Nitrogen utilization, yield, quality and soil properties in a sugarbeet crop amended with municipal solid waste compost

The aim of this research was to study different ways of nitrogen (N) fertilization and soil tillage management to ensure high yield, quality and correct usage of the available resources. Therefore, a two-year field experiment (2001 and 2003) was carried out on a sugarbeet crop grown in a Mediterranean environment to evaluate the effects of two soil tillage depths (10-15 and 40-45 cm) and of a municipal solid waste (MSW) compost application, compared to mineral N fertilization. The following fertilization treatments were compared: MSW compost at 100 kg N ha−1 (Ncom); mineral N fertilizer at 50 kg ha−1 (N50) and at 100 kg ha−1 (N100); MSW compost combined with mineral N fertilizer (Nmix) (50 kg ha−1 as organic N plus 50 kg ha−1 as mineral N); slow release organic-mineral fertilizer (Nslow) and an unfertilized control (Contr). In each trial year, growth parameters, plant and soil N indicators, yield, quality, N uptake and N efficiency, soil chemical characteristics and N mineral deficit in the soil were determined. The findings of this research highlighted that MSW compost was an important N source for sugarbeet, especially when MSW compost was combined with mineral N fertilizer. In fact, the Nmix treatment did not determine any significant reduction in root (32.5 vs. 36.4 t ha−1 of N100) and sucrose yields (3.56 and 3.65 ha−1). Furthermore, it presented a significantly lower amount of one of the most important qualitative parameters, the alfa amino N (1.74 and 1.97 meq 100 g−1 of N100), and ensured the least soil N deficit in 2003. The application of MSW compost significantly increased the extracted organic carbon in both 2001 (37% of increase for compost treatment in respect to unfertilized control) and 2003 (24%). Higher values were also recorded for total organic carbon in 2001 (20% of increase) and for humified organic carbon in 2001 (27%) and in 2003 (16%), whereas its application did not increase the total content of heavy metals. Finally, among plants and soil N indicators tested, the petiole nitrate content was the only one significantly and positively correlated with root and sucrose yields, indicating that it was an effective tool to monitor N supply. © 2007 by The JG Press, Inc. All rights reserved.