The effect of planting date on maize: Phenology, thermal time durations and growth rates in a cool temperate climate

Abstract

Field experiments were established in the Waikato and Manawatu regions of New Zealand over two cropping seasons (2006–2007), differing primarily in rainfall and soil type, to establish how planting date (PD) influenced maize phenology and growth processes across a range of environmental conditions. Though not significantly different to 8°C, a base temperature of 8.6–9.4°C (Tb8.6–Tb9.4) adequately estimated thermal time (TT) durations for the emergence-flowering phase while Tb0 was more satisfactory for estimating grain filling duration.Delayed planting either reduced (Waikato) or increased (Manawatu) the emergence-flowering duration and this was associated with changes in leaf number and phyllochron length. The phyllochron averaged 47°Cd, but increased to 51°Cd when soil temperature, radiation and precipitation between emergence and tassel initiation were respectively >22°C, ≤17MJm−2d−1 and ≤30mm. Sub-optimal temperatures and radiation under late plantings triggered a source limitation, leading to assimilate remobilization, reduced grain filling duration and resulted in higher grain moistures at physiological maturity (36% vs. 30%). When rainfall between emergence and flowering was ≥234mm, increases in average daily irradiance (19.5–21.4MJm−2d−1) and mean temperature (15–18°C) increased pre-flowering crop growth rate (CGR) by 1gm−2(°Cd)−1. With late planting, higher pre-flowering radiation (≥21MJm−2d−1) and temperatures (≥17°C) increased CGR while low post-flowering radiation (13MJm−2d−1) and temperature (15.7°C) reduced CGR. Kernel growth rate (KGR) was more stable across PDs and hybrids when TT was used (0.36–0.38mg (°Cd)−1). Provided temperature was ≥19°C, low daily irradiance (11MJm−2d−1) did not significantly reduce KGR. More rapid leaf senescence occurred for early and late plantings, and this was attributed to source–sink imbalances caused by assimilate accumulation or shortage. Leaf senescence rates in the absence of water stress were 0.03% (°Cd)−1 between anthesis and mid grain-fill, and increased to 0.2% (°Cd)−1 towards the end of grain filling.