to water loss and low yield.


 

Maintaining soil moisture condition by giving irrigation at 80% available water along with application of nitrogen at 100% of recommended dose as per Fertilizer Recommendation Guide and irrigation at 60% available water using 125%, recommended dose facilitate superior growth and development of maize that results the maximum yield and improved grain primary nutrient contents of this crop. The crop’s water use efficiency was also increased with above mentioned irrigation and nitrogen levels. Both low water application and low nitrogen dose contributed reduced yield of maize. The study’s findings may lead to the conclusion that providing irrigation at 80% available water with applying 100% of recommended dose of nitrogen may be the best option for the farmers to improve maize yield while avoiding the negative effects of excessive nitrogenous fertilizer use on soil and environment at the same time reducing farmer’s cost of production.
 

None.