THE INFLUENCE OF PLANTING DATE, CULTIVAR, ROW SPACING AND PLANT POPULATION ON THE MORPHOLOGICAL AND PHYSIOLOGICAL DEVELOPMENT OF THE SOYBEAN (GLYCINE MAX (L.) MERRILL) PLANT

MUHAMMAD ABDUR RAZZAQUE, Purdue University

Abstract

Two soybean cultivars were compared at six population levels, two row spacings and two planting dates (1981) and three planting dates (1982) at Lafayette, Indiana. The largest effect on seed yield was due to planting date, followed by row spacing and plant population. The late June planting produced a 63% (1981) and a 74% (1982) yield relative to early June planting and a 62% (1982) yield relative to early May planting. At equal populations soybeans planted in 18 cm rows produced an average 10% and 7% higher seed yield in 1981 and 1982, respectively. Critical populations below which the soybean cannot maintain 90% of maximum yield were calculated from prediction equations on the basis of a modified Mitscherilich response curve. These populations were identified as 100,000 plants/HA for the two early plantings but increased to about 175,000 plants/HA for late June plantings. Individual soybean plants were found to be capable of a ten fold increase in seed yield in response to reduced plant densities at the 2 early planting dates but only a seven fold increase at the late June planting. As population was reduced, seed weight borne on branches increased from less than 10% to 70%. Seed weight per plant was determined largely by the number of pods per plant (R('2) = .96 - .98). Correlation coefficient (r) between season-long light interception and seed yield was 0.50 at populations of 25,000 through 400,000 plants/HA and 0.58 at populations below 200,000 plants/HA. Decreased population was also associated with increased net photosynthesis (mean of three canopy position), root nodule mass and activity (actylene reduction) per plant and per gram nodule fresh weight (specific nodule activity). The photosynthetic activity of lower canopy leaves was equivalent to that of upper canopy leaves at populations below 100,000 plants/HA. Delayed planting increased correlation between LAI and seed yield. The correlation coefficient (r) values were 0.71, 0.78 and 0.87 for 10 May, 7 June, and 23 June, respectively. Leaf area indices of 4.4 and 5.3 intercepted 95% of incident light for Century in 18 cm and 71 cm row widths, respectively. Soybeans in 18 cm rows achieved 95% interception 8-10 days earlier than in 71 cm rows. At flower initiation, 25-35% more light was intercepted by the 18 cm rows and ultimately narrow rows harvested 10% more season-long light. Leaf area indices for soybeans planted on 10 May, 7 June and 23 June were 6.9, 5.9 and 6.0 at optimum seed yield ((GREATERTHEQ) 95% of maximum yield).

Degree

Ph.D.

Subject Area

Agronomy

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