Introduction

Large seeded virginia type peanut is the preferred market type grown in the Virginia-Carolina (VC) region. The price of certified seed is approximately $2.05/kg making the cost of $277/ha, a significant input cost when planting the recommended seed density of 140 kg/ha or 200 thousand seeds/ha (Jordan et al., 2018). Research conducted in Virginia, on virginia type peanut, in the 1980's indicated that higher seeding density (215 thousand seeds/ha) produced significantly (P<0.01) higher yield and economic value than lower seeding density (144 thousand seeds/ha) (Mozingo and Coffelt, 1984). Similarly, studies on runner type peanut had positive relationships between seeding density and pod yield. For example, when increasing seeding density from 10 to 20 seeds/m, Sorenson et al. (2004) reported 8.5% pod yield increase and Sconyers et al. (2007) showed 16% higher yields when planting 22.6 seeds/m compared to 12.5 seeds/m. Sarver et al. (2016) reported that increasing seeding density from 3.3 plants/m to 13.1 plants/m increased pod yield from 5200 kg/ha to 6500 kg/ha, and decreased Tomato spotted wilt virus (genus Tospovirus; family Bunyaviridae) (TSWV).

Peanut yield response to seeding density is cultivar dependent in many crops including corn (Zea mays L.) (Nafziger, 1994), soybean [Glycine max (L.) Merr.] (Buerlein, 1988), and peanut (Sullivan, 1991). The new available virginia type cultivars showed improved yield, i.e. in Virginia, average state yield during the 1980's was 2976 kg/ha and during the last decade 4560 kg/ha, (USDA, 2019); and biomass (Simmons, personal communication) than the old cultivars. Therefore, to produce optimally, the new cultivars may require more nutrients and water, which could be supplied at no additional costs by decreasing plant population to make more resources available to individual plants. If newly released cultivars can produce similar yields with less plants per hectare, reducing the seeding density could greatly lower the cost incurred by growers in the Virginia-Carolina region.

Due to the indeterminate growth habit and the effect of weather on plant development, i.e., dry seasons delay while hot summers rush maturity, determining the optimum digging date is essential for maximizing yield, quality, and the economic return. Jordan et al. (2003) showed that digging within the optimum harvest maturity window (Williams and Drexler, 1981) did not affect yield or grade. Literature has consistently reported, however, that digging either too early or too late produced negative effects on peanut yield and quality (Mozingo et al., 1991; Wright and Porter, 1991; Jordan et al., 1998). For example, digging peanut two wk early reduced yield by 15% (Wright and Porter, 1991); and delayed digging caused decrease to both pod yield and gross value, with economic loss as high as $500/ha (Mozingo et al., 1991; Jordan et al., 1998). However, in North Carolina, early maturing cultivars responded differently to digging with some being more stable in terms of yield and economic value over digging dates than others (Jordan et al., 1998). Research is limited with respect to defining response to digging date of more recently released virginia market type cultivars. Generally, virginia market types require 135 to 155 DAP to reach maturity, while runners may need over 155 DAP (Balota et al., 2018).

The objective of this research was to determine the effect of seeding density and digging date on yield, market grade characteristics, and economic return of more recently released virginia market type peanut cultivars.

Peanut requires at least 600 mm precipitation from planting to physiological maturity (Rowland et al., 2012); and this standard was achieved in both years of this experiment. In 2016, peanuts received 917 mm cumulative precipitation from planting to 130 DAP in mid-Sep and 34% additional precipitation before dig at 150 DAP in mid-Oct, in Suffolk (Table 2). A similar precipitation pattern was recorded at Lewiston and, in both locations, the amount of rainfall received from mid-May to mid-Oct exceeded by 70% the 30-yr average precipitation of 685 mm in Suffolk and 691 mm in Lewiston-Woodville. Year 2017 was, however, close to normal and cumulative precipitation from planting to first dig (130 DAP) was 633 mm in Suffolk and 561 in Lewiston-Woodville; then cumulative precipitation slowly increased at both locations but not more than 644 mm in Suffolk and 604 mm in Lewiston-Woodville in mid-Oct.

Peanut is known to require 2200 GDD from planting to physiological maturity, but new cultivars are increasingly earlier maturing than older cultivars. For example, virginia market type cultivars developed at the turn of the century needed 1800 GDD to mature, in comparison with 2500 GDD needed by cultivars developed prior to that (Balota and Phipps, 2013; Caliskan et al., 2008; Jordan et al., 2018). The cultivars included in this work included Bailey, released in 2008, (Isleib et al., 2011); and Sullivan and Wynne released in 2013 (North Carolina Crop Improvement Association, 2020). They are among the most recent cultivars currently in production in the VC region and have optimum maturity at around 140 DAP (Balota et al., 2018; Jordan et al., 2018). Recorded GDD at 140 DAP was 1578 GDD in average of the two locations in 2016 and 1447 GDD in 2017 (Table 2). Even though more humid than 2017, 2016 was 2 to 3 C warmer in Aug and Sep than same months in 2016. The 30-year GDD average for both locations from 1 May through 30 Oct is 2400 GDD.

This work was supported with funding from the National Peanut Board, North Carolina Peanut Growers Association, Virginia Peanut Board, and Virginia Crop Improvement Association. Appreciation is expressed to staff at both research stations for technical assistance with this research.

Literature Cited

Balota M. Phipps P. 2013. Comparison of Virginia and runner-type peanut cultivars for development, disease, yield potential, and grade factors in eastern Virginia. Peanut Sci. 40: 15- 23.

Balota M. Isleib T.G. Oakes J. Anco D. 2017. Peanut Variety and Quality Evaluation Results. I. Agronomic and Grade Data. Virginia Cooperative Extension.