Effect of seed size on soil cover, yield, yield components and nitrogen uptake of two-row malting barley

Several important factors around sowing affect germination, emergence, crop stand establishment, early vigor and consequently, yield formation in crop cultivation. Among those factors are soil cultivation and sowing method (conventional tillage, conservation tillage, no-till), seeding rates, sowing dates, row and inter-row spacing, plant population density, uniformity of the seed distribution, nutrient supply in the soil, soil reaction, waterlogging, allelopathy caused by decomposing crop residue (Varga et al., 2000; Agegnehu and Honermeier, 1997; Bavec et al., 2002; Kübler et al., 2002; Munir, 2002; Steffens et al., 2005; Tsybulya, 2002; Lošák et al., 2012Chovancova et al., 2015; Neugschwandtner et al., 2015a; b) and sowing rates in intercropping designs (Neugschwandtner and Kaul, 2014; 2016).

Further, seed quality is important for emergence and compensation of stress affecting germination and the seedling (Heyland and Meer, 1992). Seed value is determined by inner and outer characteristics, among those are, for example, purity (of the seed lot), germination capacity, germination speed, seed vigor and the mean seed size (thousand kernel weight) (Klapp, 1967). Seed quality can be impaired by mechanical damage and stress cracks during drying and conditioning (Naplava et al., 1994; 1995) and enhanced through pre-treatment by either pre-soaking or application of plant growth regulators or nutrients; thereby cold tolerance, emergence, development and yield can be enhanced (Aufhammer and Federolf, 1992a, b; Heyland and Meer, 1992; Bavec et al., 2002). Diverse results for the effect of seed size have been reported. A higher germination rate, seedling and root length and higher yield have been reported for spring oat with a larger seed size (Guberac et al., 1998) and an increase in yield and yield components for spring barley (Rukavina et al., 2002). Contrastingly, Gan and Stobbe (1995) reported that seed size did not affect spring wheat emergence and yield, whereas sowing depth did.

The aims of this study were to compare the effects of seed size on: (i) soil coverage, (ii) yield and yield components and (iii) nitrogen (N) concentrations, N yield and N utilization for two malting barley varieties under Pannonian climate conditions in eastern Austria to gain knowledge whether the sowing of optimized seed size might be a promising cultivation technique.

Total germination did not differ between seed sizes as also shown by others for spring malting barley (Rukavina et al., 2002) or winter wheat (Zareian et al., 2013). However, a tendency that larger seeds may enable a higher germination can be drawn from the results. Guberac et al. (1998) have shown for oat and Gross (1984) for six monocarpic perennial plants that larger seed size resulted in higher germination (due to the larger endosperm).

With increasing seed size, higher soil coverage occurred in the first year, probably due to higher emergence and/or higher early vigor of seedlings and plants emerging from larger seeds. A positive correlation of seedling growth with seed size (and seed N content) has been shown for maize (Krug, 1969). Soil coverage by plants is essential for radiation interception and for soil protection against erosion processes (Klima et al., 2016). Soil cover differs between crops and is affected by sowing date and winter survival of autumn sown crops (Neugschwandtner et al., 2015a, d). Similar to late sowing dates, a delay in emergence (as observed in the second experimental year) also considerably delayed full soil cover.

Seed size did not affect AGDM or grain yield, but grain yield differed between varieties and years. Among yield components, ear density and TKW but not grains ear^-1 were affected by seed size. Both varieties had a higher ear density with the largest seed size compared to the smallest seed size. Aufhammer and Kübler (1987) have reported that for achieving a good yield, ear density is of higher importance whereas the number of grains ear^-1 is of less importance for two-row barley than for six-row barley, and that complete grain yield compensation of low ear density by higher formation of spikelets is not possible. No differences occurred between seed sizes for grains ear^-1. Especially for two-row barley, higher ear densities might result in problems during grain filling and might impair TKW (Aufhammer and Kübler, 1987). This is supported by our observation that the medium seed size of Tatum (2.5–2.75), which produced the highest ear density, showed also the lowest TKW. Heyland and Triebel (1986) have reported for winter wheat that above average ear density may be compensated with both successively formed yield components, whereas with an ear density around average full compensation can already be achieved by only the next formed yield component, which is grains ear^-1. For winter wheat, sowing larger seeds resulted in better vegetative development (with faster field emergence and more tillers plant^-1 but a less productive tillering – the combination of both resulted in no differences in ears plant^-1 between seed sizes) and better reproductive development (with more fertile spikelets ear^-1, grains plant^-1 and grain yield plant^-1) (Heyland and Scheer, 1984).

The aim of malting barley production is to produce large grains, which generally have a high starch and a low protein level (Fox, 2006). Specifically, Magliano et al. (2014) reported that thin grains have more protein than large grains when total grain samples had a low protein content, that is, when the sample came from an environment with a low relative abundance of nitrogen. We observed an interaction of variety × year for the harvested grain fractions but no effect of the size of sown seeds. In 2013, Paula had a higher increase of the > 2.8 fraction than Tatum compared to 2012. Contrary to our observations that harvested grain fractions are not affected by the size of the sown seed, several aspects influence grain size. Among those are genetic factors (Fox, 2006), environmental conditions, for example, drought and high temperature during grain filling decreased grain weight with a stronger effect of drought than temperature (Savin and Nicolas, 1996). Further, grain size increases with N fertilization, with a higher effect of splitting N doses than just increasing them (Aufhammer and Kübler, 1989). Heat stress may also increase grain N concentration (Passarella et al., 2008). In the drier and hotter year 2012, we observed a lower TKW and a higher share of small seeds but also lower grain N concentration.

Nitrogen concentrations and yields were not affected by seed size. No differences were observed for all assessed N parameters between varieties except for the N yield of the AGDM, which was higher for Tatum than for Paula. Between years, grain N concentration, N yield of grain, N harvest index and NUtE for grain production were higher in 2013 than in 2012. Differences between years for these parameters have already been reported for barley as well as pea and oat (Neugschwandtner et al., 2015c) as both the absolute and relative crop growth rates (Neugschwandtner et al., 2013) and nitrogen uptake rate and the relative nitrogen uptake rate (Neugschwandtner et al., 2014) differed between years as growth processes are influenced by environmental conditions (temperature, solar radiation, water and nutrient supply) (Connor et al., 2011).

In one year, seed size increased soil coverage. Aboveground biomass and grain yield were not affected by seed size. Larger seed size increased ear density, but with higher ear density, the TKW decreased. Seed size did not affect harvested grain size fractions or nitrogen concentrations and nitrogen yields.