Integrated Management of Inorganic and Organic Nitrogen and Efficiency in Potato Systems

A potato ( Solanum tuberosum L.) experiment from 2002 to 2004 examined fallow or winter rye ( Secale cereale L.) (average residues ∼1 Mg ha −1 ) cover crop systems with a split‐plot design of 0 or 5.6 Mg ha −1 poultry manure. A 75‐L container experiment used field trial soil to evaluate N dynamics in the presence and absence of N fertilizer. Organic N source (manure, cover crop residues, or both) availability was used to adjust fertilizer rate downward to provide an estimated 224 kg N ha −1 for all treatments. Plant growth, N uptake, and tuber yield were monitored, along with soil organic N status and light‐fraction organic matter. In the field, the integrated treatment (179 kg N ha −1 fertilizer + manure) consistently increased tuber yield and N uptake efficiency by 20% compared with the unamended conventional management (224 kg N ha −1 fertilizer). Similarly, tuber yield and N uptake in the integrated treatments of the container experiment were 14 to 33% higher than the fertilized, unamended treatment. In the absence of fertilizer, rye cover crop and manure enhanced tuber yield 40 to 210% compared with unamended plants. The release of N from diverse sources was in apparent synchrony with plant demand, as indicated by monitoring of NO 3 –N dynamics and the presence of light‐fraction N. Although manure application was associated with higher N input, subsoil NO 3 –N in manured and unmanured treatments averaged 6.7 and 7.9 mg kg −1 , respectively. High productivity and N efficiency were associated with integrating organic and inorganic N sources, which represents an environmentally and agronomically sound management strategy.