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SOIL FERTILITY & PLANT NUTRITION

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

Department of Crop and Soil Sciences, Michigan State Univ., W.K. Kellogg Biological Station, East Lansing, MI 48824-1325

^* Corresponding author (snapp{at}msu.edu).

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 NO₃–N dynamics and the presence of light-fraction N. Although manure application was associated with higher N input, subsoil NO₃–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.

Abbreviations: LFOM, light-fraction organic matter • NMP nitrogen mineralization potential