Effect of Fertilizer and Plant Population on Yield of Soybeans1

Abstract

AbstractThe combined effects of fertilizer and plant population on the yield of soybeans (Glycine max (L.) Merr.) have not been defined clearly, because in practically all related studies, each has been investigated independently of the other. The present study was conducted to measure these combined effects on ‘Calland’ soybeans. Soybeans received 336 kg/ha N, 155 kg/ha P, and 279 kg/ha K in 1971, but no fertilizer applied in 1972. Plant populations were 100,000 plants/ha grown in 76‐cm rows both years, and 400,000 plants/ha grown in 76‐cm rows in 1971 and both 38‐ and 76‐cm rows in 1972.A significant yield response to directly applied fertilizer was obtained at a plant population of 400,000 in 1971, but not at 100,000. In 1972 the carry‐over fertilizer produced a significant yield response at 400,000 plant population in 38‐cm rows, but not in 76‐cm rows. However, there was a significant response (P = .10) at 100,000 plants/ha in 76‐cm rows. No significant yield differences were found among plant populations either year. The 38‐cm row spacing yielded significantly more than the 76‐cm row spacing at the 400,000 plant population where fertilizer was applied, but row spacing had no effect on yield of unfertilized soybeans.It was concluded that, although inconsistencies do occur, fertilizer can contribute significantly to higher soybean yields whether applied directly or utilized as a carry‐over from a previous crop, and that plant populations as low as 100,000 plants/ha can produce yields equal to those produced by a higher population (400,000 plants/ha) under both fertilized and unfertilized conditions.