Selection of Planting Pattern and Plant Population Density (PPD) for Medium and Late Maturing Soybean Varieties (Glycine Max (L.) Merrill) in the Tropics

Abstract

An experiment was conducted in the tropics at Awassa (7⁰04'N, 38⁰31'E, 1700m a.s.l) from 2005-2006 in order to determine effects of planting patterns and plant density on growth and yield of soybean. Results showed that Belessa-95 variety had significantly (p<0.05) taller plants with lowest pod height, larger leaf area, greater leaf area index at R2 (stage 50% flowering) and taller plants at R7 (stage of physiological maturity). Similarly, grain yield per unit area was significantly higher (p<0.01) different from Belessa-95 than Awassa-95 variety. The yield performance of soybean was positively associated with hundred seed weight (r=0.73, p<0.001), seeds/pod (r=0.56, p<0.001), pods/plant (r=0.53, p<0.001, plant height (r=0.73, p<0.001) and harvest index (r=0.63, p<0.001). The number of branches/plant were significantly higher (p<0.05) in rectangular rows than either paired rows or equidistant rows. First pod height was significantly higher (p<0.05) due to equidistant rows than either paired rows or rectangular rows. Paired rows gave significantly higher (p<0.01) harvest index and grain yield/plant than equidistant rows. Grain yield/plant was comparable from rectangular and paired rows. Significantly greater (p<0.05) number of branches/plant, seeds/pod, pods/plant, hundred seed weight, harvest index and grain yield/plant were recorded due to 20plants/m2 than other plant densities. However, there was not significant difference due to 20 and 30 plants/m2 in number of branches/plant, pods/plant and hundred seed weight. But significantly higher leaf area index (p<0.05), first pod height (p<0.05) and grain yield/unit area (p<0.01) were obtained due to 50 plants/m2 than other plant densities. Leaf area index and first pod height due to 40 and 50 plants/m2 were not significantly different and grainyield/m2 due to 30, 40 and 50 plants/unit area were also comparable. Planting pattern x plant density interactions brought significant effect on most growth and yield related traits unlike variety x planting pattern and variety x plan density interactions. Similarly, the interaction effect of planting pattern, plant density and variety was significant on harvest index, grain yield/plant and grain yield/unit area. Results indicated that grain yield/unit area was significantly higher (p<0.01) due to 30 plants/m2 grown in rectangular rows (60 cm x 5.5 cm) in Awassa-95 variety, but grain yield/m2 was significantly higher (p<0.01) due to 30 plants/m2 grown in rectangular rows (60 cm x 5.5 cm) and paired rows (90/30 cm x 5.5 cm) in variety Belessa-95. This study indicated that lower plant populations employed with rectangular or paired rows than are previously recommended for early and late maturing varieties provide way to optimize grain yield under sub-humid growing conditions of Awassa.