Effect of crop rotations on potentially mineralizable-N and amino compounds in a Black Chernozem at Indian Head
The effect (i) of fertilization on fallow-wheat (F-W), F-W-W, and continuous wheat; (ii) of baling straw on F-W-W (fertilized); (iii) of including sweetclover as green manure (GM) in F-W-W (unfertilized); and (iv) of including bromegrass-alfalfa cut for hay (H) in a 6-yr mixed rotation (F-W-W-H-H-H), on soil organic matter nitrogen (N) characteristics was determined in the top 15 cm of a thin Black Chernozem at Indian Head Saskatchewan after 30 years of treatments. Treatment effects were apparent from analysis of Kjeldahl N, amino N released during hydrolysis with 6M HCl, and with potentially mineralizable N (N0) and its rate constant (k). However, the "potential rate of mineralization" (N0 × k) proved to be the most powerful tool in segregating treatment effects. The relative molar distribution (RMD) of amino acids showed significant increases in aspartic acid and decreases in arginine and leucine, but these differences were mainly related to the influence of the 6-yr and fertilized continuous wheat being different from the shorter or unfertilized systems. It was concluded that fertilizers are as effective as legume green manure or grass-alfalfa in increasing soil organic matter and improving its quality (N supplying power) in this medium fertility soil where moisture is rarely limiting to crop production. Secondly, it was suggested that the parameter N0 × k could be a powerful tool for scientists to use in assessing soil quality. Finally, we estimated that the F-W and F-W-W rotations, especially when not fertilized or when straw was baled, had continued to cause losses in total N; that fertilized F-W-W and unfertilized continuous wheat was maintaining the organic N, while the legume-containing and fertilized continuous wheat systems had increased the organic matter compared to the level at the start of the experiment (i.e., following many years of conventionally tilled F-W and F-W-W).
Soils and Crops Workshop