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CROPPING SYSTEMS

Yield and Growth Components of Potato and Wheat under Organic Nitrogen Management

Group of Crop and Weed Ecology, Wageningen Univ., P.O. Box 430, 6708 AK Wageningen, the Netherlands, and Plant Res. Int., P.O. Box 16, 6700 AA Wageningen, the Netherlands

* Corresponding author (adln{at}cbs.nl)

Received for publication January 4, 2001. In order to optimize N management in organic farming systems, knowledge of crop growth processes in relation to N limitation is necessary. The present paper examines the response of potato (Solanum tuberosum L.) and wheat (Triticum aestivum L.) to N with respect to intercepted photosynthetically active radiation (PAR), light use efficiency (LUE), and leaf N concentration ([N]). Potato and wheat cultivars were grown in field experiments (1997 and 1998) at three N levels: no N (N1), cattle (Bos taurus) slurry (N2), and cattle slurry supplemented by mineral N fertilizers (N3). Estimated available N from the soil (0–0.9 m) plus added fertilizer was 80 (N1), 150 (N2), and 320 (N3) kg ha^-1 for potato and 115 (N1), 160 (N2), and 230 (N3) kg ha^-1 for wheat. Nitrogen deficiency was quantified by an N nutrition index (NNI; 1 = hardly limited, 0 = severely limited). Nitrogen deficiency increased in the N1 and N2 treatments up to 20 (potato) and 50 (wheat) d after emergence, with small changes thereafter. An increasing N limitation in potato (NNI = 1–0.55) resulted in a linear decrease in crop dry weight and cumulative intercepted PAR and in a linear increase of the harvest index, whereas the LUE decreased only at NNI values below 0.65. Crop dry weight and cumulative intercepted PAR for wheat decreased linearly with N limitation (NNI = 0.9–0.6), but the harvest index and LUE were unaffected. For both crops, N limitation to 0.55 caused a linear decrease in maximum leaf area index, the rate of foliar expansion, leaf area duration, and to a lesser extent, leaf [N]. In conclusion, both crops respond to N limitation by reducing light interception while maximizing the LUE and leaf [N].

Abbreviations: DAE, days after emergence • LAI, leaf area index • LUE, light use efficiency • [N], N concentration • N1, unfertilized • N2, fertilizations with cattle slurry • N3, fertilizations with cattle slurry supplemented by mineral N • N_LA, areal leaf N content • NNI, nitrogen nutrition index • N_min, soil mineral N content • PAR, photosynthetically active radiation • REML, residual maximum likelihood

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