Effects of different composts on soil nitrogen balance and dynamics in a biennial crop succession
Italy is faced with increasing pressures to reduce the amount of refuse disposed of in landfills. Compost represents a contribution to solve this problem. To give information for the correct management of composts as nitrogen fertiliser, it is necessary to assess their nitrogen release rhythm compared with the crop needs. This semi-field trial investigated the performance of three different composts coming from food processing industry residues and municipal waste (C1), green cuttings residues and the organic fraction of municipal waste solid residues (C2), municipal sludge and green cuttings residues (C3) as nitrogen source on a two-year crop succession. The influence of compost used as N-fertilizer was studied in lysimeters over a period of 2 years (2003-2005). The experiment was carried out at the Experimental Farm of Padova University Faculty of Agricultural Sciences on potato (cv. Agata) and two catch crops (ryegrass - Lolium multiflorum Lam., cereal rye - Secale cereale L.), using three types of compost as unique nitrogen source, compared with an unfertilized control. The compost N-level was 200 kg ha-1 per year, applied prior to the potato crop. The experiment had a completely randomized design, with 12 replications. Nitric nitrogen concentration was measured every one-two weeks in the soil throughout the trial period. Crop yields were measured and samples of produce were taken to be analysed for N concentration and calculate N uptake. With the only exception of compost derived from food processing industry residues and municipal waste (C1), immediately after the first application, compost fertilization did not increase the nitrogen concentration in the soil compared to the unfertilized treatment. Potato yield, in both seasons, was increased by C1 application, while C2 and C3 did not induce significant differences with respect to the control. No significant differences in yield and N uptake were found in catch crops. Taking the whole crop succession, the application of compost maintained the apparent N balance (input-uptake) at around -100 kg ha-1, while it exceeded 400 kg of deficit without fertilization. The compost nitrogen mineralization rate was estimated at around 36-44%, without differences among compost types.