Short‐Season Soybean Yield Compensation in Response to Population and Water Regime

Abstract

Short‐season soybean [Glycine max (L) Merr.] production systems, such as double cropping and late sowing, require high populations to optimize yield, but effects of high populations on seed number and seed mass are unknown. We evaluated plant population effects on yield compensation, stability of harvest index, assimilate partitioning for seed number, and seed‐filling characteristics for 2 yr near Keiser, AR. The study had two cultivars, two levels of irrigation, and three row spacings that each had five levels of population ranging from 6 to 134 plants m−2 Increasing population reduced yield per plant but increased yield per unit area. Harvest index was relatively constant across populations for a given year and irrigation regime, and yield was closely associated with biomass at maturity. At high populations, plants maintained individual seed mass by reducing the proportion of shell mass per pod. Final individual seed mass, seed growth rate (SGR), and the length of effective filling period did not change with increasing population for irrigated or nonirrigated treatments. Reductions in yield caused by low population density were due to low seed number. Seed number per square meter was directly proportional to the ratio of crop growth rate (CGR) to SGR. For short‐season production, high populations ensured early canopy coverage and maximized light interception, CGR, and crop biomass, resulting in increased seed number and yield potential.

Soybean Yield Formation: What Controls It and How It Can Be Improved

“…Although some have reported mild adverse effects of drought on seed per pod (Ramseur et al, 1984;Pandey et al, 1984), others have shown no effect (Lawn, 1982;Elmore et al, 1988). In contrast, consistent reports have shown pod m -2 is reduced by drought during the R1-R6 seed formation period (Sionit and Kramer, 1977;Ramseur et al, 1984;Pandey et al, 1984;Snyder et al, 1982;Neyshabouri and Hatfield, 1986;Cox and Jolliff, 1986;Ball et al, 2000). Based on these results, we conclude that reduced seed m -2 from drought stress is derived predominately from reduced pod m -2 rather than seed per pod.…”

“…pod and seed numbers produced during the emergence to R6 period were reduced by the lower CGR so that seed size (produced during the R5 to R7 seed filling period) could remain constant. Plant population studies conducted under short-season conditions also have outlined a yield-control mechanism very similar to those described for narrow vs. wide row spacing and shade (Ball et al, 2000(Ball et al, , 2001Purcell, 2002). Increasing plant population above the normal recommendation of 25-35 plant m -2 increased LI early in the vegetative period [similar to the findings for narrow vs. wide row spacing ] resulting in an accelerated CGR during the R1 to R5 period, greater dry matter accumulation, and yield (Ball et al, 2000).…”

“…Plant population studies conducted under short-season conditions also have outlined a yield-control mechanism very similar to those described for narrow vs. wide row spacing and shade (Ball et al, 2000(Ball et al, , 2001Purcell, 2002). Increasing plant population above the normal recommendation of 25-35 plant m -2 increased LI early in the vegetative period [similar to the findings for narrow vs. wide row spacing ] resulting in an accelerated CGR during the R1 to R5 period, greater dry matter accumulation, and yield (Ball et al, 2000). Purcell et al (2002) determined that increased yield responded linearly to increased photosynthetically active radiation accumulated across the emergence to R5 period.…”

“…This shortens the seed filling period causing reduced seed size and yield (De Souza et al, 1997). When soybean faces seasonal drought or drought initiated by R1, yield loss results predominately from reduced pod and seed numbers and seed size is relatively unaffected (Sionit and Kramer, 1977;Ramseur et al, 1984;Pandey et al, 1984;Meckel et al, 1984;Cox and Jolliff, 1986;Constable and Hearn, 1980;Lawn, 1982;Ball et al, 2000). Thus, when confronted with drought stress, soybean reduces seed m -2 so that normal seed size can be maintained.…”

Results Regaring Yield Elements Obtained at Different Densities at Certain Soybean Varieties

“…The increase of plant population reduce yield of individual plants but increases yield per unit of area (RA Ball et al, 2000).…”