How much phosphorus do crop residues release under conventional and zero tillage systems?
In a field experiment conducted at Fort Vermilion in north-western Alberta, we used the litter bag method to quantify phosphorus (P) release from red clover green manure, field pea, canola and wheat residues under conventional tillage and zero tillage. Wheat residues added significantly less P (1.7 kg ha-1) to the soil than the other residues (5.6-8.5 kg P ha-1). Tillage had no significant effect on residue P applied, but the trend was for slightly greater amounts under ZT than under CT. Clover released the most P (3.8 kg ha-1 under CT and 2.8 kg ha-1 under ZT, compared with 1.4 kg ha-1 or less from the other residues). There were no significant tillage effects on the amounts released by clover, pea and canola residues, but wheat immobilized 0.2 kg P ha-1 under ZT compared with 0.4 kg P ha-1 released under CT. Soil phosphate contents were not significantly different between tillage systems. Phosphate contents decreased with soil depth, especially under ZT. However, there was no tillage by soil depth interaction with canola residues, where soil phosphate was greater (although not significantly) under ZT than under CT at all depths. Uptake of P by wheat was significantly greater where pea and, to a lesser extent, canola residues had been applied than where clover and wheat residues had been applied, and tillage had no significant effects on P uptake.
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