| Short-rotation woody crop plantations of fast-growing trees, such as willow and poplar, can be grown as alternative sources of clean, renewable energy. These intensive culture systems have high nutrient demands. Application of N at three rates, (100, 200, and 300 kg N/ha) as slow-release urea and a control were used to evaluate the impact of fertilization oil second-year yields of five willow clones and one poplar clone in three plantations across New York State. Regression equations were developed to estimate standing biomass. Willow clone SV1 and poplar clone NM6 benefited from fertilization, reaching yields as high as 20.3 and 21.6 o.d. Mg/ha by the second year of the rotation, respectively. The responses of the other four willow clones were confounded greatly by weeds and unmeasured site factors, though there was some benefit from fertilization. Tree biomass response to fertilization differed by site and was a function of survival, weeds, and the interactions with site and microsite variations. Fertilizing at rates above 100 kg N/ha for a three-year rotation are recommended only when additional site data indicate a need. |
