Can using polymer-coated seed reduce the risk of poor soybean emergence in no-tillage soil?

Abstract

Adoption of no-tillage in the northern Corn Belt has lagged behind other regions because of slow warming and drying of soils early in the spring coupled with a short growing season. Cold, wet soil can lead to seed damage resulting in poor stand establishment. Because of slow warming and drying, no-tilled soils are typically sown later than conventionally tilled systems thus often requiring the use of early maturing crop cultivars. Temperature-activated polymer seed coatings might allow soybean [Glycine max (L.) Merr.] to be sown earlier than normal under no-tillage while protecting seed against damage caused by cold, wet soil and perhaps allow the use of later maturing cultivars. These ideas were tested during 2005 and 2006 in west central MN on a Barnes loam no-tilled soil previously cropped in corn (Zea mays L.). Polymer-coated seed of a maturity group (MG) 0 and I soybean were sown as early as possible (early- to mid-April) and at an average recommended time (mid-May) for the study site. Only in 2005 did the polymer coating significantly increase emergence (p < 0.0001), where maximum emergence of early sown polymer-coated seed of the MG 0 and I cultivars was 51 and 35% greater than their uncoated counterparts. Conversely, for the average sowing date in 2006, under unusually dry conditions, the polymer coating slowed seedling emergence and reduced maximum emergence, although yield was not affected. Laboratory incubations confirmed that the germination delay of soybean caused by the polymer-coating increased by decreasing initial osmotic moisture potentials. The MG I soybean out yielded the earlier maturing cultivar in both years, but sowing date did not have a significant effect either year. Results indicate that temperature-activated polymer-coated seed may reduce the risk of poor stand establishment in no-tilled soil in instances where low soil temperatures cause seed to remain in the soil for an extended time before emerging.

Introduction

No-tillage in cropping systems has become a relatively common practice. No-tillage or reduced tillage practices prevent soil erosion (Lal et al., 2007) and can help conserve and/or build soil carbon and reduce CO₂ emissions (Al-Kaisi and Yin, 2005, Gesch et al., 2007). Reduced tillage can also lead to greater profitability in corn–soybean rotation systems (Buman et al., 2004, Archer and Reicosky, 2009). Yet, the adoption of no-tillage in the northern Corn Belt has lagged seriously behind other regions primarily because of the slow warming and drying of soils in early spring coupled with a short growing season. In west central MN, soil can remained covered in snow until mid-April or frozen until mid-May (Sharratt, 2002). Johnson and Lowery (1985) compared soil temperatures at depths from 5 to 15 cm for different tillage systems in Wisconsin and found that soil temperatures decreased with reduced tillage. They reported that daily average temperature was as much as 5.9 °C lower in no-tilled compared to moldboard plowed soil in early May. Because no-tillage soils take longer to warm they are often sown later, thus requiring earlier maturing crop cultivars that have less yield potential than later ones (Popp et al., 2002).

Timely establishment of crops such as corn and soybean, especially in regions with short growing seasons, is critical for maximizing seed yields. Moreover, sowing as early as possible optimizes the use of full-season crop cultivars (Torbert et al., 2001). However, sowing too early when soil temperatures are not conducive for good germination can lead to poor emergence and hence stand establishment. Increasing the time that seed or seedlings remain in the soil prior to emergence increases the occurrences of damage leading to death or decreased seedling growth rates (Shaw, 1977, Gesch and Archer, 2005). Sparse or uneven plant stands can reduce yields in crops such as corn (Zea mays L.) (Nafziger et al., 1991, Ford and Hicks, 1992), although soybean tends to be less affected (Egli, 1993) due to its yield plasticity (Egli, 1988). The optimum temperature range for soybean seed germination is about 25–35 °C with 10 and 40 °C being the lower and upper limits, respectively (Hatfield and Egli, 1974). Soil moisture in addition to temperature can be an important determinant of soybean emergence. As demonstrated by Helms et al. (1996), low soil water content at sowing for an extended period can significantly reduce soybean emergence, which is exacerbated by temperature stress.

A temperature-activated polymer coating has been developed for corn and soybean seed that offers the potential to allow for earlier than normal sowing and has been promoted for use in no-tillage systems (Hicks et al., 1996, Lessiter, 2000). Archer and Gesch (2003) reported that the use of polymer-coated seed for early sowing in MN could increase farm profits through reducing yield-loss due to late planting and increasing crop yields by the use of longer season cultivars. The seed coating is designed to restrict water entry by interaction of hydrophilic surface groups on the polymer until a critical temperature is reached, upon which these hydrophilic chains break-down and allow water to pass through the coating (Hicks et al., 1996). Thus, this technology could potentially protect seeds against damaged caused by extended exposure to cold wet soils allowing for early sowing (Watts, 1974, Zaychuk and Enders, 2001). Indeed, Gesch and Archer (2005) found that temperature-activated polymer-coated corn in west central MN could be sown as much as 4–5 weeks earlier than average without significantly sacrificing stand establishment. However, because the polymer coating delays germination and emergence, it may have negative consequences on plant stands, especially for soybean, if sown too late into warm soil (Sharratt and Gesch, 2008).

The objective of this study was to determine the effect of a temperature-activated polymer coating on emergence and yield of soybean sown as early as possible and at an average time in a no-tilled soil; and secondarily, to determine the potential to extend the maturity group (MG) of soybean grown for the region using ultra-early sown polymer-coated seed. In west central MN the average or normal time for sowing soybean is mid-May.