Exchangeable Ammonium- And Nitrate-Nitrogen Related to Yields of Conquest Barley Grown as Second or Third Crop After Fallow in Northeastern Saskatchewan

Exchangeable ammonium- plus nitrate-nitrogen measured to a depth of 60 cm in 18 stubble fields during 1967, 1968 and 1969 in Black, Dark Gray and Gray Wooded soils of northeastern Saskatchewan was inversely related by regression analyses to yield increases of Conquest barley (Hordeum vulgare L.) (R2 = 63.8%) obtained from N fertilizer (phosphorus applied at 20 kg/ha). Sodium bicarbonate-extractable P was a significant variable in the multiple regression analyses, increasing the R2 value to 74.6%. Nitrate-nitrogen alone also was significantly related to yield increase from N fertilizer (R2 = 63.0%). Including NaHCO3-extractable P in the regression did not improve the relationship (R2 = 63.6%). Exchangeable ammonium-nitrogen values ranged from 3.7 to 24.1 μg N/4 g soil. Nitrate-nitrogen values were in a range of 4.9 to 75.2 μg N/4 g soil. Although there were significant amounts of exchangeable ammonium-nitrogen in the soils, a definite conclusion to retain exchangeable ammonium as an availability index for soil nitrogen could not be made from the regression analyses. The mean protein content of the grain was significantly related by regression to nitrogen soil tests. Increased yield from nitrogen fertilization resulted in a decrease in phosphorus content of the grain.