Effects of grain lentil-wheat and monoculture wheat on crop production and N fertility in a Brown loam
Low commodity prices and a desire by producers on the Canadian prairies to reduce fertilizer N inputs has resulted in a marked increase in grain lentil production in recent years. Because a large proportion of the pulse crop N is exported in the grain, it is generally believed that lentil, even though it fixes N2, contributes little extra N to the soil system. Results of a 12-year study at Swift Current on an Orthic Brown Chernozem silt loam, were used to assess the N economy of four wheat rotations, of various lengths and levels of N fertilization, with a wheat-lentil (W-Len) rotation. Except for a continuous wheat (Cont W) system that received mainly P fertilizer, all other systems received N and P based on soil tests. Neither grain nor straw yields of the associated wheat crop were influenced by the presence of lentil in the rotation; but, N concentrations in both grain and straw of the wheat in W-Len were increased compared to the monoculture wheat. Nitrate N in the root zone ( 0-90 cm) in spring and at harvest was greatest under F-W, followed by W-Len, then F-W-W and Cont W receiving N and P, and lowest in Cont W receiving mainly P. In recent years, there was a marked increase in the amount of soil NO3-N found in the root zone under the W-Len rotation. Similarly the estimated apparent net N mineralization during the growing season increased and the fertilizer N requirement for this system decreased, indicating a cumulative enhancement of the N supplying power of the soil. Therefore, soil testing laboratories should make a downward adjustment in their fertilizer N recommendations for producers that use a 2-yr W-Len rotation. Finally, there was less NO3-N leached below the root zone of W-Len than Cont W (N+P) which argues well for the use of this rotation for sustainability.
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