RESIDUAL EFFECTS OF PHOSPHORUS FERTILIZER. II. FOR WHEAT AND FLAX GROWN ON CHERNOZEMIC SOILS IN MANITOBA

Abstract

Broadcast applications of 0, 100, 200 and 400 kg P/ha were made on two Chernozemic soils in 1965. The soils were cropped for 8 yr in a continuous wheat-flax rotation. In each year, crops grown on the phosphorus treatments yielded more and had higher phosphorus content than crops grown without added phosphorus. Over 8 yr of cropping, 100 kg P/ha was the most efficient treatment in increasing yield. Yield increases beyond 100 kg P/ha were either not significant or only marginally significant. Wheat used twice as much phosphorus as did flax. Together the two crops used approximately 30, 22 and 14% of the 100, 200 and 400 kg P/ha applied. The NaHCO3-extractable phosphorus level of the 100 kg P/ha treatment after 8 yr of cropping was reduced to about 8 kg P/ha which is considered to be inadequate for crop production. Soils treated with 200 and 400 kg P/ha contained high levels of NaHCO3-extractable P (20–54 kg P/ha) and little response in yield to additional P would be expected in the near future. Annual variation in yield and phosphorus uptake by the crops were affected by water supply. In years of high water supply, yield and phosphorus uptake were generally higher than in years of low water supply.