Biol Fertil Soils (1994) 17:269-275 9 Springer-Verlag 1994 Richard T. Koenig 9 Verlan L. Cochran Decomposition and nitrogen mineralization from legume and non-legume crop residues in a subarctic agricultural soil Received: 14 June 1993 Abstract An understanding of the C and N dynamics of crop residues is important for efficient nutrient manage- ment. The present experiment was conducted to deter- mine the rate of mass and N loss from alfalfa, faba bean, barley, and rape crop residues in a subarctic agricultural soil. Mass, C, and N losses were measured from residues contained in mesh bags and placed on the soil surface or buried 15 cm below the surface. The mass loss from Octo- ber, 1988, to May, 1989, was the same for surface and buried alfalfa, barley, and rape residues, averaging 40, 20, and 61%, respectively, while surface and buried faba bean residue sustained 30 and 40~ mass loss, respectively. The mass loss of the buried residues continued over the sum- mer but not of those placed on the soil surface, resulting in an average 23 % greater mass loss of the buried materi- als after 1 year. The N loss from October to May was simi- lar from the surface and from the buried placements for the alfalfa, faba bean, and rape residues, averaging 11.3, 10.3 and 38.4gNkg -1 residue, respectively, while the surface and buried barley lost 2.9 and 4.2 g N kg -1, re- spectively. The C : N ratio of all of the residues increased during the winter. These data indicate that the rate of de- composition and N mineralization from crop residues in subarctic environments can equal that measured in tem- perate climates. Furthermore, the concurrent loss of mass and N combined with an increase in the C : N ratio of the residues suggests that physical rather than biological pro- cesses were functioning during the winter. Most of the mass and N loss from these residues occurred during the winter, out of phase with crop demand, thereby creating Richard T. Koenig Agricultural and Forestry Experiment Station, University of Alaska, 309 O'Neill Building, Fairbanks, AK 99775, USA Verlan L. Cochran (~) U.S. Department of Agriculture, Agricultural Research Service, 309 O'Neill Building, Fairbanks, AK 99775, USA the potential for N loss from the system and inefficient use of crop residue N. Key words Crop residues 9Decomposition 9N mineral- ization 9Subarctic soil 9Alfalfa 9Faba bean 9Barley 9 Rape Introduction Crop residues are important for maintaining soil physical properties such as aggregate stability and water-holding capacity. Furthermore, crop residues preserve the fertility status of the soil by maintaining organic matter levels and providing a reservoir of essential plant nutrients, particu- larly N (Kononova 1966). The extent to which crop residues influence plant growth is determined, in part, by the decomposition and N mineralization rates of the resi- dues, and the concurrent timing of N release and crop de- mand. Therefore, there is a need to understand the C and N dynamics of crop residues in order to effectively man- age these materials as a nutrient source. The mass and N dynamics of crop residues in agricul- tural systems have been well characterized (Smith and Douglas 1971; Douglas et al. I980; Christensen 1985b; Wessen and Berg 1986; Andren 1987; Mueller and Sund- man 1988; Stott et al. 1990; Cochran 1991). However, grain straw dynamics have received the most attention, with little focus on other types of crop residues (Smith and Douglas 1971; Douglas et al. 1980; Stott et al. 1990; Cochran 1991). While the average rate of crop residue decomposition measured in temperate ecosystems exceeds that at higher latitudes (Brown and Dickey 1970; Smith and Douglas 1971; Wessen and Berg 1986; Cochran 1991), relatively lit- tle decomposition may occur in either environment dur- ing the winter months (Smith and Douglas 1971; Cochran 1991). For example, Smith and Douglas (1971) and Doug- las et al. (1980) measured < 10O7o mass loss from wheat straw residue during the period November to March at a latitude near 45 ~ At higher latitudes (> 60 ~ the de-