Impiego di urea stabilizzata con 3,4-dimetilpirazolo fosfato in un terreno di risaia: I. Influenza sulla produzione e sulle perdite per lisciviazione di N nitrico

[Autom. eng. transl.] Nitrification inhibitors can reduce nitrogen losses by leaching and the effect should be more evident in sandy soils subjected to drastic irrigation regimes where water percolation is high. This two-year lysimeter study evaluated the efficacy of 3,4-dimethylpyrazole phosphate (DMPP) as a nitrification inhibitor and its influence on leaching losses from a loose sandy soil cultivated with rice, kept continuously submerged or at 20% of the field humidity (non-submerged treatment) by sliding irrigation. Urea was applied at doses of 150 and 200 kg N ha-1, respectively in two successive growth seasons, with and without DMPP added to the fertilizer at a dose of 1% with respect to urea. The fertilizer N was administered in three equal doses in both years in correspondence with the implantation and panic stage phenological stages, corresponding to the periods of maximum nitrogen requirement of the crop. The application of urea stabilized with DMPP produced significantly lower levels of N-NH4 in the undissolved soil compared to the treatment with urea alone for over 150 days, corresponding to the entire cycle of cultural development. Conversely, in submersion the concentrations of N-NH4 differed discontinuously between the two fertilizing treatments, fluctuating within a range comparable to that of the non-submerged soil that received only urea. Nitrification was much faster in the soil fertilized with urea compared to the addition of DMPP + urea, maintaining significantly higher levels of N-NO3 over time, with the exception of the submerged soil, where the nitrification inhibitor was effective only with application of the nitrogen fraction to the plant. In submersion the N-NO3 levels were significantly lower than in the non-submerged soil and, relative to the 150 kg N ha-1 dose, not differentiated from the non-fertilized control. N-NO3 concentrations in leaching waters showed, at both doses of 150 and 200 kg N ha-1, a marked decreasing trend after the peak of maximum concentration at about 40-50 days from the application of the first fraction of N fertilizer, regardless of the irrigation regime imposed on the soil. Leaching N-NO3 losses were relatively higher from non-submerged soil with significantly lower concentrations using DMPP + urea compared to treatment with urea alone. At the dose of 150 kg N ha-1 no significant differences were found between nitrate levels in the non-fertilized control water and nitrification inhibitor treatment already from the application of the second N fertilizer fraction. Nitrification inhibitors can reduce potential N-NO3 losses from non-point source pollution along with appropriate use of irrigation systems and nitrogen fertilizer application. From this point of view the two-year period of tests with the use of 3,4-dimethylpyrazole phosphate formulated with urea has shown both the efficacy of the product as a nitrification inhibitor and the ability to reduce the losses of N-NO3 by leaching, especially from the soil not submerged during rice cultivation. Although paddy rice submerges have a lower impact on groundwater than non-submerged cultivation, it nevertheless has a greater potential risk for the emission of nitrogen and methane compounds into the atmosphere: it is necessary to improve the irrigation technique while reducing the 'environmental impact