Evaluating the effects of diverse mulches on maize yield, water use efficiency, and economic viability under varying saline drip irrigation regimes

Introduction

Maize (Zea mays L.) ranks as the third most important cereal crop globally, serving as a crucial source of food, feed and industrial raw materials. In India, maize contributes significantly to food security, with an area of 11.24 million hectares producing 37.67 million tonnes during 2023-24 (DES, 2023-24). In Andhra Pradesh, maize is cultivated on 0.292 million hectares with an impressive productivity of 6225 kg ha⁻¹ (des.ap.gov.in, 2023-24) [5] . However, the escalating scarcity of quality irrigation water, particularly in coastal regions, poses a major challenge to sustainable maize production. Increasing reliance on saline groundwater for irrigation has aggravated soil salinization problems, adversely impacting crop growth, nutrient uptake and yield (Elsiddig et al., 2022 and Ibrahim et al., 2018) [6,10] . Maize is moderately sensitive to salinity, with optimal yield obtained when irrigation water EC remains below 1.7 dS m⁻¹ (Ayers and Westcot, 1999) [2] . Drip irrigation has emerged as a promising technique to mitigate salt stress by delivering water precisely to the root zone, thereby minimizing salt accumulation (Kang, 1998) [11] . Additionally, mulching with organic (straw) or inorganic (plastic) materials improves soil moisture retention, reduces evaporation, modifies soil temperature, and prevents salt buildup (Lessa et al., 2019; Barbosa et al., 2021) [12,3] . Plastic mulch, in particular, enhances water use efficiency and nutrient availability, contributing to better crop performance under saline irrigation. Given these considerations, the present study aimed to evaluate the interactive effects of saline water irrigation and mulching on maize growth, yield, WUE, soil properties, and economics under coastal agro-climatic conditions.

Materials and Methods

The field experiment was carried out during rabi 2024-25 at Agricultural College Farm, Bapatla (15°54' N, 80°30' E, 5.49 m MSL) under Krishna agro-climatic zone with 12 treatments. The experiment was laid out in a split-plot design with three replications. The main plot treatments comprised four salinity levels: M to achieve the required EC levels. These treatments were imposed from 20 DAS onward based on the calculated crop water requirement using the IW/CPE ratio. Meteorological observations during the crop period indicated a mean maximum temperature of 31.5 °C, minimum temperature of 20.4 °C, mean relative humidity of 67.5% to 87.0%, and a total rainfall of 20.3 mm over 3 rainy days. Plants were selected randomly, and their growth was observed. Attributed yield was recorded at harvest using kernel yield and harvest index, and water use efficiency were calculated.

Gross net returns and benefit-cost ratios were calculated using the cost of cultivation. Based on the field data, the data collected for crop growth, yield attributes and yield were statistically analyzed for variance.

Results and Discussion

Maize Kernel yield Kernel yield varied significantly among treatments. BAW recorded significantly the highest yield (8200 kg ha⁻¹), followed by 2 dS m⁻¹ (7704 kg ha⁻¹) and 4 dS m⁻¹ (7216 kg ha⁻¹), while 6 dS m⁻¹ recorded the lowest (5238 kg ha⁻¹).

The reduction in yield under high salinity is due to energy diversion from yield formation to stress mitigation. These results align with those of Shehzad et al. (2020) [16] and Feng et al. (2017) [8] . Among mulch treatments, plastic mulch recorded significantly higher kernel yield (7552 kg ha⁻¹), followed by straw mulch (7084 kg ha⁻¹), and no mulch (6632 kg ha⁻¹). Absy et al. (2020) [1] , who reported that the use of black plastic mulch stimulated root growth through enhanced soil temperature and moisture conservation, ultimately leading to improved grain yield per plant. The interaction between salinity and mulch was significant. [9] . Among mulching treatments, plastic mulch recorded significantly higher stover yield (8646 kg ha⁻¹), followed by straw mulch (8286 kg ha⁻¹), and no mulch (7836 kg ha⁻¹). The interaction was significant, with BAW and plastic mulch recording significantly the highest (9939 kg ha⁻¹), and 6 dS m⁻¹ with no mulch the lowest (6316 kg ha⁻¹).

Water use efficiency (WUE):

Significantly higher WUE was recorded under BAW (21.5 kg ha⁻¹ mm⁻¹), which was statistically on par with 2 dS m⁻¹ (19.3 kg ha⁻¹ mm⁻¹) and 4 dS m⁻¹ (18.1 kg ha⁻¹ mm⁻¹), while significantly the lowest WUE was observed at 6 dS m⁻¹ (13.1 kg ha⁻¹ mm⁻¹) (Table .3 & Fig. 3). The consistent water application by drip system minimized deep percolation losses and maintained optimal root zone moisture, even under saline conditions. This aligns with findings by Wang et al. (2021) [17] and Mrudhula et al. ( 2021) [14] . Among mulching treatments, plastic mulch recorded significantly the highest WUE (20.3 kg ha⁻¹ mm⁻¹), followed by straw mulch (19.1 kg ha⁻¹ mm⁻¹), which were significantly superior to no mulch (17.2 kg ha⁻¹ mm⁻¹). The increase in WUE under mulched conditions may be due to soil warming and enhanced early crop growth, which boosted biomass and yield, as reported by Zhang et al. (2011) [18] . The interaction between salinity and mulch was significant, with the highest WUE (22.9 kg ha⁻¹ mm⁻¹) recorded under BAW with plastic mulch and the lowest (12.6 kg ha⁻¹ mm⁻¹) under 6 dS m⁻¹ with no mulch. ). The improvement in returns with best available water was mainly due to increased kernel and stover yields. Similar reductions in returns under high salinity were reported by Emdad and Fardad (2000) [7] , while Rawal (2013) [15] observed a steep decline in net income under elevated salinity levels. Among the mulching treatments, plastic mulch resulted in the highest gross and net returns due to its effect on crop growth and water conservation. However, straw mulch recorded the highest B:C ratio (1.9), which was statistically on par with plastic mulch (1.8), both being superior to no mulch (1.8).

Although plastic mulch improved yield and income, its higher cost reduced profitability, making straw mulch more cost-effective. These results are in line with Mondal et al.

(2008) [13] , who reported the highest gross returns under black polythene mulch, and Cai et al. (2015) [4] , who emphasized the role of straw mulch in improving yield and economic efficiency under saline conditions.

Conclusion

The present study highlights the significance of combining saline water irrigation with appropriate mulching to sustain maize productivity in coastal regions. Drip irrigation with saline water up to 4 dS m⁻¹ did not significantly reduce maize growth, yield or WUE compared to BAW irrigation, indicating the crop's tolerance to moderate salinity under precise water application. Mulching, particularly plastic mulch, significantly improved soil moisture conservation, minimized salt accumulation, enhanced nutrient uptake, and boosted yield and WUE compared to no mulch and straw mulch. The integration of moderate saline water irrigation (≤ 4 dS m⁻¹) with plastic mulch proved to be the most effective strategy, achieving higher maize yields, improved soil health, greater WUE, and superior economic returns. These findings support the adoption of mulching and efficient drip irrigation to overcome water scarcity and salinity challenges for maize cultivation in coastal agroecosystems.

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