Saturday, 15 July 2006

Soil Fertility Status of Ultisols as Influenced by Arecanut Based Cropping System and Nutrient Management through Organic Matter Recycling.

Ravi Bhat and Sujatha S. Central Plantation Crops Research Institute, Regional Station, Vittal - 574 243, Karnataka, India

Ultisols (Laterite soils), in humid tropics of West coast of India, are associated with several constraints like low CEC (3-15 cmol (p+) kg-1), acidity, P fixation, leaching of N, K and Ca due to heavy annual rainfall of 300-400 cm and reduced nutrient use efficiency ultimately leading to low productivity. Efficient and environmentally safe management of soil fertility is indispensable to achieve optimum productivity per unit area. Arecanut (Areca catechu L.), which belongs to family Palmae, is predominantly grown on these soils. Arecanut based cropping system (ABCS) with cocoa (Theobroma cacao L.), banana (Musa spp), clove (Syzygium aromaticum), black pepper (Piper nigrum L.) and coffee (Coffea arabica) as component crops is successful on these soils, which has high nutrient requirement placing a great demand for nutrients on the soil + fertilizer system. The system generates considerable quantity of organic wastes rich in lignin and cellulose which has high potential for recycling. Therefore, an experiment was conducted during 1999-2003 in an existing ABCS established during 1983 to study the impact of the system and nutrient management through recycling of vermicomposted organic wastes using African night crawler earthworm (Eudrilus euginae) on the nutrient status at Central Plantation Crops Research Institute, Regional Station, Vittal, Karnataka, India. The experiment was laid out in randomized block design with four treatments and five replications. The treatments included Organic Matter Recycling (OMR), 1/3rd of recommended NPK + OMR, 2/3rd of recommended NPK + OMR and recommended NPK + OMR. The recyclable biomass produced from the system varied between 8.72 10.35 Mg ha-1 year-1. The nutrient content in vermicompost was 1.71% N, 0.21% P and 0.43% K. Significant variability (P<0.05) in nutrient status of Ultisols was observed due to arecanut based cropping system and nutrient management through organic matter recycling. Organic matter recycling maintained sufficient mineral N and available P levels in soil at par with integrated nutrient management treatments. No significant correlation between yield and soil NP and leaf NP indicated the beneficial effects of organic matter recycling in the form of vermicompost in sustaining crop yields and N and P supply to soil with minimum or no inorganic fertilizer input levels. The availability of K increased significantly with integrated use of inorganic fertilizer and OMR compared to only OMR at both soil depths. Significant depletion of available K in all crop rhizospheres at both soil depths during experimental period revealed the necessity of including K in the fertilizer schedule of the system due to heavy K feeding nature of all the component crops and leaching losses. Crop rhizospheres showed significant variation in organic carbon status. However, nutrient management had no significant impact on organic carbon status. The organic carbon content in banana (1.58-1.78%) and coffee (1.51-1.77%) rhizospheres was improved over initial status (1.40%) in 1999. Conjunctive use of 2/3rd recommended NPK + OMR significantly increased microbial quotient both at 0-30cm (2.95) and 30-60cm (2.05) soil depth. Significant variability (P<0.01) in microbial quotient was noticed in rhizosphere of different crops with cocoa registering higher value of 3.90. Significant variation in soil pH in rhizosphere of different crops was noticed with sharp decline in cocoa rhizosphere treated with integrated use of OMR and 2/3rd to full dose of recommended NPK. Overall, positive impact of ABCS was noticed with increase in soil pH to 5.18 and 4.95 at 0-30 and 30-60 cm soil depth, respectively in 2002 compared to the reported value of 4.70 and 4.45 in 1988, enrichment of organic carbon with 58 105 % increase and adequate availability of P during the same period. The study indicated that application of N and P through inorganic fertilizers could be reduced or skipped. However, the system proved exhaustive with regard to the availability of K requiring continuous application of K through inorganic fertilizer. Available P content reduced by 74% at 30-60 cm depth compared to 0-30 cm depth (42.8 g g-1) indicating the very less mobility P beyond 30cm depth in Ultisols.

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