Spring wheat yield response to variable seeding rates in organic farming systems at different fertility regimes

Seeding rates in organic systems should balance a crop's competitive ability while maintaining grain yield and quality. A 2-yr study assessed the response of spring wheat (Triticum aestivum L.) to variable seeding rates (1 x conventionally recommended rate, 1.25 x, 1.5 x and 2 x) in a plot experiment in Nova Scotia and on organic farms across Canada. The plot experiment was a two-factor factorial assessing seeding rate and fertility. For the Canada-wide experiment, the four seeding rates were completely randomized on each farm. Wheat yield was highest at the 2 x seeding rate in 2003, but average crop emergence across all treatment combinations was only 56%. In 2004, crop emergence was 76% and the 1.25 x, 1.5 x and 2 x seeding rates had greater yield than the 1 x rate. Seeding rate affected plant density and heads per square metre, but no differences were observed among rates for kernels per head or thousand kernel weight. Grain protein content was similar among seeding rates and was increased by the high fertility treatment. On farms, a 1.25 x seeding rate was sufficient to maximize yield when averaged across all sites. Increasing seeding rate by at least 1.25 x the conventionally recommended rate appears to be an appropriate management practice for organic production.