Nitrogen fertilization of 'I-214' poplar trees with urea and different slow-release fertilizers: Yield, economic and environmental aspects

With an adequate cultivation methodology, in suitable environments, hybrid poplars can produce over 200-210 m3 ha-1 of wood in 10 years (with 278 trees ha-1). Some cultural inputs are fundamental for good yields, some others like fertilization can be evaluated because in the face of high environmental and economic costs they do not always increase the stand productivity. The purpose of this work is to show the variability of the poplar response to N fertilization and make a simple environmental and economic evaluation of this cultural practice. Four poplar trials with clone 'I-214' have been cultivated in different sites of Northern Italy and fertilized with Urea and other five N slow-release fertilizer and compared with no-fertilized plots. Growth and pedo-climatic data were collected. For the environmental and economic evaluation data were collected thought bibliography, dealers and farmers interviews. The trees response to N input can vary from no response up to a statistically greater yield; this variability was documented both between site and site, and within the same site between product and product. The environmental impact of the sole N fertilization input is always negative (net atmosphere CO2 eq. emissions), due to the high emissions for production; the economic income can vary from a loss of money, (no positive effect of fertilization), to an interesting net gain due to increase of yield. The N fertilization of poplar stands is a practice with high economic and environmental costs that it must be assessed on a case-by-case basis.