Relationship Between Nitrogen Analysis of Soybean Tissues and Soybean Yields1
- U. R. Pal and
- M. C. Saxena2
In order to determine the applicability of N analysis of plant tissues as a diagnostic tool for N nutrition, it is essential to study the N status of soybean [Glycine max (L.) Merr.] plants under varying N supply. Field experiments were conducted to determine the effect of N fertilization at the rates of 0, 25, 50, 100, and 200, and 300 kg N/ha on the N concentration and accumulation in different plant parts of nodulating (inoculated and un-inoculated) and non-nodulating isolines of ‘Clark’ and ‘Harosoy’ soybeans at various stages of growth and to correlate the N status of soybean plants with yields.
The N concentration in stems, leaves, and petioles decreased with plant age, whereas in pods the N concentration increased. In contrast, N accumulation in stems, leaves, petioles, and whole plant followed a sigmoid pattern with plant development, while in pods it increased linearly. The rate of N accumulation (kg/ha/day) followed a bell-shaped pattern and was maximum during the pod-filling stage. Nitrogen fertilization had little effect on N concentration, amount of N in different plant parts or whole plants, N accumulation rate and seed yield/plant in inoculated nodulating isolines. However these attributes were increased conspicuously in non-nodulating isolines and brought to the levels of inoculated nodulating isolines at higher rates of N fertilization (Le., 200 and 300 kg N/ha). The uninoculated nodulating isolines were similar to non-nodulating isolines in virgin soils for soybean cultivation.
Total N concentration and NO3-N content of leaves showed better correlation with seed yields than total N accumulation in leaves/plant and total N accumulation/ plant. A total N concentration of 4.0% to 4.5% at 65 days was associated with highest yields in both ‘Clark’ and ‘Harosoy’. About 1900 ppm NO3,-N content of leaves at 50 days in ‘Clark’ and about 1450 ppm NO3,-N content of leaves at 65 days in ‘Harosoy’ were associated with highest seed yields. Based on the correlation values in different seasons for the two cultivars, total N concentration (%) seemed to be the best diagnostic criterion for N nutrition of soybeans.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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