Harvest Index of Soybeans as Affected by Planting Date and Maturity Rating¹

Abstract

Selection for high harvest index has been used by plant breeders to improve the seed yield of several crop plants, but in soybean [Glycine max (L.) Merrill] errors in the estimate of harvest index may occur because of interactions with maturity or seeding date and because harvest index measured at maturity does not include leaf and petiole dry weights. The objective of this study was to examine harvest indices of 10 soybean genotypes representing a wide range of maturity and seeded on several dates and to compare estimates of harvest index calculated from biological yield measurements with and without leaf and petiole dry weights. Vegetative yield at the time of leaf senescence and seed yield at maturity were measured in 10 cultivars of soybean (two from each of maturity groups I–V) planted in a silt loam soil (fine, montmorillonitic, mesic Udollic Ochraqualfs) at five dates from late April through early July. Biological yield was defined as total above ground plant yield and harvest index was calculated as the ratio of seed yield to biological yield. A positive relationship was detected between biological and seed yield, presumably because of a strong photoperiod response. As biological yield increased, seed yield increased proportionally and harvest index stayed the same. Premature killing by frost decreased the harvest index. Variability for harvest index among cultivars within the same maturity group was indicated, but this was influenced by planting date and maturity group. It was concluded that selection for increased harvest index in soybean would have to be done within cultivars representing a narrow range of maturity and planted at the same time.

Understanding the variability in soybean nitrogen fixation across agroecosystems

“…We estimated an HI of 0.36, based on measurements from farms included in this study of plant biomass for Vinton 81 soybeans at peak growth and seed yields at full maturity during previous experiments (unpublished data). This value is in agreement with the average HI value measured by Johnson and Major (1979) across Maturity Group I soybean varieties. We assumed an average seed N concentration of 6.8% N, based on average values measured for Vinton 81 soybean seed N concentration across 15 fields in the study area in 2002, 2003, and 2004 (unpublished data).…”

Influence of late planting on light interception, radiation use efficiency and biomass production of four sweet sorghum cultivars

“…However, soybean plantings following wheat are often delayed due to slow wheat maturation or excess precipitation. Soybean yields are known to decline as much as 43 kg ha −1 d −1 for each day that plantings are delayed beyond the third week of June (Johnson and Major, 1979). Thus, producers often abort plans to plant soybean when faced with July planting dates.…”

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“…This result contradicts the view that harvest index is a constant across environmental factors (Johnson and Major, 1979), or that harvest index and yield are not related across years (Schapaugh and Wilcox, 1980). However, previous studies have indicated that cultural factors such as planting date and plant population do affect harvest index (Board et al, 1990;Carpenter and Board, 1997).…”