Abstract Insight into nutrient cycling is gained by un- derstanding the dynamics and quantifying nutrient min- eralization from decomposing crop residues. Since wheat (Triticum aestivum L.), canola (Brassica napus L.) and pulse crops such as pea (Pisum sativum L.) are common- ly grown in rotation, our objectives were to: (1) com- pare, using the mesh bag technique, the dry matter (DM) loss and release of N and P of straw and root residues of those crops in the 10–11 months following harvest, and (2) determine the influence of N fertilizer on residue de- composition and nutrient release. The no-tillage study started in autumn 1997 when straw residues were placed on the soil surface and root residues were buried in the soil, and sampled periodically through the 1998 growing season. Wheat was grown in 1998 and received 0 or 60 kg N ha –1 . The study was repeated in 1998/1999. Wheat straw decomposed more slowly than canola or pea straw (losing an average of 12%, 24% and 25%, re- spectively, of initial DM in 10–11 months), however, the converse was noted for root residues (42%, 26% and 19% of initial DM). Average net N mineralization from wheat, canola and pea straw was essentially 0, 0.7 and 5.6 kg N ha –1 , respectively. Phosphorus released from straw ranged from 0.5 kg ha –1 for pea to 0.75 kg ha –1 for canola. Net N and P mineralization from root varied lit- tle between crop species: 0.9–1.6 kg N ha –1 and 0.1–0.3 kg P ha –1 . Nitrogen fertilization increased DM loss, and N and P release from straw residues. Keywords Decomposition · Mineralization · Nitrogen · Phosphorus · Root and straw residues Introduction In recent years there has been a reduction in mixed farm- ing and an increase in farms without livestock and prac- ticing continuous grain production in North America and Europe. As a result, crop rotation with cash crops such as oilseed and pulse crops rather than legume forage crops has become quite common in farming systems. In such crop production systems, crop residues are the main source of organic materials that provide energy for het- erotrophic soil microorganisms and maintain soil organic matter levels. Plant nutrients are recycled as microbes decompose the plant residues. The decomposition and nutrient loss of cereal straw residues have been studied extensively (Brown and Dickey 1970; Douglas et al. 1980; Christensen 1986). However, despite the impor- tance of roots as a source of soil organic matter, their de- composition and mineralization have received relatively little attention. Field studies of prairie grassland suggest that roots decay more rapidly than foliage (Seastedt 1988; Seastedt et al. 1992). Seyni and Salema (1995) found in a greenhouse study that cowpea (Vigna ungui- culata L.) root contributed 7–22% of the N uptake of the following millet crop compared to 4% for millet root. Pulse crop and canola (or oilseed rape; Brassica napus L.) residues usually contain higher concentrations of N and P, and therefore return more of those nutrients to the soil, than cereal residues (Strong et al. 1986; Armstrong et al. 1994). Armstrong et al. (1994) reported that pea (Pisum sativum L.) straw in Australia contained 19–50 kg N ha –1 . However, in northwestern Alberta, Canada, pea straw returned an average of 22 kg N ha –1 compared to 16 kg N ha –1 for wheat straw and 50 kg N ha –1 for canola straw (Soon and Clayton 2002). Moreover, Bremer and van Kessel (1992) estimated that only 7% of N in lentil (Lens culinaris L.) straw was mineralized in the follow- ing growing season, similar to wheat (Triticum aestivum L.), and concluded that lentil straw was not a significant source of N. Few studies have compared mass and nutri- ent loss in the field of residues of crops such as canola and pea with those of cereal crops. Such data are required to better understand the role of various crop residues in nutrient cycling in agro-ecosystems. Also few studies have been conducted in cold agricultural soils (e.g. Cochran 1991; Koenig and Cochran 1994). Therefore, we initiated Y.K. Soon ( ✉ ) · M.A. Arshad Agriculture & Agri-Food Canada, Research Branch, P.O. Box 29, Beaverlodge, Alberta, T0H 0C0, Canada e-mail: soony@agr.gc.ca Tel.: +1-780-3545134, Fax: +1-780-3548171 Biol Fertil Soils (2002) 36:10–17 DOI 10.1007/s00374-002-0518-9 ORIGINAL PAPER Y. K. Soon · M. A. Arshad Comparison of the decomposition and N and P mineralization of canola, pea and wheat residues Received: 20 June 2001 / Accepted: 30 May 2002 / Published online: 23 July 2002 © Springer-Verlag 2002