Effect of different nitrogen sources on plant characteristics and yield of common bean (Phaseolus vulgaris L.) F. Fernández-Luqueño, V. Reyes-Varela, C. Martínez-Suárez, G. Salomón-Hernández, J. Yáñez-Meneses, J.M. Ceballos-Ramírez, L. Dendooven * Laboratory of Soil Ecology, GIB, Department of Biotechnology and Bioengineering, Cinvestav, México D.F, C.P. 07360, Mexico article info Article history: Received 26 June 2008 Received in revised form 17 July 2009 Accepted 18 July 2009 Available online 20 August 2009 Keywords: Active and total nodules Organic agriculture Vermicompost Wastewater sludge abstract Wastewater sludge can be used to fertilize crops, especially after vermicomposting (composting with earthworms to reduce pathogens). How wastewater sludge or vermicompost affects bean (Phaseolus vul- garis L.) growth is still largely unknown. In this study the effect of different forms of N fertilizer on com- mon bean plant characteristics and yield were investigated in a Typic Fragiudepts (sandy loam) soil under greenhouse conditions. Beans were fertilized with wastewater sludge, or wastewater sludge vermicom- post, or urea, or grown in unamended soil, while plant characteristics and yield were monitored (the una- mended soil had no fertilization). Yields of common bean plants cultivated in unamended soil or soil amended with urea were lower than those cultivated in wastewater sludge-amended soil. Application of vermicompost further improved plant development and increased yield compared with beans culti- vated in wastewater amended soil. It was found that application of organic waste products improved growth and yield of bean plants compared to those amended with inorganic fertilizer. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Sludge originating from wastewater treatment contains nutri- ents and organic material (Brennan and Hartenstein, 1984). Wastewater sludge is widely used to improve soil fertility or re- store degraded soils. The N mineralization rate of the organic material in the sludge when added to soil depends on the appli- cation rate, sludge C:N ratio, soil characteristics and tempera- ture (Er et al., 2004). Sludge, however, can also contain contaminants such as metals, pathogens and organic or inor- ganic pollutants. Throughout the world current regulations require pathogen reduction and periodic monitoring for some metals prior to land application (Bright and Healey, 2003; Harrison et al., 2006). Wastewater sludge is often dumped in landfills or incinerated, resulting in a loss of a potential source rich in plant nutrients. Wastewater sludge composting or vermicomposting have been proposed as techniques to reduce pathogens and organic contam- inants while generating a valuable product rich in plant nutrients. It has been reported that vermicompost of wastewater sludge increases crop yields (Correa et al., 2005; Cordovil et al., 2007) and appears to give better grain yields than wastewater sludge (Valdez-Pérez, 2007). The common bean (Phaseolus vulgaris L.) is one of the main agri- cultural crops in the world. The most important producing coun- tries are Brazil, China, India, Mexico and the USA, where yields vary between 600 kg ha 1 in Mexico and 1600 kg ha 1 in the USA. Lower yields of common bean are usually a result of inade- quate water supplies, diseases, pests and poor soils (Martínez- Romero, 2003). Although beans frequently grow in symbioses with Rhizobium, an N 2 fixing bacteria, they are often fertilized (Martínez-Romero, 2003). The response of the Rhizobium-bean symbiosis to added nitrogen fertilizer is determined by time of application (growth stage), application rate and form of N. The NO  3 form is more inhib- itory to nodulation than NH þ 4 , especially if added shortly after planting (Muller and Pereira, 1995). Although added NO  3 reduces nodulation in common bean plants, NO  3 -supplied plants showed significantly higher dry mass, specific leaf area and leaf expansion and lower chlorophyll and N content than NH þ 4 supplied plants (Bruck and Guo, 2006). The objective of this study was to investigate the effect of the application of different N sources (urea, wastewater sludge and vermicompost) on bean characteristics and yields. Beans were cul- tivated in the greenhouse and fertilized with wastewater sludge at two application rates, wastewater sludge vermicompost or urea, while plant characteristics and yield were monitored. Urea was used, as it is the N fertilizer most commonly used in Mexico. Two application rates of wastewater sludge were used to determine if larger amounts added inhibited bean growth. 0960-8524/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2009.07.058 * Corresponding author. Tel.: +52 55 57473319; fax: +52 55 57473313. E-mail address: dendoove@cinvestav.mx (L. Dendooven). Bioresource Technology 101 (2010) 396–403 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech