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Organic amendment due to their variable mineralization, immobilization and adsorption capabilities need different management strategies and integration with chemical fertilizers for maximum benefits. in this regard a series of laboratory and field experiments were conducted to evaluate the role of Farmyard manure (FYM), poultry manure (PM) and biochar (BC) in Zn availability under diverse calcareous soils of Peshawar (16.6 % CaCO3) and Charsadda (6.5 % CaCO3). These studies included Zn adsorption as influenced by these amendments in Peshawar soil [Piedmont alluvium, silty clay loam, Ustochrept] followed by incubation experiment for evaluating their role in improving soil [Zn]. Finally, the effect of amendments and applied Zn was studied in field conditions in both soils for two seasons. The first season crop was maize to which these amendments and Zn levels were applied whereas the wheat was used for their residual effect. The adsorption of Zn was assumed to be the difference between initially applied Zn (IZnA) and equilibrium Zn concentration (EZnC) in soil solution after 20 h continuous shaking. The soils amended with FYM, PM or BC each at 10 g kg-1 exhibited higher Zn adsorption (x/m) at higher IAZn (40 mg to 360 mg Zn L-1) but at lower IZnA < 20 mg Zn L-1 the reverse was observed. The data in non-treated soils were fit to both Langmuir and Freundlich models but in treated soils these models were fit only when the data for initial IAZn were disregarded. The higher maximum adsorption potential b (in case of Langmuir) and K (in case of Freundlich) values as well as maximum buffering capacity (MBC) in amended soil reveals the role of organic amendments in maintaining Zn in soil solution and availability to plants. The adsorption maximum as indicating by b and K was higher for BC followed by FYM but MCB and 1/n values that reflect the buffering capacity were higher for FYM than BC or PM. The lower adsorption at IZnA < 20 mg Zn L-1 but higher at > 20 mg Zn L-1 for amended soil suggests its contrasting effect at different IZnA levels. This reveals that organic amendments will increase the Zn nutrition in low concentrated Zn soils but on the other side can help in reducing its availability in highly contaminated soils. The incubation study was conducted to evaluate the comparative role of FYM, PM and BC in maintaining soil Zn of high limed, Peshawar and low limed, Charsadda soils during 84 days of incubation. The soils were first amended with the given organic xvi amendments at 10 g kg-1 and then supplied with Zn levels at 0, 1.5 and 3.0 mg kg-1 soil. The treatments were arranged in completely randomized design with 4 (amendments type) x 3 (Zn levels) x 2 (soil types) factorial arrangements replicated three times. Significantly higher AB-DPA extractable [Zn] levels were observed by PM followed by FYM in the initial intervals but by BC after 56 d of incubation suggesting its increasing role in soil fertility in long run. The combine application of amendments with Zn levels, further improved the recovered AB-DTPA extractable Zn at given incubation advocating the potential advantage of integrated use of organic and inorganic amendments in the given soils. Among amendments, the PM+Zn exhibited higher [Zn] in both soils followed by FYM+Zn. However, the effect of BC+Zn which remained lower to FYM+Zn in both soils at earlier incubation intervals superseded it at later stage affirming the potential role of BC in the long run. This incubation study corroborates the field trials where the BC+Zn was better in wheat whereas the FYM+Zn in maize. In the field experiments, Zn at 0, 3 and 6 kg ha-1 were applied alone or in combination with FYM, PM or BC each at 20 t ha-1 in both sites. After maize, the same plots were sown with wheat crop for residual effect. Growth and yields of first season maize and succeeding wheat crop increased with increase in Zn levels and amendment application but the response was comparatively higher in high limed Peshawar than Charsadda soil that may be attributed to its initially lower fertility and poor soil conditions. Among amendment, PM showed better performance in increasing crop growth and yields in both locations and crops followed by FYM in maize but in succeeding wheat the biochar became more effective withstanding statistically at par to both PM and FYM. This increasing promising effect of BC with time reveals its lower but long lasting effects in crop production. The application of Zn with amendments also significantly increased the grain Zn and postharvest soil [Zn] in both locations and crops. PM was more effective but with either 3.0 or 6.0 kg Zn ha-1 it induced similar increases over control in contrast to FYM and BC where grain Zn increased with increase in applied Zn levels. This could be attributed to high Zn contents in PM that need less applied Zn. Results concluded that application of PM with 3.0 kg Zn kg-1 and FYM and BC with 6.0 kg Zn ha-1 would be the optimum levels for first season crops but in the succeeding crops as residual effects higher Zn application would be required irrespective of amendment type in the given soil and climatic conditions. Furthermore, the application of BC is recommended for long lasting results but its initial higher cost may hinder its application at larger scale Key words: Organic amendments, zinc, plant growth, Zn adsorption, biochar, isotherm model, , calcareous soil
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