Effects of Nitrogen Rates and Split Applications on Maize Yield in Semi-Arid Conditions ^†

Abstract

Efficient nitrogen management is crucial for maize productivity in semi-arid regions. A field experiment was conducted in Autumn 2023 at Bahauddin Zakariya University, Multan, using RCBD with three replications to assess nitrogen rates (0, 80, 160, 240, 320 kg ha⁻¹) and application methods (two vs. three splits). Growth and yield traits were recorded. The results showed significant effects of nitrogen, with the highest grain yield (7.35 t ha⁻¹) at 240 kg ha⁻¹ in three splits, enhancing nutrient use efficiency. Higher nitrogen content (320 kg ha⁻¹) reduced yield, indicating diminishing returns. The optimized nitrogen rate and timing improved maize productivity in water-limited environments.

1. Introduction

Nitrogen fertilization plays a pivotal role in maize (Zea mays L.) production, particularly under semi-arid conditions where water scarcity limits nutrient availability and crop performance. The application rate and timing of nitrogen not only determine yield outcomes but also influence nitrogen use efficiency (NUE) and environmental sustainability. Optimized nitrogen management has been reported to improve grain yield and reduce nitrogen losses by synchronizing nutrient availability with crop demand [1,2,3].

Previous studies have demonstrated the advantages of split nitrogen applications compared to single applications. For example, a three-way split application at sowing, knee height, and tasseling improved agronomic efficiency and recovery efficiency by nearly 30% compared to pre-plant treatments on coarse-textured soils [4]. Similarly, integrated fertilization strategies combining biofertilizers with chemical and organic amendments under moderate deficit irrigation improved grain yield by 22–26% compared to chemical fertilizer alone [5]. However, the optimum nitrogen rate varies with soil type, irrigation regime, and local environmental conditions. In Northeast China, optimum rates were reported between 205 and 305 kg ha⁻¹, depending on whether yield maximization or economic profitability was prioritized [6,7].

In Pakistan, maize yield responses to nitrogen application are often constrained by semi-arid environments. Wasaya et al. [8] found that applying 200 kg N ha⁻¹ resulted in a 21% higher grain yield compared to lower rates, while studies in other regions suggested that rates between 180 and 250 kg N ha⁻¹ are suitable for semi-arid systems under irrigation [9,10,11]. The interaction between nitrogen application and irrigation is critical, as deficit irrigation combined with optimized nitrogen management enhances both water productivity and NUE [5,12].

Despite extensive global research, limited data are available on the effects of split nitrogen applications under semi-arid conditions in Pakistan. To address this gap, this study was designed to evaluate different nitrogen rates and split applications on maize growth, yield components, and overall productivity. The objective was to identify the nitrogen management strategy that maximizes maize yield and improves NUE under the semi-arid agro-ecological conditions of Multan, Pakistan.

2. Materials and Methods

A field experiment was carried out during the Autumn 2023 season at the Agronomic Research Area, Institute of Agronomy, Bahauddin Zakariya University, Multan, Pakistan. The site is located at 31°25′ N latitude, 73°09′ E longitude, and 184 m above sea level. The climate of the region is semi-arid, characterized by hot summers and mild winters.

Before sowing, composite soil samples (0–30 cm depth) were collected and analyzed for physico-chemical properties. The soil was classified as clay loam, slightly alkaline (pH 8.1), with low organic matter content (0.71%) and nitrogen levels (0.0475%). Available phosphorus was very low (4.25 ppm), while potassium was sufficient (174.3 ppm).

The study was conducted using a randomized complete block design (RCBD) with a factorial arrangement and three replications. Treatments included five nitrogen rates: N₀ (0 kg ha⁻¹, control), N₁ (80 kg ha⁻¹), N₂ (160 kg ha⁻¹), N₃ (240 kg ha⁻¹), and N₄ (320 kg ha⁻¹). Two nitrogen application methods were evaluated: S₁ (two splits, with 50% applied at sowing and 50% at tasseling) and S₂ (three splits, with 33.3% applied at sowing, 33.3% at knee height, and 33.3% at tasseling). The net plot size was 3 m × 5 m, resulting in a total of 30 experimental plots.

The field was prepared with two passes of a tractor-mounted cultivator followed by planking. Hybrid maize variety Pioneer-30Y87 was sown on 15 July 2023 at a spacing of 75 cm × 25 cm using a seed rate of 25 kg ha⁻¹. Phosphorus (100 kg ha⁻¹ as SSP) and potassium (100 kg ha⁻¹ as MOP) were applied at sowing. Nitrogen was supplied as urea according to treatment levels. The field was irrigated five times, beginning 15 days after sowing and ending a week before harvest. Hoeing was performed twice for weed control, and carbofuran granules (18 kg ha⁻¹) were used to manage stem borers.

Growth and yield attributes were recorded following standard procedures. Plant height (cm) was measured from the base to the tassel of ten randomly selected plants per plot. Cob traits, including cob length, cob diameter, and grain rows per cob, were measured from ten cobs per plot, while grains per cob were counted from randomly selected cobs. The 1000-grain weight (g) was determined after drying and weighing. Grain yield (t ha⁻¹) was calculated from shelled grains and converted to a per-hectare basis, whereas biological yield (t ha⁻¹) represented the total aboveground biomass per plot. The harvest index (%) was computed as grain yield divided by biological yield multiplied by 100.

Data were analyzed using Statistix 8.1 software. Treatment means were compared using the Least Significant Difference (LSD) test at the 5% probability level [13].

3. Results

Nitrogen rates and split applications had significant effects on all measured growth and yield attributes of maize. Detailed results for each parameter presented below in

Table 1. Mean Values of Nitrogen Rates and Split Application on Agronomic Parameters of Maize.

	Plant Height (cm)	Cob Length (cm)	Cob Diameter (cm)	Grain Rows	Grains Cob−1	1000-Grain Weight (g)	Grain Yield (t ha−1)	Biological Yield (t ha−1)	Harvest Index (%)
	Mean Values of Nitrogen Rates kg ha−1
(N0) 0 kg ha−1	184.67 ± 2.8 d	11.67 ± 0.4 d	3.32 ± 0.2 d	10.63 ± 0.5 d	378.0 ± 10.2 d	195.56 ± 6.5 e	3.30 ± 0.3 e	10.00 ± 0.5 e	33.00 ± 0.3 e
(N1) 80 kg ha−1	214.33 ± 3.0 c	14.26 ± 0.5 c	3.82 ± 0.3 c	11.00 ± 0.5 c	479.97 ± 12.3 c	228.12 ± 6.3 c	5.36 ± 0.4 c	12.85 ± 0.6 d	41.65 ± 0.4 c
(N2) 160 kg ha−1	236.50 ± 3.2 b	14.94 ± 0.5 b	4.45 ± 0.3 b	13.03 ± 0.6 b	537.24 ± 15.4 b	255.82 ± 7.0 b	6.61 ± 0.4 b	14.80 ± 0.7 c	44.63 ± 0.4 b
(N3) 240 kg ha−1	242.50 ± 3.5 a	16.45 ± 0.6 a	4.53 ± 0.4 a	15.04 ± 0.7 a	593.90 ± 15.7 a	275.40 ± 7.5 a	7.35 ± 0.5 a	16.10 ± 0.8 a	45.65 ± 0.5 a
(N4) 320 kg ha−1	205.00 ± 2.5 c	13.55 ± 0.4 c	3.47 ± 0.2 c	11.73 ± 0.6 c	442.24 ± 11.2 c	220.34 ± 6.8 d	5.98 ± 0.3 c	12.75 ± 0.5 d	41.45 ± 0.4 c
	Mean Values of Split Doses
S1 (2 Splits)	210.6 ± 3.5 b	13.28 ± 0.4 b	3.73 ± 0.3 b	11.68 ± 0.5 b	457.87 ± 12.3 b	234.23 ± 6.2 a	5.97 ± 0.4 b	13.00 ± 0.5 b	39.84 ± 0.3 b
S2 (3 Splits)	222.6 ± 3.2 a	15.06 ± 0.4 a	4.10 ± 0.3 a	13.29 ± 0.6 a	514.67 ± 15.4 a	228.87 ± 6.5 b	6.26 ± 0.3 a	13.78 ± 0.5 a	41.91 ± 0.4 a

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3.1. Plant Height

Nitrogen application significantly increased plant height shown in Table 1. The tallest plants (242.50 cm) were recorded at 240 kg ha⁻¹ (N₃), while the shortest (184.67 cm) occurred in the control (N₀). Among application methods, three splits (S₂) resulted in taller plants (222.6 cm) than two splits (S₁: 210.6 cm). The interactive effect showed that N₃ with S₂ produced the maximum plant height.

3.2. Cob Length

Cob length increased progressively with nitrogen application shown in Table 1. The maximum cob length (16.45 cm) was observed at 240 kg ha⁻¹ (N₃), while the control (N₀) recorded the lowest (11.67 cm). Split application further enhanced cob length, with S₂ (15.06 cm) outperforming S₁ (13.28 cm).

3.3. Cob Diameter

Cob diameter followed a similar trend shown in Table 1. The largest diameter (4.53 cm) was achieved at 240 kg ha⁻¹ (N₃), while the lowest (3.32 cm) was in N₀. Split applications produced thicker cobs in S₂ (4.10 cm) compared to S₁ (3.73 cm).

3.4. Grain Rows per Cob

The number of grain rows per cob significantly increased with nitrogen shown in Table 1. The maximum (15.04 rows) was recorded at N₃, while N₀ had the lowest (10.63 rows). Among application methods, S₂ resulted in more rows (13.29) than S₁ (11.68).

3.5. Grains per Cob

The number of grains per cob was the highest (593.90) at N₃ and the lowest (378.0) at N₀ shown in Table 1. Split applications significantly improved results, with S₂ producing more grains (514.67) than S₁ (457.87).

3.6. 1000-Grain Weight

Nitrogen levels significantly influenced 1000-grain weight shown in Table 1. The heaviest grains (275.40 g) were recorded at N₃, while N₀ produced the lowest (195.56 g). Unlike other parameters, S₁ produced slightly higher grain weight (234.23 g) compared to S₂ (228.87 g).

3.7. Grain Yield

Grain yield peaked at 7.35 t ha⁻¹ under N₃, whereas the lowest yield (3.30 t ha⁻¹) was recorded in N₀ shown in Table 1. Split applications improved yields, with S₂ (6.26 t ha⁻¹) outperforming S₁ (5.97 t ha⁻¹). The combined effect of N₃ with S₂ produced the maximum yield.

3.8. Biological Yield

Biological yield followed the same trend as grain yield shown in Table 1. The maximum (16.10 t ha⁻¹) was observed at N₃, while the lowest (10.00 t ha⁻¹) was in N₀. Split applications improved biological yield, with S₂ (13.78 t ha⁻¹) higher than S₁ (13.00 t ha⁻¹).

3.9. Harvest Index

The harvest index ranged from 33.00% (N₀) to 45.65% (N₃) shown in Table 1. Among splits, S₂ resulted in a higher index (41.91%) than S₁ (39.84%). The maximum harvest index was obtained under N₃ with three splits.

3.10. Correlation Among Parameters

A correlation heatmap (Figure 1) demonstrated strong positive associations between grain yield, plant height, cob traits, and biological yield, indicating that improvements in growth traits directly translated into yield advantages.

4. Discussion

Nitrogen management played a decisive role in enhancing maize growth and yield in semi-arid conditions. In this study, increasing nitrogen rates improved plant height, cob characteristics, grains per cob, and yield attributes up to 240 kg ha⁻¹ (N₃). Beyond this level, yield declined, indicating that excessive nitrogen reduced efficiency and could divert assimilates toward vegetative growth rather than reproductive development. Similar trends have been reported, where nitrogen application significantly increased maize grain yield and growth parameters under semi-arid conditions [1,2].

Split applications consistently outperformed two-split treatments, particularly for plant height, cob traits, grains per cob, and biological yield. This highlights the importance of synchronizing nitrogen supply with crop demand to minimize losses and enhance nutrient uptake. Comparable findings have been documented in coarse-textured soils, where three-split applications improved agronomic efficiency and recovery efficiency by 30% compared to single preplant applications [3].

The results align with earlier studies indicating that nitrogen rates of 180–250 kg ha⁻¹ are optimal for maize productivity in semi-arid systems with sufficient irrigation [4,5,6]. For example, Wasaya et al. [7] observed a 21% increase in grain yield at 200 kg ha⁻¹ compared to lower rates in Pakistan. Similarly, Hammad et al. [8] found that 250 kg ha⁻¹ nitrogen under adequate irrigation maximized kernel weight, whereas deficit irrigation required lower nitrogen inputs. This supports the interaction observed in our study, where excessive nitrogen beyond 240 kg ha⁻¹ did not improve yield, particularly under semi-arid irrigation regimes.

The slightly higher 1000-grain weight recorded in two-split applications (S₁) compared to three-split applications (S₂) suggests that late nitrogen supply may promote vegetative growth at the expense of grain filling. Torbert et al. [9] also observed that delayed nitrogen supply could shift assimilate partitioning, reducing kernel weight. Therefore, while split applications enhance yield components overall, balanced nutrient supply at critical growth stages remains essential.

These results reinforce the conclusion that optimized nitrogen rates coupled with well-timed split applications can maximize yield, improve NUE, and reduce environmental risks in semi-arid maize systems. Incorporating both chemical and organic nitrogen sources, as highlighted by Ncube et al. [10] and Wang et al. [11], may further enhance sustainability by improving soil fertility and water productivity.

5. Conclusion

Nitrogen management significantly influenced maize growth and yield under semi-arid conditions. Optimal yield (7.35 t ha⁻¹) was achieved at 240 kg ha⁻¹ with three-split applications, enhancing nutrient use efficiency. Excess nitrogen beyond this level reduced yield, indicating diminishing returns and inefficient resource use. Split applications proved more effective than two-split methods by synchronizing supply with crop demand. Thus, balanced nitrogen rates and well-timed applications are crucial for maximizing productivity and sustainability in semi-arid maize systems.