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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

View larger version (32K): [in a new window]   Fig. 1. Relationship between N uptake and total dry matter production of (A and B) potato and (C and D) wheat in (A and C) 1997 and (B and D) 1998. For each day after emergence (DAE), the line was fitted according to Eq. [2] (broken lines) and at each N level according to Eq. [3] (solid lines). Data values are DAE of periodic samplings. Open symbols represent potato cultivar Junior and wheat cultivar Axona, and closed symbols represent potato cultivar Agria and wheat cultivar Baldus for N1 (circles), N2 (triangles), and N3 (squares).

View larger version (13K): [in a new window]   Fig. 2. Relationship between crop dry matter production (W; Mg ha-1) and critical N concentration ([N]) in (A) potato (Greenwood et al., 1990) and (B) wheat (Justus et al., 1994). Symbols are 95% of the calculated maximum W (Eq. [2] in text), as derived from Fig. 1. Open symbols are for 1997 and closed symbols are for 1998.

View larger version (34K): [in a new window]   Fig. 3. Course of the N nutrition index (NNI) (see Eq. [1]) with days after emergence (DAE) of (A and B) potato and (C and D) wheat in (A and C) 1997 and (B and D) 1998. Bars represent the LSD (P = 0.05) at each sampling date. Data values are average NNI values at the largest possible DAE that cultivars could be compared. Open symbols represent potato cultivar Junior and wheat cultivar Axona, and closed symbols represent potato cultivar Agria and wheat cultivar Baldus for N1 (circles), N2 (triangles), and N3 (squares). Y, year; N, nitrogen; C, cultivar; *, **, and ***, significant at the 0.05, 0.01, and 0.001 levels, respectively; NS, nonsignificant at the 0.1 level.

View larger version (32K): [in a new window]   Fig. 4. Influence of average N nutrition index (NNI) on the relative values of (A) crop dry weight, (B) cumulative intercepted photosynthetically active radiation (PAR), (C) light use efficiency (LUE), and (D) harvest index of potato at about 52 d after emergence (DAE) in 1997 and 47 DAE in 1998. The values are relative to maximum or critical values given in Table 4. Points represent individual replicates. Solid regression lines include all points, except those indicated by arrows. Dotted lines represent separate years.

View larger version (28K): [in a new window]   Fig. 5. Influence of average N nutrition index (NNI) on relative values of (A) crop dry weight, (B) cumulative intercepted photosynthetically active radiation (PAR), (C) light use efficiency (LUE), and (D) harvest index for wheat at 102 d after emergence (DAE) in 1997 and 86 DAE in 1998. The values are relative to maximum or critical values given in Table 5. Points are for individual replicates. Solid regression lines include all points. NS, nonsignificant at the 0.1 level.

View larger version (24K): [in a new window]   Fig. 6. Influence of average N nutrition index (NNI) on average (A) areal leaf N content (NLA; g m-2), (B) leaf N concentration ([N]; g kg-1), and (C) leaf area duration of potato at about 52 d after emergence (DAE) in 1997 and 47 DAE in 1998. Influence of NNI on (D) thermal time till 50% intercepted photosynthecially active radiation (PAR) at start of the season and (E) maximum leaf area index (LAI) of potato. Points are for individual replicates. Lines are regression lines for each cultivar and year separately. Parameter estimates of lines are in Table 6.

View larger version (21K): [in a new window]   Fig. 7. Influence of average N nutrition index (NNI) on average (A) areal leaf N content (NLA; g m-2), (B) leaf N concentration ([N]; g kg-1), and (C) leaf area duration of wheat at 102 d after emergence (DAE) in 1997 and 86 DAE in 1998. Influence of NNI on (D) thermal time till 50% intercepted photosynthecially active radiation (PAR) at start of the season and (E) maximum leaf area index (LAI) of wheat. Points are for individual replicates. Lines are regression lines for each cultivar and year separately. Parameter estimates of lines are in Table 7.