Lowest effective and optimum poultry manure dose for reclaiming burnt soils: pot experiments
Castro, A. | Gonzalez-Prieto, S.J. | Villar, M.C. | Carballas, T.
Poultry manure (PM) efficacy to improve burnt soil revegetation was evaluated to determine the lowest effective and the optimum dose for burnt soil reclamation. A (15)N-labelled forest soil (LS) was used to set up six treatments: LS, laboratory burnt LS (BLS) and BLS with PM dose equivalent to 1 (BLS + PM1), 2 (BLS + PM2), 4 (BLS + PM4) and 8 Mg dry PM ha(-1) (BLS + PM8). Ryegrass was sown in all treatments and grown for 3 months in a greenhouse. At harvesting, in the BLS treatment: (1) ryegrass yield was very low and the shoot:root ratio was high; (2) ryegrass-N content was closer to that of metabolic tissues or young plants than to structural tissues or mature plants; (3) most of the available endogenous N still remained in the soil inorganic N pool. These results suggested that, although seed germinated normally, ryegrass growth was stopped at an early developmental stage, producing small and weak plants unable to protect the burnt soil against erosion and to exploit the post-fire pulse of available N which, consequently, could be lost. The addition of PM to BLS increased the ryegrass yield from the lowest dose (BLS approximately equal to LS < BLS + PM1 < BLS + PM2 < BLS + PM4 < BLS + PM8; P < 0.05), the increase of the phytomass yield per Mg of added PM varying as follows: PM8 < PM1 less than or equal to PM4 < PM2. The uptake of soil-available N by the ryegrass was greatly enhanced in all manured treatments, but the contribution of PM-N to plant nutrition was only significant in BLS +PM4 and BLS + PM8 treatments. The lowest effective PM dose was PM1 and the optimum cost-to-benefit ratio treatments were PM2 and PM4.
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