High-yielding rice cultivars perform best even at reduced nitrogen fertilizer rate

A production system consisting of high-yielding cereal crop cultivars, together with high inputs of fertilizers, chemicals, and irrigation has increased yields in developed and developing countries during the past decades. This has led many to believe that high-yielding cereal cultivars may not be used in alternative cropping systems in which external inputs and adverse environmental effects are minimized. The objective of this study was to test the hypothesis that high-yielding temperate rice (Oryza sativa L.) cultivars do not perform well under a reduced N fertilizer rate. A field experiment was conducted from 1992 through 1994 at Hokuriku National Agricultural Experiment Station, Japan, on soil classified as clayey montmorillonitic, mesic Typic Endoaquepts. Thirteen rice cultivars released between 1893 and 1995 and one breeding line were grown at conventional (120 kg ha(-1)) and reduced (40 kg ha(-1)) N fertilizer rates, with a sufficient supply of other nutrients and water. Insects, diseases, and weeds were controlled by agrochemicals. In spite of contrasting weather from 1992 through 1994, there were highly positive correlations in grain yield of the rice cultivars between conventional and reduced N rates. At the reduced N rate, high-yielding cultivars Akichikara, Fukuhibiki, Habataki, Hokuriku 153, and Xin Ging Ai 1 consistently surpassed others not only in grain yield (P < 0.01), but also in aboveground dry matter (DM), harvest index (111), N utilization efficiency (NUE), and sink capacity (P < 0.01) with two exceptions. There are significant advantages to the use of high-yielding rice cultivars at reduced N fertilizer rates, giving such cultivars potential benefits in alternative cropping systems for temperate regions.