Influence of seed phosphorus content on seedling growth in wheat: implications for organic and conventional farm management in South East Australia

Fertilizer trials involving application of phosphorus (P) as both rock phosphate and superphosphate were conducted on adjacent organic and conventional farms in SE-Australia in 1991 and 1992. Seed P concentration and seed P content (P concentration multiplied by seed mass) were higher on the organic farm in 1991 when rainfall was below average, but were higher on the conventional farm in 1992, a wetter year. Addition of superphosphate increased seed P content and concentration on both farms in 1991 and on the organic farm in 1992. These results indicated that seed produced on a conventional farm with addition of fertilizers containing soluble P is likely to have a significantly greater seed P content than seed produced on an organic farm with application of rock phosphate or with no fertilizer addition. Seed harvested from these trials were sorted into small and large seeds to provide seed with a wide range of P contents: 29-169 micrograms. Heavier seeds had a higher P content. Seeds were germinated and grown for three weeks in field soil in a glasshouse. Heavier seeds were more likely to have germinated after 48 h. Seedling shoot dry mass after three weeks was significantly positively influenced by seed P concentration and seed mass, that is, shoot dry mass positively correlated with seed P content. Root dry mass after three weeks also correlated positively with seed P content. However, seedling relative growth rate was not correlated with seed P content. Seed nitrogen content and concentration did not significantly influence seedling growth. The origin of the seed, that is, whether it was produced on an organic or conventional farm, the year it was harvested, and the fertilizer treatment the parent crop had received all did not significantly affect seedling growth. Enhanced early growth of seedlings may be particularly important on organic farms where herbicides are not applied and seedlings may face increased weed competition. It is suggested that organic farmers may benefit from grading out heavier seeds for sowing.