Performance of dual-purpose sorghum varieties under different planting dates and fertility levels

Introduction

A grain breeder measures sorghum success by the weight of clean seed per hectare; a dairy farmer measures it by the tonnage of palatable stover left standing after harvest. These two perspectives collide in the semi-arid tropics, where sorghum (Sorghum bicolor L. Moench) is expected to deliver both a cash grain crop and a dry-season roughage supply from the same planting [1] . Dual-purpose varieties attempt to reconcile the conflict by combining acceptable grain yield with tall, leafy stalks that retain digestibility at harvest [2] . Planting date governs the photoperiod and temperature regime that a sorghum crop encounters during its reproductive phase. Early planting (mid-June) in the Gezira irrigated scheme exposes the crop to heavy seasonal rainfall during grain filling, increasing the risk of grain mould, while late planting (mid-July) shortens the growing season and reduces total biomass accumulation [3] . Fertility management adds a second axis of variation: nitrogen drives tiller number and leaf area, phosphorus supports root development, and potassium improves stalk strength and drought tolerance [4] . Despite the obvious interaction among these three factors, most sorghum trials in Gezira State have tested varieties, planting dates, and fertility levels in isolation or in two-factor combinations [5,6] . No factorial trial combining all three under Gezira irrigated scheme conditions has been reported. This research was designed to fill that gap by evaluating three dual-purpose varieties across three planting dates and three fertility levels in a split-plot layout replicated over two rainy seasons.

Field Experimental Design

The experiment followed a split-plot design with planting dates as main plots and a factorial combination of varieties and fertility levels as sub-plots. Each main plot (planting date) was divided into nine sub-plots (3 varieties × 3 fertility levels), giving 27 treatment combinations replicated three times -a total of 81 sub-plots. Sub-plot size was 5 m × 3 m with 1 m alleys between main plots and 0.5 m between sub-plots. Sowing was done manually in rows spaced 45 cm apart, with 15 cm intra-row spacing, and thinned to one plant per hill at 15 Physiological maturity (BBCH 87, black layer formation) was reached at 102-118 days after sowing [7] .

Material and Methods

Material

Methods

Nitrogen was applied in three equal splits -at sowing, at knee-high stage (30 DAS), and at panicle initiation. Full doses of P and K were applied as basal. Growth parameters (plant height, leaf area index, dry matter accumulation) were recorded at 30-day intervals. At harvest, grain yield (q ha⁻¹ at 12% moisture), stover yield (q ha⁻¹ at sun-dry weight), panicle weight, test weight (1000-grain weight), and harvest index were determined from the net plot area (4 m × 2.4 m). Data were analysed by split-plot ANOVA; means were separated by LSD at p< 0.05 [9] .

Results

Table The July 15 planting consistently underperformed: grain yield fell by 17-24% and stover yield by 16-20% relative to the July 1 planting across all variety × fertility combinations. This decline was driven by a shorter vegetative phase (103 vs. 108 days to maturity), fewer leaves per plant at anthesis (9.2 vs. 11.4), and reduced dry matter partitioning to panicles. In contrast, the June 15 and July 1 dates produced statistically similar yields, though July 1 showed a slight numerical advantage in grain output.

Comprehensive Interpretation

The strong linear relationship between grain and stover yields (R² = 0.93) confirms that dual-purpose selection has not created a trade-off at the fertility levels tested here. SPV 2217 topped the ranking at every fertility level, reflecting its genetic potential for both tall stature and heavy panicles. The variety × fertility interaction was significant (p< 0.01), with SPV 2217 responding more steeply to additional nitrogen than CSV 15, suggesting that the older variety has already plateaued at moderate fertility [10] .

Discussion

SPV 2217's top-ranking grain yield (40.1 q ha⁻¹) exceeds the 34-37 q ha⁻¹ reported for this variety in initial multi-location trials coordinated by ARC Sudan, probably because the Gezira irrigated scheme's deep Vertisol provided a more favourable moisture regime than the sandy aridisols used in those trials [11] . The mechanism is straightforward: deeper soil moisture buffers the crop during late-season dry spells, sustaining leaf area duration and grain filling rate. For the Gezira farmer, SPV 2217 represents a step up from CSV 15 -an older variety still widely grown in the region -without sacrificing stover palatability [12] . The yield penalty from late planting (July 15) matches findings from Marathwada and Blue Nile State, where each week's delay beyond the optimum window reduces sorghum biomass by 5-8% [13] . The proximate cause is a shorter vegetative period, which limits tiller number and final leaf area index. But the indirect effect is equally damaging: lateplanted crops in the Gezira irrigated scheme encounter receding soil moisture during grain filling (October), when evaporative demand is still high [14] . The absence of a planting-date effect on harvest index (0.31-0.32 across dates) means that both grain and stover declined proportionally under late planting, preserving the dualpurpose character. This is an encouraging sign for extension International Journal of Agriculture and Food Science https://www.agriculturaljournals.com workers advising farmers who miss the early window -lateplanted sorghum still produces usable stover, just less of it [15] . Fertility response plateaued between the medium (90:45:45) and high (120:60:60) doses in CSV 15 but continued to rise in SPV 2217, indicating that the newer variety can exploit higher soil nutrient availability more effectively. Economically, the marginal return on the additional 30 kg N ha⁻¹ was positive for SPV 2217 (B:C ratio 3.2 vs. 2.7) but not for CSV 15 (2.4 vs. 2.3) [16] .

Conclusion

This research aimed to identify the best combination of variety, planting date, and fertility level for dual-purpose sorghum in the Gezira irrigated scheme. After two rainy seasons, SPV 2217 planted on July 1 at 120:60:60 kg N:P₂O₅:K₂O ha⁻¹ delivered the highest grain yield (40.1 q ha⁻¹) and stover yield (82.1 q ha⁻¹). Late planting (July 15) reduced total biomass by 16-24% regardless of variety or fertility. Farmers in the Gezira should target the last week of June to the first week of July as the optimum sowing window and pair SPV 2217 with the higher fertility dose where soil test values support it. Future research should extend the planting-date window to include a very early date (June 1) and evaluate stover quality traits -digestibility, stem sugar content -alongside yield to give dairy-integrated farmers a fuller picture of each variety's feeding value [17,18] .

Acknowledgement

Acknowledgements Contributions:The authors thank field workers at the Agronomy Research Farm for plot preparation, sowing, and harvest operations carried out meticulously across both seasons.Funding Sources: Financial support was provided by the Sudan Agricultural Research Corporation Sorghum Programme through the Institute's research allocation.Institutional Support: University of Gezira provided land, irrigation facilities, and laboratory access for the duration of the trial.

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