Nutrient management strategies for enhancing productivity of rabi maize in calcareous soils

Introduction

Calcareous soils occupy roughly 30% of the earth's arable surface, and in tropical Asia, they present a stubborn challenge for maize growers [1] . High soil pH (7.5-8.5) and free calcium carbonate convert applied phosphorus into insoluble calcium phosphate within hours, while zinc precipitates as zinc carbonate, leaving crops starved of two nutrients they badly need [2] . Rabi maize grown in the dry season with residual soil moisture or limited irrigation faces these constraints at a time when cool temperatures already slow root growth and nutrient absorption [3] . Standard fertilizer recommendations developed for neutral soils often underperform on calcareous substrates. The recommended dose of NPK may deliver adequate nitrogen but falls short on P and Zn because fixation losses aren't accounted for [4] . Organic amendments like farmyard manure (FYM) can partially buffer this fixation by chelating micronutrients and releasing organic acids that solubilize fixed P [5] . Site-specific nutrient management (SSNM), which adjusts inputs to actual field-level deficiencies, offers another approach but requires soil testing infrastructure that many tropical farmers lack [6] . Indonesia's calcareous soils, particularly on Java and Sulawesi, support a growing rabi maize area as farmers diversify beyond rice [7] . Yet systematic comparisons of nutrient strategies for this system remain scarce. This research aimed to: (i) compare grain yield and nutrient uptake responses to six management strategies on calcareous soil; (ii) assess the combined effect of zinc supplementation and organic amendment on P and Zn availability; and (iii) evaluate SSNM as an alternative to blanket fertilizer recommendations.

Materials and Methods

Materials

The research was conducted during two rabi seasons (May-September 2022 and May-September 2023) at the IPB University Experimental Farm, Bogor, West Java, Indonesia (6°33'S, 106°44'E). Maize hybrid Pioneer P35 was used. Urea, triple superphosphate, muriate of potash, and zinc sulfate heptahydrate (ZnSO₄•7H₂O, 21% Zn) were from PT Petrokimia Gresik.

Methods

Six treatments were applied: T1 unfertilized control, T2 RDF (150:75:60 kg NPK/ha), T3 RDF + ZnSO₄ (25 kg/ha), T4 RDF + FYM (10 t/ha), T5 RDF + ZnSO₄ + FYM, T6 SSNM based on soil test values using the Nutrient Expert decision tool [8] . Grain and stover were harvested at physiological maturity. Plant samples were digested and analyzed for N (Kjeldahl), P (vanadomolybdate), K (flame photometry), and Zn (AAS). Soil samples (0-30 cm) were collected pre-and post-season. Available N was estimated by alkaline permanganate, P by Olsen's method, and DTPA-extractable Zn [9] . ANOVA was performed in R 4.3 with Tukey's HSD at p ≤ 0.05.

Field experimental design

A randomized complete block design with six treatments and four replications was used. Plot size was 6 m × 5 m with 1-m borders. Maize was sown at 60 × 25 cm spacing (66,667 plants/ha). FYM was incorporated 15 days before sowing. N was split-applied: 50% basal + 25% at V6 + 25% at tasseling. Full P, K, and Zn were applied basally [10] .

Seasonal conditions

The 2022 rabi season had 412 mm rainfall (May-September) with mean temperature 26.3 °C; 2023 received 387 mm with mean 26.7 °C. Both seasons experienced a dry spell of 18-22 days during the grain filling stage. Treatment × season interaction was non-significant for grain yield (p = 0.41), permitting data pooling [11] .

Soil characteristics

The experimental soil was a calcareous Inceptisol with pH 7.8, free CaCO₃ 12.4%, organic carbon 0.82%, available N 168 kg/ha, Olsen-P 6.3 kg/ha (low), exchangeable K 142 kg/ha, and DTPA-Zn 0.54 mg/kg (deficient, threshold 0.6 mg/kg). Texture was clay loam (32% sand, 34% silt, 34% clay) [12] .

Results

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Table 2 presents nutrient uptake. T5 maximized total N (102.4 kg/ha), P (22.6 kg/ha), K (81.7 kg/ha), and Zn (378 g/ha) uptake. FYM addition (T4 vs T2) increased P uptake by 20.7%, reflecting organic acid-mediated P solubilization. Zinc uptake nearly doubled from T2 (217 g/ha) to T5 (378 g/ha)

. Figure 1 presents the nutrient uptake heatmap across treatments, showing T5 consistently at the highest level for all four nutrients. Figure 2 compares grain and stover yields, illustrating that yield responses to nutrient integration exceeded simple additive effects of individual amendments.

Discussion

The 26.2% yield advantage of T5 over RDF alone demonstrates that calcareous soil constraints require more than standard NPK. FYM's organic acids (citric, oxalic, malic) likely competed with phosphate for calcium binding sites, increasing P availability [5] . The 20.7% P uptake increase with FYM (T4 vs T2) supports this mechanism. Zinc supplementation separately boosted yield by 9.3% consistent with the soil's DTPA-Zn level of 0.54 mg/kg, just below the deficiency threshold [2,4] . SSNM's comparable performance (6.52 vs 6.89 t/ha, nonsignificant) suggests that soil-test-based adjustments can match integrated approaches when properly calibrated [6,8] . However, SSNM requires testing infrastructure that may limit smallholder adoption. The synergistic effect of combining Zn and FYM with RDF yield exceeded additive predictions by 8.7% points to FYM-mediated chelation enhancing Zn availability beyond what ZnSO₄ alone provides [9] .

Conclusion

Integrated nutrient management combining RDF with zinc sulfate and farmyard manure produced the highest rabi maize yield (6.89 t/ha) on calcareous soil, exceeding RDF alone by 26.2% and the control by 116.7%. This approach maximized uptake of N, P, K, and Zn through organic acid-mediated solubilization of fixed nutrients. SSNM performed comparably and offers a viable alternative where soil testing is accessible. For calcareous soils with low P and Zn availability, standard NPK recommendations are insufficient zinc supplementation and organic amendments should be standard practice.

Acknowledgement

AcknowledgementsThis research was supported by institutional funds from IPB University, Faculty of Agriculture. The authors thank IPB for field station and laboratory access, and acknowledge farm technicians for plot maintenance and sample collection.

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