MANAGEMENT AND CROP ROTATION EFFECTS ON NITROGEN USE EFFICIENCY

摘要

Inclusion of legumes in crop rotations can reduce dependence on N fertilizers for crop production, however, there have been few attempts to evaluate and compare the nitrogen use efficiency (NUE) of crop rotations over the entire rotation cycle. Here we report results from field experiments on management and crop rotation effects on NUE of cropping systems. We define NUE as the ratio of total photosynthate (i. e., glucose) production in a rotation cycle to total fertilizer N. The NUE of three-course rotations managed under no-till followed the order pea (Pisum sativum L.)-wheat (Triticum aestivum L)-wheat > wheat monoculture > canola (Brassica rapa L.)-wheat-wheat. In another rotation experiment comparing no-till (NT) with conventional tillage (CT), NUE was higher with CT than NT during the first four years, and higher with NT than CT during the next four years. The NUE of the rotations was in the order: pea-wheat-canola-wheat > fallow-wheat-canola-wheat > continuous wheat In a comparison of CT vs. NT, and no lime vs. lime applied (7.5 Mg·ha~(-1)) to a pea-barley (Hordeum vulgare L.)-canola rotation grown on an acid soil of pH 5.0, NUE was higher in NT than CT, and in limed than unlimed treatments. Higher NUE for these studies resulted from greater N uptake associated with higher crop yields. Growing pea in a rotation has two benefits: by fixing N_2 it reduces the rotation requirement for fertilizer N. In addition, pea typically increases the yield of the sequent cereal crop while reducing the N fertilizer requirement An experiment that assessed the NUE of wheat in relation to slope position on hummocky landscapes found higher NUE on lower slope, due to greater soil N and water availability there, than on upper slope position.