EFFECTS OF CROP ROTATIONS AND FERTILIZATION ON YIELDS AND QUALITY OF SPRING WHEAT GROWN ON A BLACK CHERNOZEM IN NORTH-CENTRAL SASKATCHEWAN

Abstract

Effects of rotation length, crop sequence, and fertilization on yields and quality of spring wheat (Triticum aestivum L.) were examined for eight crop rotations over a 27-yr period (1960-1986) on an Orthic Black Chernozem at Melfort, Saskatchewan. The silty clay loam soil had an initial organic N content of about 0.55% (0-to 15-cm depth). During 1960-1971, fertilized plots received N and P based on general recommendations for the region; thereafter, fertilizer was applied based on soil tests. Yields of wheat grown on fertilized fallow were similar for fallow-wheat, fallow-wheat-wheat (F-W-W), and a 6-yr fallow-wheat-legume hay rotation (avg. 2519 kg ha−1 in 1960-1971 and 3036 kg ha−1 in the wetter 1972-1986 period). In contrast, yields of wheat grown on fertilized stubble in a F-W-W rotation (avg. 2113 kg ha−1 in 1960-1971 and 2775 kg ha−1 in 1972-1986) averaged 34% higher than yields of continuous monoculture wheat due to fewer observed weed and disease problems. Fertilized stubble wheat yields in F-W-W averaged 88% of comparable fallow wheat yields, while continuous wheat averaged only 66%. Fertilizer increased fallow wheat yields by 14-18%. Stubble wheat yields were increased 11–16% for 3-yr rotations and 26% for continuous wheat during 1960-1971 when relatively low rates of N fertilizer were applied, and 22–31% and 49% for these same rotations, respectively, during 1972-1986 when moisture was more favorable and soil test criteria were used. Inclusion of grass-legume hay or legume green manure crops in the rotations provided no yield benefit for subsequent wheat crops in this fertile soil. The yields of wheat from fertilized rotations increased significantly with years of study reflecting the higher fertilizer rates used in later years and use of improved production technologies. Wheat yields of unfertilized treatments generally increased or showed no trend with time, thus providing no evidence of declining soil fertility. Crude protein concentration and total N yield of the grain were significantly increased by fertilization and inclusion of a grass-legume hay crop in the rotation. Total grain P yield of wheat was also influenced by fertilizer and by rotation, while volume weight of grain was unaffected by treatment.Key words: N and P fertilizer; grass-legume hay; legume green manure; crop sequence; protein