Agronomic evaluation of a homogenous nitrogen-phosphorus-sulphur fertilizer in southern Manitoba

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Kroeker, Myron P.
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Field studies and a growth chamber study were conducted to evaluate the effect of a homogeneous nitrogen-phosphorus-sulphur (NPS) fertilizer on the emergence and crop utilization of phosphorus (P) and sulphur (S). In the field study, spring wheat (Triticum aestivum L. cv. AC Barrie) and spring canola (Brassica napus L. cv. DKL 34-55) were grown in southern Manitoba and fertilized with NPS, monoammonium phosphate (MAP) + ammonium sulphate (AS), MAP + elemental S-bentonite (So), MAP only and a control (no P or S); and S was applied at 0,5, 10, 15 and 20 kg ha-1. Wheat and canola emergence was not affected by any of the seed-placed P and S fertilizer sources or S rates used in the study. The NPS and other P fertilizer sources increased dry matter yield 6 - 10% in wheat at midseason but not at maturity; canola yields were not increased by P and S fertilization at any stage. At midseason, all of the phosphate fertilizers increased P uptake by 8 - 13% in wheat and 23 - 45% in canola, while NPS and MAP + AS increased S uptake by wheat 7 - 9 %. At maturity, all of the P fertilizers increased total P uptake by 9 - 12% in wheat but not in canola, and all responses to S fertilization had disappeared. To determine the availability of P, SO4 and So in NPS fertilizer, two S-deficient soils were used for a growth chamber study. Spring canola was fertilized with NPS, MAP + AS, MAP + So, MAP only, AS only and a control (no P or S). At 45 days after emergence, the canola was harvested and dry matter yield, P and S uptake were measured. After this harvest, the soils were incubated to simulate potential So oxidation conditions between cropping seasons in Manitoba. The pots were then replanted to a second crop of canola to measure residual P and S supplied by NPS fertilizer. In the first canola crop, dry matter yield and apparent P fertilizer use efficiency of NPS fertilizer was 75% and 81% of that for MAP + AS respectively. The apparent S fertilizer use efficiency for NPS was 35% of that for MAP + AS. When the second crop was grown without P and S fertilization, dry matter and residual P and S uptake were highest for the NPS treatment; however, the cumulative dry matter yield (crop 1 + 2) produced with NPS fertilizer was 83% of that for MAP + AS. The apparent P fertilization efficiencies for MAP + AS and NPS fertilizers were 54 - 56% over the two cropping periods. However, the apparent S fertilizer use efficiency of NPS fertilizer was approximately 50% lower than MAP + AS. Overall, the studies indicated that NPS fertilizer was not detrimental to wheat and canola emergence at the rates used in the study; the availability of P from NPS fertilizer appeared to be at least equivalent to MAP; and that only the SO4-S portion of NPS fertilizer appeared to be available to crops, with no measurable amount of oxidation of the So-S portion.