Dynamics of N Derived from 15N-labeled Rye in Soil–tomato System as Influenced by Cover Crop Residue Management

The nitrogen (N) contribution of rye ( Secale cereale L.) to tomato production may increase when grown and applied with hairy vetch ( Vicia villosa R.) to the soil. To examine the uptake and recovery efficiency by tomatoes and retention in the soil of N derived from 15 N-labeled rye applied as a monoculture and biculture with hairy vetch, a Wagner pot examination was conducted under plastic high tunnel conditions in Sapporo, Japan. Irrespective of cover crop residue management, the peak of rye-derived N uptake occurred between 4 and 8 weeks after transplanting (WAT) and ceased between 8 and 12 WAT. Rye-derived N uptake by tomatoes (shoot + fruit) was 58.3% greater in rye monoculture treatment than in the biculture of hairy vetch and rye treatment because of higher rye-derived N input, whereas rye-derived N recovery was greater in the biculture treatment (34.0%) than in monoculture treatment (26.9%). The soil retained 47.0% and 52.5% of the rye-derived N input in the biculture (972 mg N/pot) and rye monoculture (1943 mg N/pot) treatments, respectively. Rye-derived N stored in the roots and possibly lost was estimated at 19.0% and 20.6% of the rye-derived N input in the biculture and monoculture treatments, respectively. Hairy vetch in the biculture treatment contributed 46.2% more N to tomato production than rye, and the hairy vetch N contribution was more significant during the late period (4–8 WAT) than the early period (0–4 WAT) of tomato cultivation. Therefore, the biculture may change the N release pattern from both hairy vetch and rye, with the cover crops releasing high amounts of N in both the early and late periods of tomato cultivation. These results may help improve N management in vegetable production systems by maximizing the use of plant-derived N by crops, thereby reducing N fertilizer inputs.