In view of scarcity of information, effectiveness of toxicity characteristics leaching procedure (TCLP) in assessing metal hazards of polluted soils was evaluated in relation to human health. Total metal content in the soils studied were 1657 ± 2335 mg kg⁻¹ for Zn, 351 ± 180 mg kg⁻¹ for Cu, 166 ± 79.9 mg kg⁻¹ for Ni, 249 ± 269 mg kg⁻¹ for Pb and 18.6 ± 23.2 mg kg⁻¹ for Cd. The TCLP requires a buffering of acidic leaching extraction based on the soil reaction. The TCLP extractable (reagent 1) metal content was varied as 177 ± 376 mg kg⁻¹ for Zn, 10.9 ± 28.5 mg kg⁻¹ for Cu, 23.1 ± 67.2 mg kg⁻¹ for Ni, 2.79 ± 10.3 mg kg⁻¹ for Pb and 4.92 ± 16.3 mg kg⁻¹ for Cd across the experimental soils. Reagent 2 extractable Zn, Cu, Ni, Pb and Cd were recorded as 136 ± 364, 3.16 ± 1.79, 1.49 ± 2.73, 0.57 ± 2.20 and 1.95 ± 6.92 mg kg⁻¹, respectively. In case of spinach, the values of hazard quotient (HQ) varied from 0.055 to 0.972, 0.002 to 0.019, 0.008 to 0.181, 0.066 to 5.489 and 0.044 to 11.32 in respect of Zn, Cu, Ni, Pb and Cd, respectively. The ranges of HQ for intake of Zn, Cu, Ni, Pb and Cd through consumption of wheat grain were 0.36–1.88, 0.02–0.12, 0.05–0.80, 0.13–1.21 and 0.10–59.5, respectively. While comparing the effectiveness of assessing metal hazard of TCLP with that assessed in terms of HQ, it is clear that in some soil samples the critical value of HQ (>0.5) exceeded for Pb (spinach), whereas TCLP extractable Pb content in those soils were within the safe limit i.e. <50 mg kg⁻¹. It appears that TCLP method is not only useful for judging the ecological risk of metal polluted soil but also assessing the suitability of soil for crop production, provided permissible limit of TCLP should be revised.

Understanding of the potassium (K) nutrient cycle and its microbial transformation of unavailable forms of soil K to plant-available K is crucial in any agroecosystem for strategic nutrient management through inorganic fertilizer, crop residue (CR), and microbial applications. Therefore, the present investigation was undertaken to study the effect of crop residue and K management practices on crop productivity, K mobilization from native soil K-pool, and crop assimilation of K under a zero-till maize–wheat cropping system. The experiment consisted of four residue levels (0, 2, 4, and 6 Mg ha⁻¹) and five K levels (0, 50%, 100%, 150% RDK [recommended dose of K] and 50% RDK + potassium solubilizing bacteria, KSB). Results showed that CR retention at 6.0 Mg ha⁻¹ significantly improved grain yield (of maize by 10.17%; wheat by 9.87%), dry matter accumulation, K uptake and redistribution in native soil K pools (water soluble K (WSK), exchangeable K (EK) and non-exchangeable K (NEK)) at 30 and 60 days after sowing and at harvest as compared to no CR. Among the K management, 50% RDK+KSB reported significantly higher grain yield (of maize by 26.22%; wheat by 24.70%), dry matter accumulation, K uptake, and native K pools (WSK, EK, and NEK) at different growth stages compared to no K. Total K did not differ significantly due to residue and K management. The highest actual change of K reported with 6.0 Mg ha⁻¹ CR (51 kg ha⁻¹) and 50% RDK+KSB (59 kg ha⁻¹) over control. Significant (p ≤ 0.01) positive correlation was found among grain yield, dry matter accumulation, K uptake, the actual change in K and different native K pools. It can be concluded that retention of 6 Mg ha⁻¹ CR and supply of 50% K through inorganic fertilizer along with seed inoculation of KSB biofertilizers, improved crop growth, productivity by enhancing K assimilation as a consequence of the release of non-exchangeable K and through the application of CR and K treatments under a zero tillage maize–wheat system.

With increasing adoption of conservation agriculture (CA), understanding of the impact of tillage, and residue retention and nutrient management options on the transformation of soil phosphorus (P) will give a brief idea of the extent of bioavailability of the different fractions, as low P availability in soil limits crop production. Thus, transformation and bioavailability of P through sequential fractionation was studied (0–5 and 5–15 cm) in maize-wheat cropping system with treatments consisting of four levels of tillage and residue regime (TR) as main plots i.e. conventional tillage (CT-RR); conventional tillage with residue incorporation (CT+RI+GI), maize and wheat on permanent beds with residue retention (PB+RR) and maize, wheat and green gram on permanent beds with residue retention (PB+RR+GR), and three nutrient management (NM) options in sub-plots i.e. farmer's fertilizer practice (FFP); recommended dose of fertilizers (RDF) and site-specific nutrient management (SSNM) in a split-plot design with three replications. Results showed that PB+RR+GR resulted in highest soil microbial biomass P (SMBP), Olsen-P, labile and moderately labile-P content amongst TR systems at 0–5 and 5–15 cm depths. The TR systems influenced the HCl-P but not the residual-P and total-P. Complete CA significantly increased total organic P (TPo) by 6.28% in the top 5 cm layer. Among the NM options, highest SMBP, Olsen P and labile P were registered under SSNM. The mean distribution of P fractions was: residual-P (32.1%) > HCl-P (27.8%) > NaOH-Po (22.2%) > NaHCO₃-Po (9.06%) > NaOH-Pi (6.28%) > NaHCO₃-Pi (1.39%) > water soluble P (WSP) (1.11%). The WSP was positively correlated with NaHCO₃-Pi, NaHCO₃-Po, NaOH-Po and TPo in both soil layers. Olsen P and SMBP were also positively correlated with labile P and NaOH-Po. The study showed that nutrient applied through SSNM approach rather than blanket recommendation enhanced the labile and available P in soil under CA.

The indiscriminate use of chemical fertilizers can deteriorate soil, grain, and environmental quality; still, these can be restored if integrated nutrient management options with inclusion of legumes in the cropping system are adopted. A long-term (19 year) rice-wheat system experiment was examined to find out the best nutrient management practices (BNMP) through recommended dose of fertilizers (RDF), integrated plant nutrition system (IPNS), soil test crop response (STCR), farmyard manure (FYM), along with the inclusion of pulses (berseem and cowpea). Seven nutrient management practices were applied in combination of organic and chemical fertilizer in the rice-wheat system. Results showed that a significant variation was seen in phosphorus (P) fractions among the treatments and soil depths. The results showed a significantly (p < 0.05) higher contribution to phosphorus availability by Residual-P followed by NaHCO₃-Po > NaOH-Pi > NaOH-Po > HCl-P > NaHCO₃-Pi > available P and lowest in WSP under different long-term management options in rice-wheat system after completing 19 crop cycles. Variations in soil P-fractions with depth were compared to different treatment combination, and a considerable increase in all the major P-fractions was noticed. The continuous application of various IPNS options as organic farming (OF), RDF, STCR, and the inclusion of pulses (berseem and cowpea) significantly improved all P fractions in the soil system and offered an added benefit in terms of sustainability of production and soil health compared to the solo application of chemical fertilizers. Overall, results showed that IPNS options (berseem and cowpea) showed its superiority over the rest of the treatment. This study suggests that the inclusion of pulses would increase P-availability in soil system.

Continuing soil degradation remains a serious threat to future food security. Soil aggregation can help protect soil organic matter from biodegradation; it affects soil physical (aeration), chemical (water infiltration), and biological (microbial) activities. The integrated plant nutrition system (IPNS) and organic farming (OF) options have been contemplated as a sustainable strategy to sustain soil aggregate stability under adverse climatic conditions and a possible tool to restore degraded soil systems. Results suggested that the application of plant nutrients based on IPNS and soil test crop response (STCR) including mineral fertilizers and organic manure (farmyard manure: FYM) improved soil aggregate stability and mean weight diameter (MWD) under rice–wheat cropping systems. A long-term (19 year) cropping system (rice–wheat) experiment was examined to identify best nutrient management practices. Seven nutrient supply options were applied: organic, mineral fertilizer in combination with IPNS, IPNS + B/IPNS + C to improve soil aggregate stability and MWD after completing 19 cropping cycles of rice–wheat cropping systems. Results showed that significantly higher (+31%) macroaggregates were dominant in the surface soil layer than in the subsurface soil. The significantly highest macroaggregates were observed under OF (60.12 g 100 g⁻¹ dry soil) management practices followed by IPNS options. The MWD was significantly increased (+17%) between surface and subsurface soil. Maximum MWD was reported with OF (0.93 mm) management practices followed by the IPNS + C (0.78 mm), IPNS + B (0.77 mm), IPNS (0.70 mm), STCR (0.69 mm), NPK (0.67 mm), and unfertilized control (0.66 mm) plots. Overall, results suggest that the adoption of IPNS options, such as organic farming (OF), RDF, STCR, and inclusion of pulses (berseem and cowpea), significantly improved all soil aggregation fractions in the soil system and also offered an additional benefit in terms of soil sustainability.