Nutrient removal by rice–wheat cropping system as influenced by crop establishment techniques and fertilization options in conjunction with microbial inoculation

The study addresses how crop establishment techniques (CETs) and nutrient management strategies (rates and sources of N, P, Zn fertilization, and microbial inoculation) influence nutrient removal and soil nutrient status within the rice–wheat cropping system (RWCS). Given the large share of national fertilizer use and energy consumption by rice and wheat in India, and concerns about negative soil nutrient balances, there is a need to optimize CETs (e.g., puddled transplanted rice–conventional wheat; system of rice intensification–system of wheat intensification; aerobic rice–zero-tillage wheat) and fertilization schemes. The hypothesis is that nutrient rates and sources can differentially affect plant uptake and soil pools across CETs, and that microbial inoculants could improve N and P acquisition and soil biological properties. The objective was to compare six CET–nutrient management combinations for their effects on N, P, K, Zn and Fe uptake, soil available P, K and Zn fractions, and soil microbial indicators over two RWCS cycles.

The paper outlines the emergence and mixed yield evidence of the System of Rice Intensification (SRI), the water-saving but constraint-prone Aerobic Rice System (ARS), and adoption of zero-tillage wheat due to operational and residue management benefits. It highlights the disproportionate nutrient and energy demand of rice–wheat systems in India and a national negative nutrient balance, motivating evaluation of CET impacts on nutrient dynamics. Prior work supports the potential of microbial inoculants (cyanobacterial N fixation; bacterial P solubilization/mobilization) to complement chemical fertilizers, given low P use efficiency and environmental costs of high N use. Widespread soil Zn deficiency, crop yield and nutritional responses to Zn, and human nutrition relevance justify Zn fertilization treatments. Literature also documents CET-induced changes in soil properties, nutrient availability, and crop performance, as well as conservation agriculture effects on soil biology and nutrient cycling.

Location and soil: Field experiments were conducted at ICAR–Indian Agricultural Research Institute, New Delhi, India (28°38′N, 77°10′E; 228.6 m amsl) under a subtropical semi-arid climate. Rainfall during rice seasons was 1349.8 mm (2013) and 451.4 mm (2014), and during wheat seasons 147.6 mm (2013–14) and 308.6 mm (2014–15). Topsoil (0–15 cm) was sandy clay loam, pH 7.6, organic C 5.4 g kg⁻¹; initial available N (KMnO₄): 257 kg ha⁻¹; Olsen P: 17 kg ha⁻¹; NH₄OAc-K: 327 kg ha⁻¹; DTPA-Zn: 0.85 mg kg⁻¹. Experimental design: Split-plot with three main-plot CETs and nine subplot nutrient management treatments, replicated three times, across two RWCS cycles (2013–14, 2014–15). CETs (main plots): (i) Puddled transplanted rice followed by conventional drill-sown wheat (PTR–CDW), (ii) System of rice intensification followed by system of wheat intensification (SRI–SWI), (iii) Aerobic rice system followed by zero tillage wheat (ARS–ZTW). Sowing/transplanting dates were coordinated to match crop durations across CETs each year (mid-June for rice, mid-November for wheat). Nutrient treatments (subplots): T1 Control (no fertilizer); T2 RDN (100% recommended N and P); T3 RDN + Zn; T4 75% RDN; T5 75% RDN + Zn; T6 75% RDN + MC1; T7 75% RDN + MC1 + Zn; T8 75% RDN + MC2; T9 75% RDN + MC2 + Zn. RDN per crop: 120 kg N ha⁻¹ and 25.8 kg P ha⁻¹ (as P). Zn: 5 kg Zn ha⁻¹ (as ZnSO₄·7H₂O) per crop. K applied uniformly to all plots: 49.8 kg K ha⁻¹ per crop (as muriate of potash). Urea and single superphosphate were N and P sources. Microbial inoculants: MC1 = Anabaena sp. (CR1) + Providencia sp. (PR3) consortium; MC2 = Anabaena–Pseudomonas biofilm. Formulations were prepared with vermiculite:compost (1:1) as carrier (paddy straw compost C/N 16.22:1, humus 13.8%, pH 7.34); cyanobacterial and bacterial CFUs ~10⁴ and 10⁶ g⁻¹ carrier, respectively, following established protocols. Measurements: Biological yield (net plot harvest), plant N (Kjeldahl), P (vanado-molybdo colorimetry), K (flame photometry), Zn and Fe (AAS). Soil available P (Olsen NaHCO₃-extractable), K (1 N NH₄OAc-extractable), Zn and Fe (DTPA-extractable via AAS). Microbial biomass carbon (fumigation method) and soil chlorophyll (acetone:DMSO extraction). Partial factor productivity (PFP) and agronomic use efficiency (AUE) for N and P were computed from grain yield and nutrient applied. Data were analyzed by ANOVA (F-test) with LSD at p=0.05; interactions evaluated where significant.

- System yields were statistically similar across CETs, but nutrient management significantly influenced yields. RDN + Zn in ARS–ZTW produced the highest biological yield, on par with 75% RDN + MC1 + Zn and 75% RDN + MC2 + Zn across CETs. MC1 and MC2 increased system biological yield by ~0.99–1.11 and 1.12–1.19 Mg ha⁻¹, respectively; Zn fertilization further increased yields across nutrient regimes. - Nutrient uptake: System N uptake ranged 129.4–290.2 kg ha⁻¹. Among CETs, ARS–ZTW was highest (≈237.7–245.7 kg ha⁻¹); among treatments, RDN + Zn was highest (≈281–290 kg ha⁻¹). Microbial inoculation increased system N uptake by ≈28.3–33.0 kg ha⁻¹. Zn fertilization increased N uptake when combined with RDN and with 75% RDN ± MCs (magnitude 6–36 kg ha⁻¹ depending on combination and year). Compared with 75% RDN and control, RDN increased N uptake by ≈38–40 and 90–95 kg ha⁻¹, respectively. - P and K uptake were significantly higher in ARS–ZTW than PTR–CDW and SRI–SWI. Applying 75% RDN + MC1 or MC2 + Zn in ARS–ZTW raised P uptake by 5.4–6.9% over the same treatments in PTR–CDW and SRI–SWI; K uptake increases were 21.9–26.5 and 25.4–29.1 kg ha⁻¹. RDN + Zn in ARS–ZTW increased P uptake by 0.7–1.0 kg ha⁻¹ and K uptake by 6.8–12.0 kg ha⁻¹ over PTR–CDW and SRI–SWI. - Zn and Fe uptake: The greatest driver of Zn uptake was N and P application rate (increase 101.4–282.7 g ha⁻¹), followed by microbial inoculation (88.3–95.5 g ha⁻¹), Zn fertilization (76.8–79.3 g ha⁻¹), and CETs (18.3–23.1 g ha⁻¹). For Fe, N and P rate had the largest effect (457.8–1350.6 g ha⁻¹), while CET effect was smallest (42.0–47.5 g ha⁻¹). Highest Fe uptake occurred in PTR–CDW (~5600 g ha⁻¹), with ARS–ZTW lower but close. - Soil available nutrients after two cycles: Olsen P increased under RDN and under 75% RDN + MC1/MC2 (with or without Zn), but not under 75% RDN alone or control. RDN had 6.3–11.3 kg ha⁻¹ higher available P than 75% RDN. PTR–CDW and SRI–SWI had higher soil P than ARS–ZTW by ~1.75–3.12 kg ha⁻¹. - Soil K (NH₄OAc-extractable) decreased in all treatments despite uniform K application (49.8 kg K ha⁻¹ per crop); decreases over initial were 131–147 kg ha⁻¹ (first year) and 27.6–42.7 kg ha⁻¹ (second year). Variation was mainly governed by plant K uptake. - Soil DTPA-Zn increased primarily due to Zn fertilization; increases were ≈4284–5362 g ha⁻¹ across CETs per year, with smaller effects of N,P rates and microbial inoculation. - Soil biological indicators: In rice, SRI had higher soil chlorophyll and MBC in year 1; in year 2 SRI and PTR were on par and superior to ARS. In wheat, ZTW was superior in year 1 (on par in year 2). Treatments with MCs (especially 75% RDN + MC2) showed the highest soil chlorophyll and MBC; both indicators positively correlated with biological yield. - PFP and AUE: ARS–ZTW had higher PFP for N and P than other CETs by ~0.2–0.4 kg grain kg⁻¹ N and 0.8–2.1 kg grain kg⁻¹ P. PTR–CDW had higher AUE for N and P (≈+1.53–1.55 and +7.1–7.2 kg grain increase per kg nutrient). Microbial inoculation with 75% RDN improved PFP and AUE versus 75% RDN alone; Zn addition further improved both metrics. - Nutrient balances: Of total available P (initial soil + fertilizer), 36.9–40.8% was removed by crops, 7.6–8.7% remained as NaHCO₃-extractable; 50.4–55.3% was not NaHCO₃-extractable (fixed/losses). K balance was negative in all treatments and years, indicating insufficiency of current K application. Of total available Zn (initial + fertilizer), only 11.6–18.5% was taken up by crops, while 54.2–90.5% accounted for increases in DTPA-Zn; actual Zn balance was 1484–1927 g ha⁻¹ lower than calculated balances. - Overall, ARS–ZTW improved system nutrient uptake (N, P, K, Zn) relative to other CETs, microbial inoculation enhanced nutrient uptake and soil biological status, and Zn fertilization raised soil DTPA-Zn and supported higher N uptake.

Findings support the hypothesis that nutrient rate/source and CETs interact to influence nutrient uptake and soil status in RWCS. While system yields were comparable among CETs, ARS–ZTW enhanced system-level nutrient uptake and nutrient use efficiency (PFP), likely due to improved root environment and zero-till wheat performance. Microbial consortia (MC1, MC2) contributed biologically fixed N and solubilized P, improving plant nutrient acquisition, soil microbial activity (MBC, chlorophyll), and maintaining or increasing soil Olsen P at reduced fertilizer rates (75% RDN). Zn fertilization significantly increased DTPA-extractable Zn and, in combination with adequate N and P, supported higher N uptake through improved crop growth. Potassium balances were negative across all treatments, indicating that recommended K rates were inadequate for RWCS demand and residue recycling/adjusted K fertilization is needed. Overall, rate of N and P application exerted the strongest effect on nutrient uptake, followed by Zn fertilization and microbial inoculation, with CETs having smaller but meaningful impacts.

The study demonstrates that adopting aerobic rice followed by zero-tillage wheat (ARS–ZTW), combined with microbial inoculation (Anabaena–Providencia consortium or Anabaena–Pseudomonas biofilm) and appropriate Zn fertilization, enhances system-level nutrient uptake (N, P, K, Zn), improves soil biological health, and increases soil DTPA-Zn in RWCS without compromising yield. Microbial inoculants enable reduced fertilizer inputs (75% RDN) while sustaining nutrient uptake and improving P availability. However, current K fertilization is insufficient given consistent negative K balances, necessitating revised K management and residue recycling. Future research should optimize inoculant deployment across water regimes and CETs, refine K recommendations under conservation practices, and assess long-term soil nutrient pools and environmental outcomes.