Concentrating stubble into windrowed strips affects subsequent crop production, soil testing and fertiliser decisions. Wayne Pluske (Equii), Ryan Walker ( Apal Laboratories) and John Young (Wyening Mission Farm) looked at nutrient redistribution post-harvest. They measured plant material (dry matter as t/ha) and nutrient content of canola and wheat crops. The aim was to gauge the nutrient cost of windrowing stubble behind the header.
In November 2017, the researchers took initial biomass and nutrient measurements from both crops before harvest. Half the canola was swathed and windrowed pre-harvest. The rest was harvested by direct heading. Yield monitors measured yields for both crops during harvest. The 12.2m header placed the straw/chaff in a 1.2m windrow. Researchers took biomass and nutrient measurements post-harvest from the grain, standing residues and the straw/chaff windrow.
- Most of the P in plants was removed in seed at harvest.
- About one-third of N remained on the paddock after harvest for both canola and wheat.
- Only 11% of K in canola and 33% of K in wheat was removed in seed.
- Windrowing behind the header concentrated large quantities of plant-available N and K into strips.
The difference in nutrient concentration after harvest within the windrow strips was valued at $499/ha (wheat) and $518/ha (canola) in fertiliser equivalents. This needs further investigation as it has major implications for soil testing, fertiliser decisions and stubble management.