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 it s decomposition. The timing of N release to soil affects both the nutrition of the subsequent crop and also the environment, which could possibly be a ltered by biocides produced by marigold. Decomposition was quantified in th e field by monitoring residues of marigold and cereal rye (Secale cereale L .), a common rotation crop, over time in litter bags subjected to different renditions, Marigold decomposition proceeded normally and without toxic ef fects on decomposers. In the fall of rotation years, topsoil NO3 concentrat ion was usually higher under marigold (1.1 mg kg(-1)) than under rye rotati on (0.3 mg kg(-1)), but this depended on the method of marigold management. In marigold plots, fall NO3 levels were greatest where plants were mowed e arly (August) or fertilized with 90 kg N ha(-1) and lowest where plants wer e left standing over winter. In plots where marigold was mowed in September or left standing, fall NO3 levels were sometimes no higher than in rye plo ts. 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 k g 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).