Canola: are safe rates of P changing?
Most canola hybrid varieties grown today are capable of extracting large quantities of available soil and fertilizer phosphate (P) for seed production; however, P depletion rates far exceed current fertilizer P recommendations. Continuous cropping of canola combined with its high P demand has resulted in P deficient soils. Consequentially, producers must apply fertilizer above the current recommended rates to reach target yields, however, seed burn associated with N-based fertilizers are a concern. To remedy this problem, producers utilize knife openers which allows for expanded spread between seed and fertilizer to safely place fertilizer within the seed row. The objective of this study was therefore to evaluate the impact of rate and placement of fertilizer P either alone or in combination with fertilizer ammonium sulfate across a range of soil and climatic conditions in the traditional canola growing areas of Saskatchewan. The trial was designed as a randomized complete block with four replicates. Treatments consisted of ten fertilizer rates (0, 20,40,60, 80 P2O5 kg/ha & 15S + 0, 15S + 20, 15S + 40, 15S + 60, 15S + 80 P2O5 kg/ha) and two placement methods (side band vs. seed placed). Trials were established at three locations with varying soils conditions in Melfort, Indian Head and Scott, Saskatchewan. Preliminary result indicates that response to rate and placement were site- specific. At Scott, the interaction of P rate x placement was significant for plant density, dry weight, yield, and % green seed (GS). Side banded P rates exceeding 40 kg/ha resulted in the greatest plant stands along with the highest early season growth, seed production and lowest % GS. A significant decline was detected for treatments with additional seed placed S at both Scott and Melfort. At Melfort, only P rate had a significant effect on dry weight, yield and % GS with rates exceeding 40 P2O5 kg/ha. In contrast, the effect of placement and rate were significant on early season dry weight, however, yield and % GS were not influenced by either rate or placement at Indian Head. Overall, side banded P rates exceeding 40 kg/ha had a positive effect on yield and %GS compared to seed placed P either alone or in combination with seed placed S of 15 kg/ha.
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