Oat and rye root decomposition effects on nitrogen mineralization

Decomposition and mineralization of cover crop rents needs to be understood to determine if N taken up by cover crops is mineralized during main crop growth. Two experiments were conducted in a controlled environment to measu re decomposition of oat (Avena sativa L, 'Ogle') and rye (Secale cereale L. 'Rymin') root residues and to examine its effect on soil N mineralization, In the first, oat and rye roots were mixed with soil and in the second, ro ots were grown in situ. At 7, 14, 28, 56, 84, and 112 d after the start of decomposition, denitrification, soil NO3- and soil NH4+ were measured to de termine net mineralized N. Soil respiration and C and N contained in roots and coarse soil organic matter were measured to determine decomposition, Al l treatments in both experiments showed an increase in net mineralized N du ring the first 56 d, After 56 d, net mineralized N in the control remained relatively constant, whereas mineral N continued to accumulate in the treat ments with root residues. Net N mineralization of the rye and oat root trea tments did not differ. Roots mixed with soil had high respiration rates dur ing the first 3 d and there were no differences between oat and rye root tr eatments. In the roots in situ experiment, however, respiration peaked for oat roots at Day 12 and for rye roots at Day 33, The oat treatment also had less C and N remaining in roots and coarse organic matter throughout the e xperiment. Even though oat roots decomposed faster than the rye roots, we p redict that <55% of the N contained in the roots of a spring-killed oat or rye cover crop will become available to the following crop.