Residue Decomposition and Soil Nitrogen are Affected by Mowing and Fertilization of Marigold

To suppress root‐lesion nematodes ( Pratylenchus penetrans Cobb), marigold ( Tagetes sp.) is grown as a rotation crop; however, little is known about its decomposition. The timing of N release to soil affects both the nutrition of the subsequent crop and also the environment, which could possibly be altered by biocides produced by marigold. Decomposition was quantified in the field by monitoring residues of marigold and cereal rye ( Secale cereale L.), a common rotation crop, over time in litter bags subjected to different conditions. Marigold decomposition proceeded normally and without toxic effects on decomposers. In the fall of rotation years, topsoil NO 3 concentration was usually higher under marigold (1.1 mg kg −1 ) than under rye rotation (0.3 mg kg −1 ), but this depended on the method of marigold management. In marigold plots, fall NO 3 levels were greatest where plants were mowed early (August) or fertilized with 90 kg N ha −1 and lowest where plants were left standing over winter. In plots where marigold was mowed in September or left standing, fall NO 3 levels were sometimes no higher than in rye plots. Overwinter N release from bags of marigold shoots (stems and leaves) on the soil surface (39 kg ha −1 ) was less than that from buried bags (119 kg ha −1 ). Together, these results suggest that a marigold rotation may be a viable alternative to rye, but to minimize N loss, marigold crops should be left standing over winter and preplant fertilized with 45 kg N ha −1