Response of split application of nitrogen on growth and yield of sweet corn (Zea mays saccharata L.)

Introduction

Maize (Zea mays L.) is one of the world's leading cereals after rice and wheat and is known as the "Queen of cereals" because of its wide genetic diversity, climatic adaptability and diverse uses. It is cultivated from tropical to temperate regions for grain, fodder, food and industrial products. Among its types, sweet corn (Zea mays var. saccharata L.) has gained considerable commercial importance due to its sweet, tender kernels, resulting from a recessive gene that restricts the conversion of sugar into starch in the endosperm. Harvested at the milk stage, it is consumed fresh, boiled, roasted or canned and is widely used in soups, salads and confectionery. Thus, sweet corn offers good opportunities for crop diversification and improved farm income, particularly near urban markets. Nitrogen is a key nutrient influencing sweet corn productivity as it forms an essential component of chlorophyll, amino acids and nucleic acids and promotes leaf growth, photosynthesis and cob development. However, nitrogen is highly mobile and can be lost through leaching, volatilization and denitrification. Therefore, efficient scheduling of nitrogen applications is as important as the total quantity applied. Farmers commonly apply nitrogen as a basal dose or in two splits at sowing and the knee-high stage, which may cause excessive availability during early growth and deficiency during later stages of high crop demand. Splitting nitrogen into smaller applications according to critical crop growth stages, such as vegetative growth, tasseling and cob development, can improve nutrient availability, reduce losses and enhance nitrogen-use efficiency, fresh cob yield and fodder yield. Therefore, the present investigation was undertaken to evaluate eight nitrogen split-application schedules and their effects on growth, yield attributes, yield and economics of kharif sweet corn.

Materials and Methods

The experiment was conducted during kharif 2021 at the Agricultural Research Farm, Department of Agronomy, College of Agriculture, VNMKV, Parbhani, Maharashtra. The experimental soil was deep, clayey in texture, slightly alkaline in reaction, and well drained, with low available nitrogen, low available phosphorus and high available potassium. The site lies at about 19°16' N latitude and 76°47' E longitude at an elevation of roughly 409 m above mean sea level, and falls in the assuredrainfall zone of the South-West monsoon belt; the mean maximum and minimum temperatures during the crop season were 30.95 °C and 22.25 °C respectively, with a mean relative humidity of about 65-90%. The sweet corn variety Sugar-75 was sown by dibbling on 7 July 2021 at a spacing of 60 cm × 20 cm in a Randomized Block Design comprising eight nitrogen scheduling treatments replicated three times (24 plots in all), with a gross plot size of 5.4 m × 4.5 m and a net plot size of 4.5 m × 4.2 m. A uniform, recommended dose of nitrogen was applied to all treatments except the control, but the timing and number of splits differed as summarized in Table 1. Phosphorus and potassium were applied uniformly as a basal dose at sowing in all treatments, and recommended package of practices was followed for the rest of the crop management. [9] , and treatment means were compared using the critical difference at 5% probability.

Results and Discussion

Growth attributes

The mean initial and final plant stand of sweet corn (78.35 and 75.52 per plot, respectively) did not differ significantly among treatments, confirming that crop establishment was uniform and that the differences recorded later were attributable to nitrogen scheduling rather than uneven germination.

Growth characters recorded at harvest are summarized in Table 2.

Plant height, number of functional leaves, leaf area and total dry matter accumulation increased steadily up to about 60 days after sowing and then more slowly toward harvest. At 30 DAS none of these characters differed significantly among treatments, indicating that the early nitrogen dose had not yet produced a measurable growth response; from 45 DAS onward, however, treatment differences became significant and remained so up to harvest. [2,10,14] .

Yield-attributing characters

The number of cobs per plant was largely a varietal trait and did not vary significantly with nitrogen scheduling, but cob length, cob weight (with and without husk), number of grains per cob and grain weight per cob were all significantly influenced by treatment (Table 3), while test weight remained statistically unaffected. Treatment T8 again gave the highest values for every significant character, on par with T5 and significantly superior to the remaining schedules; the control produced the smallest, lightest cobs with the fewest grains. The build-up of cob size and grain number under frequent nitrogen splitting is consistent with better assimilate supply during the cob-formation and grainfilling window, in line with the observations of Pandey and Chaudhary (2014) [8] and Shah (2010) [12] .

Yield and economics

Fresh cob yield, green fodder yield and biological yield followed the same trend as growth and yield-attributing characters (Table 4). Treatment T8 gave the highest fresh cob yield (22,378.6 kg ha⁻¹), green fodder yield (42,688.2 kg ha⁻¹) and biological yield (65,066.8 kg ha⁻¹), remaining statistically at par with T5 but significantly better than the rest; the control yielded the least on every count. Harvest index also improved modestly with splitting, from 30.84% in the control to a maximum of 34.39% under T8, suggesting that frequent nitrogen application not only increased total biomass but also shifted a somewhat greater share of that biomass into the economic (cob) fraction. These trends corroborate earlier findings of yield gains from split nitrogen scheduling in sweet corn and maize (Harikrishna et al., 2010; Amanullah et al., 2009) [2,6] . The improved biomass and yield under frequent splitting translated directly into better economics (Table 5). The highest gross monetary return (Rs. 2,32,041 ha⁻¹) and net monetary return (Rs. 1,33,898 ha⁻¹) were realized under T8, on par with T5, giving the most favourable benefit-cost ratio of 2.36 among all treatments compared with 1.88 for the untreated control. Even though the cost of cultivation rose slightly with additional split applications, largely on account of extra labour for fertilizer application, the yield gains more than compensated for this added cost, making the four-split schedule the most remunerative option among those tested. Similar economic advantages of split nitrogen application in sweet corn have been reported by Abhishek et al., (2020) [1] and Rani et al., (2011) [11] . Post-harvest soil analysis showed a broadly similar pattern of nutrient depletion across treatments, with available nitrogen, phosphorus and potassium status declining somewhat more where crop uptake and yield were higher, indicating efficient utilisation of applied nitrogen by the higher-yielding split-application treatments rather than nutrient carry-over.

Conclusion

Among the different treatments, dividing nitrogen into four equal parts 25% as basal and 25% each at 30, 40 and 50 days after sowing gave the tallest, most leafy plants with the largest leaf area and dry matter accumulation, translated into the heaviest, longest cobs with the most grains, and produced the highest fresh cob yield, green fodder yield, biological yield and harvest index.

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