RICE VARIETY DIFFERENCES IN DRY-MATTER AND NITROGEN ACCUMULATION AS RELATED TO PLANT STATURE AND MATURITY GROUP

Differences in nitrogen (N) use by different varieties of rice (Oryza sativa L.) have been reported by numerous researchers. Some have indic ated that N fertilization required for maximum yield differs between m odern varieties and old varieties (varieties no longer in production); others have suggested that among modern varieties, semidwarf varietie s require higher N rates than taller varieties. The objectives of this study were to evaluate differences in dry matter and N accumulation a mong modem long-grain varieties in relation to plant stature (tall ver sus semidwarf) and maturity group (early versus very early), and to co mpare old varieties and modern varieties. A greenhouse pot experiment with Crowley silt loam (fine, montmorillonitic, thermic Typic Albaqual f) was conducted to compare old and modern long-grain varieties at 52 days after sowing. Based on the results of the pot experiment, three v arieties each from six variety groups (old varieties, modern medium-gr ain varieties, and four groups of modern long-grain varieties) were pl anted in the field on Crowley silt loam soil. Each variety was fertili zed with three preflood N levels (0, 67, and 135 kg N ha(-1)). Plants were harvested 49 days after sowing and 25 days after 50% heading. Old and modern long-grain varieties did not differ in total N accumulatio n at any N level. However, long-grain varieties produced more grain th an the old varieties at all N levels, and among long-grain varieties, semidwarf varieties produced more grain than tall varieties when 135 k g N ha(-1) were applied. Early and very early varieties did not differ in total N accumulation or grain yield. Varieties that produced a hig her grain yield did so by partitioning more N to grain than straw, Mod ern medium-grain varieties accumulated more N than old and long-grain varieties and produced more grain with both 67 and 135 kg N ha(-1). Me dium-grain varieties had a higher harvest index and physiological effi ciency than old varieties but did not differ from long-grain varieties . This suggests that medium-grain varieties also partition more of the ir N into grain than straw and possibly are able to absorb more N from soil than old or long-grain varieties.